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Title: Fossil plants, Vol. 3
A text-book for students of botany and geology
Author: A. C. Seward
Release date: May 23, 2025 [eBook #76146]
Language: English
Original publication: Cambridge: Cambridge University Press, 1917
Credits: Peter Becker, Robert Tonsing and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK FOSSIL PLANTS, VOL. 3 ***
CAMBRIDGE BIOLOGICAL SERIES
FOSSIL PLANTS
CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, +Manager+
=London=: FETTER LANE, E.C.
=Edinburgh=: 100 PRINCES STREET
[Illustration]
=London=: H. K. LEWIS AND CO. +Ltd.+, 136, GOWER STREET, W.C.
=London=: WILLIAM WESLEY AND SON, 28, ESSEX STREET, STRAND
=New York=: G. P. PUTNAM’S SONS
=Bombay, Calcutta and Madras=: MACMILLAN AND CO., +Ltd.+
=Toronto=: J. M. DENT AND SONS, +Ltd.+
=Tokyo=: THE MARUZEN-KABUSHIKI-KAISHA
_All rights reserved_
[Illustration: CHARLES RENÉ ZEILLER
Membre de l’Institut
Inspecteur général des Mines
Professeur à l’École Natˡᵉ Supérieure des Mines
(1847–1915)]
FOSSIL PLANTS
A TEXT-BOOK FOR STUDENTS
OF BOTANY AND GEOLOGY
BY
A. C. SEWARD
M.A., F.R.S., +Hon. Sc.D. Dublin+
PROFESSOR OF BOTANY IN THE UNIVERSITY;
MASTER OF DOWNING COLLEGE AND HONORARY
FELLOW OF EMMANUEL COLLEGE, CAMBRIDGE
WITH 253 ILLUSTRATIONS
VOLUME III
PTERIDOSPERMEAE, CYCADOFILICES, CORDAITALES,
CYCADOPHYTA
CAMBRIDGE:
AT THE UNIVERSITY PRESS
1917
TO THE MEMORY OF MY FRIEND
CHARLES RENÉ ZEILLER
ILLUSTRIOUS AS A MAN OF SCIENCE
AND A NOBLE-HEARTED GENTLEMAN
WHOM TO KNOW WAS TO REVERE
PREFACE
In the Preface to Volume II published in 1910 I rashly stated that
it was my intention “to devote such space as is available within the
limits of a text-book to the neglected subject of the geographical
distribution of plants at different stages in the history of the
earth,” also that Volume III would be completed with as little delay as
possible. Though nearly seven years have elapsed since the publication
of the second volume it may fairly be said that the delay is not
entirely due to causes which it was in my power to control. The subject
of geographical distribution receives no connected treatment in Volumes
III and IV for the simple reason that I underestimated the space
required for the description of the Gymnosperms. The alternatives were
either to insert a greatly compressed survey of the successive floras
of the world at the end of Volume IV or to attempt a fuller and less
technical treatment of the subject in a separate book. In choosing the
latter course I am conscious that a further obligation is undertaken
which it may not be possible to fulfil; but the risk is deliberately
taken. Volume IV is in the press and will, it is hoped, be published
before the end of 1917.
It is a pleasant duty to repeat my thanks to many friends who have
helped me in various ways. Dr Kidston generously and without reserve
allowed me access to his splendid collection of Palaeozoic plants,
and the frequent occurrence of his name in the list of illustrations
shows how freely I have availed myself of his kindness. He has read
some of the chapters and greatly assisted me by his friendly criticism
and encouragement. By reading the proofs of this volume Dr Scott has
further increased my already large debt to him. It is impossible to
thank him adequately; he not only corrected many careless mistakes but
by wise counsel and advice he rendered me a service which I greatly
appreciate.
The exchange of views with Prof. Zeiller has been a constant source of
profit and enjoyment, and it is hard to realise that the completed book
will not receive his kindly criticism. He was a singularly unselfish
and generous colleague, always ready to help fellow workers, and he
had the faculty in an unusual degree of influencing those who had the
privilege of his friendship by his sound advice and lovable personality.
The death of Count Solms-Laubach has deprived Palaeobotany of one of
its most learned and strongest supporters. In common with all students
of fossil plants I owe much to the critical treatment of the subject
in the _Einleitung in die Paläophytologie_. Prof. Jeffrey has very
kindly given me several photographs and sections which have been of
great service, and I am similarly indebted to Prof. Zalessky. To Prof.
Nathorst my thanks are due for the great interest he has taken in my
work and for his generosity in providing drawings and showing to me
many of the treasures in the famous Stockholm Museum. Prof. Bertrand
and Prof. Lignier freely supplied photographs and drawings of specimens
in their possession, and I am particularly grateful to them for the
willingness with which they always responded to my requests.
Through the death of Prof. Lignier in March 1916 Palaeobotany has
been deprived of another original thinker who devoted himself with
whole-hearted enthusiasm to botanical research and for many years
faithfully served the University of Caen: he was a generous friend to
whom one never appealed in vain for assistance. Through the kindness
of the Director of the Indian Geological Survey I have been able to
examine several fossils from the Calcutta Museum described by Oldham
and Morris and by Feistmantel. With the Director’s permission several
photographs and drawings made for a forthcoming paper to be published
by the Indian Survey are reproduced in this volume. I take this
opportunity of thanking friends in Australia who recently afforded me
facilities for examining fossil plants in their charge, and I would
especially thank Mr A. B. Walkom of the University of Brisbane, who
has recently undertaken an investigation of the rich plant-beds in the
Ipswich district, for all that he did to enable me to make the most of
a very short time available for palaeobotanical work.
For the loan of specimens and for other help I am indebted to Prof.
Bayly Balfour, Prof. Bower, Prof. Margaret Benson, Prof. Oliver, Sir
David Prain, Dr Smith Woodward, Prof. Weiss, the Director of the
Geological Survey, Dr A. H. Church, Dr Arber, and other friends. I
would also acknowledge a debt, by no means inconsiderable, to my
Colleague Mr Hamshaw Thomas. Among younger friends in the Cambridge
Botany School to whom I am indebted I wish particularly to thank Miss
Ruth Holden, Miss Bancroft, Mr Sayers, Mr Dutt and others who have
rendered me willing help.
In the List of Illustrations mention is made of Corporate Bodies and
individuals from whom blocks have been obtained, and I am grateful to
them for readily responding to my applications.
My Wife, though prevented by more urgent calls in the later stages of
my task from giving as much time to the illustrations as in the two
former volumes, has contributed several drawings, and my daughter
Phyllis Seward has also given me much help in preparing drawings from
previously published figures.
In spite of the vigilance and wise counsel of many friends numerous
blemishes remain and for these the author is alone responsible.
A. C. SEWARD.
+Downing College Lodge+,
_February 10, 1917_.
* * * * *
+Note.+ The letters A and B added to references in the footnotes
indicate that the works will be found in the Bibliographies at the
end of Volumes I and II.
TABLE OF CONTENTS
CHAPTER XXVIII
CYCADALES (Recent). Pp. 1–34.
CHAPTER XXIX
PTERIDOSPERMEAE (continued from Volume II). Pp. 35–85.
PAGE
I. =LYGINOPTERIDEAE= 35–85
=Lyginopteris= 35–70
_Telangium_ 54, 55; _Lagenostoma_ 55–64; _Lagenospermum_
64–66; _Pterispermostrobus_ 66, 67.
=Heterangium= 70–85
_Sphaerostoma_ 78–81.
CHAPTER XXX
II. =MEDULLOSEAE= 86–165
i. _Medullosa_ 86–109, 156–163
_Myeloxylon_ 106–110; _Neuropteris_ 110–117;
_Alethopteris_ and _Linopteris_ 113; _Trigonocarpus_
117–124; _Codonotheca_ 124–126; _Schützia_ 126–128;
_Whittleseya_ 128–131; _Dolerophyllum_ 132–139;
_Ottokaria_ 139–141; _Strobilites_ 141, 142.
ii. =Colpoxylon= 142–145
iii. =Rhexoxylon= 146–149
iv. =Sutcliffia= 149–156
_General considerations suggested by the anatomical
features of Medullosa_ 156–163
II. =A. STELOXYLEAE= 163–165
=Steloxylon= 163–165
CHAPTER XXXI
PTERIDOSPERMEAE. (Foliage and seeds.) Pp. 166–174.
_Pecopteris Pluckeneti_ 166–168; _Eremopteris artemisaefolia_
169–172; =Wardia= 172, 173; _Adiantites bellidulus_ and
_Lagenospermum Arberi_ 173, 174.
CHAPTER XXXII
CYCADOFILICES. Pp. 175–213.
I. =MEGALOXYLEAE= 175–180
=Megaloxylon= 175–180
II. =RHETINANGIEAE= 181–183
=Rhetinangium= 181–183
III. =STENOMYELEAE= 183–185
=Stenomyelon= 183–185
IV. =CYCADOXYLEAE= 185–190
=Cycadoxylon= 185–187
=Ptychoxylon= 187–190
V. =CALAMOPITYEAE= 190–200
=Calamopitys= 190–196
_Kalymma_ 194–196
=Eristophyton= 197–200
VI. =CLADOXYLEAE= 200–210
=Cladoxylon= 201–207
=Völkelia= 208–210
VII. =PROTOPITYEAE= 210–213
=Protopitys= 210–213
CHAPTER XXXIII
CORDAITALES. Pp. 214–299.
A. =POROXYLEAE= 214–219
=Poroxylon= 214–219
B. =CORDAITEAE= 219–284
=Cordaites= 219–265
_Noeggerathiopsis_ 238–243; _Rhiptozamites_ 244,
245; _Phylladoderma_ 244; _Euryphyllum_ 245;
_Artisia_ 246–248; _Dadoxylon_ 248–260;
_Metacordaites_ 260, 261; _Cordaianthus_ 264–270;
=Mesoxylon= 270–275; =Pelourdea= 277–281;
=Niponophyllum= 282, 283; =Titanophyllum= 283, 284.
CHAPTER XXXIV
C. =PITYEAE= 285–299
=Pitys= 285–289
=Archaeopitys= 290
=Callixylon= 291–293
=Coenoxylon= 293, 294
=Parapitys= 294, 295
=Mesopitys= 295, 296
=Antarcticoxylon= 296–299
CHAPTER XXXV
PALAEOZOIC GYMNOSPERMOUS SEEDS. Pp. 300–365.
I. +Lagenostomales+ 308–318
=Physostoma= 309–312; =Conostoma= 313–316;
=Sphaerostoma= 316; =Lagenostoma= 316; =Gnetopsis=
317, 318.
II. +Trigonocarpales+ 318–332
=Trigonocarpus= 319–321; =Tripterospermum= 321;
=Ptychotesta= 321; =Hexapterospermum= 321–323;
=Polypterospermum= 323; =Pachytesta= 323–326;
=Stephanospermum= 326–329; =Polylophospermum= 329,
330; =Codonospermum= 330, 331; =Aetheotesta= 331,
332; =Eriotesta= 332; =Gaudrya= 332.
III. +Cardiocarpales+ 332–356
=Cardiocarpus= 338–340; =Cyclospermum= 340,
341; =Cycadinocarpus= 341; =Rhabdocarpus= and
=Rhabdospermum= 341–345; =Mitrospermum= 345,
346; =Diplotesta= 346; =Leptocaryon= 346, 347;
=Taxospermum= 347; =Compsotesta= 347, 348;
=Samaropsis= 348–354; =Cordaicarpus= 354–356.
IV. +Miscellaneous Seeds+ 356–365
i. =Hexagonocarpus= 356,357; =Decagonocarpus= 357;
=Polypterocarpus= 357, 358; =Rhynchogonium=
358–360; =Boroviczia= 360; =Diplopterotesta= 360,
361; =Musocarpus= 361; =Holcospermum= 361–363.
ii. =Malacotesta= 363; =Thysanotesta= 364;
=Carpolithus= 364, 365; _Microspermum_ 365.
CHAPTER XXXVI
CYCADOPHYTA (+Fossil+). Pp. 366–420.
=BENNETTITALES= 367–420
=Cycadeoidea= 367–417
=Cycadella= 417, 418
=Amphibennettites= 418
=Vectia= 419, 420
CHAPTER XXXVII
=BENNETTITALES= (_continued_) 421–477
=Williamsonia= 421–463
=Wielandiella= 463–467
=Williamsoniella= 467–473
=Cycadocephalus= 473–475
=Weltrichia= 475–477
CHAPTER XXXVIII
CYCADOPHYTA. Pp. 478–506.
i. =Bucklandia= 480–490; =Cycadeomyelon= 490, 491;
=Colymbetes= 491–494; =Cycadeolepis= 494–496.
ii. =Carpolithus= 497–500; =Cycadospadix= 500, 501;
=Beania= 502; =Zamiostrobus=, =Cycadeostrobus=
503–505; =Androstrobus= 505, 506.
CHAPTER XXXIX
CYCADOPHYTA (+Fronds+). Pp. 507–591.
I. +Bennettitales+ 512–566
=Ptilophyllum= 512–529; =Zamites= 529–537;
=Otozamites= 537–545; =Dictyozamites= 546–548;
=Pterophyllum= 548–558; =Cycadites= and
=Pseudocycas= 558–566.
II. +Nilssoniales+ 566–587
=Nilssonia= 566–578; =Ctenis= 578–583; =Pseudoctenis=
584–587.
III. +Incertae sedis+ 587–591
=Sphenozamites= 587–589; =Plagiozamites= 589, 590;
=Cycadorachis= 590, 591.
+List of Works referred to in the Text+ (Vols. III & IV). 592–639
+Index+ 640–656
LIST OF ILLUSTRATIONS
Several of the illustrations are printed from blocks for which I am
indebted to learned societies or to individuals. The sources from
which clichés were obtained are mentioned within square brackets.
The names of donors of photographs or drawings are added after the
descriptions of the figures.
+Frontispiece.+ Charles René Zeiller. From a photograph given to me by
Madame Zeiller.
FIG. PAGE
377. _Cycas circinalis_. A. Malins Smith 2
378. _Cycas revoluta_. [G. R. Wieland.] 3
379. _Encephalartos horridus_ 3
380. _Cycas circinalis_. [Encyclopaedia Britannica.] 4
381. _Cycas revoluta_ and _Zamia Loddigesii_ 5
382. _Encephalartos Ghellinckii_. [Camb. Phil. Soc.] 11
383. _Cycas siamensis_. [Encyclopaedia Britannica.] 12
384. _Cycas circinalis_ 13
385. _Cycas Micholitzii_ and _Zamia angustifolia_ 14
386. _Encephalartos Altensteinii_; _Dioon edule_. S. M. Wadham. 15
387. Cycadean Fronds 16
388. _Zamia Wallisii_ 17
389. _Zamia integrifolia_. [Camb. Univ. Press.] 18
390. _Zamia Loddigesii_ 18
391. _Bowenia spectabilis_. [Encyclopaedia Britannica.] 20
392. _Cycas pectinata_, _C. Riuminiana_, _C. angulata_,
_Encephalartos_, and _Stangeria_ 21
393. _Stangeria_, _Encephalartos_, and _Ceratozamia_ 22
394. _Macrozamia Preissii_. [Camb. Univ. Press.] 23
395. _Zamia floridana_. [G. R. Wieland.] 24
396. _Dioon edule_, _Cycas circinalis_, etc., _Encephalartos_,
_Bowenia_, _Macrozamia_, _Microcycas_ 26
397. _Stangeria paradoxa_. [New Phytologist; A. G. Tansley.] 29
398. _Macrozamia_ 29
399. Cycadean foliar bundles 31
400. _Cycas Micholitzii_. [Camb. Phil. Soc.] 33
401. _Lyginodendron Landsburgii_. R. Kidston 37
402. _Lyginopteris oldhamia_. [Camb. Phil Soc.] 39
403–405. _Lyginopteris oldhamia_ 41, 44, 48
406. _Lyginopteris oldhamia_. F. W. Oliver 49
407. _Crossotheca Hoeninghausi_. R. Kidston and other sources 53
408. _Lagenospermum Sinclairi_; _Lagenostoma_; _Calymmatotheca
Stangeri_; _Crossotheca Hoeninghausi_ 57
409. _Lagenostoma_ 58
410. _Lyginopteris oldhamia_ 69
411, 412. _Heterangium Grievii_ 73, 76
413. _Sphenopteris elegans_ 78
414. _Sphaerostoma ovale_ 79
415. _Heterangium Grievii_; _H. tiliaeoides_; _Lyginopteris_ root 82
416. _Medullosa_ (stem-anatomy) 92
417. _Medullosa centrofilis_ 96
418. _Myeloxylon radiatum_; _Medullosa stellata_; _M. Leuckarti_ 103
419. _Medullosa Leuckarti_ 104
420. _Myeloxylon radiatum_; _Medullosa anglica_, and _Medullosa_ sp. 107
421. _Potoniea adiantiformis_; _Linopteris obliqua_; _Neuropteris
heterophylla_ 111
422. _Neuropterocarpus Kidstoni_. [Edinburgh Royal Society.] 114
423–426. _Trigonocarpus Parkinsoni_ 118, 120, 121
427. _Codonotheca caduca_. [New Phytologist.] 125
428. _Whittleseya elegans_; _W. brevifolia_ 128
429. _Whittleseya elegans_ 130
430–432. _Dolerophyllum Goepperti_ 133, 134, 137
433. _Ottokaria bengalensis_. [Indian Geol. Survey.] 140
434. _Strobilites Milleryensis_ 141
435, 436. _Colpoxylon aeduense_ 143
437, 438. _Rhexoxylon africanum_ 146, 148
439, 440. _Sutcliffia insignis_ 150, 151
441. _Steloxylon Ludwigii_ 163
442. _Pecopteris Pluckeneti_ 167
443. _Eremopteris artemisaefolia_; _Samaropsis acuta_ 170
444. _Samaropsis acuta_. R. Kidston 171
445. _Wardia fertilis_ 172
446–448. _Megaloxylon Scotti_. [Camb. Phil. Soc.] 176–178
449, 450. _Rhetinangium Arberi_. W. T. Gordon 182
451. _Stenomyelon tuedianum_ 183
452. _Stenomyelon tuedianum_. R. Kidston 185
453. _Ptychoxylon Levyi_; _Cycadoxylon Fremyi_; _C. robustum_ 188
454, 455. _Calamopitys Saturni_. M. Zalessky 191, 192
456. _Kalymma grandis_ 195
457. _Eristophyton fasciculare_ 197
458. _Eristophyton Beinertianum_. M. Zalessky 199
459. _Cladoxylon mirabile_; _C. dubium_; _C. taeniatum_; _Syncardia
pusilla_ 202
460. _Cladoxylon Kidstoni_; _C. mirabile_ 206
461. _Völkelia refracta_ 209
462. _Protopitys Buchiana_ 211
463. _Poroxylon Edwardsii_. C. E. Bertrand and F. W. Oliver 216
464. _Poroxylon Edwardsii_; _P. Boysseti_. C. E. Bertrand 218
465. _Cordaites_ leaf. (_C. Felicis._) R. Kidston 228
466. _Cordaites principalis_; _Artisia transversa_. R. Kidston 231
467. _Cordaites lingulatus_ 234
468. _Cordaites_ (_Rhizo-Cordaites_); _Cordaites circularis_; _Cordaites_
sp. cf. _C. Lacoei_; _C. crassifolius_ 237
469. _Cordaites aequalis_; _C. Clerci_. M. Zalessky 239
470. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. G. R. Wieland. 241
471. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. [Geological
Society.] 241
472. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. [Geol. Surv.
India.] 242
473. _Cordaites_ stem 246
474, 475. _Dadoxylon materiarum_ 257
476. _Dadoxylon Pedroi_ 259
477. _Cordaites_ root 262
478. _Cordaites?_ root. T. N. Leslie 263
479. _Cordaianthus_. F. E. Weiss 265
480. _Cordaianthus Pitcairniae_; _C. Volkmanni_ 266
481. _Cordaianthus Grand’Euryi_; _C. Williamsoni_; _C. Zeilleri._
C. E. Bertrand 268
482. _Cordaianthus microsporangia_ 270
483. _Mesoxylon Sutcliffii_ 272
484. _Pelourdea vogesiaca_. [Geologists’ Assoc.] 279
485. _Titanophyllum Grand’Euryi_ 284
486, 487. _Pitys antiqua_ 286, 287
488. _Pitys primaeva_ 288
489. _Callixylon Trifilievi_. M. Zalessky 292
490. _Mesopitys Tchihatcheffi_ 296
491. _Antarcticoxylon Priestleyi_ 298
492. Diagram of a synthetic type of seed 303
493. _Lagenostoma ovoides_; _L. Lomaxi_; _Physostoma elegans_;
_Telangium Scotti_; _Stephanospermum akenioides_ 311
494. _Stephanospermum akenioides_; _Conostoma oblonga_; _Gnetopsis
elliptica_; _Physostoma elegans_; _Mitrospermum compressum_ 314
495. _Polypterospermum Renaultii_; _Ptychotesta tenuis_;
_Polylophospermum stephanense_; _Hexapterospermum
stenopterum_; _Diplotesta avellana_; _D. Grand’Euryana_;
_Taxospermum Grüneri_ 322
496. _Pachytesta incrassata_; _Polypterocarpus anglicus_ 324
497. _Pachytesta_ 325
498. _Codonospermum olivaeforme_; _Aetheotesta elliptica_ 330
499. _Samaropsis emarginata_ 337
500. _Cardiocarpus drupaceus_ var. _expansus_ 339
501. _Cardiocarpus sclerotesta_; _Rhabdocarpus cyclocaryon_ 340
502. _Samaropsis fluitans_; _S. emarginata_; _S. bicaudata_; _S.
Seixasi_; _S. barcellosa_; _S. Newberryi_; _Cordaicarpus
Cordai_ 350
503. _Samaropsis Leslii_ 352
504. _Samaropsis Milleri_. [Geol. Surv. India.] 353
505. _Cordaicarpus Cordai_ 355
506. _Holcospermum sulcatum_; _Codonospermum anomalum_;
_Diplopterotesta spitzbergensis_; _Gnetopsis elliptica_;
_Thysanotesta sagittula_; _Rhynchogonium costatum_;
_Boroviczia Karpinskii_; _Hexagonocarpus Noeggerathi_;
_Rhabdospermum tunicatum_ 359
507. _Cycadeoidea marylandica_. [G. R. Wieland.] 373
508, 509. _Cycadeoidea Wielandi_ [G. R. Wieland.] 375, 376
510. _Cycadeoidea_ sp. 377
511. _Cycadeoidea Gibsoniana_ 377
512. _Cycadeoidea ingens_. [G. R. Wieland.] 378
513–515. _Cycadeoidea_. [G. R. Wieland.] 380–383
516. _Cycadeoidea Dartoni_ 384
517–523. _Cycadeoidea Gibsoniana_ 387–394
524–527. _Cycadeoidea_ (_Bennettites_) _Morierei_. [O. Lignier.] 397–402
528–532. _Cycadeoidea dacotensis_. [G. R. Wieland.] 404–408
533. _Cycadeoidea colossalis_. [G. R. Wieland.] 410
534. _Cycadeoidea Reichenbachiana_. [A. Rothpletz.] 411
535–537. _Cycadeoidea gigantea_. [Geological Soc.] 413, 414
538. _Cycadeoidea micromyela_ 415
539. _Cycadeoidea Jenneyana_ (_?_) [G. R. Wieland.] 416
540. _Vectia luccombensis_. [Trustees of the British Museum.] 419
541–543. _Williamsonia gigas_ 424–427
544. _Williamsonia gigas_. [Yorkshire Nat. Union.] 428
545. _Williamsonia gigas_. A. G. Nathorst. 429
546, 547. _Williamsonia gigas_ 430, 431
548. _Williamsonia gigas_. O. Lignier. 432
549, 550. _Williamsonia gigas_. [Cambridge Phil. Soc.] 435, 436
551. _Williamsonia spectabilis_. A. G. Nathorst. 437
552. _Williamsonia spectabilis_. [Geological Soc.] 438
553, 554. _Williamsonia Leckenbyi_. A. G. Nathorst. 439, 440
555, 556. _Williamsonia whitbiensis_. A. G. Nathorst. 441
557. _Williamsonia_ sp. [Indian Geol. Survey.] 444
558. _Williamsonia Blandfordi_. [Indian Geol. Survey.] 446
559. _Williamsonia Carruthersi_ 447
560. _Williamsonia Bucklandi_ 449
561. _Williamsonia scotica_ 450
562–564. _Williamsonia scotica_. [Royal Society.] 451–453
565. _Williamsonia spectabilis_; _W. whitbiensis_; _W. mexicana_ 459
566, 567. _Wielandiella angustifolia_ 463, 464
568. _Wielandiella angustifolia_. A. G. Nathorst. 466
569–573. _Williamsoniella coronata_. [Royal Society.] 468–471
574. _Cycadocephalus Sewardi_. A. G. Nathorst. 474
575. _Bucklandia anomala_ 482
576. _Bucklandia Milleriana_ 484
577. _Bucklandia Yatesii_ 485
578. _Bucklandia buzzardensis_. [Trustees of the British Museum.] 486
579. _Bucklandia indica_. [Trustees of the British Museum.] 488
580, 581. _Colymbetes Edwardsi_ 492, 493
[Trustees of the British Museum.]
582, 583. _Cycadolepis_ sp. 495
584, 585. _Carpolithus conicus_ 498
[Trustees of the British Museum.]
586. _Beania gracilis_. [W. G. Carruthers.] 502
587. _Ptilophyllum pecten_. [Trustees of the British Museum.] 513
588, 589. _Ptilophyllum pecten_ 514, 516
[Geological Surv. India.]
590. _Ptilophyllum pecten_ and _Williamsonia Blandfordi_ 517
[Geological Surv. India.]
591. _Ptilophyllum cutchense_. [Geological Society.] 518
592. _Ptilophyllum pecten_ 519
593. _Ptilophyllum pecten_. [Geological Society.] 519
594. _Ptilophyllum pecten_ 520
595. _Ptilophyllum pecten_ 523
596. _Ptilophyllum pecten_. [Trustees of the British Museum.] 523
597. _Ptilophyllum boreale_. A. G. Nathorst. 526
598. _Ptilophyllum antarcticum_; _P. Anderssoni_ 527
599. _Zamites gigas_. [Encyclopaedia Britannica.] 533
600. _Zamites recta_ 534
601. _Zamites Buchianus_; _Z. Carruthersi_; _Z. Zitteli_ 535
602. _Zamites Buchianus_ 536
603. _Otozamites Goeppertianus_; _O. Bechei_ 538
604. _Otozamites Bechei_ 539
605. _Otozamites Bechei_ 541
606. _Otozamites Beani; O. Bunburyanus_ [Encyclopaedia Britannica.] 542
607. _Otozamites bengalensis._ [Geological Surv. India.] 542
608. _Otozamites Kliptsteini._ [Geological Society.] 545
609. _Dictyozamites Hawelli_ 548
610. _Pterophyllum Jaegeri_ 549
611. _Pterophyllum Nilssoni; Nilssonia mediana_ 551
612. _Pterophyllum Fayoli_ 552
613. _Pterophyllum Braunianum_ 554
614. _Pterophyllum Nathorsti; Nilssonia tenuicaulis_ 556
[Royal Society of Scotland.]
615. _Pterophyllum Nilssoni_ [Trustees of the British Museum.] 557
616. _Pterophyllum Lyellianum_ [Trustees of the British Museum.] 557
617. _Pseudocycas insignis_ 562
618. _Pseudocycas Saportae._ [Encyclopaedia Britannica.] 564
619. _Nilssonia pterophylloides; N. brevis; N. polymorpha_ 567
620. _Nilssonia brevis; N. saighensis_ 570
621. _Nilssonia rajmahalensis._ [Geological Surv. India.] 571
622. _Nilssonia compta._ [Trustees of the British Museum.] 574
623. _Nilssonia princeps._ [Geological Surv. India.] 577
624, 625. _Ctenis_ sp. [Manchester Phil. Lit. Society.] 579
626. _Ctenis sulcicaulis_ 583
627. _Pseudoctenis eathiensis_ [Trustees of the British Museum.] 584
628. _Sphenozamites Rochei_ 588
629. _Sphenozamites Belli._ [Trustees of the British Museum.] 588
CHAPTER XXVIII.
CYCADALES (+recent+).
Among the fossil genera described in the last chapter of the second
volume some were spoken of as true Ferns though most of them, it
was added, ‘may safely be regarded as plants which will ultimately
be shown to belong to some other group, in most cases that of the
Pteridosperms.’ Since this was written additional evidence has
been obtained in favour of the inclusion of certain genera in the
Pteridosperms. In the case of _Taeniopteris_, one of the genera already
described, there is reason to believe that at least one species is a
member of the Cycadales and not a true Fern as formerly supposed.
The Pteridosperms so far described are represented for the most part
by sterile leaves preserved as impressions, the genera founded on
more satisfactory material having been reserved for treatment in this
volume. As these genera are founded to a large extent on anatomical
characters oscillating in their essential features between recent Ferns
and Cycads, it is important that the student should be in possession of
the anatomical characteristics of both of these classes; and for this
reason a general account of recent Cycads is intercalated between the
Pteridosperms already described and those reserved for treatment in
this volume.
* * * * *
The section of the Gymnosperms known as the Cycadales, represented
by nine recent genera and less than 100 species, is of exceptional
importance phylogenetically and demands special attention from
palaeobotanical students. Familiarity with the morphology of recent
forms is essential not only in relation to extinct cycadean plants
but also to types which, though not sufficiently close to surviving
species to be included with them in one class, exhibit features
regarded by many botanists as indications of an affinity either to true
Cycads or to some generalised stock of which they are an offshoot.
The Cycads of to-day may fairly be spoken of as anachronisms, plants
appropriate to a former age but out of harmony with the present. They
are confined to tropical and sub-tropical regions in both the old
and new world. In habit many of them resemble tree-ferns, but the
columnar stem, which may live to a great age and attain a height of
20 metres, differs from that of ferns in its gradually tapered form
consequent on the presence of one or more cambial cylinders. Though
often unbranched (fig. 377) branching of the main trunk is by no means
unusual (fig. 378; fig. 381, B). Many Cycads are geophilous and
have short tuberous stems (figs. 383, 395, 1_a_; 396, E): the genus
_Zamia_ includes a few epiphytic forms[1]. The typical cycadean stem
is covered with persistent petiole-bases with or without an admixture
of smaller scale-leaf bases (figs. 379, 380), while in several species
a transversely wrinkled or irregularly fissured periderm forms the
superficial tissue (figs. 381, B; 383). The foliage-leaves are
relatively large and, with the exception of the bipinnate fronds of
_Bowenia_ (fig. 391), they are always pinnate. The fronds usually form
a terminal crown (figs. 377, 379) and as many as 100 may be produced
from one bud. In _Zamia pygmaea_[2] the fronds are only 10–12 cm. long,
but in some cycads they reach a length of several metres. On both
young foliage-leaves and scale-leaves long and very rarely branched[3]
unicellular hairs (fig. 396, N) form a characteristic feature and take
the place of the ramental scales of the majority of ferns. The apex of
the stem shown in fig. 386, A is covered with a mass of woolly hairs
and several scale-leaves are seen on the lower part of the bud.
[Illustration: Fig. 377. _Cycas circinalis._ From a photograph taken
by Mr A. Malins Smith at Teldeniya (Ceylon).]
[Illustration: Fig. 378. _Cycas revoluta_, as grown by Japanese
horticulturalists. (After Wieland.)]
[Illustration: Fig. 379. _Encephalartos horridus._]
[Illustration: Fig. 380. _Cycas circinalis._ Stem showing alternate
zones of leaf-bases (F) and scale-leaf bases (S). (From the
_Encyclopaedia Britannica_.)]
[Illustration: Fig. 381. A. _Cycas revoluta_, megasporophylls. B.
_Zamia Loddigesii_, branched stem.]
All recent Cycads are dioecious. The reproductive shoots, except the
megasporophylls of _Cycas_—which have departed to a less extent than
those of other genera from the foliage-leaf plan (fig. 381, A; fig.
392, A–C) and are borne in a terminal cluster through which the stem
subsequently pushes its way—consist of a varying number of micro-
or mega-sporophylls in dense spirals on the axis of an elongated or
oval strobilus (figs. 386, B, 393, 394). The microsporophylls are
occasionally verticillate[4]. The strobili are sometimes though rarely
branched[5] and generally but by no means invariably[6] terminal on
the main stem which branches sympodially[7]. A striking example of
lateral strobili has recently been described by Chamberlain[8] who
figures a stem of _Macrozamia Moorei_ with fertile shoots wedged among
the persistent petiole-bases, a condition very similar to that in
the Mesozoic Bennettitales. Pearson has also described clear cases
of laterally-borne cones in _Encephalartos._ _Cycas_ exhibits two
kinds of branching, the female plants being monopodial while in the
male the branching is sympodial. The microspores are produced in
sporangia grouped in more or less well defined sori (figs. 389, A; 392,
E–G). There is no definite annulus, but in the occurrence of groups
of thick-walled cells some microsporangia recall those of certain
ferns[9]. The ovules vary considerably in size, sometimes exceeding
5 cm. in diameter: there are usually two on each megasporophyll
(figs. 393, C; 394; 395, 1_d_) but in most species of _Cycas_ (fig.
392, B) and occasionally in other genera the number is larger[10]. A
thick integument encloses the nucellus with which it is fused except
in the apical region (fig. 396, A, B). Below the comparatively long
micropylar tube is a well-developed pollen-chamber (fig. 396, B′, _p_),
a striking feature of Cycadean ovules, immediately above the megaspore;
the latter is filled with prothallus-tissue and bears a small apical
group of archegonia on the floor of a depression (fig. 396, A–B′).
In _Microcycas_[11] as many as 200 archegonia are recorded—a very
exceptional case—and these are not confined to the apical region,
though only the apical archegonia are functional. Each archegonium
is characterised by a very large oval egg-cell and a much reduced
neck[12]. The microspores usually produce a single prothallus-cell, a
stalk-cell, and body-cell, and from the body-cell are developed two
spirally ciliated spermatozoids (fig. 396, M). In this respect also
the monotypic genus _Microcycas_ is peculiar: it may have as many as
8 body-cells and 16 male gametes in a single pollen-tube (fig. 396,
G), while in _Ceratozamia_[13] 4 gametes have been seen in one tube.
The pollen-tube grows like a fungal mycelium into the nucellar tissue
and the male gametes are formed in the distended proximal end which
on bursting liberates the motile sperms with the watery cell-sap.
Fertilisation is succeeded by the development of a homogeneous
proembryo partially or completely filling the zygote (fertilised
egg): by the formation of long suspensors the embryo is brought into
contact with the food-store of the prothallus. In some Cycads, _e.g._
_Encephalartos_, the embryogeny exhibits a close resemblance to that of
_Ginkgo_[14]. The embryo is dicotyledonous[15].
The single stele of the stem is characterised by a large pith which
in some genera (_e.g._ _Encephalartos_, _Macrozamia_) contains an
anastomosing system of collateral bundles. The vascular tissue of a
cycadean stem forms a cylinder of secondary xylem and phloem, the
primary xylem being represented only by a few, usually crushed,
protoxylem elements on the inner margin of the reticulately pitted
or scalariform tracheids. Both xylem and phloem are traversed by
numerous broad and deep medullary rays[16]. The looser texture and
more parenchymatous structure of Cycadean wood afford a ready means
of distinguishing it from the wood of Conifers: for the Cycadean
type the term _manoxylic_ is proposed and _pycnoxylic_ for the more
compact coniferous wood[17]. Rims (or ‘bars’) of Sanio, of which
much has been said in discussions on the phylogeny of Conifers, have
recently been described in the petiolar xylem of _Cycas revoluta_:
the rims are short and ‘cling closely to the borders of the pits,’
features which also characterise the rims found in the cones of the
Araucarineae and in the root- and cone-wood of certain Pines[18]. In
some Cycads the secondary xylem and phloem form a single cylinder,
but in others (_Cycas_, _Encephalartos_, _Macrozamia_, _Bowenia_) the
cambium is succeeded by one or several concentric cylinders of meristem
which have their origin in the pericycle. The spasmodic occurrence
of separate arcs of inversely orientated secondary xylem and phloem
between the normal cylinders is a feature of importance from the
point of view of comparison with the Palaeozoic Medulloseae[19]. The
occurrence of concentric cauline strands in the cortex of _Cycas_ is
also a peculiarity worthy of notice. Successive bands of periderm, and
occasionally a considerable amount of phelloderm[20], are formed in the
peripheral region of the stem.
The leaf-traces in an adult stem exhibit a striking feature in their
indirect or girdle-like course to the leaves (fig. 396, H, _g_) and
in the gradual change from an endarch (fig. 396, O) to an apparently
mesarch structure (fig. 400) as they pass from the perimedullary zone
to the petiole: except at the base of the petiole the vascular bundles
of the frond-axis consist of (i) centripetally developed xylem with a
median protoxylem and a much smaller amount of centrifugal xylem (fig.
400) separated by a few parenchymatous elements from the centripetal
xylem, (ii) an external arc of protophloem and within this metaphloem
and parenchyma[21]. In the slender petiole of _Bowenia_ there are a few
collateral bundles arranged in the form of a circle or ellipse[22];
in _Cycas_ and some other genera the more numerous bundles form a
pattern like an inverted U, and in some species of _Encephalartos_ the
number is greater and the strands more irregularly scattered[23]. In
the vegetative stems there is no centripetal xylem in the stele, but
scattered centripetal tracheids occasionally occur internal to the
protoxylem in the steles of the peduncles[24].
* * * * *
=Cycadeae.= Megasporophylls each bearing 2–8 ovules, borne separately
like foliage-leaves and not in strobili. Pinnae have a midrib but no
lateral veins (figs. 384, 387, A). _Cycas_ (fig. 377).
=Zamieae.= Both kinds of sporophylls form strobili. Pinnae have
several dichotomously branched, more or less parallel veins. _Zamia_
(figs. 388–390), _Macrozamia_, _Encephalartos_ (figs. 379, 386, C),
_Ceratozamia_, _Dioon_ (fig. 386, B), _Microcycas_.
=Stangerieae.= Strobili as in Zamieae. Pinnae fern-like, numerous
dichotomously branched lateral veins given off from a midrib.
_Stangeria._
=Bowenieae.= Leaves bipinnate (fig. 391), strobili as in Zamieae.
_Bowenia._
_Distribution._ The most widely spread genus, _Cycas_, occurs in Siam,
India, the Nicobar Islands, Ceylon, Madagascar, and Australia, in
many of the islands in the Indian and Pacific oceans, in New Guinea,
Borneo, New Caledonia, New Britain, China and Japan[25]. _Zamia_, the
most northerly genus, extends from North Mexico and Florida through
Central America and some of the West Indian islands to Ecuador,
Bolivia, Chile, and Peru. _Dioon_ and _Ceratozamia_ are confined to
South Mexico, and _Microcycas_ flourishes on the Cuban mountains. The
continent of Africa possesses two endemic genera _Encephalartos_ and
_Stangeria._ _Encephalartos_ extends from Cape Colony through Natal and
Zululand to Zanzibar and Mombasa[26]: a specimen in the Kew Herbarium
(probably _E. Hildebrandti_) is said to have been collected as far
north as the Soudan. Two species are recorded from the Congo[27] and
_E. Barteri_, discovered by Barter in Central Africa, is recorded from
the Gold Coast[28]. _Stangeria_ has a much more limited range in S.E.
Africa[29]; Australia possesses _Macrozamia_, represented by several
species in Western Australia, New South Wales and Queensland, _Cycas_
in Queensland and the Northern territory and the Queensland genus
_Bowenia_. There are no Cycads in New Zealand. As a whole Cycads have
a limited range and with the exception of _Cycas_ and _Zamia_ none of
them extend beyond the limits of a single continent. They are as a rule
not gregarious plants and play a subordinate part in the facies of the
vegetation. _Macrozamia_ forms dense thickets[30] in some districts
and occurs both in exposed situations and in association with Palms
in damp Queensland forests. Chamberlain[31] speaks of 100 plants
of _Dioon edule_ as visible in one view in South Mexico where the
species forms a mountain forest. In Florida _Zamia pumila_[32] grows
in dense moist woods, a habitat in contrast to that of many Cycads.
The Mexican _Ceratozamia_ is associated with luxuriant vegetation,
while its compatriot _Dioon_[33] lives in blazing sunshine. Sir
Joseph Hooker[34] speaks of _Cycas_ living in the deepest and hottest
valleys in Sikkim. _Encephalartos_ is essentially a xerophilous genus.
_Stangeria paradoxa_ is said to be confined to forests in Cape Colony,
and another species grows among the grass of the Park-lands in open
country[35]. While it is true that many Cycads are characteristic of
dry regions some species flourish in places where shade and moisture
are abundant.
Though it is impossible in many cases to form an estimate of the age
of individual plants, there are clear indications that some specimens
afford notable instances of longevity. Chamberlain estimates the age of
some plants of _Dioon spinulosum_ as exceeding 400 years and mentions
an example of _D. edule_ that is probably 1000 years old. An unusually
tall plant of _Encephalartos_ in the Botanic Garden of Amsterdam
is believed by Prof. de Vries to have reached the venerable age of
2000 years[36]. The restricted range and in many cases the solitary
existence of recent Cycads, with their tall stems clothed with the
persistent cork-covered stumps of thousands of fronds, deepens the
impression of antiquity derived from a study of the geological history
of this dwindling race.
_Stems._ The tall columnar stems of some species of _Cycas_, often
branched or bearing numerous ovoid buds like enlarged bulbils[37],
are characterised by the regular alternation of large and small
leaf-bases as seen in the stem of _C. circinalis_ reproduced in fig.
380. In older stems of this species the leaf-bases are exfoliated and
the stem is covered with wrinkled and fissured cork; but in _Cycas
revoluta_ the leaf-bases are even more persistent. The columnar but
relatively stout stems of _Encephalartos_ (figs. 379, 382, 386, A) and
_Ceratozamia_ are similarly encased in a covering of petiole-bases, but
in these genera the differences between foliage-leaves and bud-scales
is much less obvious and there is no zonal alternation. On the stems
of _Macrozamia_ the rhomboidal leaf-bases are more uniform in size
and there are no scale-leaves. The tall and often palm-like stems of
_Microcycas_ sometimes show transverse rings on the bark marking
the position of former terminal buds, and in older trunks these may
disappear, leaving a fissured bark[38]. In _Cycas siamensis_ the
tuberous stem is similarly covered with a rough bark (fig. 383) and the
stems of _Zamia_ are also characterised by an absence of persistent
leaf-bases (figs. 381, B; 395, I_a_, _a_). It is pertinent to remind
the palaeobotanical student of the occurrence of flowering plants
with stems closely simulating those of some Cycads. Prof. Bower[39] in
describing _Rhynchopetalum montanum_, an Abyssinian Lobeliaceous plant,
drew attention to the similarity in surface-features and to some extent
in anatomical structure to cycadean stems. The resemblances are further
emphasised in a more recently published account of the same species
under a different name, _Lobelia Rhynchopetalum_[40].
[Illustration: Fig. 382. _Encephalartos Ghellinckii._ (¹⁄₁₁ nat.
size.)]
[Illustration: Fig. 383. _Cycas siamensis._ (From the _Encyclopaedia
Britannica_.)]
_Fronds._ A general acquaintance with the various types of fronds
illustrated by recent Cycads is important to the student of fossils
not only to enable him to compare existing and extinct forms but
as affording safeguards against possible sources of error in the
description and identification of impressions[41]. The vernation
exhibits less uniformity than in Ferns: in _Cycas_ the rachis is
straight and the pinnae circinately coiled (fig. 220, B, vol. +ii.+
p. 283); in _Zamia_ and _Stangeria_ the rachis is bent and the pinnae
straight, while in _Ceratozamia_ and other genera both the axis and
leaflets are straight. As Braun pointed out, there is as a rule no
terminal leaflet, or it may be pushed to one side giving a forked
appearance to the frond apex[42].
[Illustration: Fig. 384. _Cycas circinalis_, abnormal frond. (From a
specimen in the British Museum.)]
_Cycas._ The presence of a strong midrib and the absence of lateral
veins are distinguishing features: the lower margin of the lamina is
frequently decurrent (fig. 387, A). In _C. circinalis_ the pinnae
may reach 40 cm. in length with a fairly uniform breadth of 2 cm. A
frond of this species in the British Museum, not quite complete, has
a length of 112 cm.: on the lower part of the rachis strong spines
replace the leaflets and near the apex of the leaf concrescent pinnae
form a continuous lamina traversed by seven ribs and dissected at the
margin into acuminate teeth (fig. 384): some of the pinnae are forked
as in _Cycas Micholitzii_[43] (fig. 385). Several years ago I noticed
a similar instance of concrescence in a small plant of _C. circinalis_
in the Royal Gardens, Kew (fig. 387, I). In _Cycas Micholitzii_
the pinnae, reaching a length of 20 cm., are repeatedly and deeply
forked (fig. 385, A, B; fig. 400): the pinnae of _C. Rumphii_ var.
_bifida_[44] are also deeply dissected. _Cycas Beddomei_ has very
narrow pinnae (15 cm. × 2 mm.) similar to those of the Wealden species
_Cycadites Saportae_, and it is noteworthy that narrow leaflets with
a strongly revolute lamina would produce casts with two parallel ribs
(the grooves between the midrib and the edge of the lamina) simulating
the double midrib of the fossil genus _Pseudocycas_. In some fronds,
_e.g._ _C. Cairnsiana_, the midrib is hardly visible on the upper
face of a dried pinna which shows a longitudinal wrinkling simulating
parallel venation.
[Illustration: Fig. 385. A, B, _Cycas Micholitzii._ (After
Thiselton-Dyer.) C, _Zamia angustifolia._]
_Encephalartos._ The fronds of this genus, in _Encephalartos
Laurentianus_[45] reaching the exceptional length of 7 metres, bear
alternate pinnae exhibiting a considerable range in form and breadth.
In _E. longifolius_, _E. Altensteinii_ (fig. 386, C), _E. Lehmanni_,
etc., the pinnae are for the most part linear, reaching a length of
20 cm. and a breadth of 2 cm.: in _E. caffer_ (fig. 387, D), _E.
latifolius_, and others the pinnae are broader and shorter and often
spinous. A frond of _E. longifolius_ or _E. Altensteinii_ may bear both
entire and lobed, spinous pinnae. In _E. Frederici-Guilielmi_ (fig.
387, G) and _E. Ghellinckii_[46] (fig. 382) the pinnae are very narrow
and almost filiform, with revolute edges. The thick and leathery pinnae
of some species are attached obliquely to the edge or to the upper
sloping sides of the rachis which forms a prominent ridge between the
rows of leaflets, and characteristic oval scars are left on the fall
of the pinnae (fig. 387, D, G′). The lamina in most species contains
several veins more or less parallel to the margins and often much more
prominent on the lower than on the upper surface.
[Illustration: Fig. 386.
A. _Encephalartos Altensteinii_, apex of stem.
B. _Dioon edule_,megastrobilus. (From a photograph by Mr S. M. Wadham.)
C. _Encephalartos Altensteinii_, frond.]
[Illustration: Fig. 387. Cycadean fronds. A, _Cycas circinalis_;
B, _Macrozamia Fraseri_; C, _Macrozamia Denisoni_; D, _Encephalartos
caffer_; E, F, _Dioon edule_ from below and above; G, _Encephalartos
Frederici-Guilielmi_, G′, side-view; H, _Ceratozamia mexicana_; I,
_Cycas circinalis_, lower part of young frond.]
_Zamia._ In _Zamia angustifolia_ (fig. 385, C) and _Z. linifolia_ the
pinnae are long and very narrow: the other extreme is represented by
_Z. Wallisii_[47] (fig. 388) with broad ovate segments reaching a
length of nearly ·5 metre and attached to the rachis by a short stalk;
the veins are prominent and dichotomously branched. Other forms of
pinnae are represented by _Z. integrifolia_, _Z. floridana_, and _Z.
Loddigesii_ (figs. 389, 390, 395). The broad and short pinnae of
_Z. furfuracea_[48] bear a close resemblance, except in the absence
of an auriculate base, to those of some species of the fossil genus
_Otozamites_. The broadly linear pinnae of _Z. pseudoparasitica_ (45
cm. × 3 cm.) often show longitudinal wrinklings on drying which suggest
comparison with the corrugated lamina of the fossil species _Nilssonia
brevis_. A basal pad or callosity on the slender bases of the pinnae is
characteristic of many _Zamia_ fronds.
[Illustration: Fig. 388. Pinna of _Zamia Wallisii_. From a drawing
after A. Braun in the Kew Herbarium. (⅓ nat. size.)]
[Illustration: Fig. 389. _Zamia integrifolia_ bearing a megastrobilus
and showing foliage-leaves and scale-leaves. A, microsporophyll; B,
megasporophyll. (After Rendle, from Jacquin.)]
[Illustration: Fig. 390. Small frond of _Zamia Loddigesii_. (⅔ nat.
size.)]
_Ceratozamia._ The fronds bear a fairly close resemblance to those
of _Macrozamia_: in _Ceratozamia mexicana_ the linear pinnae reach a
length of over 30 cm. and a breadth of 2–3 cm.; the lamina tapers to a
narrow apex and is more abruptly contracted at the base (fig. 387, H).
The veins in _Ceratozamia_ are sub-parallel and dichotomy occurs up to
the middle of the lamina[49]. A striking feature is the occurrence of
two opposite stipule-like projections a short distance above the base
of the petiole.
_Macrozamia._ A noteworthy feature in some species is the attachment of
the linear pinnae along the middle line of the rachis (fig. 387, C); in
others (fig. 387, B) the leaflets are attached laterally and may have
a basal callosity. The parallel veins, which branch dichotomously near
the base of the lamina, are often much more prominent on the lower than
on the upper face. In _M. heteromera_[50] (fig. 396, F, F′) the narrow
pinnae are deeply forked and strongly revolute. The spirally twisted
rachis of _M. spiralis_, _M. heteromera_, etc., is a striking feature
recalling the Rhaetic fern _Camptopteris spiralis_ Nath[51].
_Dioon._ The arrangement of the linear pinnae of _D. edule_ (fig. 386,
B), _D. spinulosum_, and _D. Purpusii_[52] forms a ready means of
distinguishing the fronds of this genus: the pinnae, often contiguous
and at right-angles to the rachis, are attached in a lateral groove
by an expanded and slightly decurrent base. The difference between
the lower and upper face of a frond (fig. 387, E, F) affords a good
illustration of a common source of error in the identification of
fossil specimens. The leaflets of _D. spinulosum_, which except in
their spinous margin are very similar to those of _D. edule_, may
reach a length of 15 cm. and a breadth of 8 mm. The parallel veins are
unbranched[53].
_Microcycas[54]._ The pinnae of this genus, very like those of the
Wealden species _Zamites Buchianus_, reach a length of 20 cm. and a
breadth of 8 mm.: on falling they leave oblong scars resembling those
on the rachis of _Encephalartos_.
_Stangeria._ This genus is particularly interesting because of its
fern-like habit and venation. The large fronds of _S. paradoxa_[55]
bear broadly linear acuminate pinnae with entire, unevenly lobed,
serrate, or pinnatifid margins. Some leaflets are so deeply dissected
as almost to justify the appellation pinnate. Both entire and dissected
leaflets may occur on one frond and the lower ones may be stalked while
the upper pinnae are sessile. The venation agrees closely with that of
the genus _Taeniopteris_[56].
_Bowenia._ The large fronds of this genus (fig. 391) are peculiar in
being bipinnate; they may reach a length of 2 metres and have a long
slender petiole: the asymmetrical lamina of the segments, entire or
deeply serrate, is attached by a very short stalk; the veins branch
dichotomously[57] and diverge slightly. Both entire and serrate pinnae
may occur on the same plant, but Chamberlain has revived André’s
specific term _serrulata_ in preference to the generally adopted
designation for the serrate forms, _B. spectabilis_ var. _serrata_[58].
[Illustration: Fig. 391. _Bowenia spectabilis_, frond. (From the
_Encyclopaedia Britannica_.)]
_Reproductive shoots_[59]. In _Cycas circinalis_, _C. Rumphii_, and
other species the megasporophylls reach a considerable length and bear
several lateral ovules each of which may be as large as a goose’s
egg: the sterile distal end has the form of a spear-point with an
irregularly serrate edge. In _C. revoluta_, _C. pectinata_, etc., the
sterile part is deeply dissected and may break off (fig. 392, A) from
the fertile portion of the sporophyll. The megasporophylls of _C.
Riuminiana_ exhibit a striking variation in form (fig. 392, B, C);
some are 15 cm. long with several ovules, while others, reduced to 8
cm., bear only two ovules and resemble the sporophylls of _Dioon_.
In all other genera the megasporophylls are aggregated into cones,
but in _Dioon_ the strobili are characterised by their more ovoid
form and by the looser arrangement of the sporophylls (fig. 386, B),
each of which consists of a horizontal stalk expanded distally into
a broadly lanceolate upturned end covered with a thick felt of hairs
and bearing at its base usually 2, rarely 5–6, ovules on cushion-like
swellings. In _Dioon spinulosum_ the cones may be 50 cm. long. Between
the cones of _Microcycas_, over 90 cm. long, and those of some Zamias,
a few centimetres long, there are many intermediate forms. The large
strobilus of an _Encephalartos_ reproduced in fig. 393, D, shows the
convex ends of the sporophylls with a jagged edge, and in monstrous
cones the marginal lobes may be abnormally developed and assume the
appearance of pinnae[60]. Each megasporophyll bears two large ovules
(fig. 393, B). In certain species of _Encephalartos_ the swollen ends
of the sporophylls have a truncate centre like the flattened umbo of
some Pines (fig. 392, D). The presence of two divergent spines is a
peculiarity of the megasporophylls of _Ceratozamia_ (fig. 393, C):
in _Macrozamia_ (fig. 394) the distal ends are prolonged as tapered
processes. The surface of the strobilus of _Stangeria_ is formed by
imbricate and rounded ends of sporophylls (fig. 392, H) not unlike the
cone-scales of _Pinus excelsa_ or _P. cembra_. The megasporophylls of
_Zamia_ are expanded into regular cushion-like hexagons with a flat
central area (figs. 389, B; 395, I_b_).
[Illustration: Fig. 392.
A. _Cycas pectinata_, apex of megasporophyll. (¾ nat. size.)
B, C. _Cycas Riuminiana_, megasporophyll. (¾ nat. size.)
D. _Encephalartos Altensteinii._ Distal end of megasporophylls. (From
the _Gardeners’ Chronicle_.)
E, F. _Cycas angulata_, microsporophyll and sorus.
G, I. _Ceratozamia mexicana_, I, microsporophyll with scars of sori
(_s_); G, sorus. (After Thibout.)
H. _Stangeria paradoxa_, megastrobilus.]
[Illustration: Fig. 393.
A. _Stangeria paradoxa_, part of microstrobilus.
B, D. _Encephalartos villosus_, megastrobilus in surface-view and in
section. (¼ nat. size.)
C. _Ceratozamia mexicana_, single megasporophyll.]
[Illustration: Fig. 394. _Macrozamia Preissii_, megastrobilus and (A)
single megasporophyll; _a_, axis of cone; _p_, stalk of megasporophyll;
_s_, unripe seeds. (After Rendle.)]
[Illustration: Fig. 395. _Zamia floridana._ I_a_, complete plant;
_a_, main trunk; _b_, branch-scar; _c_, secondary root; _d_, primary
tap-root. (⅛ nat. size.) I_b_, I_c_, megastrobilus. (¼ nat. size.)
I_d_, megasporophyll. (½ nat. size.) I_e_, pinna. (¾ nat. size. After
Wieland.)]
The microsporophylls (figs. 389, A; 392, E) are in all genera
aggregated into strobili which often bear a close resemblance to
seed-cones (fig. 393, A). On a single sporophyll of _Cycas circinalis_
there may be as many as 700 sporangia while in _Zamia floridana_ there
are only two microsporangia. The spore-output is large and in extreme
cases, _e.g._ in _Dioon spinulosum_, the average number of spores in a
sporangium is said to be 30,000[61].
_Seeds._ In the great majority of recent species the seeds may be
described as large and afford a striking contrast to the small seeds
of the Mesozoic Bennettitales. A feature of interest from the point
of view of comparison with Palaeozoic seeds is the absence of a
resting stage, germination in some cases following seed-fall without
an interval. As Warming pointed out, the embryo is often undeveloped
when the seeds are shed. An interesting fact is recorded by Capt.
Dorrien-Smith[62] with regard to seed-dispersal: he describes the
heavy pebble-like seeds of a _Macrozamia_ as being hurled from the
ripe cones a distance of 12 ft. The seeds of _Cycas_ are platyspermic;
the woody shell exposed on removal of the outer flesh is slightly
flattened and has two prominent angles, but three-angled seeds may
occur as in _Ginkgo biloba_ (fig. 631, C). In other genera the seeds
are radiospermic. The seed of _Encephalartos Altensteinii_[63] (fig.
396, D) has a square-cut distal end with a small papilla at the
summit of the unusually long micropylar canal (17 mm.). The stone of
this seed (fig. 396, C) shows parallel curved ridges which mark the
position of vascular strands in the inner region of the outer flesh.
The large ovules of _Cycas circinalis_[64] have an integument 1 cm.
thick consisting of an outer and inner flesh and an intervening stony
layer which reaches its greatest development at the base and apex.
Three vascular strands enter the base of the seed, the concentric
strand breaks up in the broad inner flesh into a group of bundles which
embrace but do not penetrate the lower end of the nucellus. Each of
the two lateral strands branches in the outer flesh near its entrance
into the seed; the outer and larger collateral and mesarch bundle
passes up close to the surface of the shell to the seed-apex, while the
inner branch penetrates the shell and, occasionally branching, passes
up the inner region of the inner flesh as far as the micropyle.
In other seeds the tracheal supply of the outer flesh consists of
several bundles and not two as in _Cycas_. The inner flesh abuts on
the nucellus and is connected with it except at the apex (fig. 396,
B). In ripe seeds the nucellus is reduced to a thin membrane enclosing
the large megaspore at the upper end of which is a depression (fig.
396, B′) or sometimes two depressions (fig. 396, I) in the prothallus
containing the archegonia. In the seed of _Dioon edule_[65] (fig. 396,
A) the position of the absciss-layer (_s_) is indicated by a slight
transverse constriction. In the seeds of _Bowenia_, constructed on the
same plan, the inner series of vascular strands appears to be nucellar
in position, thus differing from the strands in _Dioon_, _Cycas_, and
other genera which are confined to the integument. Miss Kershaw[66] in
describing _Bowenia_ speaks of an upper and a lower pollen-chamber; the
former serves as a storage-place for the microspores prior to their
further development in the lower chamber. Dr Stopes[67] regards the
integument as double in origin, a view suggested by Griffith[68] in
1835, and as homologous with the single integument _plus_ the cupule
of _Lagenostoma_. This view is supported by Mrs Thoday[69]: on the
other hand Miss Kershaw’s investigation of _Bowenia_ seeds leads her
to regard the integument as single. Although there would seem to be a
_prima facie_ case in favour of the dual nature of the integument, the
arguments on the other side have greater weight[70].
[Illustration: Fig. 396.]
[Illustration: Fig. 396.
A. Seed of _Dioon edule_ in longitudinal section; _a_, integument;
_v_, vascular tissue; _m_, prothallus; _n_, nucellus; _p_,
pollen-chamber; _s_, absciss-layer; _ar_, archegonia. (After
Chamberlain.)
B, B′. Seed of _Cycas circinalis_; _a_, _v_, integument (sarcotesta)
and vascular tissue; _b_, sclerotesta; _c_, inner sarcotesta; _m_,
_n_, prothallus and nucellus. (After Stopes.)
B′. Apex of nucellus; _p_, pollen-chamber; _i_, integument; _n_,
nucellus; _ch_, archegonial chamber; _ar_, archegonia.
C, D. Seed of _Encephalartos Altensteinii_; C, surface of stone.
(After Stopes.)
E. Stem of _Bowenia serrulata_; _g_, level of ground. (After
Chamberlain.)
F, F′. Pinnae of _Macrozamia heteromera_.
G. Pollen-tube of _Microcycas Calocoma_. (After Caldwell.)
H. Transverse section of stem of _Encephalartos horridus_; _s_, stele;
_g_, girdle-bundles. (After Mettenius.)
I. Apical view of prothallus of _Cycas_ showing two archegonial
chambers (_ch_). (After Treub.)
K. _Encephalartos Barteri._ Transverse section of stem; _x_, xylem;
_p_, phloem. (After Matte.)
L. _Cycas siamensis._ Transverse section of vascular tissue of young
stem. (After Matte.)
M. _Cycas revoluta_; two motile sperms. (After Miyake.)
N. Long hair with short basal cell from the petiole of _Macrozamia
heteromera_. (After Robertson.)
O. Vascular bundle of _Dioon edule_ from base of petiole; _p_, phloem;
_c_, cambium. (After Mettenius.)]
Recent observations point to the probability that insects play a part
in the pollination of cycadean ovules. Kraus[71] drew attention to the
strong smell emitted by the microstrobili of _Dioon edule_ and noticed
that small bees were attracted to the ripe strobili of _Macrozamia_,
while odourless cones of a neighbouring _Ceratozamia_ received no
attention. Pearson[72] and Rattray[73] have obtained evidence that
beetles and weevils act as pollinators to species of _Encephalartos_.
_Anatomical features._ Allusion has already been made to some of the
more striking anatomical features; the large pith, the occasional
occurrence of medullary vascular bundles, the presence of one or more
cambiums, the large size of the medullary rays, etc. It is worthy of
remark that the occurrence of an anastomosing system of medullary
bundles is not a constant feature within a genus; in _Macrozamia
Fraseri_ such a system is present, but absent in _M. Denisoni_[74]. In
the pith of stems with no medullary bundles cylinders of collateral
bundles may occur in connexion with a fertile shoot. These bundles
arise from the inner face of the main cylinder and pass upwards as
a domical system into the base of the terminal strobilus which is
eventually pushed to one side by the growth of a lateral bud[75].
The secondary xylem tracheids are usually provided with several
rows of bordered pits on the radial walls and resemble those of the
Araucarieae[76], but in Cycads the pits are often not contiguous
and less compact in their distribution. The wood of _Stangeria_
is peculiar in consisting of scalariform tracheids[77] (fig. 397).
Chamberlain describes growth-rings in the wood of _Dioon_; but this is
exceptional. In tangential sections of the stele leaf-trace bundles
are constantly seen passing horizontally through the broad and deep
medullary rays. The pith-cast of a cycadean stem reproduced in fig. 398
shows the wide meshes in the reticulum of tracheal tissue originally
occupied by parenchyma, which on decay left lenticular depressions
represented on the cast by tapered convex areas occasionally bearing
the impress of an outgoing trace in the form of a narrow groove.
The secondary phloem often rivals the xylem in breadth and is not
always easily distinguishable from it; it consists of sieve-tubes,
parenchyma, and fibres. The secondary cambial cylinders characteristic
of _Cycas_, _Encephalartos_, _Macrozamia_, and _Bowenia_, to which
reference was made in the summary of anatomical features, arise in the
pericycle, and a few layers of pericyclic parenchyma occur between
adjacent extrafascicular cylinders of xylem and phloem. In a stem of
_Cycas media_ 35 cm. in diameter examined by Worsdell there were 12
concentric cylinders. Matte[78] and Miss Dorety[79] have described
partially flattened arcs of extrafascicular xylem and phloem in the
hypocotyl of _Ceratozamia mexicana_. Worsdell[80] first drew attention
to the occasional occurrence of short tracheids on the inner edge of
the secondary wood and to the spasmodic development of cambial arcs in
the tissue between the extrafascicular cylinders forming strands of
inversely orientated xylem and phloem. More recent work by Matte gives
support to Worsdell’s comparison between Medullosan stems and those of
recent Cycads with inversely orientated arcs or concentric vascular
cylinders. The French author draws attention to the close resemblance
between the seedling stems of such species as _Encephalartos Barteri_
(fig. 396, K) and _Cycas siamensis_ (fig. 396, L) with their polystelic
type of structure and the adult stems of _Medullosa_[81]. In the stems
of _Dioon_, _Microcycas_, _Stangeria_, and _Zamia_ no extrafascicular
cylinders are recorded. Two main vascular bundles enter the cortex
from each leaf-base and in most stems these diverge right and left
and more or less completely encircle the stele before passing through
the medullary rays and joining the inner portion of the xylem of
the stele either as double or single bundles. These girdle-bundles
(fig. 396, H) first described by Karsten and Mettenius form a very
characteristic cycadean feature[82]. Adjacent girdles are joined
by connecting cortical bundles and, in addition, there are cauline
collateral bundles in the cortex which form an anastomosing system.
In some cases, _e.g._ species of _Macrozamia_ and occasionally in
_Stangeria_, the female peduncle of a _Ceratozamia_, and in seedlings
of _Bowenia_ and _Cycas revoluta_[83], the leaf-traces pursue a direct
course from petiole to stele as in stems of Bennettitales. It is
noteworthy that in seedlings of _Microcycas_[84], a genus characterised
by a large number of male gametes—presumably a primitive feature—the
leaf-traces are of the girdle-type. The two bundles at the base of a
petiole by repeated subdivision give rise to the numerous collateral
strands of the rachis. A leaf-trace in its passage to the leaf is like
that of a Conifer in having the protoxylem on its inner edge, whereas
in the petiole and elsewhere in the frond it is characterised by an
arrangement of the xylem that has usually been described as mesarch. A
typical vascular bundle from a cycadean frond is seen in fig. 399, C;
by far the greater part of the xylem is centripetal, the centrifugal
xylem being confined to an arc of scattered tracheids or a small strand
separated by a few parenchymatous cells from the protoxylem.
[Illustration: Fig. 397. Tracheids from the stem of _Stangeria
paradoxa_. (After Marsh.)]
[Illustration: Fig. 398. Pith-cast of a _Macrozamia_ stem, (⅖ nat.
size.)]
[Illustration: Fig. 399. Sketches illustrating the changes in the
structure of Cycadean vascular bundles in their course from stem to
leaf: _cp_, _cf_, centripetal and centrifugal xylem; _p_, phloem; _px_,
protoxylem. (After Marsh.)]
As considerable stress has been laid on the anatomical features of the
cycadean foliar bundles in discussions on the affinities and phylogeny
of certain Palaeozoic genera, it is important to consider the facts
more closely[85]. French anatomists described the cycadean bundle as
diploxylic on the ground that the centripetal and centrifugal xylems
are distinctly different things, the centripetal xylem being primary—a
relic of a former organisation—and the centrifugal xylem secondary
and homologous with the normal wood of the cauline bundle. The term
mesarch has in recent years been applied to the cycadean type of
bundle. A mesarch bundle is, however, one in which centripetal and
centrifugal xylem are alike in origin, both being primary structures
derived from a desmogen strand. Typical mesarch bundles occur in
several recent ferns; in the stele of the Osmundaceae, _Gleichenia_,
and other genera; but in these plants the xylem is all produced
directly from one primary desmogen region and there is no question of
‘primary’ and ‘secondary’ as in the two portions of the xylem of a
cycadean bundle. Recent researches into the development of cycadean
foliar bundles show that they do not conform to the mesarch type as
generally understood. A leaf-trace at the base of a petiole (fig. 399,
A) comprises centrifugal xylem only, and this consists of regular rows
of tracheids separated by medullary rays: in the lower part of the
petiole the structure is gradually modified, the centrifugal xylem
is reduced and the formation of centripetal xylem is initiated. At a
higher level (fig. 399, B) the centripetal xylem is in excess of the
centrifugal and the latter, for a time connected with the former,
eventually becomes separated by a few parenchymatous cells from the
protoxylem and persists as a small strand or arc of tracheids. Fig.
399 illustrates stages in the transformation of a typical collateral
bundle, at the base of a _Stangeria_ petiole, into one in which the
xylem is almost wholly centripetal at a higher level in the axis of
the frond. A cambium is present in all: in B the centrifugal xylem
is more or less clearly differentiated into two portions, loosely
arranged tracheids near the phloem, and the more compact groups
abutting on the centripetal xylem: figs. C–E show a further reduction
in the centrifugal tracheids. The conclusion drawn from developmental
study is that the two xylem portions of the bundle are independent
in origin[86]. Marsh has, however, shown that in _Stangeria_ bundles
near the base of the petiole the centrifugal xylem consists of rows of
secondary tracheids and an inner portion not in rows which connects the
centrifugal with the centripetal elements; this connecting portion, he
adds, is ‘probably primary and connects up the Cycadean foliar bundle
with the truly mesarch bundle of the Cycadofilices.’
[Illustration: Fig. 400. _Cycas Micholitzii_. Vascular bundles in
a forked pinna; _px_, protoxylem; _s_, sheath of thick-walled cells;
_cf_, _cp_, centrifugal and centripetal xylem.]
In the xylem portion of the bundle from the midrib of a forked pinna
of _Cycas Micholitzii_ shown in fig. 400 the centrifugal xylem
elements are unusually numerous: the space between the two xylems
is occupied by parenchyma and the whole strand is enclosed by a
sheath of crystal-containing cells, _s_, with thick inner walls.
Fig. 400, 1–4, illustrates the gradual change in the form of the
bundle in the region of dichotomy[87]. The ground-tissue of the
petiole is abundantly supplied with secretory canals and in the
hypodermal region is a cylinder of stereome. In some petioles, _e.g._
_Macrozamia heteromera_[88], the ground-tissue cells are lignified
and reticulately pitted, a feature met with in some Mesozoic cycadean
leaves[89]. In _Cycas media_ Worsdell noticed a tendency of the
leaf-trace bundles towards a concentric arrangement and similar
vascular strands are recorded in the peduncle of _Dioon edule_, in
various sporophylls[90] and in other cases. It is possible, as Worsdell
believes, that the fairly frequent occurrence of concentric bundles
in plants characterised by collateral bundles may have a phylogenetic
significance.
The pinnae are dorsiventral and the veins exarch or pseudomesarch:
secretory canals occur between (_Encephalartos_), above, or below the
veins. The mesophyll of _Cycas_ is characterised by the presence of
isolated xylem-elements passing from the midrib to the edge of the
lamina and, as Lignier[91] suggests, these may be regarded as a reduced
system of lateral conducting strands.
The epidermal cells of the leaflets have straight or slightly curved
walls except in _Stangeria_ where they are undulate and fern-like[92].
The stomata, with few exceptions confined to the lower epidermis, are
larger than in other gymnosperms (on the average ·075 × ·034 mm.) and
are more or less depressed below the surface; the guard-cells are
usually surrounded by 4–6 subsidiary cells.
The roots exhibit no feature to which attention need be called: the
pericycle is several cells broad and as in the stem there may be
extrafascicular cylinders of xylem and phloem.
CHAPTER XXIX.
PTERIDOSPERMEAE.
I. LYGINOPTERIDEAE.
LYGINOPTERIS.
The genus _Lyginopteris_ is selected for the first place in this
chapter simply on the ground that we have a fuller knowledge of its
morphology than in the case of other types. It is not regarded as the
most primitive member of its class. _Lyginopteris_ may be described
in a few words as a plant having the habit and to a large extent the
anatomical features of a Fern, but differing from existing ferns in the
possession of integumented megasporangia or seeds and in the power of
secondary growth in thickness by means of a cambium in both stem and
root. The seed (_Lagenostoma_) agrees with those of recent Cycads and
Gnetales more closely than with the corresponding organs in Conifers
or any other group, while the structure of the secondary wood is
practically identical with that of Cycads. The microsporangia occur
as groups of small bilocular sporangia, or synangia, at the tips of
fertile pinnae of highly compound fronds.
_Nomenclature and Historical Summary._ In 1866 E. W. Binney[93] of
Manchester published a short description of a small petrified stem
from the Lower Coal Measures of Lancashire and named it _Dadoxylon
oldhamium_, employing Endlicher’s term _Dadoxylon_ which that author
substituted for _Pinites_ as previously used by Witham[94]. Three
years later Williamson[95] drew attention to certain features in which
Binney’s type differs from the genus _Dadoxylon_ and substituted a new
name _Dictyoxylon_, suggested by the reticulate pitting on the walls
of the tracheids. In a subsequent paper Williamson[96] gave a fuller
description of Binney’s species and spoke of it as ‘one of the most
common plants in the calcareous nodules of the Lower Coal Measures’ of
Lancashire and Yorkshire. He connected certain casts of arborescent
dimensions with Binney’s type on the ground that the surface-features
of the casts are such as would be produced by partially decorticated
stems having a hypodermal reticulum of mechanical tissue like that
preserved in the small petrified specimen described by Binney (fig.
402). Mr Carruthers called Williamson’s attention to a paper by Mr
Gourlie[97] in which the generic name _Lyginodendron_ is instituted
for stem-casts identical in surface-features with the fossils figured
by Williamson. In spite of the much larger dimensions of the reticulum
on the casts described by Gourlie as compared with that in the outer
cortex of Binney’s stem, Williamson concluded that _Lyginodendron_ is
‘undoubtedly an inorganic cast of the prosenchymatous layer of the
bark of _Dictyoxylon_.’ It is but fair to add that Williamson was
influenced in coming to this conclusion by a discovery by Mr Nield of
a piece of a large petrified stem believed to be generically identical
with Binney’s type, but subsequently referred to a distinct genus[98],
which was comparable in size with the stems responsible for Gourlie’s
_Lyginodendron_ casts. The type-specimen of Gourlie’s _Lyginodendron
Landsburgii_[99], from Carboniferous rocks at Stevenston in Ayrshire,
Scotland, is represented in fig. 401. The convex areas represent casts
of depressions in a reticulum of cortical tissue, originally occupied
by comparatively delicate cells, which decayed or shrunk more quickly
than the enclosing framework of stronger fibrous elements that remained
as a prominent reticulum and produced the depressions bounding the
raised portions of the cast. Such a cast would undoubtedly be formed
by the stem on which Binney founded his species: the radially disposed
bands of thick-walled cells seen in the outer part of the section (fig.
402) are portions of an irregular anastomosing mechanical system, the
reticulate arrangement of which is seen in the impression of a rachis
of a _Lyginopteris_ frond shown in fig. 405, E, and indicated in the
more slender axis reproduced in fig. 404, A, _b_. This reticulate
form of cortical stereome on which Brongniart founded the genus
_Dictyoxylon_[100], a term since applied by Solms-Laubach and other
authors to a certain type of cortex not confined to a single genus of
plants, occurs also in some Palaeozoic lycopodiaceous stems[101] and in
itself cannot be regarded as a safe criterion of botanical affinity.
The largest example of Gourlie’s _Lyginodendron_ that has come under my
notice is an incomplete sandstone cast from Upper Carboniferous strata
near Harrogate reaching a length of 100 cm. and with convex areas 13
cm. long. A similar cast, 36 cm. broad, has recently been figured by
Nathorst[102] from the Culm of Spitzbergen, and from the Upper Devonian
of Ellesmere Land the same author has described impressions of a
cortical reticulum under the name _Lyginodendron Sverdrupi_[103]. These
specimens are interesting as pointing to the former occurrence in the
Arctic regions of stems—probably Lepidodendroid—reaching the dimensions
of a fairly large tree. As Potonié[104] pointed out, Gourlie’s generic
name serves a useful purpose for casts of stems of the type shown in
fig. 401 that cannot be assigned to a definite systematic position.
The genus was first used for a specimen which has nothing to do with
the plant usually spoken of as _Lyginodendron oldhamium_ (Binney).
Though loath to give up a name by which Binney’s type has long been
known, in spite of its retention in the second volume of this work I
feel compelled so far to conform to the recognised principles governing
nomenclature as to adopt Potonié’s generic term _Lyginopteris_.
[Illustration: Fig. 401. _Lyginodendron Landsburgii_. (Kidston Coll.
¾ nat. size.)]
_Lyginopteris oldhamia_ (Binney).
i. _Stem_.
1866. _Dadoxylon oldhamium_, Binney, Proc. Lit. Phil. Manchester, vol.
+v.+ p. 113.
1869. _Dictyoxylon oldhamium_, Williamson, Monthly Micros. Journ. vol.
+ii.+ p. 66.
1873. _Lyginodendron oldhamium_, Williamson, Phil. Trans. Roy. Soc. vol.
+clxiii.+ p. 404.
1899. _Lyginopteris oldhamia_, Potonié, Lehrbuch der
Pflanzenpalaeontologie, p. 171.
ii. _Leaf_.
1828. _Sphenopteris Hoeninghausi_, Brongniart, Prodrome, p. 51.
1872. _Edraxylon_, Williamson, Proc. R. Soc. vol. +xx.+ p. 438.
1874. _Rachiopteris aspera_, Williamson, Phil. Trans. R. Soc. vol.
+clxiv.+ p. 684.
1877. _Calymmatotheca Hoeninghausi_, Stur, Culm Flora, +ii.+ p. 266.
1905. _Crossotheca Hoeninghausi_, Kidston, Proc. R. Soc. vol. +lxxvi.+
p. 358.
iii. _Seed_.
1877. _Lagenostoma_, Williamson, Phil. Trans. R. Soc. vol. +clxvii.+ p.
234.
1903. _Lagenostoma Lomaxi_, Oliver and Scott, Proc. R. Soc. vol. +lxxi.+
p. 477.
iv. _Root_.
1876. _Kaloxylon Hookeri_, Williamson, Phil. Trans. R. Soc. vol.
+clxvi.+ p. 23.
[Illustration: Fig. 402. _Lyginopteris oldhamia_. Transverse section
of the type-specimen in the Binney Collection, Sedgwick Museum,
Cambridge. (After Arber.)]
i. _Stem_.
The petrified stem on which Binney founded the species was first
figured by Dr Arber[105] from a section in the Binney collection in
the Sedgwick Museum, Cambridge: this section (13 mm. in diameter)
is reproduced in fig. 402. The most striking features are: (i) the
pith consisting of an unusually large and irregular group of dark
thick-walled parenchyma, (ii) the broad cylinder of manoxylic secondary
xylem characterised by multiseriate medullary rays, (iii) the outer
cortex composed of dark radially disposed and oblique bands of
mechanical tissue separated from one another by partially destroyed
and tangentially elongated parenchymatous elements. It is this outer
cortex that Williamson aptly compared with the Roman numerals on a
clock-face. In the perimedullary region and in contact with the inner
edge of the secondary-xylem cylinder are six strands of primary xylem
representing the xylem halves of collateral bundles separated from the
primary phloem strands by the intervening cylinder of secondary wood.
Two of the primary xylem strands in lateral contact are seen in fig.
404, C; the other four occur as separate bundles. Each primary xylem
strand contains a small group of spirally thickened protoxylem elements
(_px_) associated with a few parenchymatous cells. The large primary
tracheids internal to the protoxylem are characterised by multiseriate
bordered pits on their walls, while those external to the protoxylem,
which are in contact with the innermost secondary tracheids, have
scalariform pitting. The dark patch _s_ (fig. 404, C) is a portion of
the large group of sclerenchymatous cells, shown in figs. 402, 403.
The perimedullary xylem strands of mesarch structure are the lower
portions of leaf-traces and, as Scott points out, ‘each of the bundles
surrounding the pith is, in fact, a sympodium, composed of the united
lower ends of successive adjacent leaf-traces.’ The larger of the two
bundles shown in fig. 404, C, is on the point of passing out to a leaf,
while the smaller strand is on its way to a higher level before bending
outwards through the secondary wood. Slightly beyond the middle of the
secondary xylem there is an arc of narrower tracheids comparable with
an incomplete annual ring. Although zones or arcs of narrow tracheids
are not uncommon in the wood of _Lyginopteris_ there is no satisfactory
evidence of regularly recurring seasonal changes. On the outer face of
the secondary wood are a few leaf-trace strands pursuing a vertical
course in the pericycle region; but the structure and behaviour of
these bundles are more clearly illustrated in the stem reproduced in
fig. 403. The tissue between the crushed phloem and pericycle and the
outer cortex (fig. 402) consists of radially compressed parenchyma with
scattered secretory cells separated from the more internal tissue by a
narrow band of periderm formed by a phellogen in the outer part of the
pericycle.
A larger and better preserved stem, 3·7 cm. in diameter, is seen
in fig. 403. In this stem the pith of parenchyma and scattered
sclerenchymatous nests is larger in proportion to the stele than
in Binney’s type-specimen. From the inner edge of the secondary
xylem several primary xylem-strands project as rounded wedges
or tangentially elongated groups where two traces are laterally
united in the perimedullary zone. The cylinder of secondary wood
is partially interrupted at _r_ by the bending outwards of the stele
of an adventitious root cut across transversely as it bends down
after emerging from the outer cortical region. In more or less close
association with the outer surface of the secondary xylem are four
pairs of leaf-trace bundles and one larger trace at _d_ containing
two widely separated protoxylem strands and faced externally with
an arc of secondary xylem: this is a leaf-trace which shows by the
slight constriction on the outer edge of its primary xylem that it is
beginning to divide into a pair of equal strands. A precisely similar
strand is shown on a larger scale in fig. 404, D. The twin bundles
seen at _b_, fig. 403, represent a divided leaf-trace at a slightly
higher level than the partially severed trace at _d_, and the arcs of
secondary xylem are narrower. The appearance of the double leaf-trace
at a still higher level is shown at _c_: the two strands are farther
apart and the secondary xylem has almost disappeared, while those at
_e_, nearer their entrance into the leaf-stalk, consist exclusively of
primary xylem and phloem. At _a_ the two strands of a leaf-trace, still
nearer to the petiole, are inclined towards one another preparatory
to reunion after reaching the leaf-stalk. A slender root is seen in
transverse section at _r′_ immediately outside the two leaf-bundles.
As Williamson and Scott[106] have pointed out, there are always five
leaf-traces beyond the xylem cylinder of a _Lyginopteris_ stem as seen
in transverse section, and these traces in the pericycle, separated
from one another by ⅔ of the circumference, alternate in position with
the lower portions of leaf-traces in the perimedullary region of the
same stem. The phyllotaxis is thus seen to be ⅖.
[Illustration: Fig. 403. _Lyginopteris oldhamia._ _a–e_, foliar
bundles; _f_, decurrent base of petiole; _r_, _r′_, roots; _s_, seed
(_Lagenostoma_). (× 3. Kidston Coll. 592, B.)]
The secondary wood is succeeded by a cambium of normal structure
passing gradually into a narrow band of secondary phloem which in
well-preserved stems is seen to consist of sieve-tubes and parenchyma
with medullary rays rather broader than those in the xylem. Beyond the
phloem is the comparatively broad pericycle consisting of parenchyma
with nests of sclerenchyma like those in the pith and scattered
secretory cells. In the outer layers of the pericycle a phellogen
was formed at an early stage in the growth of the plant, producing
several layers of secondary tissue, which is regarded as periderm and
forms a conspicuous feature in _Lyginopteris_ stems; it appears as a
comparatively dark sinuous band where it bends outwards to wrap round
the leaf-traces in their almost vertical course through the pericyclic
region (fig. 403). The periderm is clearly seen at _p_ close to the
crushed secondary phloem of the dividing leaf-trace in fig. 404, D. All
the leaf-traces seen in fig. 403 beyond the secondary wood are still
within the deep-seated periderm and, as Williamson and Scott showed,
each leaf-trace after emerging from the secondary wood remains in the
pericycle-zone for a length of five internodes as it very gradually
inclines outwards. Once free from this region the twin bundles bend
more sharply towards the petiole. Stated briefly, the history of
each leaf-trace from the perimedullary region to the leaf-base is as
follows: at the outer edge of the pith a single trace consists of a
mesarch xylem bundle with one protoxylem strand; it passes vertically
through five internodes and then bends out through a foliar gap in
the xylem-cylinder, and the primary tracheids receive additions from
the cambium of the stele on their outer face. As the trace leaves the
secondary xylem it bends upwards and, as seen at _d_, fig. 403, begins
to divide into twin bundles. As the trace passes higher the bisection
of the protoxylem and metaxylem is completed and the secondary
xylem-arcs are gradually lost until the separate strands of each pair
are reduced to single mesarch bundles composed wholly of primary
tracheids. As the trace bends outwards through the cortex the phloem
gradually encircles each xylem-strand until a concentric structure is
substituted for the collateral disposition of the conducting tissue.
At the same time the protoxylem strands divide and occupy a position
near the inner edge of the metaxylem. On reaching the petiole or after
passing some distance up the axis of the frond, the twin bundles unite
and usually form a V-shaped vascular strand (figs. 404, E; 405, A).
The single meristele subsequently divides into two equal portions
preparatory to the bifurcation of the petiole (fig. 406).
The inner cortex, consisting of parenchymatous tissue and many
secretory cells with an occasional group of sclerenchymatous elements
in place of the abundant nests of this tissue in the pericycle, has
been invaded in the stem shown in fig. 403 by numerous rootlets of
_Stigmaria_ and _Lyginopteris_, some of which are seen interrupting
the continuity of the outer cortex. The greater width of the cortical
region at _f_, fig. 403, is due to the decurrent base of a petiole
the meristele of which is not included in the section. The lighter
and broader bands between the cross-sections of the stereome-network
in the outer cortex are occupied by remains of tangentially stretched
parenchymatous cells, and beyond this zone in a younger stem there are
a few layers of parenchyma forming the superficial tissue, but there
appears to be no well-defined epidermal layer.
[Illustration: Fig. 404. _Lyginopteris oldhamia._
A, B. Frond fragments; _a_, pinnule; _b_, reticulum of sclerenchyma.
C. Portion of stele of the stem reproduced in fig. 402.
D. _px_, protoxylem; _s_, sclerenchyma; leaf-trace close to the edge
of the secondary xylem; _p_, periderm.
E. Petiole; _m_, meristele.
(A, Kidston Coll. 664 B; B, Camb. Botany School 508; C, Binney Coll.
179; D, E, Camb. Botany School, 93, 159.)]
Young stems have been recognised in which there is very little
secondary xylem and phloem: in these the stereome bands in the outer
cortex are closer together than in the stretched hypodermal tissue
of older shoots and the scattered sclerous nests are represented by
unthickened cells. In addition to young stems Williamson and Scott
described a distinct type of small stem in which the primary xylem
forms an almost complete ring[107] comparable with the primary xylem of
some adult Sigillarian stems (vol. +ii.+ p. 220) but distinguished by
its mesarch structure and by the reticulate pitting of the centripetal
xylem.
A characteristic feature of the stem is the occurrence of emergences
from the outer cortex which have the structure either of spinous
processes, broadly linear or flask-shaped, or of stalked glands[108]. A
portion of a glandular emergence is shown in fig. 405, B: the group of
small cells immediately below the blunt apex is in this instance still
intact though showing signs of disorganisation in the centre; but in
many cases the secretory tissue has not been preserved and the head of
the emergence is occupied by a space. A single stoma is seen at _s_ in
longitudinal section. Further reference to the emergences is made in
the description of the leaf.
It occasionally happens that a meristematic layer is formed in the
parenchymatous tissue immediately internal to some of the perimedullary
xylem strands of a _Lyginopteris_ stem from which either secondary
parenchyma is produced or a zone of secondary xylem and phloem, the
phloem facing the centre of the pith. An example of such internal
xylem was figured by Williamson[109] and similar occurrences are
more fully dealt with by Williamson and Scott[110] who consider that
the perimedullary cambium may represent an internal extension through
a leaf-gap of the normal cambial cylinder. In the stem represented
in fig. 403 there are two perimedullary xylem strands to the left
of the bottom of the V-shaped gap in the secondary xylem-cylinder,
_r_, and on the inner face of one of these, as shown in fig. 405, C,
there is a narrow arc of internal secondary xylem, _c_, between the
xylem-strand and the outer edge of one of the sclerous nests. The
sporadic occurrence of arcs of inversely orientated secondary vascular
tissue affords an interesting parallel with a similar morphological
feature in some recent Dicotyledonous genera such as _Tecoma_ and
_Iodes_. As Williamson and Scott point out, this similarity affords ‘a
striking warning against the _indiscriminate_ use of even conspicuous
anatomical characters[111].’ While admitting the necessity of guarding
against the danger of attaching importance to occasional and abnormal
characters they may have some significance as collateral evidence in
comparisons of different types of stems. It is conceivable that these
anomalous arcs of secondary tissue on the inner side of the primary
xylem strands may, as Worsdell[112] maintains, be reversions to an
ancestral character and in this sense comparable with the strands of
inverted vascular tissue in some recent Cycadean stems. The question of
relationship of _Lyginopteris_ and allied types to recent Cycads and
the Palaeozoic Medulloseae is considered in a later chapter.
In 1902 Lomax[113] described two branching specimens of _Lyginopteris_,
and more recently two others have been discovered at a locality
near Bacup in Lancashire which have been thoroughly investigated by
Miss Brenchley[114] who constructed models from drawings of serial
sections[115]. One specimen shows six leaf-bases in a length of 4¾
inches and branches spring from the axils of five of them: some of
the branches show secondary ramifications. The phyllotaxis of the
leaf-bases on a branch is always the reverse of that on the main stem,
a divergence to which no parallel was found in a selection of trees
and shrubs examined by Miss Brenchley. The secondary wood of the stem
swells below the point of exit of a branch and frequently a fairly
large amount of wood occurs in the pith when a branch is given off:
this anomalous wood may help to close the branch-gap.
ii. _Leaf_.
In his account of _Lyginopteris_ stems published in 1873
Williamson[116] suggested that the vascular bundles met with outside
the xylem-cylinder might be the leaf-traces of large fronds and
expressed the opinion that the ‘stems or petioles’ previously
described by him under the generic name _Edraxylon_ might belong to
_Lyginopteris_. A year later he substituted the name _Rachiopteris
aspera_ for the petioles previously referred to _Edraxylon_ and
inclined to the view that this type of _Rachiopteris_ may be
the petiole of the Carboniferous fronds known as _Sphenopteris
Hoeninghausi_ Brongn., an inference based to a large extent on the
occurrence of emergences on _Rachiopteris aspera_ (fig. 404, E)
preserved as petrifactions like those on impressions of _Sphenopteris
Hoeninghausi_ as figured by Brongniart (figs. 404, A; 405, D, D’). In
1890 Williamson was able to demonstrate the truth of the surmise that
_Rachiopteris aspera_ and _Lyginopteris oldhamia_ are respectively
the petiole and stem of the same plant, which he believed to be an
arborescent fern[117]. The petioles of _Lyginopteris_ fronds, which
may reach a diameter of 1 cm., are attached by a broad base to the
stem, and as already suggested by the number of internodes traversed by
each leaf-trace, the leaves are comparatively far apart. A transverse
section of a petiole is shown diagrammatically in fig. 405 A. The
hypodermal stereome is a prominent feature, but the narrow radial
plates of the stem-cortex tend to be replaced in the rachis by broader
and confluent masses of strengthening elements: the upper surface of
the petiole is slightly grooved. Glandular and spinous emergences
are often very abundant, as in the section reproduced in fig. 404,
E. A glandular emergence is seen at _a_ in fig. 405, A. The spinous
emergences may be compared with those of _Davallia_ (_Odontosoria_)
_aculeata_[118], a West Indian fern of climbing habit and with the
prickles on _Hemitelia_ and other recent Cyatheaceous fronds[119],
while capitate glands, though simpler than those of _Lyginopteris_,
occur on the leaf-stalks of some recent Polypodiaceous species[120].
The concentric meristele may consist in the lower part of the petiole
of two separate and slightly curved strands like those seen in fig.
404, E, _m_: sooner or later the two strands unite to form a wide-open
V or a W-shaped bundle with several slightly internal protoxylem
groups close to the lower edge. The two sections represented in fig.
406, A and B show the gradual divergence of the two meristeles of a
petiole as they approach the level where it divides into two equal
branches, a characteristic feature of _Sphenopteris Hoeninghausi_ and
allied fronds. At a lower level than that represented in fig. 406 the
vascular strand of the petiole would have the form of a W as figured
by Williamson in one of his earlier memoirs[121]. The phloem with
scattered secretory sacs and the adjacent tissue of the leaf-stalk are
occasionally preserved in wonderful perfection[122]. No endodermis has
been recognised. Sclerous nests are scattered in the ground-tissue as
are also secretory sacs (figs. 404, E; 405, A). A small root _r_ has
penetrated the parenchyma of the rachis shown in fig. 405, A.
[Illustration: Fig. 405. _Lyginopteris oldhamia_. A, petiole section;
_a_, glandular emergence; _r_, root. B, stalked gland; _s_, stoma. C,
inner edge of wood of a stem; _c_, arc of inversely orientated vascular
tissue. D, D’, part of a frond of _Sphenopteris Hoeninghausi_. E, part
of axis of D. (A, C, D, Kidston Coll.; B, Manchester Coll. R. 645.)]
[Illustration: Fig. 406. _Lyginopteris oldhamia._ Transverse section
illustrating branching of petiole. × 5. (From a drawing supplied by
Prof. Oliver.)]
_Sphenopteris Hoeninghausi_ Brongn.[123], founded on material from
English Coal Measures, was regarded by Williamson as the foliage of
_Lyginopteris_ chiefly on the ground of the occurrence of emergences on
the axes (figs. 404, A, B) and laminae of the impressions like those
on the petrified stems, and this comparison received support from the
resemblance of the fragments of pinnules associated with _Lyginopteris_
and its petioles in the calcareous nodules to the leaflets of
Brongniart’s type. This identification is supported by subsequent work.
The quadripinnate fronds, which attain a considerable size, resemble
those of recent species of _Davallia_ and other ferns, but the forking
of the rachis and branches of the frond is a striking feature: the
pinnae may reach a length of 15 cm.[124] The portion of carbonised
rachis shown in fig. 405, E, reveals the existence of a hypodermal
reticulum like that in the outer cortex of a _Lyginopteris_ stem and
the same feature is seen in the more slender axis represented in fig.
404, A, at _b_.[125] The pinnules are usually deeply lobed and the
segments may be comparatively broad and blunt or narrow[126] (fig. 290,
C, vol. +ii.+ p. 399; fig. 404, A, _a_, B; fig. 405, D’). The lamina
has a well marked dorsiventral structure: the palisade-tissue next
the upper surface is separated from the epidermis by small hypodermal
cells, possibly functioning as a water-storage layer, and the central
part of the mesophyll consists of loose aerenchyma: the veins are
collateral as in recent ferns and stomata occur in the lower epidermis.
Emergences are seen both on impressions (fig. 405, D’) and on petrified
specimens. A striking feature of the pinnules is the rounded surface
caused by the revolute edge of the lamina as seen in the section
reproduced in fig. 404, B. This character coupled with the occasional
occurrence of groups of short tracheal elements at the termination of
the veins denotes a tendency to a xerophilous habit.
On the strength of a very close resemblance between _Sphenopteris
Hoeninghausi_ and _Calymmatotheca Stangeri_ (fig. 408, E,
F)—characterised by fertile pinnules bearing stellate groups
of small linear valves, regarded by Stur as the open lobes of
an indusium—Zeiller included Brongniart’s type in the genus
_Calymmatotheca_. The resemblance in general habit between the two
species extends to the presence in their rachises of the _Dictyoxylon_
form of cortex[127]. The view formerly held by some authors that the
valve-like appendages to the fertile segments of _Calymmatotheca_ are
sporangia is incorrect: a re-examination of Stur’s specimen (fig.
408, E, F) has confirmed the original description[128]. The stellate
lobes are now regarded as portions of a cupular investment of a seed
similar to _Lagenostoma Lomaxi_, the female reproductive apparatus of
_Lyginopteris oldhamia_. The axes of the fertile pinnae bear small
thorn-like emergences probably identical with those on the cupule of
_Lagenostoma_ and on the petioles of _Lyginopteris oldhamia_. It was
stated in vol. +ii+ that the fronds known as _Sphenopteris Linkii_
(Goepp.) represent, with other closely allied forms, leaves belonging
to _Heterangium_ stems. This statement was based on a misconception:
the rachis of _Sphenopteris Linkii_, as I have satisfied myself by
an examination of impressions shown to me by Dr Kidston, exhibits
the reticulate pattern characteristic of _Lyginopteris_ and not the
transverse ribs characteristic of _Heterangium_.
It is not an easy task even for those most familiar with Carboniferous
fronds to distinguish clearly between species agreeing generally with
_Sphenopteris Hoeninghausi_, a species regarded by some authors as the
type of a group of very similar and closely allied forms all of which
were probably borne on stems referable to the genus _Lyginopteris_.
The species _Lyginopteris oldhamia_ as generally understood probably
includes more than one specific type, and it is safe to assert that
in the Carboniferous period _Lyginopteris_ was represented by several
forms characterised by highly compound fronds with forked rachises like
_Sphenopteris Linkii_, _S. Hoeninghausi_, and others. The features
characteristic of fronds included in the _Sphenopteris Hoeninghausi_
group have recently been described by Gothan[129]. Stur’s generic name
_Calymmatotheca_ originally applied to the species _C. Stangeri_ was
applied to _Sphenopteris Hoeninghausi_ by Zeiller, and although the
fronds of the latter type have not been found with fertile appendages
of the _Calymmatotheca_ type there can be no doubt as to the generic
identity of these, barely distinguishable, species both of which belong
to stems of _Lyginopteris_. Prof. Johnson[130] has recently described
some impressions from the Coal Measures of Ireland, which he refers
to _S. Hoeninghausi_, bearing stellate groups of lobes like those of
_Calymmatotheca_, and in one case he describes a seed in the middle of
the carbonised remains of a stellate group of cupular segments. An
examination of the specimen in Dublin convinced me that there is no
satisfactory evidence of the seed-nature of the appearance on the rock
believed by Johnson to be an elliptical _Lagenostoma_-like seed. The
actual attachment of the stellate lobes to the pinnae of the frond is
not clearly demonstrated.
iii. _Microsporangia._
In 1905 Kidston[131] announced the discovery of microsporangia on
fronds of _Lyginopteris_: he described specimens from the Coal
Measures of Dudley identified by him with _Sphenopteris Hoeninghausi_
showing sterile and fertile pinnae in organic connexion. The fertile
pinnules (fig. 407, B) are slightly expanded distally into an oval
limb about 2 mm. long bearing 6 to 7 bilocular fusiform microsporangia
3 mm. long and 1·5 mm. broad: in the immature condition the sorus is
hemispherical, the summit being formed of the incurved apices of the
sporangia. At maturity the sporangia spread out, the sorus assuming
the form of an epaulet. Fig. 408, H, shows a sorus in transverse
section and in fig. 408, G, the limb and two pendulous sporangia are
shown. The microspores, 50–70 µ in diameter, are studded with numerous
blunt spines and each spore shows a triradiate ridge. The section
reproduced in fig. 407, A, from the Coal Measures of Oldham is probably
a bilocular sporangium of the same type as those described by Kidston
from Dudley. Dr Kidston[132] describes a second type of microsporangial
sorus as _Crossotheca Hughesiana_ which agrees closely with _C.
Hoeninghausi_, but the fertile segments are not associated with any
sterile pinnae. The generic name _Crossotheca_, founded by Zeiller[133]
in 1883, was substituted for _Sphenopteris_ on the ground that
Brongniart’s species _S. Hoeninghausi_ is shown to possess sporangia
of the _Crossotheca_ type. If Kidston’s specific determination is
correct, his discovery demonstrates that _Lyginopteris_ fronds
bore microsporangia having the characters of _Crossotheca_, a type
characteristic of several Carboniferous species belonging both to the
form-genera _Sphenopteris_ and _Pecopteris_. Reference has already
been made to the difficulty of distinguishing between impressions
of fronds of the _Sphenopteris_ _Hoeninghausi_ group, a difficulty
that is illustrated by Dr Gothan’s statement[134] that the Dudley
specimens of _Crossotheca_ are not identical in the character of the
sterile pinnules with _Sphenopteris Hoeninghausi_. An examination of Dr
Kidston’s specimens led me to agree with his determination; but, it may
be asked, have we any evidence of the association with _Lyginopteris_
fronds of sporangia other than those of the _Crossotheca_ type? Prof.
Chodat[135] believes that certain petrified fragments of pinnules
occasionally met with in the calcareous nodules bearing sessile
and apparently annulate sporangia belong to _Lyginopteris_ fronds.
These sporangia appear to be identical with those named by Scott
_Pteridotheca Butterworthi_[136] and regarded by him as filicean
sporangia that cannot be referred to any known Carboniferous genus. The
piece of lamina bearing an empty sporangium, which may or may not have
possessed an annulus, reproduced in fig. 407, C, occurs in association
with the larger specimen shown in fig. 404, B, and it would seem not
unreasonable to regard both as parts of the same frond, namely a
frond of _Lyginopteris_. As Prof. Weiss[137] points out, the accurate
determination of small pieces of petrified pinnules is exceedingly
difficult and without more decisive evidence we are hardly justified in
asserting that the sporangia figured by Chodat and Scott and that shown
in fig. 407 belong to the genus _Lyginopteris_. Although the available
data appear to favour the view generally held that Kidston’s conclusion
is correct additional evidence would be welcome.
[Illustration: Fig. 407. A, B. _Crossotheca Hoeninghausi._ C. Pinnule
with a sporangium, _s_. (A, Kidston Coll. 1277; B, after Kidston; C,
Camb. Botany School, 508.)]
_Telangium._ Reference was made in vol. +ii.+[138] to the genus
_Telangium_ instituted by Dr Benson for some petrified sporangia
from the Coal Measures regarded by her as the microsporangia of a
Pteridosperm, probably _Lyginopteris_. The sporangia of _Telangium_
are similar to those of _Crossotheca_. Scott points out that they
are borne on a flat disc or lamina ‘quite comparable to a fertile
pinna of _Crossotheca_[139],’ and he concludes that these sporangia
are not generically distinct from the impressions on which the genus
_Crossotheca_ was founded. Kidston[140] regards _Telangium Scotti_,
Benson, as the microsporangium of a Pteridosperm though not of
_Lyginopteris_, on the ground that the microsporangia described by
Miss Benson are not attached to a limb and that they have a single
loculus in place of the double loculus (fig. 407, A) of _Crossotheca_.
The presence of a limb in _Telangium_ recognised by Scott removes one
of these distinguishing features. There are, however, no adequate
reasons for regarding _Telangium Scotti_ as specifically identical with
_Crossotheca Hoeninghausi_. The synangium of _Telangium Scotti_, 5 mm.
in length, consists of 6–12 sporangia united basally and opening when
ripe by longitudinal dehiscence. Fig. 493, E, shows eight sporangia
of a synangium in transverse section: the two sporangia at the lower
end of the section are less distinct than the others, some are full
of spores and others have shed their contents by the splitting of
the thin inner walls of the loculi. The sporangial walls are composed
of an outer layer of large cells with dark contents succeeded by 2–3
layers of smaller and crushed cells. The spores, 5–6 µ × 3·5–4 µ in
diameter, have a reticulately sculptured exine: Dr Benson[141] states
that they agree closely with pollen-grains found in the pollen-chamber
of _Lagenostoma ovoides_ except in their slightly smaller size; she
notes the association of _Telangium_ with fragments of the vegetative
organs of _Lyginopteris_ and draws attention to resemblances in the
structure of the tissues; but the most interesting comparison, at least
in an academic sense, is with the seed _Lagenostoma_, the integumented
megasporangium of _Lyginopteris_. Dr Benson points out that a
transverse section of a _Lagenostoma_ in the plane of the canopy,
showing the nucellar apex surrounded by radially disposed chambers
(fig. 409), presents a certain resemblance to a synangium of _Telangium
Scotti_; and it is suggested that the chambers encircling the nucellus
may represent sterilised sister-sporangia[142]. ‘The seed in fact is
assumed to be a synangium in which all but one of the sporangia are
sterile, and form an integument to the one fertile sporangium which
has become a megasporangium with one large megaspore.’ This view,
though clearly incapable of confirmation in the present state of our
knowledge, is not merely an ingenious hypothesis but a stimulating
suggestion as to possible homologies: as an argument in favour of
associating _Lagenostoma_ and _Telangium_ as the spore-bearing organs
of the same plant it has but little weight.
iv. _The Seed._ =Lagenostoma= Williamson.
_Lagenostoma Lomaxi_, Oliver and Scott ex Williamson, +MS.+
In 1877 Williamson[143] proposed the generic name _Lagenostoma_ for
some petrified seeds from the Lower Coal Measures of Lancashire and
described two species, _Lagenostoma ovoides_ and _L. physoides_: in his
+MS.+ Catalogue a third type is referred to as _Lagenostoma Lomaxi_. It
is this third type that Prof. Oliver was the first to recognise as the
megaspore-bearing organ of _Lyginopteris oldhamia_. Its structure has
been thoroughly described by Oliver and Scott[144] and these authors
contribute a judicial summary of the evidence on which _Lagenostoma_
and _Lyginopteris_ are believed to stand for one and the same plant.
The evidence is based chiefly on the following considerations: an
agreement in the structure of the vascular bundles in the investments
of the seed with those in the leaves of _Lyginopteris_; the presence
in the outer envelope of the seed of stalked glands identical with
those on the stems and petioles. The evidence does not as yet amount
to absolute proof, as the seeds, which occur either with or without
a stalk, have not been found attached to a _Lyginopteris_ frond.
But ‘where vegetative and reproductive organs presenting identical
structural features, not known to occur in other plants, are thus found
in close and constant association, the inference that the one belonged
to the other appears irresistible.’ While most botanists believe that
a satisfactory case is established there are a few[145] who refuse to
believe in a connexion between _Lagenostoma_ and _Lyginopteris_ until
an actual union has been demonstrated. The discovery by Kidston[146]
of seeds attached to pinnae bearing _Neuropteris_ pinnules and the
demonstration of organic continuity between seeds and the pinnules of
other Palaeozoic fern-like fronds supply abundant confirmatory evidence
that leaves no doubt as to the occurrence of seeds on modified pinnae
of _Sphenopteris Hoeninghausi_ and of other closely allied fronds which
represent the foliage of different forms of _Lyginopteris_. In this
connexion it is pertinent to add that Grand’Eury[147] has found seeds
of the _Lagenostoma_ type in close association with impressions of
_Sphenopteris Dubuissonis_ and other leaves of similar habit.
A seed of _Lagenostoma Lomaxi_ reaches a length of 5·5 mm. with a
maximum diameter of 4·4 mm.; it is broadly oval or barrel-like (fig.
408, C) and when immature was invested by a loose irregularly lobed
glandular envelope (fig. 408, B) from which the seed eventually
freed itself by a natural process of abscission. The central body or
nucellus, except in the apical region, is concrescent with a fairly
stout integument or testa (fig. 408, C, _f_) the outer portion of
which is characterised by regular longitudinal rows of palisade-like
cells comparable with the broad palisade-layer in the sporocarp of
_Pilularia_. On the exposed surface of this palisade-tissue are small
dark structureless pegs[148], possibly the remains of a mucilaginous
layer such as occurs on the seed-coats of some recent Flowering
plants. At the base of the nucellus the chalazal region, fig. 408, C,
_ch_, is provided with sclerous elements and forms a hard investment
to the axial vascular strand from the pedicel. It is at the base
of this chalazal region that the seed is eventually cut off by an
absciss-layer. The integument is supplied throughout its length by nine
vascular bundles of endarch, or approximately endarch, structure. The
free portion of the integument seen from the outside (fig. 408, B) has
the form of a fluted cone with a circular opening at its summit. The
greater part of this domical apex, as seen in longitudinal section in
fig. 408, C, appears to be hollow, but in the living state the dome, or
canopy as Williamson called it, was filled with parenchyma in which the
vascular bundles were embedded and, as shown in the transverse section
in fig. 409, the canopy is divided into compartments by radial septa
which in its basal region are replaced by regular and deep furrows
on the inner face. Enclosed by the canopy, with its outer surface
fluted as the result of the partial collapse of the outer wall of each
compartment due to the decay of the filling tissue, is the flask-shaped
apex of the nucellus; between the apical cone of nucellar parenchyma
and the superficial layer is an annular cavity which Williamson[149]
called the lagenostome. The parenchymatous core tapers to a narrow
summit which slightly overtops the integument and is constricted at the
broad base (fig. 493, A, B; page 311). The bottle-shaped apical tissue
is separated by an annular space, _c_, fig. 493, B, from the limiting
layer of the nucellus: this space is the pollen-chamber formed in the
living seed by the disorganisation of the subepidermal cells of the
nucellar apex. The pollen-chamber is a feature characteristic of recent
cycadean ovules (see p. 6). In _Lagenostoma_ the annular form of the
pollen-chamber is a peculiarity distinguishing this type of seed from
those of recent Gymnosperms and most other Palaeozoic seeds. As Oliver
says, it marks an ‘advance in precision’[150] over other forms as the
microspores which fall into the chamber are brought direct to the
surface of the underlying megaspore and presumably to the archegonia
which, it is reasonable to believe, were disposed in a circle at the
base of the annular crevice. Microspores frequently occur in the
pollen-chamber and some have been discovered apparently in the act of
liberating male gametes[151].
[Illustration: Fig. 408. A, A′, _Lagenospermum Sinclairi._ B,
_Lagenostoma_, restoration. C, _Lagenostoma Lomaxi_; _c_, micropyle;
_d_, space between integument and nucellus; _e_, cupule; _f_,
integument; _ch_, chalaza. D, microspores of _Lagenostoma ovoides._
E, F, _Calymmatotheca Stangeri._ G, H, _Crossotheca Hoeninghausi._
H, section of G in line of arrow. (A, after Arber; B, C, E, F, after
Oliver; D, after Benson; G, H, after Kidston.)]
[Illustration: Fig. 409. _Lagenostoma._ Transverse section near the
micropyle, showing the pollen-chamber, _pc_, the space, _s_, between
the nucellus and integument, the fluted canopy with vascular bundles,
_v_. (After Oliver.)]
The outer wall of the nucellus is bounded externally by a similar
circular space (_d_, figs. 408, C; 493, B) which separates it from the
domical canopy. In the great majority of specimens the central tissue
of the seed is not preserved and an empty sac supported from the base
of the nucellus-apex occupies nearly the whole of the interior: the
shrunken wall of the sac is all that remains of the large megaspore.
It would seem, then, that the nucellus was almost completely destroyed
as a consequence of the growth of the megaspore or embryo-sac, which
eventually occupied nearly the whole of the seed-body.
In an exceptionally well preserved specimen recently described and
admirably illustrated by Mr McLean[152] part of the parenchymatous
tissue of the prothallus which originally filled the megaspore is
clearly seen: its surface-layer consists of small cells succeeded by
a broad band of radially elongated elements closely resembling the
alveoli in the prothalli of some recent Gymnosperms, particularly
certain Conifers. No archegonia have been discovered. The cupular
envelope of immature seeds, compared by Oliver and Scott with the
lobed and glandular husk of _Corylus colurna_ L.[153], receives
several vascular bundles of collateral and mesarch structure from the
axial strand, and these subdivide as they ascend. The glands which
occur on all parts of the cupule are sessile or stalked and identical
with those on the vegetative organs of _Lyginopteris_. Assuming that
pollination occurred at a comparatively early stage in the development
of the seed when the cupule was still intact, it is conceivable, as
Sir Joseph Hooker suggested, that the glandular secretion may have
attracted insects and so aided in the transport of pollen which were
perhaps drawn down the narrow pollen-chamber by exuded mucilage as in
recent Conifers. The evidence obtained in recent years in favour of
insect-pollination in certain Cycads and in _Welwitschia_ lends support
to this view: the dragon flies hovering over a fertile _Lyginopteris_
frond in a recent restoration[154] may be a legitimate addition.
A striking feature of _Lagenostoma_ as of other Palaeozoic seeds is
the absence of an embryo: this and other considerations have led
certain authors, notably Chodat[155], to question the justification
for the use of the term seed. Various suggestions have been offered in
explanation of this fact. In recent Cycads, as already pointed out, the
development of the embryo does not always occur before seed-fall. It
may be that these older seeds had no resting-period or there may have
been a period of rest after fertilisation and not as now at a stage
subsequent to the formation of the embryo[156]; it is also suggested
by Scott that ‘the nursing of the embryo had not yet come to be one of
the functions of the seed, and that the whole embryonic development was
relegated to the germination stage[157].’ In this connexion reference
may be made to a statement by Miss Gibbs[158] who speaks of seeds of
a _Podocarpus_ picked up from the ground in apparently a mature state
and with the associated bracts coloured and swollen as though ready
to aid in dispersal but with no embryo: the seeds had matured before
fertilisation and fell from the tree after pollination. Whatever
may be the true explanation of the absence of embryos this negative
character should not be allowed to outweigh the evidence furnished
by morphological features as to the applicability of the term seed.
As Prof. Oliver says, ‘there is a long chapter in evolution to be
deciphered before we can connect ... the seed of _Lyginodendron_ with
the sporangium of any fern at present known to us’[159].
The cupule of _Lagenostoma_ has been homologised with the outer
part of the integument of a recent cycadean seed[160] which, it is
suggested, consists of an inner and an outer envelope that have become
concrescent, and this hypothesis is supported by another author by a
comparison between _Lagenostoma_ and Gnetalean seeds[161]. A comparison
has also been made between the collar of a _Ginkgo_ seed and the much
more conspicuous cupule of _Lagenostoma_[162]. Dr Benson and Miss
Welsford[163] institute a comparison between the vascular supply of the
outer integument of the ovules of _Carpinus_ and _Morus_ and that of
the cupule of _Lagenostoma_, a comparison suggested by Miss Kershaw’s
remarks[164] on the similarity between the vascular system of the
ovules of _Myrica Gale_ and _Trigonocarpus_. In 1908 Dr Benson[165]
described some germinating microspores in the pollen-chamber of another
species of _Lagenostoma_, _L. ovoides_, and recognised what she
believed to be antherozoids. I am indebted to this author for allowing
me to make a drawing from her section (fig. 408, D). Two microspores
are seen with thick outer walls showing irregular holes probably of
secondary origin and not part of a regular reticulum as Dr Benson
suggests. Close to the upper microspore is a hemispherical body, _s_,
described as a male gamete, and a similar body is seen still enclosed
by the lower microspore. It is by no means improbable that these are
antherozoids: they were presumably ciliate like those of _Ginkgo_ and
recent Cycads (fig. 396, M). The microspores are approximately 70μ in
length and the supposed antherozoids have a maximum diameter of 45μ,
the latter being about ⅔ the size of the sperms of _Microcycas_ and ⅙
the diameter of those of _Zamia_. The smaller and more delicate cells
near the lower microspore (fig. 408, D) are no doubt fungal cells as
Miss Benson suggests. With reference to the difficulty of determining
the nature of Miss Benson’s supposed gametes it is worth calling
attention to some figures given by Zopf[166] of vesicular cells and
sporangia of the Phycomycetous genera _Rhizophidium_ and _Lagenidium_
in the pollen of Flowering plants and Pines. It has been suggested by
Burlingame[167] that the ‘gametes’ may be prothallial cells; but this
is very improbable.
_Lagenostoma ovoides_ Williamson.
In the memoir in which the genus was founded Williamson described
two species from the Lower Coal Measures of Lancashire, _Lagenostoma
ovoides_ and _L. physoides_[168]. The seeds described under the
latter name had previously been assigned by him to another new genus,
_Physostoma_, and named _P. elegans_[169]. _Lagenostoma physoides_
was afterwards figured by Butterworth[170] who recognised some new
features. For this species Prof. Oliver[171] has adopted Williamson’s
earlier name, _Physostoma elegans_. The former species, which has
recently received exhaustive treatment by Miss Prankerd[172], agrees
generally in its morphological characters with _L. Lomaxi_, but
differs in the structure of the surface-tissue of the integument and
in some anatomical features. Moreover no cupules have been found and
there is ‘very little trace of a layer of separation’ such as occurs
in _L. Lomaxi_. Over the surface of the integument is a layer of
prismatic cells, much shorter and less palisade-like than those in _L.
Lomaxi_, and there are none of the pegs which are a constant feature
in that species. There are, however, indications that mucilage was
poured out by the rupture of the distended cells. Some microspores
were found in the pollen-chamber with an average size of 72 × 53μ;
they may be as much as 90μ long. None were observed with sperm-like
contents like those described by Dr Benson. Miss Prankerd discusses
the morphology of the integument in relation to that of cycadean seeds
and makes an instructive comparison between the lagenostome (that
is the modified nucellar apex) and such fern sporangia as those of
_Angiopteris_, _Osmunda_, and _Schizaea_, but especially the sporangia
of _Senftenbergia_[173] with their multiseriate annulus.
An interesting feature is shown in the longitudinal section reproduced
in fig. 493, A (p. 311). The apex of the nucellar cone appears to be
composed of thick-walled, dark cells and it is suggested that this
may have served as a stopper blocking up the circular orifice of the
pollen-chamber (seen below the apex between the nucellar cone and the
thick surface-layer of the nucellus) and serving as a protection to the
embryo. A comparable closing-up of the micropyle occurs in the seeds of
_Gnetum Gnemon_[174] and in the beak of cycadean seeds. At the time of
pollination, when the pollen-chamber must have extended to the apex of
the lagenostome, the tip of the nucellar cone may have secreted some
sticky substance to which the microspores would adhere.
Prof. Lignier[175] has recently described some large megasporangia
from the Westphalian Coalfield of Ostrau in Austrian Silesia which he
made the type of a new genus _Mittagia_, after Herr Mittag, Director
of Mines. Two sporangia, between 2 and 3 mm. in diameter, were found
in close association as though belonging to a single sorus; one was
empty and the other contained four megaspores. The structure of the
thick wall of the sporangia is very similar to that of the testa
of _Lagenostoma Lomaxi_, but it apparently split into two valves.
Lignier refers the new type, _Mittagia seminiformis_, to some
unknown Palaeozoic group of heterosporous Filicineae, possibly the
ancestral stock of the Pteridosperms, and he thinks it probable that
the sporangia resembled seeds in their facilities for dispersal. In
the structure of the sporangial wall _Mittagia_ also resembles the
sporocarp of _Pilularia_.
_Seeds presented as impressions, without internal structure,
superficially resembling Lagenostoma._
_Lagenospermum_ Nathorst.
This generic name is adopted for seeds represented by casts or
impressions agreeing in external features with _Lagenostoma_ but
which on the available evidence cannot be confidently assigned to
that genus[176]. Two types of seed were described by Arber[177]
from the Lower Coal Measures of Scotland as _Lagenostoma Kidstoni_
and _L. Sinclairi_: the former has been removed by Oliver[178] to
_Physostoma_ and both are included by Arber[179] in a recent paper in
the genus _Radiospermum_. This new generic term is proposed by Arber
for a number of small sub-cylindrical seeds founded on impressions
including ‘small seeds which, when the structure is preserved,
are known as _Lagenostoma_, _Physostoma_, and _Conostoma_.’ The
question of nomenclature is invariably raised by cases in which
impressions resemble in their superficial characters genera founded on
anatomical characters: the seeds originally referred to _Lagenostoma
Sinclairi_ afford a good example of this difficulty. Nathorst has
recently proposed the generic name _Lagenospermum_ as preferable
to _Lagenostoma_ and _Radiospermum_ in the case of _Lagenostoma
Sinclairi_ and similar seeds which afford no proof of the possession
of such morphological characters as would justify their inclusion in
the genus _Lagenostoma_ but which may be examples of that genus. As
Nathorst points out, the adoption of _Radiospermum_ for _L. Sinclairi_
is inadvisable on the ground that it is also applied to seeds of a
different type. The type-species of _Lagenospermum_ is _L. Sinclairi_
and Nathorst describes additional species from Lower Carboniferous
rocks in Spitzbergen.
_Lagenospermum Sinclairi_ (Arber ex Kidston +MS.+).
Although it is not certain that these seeds are morphologically
identical with the genus _Lagenostoma_, a brief description is
intercalated here as the habit of the seed-bearing axes supplies a
probable key to the habit of the fertile fronds of _Lyginopteris_.
The type-specimens were collected by Mr Sinclair from the Lower
Coal Measures of Ayrshire, Scotland, and recorded by Kidston as
_Lagenostoma_ sp.: they were afterwards named by him in manuscript
_L. Sinclairi_ and handed to Dr Arber for description. The seeds are
elliptical-oblong, 4–5·5 × 1·5–3 mm., radially symmetrical and enclosed
by a loose envelope which is longitudinally ribbed and divided distally
into several linear-lanceolate lobes (fig. 408, A, A′). This covering,
though much longer than the cupule of _Lagenostoma Lomaxi_, is probably
a homologous structure. The most interesting point is the attachment
of the seeds to slender branches of a compound axis (fig. 408, A). It
is probable that the seeds were borne on a frond characterised by the
reduction or complete abortion of the sterile lamina or perhaps, as
in the recent Fern _Thyrsopteris elegans_[180], some of the pinnae of
a large compound frond were fertile. It is worthy of note that Arber
recognised pinnules of _Sphenopteris obtusiloba_[181] in association
with _L. Sinclairi_, a fact, as he says, in itself of no value but
which acquires significance in view of the discovery by Carpentier[182]
of cupules in close proximity to the same species of frond. Specimens
described by Dr Stopes from Westphalian rocks of New Brunswick as
_Pterispermostrobus bifurcatus_[183] bear a close resemblance to _L.
Sinclairi_.
_Lagenospermum oblongum_ (Kidston).
The species recently described by Dr Kidston[184] as _Lagenostoma
oblonga_ from the South Staffordshire coal-field appears to be closely
allied to Arber’s _L. Sinclairi_: it is represented by pairs of seeds
borne at the ends of forked branchlets: the seed is 2·5 mm. long by 1·5
mm. broad and is surrounded by a longer oblong cupule divided distally
into 6 free lobes.
A larger type of seed, 3 cm. long and 2·5 cm. broad, is described by
Kidston[185] from the same coal-field as _Lagenostoma? urceolaris_. A
characteristic feature is the truncate apex surrounded by a prominent
canopy formed of the expanded apical free portion of the integument.
The lack of anatomical data in both these seeds is a reason for the
substitution of some less committal term than _Lagenostoma_.
Grand’Eury[186] and Carpentier[187] have published accounts of
impressions of seeds from the Coal Measures of France compared by them
with species of _Lagenostoma_ though not assigned to new species.
These and similar seeds should be referred to Nathorst’s genus
_Lagenospermum_.
The difficulty of recognising the true nature of seed-like impressions
is illustrated by some specimens in the Goldenberg collection in
Stockholm described by Arber[188] as _Carpolithus Nathorsti_: these
consist of pieces of _Sphenopteris_ pinnae probably, as Zeiller
suggested, _Sphenopteris Schaumburg-Lippeana_ (Stur) bearing at
the ends of the segments of deeply divided pinnules what appeared
to be seeds 1 mm. long, oval and longitudinally ribbed, and
possibly enclosed in a cupule. Arber considered the ‘seeds’ to be
related to _Lagenostoma_, probably belonging to some member of the
Lyginopterideae. An examination of the specimens by Nathorst[189]
showed that the supposed seeds are collections of spores; but whether
the spores of a true Fern or the microspores of a Pteridosperm cannot
be determined.
_Pterispermostrobus_ Stopes.
_Pterispermostrobus bifurcatus_ Stopes.
Dr Stopes[190] has recently called attention to a resemblance between
specimens from the Westphalian of New Brunswick, described by her as
_Pterispermostrobus bifurcatus_, and _Lagenospermum Sinclairi_. The New
Brunswick fossil is made the type of a new genus _Pterispermostrobus_,
which is employed for fructifications of Pteridosperms that cannot
be associated with a known species of parent and may be either seeds
or complex male organs borne on a definitely branched rachis. The
type-species is represented by a slender axis bearing lateral branches
divided into two widely divergent arms each of which bears a terminal
body, 4 × 3 mm., characterised by 3–5 apical lobes extending 2 mm.
beyond the distal end of the seed-like organ and resembling a cupule.
In this as in many other cases it is impossible to determine the
true nature of the reproductive bodies, whether they are small seeds
or groups of microsporangia: the new generic name serves a useful
purpose though it is not always possible definitely to refer doubtful
fructifications of this kind to a Pteridosperm. The organs in question
may also be compared with _Codonotheca_[191].
_Pterispermostrobus pusillus_ (Nathorst).
The name, _Codonotheca pusilla_, is given by Nathorst[192] to some
doubtful specimens from the Culm of Spitzbergen representing short
stalks bearing linear-lanceolate scale-like bodies, 9–10 mm. long
by 1 mm. broad, coalescent at the base. Nathorst compares them
with Sellard’s species, _Codonotheca caduca_, but adds that they
may be cupules of some Pteridosperm and calls attention to their
resemblance to some fossils figured by Carpentier as _Calymmatotheca
acuta_. Both Nathorst’s species and the French specimens described
by Carpentier[193] as cupules may be referred to Dr Stopes’ genus
_Pterispermostrobus_ as their morphological nature cannot be determined.
+v.+ _Roots._
In 1876 Williamson[194] described some petrified vegetative organs
from the Lower Coal Measures of Lancashire under the name _Kaloxylon
Hookeri_ characterised by a division of the secondary xylem into
cuneate masses (fig. 415, C) like those in some recent Bignoniaceous
stems. Williamson at first believed _Kaloxylon_ to be a stem, but in a
later memoir he expressed the opinion that ‘it is difficult to believe
that these organs have been other than roots’[195]. Felix[196] had
meanwhile described a specimen from the Coal Measures of Westphalia as
_Kaloxylon cf. Hookeri_ and suggested that it might be a waterplant. In
1894 Williamson and Scott[197] demonstrated that _Kaloxylon Hookeri_
is the root of _Lyginopteris_, a conclusion independently reached by
Hick[198].
The roots of _Lyginopteris_ arise on all sides of the radially
symmetrical stem in the pericycle region; they are copiously
branched as is shown by the abundance of roots of various sizes in
close association. No roots have been discovered exceeding 1 cm. in
diameter nor have any been recorded with secondary periderm-tissue.
The absence of root-hairs and the more or less lacunar structure of
the cortex are indicative of swampy ground. It is seldom that the
palaeobotanist has an opportunity of investigating the growing-points
of Palaeozoic plants, and for this reason some well-preserved apices
of _Lyginopteris_ roots, attributed to that genus on the ground
of constant association with fragments of stems in the calcareous
nodules of Dulesgate, are of special interest. One of these specimens
was figured by Dr Stopes and Mr Watson[199] in their account of
plant-bearing nodules, and a description of that and other examples has
since been published by Prof. Weiss[200]. A longitudinal section of a
root-tip, ·21 mm. in diameter at its broadest part, shows a root-cap
which suggests an origin from a single cell, but an examination of
the plerome-cylinder in a slightly tangential section does not afford
conclusive evidence of the occurrence of a single initial cell. Weiss
on the whole inclines to the view that _Lyginopteris_ possessed a
single apical cell like the roots of Leptosporangiate Ferns, though he
prefers to leave the decision open. Attention is drawn to the fact that
the plate of tracheidal tissue in emerging lateral rootlets is vertical
as in Phanerogams and not horizontal as in recent Pteridophyta.
The vascular tissue of a _Lyginopteris_ root (fig. 410) consists of
from three to eight alternate strands of centripetal xylem and phloem,
and with the metaxylem is associated a small amount of conjunctive
parenchyma which does not form a central pith. The pericycle, one to
several layers broad, is succeeded by an endodermis which occasionally
shows the characteristic thickenings on the radial walls. A broad
cortex of thin-walled lacunar tissue with numerous secretory cells is
bounded externally by a superficial cylinder of two or more layers
of comparatively large and thin cells, the outermost of which are
radially elongated. This superficial tissue forms a striking feature
by which a _Lyginopteris_ root may often be recognised at a glance.
The root represented in fig. 410, approximately 2 mm. in diameter, has
a heptarch stele divided into seven xylem-groups by crushed bands of
parenchyma and a protoxylem strand occupies the apex of each projecting
angle (fig. 410, _px_). The superficial cylinder of clear cells is seen
at _a_. A very small root is seen at _r_ in fig. 410.
[Illustration: Fig. 410. _Lyginopteris oldhamia_, young root. × 30.
(Kidston Coll. 403.)]
Fig. 415, C, represents part of an older root in which the pentarch
primary xylem is enclosed by broad wedge-like groups of secondary
xylem and phloem separated by conspicuous medullary rays opposite the
protoxylem strands (_px_). Crushed primary phloem arcs, _p_, are often
clearly recognisable beyond the cambium. The secondary thickening,
as Williamson and Scott state, ‘takes place exactly in the manner
typical of roots of Dicotyledons, so that this fossil might very well
be used for purposes of demonstration as illustrating the secondary
growth of a root with diagrammatic clearness’[201]. The young roots
of _Lyginopteris_ resemble in many respects those of Marattiaceous
Ferns, though the presence of a single apical cell, if such occurs, is
a distinguishing feature; but in the presence of secondary conducting
tissue they agree with those of Phanerogams.
_Distribution of Lyginopteris._
The frequency with which petrified fragments of _Lyginopteris_
stems occur in the calcareous nodules of the English coal seams
shows that the genus must have been plentifully represented in the
Upper Carboniferous vegetation, and the occurrence in both North
American[202] and European localities of fronds identical with or
closely resembling _Sphenopteris Hoeninghausi_ affords evidence of wide
geographical range. Petrified specimens were recorded by Felix[203]
from Westphalia in 1886, and Zalessky[204] has recently discovered
_Lyginopteris_ in the Donetz coal-basin of Russia. An investigation
by Kubart[205] of the calcareous nodules, to which attention was
first drawn by Stur, in the Ostrau Coal Measures led to the discovery
of several examples of _Lyginopteris_ stems. The descriptions and
figures so far published are hardly sufficient to enable us to
estimate the degree of relationship to the English type, but some of
the stems appear to be new species and Kubart considers them all to
be specifically distinct from _Lyginopteris oldhamia_. _Lyginopteris
heterangioides_ contains scattered tracheids in the pith and thus
affords an interesting transitional type between _Lyginopteris_ and
_Heterangium_. In _L. lacunosum_ the inner cortex is lacunar and
the primary xylem bundles pursue an independent course in the stele
in contrast to the anastomosing arrangement in _L. oldhamia_ and in
another Hungarian species _L. tristichum_. The species recorded by
Kubart occur in the Millstone grit and the Coal Measures.
The geological range of _Lyginopteris_ as represented by petrified
stems does not extend beyond the limits of the Carboniferous system.
=HETERANGIUM.=
The generic name _Heterangium_ was first used by Corda[206] for a
piece of stem from the Coal Measures of Radnitz, Bohemia, represented
by part of the vascular axis of a stem consisting of strands of
large reticulately pitted tracheids intermixed with parenchyma and
exhibiting structural features differing apparently from those of any
known type. Corda’s material has been re-examined by Kubart[207] who
figures a section from it. _Heterangium_ is a genus closely allied to
_Lyginopteris_ both in habit and in general anatomical characters. The
stem is monostelic; the vascular cylinder prior to secondary thickening
resembles the protostele of certain recent species of _Gleichenia_ and
may be compared also with _Trichomanes scandens_[208]. It agrees with
that of _Lyginopteris_ in the possession of primary mesarch bundles
but differs in the substitution of a cauline axial mass of metaxylem
for the pith of _Lyginopteris_. The secondary vascular tissue agrees
closely with that of recent Cycads and _Lyginopteris_. A characteristic
feature is the occurrence of numerous horizontal bands of sclerous
cells in the cortex (fig. 412) of the stem and in the ground-tissue of
the rachis and larger branches of the fronds. The stem was erect and
rarely branched ‘giving off large foliar appendages at somewhat distant
intervals and from its entire circumference’[209]. Our knowledge of the
reproductive organs is less precise than in the case of _Lyginopteris_;
but we are justified in asserting that _Heterangium_ is a Pteridosperm
which in all probability bore fern-like microsporangia and seeds
similar in general plan to _Lagenostoma_.
The association of some seeds included in Williamson’s genus
_Conostoma_ with _Heterangium Grievii_ in the Pettycur beds and their
resemblance to _Lagenostoma_, the seed of _Lyginopteris_, suggested
the possibility of actual connexion: further evidence in support of
this view has recently been brought forward by Dr Benson[210] in the
case of a species of _Conostoma_ which she transfers to a new genus
_Sphaerostoma_.
The two species _Heterangium Grievii_ and _H. tiliaeoides_ are
described in illustration of the genus and reference is made to a few
other types.
_Heterangium Grievii_ Williamson.
(_Stem_.)
1872. _Dictyoxylon Grievii_, Williamson, Brit. Ass. Rep. (Edinburgh
Meeting), p. 112.
1873. _Heterangium Grievii_, Williamson, Phil. Trans. R. Soc. Vol. 162,
p. 404.
(Leaf.)
[1720. _Fumaria officinalis_, Volkmann, Silesia subterranea, p. 111, Pl.
+xiv.+ fig. 2.]
1822. _Filicites_ (_Sphenopteris_) _elegans_, Brongniart, Class. Vég. p.
233.
1828. _Sphenopteris elegans_, Brongniart, Hist. Vég. Foss. p. 172.
1836. _Cheilanthites elegans_, Goeppert, Foss. Farnkr. p. 233.
1877. _Diplothmema elegans_, Stur, Culm Flora, +ii.+ p. 130.
i. _Stem_.
At the Edinburgh meeting of the British Association Williamson[211]
gave a brief account of some petrified stems from the Lower
Carboniferous strata of Burntisland on the Firth of Forth which he
included in the genus _Dictyoxylon_. One of these was named _D.
Grievii_ after Mr Grieve the discoverer of the specimens. In a later
and more complete description Williamson adopted Corda’s generic name
on the ground of the close resemblance of the Scotch stem to the
Bohemian fragment _Heterangium paradoxum_. In 1873[212] Williamson
added new facts in regard to _H. Grievii_ and in 1890[213] he described
a very closely allied type from the Lower Coal Measures of Lancashire.
Five years later his descriptions were considerably extended and
modified in the joint memoir with Dr Scott[214].
The great difference in age between the English Upper Carboniferous
stem and the Scotch specimens from the Lower Carboniferous beds of
Burntisland suggests a probable specific difference. Dr Scott has
recently adopted the name _Heterangium Lomaxi_, proposed but not
published by Williamson, for the English type. Though in the following
account the species _Heterangium Grievii_ is treated in the broader
sense it should be recognised that the geologically younger stem
is worthy of specific recognition; it is characterised, to quote
Scott[215], by ‘the great distinctness of the primary xylem strands,
by their nearly exarch structure, with little primary centrifugal
wood, by the abundant secretory sacs of the stele, and by the rather
scattered leaves.’
[Illustration: Fig. 411. _Heterangium Grievii_. _lt_, _a_, _b_, _c_,
leaf-traces; _p_, pericycle with periderm; _ph_, phloem; _x_¹, _x_²,
primary and secondary xylem; _px_, protoxylem; _r_, root; _s_, sclerous
tissue.]
_Heterangium Grievii_ has a radially symmetrical stem bearing compound
leaves with decurrent petioles which give to the otherwise cylindrical
axis an angular outline as seen in transverse section (fig. 411, A).
The phyllotaxis appears to be ⅜. The stem rarely exceeds 1·5 cm. in
diameter: in the centre is a comparatively large stele consisting in
young stems of primary xylem and phloem, but in older stems these
are separated by a cylinder of secondary vascular tissue which in
this species is always narrower than in _Lyginopteris oldhamia_ and,
as Williamson pointed out, often of unequal thickness on different
radii. The medullated stele of _Lyginopteris_ is replaced by a solid
xylem-cylinder consisting mainly of groups of large tracheids, reaching
·3 mm. in diameter, with multiseriate bordered pits (fig. 411, D)
embedded in an anastomosing parenchymatous tissue-system. In the stele
reproduced in fig. 411, B, which with the exception of a very narrow
zone of secondary xylem, _x_², consists entirely of primary xylem,
_x_¹, the parenchyma is represented by a darker reticulum (_cf._ fig.
415, B) dividing the metaxylem into islands as in _Gleichenia_. In
the peripheral portion of the xylem the tracheids are rather narrower
and arranged in more definite groups in many of which is a single
strand of narrow spiral elements (fig. 411, A′, _px_) close to the
outer margin. These peripheral primary bundles in which protoxylem
is recognisable may be described as leaf-traces of mesarch structure
consisting of centripetal xylem and, to a much less extent, of smaller
centrifugal elements for the most part with dense spiral bands in place
of the multiseriate pits of the rest of the metaxylem. The structure
of these leaf-traces is practically identical with that of the primary
bundles of _Lyginopteris_. There is, however, a difference to which
attention is drawn by Williamson and Scott. While in _Lyginopteris_ in
any transverse section the primary bundles in the stele are equal in
number to the leaf-traces in the pericycle and cortex, in _Heterangium_
the peripheral groups in the stele may be as many as twenty, a number
considerably in excess of the leaf-traces beyond the limits of the
primary xylem of the stele. It may be that the leaf-trace of each
leaf, which joins the stele at a distance of 6–10 internodes below
its entrance into the cortex from the leaf-stalk, may branch in its
descent in the axial region, or some of the primary groups of xylem may
be confined to the axial region and independent of the leaf-traces.
Portions of the peripheral region of the stele may be occupied by
metaxylem groups without protoxylem and identical with those which make
up the bulk of the metaxylem.
Scott[216] has recently published a note in which he states that most
of the British Coal Measures Heterangiums were polydesmic. Two bundles,
and not a single strand as in the Scotch _H. Grievii_, leave the stele
for each leaf, and these divide into four, in some cases at least,
before entering the petiole.
The secondary xylem is continuous at its inner edge with the outermost
primary tracheids (fig. 411, A′) and consists of rows of tracheids,
1–3 elements broad, alternating with numerous broad medullary rays
of radially elongated parenchyma. Beyond a typical cambium-zone the
secondary phloem consists of parenchyma and sieve-tubes bounded by
crushed arcs of primary phloem. Abutting on the phloem is a pericycle
composed of several layers of small parenchymatous cells (fig. 411,
A, _p_) and in the outer layers of this tissue a phellogen (fig. 411,
C, _p_) and some periderm are usually present though, as Williamson
and Scott point out, the periderm is less regular and narrower than
in _Lyginopteris_. The inner cortex, composed of short parenchymatous
cells, is traversed by numerous narrow bands of dark, thick-walled
cells similar in the structure of the elements, though peculiar in
the horizontal elongation of the groups, to the sclerous nests in the
pericycle and pith of _Lyginopteris_. These characteristic bands are
chiefly seen in the oblique longitudinal section of a stem represented
in fig. 412. In this section, 25 mm. in length, the lighter band, _p_,
is the pericycle and in it a few obliquely cut leaf-traces are shown as
dark patches. The horizontal bands are similar in structure and shape
to the diaphragms of thick cells in the pith of _Abies magnifica_[217],
and in both plants they probably serve as supports to the softer
parenchyma. There may be as many as 46 bands in a vertical length of
cortex of 1 inch (about 19 per centimetre). It was the occurrence of
precisely similar transverse lines on the carbonised impressions of the
rachis of _Sphenopteris elegans_ that led Kidston[218] to suggest a
connexion between that species and the stem of _Heterangium Grievii_.
The outer cortex, consisting of alternate strands of parenchyma and
stereome similar to that of _Lyginopteris_, is much narrower and a less
conspicuous feature than in _Heterangium_; the stereome bands do not
form so regular a hypodermal network and extend much further vertically
without anastomosing. The epidermis has been described as a layer of
fairly thick cells showing in one case an appearance of a depressed
stoma[219]. There are no secretory canals like those of Cycads but,
as in _Lyginopteris_, scattered cells with dark contents in the
stem-tissues probably represent secretory sacs.
The leaf-traces on leaving the stele pursue a very gradually ascending
course to the petiole; they retain their collateral structure in the
pericycle and cortex and have no secondary xylem, but become concentric
as they enter the base of a leaf.
[Illustration: Fig. 412. _Heterangium Grievii_. Oblique longitudinal
section of stele and part of cortex; _p_, pericycle. × 3. (Kidston
Coll. 529.)]
Before passing to the description of the leaves, the more striking
features in the stem may be summarised with reference to the
diagrammatic sketches shown in fig. 411. Fig. 411, A, represents a
section of _Heterangium Grievii_ approximately 2 cm. in its maximum
diameter; at the periphery of the primary xylem, _x_¹, and close to its
outer margin are several protoxylem groups, not shown in the drawing,
each of which marks the position of a mesarch trace. The zone of
secondary xylem, _x_², is interrupted by the exit of leaf-traces and
one of these is seen at _a_ in fig. 415, A, separated from the central
primary xylem by a foliar gap filled with parenchyma. The pericycle
is shown at _p_ in fig. 412 and its outer boundary at _p_ in fig.
411, A. Beyond the pericycle is the broad parenchymatous cortex with
leaf-traces, _lt_, and some sclerenchymatous patches, _s_. The vascular
strand _a_ is passing into the base of a leaf-stalk. In the stem shown
in fig. 411, B, 1·4 cm. × 7 mm., a decurrent petiole is seen at the
upper end with its single vascular strand, _a_, and two sclerous nests;
a similar though detached leaf-base occurs at the opposite end of the
long diameter. Other leaf-traces are seen at _b_ and _c_. From the
left-hand side of the stele a curved strand of tracheids is passing out
to supply a root, _r_.
ii. _Root_.
Adventitious roots of endogenous origin are occasionally met with in
_Heterangium_ stems, but we have less information as to their anatomy
than in the case of _Lyginopteris_. In a specimen of _Heterangium
Lomaxi_ figured by Williamson and Scott[220] three roots are seen in
a vertical series growing outwards through the cortex of a stem. The
roots agree generally with those of _Lyginopteris_ but the outermost
cortical layers possess no special features.
iii. _Leaf_.
The large compound fronds long known as _Sphenopteris elegans_
were recognised by Kidston as the leaves of _Heterangium_ by the
closely arranged transverse striae or narrow ribs on the rachis and
pinnae which are the expression on the carbonised impressions of
the horizontal plates of sclerous tissue in the petrified stems and
petioles of _Heterangium_. The dichotomously branched fronds are
included by Stur in his genus _Diplotmema_ and that author figures
several typical examples in his ‘Culm Flora’[221]. Fig. 413, A,
shows a forked axis with the bases of more slender branches and the
characteristic transverse bands and in fig. 413, B, part of a pinna
is reproduced. In general appearance, except in the bifurcating
pinnae, the fronds resemble those of _Davallia tenuifolia_ with which
Brongniart compared the Palaeozoic species. There is little doubt
that _Sphenopteris dissecta_ and some other species were also borne
on _Heterangium_ stems. The rachis and petioles differ from those of
_Lyginopteris_ fronds in the absence of emergences (_cf._ fig. 404,
E). The petioles (fig. 411, B, _a_) have a single concentric vascular
bundle with internal protoxylem.
[Illustration: Fig. 413. _Sphenopteris_ (_Diplotmema_) _elegans_. A.
Forked rachis with bases of lateral branches (Kidston Coll.); B, pinna.
(After Stur.)]
iv. _Reproductive organs_.
As yet no satisfactory evidence has been published with regard to
the nature of the microsporangia but in all probability these were
constructed on the same plan as those of _Lyginopteris_. There is a
strong _prima facie_ case for assigning the seed _Sphaerostoma_ to
_Heterangium_: absolute proof of organic connexion is still lacking
though Dr Benson’s recent account of the seeds associated with
_Heterangium Grievii_ almost amounts to demonstration of continuity
between vegetative organs and seeds.
_Sphaerostoma ovale_ (Williamson).
[Illustration: Fig. 414. _Sphaerostoma ovale_. A. Longitudinal
section showing the cupule, _c_, integument, _e_, _f_, with vascular
bundle, _v_, the upper part of the nucellus, _n_, and megaspore,
_m_; _a_, archegonia. B. Transverse section through the roof of the
pollen-chamber, _pc_, and the summit of the nucellus, _n_. (After
Benson.)]
In 1877 Williamson described some detached petrified seeds from the
Lower Carboniferous rocks of Fifeshire, Scotland, as _Conostoma ovale_
and _C. intermedium_. Dr Benson’s investigation[222] of these two
forms leads her to confirm Williamson’s doubts as to the validity of a
specific separation and she assigns the single type to the new genus
_Sphaerostoma_. The seeds are always associated with the vegetative
organs of _Heterangium Grievii_. In 1909 Oliver[223] expressed the
opinion that the Burntisland species of _Conostoma_ (= _Sphaerostoma_)
is probably the seed of _Heterangium_. The seed consists of a central
body representing the nucellus, an inner integument, and an enveloping
cupule or outer integument: most specimens have lost the cupule and in
this condition they are 3·5 mm. long with a maximum breadth of 2·2 mm.
In the middle the seed is circular in transverse section and octagonal
near the base and apex. The free apical part of the integument forms
a frill (canopy) round the micropyle and extends beyond the nucellar
apex which consists of a relatively flat plinth surmounted by a central
dome or lagenostome (fig. 414). The lagenostome is surrounded by an
annular pollen-chamber on to the lower surface of which abuts the
large embryo-sac, and remains of archegonia were noticed below the
pollen-chamber. The roof of the chamber in the young state consists of
a layer of thin-walled cells extending across the flattened apex of
the nucellus, _n_, but as the pollen-chamber becomes differentiated
from the nucellar tissue by the disorganisation of the zone of cells
its roof-cells thicken their vertical walls and assume the structure
of a multiseriate annulus, which acts as a mechanism for opening the
pollen-chamber by a circular dehiscence in such a way that the edge of
the ruptured roof of the pollen-chamber slightly overlaps the periphery
of the central column of nucellar tissue after it has returned to its
original position subsequent to the entrance of the microspores. The
micropylar region is surrounded by eight lobes of the integument and
each is characterised by a crest of radially elongated cells, fig. 414,
_f_, especially prominent on the outer side. External to this is the
slightly longer cupular sheath (fig. 414, _c_) which may also have been
lobed. The surface of the integument below the terminal crests consists
of a layer of cells with small papillae which eventually ruptured and
discharged mucilage. Both integuments have a vascular supply, that of
the inner integument being represented by eight vascular bundles, some
of which were found to have mesarch xylem, given off from the single
strand in the pedicel. Fig. 414 shows the apical region of a seed
of _Sphaerostoma_: the flat-topped nucellar cap, _n_, is surrounded
by the annular pollen-chamber, _pc_, below which are indicated the
archegonia: the wall of the megaspore (embryo-sac) is seen at _m_ and
external to this vascular bundles, _v_, run up the inner portion of
the integument accompanied by some large cells (aqueous tissue). The
elongated epidermal cells at the apices of the lobes of the integument
form the frill, _f_, and at a lower level the cells of the same layer
are much smaller and papillate (_e_): the outer integument, _c_, forms
the so-called cupule. The transverse section shown in fig. 414, B,
is taken at the level of the roof of the pollen-chamber and of the
nucellar cap; it illustrates the contrast between the ‘multiseriate
annulus’ and the central column of small parenchyma.
_Sphaerostoma_ differs from _Lagenostoma_ in the whorl of crests around
the micropyle, in the nearly hemispherical form of the lagenostome
and in the relatively wider pollen-chamber with its peculiar form of
dehiscence. Miss Benson, while regarding _Sphaerostoma_ as similar to
_Lagenostoma_ in general plan, believes the distinguishing features of
the former to be such as are consistent with a more primitive form.
An important argument in support of connecting this seed with
_Heterangium_ is derived from the juxtaposition of some seeds and
portions of _Heterangium_ petioles, a juxtaposition that is believed to
demonstrate original continuity.
Grand’Eury[224] has recorded the association of two species of leaves,
_Sphenopteris elegans_ and _S. dissecta_, with small seeds compared by
him with _Lagenostoma_. In the absence of petrified specimens it would
be practically impossible to distinguish between _Lagenostoma_ and
_Conostoma_ or _Sphaerostoma_.
Carpentier[225] has described some impressions from French Westphalian
beds as _Conostoma_ and he records cupules without seeds on fronds of
_Sphenopteris obtusifolia_ which he speaks of as having transverse
striations like those of _Heterangium_. Dr Kidston pointed out to me
that the surface-features of the _Sphenopteris_ rachis are probably
due to ramental scales and not to the presence of horizontal sclerous
bands. Carpentier’s seeds may be compared with _Lagenospermum
Sinclairi_.
_Heterangium tiliaeoides_ Williamson, Phil. Trans. R. Soc. Vol. 178, p.
289.
This species, founded by Williamson on material from the Lower Coal
Measures of Halifax, Yorkshire, while agreeing in the structure of
the primary stele and in the general features of the cortex with the
older _Heterangium Grievii_, is clearly distinguished by certain
well-marked characters. Sclerous groups occur in the inner cortex as
in _H. Grievii_ but they are present also in the pericycle. The
peripheral leaf-traces in the stele show the mesarch structure rather
more distinctly than in _H. Grievii_, and the secondary xylem, which
forms a much broader cylinder than in the Scotch type, is divided by
broad medullary rays into characteristic cuneate masses each of which
rests at its base on the centrifugal tracheids of a leaf-trace strand
of xylem (fig. 415, B). The most striking distinctive feature is
afforded by the secondary phloem, which is often preserved in wonderful
perfection; this is unusually thick and owing to the tangential
expansion of the principal medullary rays the secondary phloem is
divided into separate masses which decrease in breadth towards the
external arcs of primary phloem. The triangular form of the phloem
rays, composed of tangentially stretched parenchyma, suggested the
specific name _tiliaeoides_ on account of their striking resemblance
to the rays of _Tilia_. The leaf-traces are nearly always in pairs as
they pass out through the cortex; they subsequently divide and appear
as four vascular strands in the petiole. The portion of stem reproduced
in fig. 415, _B_, 8 mm. broad, shows clearly the separation of the
secondary xylem and phloem into wedge-shaped groups: in each group
there are several narrow medullary rays. The extrastelar tissues are
represented by a few fragments only. Several layers of crushed periderm
occur in the pericyclic region but the more external tissues have been
almost completely exfoliated[226].
[Illustration: Fig. 415. A, B, _Heterangium_. A, _H. Grievii_, _a_,
leaf-traces. B, _H. tiliaeoides_. C, root of _Lyginopteris_.
(A, B, Kidston Coll., 529, 294; C, Williamson Coll., 1631.)]
Reference has already been made to _Heterangium Lomaxi_, the English
type originally included by Williamson in _Heterangium Grievii_. The
provisional species _Heterangium cylindricum_ Williamson and Scott[227]
differs, as Scott says, in no important respect from _H. Lomaxi_ and
should not be retained. A new species, _H. minimum_ Scott[228], has
been founded on a very small stem from the Coal Measures of Dulesgate
in which the leaf-traces leave the stele as single bundles as in the
Scotch _H. Grievii_.
The French species _Heterangium Duchartrei_[229] Ren. from Permian
rocks was originally referred by Renault to the genus _Poroxylon_: it
is represented by little more than the xylem of the stele and bears
a close resemblance to _H. tiliaeoides_. _Heterangium punctatum_ Ren.
and _H. Renaulti_[230] (Brongn.) also from the Permian of France were
originally placed in the genus _Lycopodium_ and afterwards recognised
as stems of _Heterangium_. A fourth French Permian species, _H.
bibractense_[231], is peculiar in the possession of a very small
primary stele encircled by deep wedges of secondary xylem, but without
more information it is impossible to speak with confidence as to
its systematic position. Kubart[232] has recently published brief
descriptions of some stems from the Ostrauer coal-basin in Moravia all
of which he regards as specifically distinct from the English types.
In _Heterangium Sturi_ the primary xylem is almost exarch and the
peripheral xylem groups are not very clearly defined: in _H. alatum_,
so called from the presence of lateral wings on the petioles, the
leaf-trace strands are more sharply differentiated from the rest of
the stele. _H. polystichum_ is a similar type, and _H. Andrei_, with a
relatively larger amount of parenchyma in the stele and thicker stems
forms an additional link between _Heterangium_ and _Lyginopteris_[233].
Prof. Johnson[234] has described a species of _Heterangium_, _H.
hibernicum_, from Upper Devonian and Lower Carboniferous beds in Co.
Cork, Ireland, based on some impressions of frond fragments without any
pinnules. The occurrence of numerous transverse striae on the rachis
and lateral branches suggests comparison with _Heterangium_ fronds,
but an examination of the specimens led me to suspect that some at
least of the striae are cracks and not original features. The presence
of spur-like appendages from the lower surface of the pinnae near
their origin from the rachis is recorded as a peculiar character, and
some obscure oval bodies, the nature of which is extremely doubtful,
are considered to be seeds. The imperfection of the material hardly
justifies the institution of a new species of _Heterangium_.
_Heterangium_ ranges from the Lower Carboniferous to the Permian strata
and is thus older than _Lyginopteris_ which in the form of petrified
stems is not recorded from the Lower beds of the Carboniferous system.
_Heterangium_ has been described as having a ‘great preponderance
of fern-like characters,’ but having regard to the resemblance of
the primary xylem of the latter to that of the Osmundaceae it would
seem doubtful whether in their relation to the Ferns there is any
important difference. _Heterangium_ may safely be spoken of as the
more primitive genus. The polydesmic character of the petioles of most
species is particularly interesting as it brings the genus nearer to
the Medulloseae and to _Rhetinangium_[235].
CHAPTER XXX.
II. MEDULLOSEAE.
The term Medulloseae was first employed by Goeppert and Stenzel[236]
for a family of Palaeozoic plants that appears to have reached its
maximum development in the Permian period: the oldest representatives
so far discovered are of Upper Carboniferous age. Our knowledge of the
family is chiefly derived from a study of the anatomical characters
of stems, and it is therefore on this basis that any grouping of
genera or species should be attempted. Although there is little
information with regard to the reproductive organs of _Medullosa_,
the type-genus, it is certain that the Medulloseae are Pteridosperms
differing from members of that group included in the Lyginopterideae in
the presence of more than one stele in the stem, in the habit of the
fronds, and in the structure of the rachis, as also in the structure
of the seeds, though these organs bear a fairly close resemblance
to the seeds of _Lyginopteris_ and _Heterangium_. The fronds of the
Lyginopterideae are of the _Sphenopteris_ type while in the case of
such species of _Medullosa_ as afford evidence of connexion between
stems and leaves the latter have the characters of _Neuropteris_,
_Alethopteris_, _Odontopteris_, _Linopteris_, and other form-genera
usually included in the Neuropterideae. Dr Lotsy[237] speaks of
_Lyginopteris_ and _Heterangium_ as members of the Sphenopteridophylla
and assigns species of _Medullosa_ either to the Neuropteridophylla
or to the Pecopteridophylla, the latter subdivision including species
with fronds of the _Alethopteris_ type. There is, however, little
doubt that other forms of leaves, such as _Odontopteris_ and possibly
_Taeniopteris_, were borne on Medullosan stems. It is undesirable
except in the absence of more trustworthy criteria to make use of
so protean a feature as leaf-form as a basis of classification. The
name Neuropterideae has been frequently employed for Pteridosperms
other than the Lyginopterideae on the ground that the foliage of
_Medullosa_ is represented by species assigned to form-genera included
in the Neuropterideae. It is, however, preferable to restrict the
family-name Neuropterideae to fronds and to speak of the second family
of Pteridosperms as the Medulloseae, including the genera _Medullosa_,
_Sutcliffia_, and _Rhexoxylon_.
=MEDULLOSA.=
Some species of _Medullosa_ probably resembled in habit _Angiopteris
evecta_ and the larger Marattias; they had short and relatively thick
stems clothed with the large decurrent bases of long compound fronds
superficially like those of some recent Ferns and the leaves of the
Cycad _Bowenia_. It is probable that, as Zeiller[238] has pointed out,
the fronds of _Medullosa_ and of other Pteridosperms had a greater
tendency than those of true Ferns to a dichotomy of the rachis. In
other types the stems reached a considerable length and leaves and
branches were separated by several feet of bare stem. The large size
of the leaf-stalks in proportion to the diameter of the stem as shown
by such species as _Medullosa anglica_ and _M. Leuckarti_ (fig. 416)
suggests either a short and thick main axis or, in the case of long
stems bearing scattered leaves, a plant that supported itself partially
at least by a habit of growth comparable with that of tropical Aroids
or other lianes. While _Medullosa anglica_ with its contiguous
leaf-bases affords an example of the first type, the occurrence of
stems of a Permian species, _M. stellata_, 3½ metres long without
branches or leaf-scars, suggests the habit of a liane; similarly a
specimen of _Medullosa Leuckarti_ in the Chemnitz Museum bearing a few
spreading petioles but little narrower than the stem and given off at
a wide angle would seem to favour the view that some species were ill
adapted to be mechanically self-supporting plants. The longest piece of
stem that has come under my notice is a specimen of _M. stellata_ in
the Chemnitz Museum reaching a length of nearly 8 metres: some species
attained a diameter of about 50 centimetres.
_Medullosa_ is always polystelic: the plan of the vascular system
varies considerably as regards both the number and form of the steles,
but there is a uniform type of structure within the limits of each
stele that recalls the single stele of _Heterangium_. The steles
consist of a central region composed of primary xylem, originally
surrounded by phloem, which in its mesarch or exarch structure agrees
with the vascular tissue of some species of _Gleichenia_ or _Lygodium_.
To this central region a cambium added secondary xylem and phloem
either in the form of a cylinder of uniform breadth, or more frequently
the centrifugally developed xylem exceeded in amount the secondary
conducting tissue added to the inner side of the primary region. Apart
from anatomical details a Medullosan stem with its several steles,
each with secondary tissue, embedded in parenchymatous ground-tissue
resembles the stems of some Dicotyledonous climbers such as _Thinouia
scandens_, species of _Serjania_ and _Paullinia_[239].
Anatomically the main features of the stelar system of _Medullosa_,
neglecting the secondary xylem and phloem, are in closer agreement
with the stems of Ferns than with those of any other plants. It has
been shown that the genus _Heterangium_ bears a close resemblance to
_Gleichenia_ in the structure of the primary stele (fig. 418, C): one
of the oldest types of _Medullosa_, _M. anglica_, may be described
as a _Heterangium_ with three steles and may be compared with a
dictyostelic Fern in which the irregular vascular framework is made
up of three main strands. In certain types of _Medullosa_ (fig. 416)
the ground-plan of the vascular system recalls that of a solenostelic
Fern, while in others the greater complexity suggests comparison with
such Ferns as _Matonia_, _Angiopteris_, _Psaronius_, or _Cyathea_; ‘it
is as though Nature were at the Carboniferous moment in the midst of a
series of amazing engineering experiments, most of which were either
buried deep in Palaeozoic oblivion, or permitted to survive only as
vestigial relics and atavistic ghosts’[240]. Though many Medullosae
resemble Ferns there is an important difference between the two groups
in the origin of the various plans of Medullosan stelar systems: in
Ferns the leaf is the determining factor in the evolution of stelar
arrangement, while in _Medullosa_ the occasional interruption of a
solenostele or the development of an apparently complex dictyostele are
features independent of the leaf and leaf-traces. In the structure of
the secondary xylem and phloem and in root-structure _Medullosa_ agrees
with recent Cycads. The genus is in short a generalised type with
filicinean and cycadean affinities. In the possession of seeds borne on
modified pinnae of compound fronds, _Medullosa_ resembles both _Cycas_
and the Lyginopterideae. The seeds exhibit a fairly close agreement
with those of _Lyginopteris_, _Heterangium_ and recent Cycads, but
they appear to have advanced further towards the cycadean type than is
the case with the closely related seeds of the Lyginopterideae. The
microsporophylls are very imperfectly known but they were undoubtedly
much less advanced and more fern-like than the megasporophylls.
The genus _Medullosa_ is recorded from the Permian strata of Saxony,
France, and Bohemia[241]; also from the Coal Measures of England, and
the discovery of petrified petioles of _Myeloxylon_, the type borne
on Medullosan stems in European species, may be taken as evidence of
the existence of the genus in North America during the Carboniferous
period[242].
The name _Medullosa_ was applied by Cotta[243] to three types,
_Medullosa elegans_, _M. stellata_, and _M. porosa_, from the
Rothliegende of the Chemnitz district. The first of these was
recognised by Brongniart[244] as a distinct genus for which he proposed
the designation _Myeloxylon_ and this was afterwards identified by
Renault, Williamson, and other palaeobotanists as a petiole and not
a stem. Further reference is made to _Myeloxylon_ on a later page.
Cotta spoke of _Medullosa_ as the most puzzling of the genera dealt
with in his ‘Dendrolithen,’ and in spite of the many additions to our
knowledge the position of this Palaeozoic genus is still a fertile
source of speculation. The generic designation _Medullosa_ is applied
to stems, with or without petioles; petioles or rachises of fronds
that frequently occur apart from stems are referred to the genus
_Myeloxylon_. The leaves of _Medullosa_ include several well-known
species of Carboniferous and Permian genera such as _Alethopteris_,
_Neuropteris_ and others that have in recent years been transferred
from the Filicales to the Pteridosperms. In a few instances seeds
have been found in organic connexion with Medullosan foliage, and
there can be no reasonable doubt that _Trigonocarpus_, some forms
of _Rhabdocarpus_, _Pachytesta_, and other seeds represent the
integumented megasporangia of _Medullosa_ or some closely allied genus.
Before attempting to summarise the salient features of _Medullosa_ a
description of a few selected types will serve to place us in a better
position to consider the genus as a whole. The British species are
placed first on the ground that they are both geologically the oldest
though, historically, the most recently described, representatives of
the genus; and in the organisation of the stem they are simpler than
the continental species. Their resemblance to _Heterangium_ serves
to some extent to bridge the gap between the majority of species of
_Medullosa_ and the simpler types of Pteridosperms represented by
_Heterangium_ and _Lyginopteris_.
_Medullosa anglica_ Scott[245].
Prior to the discovery of this species the genus _Medullosa_ had not
been recorded from Britain. A section in the Williamson collection
recognised by Scott as that of a _Medullosa_ had been identified by
Williamson as a large _Heterangium_ stem. An undescribed specimen
was found by Arber[246] in the Binney collection at Cambridge which
afforded some additional information as to the structure of the roots.
The specimens on which Scott’s thorough description is based were
obtained by Messrs Wilde and Lomax from the Lower Coal Measures
of Lancashire. The stem of this oldest species has the habit of a
tree-fern and is almost completely invested by the stout decurrent
bases of the petioles of large spirally disposed compound fronds with
a phyllotaxis of ⅖, the leaves of the same orthostichy being separated
from one another by a vertical distance of approximately 10 cm.
A transverse section of a slightly flattened stem is shown in fig.
416, A, the bases of three petioles give to it an angular form. Its
dimensions are approximately 10 × 4 cm. The ground-tissue of two of
the petioles is continuous with that of the stem, while that of the
third leaf-stalk is cut through near its separation from the stem and
its adaxial face is already defined by a hypodermal band of stereome,
_d_. The surface of the stem is characterised by fine longitudinal
ribs caused by the slightly projecting stereome in the outer cortex,
and from the narrow furrows between the leaf-bases adventitious roots
emerge in vertical series. The position of an interfoliar furrow is
shown by a small arrow in fig. 416, A. There are three steles, 2–3
cm. × 6–10 mm. in diameter: each agrees very closely in structure
with the single stele of _Heterangium_. _Medullosa anglica_ may be
described as a polystelic _Heterangium_ and as having the same relation
to _Heterangium_ as regards the stelar system as _Primula auricula_
bears to the monostelic _Primula_. The central core of the stele (the
black patches in the diagram, fig. 416, A) consists of an anastomosing
system of tracheal groups embedded in an irregular parenchymatous
reticulum. The large primary tracheids reach a diameter of 150μ and
have multiseriate pitting: at the periphery of the primary xylem there
is a more definite grouping of tracheids as in _Heterangium_, and the
slightly internal (mesarch) protoxylem elements are associated with
scalariform and densely spiral tracheids (fig. 416, B, C) narrower than
the more internal reticulate elements. The secondary xylem is manoxylic
as in Cycads, tracheids in 2–4 radial series alternating with medullary
rays 1–3 cells broad and usually of considerable depth (fig. 416, B).
The principal rays are continuous with the parenchymatous matrix of the
central core. Thick-walled tubular elements, no doubt of the nature of
sieve-tubes, form a conspicuous feature in the phloem.
The three steles occasionally divide and fuse with one another. The
tissue between the steles is crushed and disorganised and in the living
plant was probably small in amount. In the imperfectly preserved
inner cortical region there is a sinuous band of secondary parenchyma
(periderm; fig. 416, A, _c_) developed from a deep-seated phellogen; in
older stems this formed the superficial tissue after the fall of the
leaves. There is no definite boundary between the cortex of the stem
and the petiole-bases except when the hypoderm cuts across the cortex
preparatory to the separation of a leaf-stalk. The stem-cortex and
the ground-tissue of the petioles consist of parenchyma with numerous
secretory canals, not sacs only as in _Heterangium_, and are abundantly
supplied with scattered vascular bundles of collateral and exarch
structure.
[Illustration: Fig. 416. _Medullosa_ stems. A-C, _Medullosa anglica_;
A, transverse section; _a_, accessory vascular strand; _b_, accessory
strand enclosed by periderm; _c_, band of periderm encircling steles;
_d_, sclerenchyma between leaf and stem. B and C, longitudinal
sections. (After Scott.) D, _Medullosa stellata_; _a_, star-rings;
_p_, ‘partial pith.’ (After Weber and Sterzel.) E, _Medullosa Solmsi_.
(After Weber and Sterzel.) F, Medullosa stellata, from a specimen in
the British Museum (No. 13767). G, _Medullosa stellata_ var. _cortica_;
_v_, leaf-bundles. (After Weber and Sterzel.) H, I, _Medullosa
Leuckarti_. (After Weber and Sterzel and Solms-Laubach.) K, _Medullosa
stellata_ var. _gigantea_; _a_, concentric stele; _b_, _b_, later
cylinders of centrifugal tissue. (Adapted from Weber and Sterzel.) L,
_Medullosa Solmsi_ var. _lignosa_. M, _Medullosa porosa_. (L, M, after
Weber and Sterzel.)]
The leaf-traces are furnished by the peripheral tracheal groups at
the free surface of the primary portion of each stele: each trace
is at first concentric and consists of primary xylem with one or
more protoxylem strands near the outer surface and is completely or
partially enclosed by secondary xylem and phloem. In the course of its
passage to the leaf a leaf-trace loses its secondary tissues, which
were added by the cambium during the traverse of the zone of secondary
wood, and divides into small collateral bundles consisting mainly of
spiral and scalariform tracheids. The collateral bundles accompanied
by some narrow fibres are of the _Myeloxylon_ type (fig. 420), the
xylem being wholly centripetal. In the behaviour of the leaf-traces
and in the vascular system of the petioles _Medullosa_ differs from
_Heterangium_ and _Lyginopteris_. Each leaf-base is supplied by sets
of vascular strands which pass into it from the stem at different
levels; a large leaf-base reaching 4 cm. in diameter receives as many
as 70–80 bundles. The hypoderm is like that first described in the
French species _Myeloxylon Landriotii_[247] and often spoken of as the
_Sparganum_ type of hypoderm. The branching of the rachises points
to a compound frond, and the occurrence of numerous linear pinnules
with revolute margins (fig. 420, D) in association with the stem
suggests that the ultimate segments were of the _Alethopteris_ form.
This inference receives confirmation from the occurrence of petrified
specimens of undoubted _Alethopteris_ rachises with the structure of
_Myeloxylon_. It is practically certain that the leaves borne on the
stems of _Medullosa anglica_ are those long known as _Alethopteris
lonchitica_ (Vol. +ii.+ A, p. 553, fig. 364).
An interesting feature in the stems is the occurrence of cortical
vascular strands (fig. 416, A, _a_, _b_), reaching a diameter of 7 mm.,
containing scattered tracheids in a parenchymatous core surrounded by
secondary xylem and phloem. These cauline bundles are almost identical
both in structure and distribution with the accessory steles in the
stem of a recent _Cycas_, and the agreement is emphasised by the
presence of short square-ended tracheids in the primary xylem.
The roots branch freely and may attain a diameter of more than 1
cm.: they are generally triarch and the triangular primary xylem is
enclosed by secondary xylem except opposite the protoxylem. The cortex
is like that of _Lyginopteris_ roots and a conspicuous double layer of
superficial tissue is another feature common to both (_cf._ fig. 410).
The exceptionally well preserved specimens described by Arber[248]
show very clearly the thick zone of periderm which forms the covering
of older roots, and in some of the sieve-tubes groups of dark brown
patches show the form and arrangement of the sieve-plates.
_Reproductive organs._ We have as yet no precise information in
regard to the reproductive organs of _Medullosa anglica_, but there
can be little or no doubt that the fronds bore seeds that have long
been known under the generic name of _Trigonocarpus_. Many years ago
Mr Hemingway noticed the almost constant association of the fronds
of _Alethopteris lonchitica_ with _Trigonocarpus_, and Dr Kidston’s
discovery[249] of seed-bearing _Neuropteris_ pinnae considerably
strengthened the evidence derived from mere association. The structure
of _Trigonocarpus_ is described later (p. 117) in a section devoted to
reproductive organs attributed to _Medullosa_. Nothing is known as to
the microspore-bearing organs.
While in the structure of each of the steles _Medullosa anglica_ agrees
very closely with _Heterangium_, it differs from that genus in the
presence of three steles and in the structure of the petioles which
are much less fern-like than the simpler petioles of _Heterangium_ and
_Lyginopteris_. From the continental species the British species is
distinguished by its simpler stelar system, though there is a close
correspondence as regards individual steles.
_Medullosa pusilla_ Scott.
This species, briefly referred to by Scott in 1909[250] and fully
described in a recent paper[251], is founded on material from the
Lower Coal Measures of Colne, Lancashire. It agrees in essential
features with _Medullosa anglica_, but differs in the following
particulars: the linear dimensions of the stem are about one quarter
those of a typical stem of the older species; the leaf-traces possess
little or no secondary xylem and the relatively large decurrent
leaf-bases have a narrower and simpler hypoderm. The stem has a
tri-stelar vascular system enclosed in a ring of internal periderm, and
each stele (3 mm. in diameter) consists of a roughly triangular strand
of reticulate tracheids and a small amount of scattered parenchyma. The
protoxylem is either exarch or, as in _M. anglica_, mesarch, the exact
position being difficult to determine in the available material. The
secondary xylem closely resembles that of _M. anglica_.
Scott suggests the possibility that _Alethopteris decurrens_ may be
the foliage of _Medullosa pusilla_. It is possible that there is no
specific difference between _M. pusilla_ and _M. anglica_, but on the
present evidence the employment of a distinctive name is desirable.
_Medullosa centrofilis_ de Fraine.
This species was founded by Miss de Fraine[252] on a petrified stem
from the Lower Coal Measures of Lancashire. The maximum diameter of
the flattened stem including four decurrent leaf-bases is 5 cm. The
vascular system consists of an outer group of four steles, reduced
to three by fusion in the upper part of the specimen, enclosing a
central smaller stele or star-ring (fig. 417). It is the presence
of the star-ring that distinguishes this type from the other two
British species and forms a connecting link with certain continental
Medullosae. The peripheral steles agree with the steles of _M. anglica_
but, as in _M. pusilla_, there is some doubt as to the exarch or
mesarch position of the protoxylem. In the structure of the xylem the
central stele conforms to the rest of the vascular system and a strand
of protoxylem is preserved that is almost certainly exarch. There is
evidence that the peripheral steles occasionally anastomose, but the
central stele follows an independent course at least in the piece of
stem examined. Leaf-traces are furnished by the primary xylem of the
outer steles, and they appear to be without secondary tracheids as in
_M. pusilla_. A zone of secondary cortex encloses the vascular system
as in the other British stems: it is pointed out by Miss de Fraine[253]
that this tissue, usually described as a deep-seated periderm, must
have differed from cork in that there is no sign of drying up or
decay in the tissues external to it. The leaf-bases are of the usual
_Myeloxylon_ type. In size this species is intermediate between
_Medullosa anglica_ and _M. pusilla_.
[Illustration: Fig. 417. _Medullosa centrofilis._ Transverse section
showing the deep-seated ‘periderm’ (broken line) surrounding four
steles. (After de Fraine.)]
_Medullosa stellata_ Cotta.
Cotta[254] described _Medullosa stellata_ as a stem characterised by
the occurrence of several many-rayed stellate columns (‘vielstrahlige
Sternsäule’) in a pith enclosed by a double cylinder of secondary
xylem. The so-called pith is the central ground-tissue of the stem and
the double ‘striated ring’ of Cotta is a cylindrical stele identical
in structure with each of the steles of _Medullosa anglica_ but having
a tubular form instead of forming a relatively broad and short band
(_cf._ fig. 416, D and A). Goeppert[255] in his _Permian Flora_ gave a
detailed account of the species, some of his sections being cut from
Cotta’s material, and by the employment of varietal epithets emphasised
the range of variation within the limits of the type. Goeppert and
Stenzel[256] and, several years later, Weber and Sterzel[257]
adopted the same plan as a convenient method of drawing attention to
differences in anatomical characters. As Schenk[258] pointed out,
there is a considerable risk in the case of small pieces of stems of
attaching excessive importance to structural variations, and it is
by no means improbable, as he said, that differences which are the
expression of states of preservation or stages in development have been
incorrectly regarded as distinguishing marks of individual plants.
It is, however, convenient to recognise some of the more striking
deviations from the type-species by speaking of the different forms as
varieties though, as Weber and Sterzel fully admit, such varieties and
even some of the species must be looked upon as provisional. Weber and
Sterzel give expression to the provisional nature of their grouping by
classifying the species with their varieties into form-cycles. Under
the form-cycle _Medullosa stellata_ five more or less well defined
forms are recognised, the type-species being _Medullosa stellata_ var.
_typica_[259].
_Medullosa stellata_ var. _typica_.
Part of a transverse section of a cylindrical stem is represented
diagrammatically in fig. 416, D. Very little of the cortex is
preserved: a parenchymatous axial region with scattered secretory
canals contains four oval or cylindrical vascular steles, the stellate
columns of Cotta or star-rings of later authors. These are of the
same nature as the small central stele in the English _Medullosa
centrofilis_. The central region of the stem in this specimen is
completely surrounded by a narrow cylinder of inversely orientated
secondary xylem and phloem (fig. 416, D), the phloem being on the
inner side of the xylem. Beyond the xylem is a parenchymatous band
containing scattered groups of primary xylem tracheids with spiral,
scalariform, and reticulate pitting, and this zone, which is usually
designated the ‘partial pith,’ is succeeded by a second and broader,
normally orientated, cylinder of secondary xylem and phloem. In this
section the two concentric cylinders separated by the partial pith
form a solenostele like that of several recent Ferns except in the
presence of secondary tissue. The term ‘partial pith’ applied to the
tissue between the two cylinders of secondary tissue is misleading:
this tissue (fig. 416, D, _p_) is the primary xylem of the stele and
is homologous with the primary portion of the stele of _Heterangium_
and of the steles of _M. anglica_. In many sections the continuity of
the tubular stele is broken. In a section in the British Museum cut
from one of Cotta’s specimens[260], 6 × 3·5 cm. in diameter to the
outer edge of the vascular tissue, the cylindrical stele is interrupted
at two places. An example of the interrupted type of stele is shown
in fig. 416, F, and in fig. 416, H: the latter belongs to a distinct
species. The complete type of cylindrical stele is exceptional and
occurs occasionally at different levels in the stem. An important point
is that the frequent breaks in the cylinder are not connected with the
exit of leaf-traces and do not, therefore, correspond to the foliar
gaps in the solenostele or dictyostele of a Fern.
The secondary xylem is of the cycadean type (fig. 418, B, D) like that
of _Heterangium_ and _Lyginopteris_ and several other stems. Each of
the star-rings in the axial region consists of a parenchymatous core
with scattered primary tracheids enclosed by secondary vascular tissue
(fig. 418, B). The star-ring shown in fig. 418, B, from a Chemnitz stem
illustrates the characteristic cycadean character of the secondary
xylem with broad medullary rays: some of the innermost elements are in
contact with the primary tracheids. The phloem is rendered conspicuous
by the black contents in some of the elements. Both the star-rings and
the larger peripheral steles are constructed on the same plan and agree
with the steles of _M. anglica_. The star-rings occasionally branch
and anastomose with one another and with the encircling stele. The
star-ring in fig. 416, D at _a_ is about to give off a small strand.
Leaf-traces are furnished by the primary xylem at the edge of the
‘partial pith’ of the outer stele: as a leaf-trace passes outwards
through the outer cylinder of secondary xylem the cambium invests it
with secondary xylem and phloem, but as it passes through the cortex of
the stem it becomes reduced to its primary elements, and by successive
branching gives rise to small collateral bundles which enter the
petioles. The piece of stem shown in fig. 416, G, illustrates the
exit of leaf-traces from the stele and their subsequent division into
several small bundles, _v_, which are scattered in the cortex with
strands of sclerenchyma. In a specimen identified with _Medullosa
stellata_, Schenk[261] found part of a leaf-base attached to the stem:
its vascular system was of the _Myeloxylon_ type, the bundles being
identical with those in the cortex of the stem seen in fig. 416, G.
In some stems of _M. stellata_ the outer, centrifugally developed,
portion of the main stele is very much broader than in the example
represented in fig. 416, D. The diagrammatic sketch reproduced in fig.
416, F, represents a section of a Chemnitz specimen in the British
Museum[262] in which the axial region containing several star-rings
is almost enclosed by an inner zone of secondary xylem, and beyond
the narrow primary xylem (black in the sketch) the rest of the block
consists exclusively of secondary xylem 5·5 cm. broad. This example
illustrates a common tendency in _Medullosa_ towards a large excess
of centrifugal over centripetal secondary vascular tissue. A similar
specimen of _Medullosa stellata_ is figured by Mougeot[263] from
the Vosges showing a considerable development of centrifugal xylem
comparable with that in the British Museum stem. Weber and Sterzel[264]
describe stems of _Medullosa stellata_ showing slight periodic
swellings which it is suggested, though there is no evidence in support
of the opinion, may be connected with reproductive organs.
* * * * *
_Medullosa stellata_ var. _corticata_[265]. The specimen referred to
this variety, represented in fig. 416, G, has already been quoted
as affording data with regard to the origin and behaviour of the
leaf-traces. In this type of stem the outer portion of the main stele
is narrower than in _M. stellata_ var. _typica_ and the stele never
forms a complete tube. The star-rings in the centre of the stem are
more numerous than in the type-species of the genus. In the axial
region of some stems included in the form-cycle to which _M. stellata_
belongs there may be flatter and tangentially elongated vascular
strands in addition to the cylindrical star-rings; these are termed
plate-rings.
* * * * *
In _Medullosa stellata_ var. _lignosa_[266] the outer xylem reaches a
breadth of 4 cm. and the star-rings are reduced to one. The form _M.
stellata_ var. _gigantea_[267] (fig. 416, K) is of special interest as
an example of a stem reaching a diameter of nearly 50 cm. and having
as many as 43 large and small star-rings in the axial region. A large
tubular stele like that of the type-species (fig. 416, D) surrounds the
central region, but in this form the cylindrical stele _a_ is succeeded
by concentric cylinders of normally orientated xylem and phloem (fig.
416, K, _bb_) produced by successive cambiums either cortical or
pericyclic in origin. This type of stem presents a striking resemblance
to stems of _Cycas_ and _Macrozamia_ except in the possession of a
double cylindrical stele consisting of both centripetal and centrifugal
secondary xylem and phloem separated by a zone of primary xylem
(partial pith).
_Medullosa gigas_ Renault.
This species was founded on a piece of stem from the Permian of
Autun[268], consisting almost entirely of secondary xylem, which
Brongniart had previously placed in his genus _Palaeoxylon_[269]. The
secondary xylem reaches a diameter of 45–50 cm. and in the portion of
the central region preserved there are a few vascular strands like the
star-rings of other species. The considerable development of secondary
xylem indicates a form of stem similar to some forms of _M. stellata_
(_e.g._ fig. 416, F), but as the available data are insufficient for
accurate determination Renault’s specific name is retained. Renault
describes the internal xylem cylinder (_i.e._ the centripetal xylem) as
very slightly developed or as hardly visible, a feature in which the
French specimen shows a nearer approach to the structure of a recent
Cycad.
_Medullosa porosa_ Cotta.
The second of Cotta’s species[270], which has been fully investigated
by Weber and Sterzel, is constructed on the same plan as that of _M.
stellata_, but the stem is distinguished by the greater number of
star-rings and, more especially, by the presence of an outer system
of vascular strands in the axial region (fig. 416, M): these form a
frequently interrupted cylinder of anastomosing strands characterised
by the feeble development of secondary xylem and phloem or by the
absence of this tissue on the outer face of the strands. The component
parts of this outer series occasionally fuse with the internal
star-rings.
_Medullosa Solmsi_ Schenk[271] var. _typica_ Web. and Ster.[272]
This type has a large axial region containing several very small
star-rings enclosed by two concentric zones of separate plate-rings
(fig. 416, E) each consisting of a complete flattened cylinder of
secondary xylem and phloem enclosing primary xylem. As the complete
cylindrical stele of the stem of _Medullosa stellata_ shown in fig.
416, D, was compared with the solenostele of a Fern, so in this
stem (fig. 416, E) the vascular cylinder may be compared at least
superficially with a dictyostele. From the inner circle of plate-rings
strands are given off in the form of star-rings and these pass through
the gaps in the outer system, eventually breaking up in the cortex into
numerous collateral bundles. In another form of this species, var.
_lignosa_ (fig. 416, L), the axial region is enclosed by a circle of
plate-rings like those in the type-form, but these are succeeded by a
circle of very asymmetrically developed and large steles with the outer
xylem and phloem much broader than the inner. Moreover in this form
additional cylinders of normally orientated vascular tissue are added
as in _M. stellata_ var. _gigantea_ and in some recent Cycads. It is
noteworthy that the secondary wood of _Medullosa Solmsi_ is rather more
compact than in other species, a feature in which it to some extent
agrees with the South African genus _Rhexoxylon_.
_Medullosa Leuckarti_ Goeppert and Stenzel.
In this species[273], also from the Permian of Saxony, the central
region including some star-rings is surrounded by sinuous flattened
concentric steles (snake-rings) agreeing anatomically with the steles
of other species and characterised by the comparatively small breadth
of the secondary xylem and phloem (fig. 416, H). Leaf-traces are given
off, as in _M. anglica_ and other species, from the outer edge of the
primary xylem. In some forms there is a single set of snake-rings;
in others there is a double series. Fig. 418, D, shows part of the
secondary xylem of a stele of this species from Chemnitz: the tracheids
are in some places continuous with the primary xylem, and on the outer
edge of the secondary wood is a cylinder of phloem. A section of
_Medullosa Leuckarti_ figured by Goeppert and Stenzel[274] shows some
radial rows of very thick-walled elements in the secondary phloem which
they describe as bast sclerenchyma, but Solms-Laubach[275] believes
them to be sieve-tubes. Precisely similar elements are figured by
Scott[276] in _M. anglica_ and as this author suggests the thick walls
are probably not an original feature. The structure of the primary
xylem is more clearly seen in fig. 418, C, and the relation between
primary and secondary xylem is shown in fig. 416, I, where the position
of the protoxylem may be either exarch or mesarch. The protoxylem is
only occasionally recognisable but some of the peripheral primary
tracheal groups are undoubtedly mesarch. External to the stele, a
part of which is reproduced in fig. 418, D, are strands of stereome
elements and beyond them a band of radially elongated cells that may
be ‘periderm’: still farther out there are some imperfectly preserved
vascular bundles that are leaf-traces. This species is important as
affording a complete demonstration of the organic connexion between the
stem and petioles of the _Myeloxylon Landrioti_ type which indicate
that the fronds were probably Alethopteroid.
[Illustration: Fig. 418. A, _Myeloxylon radiatum_, part of petiole.
B, _Medullosa stellata_; star-ring; × 14. C, D, _Medullosa Leuckarti_;
C, primary xylem; D, part of primary stelar tissues and secondary xylem
and phloem; × 6. (A–D, Kidston Coll., 1014, 1307, 1238.)]
The specimen on which the diagrammatic drawing reproduced in fig.
419 is based has been investigated by Weber and Sterzel[277] and by
Solms-Laubach[278]. The figure is a slightly simplified version of
that given by Weber and Sterzel; it represents the stem of _Medullosa
Leuckarti_ as a transparent object, the two lower transverse sections,
B and C, being seen in perspective through the longitudinal faces. The
steles are shaded obliquely in the longitudinal sections, and in the
three transverse sections, A, B, C, the primary xylem (partial pith)
is black and the enclosing secondary vascular tissue radially shaded.
The whole block is 9 cm. in length and 6 cm. broad. Only a part of
the axial region is shown internal to the peripheral snake-rings and
in it are the star-rings _S_, _S_, _b_, and _c_. Outside the main
steles is the narrow cortex _R_ and portions of leaf-bases _I–IV_.
The lowest section, C, shows part of a peripheral snake-ring with a
slight swelling at _f_ on its inner side which, as seen in sections
B and A, foreshadows the separation of the star-ring _S_ and the
consequent break in the continuity of the snake-ring (_d_, _e_, sect.
B). In section A the gap is closed: in the longitudinal section
between B and A the star-ring _S_ is seen to form two branches, _a_
and _b_, the branch _a_ closing the gap between _d_ and _e_ in section
B. These sections demonstrate the formation of a star-ring from the
main peripheral stele and the formation of additional star-rings by
branching.
[Illustration: Fig. 419. _Medullosa Leuckarti._ Diagrammatic sketch
of stem showing longitudinal and transverse sections: for explanation
see text. (After Weber and Sterzel.)]
Numerous vascular bundles destined for the leaves are scattered in
the cortex. The course of the decurrent leaf-base _I_ is shown on the
longitudinal faces, its boundary being marked by crowded stereome
strands (of the _Myeloxylon Landrioti_ type); other leaf-bases are
represented by _II_, _III_, and _IV_.
In habit _Medullosa Leuckarti_ differs from such a type as _M.
stellata_ in its relatively shorter and stouter stem and in the shorter
internodes.
+Leaves and Reproductive Organs.+
i. _Leaves._ It has already been stated that in some cases petioles
occur in organic connexion with Medullosan stems, notably in _M.
anglica_ and _M. Leuckarti_: in the exceptionally rich collection in
the Chemnitz Museum, which forms a fitting memorial of the work of
the late Prof. Sterzel, there is a stem of _M. Leuckarti_ bearing
large petioles of the type known as _Myeloxylon radiatum_. The
occurrence of vascular bundles in the cortex of other species of stem
identical with those in the attached petioles points to a uniform
type of leaf-structure so far as regards the petioles and rachises
of _Medullosa_. While it is clearly unnecessary to distinguish by a
special generic title the petrified portions of fronds known to belong
to certain species of stems, the frequent occurrence of detached
petioles necessitates some distinctive term. The name employed is
_Myeloxylon_: the genus was instituted by Brongniart in 1849 for
Cotta’s species _Medullosa elegans_ the petiolar nature of which was
suspected by Binney in 1872.
_Myeloxylon_ (Medullosan leaf-stalks).
1832. _Medullosa elegans_ Cotta. 1865. _Stenzelia_ Goeppert. 1876.
_Myelopteris_ Renault[279]; 1877, _Aulacopteris_
Grand’Eury[280].
There is a very close agreement in general anatomical structure
between the numerous specimens of _Myeloxylon_ from the Permian strata
of Saxony and France and the Coal Measures and Millstone Grit of
England[281]; the genus is also recorded from the Upper Carboniferous
of Kansas[282]. Two well-defined types instituted by Renault are,
however, readily distinguished by the form of the hypodermal stereome
strands. _Myeloxylon_ may be defined as follows: Oval or cylindrical
branched axes, reaching a diameter of 15 cm., bearing pinnae having
the characters of _Alethopteris_, _Neuropteris_, _Odontopteris_,
and some other genera that were formerly classed as Ferns. Below a
single-layered epidermis, in which stomata have been recognised,
occur a few layers of parenchyma: this superficial tissue, which is
rarely preserved, is succeeded by a hypodermal region consisting
of parenchymatous tissue and numerous vertical groups of narrow
thick-walled fibres arranged as radial plates or circular, oval, or
reniform strands (the _Sparganum_ type of cortex). In the hypoderm as
in the ground-tissue generally secretory canals, often accompanied
by stereome, are a characteristic feature. The vascular system is
represented by a considerable number of collateral bundles scattered
through the ground-tissue and especially abundant in the outer region:
the bundles sometimes assume a more or less regular disposition in
concentric circles. Each bundle consists of a small group of xylem
tracheids, for the most part spiral or scalariform, though reticulately
pitted elements are by no means rare, with a single protoxylem group on
the outer face next the phloem (fig. 420, B, C). As a rule the xylem
is wholly centripetal, but occasionally the exarch structure becomes
mesarch by the occurrence of a few centrifugal tracheids. The phloem,
rarely preserved (fig. 420, B), consists of narrow sieve-tubes with
parenchyma, and the bundle as a whole is often partially enclosed by a
sheath of fibres.
Superficially the anatomical structure is similar to that of the
petioles of _Angiopteris_ or _Marattia_, and both Williamson[283] and
Renault placed _Myeloxylon_ in the Ferns; but the collateral form
of the vascular bundles, the position of the protoxylem, and the
arrangement of the hypoderm tissues, are cycadean features.
_Myeloxylon radiatum_ (Renault).
[Illustration: Fig. 420. A, B, _Myeloxylon radiatum_; A, petiole ⅔
nat. size; B, vascular bundle. C, _Myeloxylon_ sp. vascular bundle;
_px_, protoxylem. D, _Medullosa anglica_; section of pinnule. (A, B,
after Zeiller; D, after Scott.)]
This type is characterised by the radially elongated stereome of the
hypoderm. Prof. Zeiller[284], who has given a very clear and concise
description of _Myeloxylon_, is disposed to regard Cotta’s _Medullosa
elegans_ as a specifically distinct form on the ground that there are
two concentric zones of stereome in the hypoderm; but this feature is
shown only in one of Cotta’s figures, and Weber and Sterzel[285] point
out that a doubting of the hypoderm zone may be caused by accidental
juxtaposition of two faulted pieces of peripheral tissue. The drawing
reproduced in fig. 420, A, shows the structural plan of an unusually
large petiole from the Permian of Autun: a portion of the outer
tissue is seen in fig. 418, A. The vascular bundle, fig. 420, C, from
a Millstone Grit specimen[286], shows the centripetal nature of the
xylem and fragments of phloem in the outer half of the bundle, with
imperfectly preserved fibres abutting on the xylem. The characteristic
hypoderm is shown also in fig. 418, A; the double xylem strand on the
left illustrates a common feature caused by the branching of vascular
bundles. Several secretory canals are scattered in the ground-tissue.
The pinnules of _Myeloxylon radiatum_, or at least of some specimens,
have been shown by Renault to be of the _Neuropteris_ type.
_Myeloxylon Landrioti_ (Renault)[287].
In this species the distinguishing feature is the occurrence of the
hypodermal stereome in the form of circular, oval, or reniform strands
in place of the radial plates of _M. radiatum_. It is this form of
petiole that was borne by the stems of _Medullosa anglica_ and _M.
Leuckarti_. In _M. anglica_ the pinnules (fig. 420, D) are of the
_Alethopteris_ type, almost certainly _A. lonchitica_. Renault and
Zeiller have described French specimens of _Myeloxylon Landrioti_
bearing pinnules like those of _Alethopteris aquilina_ and _A.
Grandini_.
_Myeloxylon topekense_ (Penhallow).
The occurrence of _Myeloxylon_ petioles in the New World was recorded
by the late Prof. Penhallow[288] who founded this species on some
imperfectly petrified specimens from Upper Carboniferous strata at
Topeka, Kansas. Enough material was available to show the _Myeloxylon_
characters, but the preservation is too imperfect to admit of a
complete diagnosis. The hypodermal stereome shows a tendency to form
tangentially extended strands in place of the more circular or radially
elongated groups in the European species.
In addition to _Alethopteris_, _Neuropteris_ (including _Cyclopteris_)
and _Odontopteris_ fronds, which are known to possess rachises with
the _Myeloxylon_ features, there is reason to believe that the Permian
_Callipteris_ fronds and possibly some of the older _Taeniopteris_
leaves may also belong to _Medullosa_[289]. It is, however, unsafe to
assume that the occurrence of _Myeloxylon_ petioles necessarily denotes
the existence of _Medullosa_. The French stem _Colpoxylon aeduense_
Brongn.[290] bore leaves with the same general anatomical features as
those of a typical _Myeloxylon_, and there can be little doubt that
other genera of the Medulloseae also possessed fronds constructed
on the same plan as those known to have been borne by _Medullosa_.
An interesting illustration of an injured organ that had produced a
wound-cambium is afforded by a _Myeloxylon_ petiole from the Coal
Measures described by Mr Holden[291].
+Reproductive Organs.+
Reference was made in volume +ii.+ to the reasons which led to the
removal of several genera of Carboniferous and Permian fronds from
the Filicales to the Pteridosperms, and in Chapter +xxix.+ of the
present volume certain species of _Sphenopteris_ are described as the
foliage of _Lyginopteris_ and _Heterangium_. It is with such genera
as _Neuropteris_, _Alethopteris_, _Linopteris_ and others that we are
now more especially concerned, as they represent some of the types of
leaves borne by _Medullosa_ and other members of the Medulloseae. The
absence of any specimens among the large number of these common genera
bearing undoubted sporangia aroused suspicion as to the correctness
of the generally accepted view that these fern-like fossils were
the leaves of Palaeozoic Ferns. Subsequently the suspicion based on
negative evidence was confirmed by researches into the anatomical
structure of the leaf-bases, petioles, and fragments of pinnae attached
to and associated with stems of _Medullosa_. It is only in a few
cases that actual organic connexion between reproductive organs and
Medullosan leaves has been demonstrated, but from such facts as are
established it is safe to make the general statement that stems of
_Medullosa_—a generic term that undoubtedly includes plants which,
had we a fuller knowledge of them as complete individuals, would be
assigned to more than one generic type—possessed fronds simulating in
habit those of certain Ferns with some of the pinnae bearing seeds
often of considerable size and in all cases of complex structure,
agreeing in many respects with those of existing Cycads, while other
fronds, or in some cases it may be other pinnae, bore microsporangia
similar in form to the sporangia of Ferns.
_a. Microsporangia._
_Neuropteris._ A. _Neuropteris heterophylla[292]._
Several examples of supposed fertile specimens of _Neuropteris_
are recorded in palaeobotanical literature, but it was not until
1887 that any satisfactory specimen was discovered. In that year
Kidston[293] described a specimen of _Neuropteris heterophylla_
from the Lower Coal Measures of Scotland in which slender forked
branchlets bear small bodies at their tips some of which appear to
represent four-valved organs (fig. 421, D), though the imperfect
state of preservation renders impossible any definite pronouncement
as to their structure. To the specimen are attached a few sterile
pinnules, showing that it is a portion of a frond of _N. heterophylla_
characterised by the substitution of reproductive organs for pinnules.
The subsequent discovery of seeds attached to pinnae of the same
species afforded strong presumptive evidence, almost amounting to
proof, of the microsporangial nature of the Scotch specimen. For
this specimen, although no precise diagnosis is possible, Dr P.
Bertrand[294] has proposed the generic name _Neurotheca_. In 1911
the Abbé Carpentier[295] described some small ovoid bodies, 1–1·5
mm. long, from the Coal Measures of France arranged in groups of 4
to 6 and in some cases said to be borne on a slender pedicel which
he found in association with _N. heterophylla_ and compared with
sporangia described by Lesquereux from the Coal Measures of Arkansas as
_Sorocladus stellata_[296]. These supposed microsporangia have recently
been assigned by Bertrand[297] to _Sphenophyllum_.
[Illustration: Fig. 421.
A. _Potoniea adiantiformis_ Zeill. (very slightly enlarged).
B. Microsporangia of _Potoniea_ (enlarged).
C. _Linopteris obliqua_; side-view of microsporophyll.
D. _Neuropteris heterophylla_, pinnules and microsporangia (?).
E. _Linopteris obliqua_, surface-view of microsporophyll.
(A, C, E, after P. Bertrand; B, after Carpentier; D, after Kidston.)]
B. _Neuropteris gigantea_, etc. _Potoniea_, Zeiller.
In 1899 Zeiller[298] instituted the name _Potoniea_ for some peculiar
fertile leaves found in the Coal Measures of Heraclea consisting
of a branched axis with cuneate segments, 7–10 × 6–8 mm., bearing
numerous fusiform bodies, 1–1·5 mm. long, at the upper edge (fig.
421, A). These marginal bodies he regarded as sporangia and expressed
the opinion that _Potoniea_ may be the fructification of some form
of _Neuropteris_, _Mariopteris_ or _Alethopteris_. Carpentier[299]
afterwards described similar though rather larger examples from
the Pas-de-Calais coal-field as microsporophyll fragments of some
Pteridosperm: he stated that similar specimens had been found by
Kidston in England. In a later work Carpentier[300] described the
sporangia as crowded in groups (fig. 421, B) in the substance of the
thick lamina of _Potoniea_, and he connected the fertile segments
with _Neuropteris gigantea_, _N. pseudogigantea_ Pot. and _Linopteris
obliqua_ (Bunb.). Similar specimens are said to have been found in
Holland and Silesia. Bertrand[301] also records the association of
_Potoniea_ with _Neuropteris gigantea_ and _N. pseudogigantea_: he
describes some specimens as belonging to _N. gigantea_ Sternb. while
others, distinguished only by small differences, he attributes to _N.
pseudogigantea_. Kidston[302] has recently drawn attention to the
inconstancy of the characters mentioned by Potonié as distinguishing
features of _N. pseudogigantea_, and he shows good cause for referring
the examples so named to _N. gigantea_. The fertile lamina is almost
orbicular in surface-view and attached to a slightly excentric pedicel;
the microsporangia are borne on the lower surface and probably in
groups as described by Carpentier.
_Neuropteris Carpentieri_ Kidston. Kidston[303] has recently described
some fertile leaflets under this name from the Westphalian series of
South Staffordshire which he identifies with French examples referred
by Carpentier[304] to _Potoniea adiantiformis_ Zeill. The fertile
pinnules are thick and sub-cyclopteroid in form; the upper surface
bears densely packed, narrow and long, microsporangia, 4 × 0·5 mm.,
containing more or less spherical microspores 45–60μ in diameter;
the ventral face of the lamina on the removal of the spores shows
several strong veins. With these are associated sterile pinnules of
the Neuropteroid type, and examples are described intermediate between
the sterile and fertile leaflets. Kidston believes the specimens to be
microsporophylls of some species of _Neuropteris_, but as the material
does not suffice for identification with any known species a new name
is proposed. It is pointed out that in some states of preservation
the leaflets resemble Goeppert’s Permian species _Dictyothalamus
Schrollianus_[305].
_Alethopteris. Linopteris._
No specimens of _Alethopteris_ fronds have so far been described that
afford any information as to the nature of the microsporangia, and we
have no means of knowing whether they were borne on naked pedicels
as in _Neuropteris heterophylla_, or on modified pinnules as in _N.
gigantea_.
Zeiller in 1888[306] described some fertile pinnules of _Dictyopteris
Schützii_ Roem. from Commentry bearing two rows of long sporangia: he
subsequently transferred this species to the genus _Linopteris_[307]
and expressed the opinion that the sporangia occur singly and not
in groups as he originally believed. Zeiller compares the fertile
pinnules with the type _Crossotheca_. Bertrand[308], as the result
of examining similar specimens, has suggested that the fringe of
pendulous bodies regarded by Zeiller as sporangia may be tooth-like
lobes of modified pinnules which served to protect microsporangia
borne on the lower surface of the lamina. The nature of the
impressions is not clear, though there is little doubt that they are
microsporophylls. The fertile pinnae of _Linopteris obliqua_ (Bunb.)
described by Carpentier[309] and Bertrand[310] closely resemble the
microspore-bearing organs which have been referred to _Neuropteris
gigantea_; they have the characters of _Potoniea_ and consist of oval
laminae similar to the sterile pinnules but about half their size: the
lamina was attached excentrically to a slender stalk (fig. 421, C, E)
and traversed by numerous occasionally anastomosing veins. No actual
microsporangia have been discovered in organic connexion with the
lamina.
_b. Megasporangia._
_Neuropteris._
Kidston’s discovery of undoubted seeds attached to pinnae of
_Neuropteris_[311] marked an important step in our more exact
knowledge of the morphology of Medullosan sporophylls. Specimens from
the ironstone balls (Coal Measures) of Coseley near Dudley showed
seeds attached to portions of pinnae bearing pinnules of _Neuropteris
heterophylla_. The seeds are approximately 3 cm. long and from 1·10
to 1·40 cm. broad; oblong and gradually tapering from the middle to a
slightly curved and obtuse apical snout (fig. 422). The outer surface
shows numerous longitudinal ribs which no doubt represent hypodermal
fibres. The preservation of the seeds, which appear to be circular in
section, is not such as to render possible a description of structural
features. In their asymmetrical form the seeds agree with the genus
_Platyspermum_ as recently defined by Arber, but Kidston’s specimens
are in all probability radiospermic. Kidston compares the _Neuropteris_
seeds with _Rhabdocarpus tunicatus_ as figured from the Commentry
coalfield[312] and with specimens from Gard named by Grand’Eury _R.
subtunicatus_[313].
[Illustration: Fig. 422. _Neuropterocarpus Kidstoni_ (Arber). (After
Kidston; × 3.)]
Additional proof of the occurrence of seeds on _Neuropteris_ fronds is
furnished by examples from the Coal Measures of Holland described by
Kidston and Jongmans[314]: these seeds are of the same general type as
those from Coseley but nearly twice as large, and they were borne at
the tips of a dichotomously branched pedicel of _Neuropteris obliqua_.
Grand’Eury in 1904[315] recorded the association of radiospermic
seeds with _Neuropteris_ fronds though no case of actual attachment
was found. It is, however, noteworthy that he speaks of the frequent
association with _Neuropteris_ of seeds characterised by six or
rarely twelve longitudinal keels, a feature recalling the sclerotesta
of _Trigonocarpus_ and allied seeds. Until petrified specimens are
available it is impossible to refer the seeds of _Neuropteris_ to a
generic type founded on structural features: the seeds described by
Kidston are, as he says, very similar in external characters to species
assigned to _Rhabdocarpus_, and there can be little doubt as to the
generic identity of the _Neuropteris_ seeds and some of the impressions
referred to _Rhabdocarpus_ which are characterised by a similarity in
form, an apical snout that gives an asymmetrical appearance to the
specimens and the presence of numerous longitudinal striations[316].
It is, however, by no means certain that these seeds possessed the
morphological features of _Rhabdocarpus_ as described by Brongniart in
petrified examples from St Étienne[317].
The seeds of _Neuropteris_ may, as Kidston suggests, agree anatomically
more closely with _Pachytesta_[318], a type that Grand’Eury associates
with _Alethopteris_ fronds. With a view to avoid the danger of
incorrectly identifying petrified specimens and impressions that
cannot be proved to belong to the same generic type, I have suggested
the restriction of the name _Rhabdocarpus_[319] to seeds that do
not furnish evidence as to internal structure, and the employment
of the designation _Rhabdospermum_ for seeds that conform to those
described by Brongniart as _Rhabdocarpus_. The seeds of _Neuropteris_
may be of the _Rhabdospermum_ type or they may agree anatomically more
closely with _Trigonocarpus_ or _Pachytesta_; they are members of
either the Trigonocarpales or the Cardiocarpales, probably the former
group. Dr P. Bertrand[320] assigns to _Neuropteris gigantea_ some
seeds of the _Hexapterospermum_ (= _Hexagonocarpus_[321]) type which
occur in association with cupule-like organs. These supposed cupules
resemble the _Potoniea_ leaflets with microsporangia also referred
to the same species of _Neuropteris_; they are characterised by a
laciniate edge and may be compared with the Indian fossil described
by Zeiller as _Ottokaria bengalensis_[322] (fig. 433). Dr Arber[323]
and Dr P. Bertrand[324] have independently proposed the generic name
_Neurospermum_ for the seeds of _Neuropteris heterophylla_ and _N.
obliqua_ in preference to _Rhabdocarpus_: the former author speaks
of the seeds of _N. heterophylla_ as _Neurospermum Kidstoni_. The
generic term _Neuropterocarpus_ used by Grand’Eury in 1904[325],
though not defined by him, has priority and avoids the adoption of a
new designation for seeds attached to _Neuropteris_ fronds. In his
definition of _Neurospermum_ Arber makes no reference to the obliquity
of the apical snout that is clearly shown in fig. 422. There is no
evidence that _Neuropterocarpus_ possessed a cupular investment
comparable with that of _Lagenostoma_. Additional instances of the
association of seeds with _Neuropteris_ fronds are recorded by Renier
from the Belgian Coal Measures, also by Bertrand and Chodat from
France: Renier found seeds associated with _N. Schlehani_ Stur and with
the same species of frond Bertrand found impressions of oval ribbed
seeds. Prof. Chodat[326] has figured some fragments of _Neuropteris_
pinnules referred to _N. auriculata_ Brongn. from the Stephanian
of France which show small seed-like bodies apparently in organic
connexion with the lamina; but the specimens are too imperfect to
afford any satisfactory evidence as to the nature of the reproductive
organs.
Lotsy[327] has expressed the opinion that the bodies attached to
_Neuropteris_ pinnae described by Kidston and other authors as seeds
may possibly be vegetative buds, but if this were the case one would
expect to find some evidence of the bud-nature in some at least of the
specimens that have already been found.
It would seem that the microsporophylls of _Neuropteris_ were
constructed on different plans, some being of the type described by
Zeiller and other observers as _Potoniea_, while others bore sporangia
on pinnae without any accompanying laminae; but our knowledge of
the latter form represented by Kidston’s specimen of _Neuropteris
heterophylla_ (fig. 421, D) is very incomplete. On the other hand the
seeds appear to have been characterised by features suggesting a close
affinity to _Trigonocarpus_ and pointing to membership of the same
family.
_Alethopteris._
Although no specimens have been discovered showing actual connexion
between fronds and seeds, it is practically certain that _Alethopteris_
leaves, or at least some species of the genus, bore seeds of the
_Trigonocarpus_ type. The association of _Trigonocarpus Parkinsoni_
with _Alethopteris lonchitica_ is too frequent to be fortuitous and
there is further evidence afforded by certain anatomical resemblances.
In France other species of _Alethopteris_, _e.g._ _Alethopteris Serlii_
and _A. Grandini_, occur in association with _Pachytesta_[328], a large
seed similar to _Trigonocarpus_, and _Trigonocarpus_ is found in the
Pas-de-Calais coal-field with _Alethopteris Serlii_.
=TRIGONOCARPUS.= Brongniart.
The generic name _Trigonocarpum_ was instituted by Brongniart in
1828[329] for ovoid longitudinally ribbed ‘fruits’ from Upper
Carboniferous strata, the type-species being named _T. Parkinsoni_. The
generic name is often altered to _Trigonocarpon_: Williamson[330], who
adopted this form, states that Brongniart substituted _Trigonocarpon_
for _Trigonocarpum_ in his _Tableau_[331], but in that work the
original termination is used, the form _Trigonocarpon_, probably the
result of a slip, appearing only in the index. In his later work on
seeds Brongniart adopted the name _Trigonocarpus_, and in recent years
this has been widely employed. Among other species named by Brongniart
are two previously referred by Sternberg to _Palmacites_. Several
examples of Brongniart’s genus were described by Lindley and Hutton,
and in their description of _T. Noeggerathii_ the statement is made
that a fractured specimen demonstrated that ‘the fossil in its ordinary
state is an interior part divested of fleshy covering’[332]; this
suspicion of the true nature of the nut-like fossils was afterwards
proved correct by the investigations of Hooker and Binney[333] and by
the later work of Williamson. The specimens on which the genus was
founded are casts of seed-cavities and it is in this state that the
seeds are usually preserved, often in large numbers, in the sandstones
of the Coal Measures, as in the block shown in fig. 423 from the famous
quarry at Peel near Bolton, Lancashire. Another type of preservation is
represented by the seeds figured by Lindley and Hutton as _Carpolithes
alata_[334], but the generic identity of the two states was not
recognised until the discovery of petrified material afforded the clue.
Figs. 424, 1, 425 illustrate the appearance of _Trigonocarpus_ when
preserved as a carbonised impression showing a thick fleshy envelope
enclosing an oval kernel with a hard wall prolonged upwards as a longer
or shorter micropyle. Casts of the seed-cavity are represented in figs.
423; 424, 2, 3. The surface of these casts occasionally shows one or
more short cylindrical projections which are probably extensions of the
sand or mud into holes formed in the testa by boring insects. The view
that _Trigonocarpus_ seeds are ‘obviously Palm fruits’ was not accepted
by Hooker and Binney who inclined to regard them as the seeds of
Conifers and compared them especially with the similar nuts of _Ginkgo_
seeds (_cf._ fig. 631, C). It was Mr Wild[335] who was first struck
by the association of _Trigonocarpus_ and the petioles of _Medullosa_
(_Myeloxylon_) and by some resemblances in structure between the testa
and the hypoderm of the petioles; though, as Scott and Maslen[336]
point out, the agreement is not so close as Wild believed, his view of
a possible connexion between the reproductive and vegetative organs
has been confirmed. Williamson extended our knowledge of the genus by
his account of _Trigonocarpus olivaeformis_ Lind. and Hutt., a form
that is specifically identical with _T. Parkinsoni_ Brongn. This author
also drew attention to the close resemblance between Brongniart’s three
genera _Trigonocarpus_, _Hexapterospermum_, _Tripterospermum_ and
expressed doubts as to the possibility of founding specific differences
on casts of the _Trigonocarpus_ type without the evidence of anatomy.
Our knowledge of the structure of _Trigonocarpus_ has in recent years
been considerably extended by the researches of Oliver, Scott and
Maslen, and Salisbury.
[Illustration: Fig. 423. Casts of the seed-cavity of _Trigonocarpus
Parkinsoni_.
(Manchester Museum. ½ nat. size.)]
_Trigonocarpus Parkinsoni_[337] Brongniart.
The seeds of this species like all examples of the genus are
radiospermic, that is radially symmetrical in contrast to the flattened
or platyspermic seeds. The complete seed is elongate oval in form when
preserved as an impression (fig. 425, A) and reaches a length of 4–5
cm.: the casts of the seed-cavity are ovoid and provided with three
prominent ridges (fig. 424, 2, 3). The testa forms a thick covering
differentiated into three regions, an outer flesh or sarcotesta,
a sclerous shell or sclerotesta, and an inner flesh. Transverse
sections show that the sclerotesta has three sharp longitudinal keels
with corresponding furrows on the inner face, and between each pair
of main ribs are 2–3 less prominent ridges, usually 12 in all (fig.
426). The sarcotesta consists of thin-walled parenchyma passing
externally into a more lacunar tissue with a palisade-like hypoderm:
the sclerotesta consists of thick cells which interlace and form an
efficient protective shell. Both the sarcotesta and sclerotesta are
continued into the apical region as the wall of the long micropyle,
the sarcotesta being prolonged beyond the sclerotesta at the apex of
the integument[338]. The micropyle is triangular in section and may
exceed in length the whole seed (figs. 425; 426, A). Its form as seen
in transverse section (fig. 426, B) suggests the presence of wings:
this appearance may be deceptive and due to pressure or, more probably,
it represents an original feature. The seed-body, that is the portion
enclosed by the integument, consists of the nucellus, represented by a
few crushed layers of cells, bounded by a well-defined epidermis; the
nucellus is separated from the integument from the base of the seed
upwards, an important feature in which this and some other Palaeozoic
seeds differ from _Lagenostoma_ and the seeds of recent Cycads which
are characterised by an integument adnate to the nucellus up to
the level of the shoulder; the seeds of the Conifer _Phyllocladus_
afford an example of separation of integument and nucellus as in
_Trigonocarpus_. The innermost layer of the nucellus consists mainly
of tracheal tissue investing the large megaspore (fig. 426, A, C,
_m_) which is preserved as a contracted membrane detached from the
nucellus after the death of the seed. At the summit of the nucellus is
a relatively small pollen-chamber (fig. 426, A, _Pc_) like a broad and
low cupola bearing a terminal beak which extended some distance into
the micropylar tube. No microspores have been found in this species,
but Oliver[339] records the occurrence of multicellular microspores in
_Trigonocarpus pusillus_. The pedicel of the seed had a central strand
of sclerous tissue penetrated by a concentric vascular bundle which
gives off six strands to supply the sarcotesta (fig. 426, C, _v_) and
then passes into the nucellus where it forms a tracheal sheath (fig.
426, A, _nt_) surrounding the lower part of the megaspore and at a
higher level breaks up into anastomosing strands of tracheids which
reach up to the plane of insertion of the pollen-chamber.
[Illustration: Fig. 424. _Trigonocarpus._ 1. Section of imperfect
seed showing a micropyle; _b_, sclerotesta; _c_, cast of seed-cavity;
2, 3, apical and basal view of seed-cast. (Approximately nat. size.) M.
S.]
[Illustration: Fig. 425. _Trigonocarpus Parkinsoni._
A. Impression showing the nucule and sarcotesta. (= _Carpolithes
alata_ Lind. and Hutt.)
B. Specimen with long micropyle. (A, nat. size; from the Lower Coal
Measures of Kilmarnock; B, nat. size; Middle C. M. of Yorkshire.
Kidston Coll., 1579 and 1062.)]
[Illustration: Fig. 426. _Trigonocarpus Parkinsoni_. A, longitudinal
section; _Sa_, _Sc_, _if_, sarcotesta, sclerotesta, inner flesh; _mi_,
micropyle; _Pc_, pollen-chamber; _v_, vascular bundles; _m_, megaspore
and prothallus; _t_, tracheal disc; _nt_, tracheids in the nucellus.
B, transverse section of the upper region showing the sarcotesta,
sclerotesta (black) and the micropyle. C, transverse section of _T.
Parkinsoni_. D, transverse section of _Trigonocarpus shorensis_. (A, C,
after Scott; B, after Wild; D, after Salisbury.)]
A second species described by Scott and Maslen as _Trigonocarpus
Oliveri_ has been further investigated by Salisbury who finds
that it is an 8-angled seed which cannot be retained in the genus
_Trigonocarpus_: its systematic position ‘must for the present remain
uncertain[340].’ Dr Arber has recently described a new species of
_Trigonocarpus_, _T. Moyseyi_[341], from the Nottingham Coal-field
(Middle Coal Measures), similar to _T. Parkinsoni_ but much broader
in proportion to its length: this species is founded on an impression
without structure.
The species _Trigonocarpus Dawesi_ Lind. and Hutt.[342], from the
Middle Coal Measures of Lancashire, was founded on casts differing
in their large dimensions from those of _T. Parkinsoni_: specimens
referred to this species were described by Fiedler[343] from Saxony
in 1857 and Lesquereux[344] figures similar casts from the Upper
Carboniferous and Permian rocks of North America.
_Trigonocarpus shorensis_ Salisbury.
This species, founded on specimens from the Lower Coal Measures of
Shore, Lancashire[345], may exceed 4 cm. in length and has a breadth
of 2·5 cm. In general plan it agrees with _T. Parkinsoni_ but there
are certain well-marked differences: the micropyle is much shorter;
the thick sarcotesta, attaining a breadth of 6 mm. at the base of the
micropyle, is characterised by the presence of six peripherally placed
vascular bundles (fig. 426, D, _v_) in contrast to the deeply embedded
bundles of _T. Parkinsoni_. Below the epidermis of the sarcotesta
is a hypoderm formed of radially disposed plates of sclerous tissue
similar to that of _Myeloxylon_ and different from the palisade-like
hypoderm of the type-species. Within the sarcotesta is a hard shell,
the sclerotesta, characterised by three prominent ribs extending from
base to apex and three shorter ribs which reach from the chalaza to
about a third of the length of the seed. The fact that the sarcotesta
and sclerotesta pass gradually into one another is a point in favour of
the view that the integument is a single structure. There appears to be
good evidence of the restriction of an inner flesh to the micropylar
region, whereas this tissue in _T. Parkinsoni_ was probably continuous
over the whole inner face of the sclerotesta. The sarcotesta is
lacunar in its outer part as in some other types of Palaeozoic seeds,
a feature probably connected with floating efficiency. _Trigonocarpus
shorensis_ occurs in association with _Myeloxylon_ petioles, and there
is a resemblance between the seed and the vegetative organs in the
structure of the hypoderm as also in the structure of the secretory
sacs which are particularly numerous in this species. Salisbury draws
attention to the close resemblance between the form of _T. shorensis_
and the seeds found in organic connexion with pinnae of _Neuropteris
obliqua_[346].
The species _T. corrugatus_ described by Renault[347] bears a close
resemblance to _T. shorensis_.
+Other Genera founded in part on Reproductive Organs which may belong
to the Medulloseae.+
=Codonotheca=, =Schützia=, =Whittleseya=, =Dolerophyllum=, =Ottokaria=,
=Strobilites=.
=CODONOTHECA.= Sellards.
_Codonotheca caduca_ Sellards. This genus was founded on some
spore-bearing bodies from the Coal Measures of Illinois[348]:
nothing is known as to the plant which bore them, but Sellards is
inclined to associate them with _Neuropteris decipiens_ Lesq.[349], a
species abundant in the same coal-field. Whatever may have been the
parent-plant it is probable, as the author of the genus believes, that
_Codonotheca_ is the microspore-bearing organ of a Pteridosperm. As
shown in fig. 427, 5, the form is that of a stalked cup consisting in
the basal portion of a stout axis, the peripheral tissue of which is
believed to have been fleshy, containing an axial rod of conducting
tissue running up to the floor of the cup, _c_, and then dividing into
six vascular strands, each of which forks into two branches. The upper
part is composed of six linear segments united basally to form the
sloping surface of the cup. On the inner face of each segment is a more
or less well-defined depression covered with large elliptical spores
·29–·31 mm. long by ·18–·19 mm. broad (fig. 427, 6, 8). The presence of
a median ridge (fig. 427, 8) indicates a bilateral origin. ‘There is
no grouping of the spores or other indication of the location of the
sporangia, which were doubtless more or less completely immersed in the
tissue, the dividing wall disappearing at maturity.’ The spores are
seen in fig. 427, 2, 3, on the inner face of the lobes. Some of the
specimens have a fairly long pedicel: in the example shown in fig. 427,
1, the fleshy part of the basal portion is not preserved, only the more
resistant vascular core. In a later account of these organs Sellards
speaks of several lying by the side of a central stalk to which he
thinks they were originally attached by slender pedicels. In view of
Dr Benson’s interpretation of the morphology of _Telangium_ it is
permissible to suggest that if a central sporangium in such a synangium
as that of _Codonotheca_ developed a megaspore and the peripheral
sporogenous lobes were sterilised, the result would be an arrangement
not unlike the apical region of the seed _Physostoma_, the tentacles
of which have been homologised with the canopy of _Lagenostoma_.
There are obvious difficulties in the way of this, perhaps strained,
comparison: the larger size of the spore-bearing linear segments of
_Codonotheca_ led Sellards to regard each as a synangium rather than
a single sporangium. But precise information as to the structure of
the American fossils is not as yet available. If the association of
_Codonotheca_ with _Neuropteris_ fronds has any significance it would
favour a reference of these organs to the Medulloseae. In the absence
of anatomical data it is impossible in some cases to distinguish
microspore-bearing organs of the _Codonotheca_ type from small seeds
enclosed in a lobed cupule or even seeds with a lobed integument:
a case in point is the New Brunswick species _Pterispermostrobus
bifurcatus_ Stopes[350].
[Illustration: Fig. 427. _Codonotheca caduca_. 1. The vascular tissue
preserved as a conical base which was originally surrounded by fleshy
tissue (_cf._ 5); I–III, VI, vascular bundles (× 2). 2, 3. Segments
with spores; _c_, floor of cup (nat. size). 4. Vascular tissue as a
cone in the middle of the fleshy base (nat. size). 5. Plan of the whole
organ opened out flat (nat. size). 6. Spores (× 28). 8. A single spore
showing median slit (× 84). (After Sellards.)]
A Spitzbergen, Culm, fossil recently described by Nathorst[351] as
_Codonotheca (?) pusilla_ is briefly referred to under the genus
_Pterispermostrobus_.
=SCHÜTZIA.= Geinitz.
This generic name was instituted by Geinitz[352] for some Permian
fossils obtained by Bergmeister Schütz and regarded by the author of
the genus as probably fertile branches of some Conifer. A more complete
account was published by Goeppert[353] in his ‘Permian Flora,’ where
the name _Anthodiopsis Beinertiana_ occurs on the Plates, printed
before the publication of Geinitz’s description, but in the text the
specimens are referred to _Schützia anomala_.
_Schützia anomala_ Geinitz.
The type-species, recorded from Bohemia and Silesia, is represented
by fertile shoots consisting of a thick main axis bearing apparently
two-ranked though probably spirally disposed short lateral branches,
each of which terminates in a receptacle with numerous crowded
linear-lanceolate bracts superficially resembling a partially expanded
inflorescence of a Composite. Goeppert believed that the branches
bore seeds and he refers to this species a number of detached,
longitudinally striated and bluntly terminated, seeds. The same author
describes other specimens from the same localities associated with
_Schützia anomala_, which he names _Dictyothalamus Schrollianus_[354]:
in habit these agree closely with _Schützia_ but the receptacles,
the reticulate appearance of which suggested the generic name
_Dictyothalamus_, bear a large number of small bodies regarded as
seeds. The preservation of the fossils is not such as to enable us to
determine their true nature but it is probable that _Schützia_ and
_Dictyothalamus_ are not generically distinct. In his description of
_Dictyothalamus_ Goeppert suggests that the two associated types may
be the male and female shoots of one plant, but he speaks of seeds in
both cases. Schimper[355], who unites _Dictyothalamus_ with _Schützia_,
regards the latter as female and the former as male.
_Schützia Bennieana_ Kidston.
This species, described by Kidston[356] from the Calciferous series of
Scotland, differs from _S. anomala_ in its much more slender axis and
in the relatively narrower and less globular clusters of bract-like
appendages. The principal axis bears three lateral branches with
terminal clusters of acute and narrow linear scale-leaves. No seeds
were found in association with the specimens.
_Schützia permiensis_ (Renault).
Renault founded this Permian species as _Antholithus permiensis_[357]
on a specimen from Lodève; it consists of an incomplete inflorescence
6·4 cm. long bearing four lateral branches with stalks 1·5 to 2 cm.
long terminated by clusters of small oval bracts 5 mm. long. Renault
compares the fossil with the recent Conifers _Glyptostrobus_ and
_Tsuga_, but it exhibits a much closer resemblance to _Schützia
anomala_.
The genus _Schützia_, originally described from Permian strata, is
recorded also from Westphalian strata in North Africa[358] as well
as from Lower Carboniferous rocks in Scotland. The data at present
available are insufficient to determine the morphological nature of the
fertile branches: the evidence adduced by Goeppert in support of the
occurrence of seeds is not convincing and the interpretation of the
bract-like appendages is still an open question; they may have formed
a cupular investment to seeds, but in the Scotch species the general
appearance rather suggests that they may be microspore-bearing organs
comparable with those of _Codonotheca_[359]. There are no adequate
grounds for supposing _Schützia_ to belong to the Coniferales, a view
advanced by some authors; it is much more likely to represent the
fertile shoots of a Pteridosperm.
=WHITTLESEYA=. Newberry.
The genus _Whittleseya_, referred by many authors to the _Ginkgoales_,
has no substantial claim to be regarded as allied to that group: its
position is still uncertain, but the recent discovery of fertile
specimens suggests the probability of a relationship to _Potoniea_ and
an identification of Whittleseya as another form of microsporophyll of
a Pteridosperm.
[Illustration: Fig. 428.
A, C. _Whittleseya elegans_. A, single leaflet, from Pennsylvania.
(After Lesquereux; ⅚ nat. size.) C, diagrammatic sketch of part
of a leaflet showing the teeth, the striated texture of the
carbonised layer, and the vein-like markings on a lower
surface. (After Thomas; enlarged.)
B. _Whittleseya brevifolia_. (After White; the smaller figure ⅚ nat.
size.)]
The generic name was given by Newberry[360] to some leaves, or possibly
leaflets, originally described by C. Whittlesey from the Coal Measures
of Ohio. Whittleseya is represented by species from several North
American localities[361] in Ohio, Pennsylvania, Arkansas, Nova Scotia,
and New Brunswick[362]; it occurs in Silesia and has recently been
found in the English Coal Measures[363]. The genus is confined to Upper
Carboniferous strata.
The leaves are fairly thick; the lamina is oblong, cuneate, broadly
triangular or linear, usually rounded and truncate (fig. 428, A,
C), generally dentate at the distal end, the proximal portion being
gradually or abruptly contracted and occasionally prolonged into a
short pedicel. The veins or ribs are parallel to the sides of the
lamina and except near the base unbranched.
_Whittleseya elegans_ Newberry.
The type-species, from North America and Europe, is characterised
by its shovel-like lamina from 3 to 6 cm. long closely resembling
in shape some lepidopterous scales; the surface is ribbed, each rib
corresponding to a tooth on the distal margin; on each of the parallel
ridges are 4–5 longitudinal lines indicating either veins or stereome
strands (fig. 428, A, C). The examination of preparations made by
Dr Kidston from a leaflet of this species enables me to add a few
facts with regard to the microspores. The spores, which cover almost
the whole surface of the lamina, show a tendency to a more or less
definite arrangement in longitudinal rows. Two types of cuticularised
membrane are represented among the associated fragments: in some
pieces of cuticle the cells are short and have straight walls while
in others the preservation is inferior and the cells appear to be
longer and narrower. One or both of these membranes probably belong
to the sporangia. The oval slit, which is a striking feature on
several of the spores (fig. 429), points to their bilateral nature
and dehiscence along the major axis. A comparison of these spores
with those obtained by Kidston from the English species _Whittleseya
fertilis_ reveals a very close agreement both in size and shape and
confirms the identification of the Staffordshire specimens as leaflets
of _Whittleseya_. The large size of the microspores and the gaping oval
aperture in some of them are features in which they agree closely with
the spores of _Dolerophyllum fertile_ described by Renault[364]. In
both cases the spores tend to be arranged in long groups and they are
practically identical in form and in the nature of the exine; those
of _Dolerophyllum_ are 280μ long while those of _W. fertilis_ reach
a length of 220μ. In some of the _Whittleseya_ spores the exine has
split as in the specimen shown in fig. 429, but in others there are two
curved lines along which dehiscence has begun, a character in which the
spores appear to be identical with those of _Dolerophyllum_ described
by Renault who speaks of dehiscence by means of an operculum. There
is, I venture to think, little doubt as to the very close affinity
of the two types. The systematic position of _Dolerophyllum_ is not
certainly established; if the generic identity of the leaves described
as _D. Berthieri_ Ren. and the petrified specimens named _D. fertile_
is assumed, it is a legitimate inference that the genus is founded on
fertile pinnules of a Pteridosperm with foliage of the _Neuropteris_
or _Cyclopteris_ form. It would seem probable that both _Whittleseya_
and _Dolerophyllum_ _fertile_ are microspore-bearing leaflets of
Pteridosperms, possibly of some Medullosan plants. The leaflets of
_Whittleseya_ agree in form fairly closely with those of _Potoniea
adiantiformis_ Zeill. described on a previous page[365] as the male
organs of a Pteridosperm.
[Illustration: Fig. 429. Microspores of _Whittleseya elegans_. A, a
group of spores; B, a single spore. (Preparations made from an American
specimen, No. 2314, in Dr Kidston’s Collection.)]
The specimens described by Lesquereux from Pennsylvania as _W.
integrifolia_ and _W. undulata_ are less satisfactory than _W.
elegans_. The Arkansas species _W. microphylla_[366], characterised
by the obcuneate form of the lamina, is said to occur not only as
detached leaflets but in loose bunches at the ends of slender axes,
a circumstance favourable to the suggestion, based on the recently
described English specimens, that the _Whittleseya_ leaves may
be fertile pinnules of a Pteridosperm frond. Among other species
attributed to Newberry’s genus is _W. brevifolia_ Wh. from Nova
Scotia[367] with much smaller broadly triangular leaves 7 mm. long
exclusive of the petiole and 8 mm. broad at the distal end (fig.
428, B). Dr Matthew[368] has also described a Canadian species _W.
concinna_ from New Brunswick in beds assigned by Dr Stopes[369] to the
Westphalian series.
_Whittleseya fertilis_ Kidston.
Since the discovery of _Whittleseya elegans_ in the Coal Measures
of Staffordshire recorded by Mr Thomas, Dr Kidston has published
an account of some specimens from the same district under the name
_Whittleseya (?) fertilis_[370]: these consist of smaller cuneate
scale-leaves or leaflets 1·4–2·4 cm. long and 8–9 mm. broad; the
lamina has a dentate upper margin and is longitudinally ribbed. The
scales occur in superposed pairs, closely fitting but not organically
connected, at least in the state in which they are preserved; each
pair forms a sporangium-like case enclosing numerous spores but the
actual sporangia or synangia have not been preserved. Kidston describes
the spores as 210–222μ in length, elliptical, and characterised in
many cases by an oval slit; they are practically identical with the
microspores of _W. elegans_.
=DOLEROPHYLLUM=. Saporta.
This name was proposed[371] primarily for a large ovoid petrified
bud composed of rolled Cyclopteroid leaves from Permian rocks in the
Ural Mountains, which had been previously described by more than one
writer under different names and regarded as a young shoot of a Palm
or other Monocotyledon. Eichwald[372], who published good drawings,
called the fossil _Noeggerathia Goepperti_. Saporta connected with this
species some leaf-impressions from the Permian of Bohemia described
by Goeppert[373] as _Noeggerathia cyclopteroides_: in his family
Dolerophylleae[374] the French author included other leaves which
are probably not closely related to the type-species, _Dolerophyllum
Goepperti_. The Dolerophylleae are spoken of by Saporta and Marion[375]
as Progymnosperms. Before the publication of Saporta’s note Grand’Eury
had instituted the genus _Doleropteris_[376] and the family
Doleropteroideae; in the former he included several forms of leaves
agreeing generally with Goeppert’s _Noeggerathia cyclopteroides_.
Zeiller[377] adopts Grand’Eury’s designation for the Russian fossil in
preference to _Dolerophyllum_, a choice justified by considerations of
priority; but the latter name is retained in this account as it was
assigned by Saporta to the specimen of greatest botanical interest,
namely _Dolerophyllum Goepperti_, and because it does not suggest
affinity to Ferns.
_Dolerophyllum Goepperti_ (Eichwald).
The type-species is from the Zechstein of Orenburg in the Urals and
no specimens having precisely the same structure have been found
elsewhere. Eichwald assigned it, with leaf-impressions of various
kinds, to the Noeggerathieae and named it _Noeggerathia Goepperti_: it
had previously been described by Kutorga[378] as _Aroides crassispatha_
and Unger[379] included it among the Palms as _Palaeospathe aroidea_.
The species has been described also by Saporta and Marion and by
Renault[380]. The following account is based on sections cut from a
specimen in the British Museum[381] which, though assigned on the label
(within a query) to France and named _Dolerophyllum Berthieri_, is
undoubtedly Eichwald’s species from East Russia.
[Illustration: Fig. 430. _Dolerophyllum Goepperti_. Bud in
surface-view, A; in longitudinal section, B, C; in transverse section,
D. (British Museum; A, ⅔ nat. size.)]
The specimen (fig. 430) is 9 cm. long and 4·2 cm. broad: at the
slightly contracted and broken base is a piece of immature axis (fig.
430, B, _a_) 12 mm. in diameter overtopped by a mass of closely packed
leaves encircling one another like the bulb-scales of an Onion (fig.
430 A, C)[382]. Most of the leaves included in the bud were attached
to the axis below the broken base. The curved, dichotomously branched,
veins are seen on some of the pieces of lamina on the surface of
the bud (fig. 430, A). The considerable breadth of the leaves is
demonstrated by the longitudinal and transverse sections. In fig. C
most of the laminae can be traced through the whole height of each
of the steep-sided arches: a few overlapping margins are seen in
fig. D. The veins are for the most part imperfectly preserved and
appear as clear spaces at regular intervals in the brown mesophyll.
The axis of the shoot consists of homogeneous parenchyma except near
the sloping sides where narrow dark bands (fig. 430, B, _a_) mark
the position of desmogen-strands of thin-walled elongated elements
representing an early stage in the development of vascular bundles
some of which have already produced spiral tracheids. Short secretory
cells accompany the immature conducting elements. The lamina slightly
exceeds 2 mm. in thickness in the broadest part: the mesophyll is
composed of large parenchymatous cells of elliptical or spherical
form often loosely attached owing to the well-developed system of
intercellular spaces. The lower epidermis, assuming that the outer
face of the rolled leaves is the morphologically lower surface, forms
a uniform layer of palisade cells characterised by their free conical
ends (fig. 431, A, B, _e_) which in some oblique sections appear as
sharply pointed papillae with almost filiform apices; but while the
cells were doubtless papillose like those of the epidermis of a velvety
petal, the pointed form is due in part to the greater distinctness of
the dark contents as compared with the lighter cell-walls. The upper
epidermis is much less distinct; it consists of smaller flattened
cells with occasional stomata. Renault[383] figures a specimen with
stomata in a better state of preservation. The vascular bundles are
rendered conspicuous by large secretory cells on the lower side, in
the larger veins in the form of an arc or irregular group (fig. 432,
A), but in the finer veins as single cells (fig. 431, A, B). These
sacs resemble the tannin cells accompanying the veins in a leaf of
_Ginkgo_ (_cf._ fig. 631, G). The xylem-elements are of two kinds,
(i) elongated spiral and scalariform conducting elements, forming a
vertical plate of a few rows in the larger veins (figs. 431, 432) or a
small compact group in the more slender veins (fig. 413, A, B); (ii)
much larger isodiametric cells with reticulate or spiral thickening
resembling the transfusion-tracheids of Conifers or, perhaps more
closely, similar elements in the leaves of _Lepidodendron_. These short
tracheids are especially abundant on the flanks of the conducting
tracheids (figs. 431, _t_; 432, A, _t_), but they sometimes form a
complete investment. In the obliquely cut vein reproduced in fig. 431,
D, the transfusion-tracheids are abundant: a few are enlarged in fig.
431, E. In the smaller veins (fig. 431, A, B) they are represented by
the larger elements, _t_, on the sides of the conducting strands. The
protoxylem lies close to the upper edge in the middle line (_px_, figs.
431, A; 432, A); it is difficult to determine its precise position,
but it would seem to be slightly internal, the bundle being not quite
endarch. No phloem was recognised in the British Museum specimen, but
it presumably occurred, if present, where the black patch is shown
in fig. 432, A. Renault describes some phloem in sections which he
examined.
[Illustration: Fig. 431. _Dolerophyllum Goepperti_. Transverse
sections of leaves. _e_, epidermis; _s_, secretory cells; _t_,
transfusion-tracheids; _px_, protoxylem. (British Museum.)]
The mesophyll next the upper surface is in most cases represented
by spaces between the veins which give a crenulated outline to the
parenchyma (fig. 430, C, D); in some places the spaces contain remains
of very loose and crowded cells suggesting the original presence of
very lacunar tissue or possibly of thin-walled storage-cells. The
confinement of stomata to what is assumed to be the upper surface may,
as Renault and others have suggested, indicate leaves which floated on
water, an inference opposed to the view that the gaps in the mesophyll
mark the position of water-tissue.
No specimens have been described which enable us to correlate with
certainty mature leaves or foliage-shoots with the petrified bud.
It is, however, not improbable that the impression from Mount Pelé
near Epinac named by Renault _Dolerophyllum Berthieri_[384] may be
correctly referred to the same genus. The type-specimen consists of
an axis, whether a rachis of a compound leaf or a shoot with simple
leaves cannot be determined, bearing partially overlapping more or less
orbicular leaves 18–20 cm. in diameter, with a _Cyclopteris_ venation.
Among other leaves of unknown affinity referred to the same genus
attention is drawn to _Dolerophyllum pseudopeltatum_ (Grand’Eury)[385]
with an orbicular lamina reaching in some specimens 22 × 19 cm.
Specimens of _Dolerophyllum pseudopeltatum_ are figured by Renault
from the Commentry coal-field[386], some of which reach a diameter
of 12 cm. The only British specimen of a leaflet of this type which
I have seen is one in Dr Kidston’s collection from the Stephanian
series, Glamorganshire. It is probable that some at least of the
impressions assigned to _Dolerophyllum_ or _Doleropteris_ would be more
appropriately included in _Cyclopteris_ or _Cardiopteris_ and may have
been borne on the axis of large Pteridosperm fronds. Grand’Eury[387]
has also called attention to the difficulty of distinguishing the
larger _Cyclopteris_ leaflets from _Dolerophyllum_. Some of the
Cyclopteroid leaflets figured by Roehl[388] on _Neuropteris_ fronds
differ but slightly from those of _D. pseudopeltatum_. The shoot
showing large leaf-scars figured by Saporta and Marion[389] as probably
the axis of a _Dolerophyllum_ may well be a piece of _Cordaites_.
[Illustration: Fig. 432. A. _Dolerophyllum Goepperti_, section of
vein. B. _Dolerophyllum Berthieri_; _s_, microspores. C. _Dolerophyllum
fertile_. D. _Dolerophyllum fertile_, microspores. (After Renault.)]
_Microsporophylls assigned to_ Dolerophyllum.
Certain problematical fossils found in association with the sterile
leaves of _Dolerophyllum Berthieri_ have been described by Renault as
the male organs of that species. These are elliptical discs, 6 × 5 cm.,
with an excentrically placed stalk: embedded in a carbonised lamina are
numerous rows of elliptical bodies, 410μ × 280μ, characterised by two
curved longitudinal grooves on the surface and regarded by Renault as
pollen-grains. The chains of these microspores radiate outwards from
the neighbourhood of the stalk and cover most of the surface of the
disc (fig. 432, B). Some silicified pieces of similar spore-bearing
discs from Grand’ Croix named _Dolerophyllum fertile_[390] afford
additional information as to these remarkable reproductive organs.
The earlier account of this species by Renault is confirmed by
Solms-Laubach[391] who examined the original sections. The peltate
fleshy discs preserved as incomplete specimens consist of lacunar
parenchyma 15–18 mm. thick traversed at right angles to the surface
by numerous loculi (fig. 432, C), circular or oval in transverse
section, containing large numbers of microspores, _s_, similar in size
and form to those on the carbonised discs of the Mt Pelé specimen.
Vascular strands occur between and parallel to the spore-chambers.
The spores contain 8–10 cells (fig. 432, D) and Renault believes that
dehiscence of the exine occurred along the two deep grooves which mark
the limits of an operculum. He emphasises the peculiar structure of
the microspores by speaking of them as prepollinia: in size and in
the presence of internal cells (? male prothallus) they resemble the
spores found in the pollen-chamber of a seed described by Renault as
_Aetheotesta elliptica_[392] which he thinks may belong to a member of
the Dolerophylleae. It has also been suggested that _Codonospermum_ may
be a seed of _Dolerophyllum_[393]. An unconvincing specimen described
by Saporta and Marion[394] as a seed-bearing bract is regarded by them
as referable to _Dolerophyllum_, but the evidence for any connexion is
far from satisfactory.
There is nothing definite to be said with regard to the affinity of
_Dolerophyllum Goepperti_ or the microsporophylls represented by _D.
fertile_ and the specimens associated with _D. Berthieri_. Renault
considers that both sterile and fertile specimens belong to the same
genus, which he assigns to a position between Pteridophytes and
Cycads. As Solms-Laubach says, the evidence supplied by the structure
of the veins of _D. Goepperti_ in favour of a cycadean alliance is
not convincing. The type of vernation is unlike that of any known
Cycad or indeed of any Gymnosperm: the large size of the leaves is
another though weaker objection to this comparison, as the pinnae of
_Bowenia_ (fig. 391) and especially those of some species of _Zamia_
(fig. 388), are of equal or larger dimensions. If, as seems probable,
the xylem-strands are mesarch that is a point of contact with recent
Cycads, but the bundle as a whole bears but a remote resemblance to
that of a cycadean leaf and is much more like the veins of _Ginkgo_.
The bud shown in fig. 430, A, is probably a young shoot and not merely
a large compound leaf. If it were an unexpanded frond of _Neuropteris_
bearing _Cyclopteris_ pinnules we should expect to find indications
of scattered desmogen-strands such as would occur in the _Myeloxylon_
type of rachis. The resemblance to most forms of _Cordaites_ is by no
means close though a few leaves referred to that genus (_e.g._ _C.
circularis_, fig. 468, B) are similar to those of _Dolerophyllum_[395].
The male organs are unlike those of any other plant: they may be
described as sporophylls with microsporangia or perhaps synangia
embedded in the mesophyll and containing microspores similar to those
of some Pteridosperms or true Gymnosperms. Attention has been called to
the close resemblance of the spores shown in fig. 432, C, D to those
recently discovered by Kidston and referred to the genus _Whittleseya_
(fig. 429), and it is very probable that the striking similarity is an
index of affinity.
=Ottokaria.= Zeiller.
_Ottokaria bengalensis_ Zeiller. A specimen of doubtful affinity
from the Lower Gondwana (Karharbari beds) of Passerabhia, India, was
originally described by Zeiller[396] as _Feistmantelia bengalensis_,
but in a postscript he substituted the name _Ottokaria_ on the ground
that _Feistmantelia_ had previously been employed by Lester Ward.
Fig. 433 is drawn from the original specimen: it consists of a stalk
attached in a slightly excentric position to an almost orbicular
lamina, 2·5 cm. in diameter, with subacute marginal teeth and traversed
by numerous radially disposed striations. Zeiller compares the fossil
with _Whittleseya elegans_ and _Rhipidopsis ginkgoides_ and assigns
it with some hesitation to the Salisburieae. An examination of the
type-specimen led me to form the opinion that it may be a cupular organ
of a Pteridosperm that enclosed a seed. The lamina is slightly concave
and has the form of a shallow cup; moreover the surface-features
resemble those of a bract rather than the regularly veined lamina of
a foliage-leaf. The specimen bears a very close resemblance to one
figured by Bertrand[397] as the cupule of _Hexapterospermum modestae_
which he connects with fronds of _Neuropteris gigantea_.
[Illustration: Fig. 433. _Ottokaria bengalensis._ (Nat. size; drawn
from the type-specimen.)]
_Ottokaria_ occurs in association with fronds of _Glossopteris indica_
and with the large seeds described by Zeiller[398] as _Cardiocarpus
indicus_. I have lately obtained some evidence in favour of
assigning Feistmantel’s seeds _Carpolithes Milleri_[399] to the genus
_Glossopteris_: among several specimens from the Lower Gondwana rocks
of India I found an example showing a seed partially covered by a
scale-leaf in its natural position which appears to be identical with
scale-leaves of _Glossopteris_. It may be that the specimen represented
in fig. 433 belongs to _Cardiocarpus indicus_, though this is a mere
guess: my belief is that _Ottokaria_ is a cupular organ that enclosed
the base of a seed borne on a Pteridosperm. There is little doubt that
as additional data are obtained it will be found that Pteridosperms
played no inconsiderable part in the vegetation of Gondwana Land.
[Illustration: Fig. 434. _Strobilites Milleryensis._ (Natural size;
after Renault.)]
=Strobilites.= Schimper and Mougeot.
_Strobilites Milleryensis_ (Renault).
This species, from the Permian of France, was placed by Renault in
_Cycadospadix_[400], but having regard to the fact that it differs
essentially in habit from Mesozoic examples of that genus the
provisional name _Strobilites_[401] is suggested. The type-specimens
are long and narrow spikes or loose strobili, 8–16 cm. long and 2–2·6
cm. broad; a stout axis bears spirally disposed bracts 8–10 mm. long
attached by a slender decurrent pedicel expanded distally into a
fan-shaped laciniate lamina with a convex upper face, and there are
said to be two seeds attached to the sides of each pedicel (fig. 434).
The oval seeds appear to be platyspermic and resemble _Samaropsis
fluitans_ Daws. Two of the strobili figured by Renault are attached
at right angles to a second axis, a habit suggesting comparison with
that of a large compound frond. Renault is inclined to regard these
fertile shoots as cycadean and suggests a possible connexion with the
Permian stems _Ptychoxylon_ or _Poroxylon_, both of which are known
to have produced fairly numerous branches. In habit the spikes are
similar to some of the longer examples of _Cordaianthus_, but their
preservation is not sufficiently good to afford accurate information as
to the relation of seed to sporophyll. _Strobilites Milleryensis_ is,
perhaps, more likely to be the fertile branch of a compound frond of a
Pteridosperm, and it is significant that the seeds have been found in
association with _Callipteris_ leaves.
=COLPOXYLON=. Brongniart.
_Colpoxylon aeduense_ Brongniart. The genus was founded by
Brongniart[402] on a piece of stem 15 cm. in diameter from the
Permian of the Autun district and regarded by him as a distinct
type, with certain resemblances to recent Cycads. A thick section in
the British Museum, 13 cm. in diameter (fig. 435, A), illustrates
the main anatomical features described by Renault[403], to whom our
knowledge of the genus is chiefly due. There are two large steles of
irregular outline closely resembling those of _Medullosa Leuckarti_
(_cf._ fig. 416, H); each consists of a band of secondary xylem with
broad medullary rays and a narrow zone of phloem enclosing a central
region composed of parenchyma, in which strands of primary tracheids,
both reticulate and spiral, pursue a more or less horizontal course,
associated with a few small groups of vertical xylem-strands at the
inner edge of the secondary wood. The manoxylic nature of the wood is
clearly shown in fig. 436; the continuous ink-line marks the position
of the cambium and the dots show the internal protoxylem. Homogeneous
parenchyma surrounds the steles and beyond this is crushed tissue
containing large secretory canals and nests of stereome fibres either
as separate groups or in contact with the canals (fig. 435, C). In the
same peripheral tissue occur scattered collateral vascular bundles
(fig. 435, D) identical with those of _Myeloxylon_. The outer cortex
of the stem is marked off from the more homogeneous inner region by
a fairly distinct line where there is some indication of periderm.
The anatomical features are clearly shown in fig. 436, a photograph
from a section in Dr Kidston’s collection. At _a_ is an imperfectly
preserved vascular bundle with a crescentic group of secondary xylem
which is probably a leaf-trace that has just emerged from the secondary
cylinder. Renault speaks of these more or less circular strands as
possibly connected with reproductive shoots, but it is more probable
that they are homologous with the strands in the pericycle and inner
cortex of _Medullosa_ and represent leaf-traces before division into
smaller collateral strands. Renault describes the stem as possessing
seven vascular cylinders in the apical region and suggests branching
of the main axis as the cause of the increase in number: there is,
however, no evidence to support such correlation. The two steles seen
in fig. 435, A, become merged at a lower level into a single stele of
sinuous form (fig. 435, B).
[Illustration: Fig. 435. _Colpoxylon aeduense_. A. Diagram of a
transverse section of a specimen in the British Museum. (V. 9393.
½ nat. size.) B. Stele; much reduced from Renault’s figure. C, D.
Secretory canal with fibres and collateral vascular bundle (Kidston
Coll., 1946).]
[Illustration: Fig. 436. _Colpoxylon aeduense_. Transverse section
of half of the stem; _a_, stele of branch. Slightly enlarged. (Kidston
Coll., 1946.)]
Beyond the facts furnished by the leaf-trace bundles in the outer
cortex and the occurrence of two large scars about 5 cm. in breadth on
a stem figured by Renault, we have no positive information as to the
form of the leaves or the structure of the reproductive organs. There
is little doubt that the fronds were large and compound like those of
most species of _Medullosa_. There is, however, some slight evidence
that _Alethopteris Grandini_ Brongn. and seeds of the _Pachytesta_ type
(fig. 497) were borne on _Colpoxylon_ stems; this rests solely on the
association in the Loire coal-basin[404] of _Alethopteris_ fronds with
stems presenting structural resemblances to _Colpoxylon aeduense_.
The striking resemblance between _Colpoxylon_ and _Medullosa
Leuckarti_ has led certain authors[405] to propose the substitution of
_Medullosa_ for _Colpoxylon_. The resemblances though close are hardly
sufficient to warrant this course. In _Colpoxylon_ the stelar system
is simpler; there is no central region with star- or plate-rings as
in _Medullosa Leuckarti_ but, as in _Medullosa anglica_, the vascular
tissue consists only of large steles without a medullary system.
_Colpoxylon_ differs from _M. anglica_ in the reduction in some parts
of the stem of the vascular system to a single stele and, moreover, the
primary portion of the steles is much more parenchymatous in structure
and contains more irregularly anastomosing tracheal strands than is the
case in _M. anglica_.
The alteration in the pattern formed by the vascular system at
different levels in some Medullosan stems, especially in _Colpoxylon_,
may be compared with the varying disposition of the vascular strands
in the thick dorsiventral rhizomes of _Polypodium heracleum_ Kunz. and
_P. quercifolium_ L. In the rhizome of _P. heracleum_ there are two
vascular systems, an outer, cortical, system in the form of a hollow
cylinder composed of a lattice-work with polygonal meshes from which
branches are given off to the roots, and a more complex medullary
system that is concerned with the emission of leaf-traces. As shown
by a series of drawings reproduced in an account by Klein[406] of the
anatomy of these species of _Polypodium_, the inner system of steles
consists of two cylinders connected towards the upper surface of the
stem by a rounded arch of vascular strands; nearer the leaf-base the
two cylinders meet and eventually a larger cylinder is produced partly
from the upper halves of the two cylinders of the previous section
and in part from the connecting arch: the remains of the two smaller
cylinders become connected with the outer vascular system. These and
other changes suggest comparison with _Colpoxylon_ as also with the
stelar changes in the stem of _Ptychoxylon_. The comparison cannot
be carried beyond the grosser features and is chiefly interesting as
affording a further illustration of a similarity in plan between some
recent Ferns and extinct Pteridosperms and other Palaeozoic genera.
[Illustration: Fig. 437. _Rhexoxylon africanum_. Transverse section
of stem showing peripheral steles and central (_c_) stele. (After
Bancroft; × 2.)]
=RHEXOXYLON=. Bancroft.
_Rhexoxylon africanum_ Bancroft. The genus _Rhexoxylon_ was instituted
for a new type of stem represented by a single incomplete specimen
from the Karroo series of South Africa: its precise geological
horizon is not known but it may be referred provisionally to the
lower or Palaeozoic portion of the series. Though our knowledge of
the morphological features of the type-species is far from complete
owing in part to the method of preservation of the specimen and in
part to the destruction of the outer portion of the vascular tissue
and the whole of the cortex, Miss Bancroft’s careful description[407]
demonstrates the existence of characters which justify the employment
of a new generic name. _Rhexoxylon_ is more nearly related to the
Medulloseae than to any other group and is particularly interesting as
the first recorded example of this group from the Southern Hemisphere.
Fig. 437 shows a transverse section (7 × 5 cm.) of the stem. The
ground-tissue consists of fairly large-celled parenchyma with sclerous
nests and a few bands of periderm. At the periphery of the stem are
radially disposed groups of vascular tissue varying in size and to
some extent in shape. Unfortunately the stem is incomplete and it is
impossible to say how much vascular or other tissue originally existed
beyond the present corroded edge. The vascular groups, or steles as
they may legitimately be called, follow a vertical course through
the length of the block (6·5 cm.) and afford only slight evidence of
branching or anastomosing. A close examination of the steles shows that
they consist of portions of two series, an inner and outer set; there
is also a curved vascular band in the central ground-tissue (fig. 437,
_c_) and some isolated and scattered patches of vascular elements.
Each stele of the inner series is made up of two parts, an outer
smaller and normally orientated group of secondary xylem and a larger
inversely orientated inner group of identical structure. A single
stele of the inner series is shown in fig. 438, B, C; the larger inner
portion consists of slightly divergent rows of tracheids and uniseriate
medullary rays and is separated from the smaller portion by a narrow
space, _a_, occupied by crushed tissue which may correspond to the
‘partial pith’ or primary xylem of a Medullosan stele. The two groups
of xylem are no doubt the products of two cambium arcs, the protoxylem
of each group being situated on the flat inner face. The cambium and
phloem are represented only by crushed brown cells on the curved outer
edge of the xylem. The separate individuality of the two portions of
each stele is indicated not only by the presence of the ‘partial pith’
but by the discontinuity of the tissue at the ends of the narrow space.
The tracheids seen at _b_, fig. C, are in oblique longitudinal section
and are probably being detached to form a leaf-trace. This type of
stele may be compared with the steles of _Medullosa Solmsi_ (fig.
416, L) but those of _Rhexoxylon_ differ in the lack of continuity of
the secondary xylem round the narrow band of crushed primary xylem.
The other steles of the inner ring exhibit the same dual nature though
with local modifications. In the stele seen in fig. 438, B, there is a
close approach to a continuous cylinder of secondary xylem especially
on the right-hand side. External to the inner series are several
portions of normally orientated secondary xylem-groups (fig. 437):
these probably represent a second series of steles separated from the
inner series by a narrow crushed arc of tissue on which the protoxylem
strands of the outer groups abut. The xylem of the outer steles agrees
in its normal orientation with the outer and smaller part of the inner
steles and, as there is no accompanying group of inversely orientated
xylem corresponding to the larger mass of secondary xylem of the inner
series, the outer strands are designated partial steles. The central
stele consists of two curved irregular bands composed of vertically and
obliquely running tracheids: the central part of this stele consists of
crushed tissue that probably represents primary xylem like that between
the two parts of each of the peripheral steles.
[Illustration: Fig. 438. _Rhexoxylon africanum_. A, radial wall of
tracheid; B, C, peripheral steles; _a_, primary portion of stele; _b_,
lateral strand. (After Bancroft.)]
_Rhexoxylon_ differs from the usual Medullosan type in the structure
of the secondary xylem which is composed of tracheids with an
Araucarian form of pitting: there are usually two alternate rows of
contiguous pits (fig. 438, A) and occasionally one or three rows.
The medullary rays are uniseriate and 3 to 15 cells in depth, a
feature characteristic of coniferous wood and not of the wood of the
Medulloseae.
In the absence of more complete information as to the anatomical
structure of this stem and of all information as to the leaves
or reproductive organs it is impossible to fix with precision
the systematic position of the genus. It is, however, clear that
_Rhexoxylon_ is closely connected with _Medullosa_ in certain
features though in the structure of the wood it exhibits important
peculiarities. The imperfectly known stem _Cladoxylon Kidstoni_[408]
shows a fairly close agreement with the African plant in the form of
the steles (fig. 460) but the pitting is scalariform.
=SUTCLIFFIA.= Scott.
_Sutcliffia insignis_ Scott.
The generic name _Sutcliffia_ was given by Dr Scott[409] to a peculiar
type of stem from the Lower Coal Measures of Shore, Lancashire, in
recognition of the valuable services rendered to Palaeobotany by the
late Mr W. H. Sutcliffe, the owner of the colliery from which several
new types of plants have been obtained. Two stems are recorded, the
type-specimen and a more recently discovered stem, also from Shore,
described by Miss de Fraine[410], which differs in several particulars
from Dr Scott’s species. In view of the well-marked peculiarities of
the second stem it is convenient to speak of it as _forma β_ instead of
including it without a distinctive epithet in _Sutcliffia insignis_. We
know nothing of the reproductive organs of the genus.
1. _Sutcliffia insignis, forma α._
This consists of a piece of stem approximately 12 × 7 cm. in diameter
characterised by a broad cortex of parenchyma with secretory sacs
and ducts and strands of mechanical tissue (fig. 439, A). Decurrent
and massive leaf-bases form a prominent feature as in the stem of
_Medullosa anglica_. The stele, though compressed before petrifaction,
was probably not quite cylindrical but more or less polygonal or
broadly triangular in section; it consists of groups of large primary
tracheids (350μ in diameter) with numerous bordered pits (fig. 439,
B, and fig. 440) embedded in an anastomosing system of parenchyma
containing scattered secretory sacs, a type of protostele like that
of _Heterangium_ and _Medullosa_ _anglica_ except in the possession
of exarch protoxylem strands. The metaxylem tracheids contiguous to
the external protoxylem elements have a dense spiral or scalariform
type of pitting. In the lower part of the stem the primary xylem is
enclosed by a cambium which has added a few secondary tracheids (120μ
in diameter), but in the upper part of the specimen the cambium is only
partially developed and the addition of secondary xylem has hardly
begun (fig. 440). A narrow band of secondary phloem was recognised in
places consisting of small-celled parenchyma with some sieve-tubes and
medullary rays continuous internally with the parenchyma of the primary
stele. In close association and occasionally in organic connexion with
the surface of the stele are several tangentially elongated and large
groups of vascular tissue associated with smaller oval strands varying
considerably in size. These groups, designated meristeles (Fig. 439,
A), are identical in structure with the main stele and are occasionally
invested by a feebly developed zone of secondary xylem and phloem. The
meristeles are detached at intervals from the parent stele around which
they form by anastomoses an irregular network: the larger meristeles
give off smaller strands and from these the actual leaf-traces are
produced by subdivision. It appears, however, that in this type
the meristeles are not completely used up in the production of the
leaf-traces, portions of them behaving as cauline vascular strands.
A protoxylem of a meristele still attached to the central protostele
occupies an internal position, and at a higher level, as separation
of the meristele is effected, the spiral tracheids occur on the inner
face. New meristeles are given off at intervals from the main stele
‘to compensate for those parts of the reticulum which were used up in
the formation of leaf-trace strands[411].’ The meristeles form the
starting-point for the leaf-traces, an intermediate system between the
main stele and the actual leaf-traces; they differ, therefore, from the
parent leaf-traces of _Medullosa anglica_, which are completely used up
by repeated subdivision. Moreover in _Sutcliffia_ the leaf-bundles are
concentric and not collateral.
[Illustration: Fig. 439. _Sutcliffia insignia_ Scott. A, B, E, forma α.
(After Scott.) C, D, forma β. (After de Fraine.)
A. Transverse section of stem; _a_, _b_, double rows of leaf-trace
bundles. The larger black masses are the meristeles; the smaller
patches represent bundles derived from the meristeles.
B. Longitudinal section of a radially symmetrical bundle from a
leaf-base.
C. The junction between the primary and secondary xylem.
D. Vascular system in transverse section: _m_, _m′_, meristeles; _s_,
main stele; _e_, extrafascicular strands; _lt_, leaf-traces; _c_,
secondary cortex.
E. Vascular bundle from petiole showing a ring of large sieve-tubes
surrounding the xylem, and portions of stereome strands.]
[Illustration: Fig. 440. _Sutcliffia insignis._ Part of the primary
xylem showing on the upper edge the beginning of secondary growth.
(Cambridge Botany School, 560.)]
A conspicuous feature of the stem of _forma α_ is the occurrence of two
double rows of vascular strands stretching across the cortex (fig. 439,
A, _a_, _b_). These are interpreted by Scott as downward continuations
in the stem of the inner surface of leaf-bases. The outer cortex of the
stem and leaf-bases has hypodermal strands of stereome which remain
separate or rarely anastomose, and form a superficial zone exactly
like that of some species of _Medullosa_. The leaf-trace bundles may
be radially symmetrical or unilateral in the arrangement of the xylem
which is in all cases completely surrounded by phloem. Fig. 439, B,
shows part of a longitudinal section of a large leaf-trace bundle:
spiral protoxylem elements (_px_) abut on the phloem (_ph_) and are
succeeded to the left by narrow scalariform and large reticulately
pitted tracheids. In the larger and radially constructed traces there
are several protoxylem-strands distributed over the surface of the
xylem, while in the smaller unilateral traces there may be one or
two protoxylem strands. A characteristic feature of the xylem of the
leaf-traces is the admixture of parenchyma with the tracheids (fig.
439, B, E) and another noteworthy character is the occurrence of large
thin-walled tubes in the phloem described by Scott as sieve-tubes and
compared with the large sieve-tubes in Marattiaceous leaf-bundles.
Immediately internal to the hypoderm is a row of leaf-bundles (fig.
439, A) each of which is accompanied by stereome strands.
The petioles, which reach a diameter of 12 cm., contain numerous,
occasionally anastomosing, concentric bundles. Nothing is known of the
fronds as a whole beyond the fact that they are spirally disposed and
had decurrent bases of large dimensions in proportion to the stem.
_Sutcliffia insignis, forma β._
This form, described by Miss de Fraine as _Sutcliffia insignis_[412],
is represented by a stem rather smaller than the type-specimen
described by Scott, though it is probably an older example of the same
species. It is distinguished by a greater development of secondary
xylem and phloem both on the main stele and the meristeles; it differs
also in the absence of the greater part of the cortex and leaf-bases
which have been cut off as the result of the formation of a deep-seated
periderm (fig. 439, D, C). The meristeles are smaller and fewer than in
the larger form and are distinguished by some other peculiarities. At
_m′_ in fig. 439, D, a meristele is seen attached to the main stele.
In _Sutcliffia insignis forma α_ the main stele is enclosed by an
irregular network of subsidiary steles or meristeles and these form
the points of departure of the leaf-traces, but the meristeles are not
completely used up in the process of conversion into leaf-traces. In
_Sutcliffia insignis forma β_ the meristeles agree in structure with
the main stele except in the smaller amount of secondary tissue: they
do not, however, form a network as in _forma α_ but occur as strands
parallel to the central stele, ‘giving off leaf-traces and ultimately
dividing up into smaller strands, often unequal in size, the primary
wood of the meristeles being entirely used up in the production of
radially symmetrical or unilateral bundles.’ In this respect, as Miss
de Fraine points out, _forma β_ agrees more closely than _forma α_ with
_Medullosa anglica_ and supports Scott’s view that _Sutcliffia_ is a
primitive type of Medullosan stem. The leaves were given off at fairly
long intervals as in some species of _Medullosa_: the leaf-traces are
exarch and similar to those of the type-species. The most striking
feature of the new stem is the presence of a vascular network (fig.
439, D, _e_) which encloses both the main steles and the meristeles;
it consists of extrafascicular strands composed of normally orientated
bands of secondary xylem and phloem often assuming a fan-like
arrangement and occasionally almost concentric or inversely orientated.
These strands are always accompanied by short, usually reticulate,
tracheids on the inner margin of the xylem: similar isodiametric
tracheids also occur in the pericyclic region. The extrafascicular
strands are believed to be secondary structures phylogenetically
independent of the meristeles and main stele, comparable with the
successive cylinders or arcs of secondary xylem and phloem in some
recent Cycads and in some species of _Medullosa_[413].
The stele is exarch and roughly triangular; except in the broader
zone of secondary tissue it agrees with the protostele of _forma α_.
The secondary xylem (fig. 439, C) possesses numerous medullary rays
3–4 cells broad and of considerable depth: the secondary phloem is
characterised by the presence of thick-walled elements, presumably
sieve-tubes, like those of _Medullosa Leuckarti_ and _M. anglica_.
The ground-tissue is rich in secretory tissue and the stem-surface,
from which the leaf-bases have been detached, is limited by a wide zone
of secondary tissue produced by a phellogen.
_Sutcliffia Williamsoni_ (Seward).
1876. _Myelopteris_ (_pars_) Williamson, Phil. Trans. R. Soc. Vol.
166, Pl. +ii.+ figs. 7, 8; Pl. +iv.+ fig. 17.
1893. _Rachiopteris Williamsoni_ Seward, Ann. Bot. Vol. +vii.+ p. 1.
1894. _Rachiopteris Williamsoni_ Seward, _ibid._ Vol. +viii.+ p. 207,
Pl. +xiii.+
1906. _Sutcliffia Williamsoni_ Scott, Trans. Linn. Soc. Vol. +vii.+
pt +iv.+ p. 62.
In an account of _Myelopteris_ (= _Myeloxylon_) published in 1876
Williamson included some sections of petioles from the Lower Coal
Measures which I afterwards with his concurrence transferred to the
genus _Rachiopteris_ as _R. Williamsoni_. In _Rachiopteris Williamsoni_
the vascular bundles are concentric and not collateral, and are
further distinguished from those of _Myeloxylon_ by the association of
parenchyma with the tracheids. In the arrangement of the bundles and
in the structure of the ground-tissue the petioles of _Rachiopteris
Williamsoni_ agree with those of _Myeloxylon_. An outstanding feature
of the vascular strands of the former is the occurrence at fairly
regular intervals in the peripheral part of the phloem of comparatively
large tubes described by me as secretory canals on the ground that
evidence was furnished of their development by the schizogenous
separation of cells to form a central canal. The canals were compared
with the large sieve-tubes of the Marattiaceae, but with the
qualification that ‘their mature form and their manner of development
are strongly suggestive of small secretory canals.’ Nothing was known
as to the stem which bore these petioles until Scott’s discovery of
_Sutcliffia_ with vascular bundles in the cortex and leaf-bases of the
same type as those of _Rachiopteris Williamsoni_. As Scott says, there
are a few distinguishing features which suggest that _R. Williamsoni_
is not specifically identical with the petioles of _Sutcliffia
insignis_, though the agreement is such as to justify the substitution
of _Sutcliffia_ for _Rachiopteris_. The tubular elements in the phloem
which I considered to be secretory canals are regarded by Scott and
Miss de Fraine as sieve-tubes.
Miss de Fraine gives an excellent summary of our knowledge of the genus
and discusses, in the light of the additional facts furnished by the
second stem, the position of _Sutcliffia_ in a phylogenetic series.
The new form strengthens the comparison instituted by Scott between
_Sutcliffia_ and _Medullosa_ and gives support to a close connexion
between the Medulloseae and the Cycadaceae. Scott lays stress on the
fact that the Medulloseae, except _Sutcliffia_, are polystelic, while
the Cycads, at least the adult stems, are monostelic. The views of
Worsdell and other botanists who believe that the Medulloseae and
the Cycads are intimately related are discussed on another page: in
reference to these views Miss de Fraine adds a caveat as to the danger
of attaching excessive importance to evidence based on seedling anatomy
when we are concerned with broad phylogenetic questions. The stele of
a cycadean stem may be derived from a protostelic type such as that of
_Sutcliffia_ by the gradual disappearance of the internal tracheids:
in _Sutcliffia_, as in some Cycads and species of _Medullosa_,
extrafascicular strands and cylinders are a characteristic feature
and these may well have arisen independently of the central stele
in response to physiological requirements. From such a type as
_Sutcliffia_ evolution may have proceeded along two lines; in one
direction new types were produced in which increasing complexity,
as represented by a multiplication of steles, was an outstanding
feature. These forms, illustrated by _Medullosa anglica_ and other more
elaborate species, proved inefficient and were unproductive. Along
another line the protostelic condition was maintained though in some
cases extrafascicular strands or cylinders and cortical steles were
superadded: it was this line that led to the recent Cycads.
_General considerations suggested by the anatomical features
of_ Medullosa.
A comparison of the stems described under the generic name _Medullosa_
reveals a considerable range in the grosser anatomical features
superadded to certain fundamental characters denoting a common
origin[414]. If additional data were available giving us a fuller
knowledge of individual plants differences between species would
be more clearly defined and would provide adequate grounds for the
institution of new genera for some of the types now included in
the comprehensive genus _Medullosa_. A proposal by Dr Lotsy[415]
to adopt the names _Pecopteromedullosa_ and _Neuropteromedullosa_
rests primarily on the relatively unimportant difference between the
fronds associated with certain Medullosan stems and, as Scott[416]
points out, this two-fold division if applied to such a species as
_Medullosa Leuckarti_ would result in its separation from species
which anatomically are clearly of the same generic type. In _Medullosa
anglica_, one of the oldest and simplest types, there are three
steles of equal importance, and each of them is practically identical
with the single stele of _Heterangium_. Each stele—as indeed all
Medullosan steles—consists of a strand of primary xylem enclosed by
secondary xylem and phloem, and it is obvious that the development
of a constantly increasing cylinder of secondary conducting tissue
about three centres would lead to serious mechanical difficulty: a
stem constructed on the plan of _Medullosa anglica_ or the smaller _M.
pusilla_ could not increase the thickness of its secondary vascular
tissue beyond a certain point without detriment to its efficiency. In
some types this difficulty is partially overcome by the production of
complete concentric cylinders of centrifugally developed conducting
tissue external to an inner system of concentric steles agreeing
individually with those of _Heterangium_ (fig. 415, B). _Medullosa
anglica_, regarded from the point of view of the architectural
efficiency of its vascular system, affords a much less promising _point
d’appui_ for further evolution than some of the forms described under
_Medullosa stellata_ in which the mechanical impasse is avoided by the
adoption of the cycadean plan as represented by such genera as _Cycas_
and _Macrozamia_. The English species _Medullosa centrofilis_ (fig.
417) affords the first example of a characteristic Medullosan feature,
namely the presence of a small concentric stele in the central region
of the stem: this so-called star-ring differs not only in its smaller
dimensions but in its more cylindrical form from the larger peripheral
steles. In the later Permian species, _e.g._ _Medullosa porosa_ and
_M. Solmsi_, the single star-ring of the older _M. centrofilis_ is
replaced by a large number of precisely similar conducting strands.
These star-rings are structurally comparable with the cortical steles
of _Cycas_ and, in position, with the medullary system of bundles in
a _Macrozamia_; they are essentially cauline and take no part in the
emission of leaf-traces. _Medullosa Leuckarti_ (fig. 416, H) resembles
in its vascular plan _M. centrofilis_, but in this larger stem there
are several star-rings and the enlarged peripheral steles are more or
less sinuous. In _Medullosa Solmsi_ (fig. 416, E) the star-rings are
still more numerous and the main vascular system consists of a double
series of concentric steles, each agreeing with the larger peripheral
steles of _M. Leuckarti_.
Some of the forms included in _Medullosa stellata_ appear to be very
different from _M. anglica_ and _M. Leuckarti_ (_cf._ fig. 416, F, A,
H), but their similarity is apparent if we imagine _Medullosa anglica_
with only one main stele (with the addition of star-rings) which is
stretched tangentially until it becomes a long and narrow plate-ring
and is then rolled into a hollow cylinder like that in fig. 416, D.
A modification of the tubular type of stele is seen in _Medullosa
stellata_ var. _corticata_ (fig. 416, G) in which the vascular
cylinder is broken up into two or more curved plate-rings, a change
superficially similar to that by which a dictyostele is produced from a
solenostele, but in _Medullosa_ it is not the overlapping of leaf-gaps
that is the cause of the change. A striking feature in the stem of
_Medullosa stellata_ represented in fig. 416, D and F (especially
F), is the inequality in breadth of the centrifugal and centripetal
xylem: this inequality is an expression of the difficulty caused by the
presence of an internal as well as an external addition of secondary
conducting tissue. A limit is set to the production of secondary
centripetal xylem by the space available for extension, whereas there
is unlimited room for increase in the case of the centrifugal tissue.
This tendency to a greater development of xylem and phloem on the
outer side of the primary portion of the steles is illustrated also in
_M. Solmsi_ var. _lignosa_ (fig. 416, L) where the outer of the two
series of peripheral steles has a much larger proportion of centrifugal
xylem. In _M. anglica_ the secondary xylem on the inner side of the
steles is not infrequently broader than the corresponding tissue on
the abaxial side[417]; but this is exceptional in the genus. A further
development of centrifugal conducting tissue without any corresponding
development of centripetal tissue is effected in certain cases (fig.
416, K, L) by the addition of concentric cylinders of centrifugal
xylem and phloem beyond the original concentric steles. The type
illustrated by _Medullosa Solmsi_ var. _lignosa_ and _M. stellata_ var.
_gigantea_ (fig. 416, L, K) at once suggests comparison with stems of
_Cycas_, _Macrozamia_, and _Encephalartos_, the chief difference being
the presence in _Medullosa_ of an inner series of concentric steles
and a central ground-tissue containing star-rings, though the latter
may be regarded as corresponding to the medullary system of bundles
in _Macrozamia_. In _Macrozamia_ the central region of the stem is
considered to be the pith of a monostelic stem, whereas in _Medullosa_
the stem is polystelic. In recent cycadean stems it is not uncommon
to find patches of inversely orientated xylem and phloem internal to
one or more of the cylinders of centrifugal vascular tissue. These
abnormal developments are considered by Worsdell[418] to be relics of
the inner portions of concentric steles possessed by the Medullosan
ancestors of recent Cycads. This interpretation affords a means of
bringing into closer relationship the polystelic Medulloseae and the
monostelic Cycadaceae, the apparent simplicity of the latter being
the result of the progressive loss of centripetal xylem and phloem,
the normal cycadean cylinder being therefore regarded as a one-sided
remnant of a concentric Medullosan stele. In other words, the Cycads
are descended from polystelic ancestors. As further evidence in support
of this view Worsdell points to the occurrence of concentric steles
in the cortex of _Cycas_ and their occasional presence in the pith
of other genera. Matte[419] has shown that in the seedling stem of
_Encephalartos Barteri_ (fig. 396, K) there are three concentric steles
each similar to a normal Medullosan stele: at a higher level in the
axis the steles become ‘unrolled’ and assume the form of one-sided
cylinders of centrifugal xylem and phloem.
In the peduncles of some recent Cycads, _e.g._ _Stangeria_, there is
a tendency towards a somewhat irregular orientation of the collateral
bundles that constitute the vascular cylinder, and tracheids
occasionally occur internal to the protoxylem of the individual
bundles[420]. Worsdell regards these features as evidence of a
Medullosan ancestry. If the sinuous plate-rings of a stem of _Medullosa
Leuckarti_ (fig. 416, H) were broken up into separate portions and
wholly or in part deprived of the centripetal xylem, the result would
be an arrangement of bundles comparable with that in a _Stangeria_
peduncle[421]. The scattered centripetal tracheids discovered by Scott
in _Stangeria_ and other cycadean peduncles are interpreted by Scott
and by Worsdell as relics of some ancestral centripetal xylem, but
with this important difference in the point of view; Scott believes
that they represent the almost completely aborted centripetal xylem
of a single stele like that of _Lyginopteris_, while Worsdell sees
in them fragmentary vestiges of the central primary xylem of two or
more Medullosan steles. An abnormal seedling of _Araucaria Bidwillii_
described by Shaw[422] exhibits features analogous to those in some
cycadean seedlings: within the normal stele a cambium forms an
inversely orientated vascular cylinder which at a lower level becomes
continuous with the outer centrifugal tissue, the whole vascular system
being eventually represented by two concentric steles. The polystelic
stage is a development of a monostelic condition, and the inner or
inverted portion of each of the two concentric steles is derived from
an inversely orientated cylinder in the central region of the root.
This abnormal root does not, however, supply an argument in favour
of the derivation of a monostelic type of stem from one that was
polystelic, but it shows a close relation between the two plans in
one organ. The seedling is not altogether normal in form apart from
structure and it is not improbable that the anatomical abnormality is
connected with some pathological cause.
It has been suggested[423] that Worsdell attaches too much phylogenetic
significance to the irregularities in the disposition and form of the
vascular bundles in the peduncle of _Stangeria_, and the criticism that
insufficient allowance is made for the possible reaction on structure
of the special physiological requirements of reproductive shoots is
well founded. Granting an overestimate of the arguments drawn from the
occasional occurrence of concentric vascular strands, a considerable
body of evidence remains in favour of Worsdell’s main contention.
Mrs Thoday[424] has drawn attention to certain features exhibited by
the inflorescence-axes of _Welwitschia_, particularly the occurrence
of concentric and inversely orientated bundles, similar to those
characteristic of the seedling of _Cycas siamensis_[425] described
by Matte, and to anatomical characters occasionally present in adult
cycadean stems and normally represented in _Medullosa_. She is of
opinion that the occurrence in _Welwitschia_ of certain Medullosan
features has a phylogenetic significance. The differences between the
Gnetales, Medulloseae, and Cycadales are considerable, and it would
seem unlikely that the anatomical resemblances described by Mrs Thoday
are of great value as criteria of close relationship. The comparison
of _Lagenostoma_ with gnetalean seeds is alluded to elsewhere. To the
statement that the presence of concentric and inversely orientated
steles in _Welwitschia_ are reminiscent of the polystelic Medulloseae,
Mrs Thoday adds the qualifying remark that the occurrence of four
concentric groups of vascular tissue in the hypocotyl of _Welwitschia_
is not sufficient to justify the conclusion that the ancestral type was
polystelic. This reservation accords with the contention of Scott and
other botanists, that the occasional occurrence in cycadean seedlings
and adult stems of anatomical features suggestive of polystely does
not in itself furnish an adequate reason for doubting that the
apparent monostely of Cycads is phylogenetically what it seems to
be, namely, an indication of monostelic ancestry. This brings us to
the question of a possible monostelic ancestor. It may be that the
Upper Carboniferous genus _Sutcliffia_ affords a clue to the problem
of the origin of the polystelic type illustrated in various forms by
_Medullosa_. The protostele of _Sutcliffia_ bears a close resemblance
to each of the three steles of _Medullosa anglica_; the fact that
_Sutcliffia_ is exarch and that _Medullosa anglica_ has mesarch xylem
is of secondary importance, particularly as exarchy is represented
within the genus _Medullosa_. The extrafascicular strands of xylem
and phloem and the accessory strands are points in which _Sutcliffia_
and _Medullosa anglica_ agree and, as Miss de Fraine[426] adds, the
meristeles of _Sutcliffia_ may be homologous with the leaf-trace
strands of _Medullosa_. Scott[427] gave expression to the characters
shared by these two types by describing _Sutcliffia_ as the most
primitive of the Medulloseae. It is suggested that the protostelic
axis of _Sutcliffia_ may be regarded as the starting-point of the
monostelic Cycads, the central mass of tracheal tissue being replaced
by a parenchymatous pith, while the extrafascicular and accessory
strands arose independently of the central stele in response to
increased physiological demands consequent on the increase in size of
the stem. From the same starting-point evolution may have progressed
along another line through such a type as _Medullosa anglica_ leading
to the more complex Permian species of _Medullosa_. Chodat’s view[428]
that the Medulloseae are Protocycadaceae, if we include _Sutcliffia_
as well as _Medullosa_ in the Medulloseae, is probably correct. There
is clear evidence of a close bond of union between recent Cycads and
the Medulloseae, and _Sutcliffia_ offers a possible means of deriving
complex polystelic types from a monostelic ancestor.
Worsdell’s opinion[429] that the stele of _Lyginopteris_ affords
evidence of derivation from a polystelic ancestor and is not
homologous with the true monostele of _Heterangium_ is opposed to
the undoubted signs of intimate connexion exhibited by these genera.
The Lyginopterideae are, as Scott[430] says, a less advanced group
than the Medulloseae and, it may be added, they are more remote from
the modern representatives of the Cycadales. The Lyginopterideae and
the Medulloseae are probably offshoots of a common stock, but the
Medulloseae occupy a position farther removed from the filicinean
ancestry than _Heterangium_ and _Lyginopteris_[431].
The relative meagreness of our knowledge of the reproductive organs of
the Medulloseae gives precedence to anatomical data in phylogenetic
considerations, but the evidence furnished by _Trigonocarpus_ and other
seeds that may fairly be assigned to Medullosan plants is in harmony
with the conclusions based on vegetative characters with regard to a
close affinity between the Medulloseae and Cycads.
The comparative examination of recent Cycads naturally suggested by any
attempt to compare the group as a whole with Palaeozoic types leads to
some apparently contradictory results. The habit of the megasporophyll
of _Cycas_ is usually quoted as a primitive attribute: the close
resemblance in plan and in manner of occurrence on the stem between
megasporophylls and foliage leaves recalls both Ferns and Medullosan
fronds. On the other hand the production of eight body-cells in the
pollen-tube of _Microcycas_[432] in place of the usual single cell may
also be regarded as a primitive character. It is perhaps possible, as
Miss Dorety[433] says, that the polyspermy may be a case of recurrence
and not a direct inheritance. _Microcycas_ differs from _Cycas_ in
having only one vascular cylinder, and if the presence of several
concentric cylinders in _Cycas_ be interpreted as an indication of
a closer connexion with a Medullosan ancestry, the _Microcycas_ type
would represent a more advanced stage in evolution. Attempts to arrange
plants according to a natural sequence are frequently frustrated by
instances of unequal progress in the development of vegetative and
reproductive organs; one or other set of members lags behind; some
characters point to the retention of primitive traits while others
indicate a marked progressive tendency. It is noteworthy that the
Mesozoic Bennettitales are characterised by a greater simplicity of
stem-structure than is the rule in recent Cycads, and both in their
vegetative features and in the structure of the seeds they are further
removed from the Medullosan type.
[Illustration: Fig. 441. _Steloxylon Ludwigii._ A, surface-view
(longitudinal) of stem showing leaf-bases. (After Solms-Laubach.) B,
longitudinal section showing anastomosing vascular strands. C, steles,
the lower one showing the emission of a leaf-trace. (B, C, after
Schenk.)]
II. A. =STELOXYLEAE.=
=Steloxylon.= Solms-Laubach.
_Steloxylon Ludwigii_ (Goeppert and Stenzel). The genus is founded
on a piece of stem from Siberia, possibly of Permian age though
not improbably older, which was originally described as _Medullosa
Ludwigii_[434]. It is characterised by numerous cylindrical and
band-like vascular strands forming an irregular anastomosing system
(fig. 441, B) and by crowded spiral leaf-scars on the exposed face.
The appearance presented by the transverse section figured by these
authors, while suggesting comparison with _Medullosa_, reveals a
distinctive character, namely the absence of a definite peripheral
system of vascular rings such as forms a striking feature of the
continental Medulloseae. A more complete description was afterwards
published by Schenk[435] who recognised more fully the peculiar
features and hinted at the possibility that the species might
more appropriately be regarded as a member of a distinct group.
Solms-Laubach[436] went a step further and instituted the generic name
_Steloxylon_, and in a later publication gave a fuller account of the
anatomical characters. The complete stem must have reached a diameter
of approximately 13 cm. The homogeneous ground-tissue forms a matrix
enclosing an anastomosing vascular system of cylindrical or oval steles
(fig. 441, C). Each strand consists of a band of secondary xylem
tracheids with one or several rows of circular or oval bordered pits
on the radial walls and narrow medullary rays usually 1–2 cells broad
and 1–4 cells deep, though occasionally deeper. No phloem is preserved.
The tissue in the centre of each stele is very imperfectly preserved,
but it is clear that the secondary xylem enclosed a central region
(‘partial pith’) like that in the steles of a _Medullosa_, doubtless
consisting of primary xylem and conjunctive parenchyma.
The stem is covered with leaf-bases of oval or circular section and
between them are small organs, probably multicellular hairs (fig. 441,
A). A leaf-base consists of an outer zone of strengthening tissue
and a parenchymatous ground-tissue traversed by two or more small
vascular strands which assume various forms. These petiolar strands
are simply portions of the main vascular system which bend outwards
at the periphery of the anastomosing network. The more noteworthy
features in which _Steloxylon_ differs from _Medullosa_, particularly
such species as _M. stellata_ and _M. Leuckarti_, are (i) the crowded
and comparatively small leaf-bases in place of the massive decurrent
petioles of _Medullosa_; (ii) the supply of the leaves by compact
branches of the stelar network instead of the bundles detached
as leaf-traces from a stem-stele of _Medullosa_ (the origin of a
leaf-trace in _Steloxylon_ is shown in fig. 441, C); (iii) the absence
of a peripheral system of vascular plate-rings and the irregular
distribution of cylindrical and plate-steles in the ground-tissue.
Nothing is known of the reproductive organs or leaves beyond the
structure of the attached leaf-bases. The opinion expressed by P.
Bertrand[437] that the fossil described by Stenzel as _Asterochlaena_
(_Clepsydropsis_) _kirgisica_ is the petiole of _Steloxylon_ was
abandoned after the additional facts published by Solms-Laubach.
As regards the affinities of _Steloxylon_: the structure of the steles
agrees closely with that of the star- and plate-rings of a _Medullosa_,
while the pitting of the tracheids is more like that in _Medullosa_
than _Cladoxylon_. In the tendency to a more radial than tangential
disposition of the band-like steles _Steloxylon_ recalls _Cladoxylon_
rather than _Medullosa_, but in _Cladoxylon_ the vascular system does
not form an irregular network as in _Steloxylon_. The information as
to the structure of the primary xylem is very meagre, but it points
to a closer connexion with _Medullosa_ than with _Cladoxylon_. On the
whole _Steloxylon_ may perhaps be defined as a genus allied to the
Medulloseae in the anatomical features of the stem more closely than
to other genera, but sufficiently distinct to be excluded from the
Medulloseae as at present understood[438].
CHAPTER XXXI.
PTERIDOSPERMS REPRESENTED BY SEED-BEARING LEAVES ONLY OR LEAVES IN
CONSTANT ASSOCIATION WITH SEEDS.
Before describing other genera represented by petrified vegetative
organs exhibiting in their anatomical features points of contact with
the Medulloseae, a short account is intercalated of some imperfectly
known seed-bearing fronds and seeds belonging to the Pteridosperms but
which do not afford sufficient data to admit of their reference to a
more precise position in a natural classification.
_Pecopteris Pluckeneti_ (Schlotheim).
In the section in Volume +ii.+ devoted to the genus _Pecopteris_
reference was made to the species _P. Pluckeneti_[439], further
treatment being deferred until other Pteridosperms had been described.
The fern-like fronds originally described by Schlotheim as _Filicites
Pluckeneti_[440] and afterwards transferred by Brongniart and other
authors to _Pecopteris_[441] are now recognised as the leaves of a
Pteridosperm. Some doubt has been expressed as to the specific identity
of the specimens figured by Schlotheim and Brongniart respectively,
but Potonié’s examination of the type-specimen of the earlier author
convinced him that Brongniart’s leaves were correctly named. The
large fronds of _Pecopteris Pluckeneti_ are characterised by the
bifurcation of the principal axis which bears opposite pairs of bi-
or tri-pinnate branches and in the angles of the bifurcations of the
rachis undeveloped buds occur on prolongations of the axis, a habit
recalling recent species of _Gleichenia_[442] (figs. 225 and 226, vol.
+ii.+). The variation in the form of the pinnules is shown in fig.
442, A, which represents both the apical portion and parts of pinnae
10 cm. lower on the rachis of a large leaf from the Coal Measures of
Radstock. The species is characteristic of the Upper Coal Measures and
is recorded also from Permian strata. In 1883 Sterzel adopted for this
species the generic name _Dicksonites_ because of the occurrence of
shallow circular cups at the end of the lowest lateral vein on some of
the pinnules which he believed to be sori of the Cyatheaceous type.
The cups have an involute margin and occasionally a small scar in the
centre (fig. 442, B). Stur[443] declined to accept Sterzel’s evidence
as satisfactory and suggested a fungal origin for the sorus-like
impressions, a view, as Sterzel objected, that is rendered improbable
by the constant position of the single cups on several pinnules. The
nature of Sterzel’s ‘sori’ has not been demonstrated: it is suggested
by Grand’Eury[444] that they mark the position of microsporangia.
Some seed-bearing specimens in Dr Kidston’s collection show cups,
like those figured by Sterzel, on pinnules from which the seeds have
fallen, and it is not improbable that they are the scars of seeds. In
1905 Grand’Eury published a description and photographs of specimens
of _P. Pluckeneti_ from the St Étienne coal-field showing hundreds of
well-preserved seeds, many of them attached to pinnules characterised
by a very slightly reduced lamina. Some fronds were found to be
entirely fertile, while others bore both sterile and fertile pinnae.
The smallest seeds, 5 mm. long and 3 mm. broad, were found at the tips
of unexpanded leaves: the mature seeds, only slightly larger, agree in
their broadly oval form and narrow marginal ‘wing’ with small examples
of _Samaropsis_[445]. The seeds were figured by Grand’Eury[446] in
an earlier work as _Carpolithes granulatus_. They are believed to
have hung free from the lamina, a conclusion based on the position
of the seeds relative to the plane of the pinnule in well-preserved
examples. Prof. Zeiller informs me that he is by no means certain
that Grand’Eury’s seed-bearing fronds should not be referred to
_Pecopteris Sterzeli_; but as that species and _P. Pluckeneti_ are
very closely allied forms and may well have borne the same general
type of fructification, the question of specific difference does not
affect the significance of Grand’Eury’s discovery. A statement was made
in vol. +ii.+[447], quoted from Grand’Eury, that the fronds of _P.
Sterzeli_ were borne on a _Psaronius_ stem, but Prof. Zeiller told me
that in his opinion the fronds and stem are merely in association and
not in organic contact. It is probable that the _Psaronius_ stem bore
fronds of some species of _Pecopteris_ with sori of the _Asterotheca_
or _Scolecopteris_ type and not seeds. _Pecopteris Pluckeneti_ and _P.
Sterzeli_ are no doubt the fronds of a Pteridosperm[448], but apart
from the seed-impressions there is no evidence as to the nature of
the reproductive organs or stem. The form of the seeds with a fairly
thick sarcotesta, which gives them a winged appearance, suggests a
member of the Medulloseae rather than a plant with seeds like those of
_Lyginopteris_ and _Heterangium_.
[Illustration: Fig. 442. _Pecopteris Pluckeneti._ A, apex and lower
pinnae (Kidston Coll., 234); B, pinnule with supposed sorus (after
Sterzel); C, pinnule with seeds (after Zeiller).]
_Eremopteris artemisaefolia_ Steinberg with _Samaropsis acuta_ Lindley
and Hutton.
The generic name _Eremopteris_ was instituted by Schimper for a type
of frond from the Coal Measures of Newcastle described by Sternberg as
_Sphenopteris artemisaefolia_. He included also a second species, _E.
Neesii_, from the Permian of Bohemia: this was removed by Zeiller to
_Callipteris_. The type-species of _Eremopteris_ is included in this
chapter on the ground that the almost constant association with the
fronds of seeds comparable with those described by White as _Aneimites_
(_Wardia_) _fertilis_ affords a strong argument in favour of assigning
_Eremopteris artemisaefolia_ to the Pteridosperms.
1826. _Sphenopteris artemisaefolia_ Steinberg, Flor. Vorwelt, Fasc.
+iv.+ p. 15, Pl. +lvi.+ fig. 1.
1833. _Sphenopteris crithmifolia_ Lindley and Hutton, Foss. Flor. Vol.
+i.+ Pl. +xlvi.+
1833. _Cardiocarpon acutum_, _Ibid._ Pl. +lxxvi.+
1869. _Eremopteris artemisaefolia_ Schimper, Trait. Pal. Vég. Vol. +i.+
p. 416.
1914. _Samaropsis acuta_ Kidston, Trans. R. Soc. Edinb. Vol. +l.+ Pt
+i.+ p. 156.
The large compound fronds of this species[449] are characterised by
the regular dichotomy of the main branches, a feature frequently met
with in Palaeozoic fern-like leaves: the cuneate or oval-cuneiform
pinnules (fig. 443, A, C) vary considerably in breadth from the typical
cuneate type of segment as figured by Brongniart[450] to narrow,
almost linear, leaflets like those of _Sphenopteris crithmifolia_.
Several spreading veins traverse the lamina. Lindley and Hutton, while
admitting a very close resemblance between their species and _S.
artemisaefolia_, adopted a distinctive name. The only evidence so far
obtained as to the stem of the plant is furnished by some specimens
in the Hutton collection (Newcastle-upon-Tyne) one of which shows a
piece of rhizome bearing several petioles (fig. 443, B): there are no
pinnules attached to the rachises but some occur in close association.
Brongniart noticed the frequent association of _Eremopteris_ fronds
with small seeds, but he regarded it as accidental. Dr Kidston[451]
has recently drawn attention to a note by Prof. Duns published in
1872 on the juxtaposition of seeds and fronds, and Mr Howse[452] in
his Catalogue of the Hutton plants considers that the seeds were borne
on the _Eremopteris_ leaves; in his synonymy of _E. artemisaefolia_
he includes _Cardiocarpon acutum_ Lind. and Hutt. as the ‘spore-cases
or sporangia.’ The _Eremopteris_ seeds are of the platyspermic
(_Samaropsis_) type, broadly oval and about 7 mm. long with an obtuse
base and two slightly divergent acute processes at the apex (fig. 444).
Some specimens in Dr Kidston’s collection from the Lower Coal Measures
of Midlothian, which were associated with _Eremopteris_ fronds, are
preserved as mummified cuticular membranes and on microscopical
examination they show clearly the presence of a pollen-chamber.
The seeds are of the _Samaropsis_ type. The drawings reproduced in
fig. 444 were made for me by Dr Kidston from two specimens, in his
collection, of exceptionally well-preserved seeds from Midlothian:
the seeds of this species vary considerably in size and form; some are
almost orbicular and show no distinction between nucule and border
(fig. 444, A) while in others (B) the impression of the flattened
and longitudinally striated sarcotesta is clearly distinguished.
Kidston is of opinion that in younger seeds there is a single apical
point replaced in a later stage of development by two cusps, as seen
in figs. A and B, formed by the opening of the micropylar tube. A
ridge in the middle of the flattened surface indicates the position
of the vascular bundles in the principal plane as in _Cardiocarpus_.
The fully developed seeds are 8–9 mm. long. The correlation of the
seeds represented in figs. 443 and 444 with _Eremopteris_ fronds
furnishes an additional illustration of the impossibility of trusting
to external form as a criterion of affinity, for it is known that
seeds of the _Samaropsis_ type were produced by Pteridosperms with
foliage represented by _Eremopteris artemisaefolia_ and _Pecopteris
Pluckeneti_, also by some members of the Cordaitales (_e.g._ fig. 480).
Dr Arber[453] has recently proposed a new generic name _Cornucarpus_
for _Cardiocarpon acutum_, but the drawings that he gives of seeds from
the Kent coal-field referred to this species suggest a type distinct
from that of Lindley and Hutton. In the absence of specimens showing
actual attachment it is impossible to say how the seeds were borne,
but the analogy of _Wardia fertilis_ and _Pecopteris Pluckeneti_ lends
support to the view that the seeds were attached to pinnules with a
reduced lamina. _Eremopteris artemisaefolia_ occurs in the Lower and
Middle Coal Measures of England: a species recorded by Kidston from
the Calciferous sandstone of Scotland as _E. Macconochii_[454] is now
believed by that author to be generically distinct[455]. With the
exception of the unsatisfactory specimen reproduced in fig. 443, B, we
have no information with regard to the habit of the stem to which the
_Eremopteris_ leaves were attached.
[Illustration: Fig. 443. _Eremopteris artemisaefolia._ A, part
of a frond with associated seeds of _Samaropsis acuta_; B, rhizome
with fragments of fronds; C, pinnule. (Drawn by Mr L. D. Sayers from
specimens in the Hutton Collection, Newcastle. A, B, ⅔ nat. size.)]
[Illustration: Fig. 444. _Samaropsis acuta._ (From drawings by Dr
Kidston of specimens in his collection, 3475 (A), 3316 (B); × 2.)]
[Illustration: Fig. 445. _Wardia fertilis_ (White). A, sterile
portion of frond; B, D, enlarged pinnules; C, seed. (After White. A,
_ca_, nat. size; B–D, × 2.)]
=WARDIA.= White.
_Wardia fertilis_ (White). Another example of a fern-like frond bearing
seeds is afforded by specimens from the Lower Pottsville series of
Virginia (correlated with the Millstone grit of British geologists)
described by Mr David White[456] as _Aneimites_ (_Wardia_) _fertilis_.
The compound fronds usually referred to the genus _Adiantides_ or
_Adiantites_[457] are characterised by cuneate pinnules with a thin
lamina and forked, slightly divergent veins (fig. 445, A, D). White
discards the name _Adiantides_ in favour of Dawson’s genus _Aneimites_
on the ground that Goeppert[458], who instituted the former term,
applied it in the first instance to leaves of _Ginkgo_ which he
identified as simple Fern fronds. In spite of this misapplication of
the name it has been constantly used and is well established. The
discovery of seeds is, however, a reason for the adoption of a new
generic name, and as White proposed _Wardia_ for the seeds it may
appropriately be extended to the fronds in place of the provisional
term _Aneimites_. The seeds which occur at the apices of slender
pedicels on pinnae bearing relatively small pinnules with a reduced
lamina (fig. 445, B, C) are rhomboidal in shape, 4·5 mm. long and 2·5
mm. broad. The bilaterally symmetrical seeds were probably enclosed,
as White suggests, in a fleshy integument which on pressure became
laterally extended as a wing-like border. In some of the seeds there
is an indication of a ‘slight collapse within the apex of the nutlet,’
which may mean the presence of a pollen-chamber; but while the
preservation is too imperfect to afford any decisive evidence as to
anatomical features, there is no reason to doubt the conclusion as to
the seed-nature of the organs described by White. Nothing is known of
the stem, though the opinion may be hazarded that _Wardia_ is a member
of the Medulloseae.
_Adiantites bellidulus_ Heer and _Lagenospermum Arberi_ Nathorst.
Reference is made to the genus _Lagenospermum_ in the account of
_Lagenostoma_[459]. The species _Lagenospermum Arberi_ has recently
been founded by Dr Nathorst[460] on some seeds obtained from Lower
Carboniferous rocks in Spitzbergen: a brief description is intercalated
here because it is probable that they were borne on fronds of the
_Adiantites_ type similar to those on which White found the seeds
described by him as _Wardia_. The seeds of _L. Arberi_, 14–18 ×
5 mm., are spindle-shaped with an obtuse apex and longitudinally
ribbed with a stalk at least 7 mm. long. Nathorst considers that
a cupule was probably present: the specimens do not convey the
impression of naked seeds and in some examples there are indications
of an investing envelope, though this may be the result of tearing
of the testa. Nathorst regards the Spitzbergen seeds as probably
specifically identical with a specimen described by Schmalhausen[461]
from Carboniferous rocks in the Urals as _Rhabdocarpus orientalis_
Eich., a species which agrees closely with _Lagenospermum nitidulum_
as described by Heer[462] (under the name _Carpolithes nitidulus_) and
Nathorst[463] from Spitzbergen. It is also possible that Kidston’s
_Rhabdocarpus elongatus_[464], from the Lanarkshire coal-field and
elsewhere, recently transferred by Arber[465] to _Platyspermum_, is
an example of the same species. The chief interest of _Lagenospermum_
lies in the fact, assuming Nathorst’s correlation of the seeds with
_Adiantites bellidulus_ Heer to be correct, that it is a typical
radiospermic seed, while _Wardia_, borne on foliage of the same general
type, is an equally typical platyspermic seed.
CHAPTER XXXII.
CYCADOFILICES.
In this chapter are included several types represented by stems,
but which in the absence of definite information with regard to the
reproductive organs cannot be assigned to the Pteridosperms.
=MEGALOXYLEAE.=
=Megaloxylon.= Seward.
This genus is represented by a single species founded on a piece of
stem from the Lower Coal Measures of Lancashire discovered in the
Binney Collection in the Sedgwick Museum, Cambridge[466]. Nothing
is known as to the leaves, reproductive organs, or roots. The
type-specimen consists exclusively of primary and secondary xylem.
_Megaloxylon Scotti_ Seward.
The type-specimen, reproduced natural size in fig. 446, A, B, consists
of a fragment of stem which at first sight bears a close resemblance
to _Cordaites_, but the apparent pith, 1·9 cm. in diameter, is the
primary xylem of the stele and is enclosed by an incomplete cylinder
of secondary xylem 2 cm. broad. The distinction between the lighter
primary xylem and the darker secondary cylinder is especially well
marked in the longitudinal section (fig. 446, B). The central region,
shown on a larger scale in fig. 447, is occupied by groups of tracheids
varying in size and shape associated with thin-walled parenchyma: the
latter is represented by lighter patches in the section. The majority
of the tracheids are characterised by their great breadth—in some
cases ·4 mm.—and their isodiametric or even horizontally elongated
and flattened form. Some of these large metaxylem elements are seen in
longitudinal section at _m_ in fig. 448 where the shrinkage and partial
decay of the parenchymatous tissue have resulted in the separation of
transverse bands of xylem simulating the discoid pith of a _Cordaites_.
The walls of these tracheal cells are covered with multiseriate pits.
With the short and sometimes flattened xylem elements occur others of
greater length, but these are chiefly met with in the more peripheral
part of the central region where some of the tracheids are much
narrower and have the form of ordinary water-conducting elements. On
one side of the primary xylem in fig. 447 an oval and more compact
group of narrow and longer tracheids is seen at _lt¹_; this is a
leaf-trace about to enter the secondary-xylem cylinder on its outward
course. The same leaf-trace is shown at _lt_ in fig. 446, B; as it
descends the trace becomes less distinct and its elongated elements
gradually merge into the general mass of metaxylem. A portion of this
leaf-trace is seen in fig. 448, B, _lt_, close to the inner edge of
the secondary xylem, _x²_, and abutting internally on the contracted
tissue, _m_, which consists mainly of large and short tracheae with
remains of associated parenchyma. The trace includes some conjunctive
parenchyma interspersed with the tracheids: on its outer surface, that
is on the abaxial edge of the ovate xylem strand as shown at _lt¹_ in
fig. 447, there are six external protoxylem strands. In the peripheral
region of the primary xylem of the section reproduced in fig. 447
there are several more or less well-defined leaf-traces, _e.g._ _lt²_,
_lt³_; these differ from that seen at _lt¹_ in their greater tangential
breadth and in the less compact arrangement of the tracheids. As each
trace is followed downwards in the primary region of the stele it tends
to become broader, especially in a tangential direction; the spiral
protoxylem strands are more widely separated (fig. 448, A, _px_) and
the elongated and comparatively narrow tracheids as they spread out
fan-wise are reduced in length, finally passing over into the broad
and short reticulately pitted cells. Each leaf-trace can be followed
through approximately four internodes before its individuality is lost
in the general mass of metaxylem. The disposition of the peripheral
traces is such as to justify the conclusion that the phyllotaxis of the
stem is ⅖.[467]
[Illustration: Fig. 446. _Megaloxylon Scotti._ A, B. Transverse and
longitudinal sections. _x¹_, _x²_, primary and secondary xylem; _lt_,
leaf-traces. Nat. size. C. Secondary xylem.]
[Illustration: Fig. 447. _Megaloxylon Scotti._ Transverse section of
the primary portion of the stele with leaf-traces, _lt_, and the inner
edge of the secondary xylem.]
[Illustration: Fig. 448. _Megaloxylon Scotti._ A, transverse section
at the junction of the primary and secondary tissues; B, longitudinal
section showing the inner edge of the secondary xylem, _x²_, a
leaf-trace, _lt_, and the metaxylem, _m_.]
The secondary xylem (fig. 446, C) resembles that of _Lyginopteris_
and _Heterangium_ though it is less parenchymatous. The medullary
rays are numerous and vary in breadth from 1 to 5 cells, while the
tracheids, with multiseriate bordered pits on their radial walls, form
bands 1 to 8 elements in breadth. There are no regular rings of growth
but occasional arcs of narrow tracheids interfere slightly with the
otherwise uniform structure of the wood. A leaf-trace in its oblique
outward course through the wood becomes completely enclosed by a
cylinder of secondary xylem and thus appears to be concentric. Owing
to the absence of any tissue external to the secondary xylem of the
stem, statements as to the subsequent behaviour of the leaf-traces on
emerging from the stele are purely hypothetical. It is, however, not
improbable that each concentric trace lost its secondary tissue and
broke up into several collateral strands, a suggestion based on the
behaviour of the leaf-traces in _Medullosa anglica_.
The most striking characteristics of _Megaloxylon_ are: (i) the
structure of the primary xylem, particularly the unusual form of the
majority of the metaxylem tracheids, a form obviously correlated
with storage rather than with conduction of water; (ii) the gradual
spreading of the leaf-traces and their absorption as they descend into
the main mass of the xylem; (iii) the exarch structure of the primary
xylem. Confining our attention to the primary region of the stele; a
comparison is at once suggested with _Heterangium_. In _Megaloxylon_
the peculiarities are the substitution of the large storage-tracheids
for the normal xylem-elements; the greater irregularity in the groups
of metaxylem; and an exarch instead of a mesarch structure. In these
last features the primary xylem agrees with that of recent species of
the Schizaeaceous Fern _Lygodium_ and the external protoxylem is a
character shared with _Rhetinangium_. The occurrence of short tracheids
similar to those of _Megaloxylon_ in the inner portion of the stele of
the Osmundaceous Fern _Zalesskya gracilis_ (Eich.)[468] may be quoted
as an example of parallel modification but, as Scott[469] points out,
the resemblance has no phylogenetic significance. The secondary xylem
though less parenchymatous than in recent Cycads agrees more closely
with the manoxylic than with the pycnoxylic type.
_Megaloxylon_ affords an interesting example of a combination of
primary stelar anatomical features, comparable in the exarch position
of the protoxylem with the stele of _Lygodium_, and secondary wood
similar to that of _Lyginopteris_ and _Heterangium_. The large
metaxylem tracheids may be regarded as derivatives of elements which
in some ancestral type were structurally fitted for the rôle of
water-transport and made up the xylem of a _Lygodium_-like stele with
little or no secondary xylem. As the cambial activity increased and
centrifugal xylem became a prominent feature, usurping the function of
the centripetal xylem, the latter became modified and fitted for a new
service.
=RHETINANGIEAE.=
=Rhetinangium.= Gordon.
_Rhetinangium Arberi_ Gordon.
The stem on which this genus is founded was discovered by Dr
Gordon[470] in the Calciferous Sandstone series of Pettycur: a
specimen collected by Dr Kidston in Berwickshire may be specifically
identical with the Pettycur plant. We know nothing of the leaves or
reproductive organs of _Rhetinangium_. The stem, approximately 2 cm.
in diameter, was probably cylindrical; it possesses a single stele
consisting mainly of a central primary region occupied by anastomosing
groups of tracheids, 130–150μ in diameter, embedded in parenchyma
containing numerous secretory sacs and ducts. In the peripheral region
of the stele the groups of tracheids consist of narrower elements
characterised by exarch protoxylem. Each peripheral group forms the
base of a wedge of secondary xylem (fig. 450, _x²_), the primary
medullary rays being in direct connexion with some of the parenchyma of
the primary xylem. The secondary tracheids, 45–85μ in diameter, have
multiseriate bordered pits on their radial walls and the rays are broad
and deep as in _Heterangium_ and _Lyginopteris_. With the exception of
the external position of the protoxylem, the stele of _Rhetinangium_
is practically identical with that of _Heterangium_, though in
_Rhetinangium_ the primary tracheids form larger and fewer groups. The
inner cortex is composed of thin-walled cells with many secretory sacs:
there are no stereome elements. In the outer cortex (fig. 449, _cr_)
radially disposed bands of stereome form a reticulum with narrow and
very long meshes like that of Medullosan petioles.
The recently recorded occurrence of polydesmic petioles[471] in
_Heterangium_ is of special interest from the point of view of the
comparison of that genus with _Rhetinangium_ and the Medulloseae.
The very broad decurrent petiole-bases are a striking feature, the
major diameter of the pulvinus-like base of the leaf-stalk exceeding
that of the stem (fig. 449, _p_). Several xylem-strands from the
peripheral region of the primary xylem go to form a single leaf-trace:
these U-shaped strands of xylem destined for a leaf are connected
laterally by parenchyma and form an irregularly corrugated band. Fig.
450 shows a petiole-trace still enclosed on each side by the secondary
xylem cylinder _x²_.
[Illustration: Fig. 449. _Rhetinangium Arberi_ Gord. Transverse
section of stem with large leaf-base; _cr_, outer cortex of stem; _p_,
petiole. (After Gordon; × 1¾.)]
There are several protoxylem groups in a leaf-trace, one on the outer
face of each xylem-strand. In the petiole the xylem groups are more
intimately connected and the trace has the form of a flat band with
abaxial protoxylem. There is no indication that a leaf-trace undergoes
division into separate strands. The roots are described as tetrarch
with well-developed secondary xylem.
[Illustration: Fig. 450. Transverse section of leaf-trace of
_Rhetinangium Arberi_ showing the exarch structure; _x²_, secondary
xylem. (After Gordon.)]
The primary xylem of _Rhetinangium_ agrees in its exarch structure with
the Palaeozoic genera _Sutcliffia_, _Megaloxylon_ and _Stenomyelon_,
also with _Lygodium_ and some other recent Ferns: the secondary wood
is of the manoxylic type like that of _Lyginopteris_, _Heterangium_
and other genera. In the general structure of the stele _Rhetinangium_
agrees with _Sutcliffia_ and, except in the exarch structure of
the primary xylem, with the steles of _Heterangium_ and _Medullosa
anglica_[472]; but the structure and origin of the leaf-traces are
characters which mark it off from _Sutcliffia_. The sclerenchymatous
bands in the inner cortex of _Heterangium_ are unrepresented in
_Rhetinangium_, and in the latter genus the abundance of secretory sacs
and ducts is a characteristic feature, moreover in _Rhetinangium_,
the leaf-trace consists of several groups of primary xylem-elements.
Dr Gordon regards _Megaloxylon_ as the type which comes nearest to
_Rhetinangium_; but the differences in the structure of the secondary
wood and the marked contrast between the leaf-traces are too pronounced
to justify a preference for _Megaloxylon_ over _Heterangium_ in the
order of affinity. Gordon considers that the undivided leaf-trace of
_Rhetinangium_ may represent a form transitional between the simple
leaf-trace of _Lyginopteris_ and the much divided type in _Medullosa_.
The external position of the protoxylem is a character to which too
much weight may easily be attached: the difference in position between
the protoxylem of _Rhetinangium_ and _Heterangium_ is in some examples
of the latter genus hardly perceptible. Kubart[473] speaks of the
stele of his species _Heterangium Sturi_ as being almost exarch.
The inconstancy in the position of the protoxylem in the xylem of
Osmundaceous stems and in the primary bundles of _Eristophyton_ and
other Palaeozoic genera is worthy of consideration in this connexion.
[Illustration: Fig. 451. _Stenomyelon tuedianum_ Kidst. Transverse
section of stem. The black patches represent leaf-traces. (After
Kidston; × 1½.)]
=STENOMYELEAE.=
=Stenomyelon.= Kidston.
_Stenomyelon tuedianum_ Kidston. The specimens on which this monotypic
genus is founded[474] were obtained from the Lower Carboniferous
rocks (Calciferous Sandstone series) at Norham Bridge, Berwickshire,
Scotland. They consist of petrified pieces of a flattened stem, a
fragment of a rachis and portions of laminae: there is no evidence as
to the nature of the reproductive organs. The original form of the stem
is obscured by the destruction of a considerable part of the cortex and
the consequent flattening of the whole with the production of wing-like
extensions of the imperfectly preserved tissues enclosing the almost
cylindrical stele (figs. 451, 452).
The stele consists of a bluntly triangular core of primary xylem,
3–4 mm. in diameter, composed almost entirely of reticulately pitted
tracheids reaching a diameter of 160μ: a few parenchymatous cells
occur in the peripheral region and a band of parenchyma extends from
the middle of each of the three sides of the xylem to the centre of
the stele, thus dividing the primary conducting tissue into three
groups which are the expression of a phyllotaxis of ⅓. The tracheids
near the outer face of each xylem-group are narrower than the others
and have scalariform pitting. The secondary xylem first appears along
the slightly concave sides of the primary stele, eventually enclosing
the whole: it consists of tracheids with multiseriate pits on the
radial walls and numerous deep medullary rays 1–6 cells broad. No
phloem is preserved though it is probable that a narrow band was
originally present. A characteristic feature is afforded by a zone of
thick-walled cells, regarded as periderm, encircling the stele and
formed by a deep-seated phellogen. On the outer face of this band there
are projecting bosses, and similar sclerous nests are scattered in the
cortex. The outer cortex has a _Sparganum_[475] type of hypoderm, that
is long vertical strands of fibres alternating with parenchyma. The
leaf-traces are formed from the blunt angles of the primary xylem; an
angle becomes nipped off as a more or less cylindrical strand enclosed
by a zone of secondary tracheids which is very narrow on the adaxial
side (fig. 452). Protoxylem was recognised only in the leaf-traces and
not in the rest of the stele. A pair of protoxylem strands occurs on
the outer edge of a prominent angle of xylem before it becomes detached
from the stele, and these form a single strand at a lower level. As a
leaf-trace passes outwards, the exarch xylem strand becomes mesarch
and there is a single protoxylem group except at a point near the
bifurcation of a trace. In its passage through the cortex a leaf-trace
divides repeatedly, the secondary xylem on the outer face of each
strand being retained for a considerable time.
Our meagre knowledge of the nature of the leaves is based on incomplete
fragments found in association with the stem. The leaf is believed to
have been simple and characterised by a thick lamina with a hypodermal
zone of sclerous strands and several vascular bundles.
[Illustration: Fig. 452. _Stenomyelon tuedianum_. Transverse section
of stele. (After Kidston; × 7.)]
As Kidston and Gwynne-Vaughan[476] remark, _Stenomyelon_ is a very
distinct type; while resembling _Sutcliffia_ in some respects it
differs from that genus not only in the structure of the primary
stele but in the absence of the system of meristeles which form so
characteristic a feature of the latter genus.
=CYCADOXYLEAE.=
=Cycadoxylon.= Renault.
This generic term[477] is applied to a few types of Permian and Upper
Carboniferous stems possessing a vascular cylinder, which may reach a
considerable breadth, of secondary centrifugally developed xylem and
phloem enclosing a large pith containing either a narrow, peripherally
placed, and more or less continuous cylinder of inversely orientated
conducting tissue or scattered bands of centripetal xylem and phloem.
The secondary xylem is manoxylic, while the internal vascular tissue
recalls that of _Ptychoxylon_ and to a less extent the inverted arcs
that are rarely met with in _Lyginopteris_ stems. A brief diagnosis
of two species may serve to illustrate the genus: a third species is
included in _Cycadoxylon_, but it is founded on material too incomplete
to admit of satisfactory diagnosis.
_Cycadoxylon Fremyi_ Renault.
This Permian species[478] is represented by a piece of stem 2–2·5
cm. in diameter (fig. 453, B) characterised by (i) a fairly broad
parenchymatous cortex with secretory canals and several hypodermal
nests of sclerous tissue, (ii) a cylinder of secondary xylem and phloem
nearly the whole of which is centrifugal, (iii) a large pith containing
several scattered narrower bands or arcs of centripetally developed
xylem and phloem. The tracheids, with 4–6 series of hexagonal pits,
form radially disposed rows, 1–4 elements broad, separated by broad and
deep medullary rays. Renault does not mention the occurrence of any
primary xylem as distinct from the secondary centrifugal xylem, but
in a section which I examined some years ago in his laboratory there
appeared to be a group of primary tracheids. There are no anastomoses
between the main cylinder and the internal bands of inversely
orientated tissue.
_Cycadoxylon robustum_ (Seward).
This species[479] is based on a piece of stem from the Lower Coal
Measures of Lancashire first described by Williamson and identified
as an unusually large example of _Lyginopteris_. Williamson and
Scott, while recognising certain features in addition to the large
size of the stem, which must have reached 14 cm. in diameter,
expressed the view that ‘there is a presumption that it really
belonged to a _Lyginodendron_, or to some plant of the same type
of structure.’ The examination of additional material led me to
adopt the name _Lyginodendron robustum_, though I suggested
that possibly _Cycadoxylon_ might be the more appropriate genus.
Subsequently Scott[480] proposed the substitution of _Cycadoxylon_ for
_Lyginodendron_.
The type-specimen consists of secondary xylem agreeing closely in
structure with _Lyginopteris_ and recent Cycads: the pith, 2·9 cm.
in breadth, is incompletely preserved; there is a narrow band of
centripetal xylem[481] at the periphery of the perimedullary region
and close to the inner face of the main mass of wood (fig. 453, C;
the black line marks the position of the centripetal xylem). Nests of
sclerous tissue and secretory canals are scattered in the medullary
parenchyma and deeper in this region are arcs of secondary parenchyma,
possibly periderm. In places the centripetal and centrifugal xylem
are in contact and occasionally the tapered ends of the rows of
centrifugal tracheids merge into groups of primary xylem elements. The
preservation in the central region is far from complete, and although
the occurrence of primary xylem groups is probable it cannot be said to
be positively established. At the inner edge of the centrifugal xylem
and in tangential longitudinal sections a few leaf-traces are seen, but
nothing is known as to the nature of the leaf-traces in their course
beyond the stele nor have we any data with regard to the leaves or
reproductive organs.
This older species differs from _Cycadoxylon Fremyi_ in the limitation
of the centripetal xylem to the outer portion of the pith and in
the presence of sclerous nests in the medullary region, though the
latter character is probably of no great taxonomic value. _Cycadoxylon
robustum_ approaches more closely to _Lyginopteris_, and although the
differences are sufficient to justify a distinctive generic name, there
can be little doubt as to a fairly intimate relationship between this
type of _Cycadoxylon_ and _Lyginopteris_.
=Ptychoxylon.= Renault.
_Ptychoxylon_[482] _Levyi_ Renault. Like many Palaeozoic genera founded
on anatomical features, _Ptychoxylon_[483] is represented only by
stems, our knowledge of the leaves being confined to the leaf-traces
in the stem which appears to have a phyllotaxis of ⅜. The stem of
this Permian species has a diameter of 5–6 cm.: the comparatively
broad cortex contains numerous secretory canals, but in place of
hypodermal strands of stereome there is a superficial periderm. The
vascular tissue, consisting of secondary xylem and phloem, assumes
different patterns at different levels. There is an outer vascular
cylinder of centrifugally developed xylem and phloem; the xylem is
manoxylic and the tracheids have 3–5 rows of bordered pits on the
radial walls. At intervals the continuity of the main stele is broken
by the formation of leaf-gaps and before one gap is repaired a second
may be produced, thus converting the cylinder into two crescentic and
infolded bands (fig. 453, A). A striking character is the occurrence
in the large parenchymatous central region of internal vascular bands
or arcs varying in size and number at different levels and composed
of centripetally developed secondary xylem and phloem. These internal
bands differ from the outer and broader cylinder both in their inverse
orientation and their limited vertical range. The connexion between
the inner and outer vascular tissue and the alteration in plan of the
conducting tissue at different levels are illustrated by fig. 453,
1–4, simplified from some of Renault’s figures of successive sections
through a vertical distance of 4–5 cm. In section 1 the main cylinder
is continuous except for a small gap where a leaf-trace is about to be
given off: there are three internal vascular bands similar in structure
to the outer stele but inversely orientated. At a higher level (section
2) the leaf-gap is larger and in it is a double leaf-trace of two
collateral strands consisting of primary centripetal xylem and a
fan-like group of secondary xylem and phloem. The free edges of the
outer stele of section 1 have curved inwards and united with the two
lateral medullary bands, while the lower internal band of section 1
has increased in extent and forms a discontinuous arc with the upper
portions enclosed by the loops formed by the infolded ends of the outer
vascular tissue. In section 3 a second leaf-gap has been formed in
the outer stele and its invaginated ends have fused with the internal
bands. In section 4 the first leaf-gap is closed and the invaginated
bands of section 3 have broken up into an irregular circle of shorter
bands. The section reproduced in fig. 453, A, shows the main cylinder
in the form of two curved and flattened loops, each composed partly
of the centrifugally developed xylem and phloem of the main stele
and in part of the inversely orientated tissue of the inner bands.
At a lower level the two bands _b_, _b_, will become detached as the
upper leaf-gap is closed and form part of an inner cylinder like the
discontinuous ellipse formed by the two bands _c_. The section of a
branch-stele is seen at _a_.
[Illustration: Fig. 453.
A. _Ptychoxylon Levyi_; transverse section of stem; _a_, stele of
branch. (After Renault.)
B. _Cycadoxylon Fremyi_; transverse section of stem. (After Renault.)
C. _Cycadoxylon robustum_; centre of stem.
1–4, diagrams of sections of the stem of _Ptychoxylon_ at different
levels. (Simplified from Renault.)]
_Ptychoxylon_ differs considerably from _Medullosa_, which Renault
included in the _Cycadoxyleae_, in the plan of the vascular system:
there is nothing corresponding to the ‘partial pith’ or primary region
which forms the central portion of the plate- and snake-rings in
_Medullosa_. The double leaf-trace and the absence of the _Medullosa_
type of hypoderm are other distinguishing features. The paired
leaf-bundles suggest comparison with _Lyginopteris_ among other
genera and, as Scott[484] points out, the internal arcs of inversely
orientated tissue which sometimes occur in the peripheral region of
the pith of _Lyginopteris_ (fig. 405, C, _c_) behave like the internal
bands of _Ptychoxylon_ in occasionally joining the main cylinder at a
leaf-gap; but the differences outweigh the resemblances. As regards the
general arrangement of the vascular tissue in two irregular concentric
circles and their connexions with one another, but not in the structure
of the xylem and phloem, there is a similarity between this genus
and such a Fern as _Matonia_. In the varying patterns formed by the
vascular system at different levels in the stem _Ptychoxylon_ resembles
the Ferns _Polypodium quercifolium_ and _P. heracleum_[485].
=CALAMOPITYEAE.=
=Calamopitys.= Unger.
In 1856 Unger[486] described several fragmentary petrifactions from
Thuringian strata of Upper Devonian age, the majority of which he
referred to the Calamarieae and the Rhachiopterideae. In an earlier
publication[487] he gave a list of species including two families,
the Haplocalameae and the Calamoxyleae, assigned by him to the
group Calamarieae: in the Haplocalameae he placed the new genera
_Kalymma_, _Calamosyrix_, _Calamopteris_, and _Haplocalamus_. These
were subsequently examined by Graf Solms-Laubach and identified as
portions of petioles, for the most part belonging to unknown stems.
In his second family, the Calamoxyleae, Unger included the single
genus _Calamopitys_ represented by the type-species _C. Saturni_. The
type-specimens have been thoroughly investigated by Solms-Laubach[488]
who instituted the family-name Calamopityeae and recognised a close
anatomical affinity between _Calamopitys_ and _Lyginopteris_, a
conclusion which led to the incorporation of Unger’s genus in the
Pteridosperms. Further data have been supplied by Zalessky[489]
and, more recently, by Scott and Jeffrey[490] who have recognised
_Calamopitys_ in Lower Carboniferous beds in Kentucky.
_Calamopitys Saturni_ Unger.
Our knowledge of this and other species is confined to stems and
petioles. One of the largest examples of the species is a piece of
stem with a diameter of 1·5 cm.: the single stele consists of a
parenchymatous pith enclosed by secondary xylem made up of tracheids
with 4–8 rows of bordered pits and medullary rays more than one cell
broad and of considerable depth. Between the inner edge of the wood
and the pith are groups of primary xylem (fig. 454, B, _x_) which,
like those in _Lyginopteris_, constitute the leaf-traces: each has a
single internal protoxylem strand (fig. 455, B). The comparatively
wide cortex consists of parenchyma with a hypoderm of the _Sparganum_
type. Each primary xylem-strand passes out as a single leaf-trace
through the secondary xylem and on emerging divides into two as in
_Lyginopteris_: these branch in the cortex and the two are replaced by
six in the leaf-base (fig. 454, B–D). As seen in figs. 454, C, 455, A,
the boundary between the stem proper and the decurrent leaf-base is
marked by a line of stereome strands. The petioles of _Calamopitys
Saturni_ agree generally in structure with the imperfect specimens on
which Unger founded his genus _Kalymma_[491], so named in reference
to the structure of the hypodermal zone. A specimen described by
Solms-Laubach as a _Kalymma_ petiole occurs in organic connexion with
a stem of _Calamopitys_ (fig. 454, C: a detached petiole is shown in
fig. 454, D). The identification by White[492] of this attached petiole
with Unger’s _K. grandis_ has been confirmed by Scott and Jeffrey. A
fuller account of _Kalymma_ (fig. 456) is given on a later page, as the
petioles so named belong to more than one species of stem.
[Illustration: Fig. 454. _Calamopitys Saturni._ B, stem with
leaf-base; _x_, primary xylem and pith; black patches represent
leaf-traces; C, stem with two leaf-bases; D, section of petiole. (After
Solms-Laubach.)]
[Illustration: Fig. 455. _Calamopitys Saturni._ A, stem with
leaf-bases; × 5. B, stele showing leaf-trace after emerging from the
secondary xylem; × 16. (After Zalessky.)]
In _Calamopitys Saturni_ we have a plant agreeing with _Lyginopteris_
in the possession of secondary xylem of the manoxylic type and in the
structure of the common primary bundles, while it is distinguished
from _Lyginopteris_ by the greater number and by the structure of the
bundles in the axis of the leaf.
_Calamopitys annularis_ (Unger)[493].
This species, originally assigned to the genus _Stigmaria_, has
a more strongly developed primary vascular system and there is a
more decided tendency towards the formation of a continuous zone of
primary xylem on the inner edge of the secondary wood; but where
the protoxylem tracheids occur the metaxylem elements form definite
strands, like those of _C. Saturni_. It has been pointed out by
Scott and Jeffrey that there is some evidence of the occurrence of
tracheids in the parenchymatous pith of this species, an important
feature distinguishing it from _C. Saturni_ and connecting it with _C.
americana_. Information with regard to the behaviour of the leaf-traces
is far from complete, but there are indications that each trace divides
into two before emerging from the secondary xylem[494]. The leaf-traces
in the cortex are concentric as in _C. Saturni_.
_Calamopitys americana_ Scott and Jeffrey.
This Lower Carboniferous species[495] from the Waverley shales
of Kentucky is represented by portions of stems and leaf-bases
and detached petioles. The secondary wood consists of tracheids,
30–60μ in diameter, with deep and broad rays; the small pits on the
tracheids form 5–6 alternating series. Phloem and cambium are very
imperfectly preserved. The outer cortex is of the same type as in other
species. At the inner edge of the secondary xylem there is a ring of
primary xylem strands of mesarch structure composed of rather larger
tracheids, 80–120μ in diameter, separated from one another by narrow
strips of parenchyma. So far the vascular tissue agrees with that of
_C. annularis_. In the American species the axial region is not a
parenchymatous pith but a protostele, consisting of parenchyma and a
larger or smaller number of tracheal groups, the number being less in
stems with a larger central region. The peripheral strands alone are
concerned with the emission of leaf-traces, as in _Heterangium_. Each
primary xylem strand divides into two as it leaves the perimedullary
zone and passes through the secondary xylem as two bundles, each being
accompanied by an arc of secondary tracheids which, in the cortical
region, completely surrounds the primary elements. At a later stage the
single protoxylem of each trace divides into two and before entering
the leaf-base there is a further division. In some specimens leaf-bases
of the _Kalymma_ type were found attached to the stem. The occurrence
of tracheids in the axial region is a distinguishing feature and
suggests a comparison with _Heterangium_, while _C. Saturni_ agrees
more closely with _Lyginopteris_; the species _C. annularis_ would
appear, from the recent observations of Scott and Jeffrey, to occupy an
intermediate position.
_Calamopitys_, as the generic designation is here employed, is confined
to central Germany and Kentucky and occurs in Upper Devonian and
Lower Carboniferous strata. There is, however, some doubt as to the
exact geological horizon of the rocks in both countries though in
neither case is there any question of an horizon higher than Lower
Carboniferous. Certain specimens from the Lower Carboniferous of
Scotland described by Scott[496] as species of _Calamopitys_ have been
made by Zalessky the type of a new genus, _Eristophyton_, and are dealt
with under that name.
_Kalymma._ Unger.
_Kalymma grandis_ (petiole of _Calamopitys_). Under the generic name
_Kalymma_ Unger described specimens from Thuringia of Upper Devonian
age which he assigned to two species, _K. grandis_ and _K. striatum_.
Solms-Laubach has shown that _Kalymma_ is not an independent stem
as Unger believed but a petiole of _Calamopitys_, and this has been
confirmed by Scott and Jeffrey who found a leaf-base with the _Kalymma_
type of structure in connexion with a piece of _Calamopitys_ stem,
probably _C. americana_. An examination of a section (2·3 cm. broad)
of Unger’s _K. grandis_ in the collection of the Geological Survey
enables me to confirm the conclusions recently published by Scott and
Jeffrey. The best specimens of _Kalymma_, which appear to be identical
in essential features with Unger’s type-species, are from Kentucky,
some from the Genessee shales of Upper Devonian age and others from
beds (Waverley shales) believed to be Lower Carboniferous. Through
the kindness of Prof. Bower I have had an opportunity of examining
sections from the older horizon in his possession. The transverse
section reproduced in fig. 456 has a diameter of 3·8 × 2·2 cm.[497]: on
one side the radially placed plates of stereome are clearly shown, and
in the outer portion of the ground-tissue is a ring of vascular bundles
varying in size and shape but with a general tendency to a radially
elongated form. The ground-tissue consists of homogeneous parenchyma:
in one place I noticed what appeared to be a large secretory canal,
but secretory tissue, generally at least, is unrepresented. The xylem
is composed of imperfectly preserved elements, which appear to have
scalariform pits; spiral protoxylem strands, embedded in the metaxylem
as two or four groups, occur near the ends of the long axis of the
bundle and in some cases also near the centre. The phloem probably
surrounded the xylem, though it is not certain whether the arrangement
was collateral or concentric: there are no secondary-xylem tracheids,
though in some places I noticed a tendency to a radial disposition
of cells at the periphery of the vascular tissue simulating an early
stage of secondary growth. Unger’s second species _Kalymma striata_ is
characterised by an arrangement of the bundles similar to that in a
petiole described by Scott and Jeffrey as _Calamopteris Hippocrepis_
which differs from _Kalymma_ in the partial substitution of bands
of vascular tissue for separate bundles and to some extent in the
disposition of the bundles. The two types of petiole _Kalymma_ and
_Calamopteris_, as Scott and Jeffrey state, are very closely allied.
Dawson and Penhallow[498] have also described _Kalymma grandis_ from
Kentucky but they, like Unger, mistook the hypodermal stereome for an
outer zone of vascular bundles. The petioles from Germany and North
America included under the name _Kalymma grandis_, though too similar
to be referred to different species, no doubt represent petioles of
stems which are unquestionably distinct types: as in the case of
_Myeloxylon_ in its relation to the genus _Medullosa_, _Kalymma_ stands
for several closely allied forms of petioles belonging to several
species of _Calamopitys_.
[Illustration: Fig. 456. _Kalymma grandis._ (From a section in the
possession of Prof. Bower; × 4.)]
=Eristophyton.= Zalessky.
_Eristophyton fasciculare_ (Scott). The generic name
_Eristophyton_[499] was proposed by Zalessky[500] for two incomplete
stems of Lower Carboniferous age provisionally[501] referred by Scott
to _Araucarioxylon_ and subsequently to _Calamopitys_[502]. The species
_E. fasciculare_ was founded on material obtained by Dr Kidston from
the Lower Carboniferous of Dumbarton, Scotland, and on a specimen in
the Williamson collection from Northumberland. There is a small pith of
parenchyma, 2–3 mm. in diameter, with eight strands of primary xylem
of varying diameter (fig. 457) and in each a single protoxylem-group.
The primary xylem elements are considerably larger than the secondary
tracheids. These xylem-bundles are leaf-traces and their disposition
points to a phyllotaxis of ⅖. The traces attain their maximum size
when about to pass out through the secondary xylem. The tracheids are
reticulate and scalariform while some have an intermediate type of
pitting. A leaf-trace on reaching the pith gradually moves further
from the xylem-cylinder and may be separated from it by 2–6 layers
of parenchyma: as it passes down the pith the protoxylem strand
assumes an almost endarch position consequent on the reduction of the
centripetal xylem. In Scott’s words, ‘each circummedullary strand
branches at regular intervals; the one branch, that on the anodic
side [turned towards the course of the genetic spiral], becomes the
leaf-trace and passes out, while the other continues its course
up the stem as a reparatory strand, until the next leaf of the
orthostichy has to be supplied[503].’ The secondary xylem consists
almost entirely of tracheids with 3–4 rows of pits on the radial walls
and medullary rays usually one cell broad varying in depth from 1
or 2 to 16 or more cells. A characteristic feature of the secondary
xylem is the occurrence on its inner face of numerous short and broad
tracheae similar to the still larger tracheae in the primary stele
of _Megaloxylon_[504]. Nothing is known as to the behaviour of the
leaf-trace in the extrastelar region, but the fact that an outgoing
trace was found to have two protoxylems points to a subdivision similar
to that of the foliar bundles of _Calamopitys Saturni_. A well-marked
difference between _Eristophyton fasciculare_ and _Calamopitys_ and
_Lyginopteris_ is the more compact structure of the secondary wood;
it is pycnoxylic and not manoxylic. Prof. Zalessky in criticising the
use of the generic title _Calamopitys_ puts forward several arguments
in support of his institution of a new designation: (i) the primary
xylem strands of _Eristophyton_ are not confined to the periphery of
the pith as is the case in _Calamopitys Saturni_, though he speaks of
one leaf-trace in the latter species separated by several layers of
cells from the xylem-cylinder; (ii) some of the pith-cells have thick
walls and dark contents in distinction to the homogeneous parenchyma
of _Calamopitys_, a feature of little importance; (iii) the difference
in the structure of the secondary wood already alluded to, though this
loses some of its significance by the occurrence of narrower rays,
more like those of _Eristophyton_, in _C. annularis_; (iv) the more
elliptical and broader pits in the secondary tracheids in place of the
more regular hexagonal form in _Calamopitys_. While admitting a certain
degree of relationship between the two types, Zalessky asserts that
as yet we have insufficient evidence to justify their generic union.
Scott[505] maintains that Zalessky does not attach sufficient weight
to the form and mesarch structure of the primary xylem bundles as a
feature common to both genera.
[Illustration: Fig. 457. _Eristophyton fasciculare._ Transverse
section showing the relation of primary (black) to secondary xylem.
(After Scott.)]
_Eristophyton Beinertianum_ (Goeppert).
1850. _Araucarites Beinertianus_ Goeppert, Mon. Foss. Conif. p. 233,
Pls. 42, 43.
1872. _Araucarioxylon Beinertianum_ Kraus, in Schimper’s Trait. Pal.
Vol. +ii.+ p. 381.
1888. _Araucarites Beinertianus_ Goeppert and Stenzel, Abh. K. Preuss.
Akad. Wiss. p. 30, Pl. +iv.+
1902. _Calamopitys Beinertiana_ Scott, Trans. R. Soc. Edinb. Vol. 40,
p. 341, Pls. +i.+, +iv.+, +v.+
1909[506]. _Ullmannites Beinertianus_ Tuzson, Result. Wiss. Erforsch.
Balatonsees, Bd +i.+ Teil +i.+ p. 24.
1911. _Eristophyton Beinertianum_ Zalessky, Com. Geol. St Pétersb. p.
24.
The pith, 13–15 mm. in diameter, is rather larger than in _E.
fasciculare_ and is characterised by the occurrence of dark sclerotic
nests surrounded by radially disposed rows of parenchyma. The primary
xylem strands are more numerous and smaller than in _E. fasciculare_
and these increase in diameter as they approach the secondary wood. In
places the primary xylem elements form a more or less continuous band
as in _Calamopitys annularis_. The largest leaf-trace bundles at the
periphery of the pith are mesarch (fig. 458), but as each trace passes
down the pith the reduction in the centripetal xylem is carried further
than in _E. fasciculare_ until the xylem-strand becomes endarch in the
lower part of its course. The secondary tracheids have usually two
contiguous rows of pits and the medullary rays are one cell broad.
[Illustration: Fig. 458. _Eristophyton Beinertianum._ A strand of
primary xylem, showing the protoxylem, _px_, abutting on the secondary
xylem. (× 35. After Zalessky.)]
There can be no doubt as to the generic identity of the two species
referred to _Eristophyton_, but the question as to the degree of
affinity to _Calamopitys_ is more difficult to settle. There is force
in Zalessky’s contention that these two stems should not be retained in
_Calamopitys_: the recently described American species, _C. americana_
Scott and Jeffrey, gives emphasis to the view that the restriction
of _Calamopitys_ to the German (and American) types is the safer
course. While _Calamopitys_ as thus restricted is almost certainly a
Pteridosperm, the inclusion of the types referred to _Eristophyton_ in
the same category rests on a more slender basis.
=CLADOXYLEAE.=
This order was founded by Unger[507] for some imperfectly preserved
stems from Palaeozoic strata in Thuringia and in it he included the two
genera _Cladoxylon_ and _Schizoxylon_. There is some doubt as to the
precise age of the Thuringian beds; they were assigned by Richter to
the Devonian system and subsequently placed in the Culm: Solms-Laubach
in his later reference to Unger’s plants favours a Devonian
horizon[508]. Unger included the Cladoxyleae in the Lycopodiales,
and though this conclusion is not accepted the position of the order
is still uncertain. His genus _Schizoxylon_ has no claim to generic
separation from _Cladoxylon_. An inspection of the illustrations in
the memoir by Richter and Unger reveals a striking resemblance in the
main anatomical features between several types assigned to different
genera and distributed among the Cladoxyleae and Rhachiopterideae
(a term first used by Corda for petrified rachises or petioles of
ferns) and other orders. Solms-Laubach[509], to whom our more accurate
information as to Unger’s plants is chiefly due, is inclined to regard
the specimens referred by Unger to the genus _Arctopodium_ as young
stems of _Cladoxylon_, and he draws attention to a close similarity
between _Hierogramma_, another of Unger’s genera, and _Cladoxylon_.
Paul Bertrand[510] goes further in considering that the following
genera represent one generic type, namely _Syncardia_ (fig. 459, F),
_Hierogramma_, _Arctopodium_, _Cladoxylon_, and _Schizoxylon_. The same
author interprets the fossils so named by Unger as stems and does
not agree with the inclusion of any of them in the Rhachiopterideae.
Without losing sight of the fact that Bertrand’s conclusion is
not based on proof but is the expression of a view suggested by a
close agreement in general anatomical plan, I venture to adopt the
designation _Cladoxylon_ in a wide sense primarily on the ground
that Bertrand’s view is probably correct and in part for the sake of
convenience of description. As Unger’s species of _Cladoxylon_ differ
from one another in features which may fairly be regarded as of minor
importance, they are included under one specific name.
=Cladoxylon=. Unger.
_Cladoxylon mirabile_ Unger[511]. The following are regarded as
specifically identical with or closely allied to _Cladoxylon mirabile_:
_C. dubium_, _Schizoxylon taeniatum_, _Hierogramma mysticum_,
_Syncardia pusilla_, _Arctopodium insigne_ and _A. radiatum_[512].
_i. Stems._ The stems assigned to _Cladoxylon_ are characterised by a
complex system of steles, either simple or branched and occasionally
anastomosing, presenting in transverse section the form of oval or
cylindrical strands or narrow, straight or curved bands arranged on
a more or less clearly marked radial plan (fig. 459, A, B, D). In
some stems the primary vascular tissue is enclosed by secondary xylem
and phloem (fig. 460, B), while in others (Unger’s _Arctopodium_,
_Hierogramma_[513], _Syncardia_) there is no evidence of secondary
thickening. The diagrammatic drawing represented in fig. 459, F, shows
a section of a small axis, regarded by Unger and Solms as a petiole (3
mm. in diameter), containing four vascular strands composed exclusively
of primary xylem, each with one or, in the case of a double strand,
two protoxylem groups. This type may be a slender stem or branch
or possibly a petiole. The other extreme, as regards complexity of
vascular structure, is represented by such stems as those shown in
fig. 459, A, B, D. In Unger’s _Cladoxylon mirabile_ (fig. 459, A;
fig. 460, B) the stem reaches a diameter of 3 cm. and consists of
several radially disposed plates of vascular tissue with an occasional
smaller oval or cylindrical stele embedded in a ground-tissue composed
of thick-walled cells. The plates are curved like a UU or sinuous
and not infrequently anastomosing. In a section of this type figured
by Unger the vascular plates appear to form a complex anastomosing
system, but Solms[514] states that the drawing exaggerates the amount
of fusion between the strands, and an examination of a section in the
collection of the English Geological Survey cut from Unger’s specimen
enables me to confirm this statement. Each vascular plate consists of a
narrow median region composed of primary tracheids with a scalariform
type of pitting surrounded by secondary tracheids with interspersed
medullary rays one cell broad. The thickness of the secondary xylem
varies considerably in the same specimen and in places this tissue
is hardly represented, a fact of importance in view of the very
striking resemblance between _Arctopodium_ and _Cladoxylon_, the
sections referred by Unger to the former genus having steles without
any secondary xylem. The occurrence of one or two elongated spaces
(shown in black in fig. 459, A) near the distal end of each plate mark
the position of the protoxylem tracheids. Fig. 459, C, represents a
stele of a stem referred by Unger and by Solms to _Cladoxylon dubium_
which shows the typical _Cladoxylon_ structure, namely the central
primary xylem with distally placed protoxylem and the enclosing sheath
of secondary xylem. In the stem shown in fig. 459, D (_C. dubium_)
there are 12 steles, each constructed on the plan already described,
differing in their relatively broader and shorter form and in the
greater breadth of the secondary xylem from those seen in fig. 459,
A (_C. mirabile_). The black areas in fig. 459, A, show the primary
xylem, and the protoxylem is seen in fig. 459, C. A stem described by
Dawson[515] as _Asteropteris noveboracensis_ from Devonian beds is
compared by him with Unger’s _Cladoxylon mirabile_ and regarded as
possibly allied to it. The radial plates of xylem in Dawson’s plant
meet in the centre like those of _Asterochlaena_ and the leaf-traces
are of the Clepsydropsoid type.
[Illustration: Fig. 459. A, _Cladoxylon mirabile_, section of stem;
B, _Cladoxylon taeniatum_, section of stem; C, _Cladoxylon dubium_,
section of stele; D, _C. dubium_, section of stem; E, _Cladoxylon (?)
mirabile_, section of petiole; F, _Syncardia pusilla_; G, development
of leaf-trace in _Cladoxylon taeniatum_. (A–E, after Solms-Laubach; F,
after Unger; G. after P. Bertrand.)]
The type of stem for which Unger founded his genus _Schizoxylon_ is
represented in fig. 459, B; there are five small steles in the centre
and external to these eleven radially arranged plates, with oval steles
between them, in the peripheral region of the stem. Each stele consists
of primary (black in the figure) and secondary xylem and agrees with
the steles in the other stems.
From the type of stem illustrated by _Cladoxylon mirabile_ to that on
which the genera _Arctopodium_[516] and _Hierogramma_[517] were founded
is a very small step: the vascular tissue has the same characters
both as regards gross and minute anatomy, but there is no evidence of
cambial activity in the stems referred to the two latter genera, a
difference in itself hardly worthy of generic recognition.
ii. _Leaves._ Before describing a second type of stem referred to
_Cladoxylon_ it is important to consider briefly such evidence as we
have as to the vascular supply of the leaves. Nothing is known of the
reproductive organs and there is no satisfactory information with
regard to the form of the fronds. Solms-Laubach has described the only
known example of a lateral branch of a _Cladoxylon_ stem (fig. 459,
E): this has a single concentric vascular strand of plate-like form
with two blunt projections and there are four protoxylem-groups, two
in the angle of the plate and two at the base of the projections. The
structure is essentially fern-like; the xylem is wholly primary. This
type of vascular strand agrees fairly closely with that of a petiole
described by Unger as _Megalorhachis elliptica_, a section of which
is in the Museum of the Geological Survey[518]. The petiole is oval
in section and laterally winged, and the meristele is tangentially
elongated and has two blunt projections almost identical with those in
fig. 459, F. There is no evidence as to the nature of the supporting
stem, but there can be little doubt as to the close connexion with
_Megalorhachis_ and the section shown in fig. 459, F. In a note
published in 1908 P. Bertrand stated that he had identified several
of Unger’s genera as stems which bore leaf-traces having the form and
structure of _Clepsydropsis_, one of the types referred by Unger to the
Rhachiopterideae and described in the second volume of this work[519]
as a Coenopteridean petiole. Bertrand points out that in the oval or
plate-like steles of _Cladoxylon_, _Arctopodium_, _Hierogramma_, etc.,
there is a single protoxylem group near the distal end of the primary
xylem, and he adds that the leaf-traces were formed of strands cut
off from the distal portions of the vascular plates. Similarly the
hour-glass-like leaf-trace in the primary rachis of _Clepsydropsis_
gives off from each end a ring of xylem to supply a secondary rachis.
These laterally detached annular strands are, he believes, similar to
the leaf-trace cut off from the steles in a _Cladoxylon_ stem. The
conclusion is that _Cladoxylon_ is a fern stem and its leaf-trace
represents the simplest form of the _Clepsydropsis_ type, namely an
oval bundle of xylem with a central protoxylem, which is also the form
of the trace given off from the stem of _Asterochlaena_. Solms[520],
while admitting that Bertrand may be correct in uniting under one
genus _Cladoxylon_ and such types as _Syncardia_, _Hierogramma_, and
_Arctopodium_, disagrees with the view that they are _Clepsydropsis_
stems. A Clepsydropsoid leaf-trace has never been found in direct
association with any of the stems of the _Cladoxylon_ type and such
evidence as there is indicates a leaf-trace of an entirely different
form (fig. 459, E). In his more recent memoir on _Asterochlaena_
Bertrand[521] draws attention to Solms’ figures of a stele of
_Cladoxylon_ (fig. 459, C) in which the distal portion is on the point
of being separated as a small annular strand. This, Bertrand considers,
would gradually become converted into a _Clepsydropsis_ form of stele
as it passed to the petiole. Bertrand’s drawings made from a section
of _Cladoxylon taeniatum_ (Ung.) (fig. 459, G) illustrate successive
stages in the departure of a leaf-trace from one of the plate-like
steles of the stem (fig. 459, B). In fig. 459, G, 1, a piece of the
stele is detached and near its extremity is a group of thin-walled
cells with protoxylem: a later stage is seen in fig. 2, and in fig. 3
a small ring of xylem is being detached which, Bertrand assumes, would
later in its course be converted into the Clepsydropsoid strand (fig.
4), which consists of primary tissue. The weak point in Bertrand’s
contention[522] is the absence of any proof of a true Clepsydropsoid
trace in connexion with a _Cladoxylon_ stem, and there is a strong
probability that the leaf-trace of _Cladoxylon_ has the form shown in
fig. 459, E.
_Cladoxylon Kidstoni_ Solms-Laubach[523].
This species, founded on imperfectly preserved material in Dr Kidston’s
collection from Lower Carboniferous rocks in Berwickshire, is referred
to _Cladoxylon_ on evidence that cannot be regarded as convincing.
The type-specimen consists of a small piece of stem about 3 cm. in
breadth showing three complete oval steles and portions of two others
which seem to be in their original position and probably formed part
of a series of peripheral steles such as those shown in fig. 459, D.
Each stele consists mainly of secondary xylem (fig. 460, A) with some
crushed tissue, presumably phloem, on its outer face. The secondary
xylem is narrower on the inner side of each stele where a wedge-shaped
piece is partially detached. In the centre there is a narrow area
parallel to the long axis of the stele containing crushed tissue which
probably consists of parenchyma and primary xylem, but the preservation
is very imperfect. The secondary xylem has a fairly compact structure
and the rays are narrow, 1–10 cells in depth. The pits of the tracheids
are described by Solms as scalariform with occasionally two rows
of elliptical pits on the radial walls. A careful examination of
the type-specimen leads me to describe the pits as uniseriate and
transversely elongated, very like those of _Protopitys_, or biseriate
and almost circular like those of Conifers, the pits of the two rows
being alternate or sometimes opposite (fig. 460, C): in places three
rows of bordered pits are present. There is a certain degree of
resemblance between the steles of this species and those of the South
African stem _Rhexoxylon_[524], but the data are inadequate for a
satisfactory comparison.
[Illustration: Fig. 460.
A, C. A single stele and tracheids of _Cladoxylon Kidstoni_. (Kidston
Coll. 630 B, 630 C.)
B. _Cladoxylon mirabile_, part of a stele. (Museum of Practical
Geology, 15872.)]
There is a close similarity between the vascular systems of
_Cladoxylon_ and _Medullosa_, but an obvious difference is the
substitution of the oval, transversely elongated, pits on the xylem
elements for the multiseriate pitting of _Medullosa_. In _Cladoxylon
Kidstoni_ the pitting shows transitional forms between a narrow
scalariform uniseriate type and a biseriate or triseriate arrangement
similar to that in the Araucarineae and Cordaitales. In _Cladoxylon_,
as limited by Unger, the presence of secondary wood is a generic
feature, but by the inclusion of _Arctopodium_ and other forms this
character no longer holds good. The inclusion of these more fern-like
stems without secondary xylem brings _Cladoxylon_ (in the wider sense)
into closer contact with _Asterochlaena_, a comparison previously
suggested by more than one author. In _Medullosa_ the development
of secondary xylem is on a larger scale than in _Cladoxylon_, and
the vascular system of the former genus assumes a more complex form.
Moreover the _Myeloxylon_ type of petiole, which is a distinctive
feature of _Medullosa_, differs widely from any form of leaf-trace
associated with _Cladoxylon_.
=Völkelia.= Solms-Laubach.
_Völkelia refracta_ (Goeppert). The generic name _Völkelia_[525] was
proposed by Solms-Laubach[526] as a substitute for _Sphenopteris_[527]
in the case of some petrified stems or petioles associated with
fragmentary impressions of fronds from Lower Carboniferous rocks in
Silesia. Both leaf-impressions and petrifactions were included in the
genus _Sphenopteris_: Solms, while retaining Goeppert’s designation for
the leaf fragments, proposed a new generic name for the petrifactions
on the ground that there is insufficient evidence of their connexion
with the leaves. The short account of Goeppert’s petrified specimen
given by Graf Solms-Laubach in his ‘Fossil Botany[528]’ is supplemented
by a fuller description in a later paper. The fragments of highly
compound fronds are characterised by very small filiform ultimate
segments, but the specimens are too imperfect to afford a clear idea of
the habit of the leaf. The ‘stem’ bears a close superficial resemblance
to that described by Unger as _Cladoxylon dubium_ (fig. 459, C, D) and
was regarded by him as an example of that species: it contains several
radially placed steles represented by fairly well-preserved xylem,
but no phloem has been recognised. The steles vary in size and shape:
five reach almost to the centre (fig. 461, A) and smaller xylem groups
occupy a peripheral position. Each stele is excentric in structure and
consists of (i) an outer zone of secondary tracheids of horse-shoe
form in transverse section, but the apparent gap in the secondary
xylem on the outer edge of each stele is due to the crushing of the
tracheal tissue and to its smaller breadth in the distal part of each
group; this is shown in fig. 461, B, where the apparent gap is seen to
be occupied by distorted and crushed tracheids, _a_, identical with
those which form the rest of the outer zone (fig. 461, B, _b_); (ii)
a zone of tracheal tissue continuous with and originally identical
in appearance—except that the elements are rather narrower—with the
outer secondary xylem; (iii) an excentrically situated island composed
of tracheids enclosing a small central area occupied by thin-walled
parenchyma. This third region, represented by black patches in fig.
461, A, in all probability represents the primary part of each stele
to which the rest of the tissue has been added by the cambium. A
striking feature of the secondary xylem is the absence of medullary
rays: the tracheids resemble those of _Cladoxylon_ and _Protopitys_
in the transverse elongation of the pits (fig. 461, D) which form
either a single row or several irregularly distributed rows. The
primary xylem consists in the peripheral region of tracheids with very
narrow scalariform pitting which at first sight suggest close spiral
bands (fig. 461, C), while the inner tracheids are either annular or
reticulate and associated with elongated parenchyma. The imperfectly
preserved ground-tissue appears to consist of homogeneous parenchyma
with radially disposed bands of stereome in the outer cortex.
[Illustration: Fig. 461. _Völkelia refracta._ A. Transverse section
of a specimen in the Breslau Museum. B. Portion of a stele; _a_, the
crushed xylem on the outer side; _b_, the inner side. C. Longitudinal
section showing the median protoxylem. D. Tracheid from the secondary
xylem. (After Solms-Laubach.)]
Our knowledge of _Völkelia_, though far from complete, justifies its
generic separation from _Cladoxylon_ from which it differs in the
lack of medullary rays and in the structure of the primary portion
of each stele. In the form and arrangement of the pits in the
secondary tracheids _Völkelia_ differs from _Medullosa_ and resembles
_Cladoxylon_. The opinion expressed by P. Bertrand[529] that _Völkelia_
is probably the stem of one of the Zygopterideae is based on the older
accounts of the genus and not on the fuller description of 1910.
=PROTOPITYEAE.=
=Protopitys.= Goeppert.
The only species so far described is that for which Goeppert founded
the genus in 1850, substituting _Protopitys_[530] for the name
_Araucarites_, adopted in an earlier paper, on the ground that
the structure of the xylem denoted a distinct generic type. The
type-species is from the Upper Devonian rocks of Falkenberg in Silesia.
_Protopitys Buchiana_ Goeppert.
1845. _Araucarites Buchianus_ Goeppert, in Wimmer’s Flor. Schlesien
(edit. +ii.+) p. 218.
1847. _Pinites Goepperti_ Unger, Chlor. Protog. p. 31.
1847. _Dadoxylon Buchianum_ Endlicher, Syn. Conif. p. 300.
1850. _Protopitys Buchiana_ Goeppert, Foss. Conif. p. 229, Pl.
+xxxvii.+ figs. 4–7; Pl. +xxxviii.+ figs. 1, 2.
In his Monograph of Fossil Conifers Goeppert figured a large piece
of stem consisting mainly of secondary wood and described the more
important anatomical features. He recognised the narrow, transversely
elongated, pits on the radial walls of the tracheids as a feature of
special interest indicating a type of pitting transitional between that
of Ferns and Conifers. A further description was given by Kraus[531]
who included under Goeppert’s name both the Falkenberg stem and a
second specimen from Basel though the latter is Triassic in age and
a distinct plant; he suggested a comparison of _Protopitys_ with
_Sigillaria_ and _Stigmaria_ rather than with Conifers. It is, however,
to Graf Solms-Laubach[532] that we owe the most thorough account of
this species. Nothing is known of the leaves or reproductive organs.
The largest piece of stem is nearly 1 ft in diameter and consists
mainly of secondary xylem resembling that of Conifers and _Cordaites_
except in the form of the bordered pits on the radial walls of the
tracheids (fig. 462, D). The centre of the stem is occupied by a
parenchymatous pith, elliptical in transverse section, enclosed by
a band of primary xylem composed of large polygonal tracheids (fig.
462, C, _x_¹) characterised by a delicate scalariform pitting on all
their walls (fig. 462, E). The primary xylem forms a narrow layer on
the sides of the ellipse, 1–3 elements broad (fig. 462, A, B), but it
increases in breadth at the ends of the long axis where the tracheids
are intermixed with parenchyma. The primary xylem and pith-tissue at
the ends of the major axis of the central region assume different
forms at different levels, owing to the detachment of leaf-traces and
the consequent formation of foliar gaps as portions of the primary
xylem pass obliquely outwards into the secondary xylem on the way to
the distichously arranged alternate leaves. The diagram, fig. 462, A,
shows the inner part of the secondary xylem (see also fig. 462, C, x²)
which at one end, _lt_, has formed an oval group about to pass out as
a leaf-trace: at the opposite end the strand is detached and divided
into two equal branches. The two swellings of the primary xylem ellipse
shown at _a_ in figs. 462, A and B, are a characteristic feature:
these are clearly seen after the leaf-trace has become detached;
at the inner edge of each of them there appears to be a protoxylem
strand. After the formation of a foliar gap these swellings of the
xylem gradually meet and so re-establish continuity below the outgoing
leaf-trace. No protoxylem has been detected in the actual trace, which
is believed to be concentric. The formation of the leaf-gap and the
shoulders bordering it constitute interesting filicinean features,
recalling corresponding characters in solenostelic Ferns. At the
upper end of the diagram, fig. 462, B, the outgoing leaf-trace is
undergoing dichotomy while at the opposite end the trace has passed
out of view. The secondary xylem shows incomplete rings or arcs of
narrower elements, which at first sight give the impression of annual
rings: the occurrence of similar incomplete or pseudo-rings is a common
feature in _Lepidodendron_ and other Palaeozoic stems. The secondary
tracheids (54·4μ in tangential diameter, 68·5μ in radial diameter) have
usually a single series of broadly oval bordered pits on the radial
walls with here and there two rows (fig. 462, D). In one case only were
the pits of the medullary rays recognised (fig. 462, F). The rays are
uniseriate, generally 1–2 cells deep, but occasionally 3 cells in depth
and very rarely deeper. The cambium is of the normal type, and in some
specimens secondary phloem was found consisting of bands, 4–5 layers
broad, of stone-cells alternating with tubular thin-walled elements,
presumably sieve-tubes.
[Illustration: Fig. 462. _Protopitys Buchiana_. A, B. Central region
of the stem showing the pith, the primary xylem (black in fig. A) and
(A) the inner part of the secondary xylem; _a_, shoulders of xylem
at the leaf-gaps; _lt_ leaf-trace; _px_ protoxylem. C. Secondary,
_x_², and primary xylem, _x_¹. D. Radial longitudinal section of the
secondary xylem. E. Scalariform tracheid of the primary xylem. F. Pits
on the medullary-ray cells. (After Solms-Laubach.)]
As Solms-Laubach says, it is highly probable that each leaf-trace,
which forks close to its exit from the primary xylem, became further
subdivided before reaching the leaf. Morphologically, _Protopitys_ is
of special importance as a type possessing characters that indicate a
connexion with Conifers or Cordaitean genera, notably the structure
of the secondary wood, while the presence of foliar gaps is a feature
reminiscent of Ferns. The primary xylem resembles that of some of
the Palaeozoic arborescent Lycopodiales, but in _Protopitys_ the
interruptions in this tissue are due to the emission of leaf-bundles,
whereas in the discontinuous primary xylem of some Sigillarias[533]
the gaps have no connexion with leaf-traces. Moreover the distichous
leaves of _Protopitys_ and the larger, branched, leaf-traces are other
distinguishing features. The pitting of the primary xylem is like
that in the Lycopodiales and Filicales, while that of the secondary
wood shows a closer approach to the coniferous type. A comparison
may also be made with the transversely elongated pits of _Cladoxylon
Kidstoni_[534].
A piece of wood agreeing anatomically with the Silesian species of
_Protopitys_ has been found in the Yoredale rocks of England[535].
The peculiarities of the genus have been emphasised by Solms-Laubach
by the institution of a family-name Protopityeae: the genus is
essentially a generalised type exhibiting in the structure of its stem
both Filicean and Coniferous features. The bordered pits differ from
those in recent Conifers in their flatter form, but in this respect
they exhibit a closer agreement with the transversely stretched pits of
_Xenoxylon phyllocladoides_ Goth.[536], a Mesozoic species.
CHAPTER XXXIII.
CORDAITALES.
A. =POROXYLEAE=.
=Poroxylon=. Renault.
In 1879 Renault[537] briefly summarised the anatomical features of
some silicified vegetative shoots from the Permian of Autun for which
he instituted a new family, the Poroxyleae. The more complete account
contains a description of two species, _Poroxylon Boysseti_ and
_P. Duchartrei_: the latter was afterwards recognised as a stem of
_Heterangium_. Renault considered this new genus to be closely allied
to _Sigillaria_ and _Sigillariopsis_ and pointed out its resemblance
to _Cordaites_. Additional species have since been described but as
yet the genus has not been found outside France in Permo-Carboniferous
strata of Autun and the St Étienne district. The results of a more
detailed investigation of the anatomy of the genus were published by
Bertrand and Renault in 1882 and since then[538] Bertrand, Renault,
and Scott have added to our knowledge of this interesting type. In
several respects _Poroxylon_ stems present a striking resemblance to
_Lyginopteris_, but the recent discovery of the genus _Mesoxylon_ has
given greater significance to the characters in which _Poroxylon_
agrees with representatives of the Cordaitales. Our knowledge of
the genus, though exceptionally full with regard to the anatomy of
vegetative shoots, does not include any precise information as to the
reproductive organs.
The slender cylindrical stems, not exceeding 2–3 cm. in diameter in
specimens so far recorded, bore large broadly linear leaves similar
in form and venation to those of some species of _Cordaites_ which
were attached singly to slightly swollen nodes separated from one
another by internodes several centimetres long. The base of the
rather fleshy lamina passes imperceptibly from the narrow lower
portion into a tangentially expanded petiole which forms a decurrent
ridge on the stem. Axillary buds frequently occur. Little is known
of the leaf-impressions, but if Grand’Eury[539] is correct in his
identification of certain specimens from French Stephanian beds as the
leaves of _Poroxylon_, the lamina reached a length of 1 met. and a
breadth of 15–20 cm. In habit the stems probably resembled some of the
larger-leaved Bamboos. The only evidence bearing on the nature of the
reproductive organs is furnished by Grand’Eury who believes that some
_Rhabdocarpus_ seeds and bractless inflorescences associated with the
leaves assigned to _Poroxylon_ belong to that genus.
The single cylindrical stele has a relatively large solid pith, the
perimedullary region being characterised by the occurrence of a row
of primary crescentic strands of centripetal xylem of exarch type,
though not improbably in some cases slightly mesarch, varying in
size and shape and forming single or paired bundles. These strands
represent the xylem of collateral leaf-traces similar to those of
_Lyginopteris_ but differing in the absence of well-defined centrifugal
elements: the curved form of some of the xylem strands gives them an
appearance similar to that of the leaf-traces of _Lyginopteris_. The
leaf-traces, except in the lower part of their course through the pith,
are double and pass through several internodes before the centripetal
tracheids die out. The secondary xylem (fig. 463) is manoxylic and very
similar to that of _Lyginopteris_ though rather less parenchymatous.
The secondary phloem and cambium are often very well preserved. No
endodermis and no distinct pericycle has been recognised. The cortex
is parenchymatous and, like the pith and to some extent the phloem,
contains numerous secretory sacs; in the outer cortex the presence of
hypodermal strands is a prominent feature. At an early stage in the
growth of the stem a deep-seated phellogen forms secondary tissue both
externally and internally and decortication ensues.
[Illustration: Fig. 463. _Poroxylon Edwardsii_. A. Transverse section
of stem. B. The central region of another stem of the same species. (A,
× 9; University College Collection; B, from a photograph supplied by
Prof. Bertrand of a specimen in the Renault Collection, Paris.)]
The bundle of each leaf-trace is accompanied by an arc of secondary
centrifugal xylem as it passes through the secondary wood and this is
retained in the leaf except in the finer veins. After entering the
petiole the leaf-trace branches and an arc of bundles is produced, the
concave side facing the upper surface of the thick lamina (fig. 464,
A). Further reference is made to the structure of the leaves in the
description of _Poroxylon stephanense_. The specimens of roots so far
described are characterised by a diarch plate of primary xylem and two
masses of secondary vascular tissue separated by two medullary rays
opposite the protoxylems. Bertrand mentions the occurrence of roots of
_P. stephanense_ with more than two protoxylem strands. The phellogen
was produced in the pericycle as in the roots of recent Gymnosperms. It
is suggested by Lignier[540] that some silicified rootlets from Grand’
Croix (Loire) described by him as _Radiculites reticulatus_ and at
first compared with roots of _Sequoia_ may belong to some Cordaitalean
plant, possibly _Poroxylon_.
_Poroxylon Edwardsii_ Renault.
This species[541] affords a good illustration of the generic
characters already summarised. The strap-like leaves are fleshy
and the occasionally forked, parallel or slightly divergent, veins
are embedded in a homogeneous mesophyll with hypodermal strands of
mechanical tissue. The pith consists of parenchyma in vertical series
with scattered secretory sacs and differs from that of _Cordaites_
and _Mesoxylon_ in the absence of transverse discs. There are 13
primary-xylem strands close to the inner edge of the secondary wood:
the centripetal tracheids are scalariform or have multiseriate pitting
like that in the secondary xylem. The structure of the leaf-traces is
clearly shown in fig. 464: the double trace seen in fig. 464, C, has
two protoxylem-strands accompanied by some parenchyma, and these are
almost enveloped by the metaxylem tracheids which abut on the secondary
wood. At this stage in its course, that is just before bending
outwards, the centripetal xylem reaches its maximum development and the
trace forms a prominent and broad twin-strand in striking contrast to
the two narrower and tangentially extended strands shown in fig. 464,
E, D. Each of these strands with a single protoxylem-group would at a
higher level assume the broader and more compact form and contain two
protoxylems as in fig. 464, C. The tracheids of the secondary xylem
have 4–7 alternate rows of contiguous alternate pits on the radial
walls: the medullary rays are 2–3 cells broad and may be 60 cells deep.
According to Renault[542] several small oblique pits occur on the
radial walls of the ray cells. The secondary phloem, separated by a
normal cambium from the xylem, forms a broad band of sieve-tubes with
lateral sieve-plates like those in _Medullosa anglica_ alternating
with tangential rows of parenchyma. The cortex is relatively narrow
and in older stems is chiefly occupied by secondary tissue formed from
deep-seated phellogens.
[Illustration: Fig. 464. _Poroxylon_. A, B, _Poroxylon Boysseti_.
A, transverse section of leaf in the region of lateral expansion of
the petiole; B, portion of vascular tissue of A. C–E, _Poroxylon
Edwardsii_. C, leaf-trace showing recent separation of the two
protoxylems; D, leaf-trace at a lower level with more widely separated
protoxylems, _px_; E, leaf-trace intermediate between C and D. (From
photographs supplied by Prof. Bertrand.)]
_Poroxylon Boysseti_ Renault.
The stems of this species agree closely with those of _P. Edwardsii_,
the chief difference being in the structure of the secondary phloem
which does not show the regular concentric alternation of sieve-tubes
and parenchyma.
_Poroxylon stephanense_ Bertrand and Renault.
This the oldest species, from Stephanian beds at Grand’ Croix,
differs in no essential features from the other representatives
of the genus. It is from a study of the leaves of this type that
Bertrand and Renault have obtained most of the facts with regard to
the anatomy of _Poroxylon_ foliage. In the median region of the fleshy
leaf the bundles are characterised by a comparatively large amount
of centripetal xylem accompanied by a considerable development of
secondary centrifugal tracheids: the bundles are connected laterally
by both centripetal and centrifugal xylem and thus at certain levels
in the lamina the vascular tissue has the form of a continuous plate
(fig. 464, A, B). The veins become independent on branching and near
the edge of the lamina they consist only of primary elements. Secretory
sacs of elongated form are scattered in the homogeneous mesophyll, and
thick stereome-strands underlie the epidermis. The epidermal cells are
rectangular and rows of stomata occur on both surfaces.
B. =CORDAITEAE=.
=Cordaites=. Unger.
A preliminary statement with regard to nomenclature may serve to
remove possible misconceptions in connexion with the application
of the generic name _Cordaites_. It has been the general practice
to apply this name to certain forms of linear leaves which are
particularly abundant in Carboniferous and Permian strata in Europe
and North America, and in recent years a few palaeobotanists have
substituted _Cordaites_ for _Noeggerathiopsis_ as the more suitable
designation for Permo-Carboniferous specimens abundant in the rocks of
Gondwana Land. It has been customary to assign to _Cordaites_ certain
reproductive shoots, seeds, and stems described under the generic
names _Cordaianthus_, _Cordaicarpus_, _Cordaicladus_, _Cordaioxylon_,
etc. Stems agreeing anatomically in their main features with those of
recent Araucarineae have long been attributed to _Cordaites_, but a
few years ago a new type of stem was discovered which, though almost
identical with that of _Cordaites_, is distinguished by the character
of the primary xylem. For this new type the name _Mesoxylon_[543]
was proposed. Nothing is known as to the reproductive organs borne
on _Mesoxylon_ stems, but the leaves are externally at least
indistinguishable from those referred to _Cordaites_. It is therefore
obvious that when we apply the name _Cordaites_ to leaves or other
plant-organs, under that designation are undoubtedly included specimens
belonging both to _Mesoxylon_ stems and to stems with the characters
of _Cordaites_ (_Cordaioxylon_). Further research may enable us to
subdivide _Cordaites_ into more precisely defined types distinguished
by well-marked morphological characters, but at present the only course
would seem to be to restrict the term _Mesoxylon_ to petrified stems
exhibiting the features of that genus and to retain _Cordaites_ as a
comprehensive designation in accordance with the general account of the
genus given in the following pages. This widely distributed and mainly
Palaeozoic genus is especially well represented in the coalfields of
France where in some localities it contributed largely to the formation
of seams of coal[544], and it is chiefly from the researches of French
Palaeobotanists that our knowledge of its morphology is derived.
_Cordaites_ has shared the fate of most other abundant fossil plants
in the distribution of its _disjuncta membra_ among several genera
and classes, but on the whole the information that is now available
enables us to reconstruct the complete plant with a greater degree of
confidence than is usually attainable.
_Cordaites_ may be described as a forest-tree closely resembling
in habit and probably in size the recent Conifer _Agathis_, more
especially such species as _A. macrophyllus_, _A. vitiensis_ and others
with leaves considerably longer than those of the Kauri Pine (_A.
australis_)[545]. The main stem reached a considerable height before
giving off scattered branches bearing spirally disposed, sessile, and
often crowded leaves[546] like the foliage of _Agathis_. The absence of
any evidence of a two-ranked arrangement of leaves on lateral branches
suggests a general tendency towards a vertical rather than a horizontal
direction of growth. The sessile and closely set leaves for the most
part of leathery texture vary considerably in length and breadth in
different types (figs. 466–472): in some the broadly linear lamina with
its parallel veins and perfectly constructed I-shaped girders (fig.
465) reached a length of nearly 100 cm., in shape like the blade of
a straight broad-sword or the leaves of a _Yucca_, torn by the wind
into strips; in other forms the lamina is shorter and more obovate,
while in some the leafy shoots must have looked like slender stems of
the smaller-leaved Bamboos. There is no proof that young vegetative
branches with their spirally rolled leaves[547] were protected by
bud-scales, but some oval triangular scales (fig. 468, C), occasionally
found in association with larger foliage-leaves, may have served that
purpose. The branches from which leaves had recently fallen at the
time of fossilisation are characterised by transversely elongated
oval scars, occasionally showing a slightly curved row of pits like
the marks of leaf-traces on the scars of a Horse Chestnut, sometimes
terminating a feebly projecting decurrent leaf-cushion (fig. 466, C).
The leaves persisted for a comparatively long period as in _Araucaria
imbricata_, and on older leafless branches the scars are transversely
stretched; the leaf-cushion loses its individuality and eventually the
development of secondary cortical tissue causes the exfoliation of the
superficial bark.
In the form and structure of the fertile shoots _Cordaites_ parts
company with _Agathis_; the trees bore no cones in the ordinary sense,
but unisexual inflorescences—whether on one plant or on different
individuals is uncertain—were produced in the axils or from a
supra-axillary position as compound spikes or compact racemes. Both the
longer female shoots and the shorter and more compact male branches are
constructed on a similar plan. The ovulate inflorescence may exceed 30
cm. in length (fig. 479); a stout axis bears two-ranked linear bracts
subtending short lateral bud-like shoots with one or several sessile
or stalked ovules (fig. 480) between the sterile scales. The seeds
are platyspermic and agree much more closely with those of Cycads
and _Gingko_ than with the seeds of Conifers. The male inflorescence
is on a smaller scale, in habit not unlike the elongated male shoot
of _Cephalotaxus pedunculata_ and some other Conifers; each bract
subtends a small oval bud composed of imbricate scales and highly
modified microsporophylls borne singly or in clusters (figs. 481,
F; 482). A microsporophyll consists of a comparatively long pedicel
bearing at its apex a few long microsporangia. The term microsporophyll
implies a morphological interpretation which is not accepted by all
palaeobotanists, some of whom prefer to regard the microsporangia as
stamens or microsporophylls reduced to their simplest terms and sessile
on an elongated flower-stalk.
The stem agrees very closely in its more important features with that
of an _Araucaria_ or an _Agathis_: the primary xylem forms the inner
surface of the thick cylinder of secondary wood, merging gradually into
it as in recent Conifers; there are no separate bundles of primary
centripetal xylem. The medullary rays are narrow: in other words
the secondary xylem is of the pycnoxylic type. The pitting of the
tracheids is Araucarian and, as in _Agathis_, the leaf-traces arise
as twin-bundles. The pith is larger than in the Araucarineae and more
homogeneous in structure; it shares with the pith of _Juglans_ and some
other recent plants an almost constant tendency to assume a discoid
structure. Anatomically the leaves agree more closely in the structure
of the vascular bundles with Cycads than with Conifers though there are
points of contact with both of these classes. The roots branch freely
and their horizontally extended arms (figs. 468, A; 478) suggest growth
in swampy ground; anatomically they conform to the recent Gymnospermous
type and there is good evidence that in some cases fungal mycelia lived
symbiotically in the cortex of coralline rootlets.
Sternberg[548] figured some leaves of _Cordaites_ from Carboniferous
rocks in Bohemia under the generic name _Flabellaria_ in the belief
that they belonged to a Palm. Brongniart substituted a new name
_Pycnophyllum_[549] on the ground that Corda had disproved the
supposed relationship with Monocotyledons. The name _Cordaites_ was
instituted by Unger[550], his definition being based on leaf-form as
well as on stem-anatomy. It has recently been proposed to revive the
forgotten designation _Pycnophyllum_[551], but the reasons given are
hardly likely to induce botanists to discard the familiar generic
name which perpetuates the memory of Corda. As already pointed out,
the name _Cordaites_, even though employed in what has always been
regarded a legitimate sense, is no doubt often given to specimens
of some other allied member of the Cordaitales which can only be
recognised as such in the case of more completely preserved material.
The naming of wood of the Cordaitean type, but which may equally well
belong to another genus, raises a difficult question: if there is
satisfactory evidence from collateral sources that the wood is that
of a _Cordaites_ Grand’Eury’s name _Cordaixylon_[552] or Schenk’s
form _Cordaioxylon_[553] may be used, though there seems to be no
adequate reason against the use of the name _Cordaites_. If there is no
confirmatory evidence available and it is impossible to say whether the
wood is that of a Conifer or a _Cordaites_, or some other plant with
the same type of secondary xylem, Endlicher’s term _Dadoxylon_[554] is
most conveniently employed. The confusion liable to follow from the
use of the two generic names _Dadoxylon_ and _Araucarioxylon_ for
wood of the same type differing only in geological age is an argument
in favour of extending _Dadoxylon_ to all specimens having certain
anatomical characters, which cannot be certainly assigned either
to the Araucarineae or the Cordaitales, irrespective of geological
age. The term _Cordaicladus_ sometimes applied to branches is hardly
necessary, but the subgeneric names _Eu-Cordaites_, _Dory-Cordaites_,
and _Poa-Cordaites_, instituted by Grand’Eury for different forms of
leaf, are frequently employed and serve a useful purpose as descriptive
terms though the characters which they connote are of small importance
and by no means always well defined or constant. For inflorescences it
is customary to adopt the name _Cordaianthus_ suggested by Grand’Eury
as a substitute for _Antholithus_ and some other terms. The same author
uses _Rhizo-Cordaites_ for roots.
The nomenclature of seeds is more difficult: in a few instances seeds
occur in organic connexion with Cordaitean shoots, but there is no
doubt that many platyspermic Palaeozoic seeds preserved as detached
fossils belong to _Cordaites_ or some other member of the group.
The difficulty is that in the present state of knowledge we cannot
definitely determine in many cases whether a seed is Cordaitean or
whether it belonged to a genus of Pteridosperms. For this reason the
account of several seeds that were probably borne on _Cordaites_ or
some allied genus is given in a later chapter devoted to Gymnospermous
seeds. There is no doubt that under the generic names _Cardiocarpus_,
_Cordaicarpus_, and _Samaropsis_ are included true Cordaitean seeds,
though it would be incorrect to say that all the seeds so named belong
to members of the Cordaitales.
_Cordaites_ reached its maximum development in the Carboniferous and
Permian periods; the genus or some closely allied types persisted into
the Triassic and Rhaetic periods, and there is reason to believe that
the group was represented in some post-Rhaetic floras. The genus is
one of many remarkable examples of the high degree of specialisation
attained by Palaeozoic plants. The complex mechanisms represented by
_Cordaites_ and similar types give force to the conviction that we
cannot hope to penetrate below the higher branches of the genealogical
tree which had its roots in a period of the earth’s history
inaccessible to botanical investigation. The plants of the present
age are to a large extent the result of evolutionary tendencies more
correctly described as the result of degeneration or simplification
than as the latest phase in a series composed of a succession of
types gradually growing in complexity. _Cordaites_ is essentially a
generalised type, a composite product of an age characterised by an
activity in the elaboration of the complex from the simple. Botanical
records furnished by the geological series available for investigation
furnish evidence of the sorting of characters among gradually
diverging races and of changes in plant-organisation tending towards
simplification and increased efficiency.
_Cordaites_, using the generic designation in a wide sense, occurs
in Carboniferous and Permian strata in Europe, North America, and
China; it is recorded from several localities in Russia and Siberia
for the most part from Permian rocks, from Permo-Carboniferous (Lower
Gondwana) beds in India, Australia, South Africa, and South America.
Wood agreeing generally in the structure of its secondary tracheids
with that of _Cordaites_ is represented in Devonian rocks, and
there can be no doubt as to the existence of Cordaitalean plants in
pre-Carboniferous floras. It is represented in the Rhaetic flora of
Tonkin and has recently been discovered in strata probably of Rhaetic
age in Mexico.
+Leaves.+
It is important to recognise the fact that leaves included under
the generic name _Cordaites_ were in many cases not borne on stems
or branches with the anatomical characters of _Cordaites_. Scott in
his account of the genus _Mesoxylon_ says, ‘I feel no doubt that
most of the British specimens of Cordaitean leaves really belong to
_Mesoxylon_, which is a much commoner type of stem in the Coal Measure
petrifications than that of _Cordaites_ itself[555].’ Some of the
Cordaitean leaves were probably attached to stems of the _Poroxylon_
type[556] and it is not improbable that, as investigations are
extended, additional genera of vegetative shoots will be discovered
provided with leaves similar at least in external characters to those
which it is customary to refer to _Cordaites_. In the present state of
our knowledge we cannot make use of anatomical characters as criteria
by which to distribute the foliage of the _Cordaites_ form among the
genera _Cordaites_, _Mesoxylon_, and _Poroxylon_, using these names as
designations of certain types of anatomical structure. The specimen
reproduced in fig. 465 is in all probability a piece of a leaf of
_Cordaites principalis_, but on anatomical grounds Miss Benson[557]
has made it the type of a new species, _C. Felicis_, and more recently
Scott[558] has brought forward evidence supporting the view that it
is a leaf of _Mesoxylon_. As, therefore, neither impressions nor
petrifications of Cordaitean leaves can in the great majority of cases
be referred with confidence to their respective genera of stems,
pending fuller information the only course would seem to be to use
the name _Cordaites_ in a comprehensive sense indicating in special
cases where evidence is available the more precise systematic position
of the specimen. The classification of Cordaitean leaves proposed by
Grand’Eury[559] is based partly on the form of the lamina and in part
on the equality or inequality of the ‘veins.’ The actual veins, which
are embedded in the fairly thick mesophyll, do not directly affect the
superficial ribbing on the carbonised impression of the leaves and, as
seen in fig. 465, the most prominent hypodermal strands of supporting
tissue which would appear as the main veins or primary ribs on an
impression do not correspond in position with the vascular bundles.
Although in some cases the largest stereome-strands coincide with the
veins, forming the upper and lower parts of I-shaped girders the centre
of which is occupied by the veins, this is by no means always the case.
Grand’Eury has drawn attention to the difference between the upper and
lower surface of some carbonised leaves: in _C. crassifolius_ (fig.
468, D)[560] there are five to seven finer ribs between each pair of
primary ribs on one face while the other shows ridges and grooves with
a rib corresponding to each. Attention is called on a later page to the
variable character of the ribbing even on different parts of the same
lamina. The lower surface of the leaf, seen in section in fig. 465,
would show a number of approximately equal ribs, or possibly primary
ribs (midway between the veins) separated by two interstitial ribs,
while on the upper face there would be three rather smaller secondary
ribs. In a section of a leaf called by Renault _C. crassus_[561], a
specific name used also by Lesquereux[562] for an impression of a
leaf originally described by Goeppert as _Noeggerathia crassa_, there
are deep stereome-strands between the veins next the lower epidermis
alternating with single smaller strands, while on the upper surface
the hypodermal strands occur only immediately above the veins. In a
section figured by Felix[563] from North Germany as _C. robustus_,
the hypodermal stereome forms continuous bands; on the upper face the
bands are uniform in thickness but next the lower epidermis they form a
series of ribs.
Grand’Eury’s subgeneric terms _Cordaites_, _Dory-Cordaites_, and
_Poa-Cordaites_ have therefore very little value as regards differences
in the ribbing of leaf-impressions: the large size of leaves included
in _Dory-Cordaites_ and the more acute apex of the lamina as compared
with the obtuse apex of smaller leaves of _Cordaites_ are features of
limited application and of minor importance as diagnostic characters.
The name _Poa-Cordaites_ is, however, usefully employed for the
narrower linear leaves with an obtuse apex.
The structure of a _Cordaites_ leaf is clearly shown in fig. 465; the
lamina is approximately 1 mm. thick and there are about 30 veins in a
breadth of 2 cm. Strong I-shaped girders with the webbing composed of
thick-walled cells divide the mesophyll into rectangular compartments:
the intervening hypodermal strands differ in number and size on the two
faces. The epidermis is not preserved: specimens of other leaves show
that the stomata[564] occur in rows on the lower surface. The mesophyll
shows no differentiation into palisade and spongy parenchyma, and in
this respect the leaf agrees with many other forms; but in some leaves
the palisade-tissue is well developed, as in _C. lingulatus_ Ren.[565]
The central region of the lamina consisted of lacunar tissue, portions
of which are preserved, with a more compact sheath of parenchyma
enclosing each vein. In some leaves there is a narrower sheath of
thick-walled cells more sharply contrasted with the mesophyll. The
vascular bundles agree in structure with those in the rachis of a
Cycadean frond more closely than with the veins of an Araucarian
or other Coniferous leaf. The xylem consists mainly of centripetal
elements which form a deltoid strand with the protoxylem at the apex,
and in close association with this is a larger or smaller amount of
narrower centrifugal tracheids: in the section shown in fig. 465 the
centrifugal xylem may extend all round the centripetal tracheids,
but it usually forms an irregular arch with its base attached to the
sides of the larger tracheal strand, _cp_, separated, except at the
base of the arch, by a small amount of conjunctive parenchyma from the
centripetal xylem. The phloem is not preserved and is represented only
by a few patches, _ph_, below the centrifugal tracheids. Dr Benson[566]
in her account of this type of leaf gives additional details and
compares the anatomical features with those in other species. The
dual nature of the xylem like that characteristic of recent Cycads
has usually been regarded as a definite feature of Cordaites leaves;
Dr Stopes, on the other hand, interprets the narrower tracheids
(occupying a position similar to those in fig. 465) in some sections
of a leaf identified with _C. principalis_ from Grand’ Croix, as an
inner sheath of transfusion elements (‘primitive transfusion tissue’)
possibly derived from the centripetal xylem with which it is clearly
connected at the sides precisely as in fig. 465; but in the Grand’
Croix leaf the phloem is enclosed within the sheath of narrower
tracheids and not external to it as it is in the section shown in fig.
465 and in a section of _C. lingulatus_ figured by Dr Stopes. It is,
however, difficult to recognise any fundamental difference between the
‘inner transfusion tissue’ and centripetal xylem. The cells of the
outer sheath in Dr Stopes’s specimens of _C. principalis_ have bordered
pits on their walls and this character is mentioned also by Renault in
other specimens.
[Illustration: Fig. 465. _Cordaites_ leaf (_Cordaites Felicis_
Bens.), probably borne on a _Mesoxylon_ stem. _cp_, centripetal xylem;
_ph_, phloem; _px_, protoxylem. (Kidston Coll. No. 2194.)]
Prof. Lignier[567] has described the structure of fragments of adult
leaves from the Stephanian of Grand’ Croix (Loire) which he refers
to _Cordaites lingulatus_, and the same author gives an interesting
account of the anatomical features of a bud of the same species. The
bud, which resembles in general appearance that of _Dolerophyllum_
(fig. 430, p. 133) is 3 cm. long, oval in transverse section—as the
result of compression—and consists of four convolute leaves and a piece
of a fifth. The outer leaves have 75 to 80 veins: the inner laminae are
sinistral in their curvature while the three outer leaves are dextral.
In the second, the first in which the tissues are recognisable, the
small desmogen-strands afford some evidence that the phloem preceded
the xylem in the order of differentiation as is often the case in
recent plants. The first tracheids occur almost in the centre of
the desmogen-strand and to these are added the other tracheids of
the centripetal xylem, the oldest elements being spiral, the next
scalariform and the later tracheids reticulate. The centrifugal
xylem is formed at a later stage, and at about the same time are
differentiated the elements called by Dr Stopes the inner sheath and
by Lignier the ‘bois diaphragmatique.’ Lignier also describes the
development and structural features of the other tissues of the young
leaves and compares the anatomical features of the French leaves with
those of _Cordaites Felicis_ described by Prof. Benson.
The main features of _Cordaites_ leaves are (i) the presence of two
kinds of xylem in the veins, the larger centripetal tracheids, or chief
water-conducting elements, and the narrower tracheids, in some cases
attached to the sides of the centripetal xylem, in others forming free
groups, usually between the protoxylem and the phloem, but sometimes
enclosing the phloem; (ii) the frequent presence of a well-defined
sheath of cells round each vein composed of comparatively thick-walled
elements comparable with the transfusion-tracheids in Conifers; (iii)
the presence of lacunar tissue in the centre of the mesophyll and in
some cases of transversely extended tracheids similar to those in some
Podocarp leaves; (iv) a well-developed system of stereome-strands
and I-shaped girders. The structural features on the whole suggest a
xerophilous type, and the frequent absence or feeble development of
palisade tissue points to diffused rather than to brilliant sunlight.
The considerable range in size and form among Cordaitean leaves as well
as the obvious dependence on conditions of preservation or growth of
such a relatively unimportant feature as the presence or absence of
the so-called false or interstitial veins—the variability of which has
been demonstrated in several instances—renders specific determination
exceedingly difficult. The following species are briefly described
rather with a view to illustrate the nature of the characters employed
by authors than as implying the existence of so many well-defined types.
_Cordaites principalis_ (Germar).
This species was founded[568] on a large specimen from the Coal
Measures of Wettin showing a fan-like cluster of longitudinally torn
and partially overlapping leaves spread out in the position that
would be assumed on the compression of a shoot with a close spiral
phyllotaxis. This form of _Cordaites_ is the most abundant in the
British Coal Measures. The broadly linear lamina is characterised by an
obtuse apex (fig. 466, A), a tendency to split into strips, close-set
parallel ribs, the stouter ribs or veins separated from one another
by 2–3 or it may be as many as 5 finer ribs or interstitial ‘veins.’
A statement by Weiss that in Germar’s type-specimen the longitudinal
ribbing of the lamina is very imperfectly preserved confirms the
scepticism that is justly felt as to the validity of this character as
a satisfactory specific criterion.
[Illustration: Fig. 466. A. _Cordaites principalis_, part of leaf.
_B. Artisia_ _transversa_, pith-cast. C. _Cordaites principalis_,
branch with leaf-scars. (A, ⅖ nat. size; B, C, nat. size; Kidston
Coll.)]
The incomplete example shown in fig. 466, A, is 19·5 cm. long and has
a maximum breadth of 3·5 cm., but the complete leaf was much larger
and tapered gradually to the comparatively broad and slightly concave
or amplexicaul base. The narrow elliptical proximal end of a specimen
figured by Kidston[569] from the Middle Coal Measures of Yorkshire is
2·8 cm. broad indicating that the tangentially expanded leaf-scars on
a branch recently deprived of its foliage must have been a conspicuous
feature. In his synonymy of this species Kidston[570] includes _Knorria
taxina_, a species founded by Lindley and Hutton[571] on a piece of
stem from the Coal Measures of Newcastle. The type-specimen, as Mr
Howse[572] states, is much larger than the published drawing and
closely resembles in the decurrent leaf-bases with broad apices the
piece of stem represented in fig. 466, C, which Kidston identifies as
_C. principalis_. Geinitz[573] refers to this species the seeds named
_Cordaicarpus Cordai_ (Gein.), but there is no evidence of connexion.
Kidston[574] points out that this seed is rare in Britain: he believes
that _Cordaianthus Pitcairniae_ (Lind. and Hutt.) is probably the
inflorescence of _C. principalis_.
_Cordaites principalis_ occurs in both Carboniferous and Permian
strata. The leaves described by Lesquereux[575] from Pennsylvania as
_C. Mansfieldi_ agree closely with _C. principalis_. Another similar or
possibly identical form is represented by _C. Ottonis_ Gein.[576]
_Cordaites borassifolius_ (Sternberg).
The leaves of this species, originally referred to _Flabellaria_[577],
resemble those of _C. principalis_ but differ in the ovate-lanceolate
and less obtuse apex and in the presence of only one or rarely two
finer striations between the stronger ribs. Corda’s drawing[578]
affords a good illustration of the crowded spiral disposition of the
foliage comparable with that on an _Agathis_ shoot. The lamina is
usually 4–8 cm. broad but in exceptional cases may reach a breadth
of 12 cm. The species occurs in the Coal Measures, especially in the
Westphalian series and in Permian rocks. Feistmantel[579] unites with
this type _Cordaianthus Pitcairniae_ (fig. 480, A), but as in other
cases there may be a confusion between _C. borassifolius_ and _C.
principalis_. Leaves described by Lesquereux as _C. communis_[580]
are, as White says, not distinguished by any well-marked characters
from this species. White[581] figures some good examples of _C.
borassifolius_ from Missouri, reaching in one case a length of 40 cm.,
showing on the lamina the fructifications of a fungus, _Hysterites
cordaitis_[582] Grand’Eury. The leaves described from Canada and the
United States as _C. Robbii_[583] Daws. are closely allied to if not
identical with Sternberg’s type. Among other species differing in
no definite character from _C. borassifolius_ is _C. lancifolius_
described by Schmalhausen[584] from the Permian of Russia.
_Cordaites lingulatus_ Grand’Eury.
The leaves of this species[585] are characterised by the obovate
lamina and bluntly rounded or almost truncate apex; it affords a
good illustration of the uncertainty of the ribbing as a diagnostic
character. The lamina of a well-preserved specimen from the Blanzy
coalfield described by Zeiller[586] reaches a length of 35 cm. and a
breadth of 10–11 cm. decreasing to 4 cm. at the base (fig. 467). In the
lower part of the lamina Zeiller describes the ribs as unequal in
prominence, the stronger ones being separated by 1–3 finer ribs, while
in the middle and upper portions the ribs appear to be of equal size.
Some of the finer ribs are due to folding of the lamina and are not
represented, as are the ribs due to the presence of stereome-strands,
by dark streaks in the detached cuticle.
[Illustration: Fig. 467. _Cordaites lingulatus._ (After Zeiller; ⅚
nat. size.)]
Reference has already been made to the anatomical features of leaves of
this species described by Lignier[587] and other authors.
_Cordaites grandifolius_ Lesquereux.
The leaves so named by Lesquereux[588], from the Coal Measures of
Pennsylvania, are distinguished by the elongate cuneate lamina, which
reaches a length of 38 cm. with a narrow base and a slightly rounded
truncate distal end, 16 cm. broad, characterised by a few broad and
shallow crenulations. By contrast with some American specimens in Dr
Kidston’s collection Lesquereux’s figures convey an imperfect idea of
the size of the leaf. A large leaf from the Coal Measures of Belgium
described by Cambier and Renier as a new species of _Psygmophyllum_,
_P. Delvali_[589], is perhaps identical with the American type; the
lamina of sub-triangular form has approximately the same dimensions;
the veins are numerous and repeatedly forked. The leaf is much longer
than any known _Psygmophyllum_ and the veins are much more numerous
than in _P. majus_ Arb.[590], the largest representative of that genus.
Palaeobotanists who have seen the type-specimen inform me that they
have no doubt as to the Cordaitean nature of the Belgian specimens,
which may be designated _Cordaites Delvali_. It is, however, not
impossible that _Psygmophyllum_ and _Cordaites_ are allied genera: our
knowledge of the former is limited to unimportant characters.
_Cordaites_ (_Dory-Cordaites_) _palmaeformis_ (Goeppert).
This Permian type, originally described by Goeppert[591] as
_Noeggerathia palmaeformis_, is characterised by numerous slender
veins: according to Weiss[592] there may be as many as 3–5 in 1 mm.
The leaf is broadly lanceolate; it tapers gradually to an acute
apex reaching a length of 80 cm. and a breadth of 10 cm. In habit
the young foliage-shoots[593] resemble those of _C. principalis_ and
_C. borassifolius_. Grand’Eury records the frequent association of
_Samaropsis_ seeds with this species; it occurs in Upper Carboniferous
and in Permian strata and is recorded from a few British localities.
_Cordaites_ (_Poa-Cordaites_) _microstachys_ Goldenberg.
Weiss[594] first figured this species from drawings supplied by
Goldenberg at whose suggestion the name _C. microstachys_ was adopted.
The type-specimen consists of a slender axis bearing numerous narrow
linear leaves and a few imperfect fertile axillary shoots. A specimen
is figured by Kidston[595] from the Upper Coal Measures of Radstock: it
is a rare type in Britain. The species is readily distinguished from
_C. principalis_ and similar forms by the narrow lamina which varies
considerably in length, rarely as long as 30 cm. and not exceeding 1
cm. in breadth. The apex is obtuse and the ribs are either equal in
strength or 1–2 finer striae may alternate with the stronger ribs. The
base of the lamina is 3–4 mm. wide and the leaf-scars have a slightly
arched upper margin and an almost straight lower edge[596]. The foliage
of this species, generally regarded as identical with _C. linearis_
Grand’Eury, bears a close resemblance to that of the Mesozoic genus
_Phoenicopsis_ from which it is distinguished by the occurrence of the
leaves in bunches.
_C. gracilis_ Lesq.[597] is a similar type. The shoot on which
Lesquereux founded his genus _Desmiophyllum_[598] may perhaps be an
example of _Poa-Cordaites_. _Poa-Cordaites tenuifolius_ Schmal.[599]
from the Permian of Russia may be identical with _C. microstachys_.
As examples of other forms of leaf referred to _Cordaites_, though as
in other cases without any proof of connexion with branches having the
anatomical features of the genus, reference may be made to _Cordaites
circularis_ Grand’Eury[600] from Gard (fig. 468, B) and a smaller leaf
from the same locality compared with _C. Lacoei_ (fig. 468, C) Lesq.
_Cordaites circularis_ is characterised by the almost orbicular lamina
traversed by slightly spreading veins; it recalls some of the larger
_Cyclopteris_ pinnules of Pteridosperm fronds and is indistinguishable
from some leaves assigned to the genus _Dolerophyllum_[601].
[Illustration: Fig. 468. A, _Cordaites_ root-system
(_Rhizo-Cordaites_); B, _Cordaites circularis_ leaf; C, _Cordaites_
sp., cf. _Cordaites Lacoei_; D, _Cordaites crassifolius_, upper and
lower surface of leaf. (After Grand’Eury.)]
The species _C. Lacoei_ was founded by Lesquereux[602] on some detached
specimens 3–12 cm. long and 1·5–5 cm. broad; it is by no means certain
that a specimen referred by Grand’Eury[603] with some hesitation to
this species is Cordaitean.
The generic name _Scuto-Cordaites_ was proposed by Renault[604] for
a specimen from Commentry consisting of a flattened branch bearing
a few imperfectly preserved leaves. The surface of the branch shows
semicircular leaf-scars on decurrent, spirally disposed leaf-cushions
and bears a certain resemblance to a slender stem of a Clathrarian
_Sigillaria_. The leaves of the type-specimen of _Scuto-Cordaites
Grand’Euryi_ appear to be broadly linear, 13 cm. long, the breadth
gradually increasing from the base: a short distance from the proximal
end the lamina is broken up into narrow segments; the veins are ·5 mm.
apart with finer striations between them.
Some specimens from Pennsylvania made by Dawson[605] the type of
a new sub-genus and named _Dictyo-Cordaites Lecoi_ agree in shape
and arrangement with some species of _Cordaites_, but differ in an
occasional anastomosis of the veins as in _Psygmophyllum flabellatum_.
It is, however, impossible to determine the true nature of the fossils
from the published figures.
+Cordaitean leaves from India, the Southern Hemisphere, and Siberia.
_Noeggerathiopsis_, Feistmantel; _Rhiptozamites_, Schmalhausen;
_Euryphyllum_, Feistmantel.+
{_Cordaites aequalis_ Goeppert.
{_Cordaites_ (_Noeggerathiopsis_) _Hislopi_ (Bunbury).
In 1845 Goeppert[606] instituted the species _Noeggerathia aequalis_
(fig. 469) and _N. distans_ for incomplete broadly linear and
obovate leaves, from Siberian Permian strata, having a contracted
base and equal parallel veins. The specimens so named are no doubt
specifically identical. Goeppert’s species _N. aequalis_ has recently
been carefully investigated by Zalessky[607] who agrees with
Kosmovsky[608] in identifying it with _Noeggerathiopsis Hislopi_
(Bunb.) and _Rhiptozamites Goepperti_ Schmal. Schmalhausen[609] had
previously pointed out the probable identity of his species with
_Noeggerathia palmaeformis_ Goepp. (= _Cordaites_). The question of
specific identity of these leaves from different localities and of
other hardly distinguishable forms is of secondary importance; the main
point is that they are all examples of Cordaitean leaves, _Cordaites_
or some allied genus, and point to the existence of this group of
Gymnosperms during Permo-Carboniferous times in Siberia, China, India,
Australia, South Africa, and S. America, also in the Rhaetic floras
of Tonkin[610] and Mexico[611]. The fragments from Devonian strata at
Iguana Creek, Australia, named by McCoy[612] _Cordaites australis_ are
probably pieces of the rachis of some large frond.
[Illustration: Fig. 469. A–C, E, _Cordaites aequalis_; D, _Cordaites
Clerci_. (After Zalessky; ⅚ nat. size.)]
Wieland[613] recently discovered Cordaitean leaves exhibiting a wide
range in size and shape in the Mixteca flora of Mexico in the lower
members of a series which extends from the ‘upper borders of the
Rhaetic’ through the Liassic to the lower beds of the Inferior Oolite.
These leaves are referred to _Noeggerathiopsis Hislopi_, and it is
clear from an examination of photographs received from Dr Wieland,
one of which is reproduced in fig. 470, that the Mexican _Cordaites_
cannot be specifically distinguished from Bunbury’s type as represented
by specimens described from India, South Africa, Siberia, Tonkin, and
elsewhere.
The occurrence of _Noeggerathiopsis_ is also recorded by Newberry from
the Rhaetic series of Honduras[614].
_Noeggerathiopsis._ This genus was founded by Feistmantel[615] for
some leaves from Lower Gondwana rocks in India originally described
by Bunbury[616] as _Noeggerathia (Cyclopteris?) Hislopi_ (figs.
470–472) and regarded by him as probably Cycadean. Several authors
have added to our knowledge of this widely spread southern type and
in many localities the leaves occur in association with platyspermic
seeds of the _Samaropsis_ or _Cordaicarpus_ type, pieces of stems with
Cordaitean leaf-scars, and petrified wood agreeing in the structure
of the secondary xylem with that of European species of _Cordaites_.
In some Permo-Carboniferous sandstones at Vereeniging, South Africa,
stumps and spreading roots (fig. 478) resembling those described from
France by Grand’Eury (cf. fig. 468, A) have also been discovered. A
remarkable occurrence of roots and prostrate stems of some forest-tree
was recorded some years ago in the bed of the Vaal river near
Vereeniging where the surface of a seam of coal was exposed over an
area of more than two acres[617]. Large branched roots (fig. 478)
spreading over the coal for a distance of several feet and thick stems
40–50 ft in length with very few branches and but little decrease in
diameter afford a striking picture of a forest-floor. The frequent
occurrence of _Cordaites (Noeggerathiopsis) Hislopi_ in the associated
strata suggests a reference of the stems and roots to that species.
Moreover the structure of the secondary xylem of some petrified pieces
of stem sent to me by Mr Leslie from Vereeniging agrees closely with
that of a European Cordaitean stem.
[Illustration: Fig. 470. _Cordaites (Noeggerathiopsis) Hislopi_. From
Mexico. (After Wieland; ⅚ nat. size.)]
[Illustration: Fig. 471. _Cordaites (Noeggerathiopsis) Hislopi_. From
Vereeniging. (A, _ca_, ⅕ nat. size; B, _ca_, ⅙ nat. size.)]
[Illustration: Fig. 472. _Cordaites (Noeggerathiopsis) Hislopi_. From
India. (Calcutta Museum; ⅔ nat. size.)]
The leaves of _Cordaites (Noeggerathiopsis) Hislopi_ vary considerably
in size, in some cases reaching a length of 80 cm. (fig. 471); the
lamina tapers gradually from a short distance behind the obtuse apex
to a relatively narrow base: in venation and form the leaves are
very similar to those of _C. principalis_ and other European and
North American species. The specimen from India represented in fig.
472 shows several spathulate leaves attached in a close spiral to
a branch. As White[618] and Zalessky have shown, the stronger ribs
are separated by less prominent striations indicating the presence
of two sizes of hypodermal strands. The obvious resemblance between
_Noeggerathiopsis Hislopi_ and species of _Cordaites_ has long been
recognised and many authors have included Feistmantel’s genus in the
Cordaitales[619]. Prof. Zeiller[620] preferred to retain the name
_Noeggerathiopsis_ as a precautionary measure, chiefly on the ground
that the stomata appeared to be less definitely arranged in rows
and more scattered than in the European leaves of _Cordaites_, and
because of the absence of interstitial veins. We have as yet little
information as to the arrangement of the stomata, but in view of the
irregularity in stomatal grouping in recent leaves this feature is,
perhaps, of minor importance. The presence of interstitial ‘veins’ has
now been established in Indian[621] and South American[622] leaves. In
a paper published in 1908[623] the name _Cordaites_ was substituted for
_Noeggerathiopsis_ and Zalessky’s recent work supports this step. The
description by Zalessky of the ribbing in Goeppert’s species _Cordaites
aequalis_ from Siberia shows how uncertain and variable a character the
venation is even in different parts of the same leaf.
_Cordaites Clerci_ Zalessky.
This species (fig. 469, D) was instituted for some small lanceolate
or spathulate leaves from the Petschora basin (Adzva River)[624]
reaching a length of 6 cm. and a breadth of 1 cm. It is separated from
_Cordaites aequalis_ on the ground that the veins are more numerous, as
many as 44 in a breadth of 1 cm.
A recent investigation by Miss Holden[625] of the carbonised
cuticles of some Indian specimens, sent to Cambridge by the Director
of the Indian Geological Survey, and a comparison of them with
preparations made from European _Cordaites_ leaves, have revealed
certain distinguishing features which support Zeiller’s view that
the Gondwana-Land leaves, though similar superficially to those of
_Cordaites_, are probably distinct. It is, however, impossible in many
cases to obtain any information with regard to epidermal characters,
and though it would seem probable that had we a fuller knowledge of
the Indian and southern hemisphere plants represented for the most
part by leaf-impressions well-defined distinguishing features would
be recognised, the comprehensive name _Cordaites_ may conveniently
be retained on the ground that in the absence of well-preserved
cuticles no satisfactory distinguishing features are exhibited by the
impressions of _Noeggerathiopsis_.
=Phylladoderma.= Zalessky.
_Phylladoderma Arberi_ Zalessky.
Zalessky[626] founded this genus on some Permian leaves from the
Petschora basin (Adzva River) which closely resemble those of
_Cordaites_ but are characterised by a coarser venation. The lanceolate
lamina reaches a length of 18 cm. and a breadth of 4·2 cm.; the veins
are 2 mm. apart and occasionally forked near the base of the leaf. The
epidermal cells have straight walls and stomata are abundant on the
lower surface. As Zalessky says, the systematic position of the leaves
is uncertain though they are probably Cordaitean. The coarseness of the
venation is a feature of minor importance and hardly worthy of generic
recognition.
_Rhiptozamites_ Schmalhausen.
This genus was instituted by Schmalhausen[627] for leaves from beds
in the Kusnezk basin regarded by him as Jurassic. These strata are
now recognised as Permian[628] and homotaxial with those from which
Schmalhausen[629] subsequently recorded the same species. The leaves,
though smaller than many of the Indian and South African specimens
of _Cordaites_ (_Noeggerathiopsis_) _Hislopi_, may belong to that
species. Zeiller and others definitely assigned the Russian leaves to
_Cordaites_.
_Euryphyllum._ The Indian leaves for which Feistmantel[630] proposed
this name are, as several writers have pointed out, in all probability
referable to _Cordaites_.
The general conclusion to be drawn from this imperfect summary of
an extensive literature is that the employment of the generic names
_Noeggerathiopsis_, _Rhiptozamites_, _Euryphyllum_, and others has
tended to exaggerate the difference between the European and Southern
botanical provinces during the Permo-Carboniferous period.
_Scale-leaves, seeds, and stems._
The occurrence of small scale-like leaves of the type represented in
fig. 468, C, in association with _Cordaites_ (_Noeggerathiopsis_)
_Hislopi_[631] in India, Brazil, Siberia, and elsewhere may mean that
these organs are scales of large foliar buds. The occurrence of several
forms of platyspermic seeds, in some cases apparently identical with
European forms and sometimes distinct types, in close association with
_Cordaites_ (_Noeggerathiopsis_) _Hislopi_ has already been mentioned.
Examples of such seeds are described in Chapter +xxxv.+ under the genus
_Samaropsis_.
There are very few satisfactory examples of Cordaitean branches from
the southern hemisphere. Schmalhausen[632] figures good specimens from
Siberian rocks from which his _Rhiptozamites_ leaves were obtained.
Branches with spirally disposed leaf-scars figured by Zeiller[633] from
the Rhaetic of Tonkin closely resemble _Cordaicladus_. Feistmantel’s
drawing of a fossil from the Karharbari series, compared by him
with a Fern rhizome[634], may be a Cordaitean branch, and the same
author describes a stem[635] from New South Wales as _Caulopteris
Adamsi_ which bears a close resemblance to a branch of _Cordaites_.
Similarly a leafy shoot described from India by Zeiller as _Araucarites
Oldhami_[636] may be compared with branches of the _Poa-Cordaites_ type.
[Illustration: Fig. 473. _Cordaites_ (or _Mesoxylon_?) stem showing
the discoid pith partially enclosed by wood. (½ nat. size.) M. S.]
+Stems.+ i. _Pith-casts._
=Artisia.= Sternberg.
A character to which authors tend to attach excessive importance
as a diagnostic feature is the almost invariable tendency of the
parenchymatous pith of _Cordaites_ to break up on contraction into
transverse diaphragms, thus producing what is known as a discoid pith.
In the stem shown in fig. 473 the pith is represented by a more or
less cylindrical cast characterised by fairly regular transverse ribs
and narrow grooves; in the upper part of the fossil the peripheral
tissue of the pith is preserved in the form of narrow plates projecting
from the inner face of the wood. As Renault[637] pointed out, this
type of pith is the expression of certain conditions of growth and is
not a satisfactory distinguishing feature of any particular genus or
family. The same tendency to form a discoid pith is characteristic
of _Mesoxylon_, and it occurs also in some other Palaeozoic genera.
Corda long ago figured a stem attributed by him to _Lomatofloyos_ with
a typical discoid pith, and a similar pith is recorded in a stem of
_Dicranophyllum_[638]. Among recent plants _Juglans regia_ affords
perhaps the most familiar instance of an identical form of pith: the
same type occurs in the white Jasmine, in _Ceropegia peltata_, and
some other flowering plants. An interesting case is that of the tree
Groundsel, _Senecio praecox_ D.C.[639], of Mexico: in this plant,
which grows in arid districts, the pith serves as a water-store and as
the water is drawn off the thick turgescent discs contract and form
thin transverse diaphragms separated by wide spaces, as is also the
case on drying in some succulent _Euphorbia_ stems. It may be that in
_Cordaites_ the medullary region also served as a water-reservoir and
the depth of the medullary discs would vary according to the state of
their contents.
The earlier writers regarded the pith-casts as stems with scars of
amplexicaul leaves: Artis[640] described specimens from the English
Coal Measures as _Sternbergia_, one of which he stated to be 6 ft
long; a few years later Sternberg[641] proposed the name _Artisia_ and
this has been generally used on the ground that _Sternbergia_ is the
name of a recent flowering plant. A specimen of _Artisia transversa_
(Art.) from the Coal Measures of Yorkshire is shown in fig. 466, B, and
similar specimens varying considerably in diameter up to about 10 cm.
are abundant in European and American Coal Measures. The prominence and
depth of the transverse ridges, the presence or absence of anastomoses
between adjacent discs are, as Zeiller[642] says, of very doubtful
value as specific characters. Dawson in 1846[643] spoke of _Artisia_ as
probably the pith of a tree, a view suggested to him by Mr Dawes. In
1851 Williamson[644] published a description of some specimens in which
a pith-cast, _Artisia approximata_ Lind. and Hutt., was enclosed by
wood showing very clearly Cordaitean characters. Further demonstration
of the true nature of _Artisia_ was supplied by Grand’Eury from St
Étienne material. If the generic name _Artisia_ is applied to all
pith-casts showing the transverse ridges and grooves like those seen
in fig. 466, B, it must be remembered that it is not safe to assume a
connexion with _Cordaites_ or _Mesoxylon_. A Liassic species described
by Lignier[645] from France as _Artisia alternans_ is quoted by
authors as evidence of the persistence of _Cordaites_ into the Jurassic
period; but in view of the fact that the discoid type of pith is not
by any means confined to _Cordaites_ or even to the Cordaitales the
occurrence of _Artisia_ is in itself of no great botanical significance.
It is also true that a discoid pith is not an invariable attribute
of stems closely allied to the genus _Cordaites_; but if these
reservations are made the use of the generic term _Artisia_ serves a
useful purpose.
ii. _Petrified stems._
=Dadoxylon.= Endlicher.
Palaeobotanical literature contains numerous descriptions of Palaeozoic
petrified wood occasionally enclosing an _Artisia_ pith-cast described
under such names as _Dadoxylon_, _Cordaioxylon_, _Araucarioxylon_,
etc., and regarded as portions of Cordaitean stems. It is, however,
certain that much of this material belonged to stems other than those
of _Cordaites_. Recent research has demonstrated the insufficiency of
the secondary xylem alone, however well preserved, as a safe guide to
generic position: stems identical in the structure of the secondary
xylem differ in that of the primary portion of the stele, and it is on
the characters of the latter tissues that several genera have recently
been founded. _Mesoxylon_ affords a striking example of the importance
of the primary xylem as a distinctive feature. As Gothan[646] points
out, the species of _Calamopitys_ recently made the type of a new
genus _Eristophyton_[647] would, in the absence of the primary xylem,
probably be regarded as Cordaitean. It is important to recognise the
limitations imposed by the imperfection of the material; we cannot
in most cases determine whether a specimen should be referred to
_Cordaites_ or _Mesoxylon_, and while it may be described as probably
Cordaitean in affinity there remains the possibility that some of the
Palaeozoic plants with secondary wood like that of _Cordaites_, if
their reproductive organs were known, would not be included in the
Cordaitales. Goeppert’s species _Araucarites Tchihatcheffi_, which
Renault[648] quotes as _Cordaites_, has recently been assigned to a
new genus _Mesopitys_[649] because of certain distinctive features of
the primary xylem. Additional examples might be quoted pointing to the
tendency of recent and more thorough investigation to establish the
fact that the occurrence of Permo-Carboniferous wood of the Araucarian
type does not necessarily denote the existence of _Cordaites_. The
question of nomenclature is necessarily raised in this connexion.
In recent years it has been customary to assign Palaeozoic wood with
Araucarian pitting to the genus _Dadoxylon_, while wood of the same
general type from more recent strata is by many authors referred to
_Araucarioxylon_[650]. This arbitrary distinction based on a difference
in age is open to serious objection. Fossil wood of the Araucarian type
is widely scattered in strata ranging from Carboniferous to Jurassic
periods; it also occurs in later formations. The fact that on the one
hand Araucarian plants, as recognised by cones and foliage-shoots, are
especially characteristic of Jurassic floras and occur more rarely in
Rhaetic and Triassic floras, and on the other hand that _Cordaites_ and
its allies reached their greatest development in Permo-Carboniferous
times, renders it probable that in the majority of cases a distinctive
name based on geological age would be in accordance with botanical
differences. But we have no satisfactory data as to the upper limits
of the Cordaiteae or the lower limits of the Araucarineae: in all
probability the two families overlapped and co-existed for more than
one geological period. It is, moreover, the plants from formations
where overlapping occurred that are the most critical from a botanical
standpoint. The age-distinction is therefore at best an artificial
one and may be seriously misleading. Potonié[651] and Gothan[652]
have emphasised the desirability of adopting the name _Dadoxylon_ for
all wood of the Araucarian type irrespective of age. If a particular
specimen can be correlated definitely with _Cordaites_ or some other
genus it should be so designated, but the fragmentary nature of the
records usually precludes this simple course. The most logical plan is
to use the name _Dadoxylon_ for all woods with Araucarian characters if
there is no sufficient reason for employing a less provisional term.
If the evidence clearly points to the Araucarineae the generic name
_Araucarioxylon_ should be added in parentheses after _Dadoxylon_,
but whether or not this is done, a statement as to the geological
age of the fossil will in itself be some assistance in enabling the
student to form an opinion on the balance of probability in favour
of a Cordaitean or an Araucarian affinity. The course suggested
by Gothan[653], namely to add _Cordaites_ after _Dadoxylon_ if an
_Artisia_ pith is present, is rendered inoperative now that we know
that a discoid pith occurs in more than one genus. In this chapter we
are concerned primarily with _Cordaites_ and with such stems as may
fairly be regarded as Cordaitean: examples of fossil wood from later
formations are dealt with in another place. A distinction between
_Araucarioxylon_ and _Cordaioxylon_ stems has been based by Felix on
the nature of the pith-casts; those of the _Artisia_ type he refers to
_Cordaioxylon_, while Palaeozoic stems with _Tylodendron_ pith-casts
are assigned to _Araucarioxylon_[654]. This distinction can, however,
only be made in the comparatively few cases in which the pith-cast is
preserved. Its validity is, moreover, open to question. A _Tylodendron_
(= _Schizodendron_) cast shows on its surface the characters of the
inner face of the secondary xylem, projecting spindle-shaped areas
representing the inner ends of medullary rays and a reticulum of
grooves formed by the more resistant and prominent inner edges of
the rows of tracheids (fig. 746). A pith-cast of a stem in which the
destruction by decay of the medullary parenchyma had not extended to
the edge of the xylem-cylinder might show transverse diaphragms. The
occurrence of _Tylodendron_ casts means that decay had extended to the
surface of the wood. But in view of the occurrence of _Tylodendron_
casts in stems that are not those of _Cordaites_ a short account of the
genus is given on another page[655].
The main features of the stem of _Cordaites_ have already been
enumerated. The stele agrees with that of _Araucaria_ and _Agathis_
and especially with _Agathis_ in the double nature of the leaf-trace.
Williamson[656] in 1877 described pieces of wood from the English
Coal Measures and the Lower Carboniferous of Scotland which he
referred to _Dadoxylon_ but without any specific name. These include
the Coalbrookdale stem in which he had previously demonstrated the
connexion between _Artisia_ and _Dadoxylon_. The structure of the
xylem is like that in _D. Brandlingii_ and the specimens may belong
to that species. The most interesting fact recorded by Williamson
is the occurrence of double leaf-traces, a feature which led him to
suspect a remote generic affinity to _Ginkgo_. This double trace may
be an important diagnostic feature but unfortunately the majority of
descriptions of species of _Dadoxylon_ throw no light on the character
of the foliar bundles.
Thomson and Allin[657] have recently pointed out that a double
leaf-trace occurs in a stem from the Permian of Kansas described by
Penhallow[658] as _Pityoxylon chasense_ and referred to that genus
because of the supposed occurrence of resin-canals in some of the
medullary rays: the canals are apparently leaf-traces traversing broad
rays in the secondary wood.
The primary xylem of _Cordaites_ is in direct continuity with
the secondary tracheids and does not form mesarch strands as in
_Mesoxylon_. The pith is usually discoid. The pitting on the tracheids
is a character of special importance: while it is true to say
that as a rule the number of pits on the radial walls of a single
tracheid is larger than in the Araucarineae, this is not always the
case. In _Araucaria_ there are occasionally as many as five rows
of alternate polygonal pits (fig. 691, A) and in some Palaeozoic
Dadoxylons there are only one[659] or two rows. The very broad zone
of transitional elements at the inner edge of the xylem-cylinder
is a characteristic feature shared by the Araucarineae[660]; the
spiral protoxylem-tracheids are succeeded by scalariform elements and
these, by the gradual anastomosing of the transverse bars, pass into
tracheids with multiseriate pitting. In this broad zone we probably
have a primitive feature, an epitome in a single stem of the course
of development of multiseriate from scalariform pitting. In some
Palaeozoic species with wood of the pycnoxylic type and agreeing
generally with typical _Cordaites_ the bordered pits are sometimes
separate and circular, and opposite pits occasionally replace the
usual alternate arrangement. Another feature on which stress has been
laid is that in _Cordaites_ the pits occupy the whole breadth of the
tracheal wall; but this, though frequently the case, is by no means a
constant feature. In _Dadoxylon Newberryi_[661] the pits tend to form
groups, leaving unpitted areas, as in the genus _Coenoxylon_[662].
In the stem of _Dadoxylon materiarum_ Daws. represented in fig. 475
the pits do not always cover the whole of the tracheid-walls: this
stem is also instructive as an example of the different appearance
presented by pitted tracheids according to the state of preservation.
In some places an oblique pore is well shown while in others only the
outer border of the pit is seen. Gothan[663] has described a specimen
in which some of the pits are circular and occupy only the central
area of the xylem elements: separate circular pits occur also in _D.
Pedroi_ Zeill.[664] (fig. 476). Similar departures from the normal
are illustrated by recent species of Araucarineae. The absence of a
torus is another feature shared by _Dadoxylon_ and true Araucarian
wood. Annual rings other than incomplete and spasmodically formed rows
of narrower tracheids are not as a rule present, and in this respect
also _Araucaria_ affords a close analogy. Thomson[665] has figured
a transverse section of a root from English Coal Measures in which
rings of growth are well defined; and other instances are recorded.
In an Australian species named by Arber _D. australe_[666], there are
well-marked rings of growth, and this is equally the case in some
Indian wood[667] of Permo-Carboniferous age, more nearly allied to
_Mesoxylon_ than to _Cordaites_, and in a _Dadoxylon_ of similar age
from South Africa. On the other hand the statement that annual rings
occur in Palaeozoic wood is often incorrect, partial rings having been
confused with regular concentric cylinders of summer elements. Dawson
and Matthew[668] described rings in _D. ouangondianum_, and Goeppert
and Stenzel[669], who examined the Canadian material, refer to circles
like annual rings; but Penhallow[670] states that there is no evidence
of true growth-rings.
The medullary rays are uniseriate and consist of thin parenchymatous
cells with unpitted walls; they vary considerably in depth, usually
comparatively shallow but in some cases 40 or 50 cells deep. In recent
Araucarineae the rays are generally shallower. The absence of special
receptacles, other than occasional resiniferous tracheids, for products
of secretion is a feature common to _Dadoxylon_ and the Araucarineae.
The phloem presents no features of special interest, but our knowledge
of this tissue is comparatively meagre.
Among other examples of large _Dadoxylon_ stems some of which no
doubt bore Cordaitean foliage—though as a rule we have insufficient
information as regards anatomical characters to enable a decision
to be made between _Cordaites_ and _Mesoxylon_—reference should be
made to the imposing array of silicified trunks in the grounds of the
Chemnitz Museum[671]. These were obtained from Lower Permian strata
at Hilbersdorf near Chemnitz from beds overlain by porphyry tuff and
resting on quartz porphyry, the volcanic material which furnished
the siliceous solutions. Several large pieces of wood were found in
association with stems of _Medullosa_ and _Psaronius_, leaves of
_Cordaites_, _Artisia_ pith-casts, and _Cardiocarpus_ seeds with
specimens of _Walchia_, _Gomphostrobus_ and other plants. Sterzel
describes a stem 16·5 met. long and 1·5 met. in diameter; on the main
trunk the branch-scars are scattered but on some branches there is
a tendency to a whorled arrangement. This and many other stems are
referred to _Araucarioxylon_ (or _Dadoxylon_) _saxonicum_, a species
first described by Reichenbach as _Megadendron saxonicum_. In one
specimen Sterzel states that the bordered pits are generally in 1–2
rows, though rarely in 3–4 rows, on the radial walls of the tracheids
which they do not completely cover: the medullary rays reach a depth of
between 20 and 30 cells. It is noteworthy that the stem 16·5 met. long
has a pith-cast of the _Tylodendron_ type.
_Dadoxylon_ (_Cordaites_) _Brandlingii_ (Lindley and Hutton).
1831. _Pinites Brandlingii_ Lindley and Hutton, Foss. Flor. Vol. +i.+
Pl. +i.+
1850. _Araucarites Brandlingii_ Goeppert, Foss. Conif. p. 232, Pls.
+xxxix.–xli.+
1890. _Cordaioxylon Brandlingii_ Schenk, in Schimper and Schenk, p.
853, fig. 408.
This species was founded on ‘a fossil giant of the vegetable kingdom’
discovered at Wideopen near Newcastle in Carboniferous strata on the
estate of Mr Brandling. The stem, 72 ft long and far from complete,
showed an irregular and not a whorled distribution of branch-scars. It
is noteworthy that in _D. medullaris_ (Goepp.)[672], a Permian species
from Saxony, the branch-scars, while for the most part irregularly
scattered, in one case showed an approach to a whorled disposition
as in recent Araucarias. Witham[673] gave a fuller account of the
structure of the stem than is included in the original description,
and the species has been described by many later authors from both
Permian and Carboniferous localities. The pith is discoid and the broad
transitional region at the inner edge of the wood is a characteristic
feature[674]. Thomson[675] points out that there is a tendency to a
retention of the scalariform type of pitting in the region of the
medullary rays. There are 1–5 rows of pits on the radial walls of the
tracheids. The rays may reach a depth of 40 cells; they are usually one
cell broad. It has recently been shown that as many as six vascular
strands[676] may form one leaf-trace instead of the customary pair,
a feature suggesting comparison with _Metacordaites Rigolloti_ Ren.
with its five foliar bundles. Other species agree very closely with
_D. Brandlingii_ and it is impossible to determine with accuracy the
precise specific limits of stems agreeing generally with this type; but
for the sake of emphasising the variation in anatomical structure it
is worth while to draw attention to a few more or less divergent forms
from different geographical areas.
_Dadoxylon protopityoides_ Felix.
An interesting feature in this Westphalian type from Germany is the
occurrence of transversely elongated pits on the tracheids[677]
associated with those of normal form closely simulating the pits in the
xylem elements of _Protopitys_.
_Dadoxylon nummularium_ White.
In this Brazilian wood[678] from Permo-Carboniferous beds the medullary
rays are very numerous, mostly uniseriate and 1–30 cells in depth.
The pits on the tracheids are in 1–2 rows and are often contiguous.
In another type, _D. meridionale_, described by the same author[679],
the pits are strictly uniseriate and generally contiguous. As White
says, the absence of the pith and cortex and of any evidence as to
the structure of the primary xylem renders impossible any definite
expression of opinion as to the affinity of these and many other
species.
_Dadoxylon Nicoli_ Seward.
Dr Arber[680] in naming this species, from the Newcastle
(Permo-Carboniferous) Series of New South Wales, _Dadoxylon australe_,
does not mention Crié’s earlier account of some wood from New Caledonia
under the name _Araucarioxylon australe_[681]. The latter generic name
according to the usage adopted in this volume should be superseded by
_Dadoxylon_, and this necessitates a fresh specific name for Arber’s
specimens. The name _Nicoli_ is suggested in place of _australe_, as
the sections on which Arber founded his species form part of the Nicol
collection in the British Museum.
The xylem shows distinct rings of growth, a feature also seen in
Indian stems of approximately the same geological age and recorded
by Shirley[682] in wood from Queensland which needs more careful
examination. The bordered pits, usually multiseriate and contiguous,
are not infrequently in 1–2 rows and separate. The uniseriate
medullary rays are very numerous as in White’s Brazilian species _D.
nummularium_, and as a rule 6–12 cells deep. Some well-preserved
specimens from Permo-Carboniferous strata in Natal and Zululand have
been described by Warren[683] as _Dadoxylon australe_ Arb., showing
interesting anatomical features, but the material almost certainly
includes more than one specific type and would repay more detailed
investigation.
_Dadoxylon materiarum_ Dawson.
This species was described by Dawson[684] from Carboniferous strata
in Nova Scotia and afterwards referred by Penhallow[685] to the genus
_Cordaites_. In the transverse section reproduced in fig. 474, A, the
tracheid-walls have been reduced in thickness by partial decay, but
some of the bordered pits are clearly shown on the radial walls; the
pits usually form 2–4 contiguous rows (fig. 475) in some cases with an
oblique pore while others are represented either by the outer border of
the pit or by the pore only. The narrow medullary rays are as a rule
uniseriate and may be 60 cells deep (fig. 474, B). Dawson states that
some specimens have large _Artisia_ pith-casts, a fact that formerly
would have been regarded as proof of the _Cordaites_ nature of the
wood, but in the absence of evidence with regard to the nature of the
primary xylem it is impossible to say whether the stem is _Cordaites_
or _Mesoxylon_.
_Dadoxylon_ sp.
Some wood received from Mr Leslie, collected at Vereeniging, South
Africa, in Permo-Carboniferous rocks, shows well-defined rings of
growth. The pits form either a single row, a double, alternate and
contiguous row, or rarely three series on the tracheid walls. The
medullary rays are usually uniseriate and 1–30 cells deep.
_Dadoxylon Kayi_ Arber.
This species is represented by some large trunks, in some cases with
a diameter of 40 cm., discovered by Mr Kay in the Coal Measures of
Worcestershire[686]. The pith is very small and shows no indication of
a discoid structure, but owing to its poor preservation no sections
could be obtained of this region. The secondary wood is characterised
by the large number of uniseriate medullary rays 1–27 cells in depth;
the tracheids have usually two or sometimes three rows of alternate and
contiguous bordered pits on the radial walls. Arber regards the absence
of a discoid pith as a fatal objection to a reference of the stems to
_Cordaites_ and speaks of them as affording further evidence of the
occurrence of Coniferae in the higher Coal Measures of the Midlands. It
is, however, impossible to determine the position of the species in the
absence of any data with regard to the structure of the perimedullary
region, and without such information we are hardly justified in
regarding _Dadoxylon Kayi_ as a member of the Coniferales.
[Illustration: Fig. 474. _Dadoxylon materiarum._ Transverse (A) and
tangential (B) sections of the secondary xylem. (Kidston Coll. 222,
224.)]
[Illustration: Fig. 475. _Dadoxylon materiarum._ A–C radial
longitudinal sections of the secondary xylem. (Kidston Coll. 225.)]
_Dadoxylon Pedroi_ Zeiller.
This species from Upper Carboniferous or possibly Lower Permian strata
in Brazil[687] has a pith 3·8 cm. in diameter composed of parenchyma
with scattered secretory sacs and characterised by the occurrence of
three equidistant bays projecting into the cylinder of wood (fig. 476,
A) which extend through the length of the specimen (6 cm.): these, as
Zeiller suggests, may be connected with the departure of leaf-traces
or branches. The xylem is entirely composed of centrifugal elements
and shows a broad transitional zone (fig. 476, B) including spiral,
scalariform, and reticulate tracheids, but the bordered pits are less
numerous and less crowded than in many species of _Dadoxylon_. The rays
are 1–2 cells broad and reach a depth of 50 cells. The most striking
features are the solid and not discoid pith with its three rounded
bays and secretory canals, also the smaller number and frequently
circular form of the pits on the tracheids. Zeiller considers that
the stem is that of some Cordaitean plant though probably not a true
_Cordaites_. White[688] questions the advisability of adopting the
generic name _Dadoxylon_ and suggests the possibility, though without
any satisfactory evidence, that it is the stem of a _Gangamopteris_.
Failing further information, there would seem to be no sufficient
reason for the institution of a distinctive generic name.
[Illustration: Fig. 476. _Dadoxylon Pedroi._ A, transverse section
showing the pith and part of the secondary wood. B, longitudinal
section of part of the secondary wood. (After Zeiller.)]
_Dadoxylon permiense_ (Renault).
This Permian species from Autun[689] differs from typical examples of
the genus in the differentiation of the pith into a central thin-walled
region contracted into transverse diaphragms surrounded by a cylinder
of stouter tissue and in the greater breadth of the medullary rays. The
tracheids have 3–4 rows of pits of the usual type. Spirally disposed,
decurrent, leaf-bases occur on the surface of the stem, and the cortex
includes secretory canals and strands of hypodermal stereome. A small
number of veins pass up the median part of the lamina which in this
respect and in its greater thickness differs from that of _Cordaites_
leaves. Renault speaks of the rays as a cycadean feature, but they are
only two cells in width and shorter than in recent Cycads.
_Dadoxylon spetsbergense_ Gothan.
In this species[690] from Spitzbergen, of doubtful age though probably
Palaeozoic, there is no xylem-parenchyma and the medullary rays are
from 2 to 5 cells deep; the bordered pits occur in 1–2 or rarely 3
rows on the radial walls of the tracheids; they are alternate but not
flattened and characterised by their small size (7μ high); they do not
cover the whole face of the tracheids. It is pointed out that in many
Palaeozoic and Mesozoic Dadoxylons the pits are larger than in recent
species (16–17·5μ as compared with 9–12μ) while in _D. spetsbergense_
they are still smaller. The large size of the medullary-ray cells
is another noteworthy feature, also the absence of annual rings, a
character possibly connected with conditions of growth in northern
regions. It is, however, pointed out by Nathorst[691] that the fossil
was not found _in situ_ and, as he says, it may have been carried by
currents from a more southern locality.
=Metacordaites.= Renault.
_Metacordaites Rigolloti_ Renault.
Renault founded this species[692] and genus on a stem from Autun which,
like _D. Pedroi_, differs in certain respects from stems usually
attributed to _Cordaites_. The pith is solid and contains secretory
ducts and cells; the tracheids have often a single row of pits, and
multiseriate pitting is much less common than in _Dadoxylon_. The
medullary rays are generally 1–6 cells deep. A striking feature is
the occurrence of groups of five vascular bundles penetrating the
secondary wood in V-shaped groups, each group being regarded as a
multiple leaf-trace, a type recently recognised by Thomson in _D.
Brandlingii_. In one of Renault’s figures a larger scar, presumably a
branch-scar, is shown immediately above a group of foliar bundles. The
genus _Metacordaites_ is considered by its author to be intermediate
between Conifers and the Cordaitales, but nearer to the former. This
conclusion is, however, based on insufficient evidence, as nothing is
known of the reproductive organs.
+Roots.+
In 1871 Williamson[693] gave an account of a petrified plant from
the Lancashire Coal Measures which he named _Dictyoxylon radicans_,
but he afterwards came to the conclusion that the specimens so named
were portions of the subterranean axis of some other plant, possibly
_Asterophyllites_, and proposed a new generic term _Amyelon_[694].
In 1874 he brought forward fresh evidence in support of connecting
_Amyelon radicans_ with _Asterophyllites_ or _Sphenophyllum_, genera
which Williamson believed to be very closely related. It has since
been recognised that _Amyelon_ is the root of _Cordaites_ or of some
closely allied member of the Cordaitales. Our knowledge of Cordaitean
roots is based chiefly on the work of Williamson and Renault[695],
and more recently Osborne[696] has added new facts of considerable
interest. In the larger roots the primary xylem may be diarch or
there may be as many as four or five protoxylem groups (fig. 477).
The primary tracheids are spiral or scalariform and the space, _s_,
separating them from the surrounding secondary xylem seen in fig. 477,
B, was no doubt originally occupied by conjunctive parenchyma. The
secondary wood is composed of tracheids, with contiguous bordered pits
identical with those in the xylem of the stem, and narrow medullary
rays. The section, 4 mm. in diameter, represented in fig. 477, A, shows
a tetrarch primary xylem strand enclosed by secondary wood composed of
rather thin-walled elements succeeded by a zone of phloem including
some secretory sacs, and beyond this is a cylinder of periderm, _p_.
In a section of a root figured by Renault from Autun the periderm is
separated from the stele by a broad band of parenchyma which appears
to be cortical, but in the British specimens the deep-seated origin
of the periderm is clearly shown: Osborne states that it arises in
a layer immediately outside the endodermis. In one of the specimens
figured by Williamson[697] the secondary wood shows clearly marked
irregular concentric lines simulating rings of growth, but there is
no evidence of any regularly recurring variation in the diameter of
the xylem-elements. From the descriptions of Williamson and Osborne it
is evident that the roots of _Cordaites_ were profusely branched and,
as the latter author has shown, the method of branching points to the
formation of coralline roots like those of recent Cycads, some Conifers
and Dicotyledons. Osborne found that the cortex of small rootlets
is composed of two zones, an outer parenchyma without cell-contents
and an inner parenchymatous tissue characterised by the occurrence in
some of the cells of tangled masses of fungal hyphae almost always
unseptate. In some cases the hyphae bear terminal vesicles similar to
those observed on fungal hyphae in the cortex of _Podocarpus_ roots.
Osborne makes out a good case for regarding the fungus as symbiotically
related to the tissues of the lateral roots, a relationship identical
with that in many existing trees, particularly _Myrica_ and _Alnus_.
It is suggested that the formation of the coralline root-tubercles is
a feature consistent with the view that _Cordaites_ lived in saline
marshes, a physiologically dry habitat favourable to the occurrence of
mycorhiza.
[Illustration: Fig. 477. A, root of _Cordaites_. B, centre of the
root enlarged; _p_, periderm; _s_, space. (Kidston Coll. 1906.)]
[Illustration: Fig. 478. Root (_Cordaites_?) exposed in the bed of
the Vaal river. (After Mellor and Leslie.)]
Reference has already been made to the habit of Cordaitean roots in the
general account of the genus (figs. 468, A, 478). The specimen shown in
fig. 478 may be a root of _Cordaites_ (_Noeggerathiopsis_) _Hislopi_,
but nothing is known as to its structure[698].
+Reproductive Organs.+
=Cordaianthus.= Grand’Eury.
We have as yet no definite knowledge of the nature of the reproductive
organs of _Mesoxylon_ and _Poroxylon_, but having regard to their
close resemblance in other respects to _Cordaites_, particularly in
the case of _Mesoxylon_, the presumption is that some of the seeds and
fertile shoots attributed to _Cordaites_ may belong to other members
of the Cordaitales. Despite the abundance of _Cordaites_, or at least
of material assigned to that genus, and the comparative frequency of
fertile shoots in actual connexion with foliage-shoots, the practical
identity of _Mesoxylon_ and _Cordaites_ leaves precludes any confident
use of the latter name in a strict sense.
In 1822 Brongniart[699] described a small bud-like fossil of Tertiary
age as _Antholithes liliacea_, and this generic name in the form
_Antholithus_ became widely used for fertile shoots or flowers from
different geological horizons. As knowledge became more precise other
names replaced _Antholithus_, though Renault[700] retained it for some
inflorescences from Commentry which could not definitely be included
in _Cordaites_. Lindley and Hutton[701] employed the genus for a
specimen, now recognised as a Cordaitean fertile shoot, from the Coal
Measures which they called _Antholithus Pitcairniae_, the specific
name being chosen to indicate a possible affinity to the Bromeliaceous
genus _Pitcairnia_. A few years later Morris[702] described a similar
inflorescence as _A. anomalus_. In 1872 Carruthers[703] substituted
Brongniart’s term _Cardiocarpon_ for _Antholithus_ and called _A.
Pitcairniae Cardiocarpon Lindleyi_ and Morris’s species _C. anomalum_.
The specific name _Lindleyi_ has been widely adopted, but there would
seem to be no adequate reason for disregarding the priority-rule.
It is, however, customary to use Grand’Eury’s term _Cordaianthus_
for all Cordaitean inflorescences. Goeppert[704] suggested the name
_Botryoconus_ for an inflorescence similar to _C. Pitcairniae_ and for
this C. E. Weiss[705] substituted _Noeggerathianthus_ on the ground
that he considered Goeppert’s specimen to be the male inflorescence of
_Noeggerathia_. Grand’Eury resuscitated _Botryoconus_[706] for some
spikes from the Gard coalfield connected by him with _Dory-Cordaites_.
The nature of the seeds borne by the inflorescences has largely
influenced authors in the choice of a generic name: Carruthers used
_Cardiocarpon_ while Zeiller[707] speaks of _Samaropsis Pitcairniae_.
The genus _Cardiocarpon_ was founded by Brongniart for compressed
cordiform seeds, but it was not until later that their gymnospermous
nature was recognised. Further reference to the nomenclature of
seeds of the _Cardiocarpon_ type will be found in Chapter +xxxv.+
The correlation by Grand’Eury and other authors of different species
of inflorescences and species of _Cordaites_ is frequently based on
association, and in the absence of more satisfactory evidence the safer
course is to deal with Cordaitean fertile shoots in a general sense.
[Illustration: Fig. 479. _Cordaianthus._ From the Middle Coal
Measures of Lancashire. (Manchester Museum; ⅓ nat. size.)]
(_a_) _Ovulate shoots._ These are represented by a considerable number
of forms in both European and American localities. In rare cases the
compound shoot reaches a length of 30 cm. (fig. 479), but it is usually
much shorter; the lateral compact buds may be more or less widely
separated: the seeds have long pedicels (fig. 480, A) or appear to
be sessile (fig. 480, B) and there may be one or several seeds on a
single lateral shoot. The seeds are platyspermic and, as seen in fig.
480, A, in some inflorescences they show very clearly the _Samaropsis_
features. It would, however, be unsafe to assume that all _Samaropsis_
seeds were borne on Cordaitean plants. Among other types of seed
referred by authors to _Cordaites_ are _Cardiocarpus_, _Cordaicarpus_,
_Sarcotaxus_, _Taxospermum_, _Diplotesta_, and _Leptocaryon_. But in
most cases there is no evidence of actual connexion between seeds and
vegetative organs, and while it is possible to state with confidence
that many of the seeds represented by impressions described as species
of _Samaropsis_ and _Cordaicarpus_ are undoubtedly Cordaitean, it is
certain that not all seeds referable to these genera were borne by
Cordaitalean plants. Cordaitean seeds are characterised by certain
morphological features recalling those found in recent Cycads and in
the seeds of _Ginkgo_ as illustrated by species of _Cardiocarpus_ and
some allied types. As most of the Palaeozoic seeds known in a petrified
state cannot be assigned to their parent-plants they are dealt with in
a separate chapter[708].
_Cordaianthus Pitcairniae_ (Lindley and Hutton).
This type of inflorescence[709] is considered by Kidston to belong to
the tree which bore leaves known as _Cordaites principalis_, but if
this is the case it is probable that the stem possessed the anatomical
characters of _Mesoxylon_.
[Illustration: Fig. 480. A, _Cordaianthus Pitcairniae_ with
_Samaropsis_ seeds. B, _Cordaianthus Volkmanni_. B′, portion of B
enlarged. (A, B, nat. size; Kidston Coll. 2374, 1174.)]
The portion of an inflorescence shown in fig. 480, A, from the Middle
Coal Measures of Yorkshire, illustrates the occurrence of the bud-like
fertile shoots and the stalked _Samaropsis_ seeds. A species described
by Renault[710] from Commentry as _Cordaianthus acicularis_ may be
identical with the British species.
_Cordaianthus Volkmanni_ Ettingshausen.
The example of this species[711] seen in fig. 480, B, shows the
relatively small size of the lateral buds, presumably unexpanded,
compared with the large subtending bracts.
=Petrified specimens of Cordaianthus.=
Our knowledge of the structure of _Cordaianthus_ is based on
the researches of Renault[712], supplemented by those of Prof.
Bertrand[713] to whose kindness I owe the photographs reproduced in
fig. 481. The inflorescences described by Renault are referred by
him to different species, but in the following brief account these
are treated from a generic standpoint. The tangential section of
_Cordaianthus Williamsoni_ Ren. shown in fig. 481, D, was originally
figured by Renault and more recently by Bertrand; it shows the spirally
disposed leaf-traces in the lower part of a stout axis, and at the
sides some vascular bundles are seen passing up into the bracts. A very
small proportion of the bracts subtend ovules; two are seen at _a_ and
_b_, and at _c_ is the tangentially cut micropylar canal of a third
borne near the apex and covered by the terminal cluster of bracts. The
ovule _a_, separated by a narrow space from its short stalk, consists
of a thick single integument—not two as stated by Renault—extended
at the apex as a micropylar canal: the apical extension is more
completely shown in the tangentially cut ovule _b_. The central body is
much contracted and the two spaces, _s_, at the base are regarded by
Bertrand as cavities in the integument separated from one another by a
central strand of conducting tissue which gives off two bundles to the
integument, one at each end of the long axis of the seed (fig. 481, A,
_v_). The dark patch, _n_ (fig. D), is the upper and broader end of
the shrunken nucellus the apex of which extends upwards as a slender
beak, and this originally no doubt fitted into the micropyle. Fig. 481,
C, shows a female inflorescence in transverse section; the stele
consists of a ring of bundles separated by broad medullary rays and
enclosing a comparatively large pith: the leaf-traces are seen in the
cortex and one is cut through as it bends out into a bract which is not
yet free from the axis. Two ovules, seen in section at _a_ and _b_, are
represented by the bilaterally symmetrical and compressed integument
enclosing small pieces of nucellar tissue. Fig. 481, E, is a transverse
section of an inflorescence at a higher level and above the apex of the
axis: there are four large ovules and one aborted ovule, _a_. Bertrand
describes two vascular bundles in the integument of the ovule _a_, one
at each end of the long axis.
[Illustration: Fig. 481. A, B, _Cordaianthus Grand’Euryi_,
ovule showing apex of nucellus, B, with microspores, _p_; _pc_,
pollen-chamber; _b_, beak of nucellus; _v_, vascular bundle.
C, transverse section of flower-bud with ovules, _a_, _b_. D,
_Cordaianthus Williamsoni_, longitudinal section; _a_–_c_ ovules;
_s_, spaces; _n_, nucellus. E, _Cordaianthus Zeilleri_, transverse
section showing four large ovules and one aborted ovule (_a_);
_v_, vascular bundle. F, transverse section of male flower; _m_,
microsporangia. (From photographs supplied by Prof. Bertrand.)]
Fig. 481, A, B, _Cordaianthus Grand’Euryi_ Ren., shows a longitudinal
section of the nucellus, 1·5 × ·7 mm., and part of the integument of
an ovule at the time of pollination, which was probably aided by the
secretion of a drop of mucilage as in the ovules of recent Conifers.
The integument, separated by a broad space from the nucellus, is cut
in the plane of the two vascular strands, _v_. From the centre of its
broad upper surface the nucellus projects upwards as a beak, _b_,
and this originally engaged with the micropylar canal formed by the
integument: the lighter patch below the beak is the pollen-chamber
(fig. 481, B, _pc_) containing two microspores, and two more, _p_, are
seen above the nucellar beak. In another species described by Renault,
_C. Lacattii_, the nucellus fills the space bounded by the integument.
* * * * *
(_b_) _Staminate inflorescences._ The male inflorescence, though
smaller, is similar in habit to the ovulate shoot: the secondary branch
consists of a short axis bearing crowded, spirally disposed, bracts,
and the actual flowers are represented by single stamens or groups of
2–3 highly specialised microsporophylls. Each microsporophyll consists
of a long filament with a central vascular strand bearing at its apex
3–4 long microsporangia (fig. 481, F, _m_) which open longitudinally
as seen in fig. 482, A. The microsporangia are 2·5–3 mm. long covered
by dark palisade cells and thin-walled parenchyma, shown as indistinct
patches in the photograph. Some of the elliptical and comparatively
large microspores are seen in fig. 482, B; the exine is finely punctate
and inside are the remains of a few thin cells in which presumably
spermatozoids were developed. The microspores shown in fig. 482,
B, have a maximum length of 0·1 mm.: Renault describes some as 0·9
mm. long while others are much smaller. Fig. 481, F, is a transverse
section of a staminate inflorescence showing near the centre five
groups of microsporangia, each sporangium having the form of a curved
incomplete dark band indicating that dehiscence has occurred.
[Illustration: Fig. 482. _Cordaianthus._ Microsporangia, A, and
Microspores, B. (University College Collection, London.)]
=Mesoxylon.= Scott and Maslen.
This generic name was instituted for stems obtained by Messrs Lomax
from the Lower Coal Measures of Lancashire[714] previously referred by
Scott[715] to _Cordaites_ and _Poroxylon_. Further investigation showed
that while agreeing closely with those genera they possessed certain
distinctive features demanding recognition. The name chosen suggests
the intermediate nature of the stems. The more striking features may
be summarised as follows: In the largest specimens so far described
the stem, including leaf-bases, reaches a diameter of 5 or 6 cm.; the
large pith consists in the central region of diaphragms of parenchyma
separated by horizontal spaces produced by splitting and shrinkage
consequent on the failure of the tissue to keep pace with the general
growth of the stem. The secondary xylem is of the Araucarian type and
has narrow medullary rays varying in depth from 1 to 25 cells. The
leaf-traces are represented by twin-bundles which fuse in the downward
direction, the level at which fusion occurs being regarded as a
specific character. The presence of centripetal xylem is an essential
feature of the traces: the occurrence of single or double traces
consisting of centripetal elements and, externally, a large amount
of centrifugal xylem is an important feature in which _Mesoxylon_
differs from _Cordaites_. The double leaf-traces divide after
emerging from the secondary wood and each strap-like leaf receives
several collateral bundles (fig. 483, C). An axillary bud may occur
at the base of each leaf (fig. 483, A, _b_). The phloem, including
sieve-tubes and secretory sacs, is succeeded by a broad pericycle,
and the comparatively narrow cortex is traversed by successive bands
of periderm. In the outer region of the cortex the presence of radial
bands of fibres is a characteristic feature. The reproductive organs
are unknown. The anatomical features are well illustrated by _M.
Sutcliffii_ first described by Scott, who provisionally placed it in
_Poroxylon_, and afterwards more fully investigated by Maslen[716].
_Mesoxylon Sutcliffii_ Scott.
The average diameter of the stem is 3 cm.: the section reproduced in
fig. 483, A, has a maximum breadth of 3·5 cm.; the leaf-bases cut at
different levels give an irregular contour to the surface like that of
a _Lepidodendron_. An axillary bud, either reproductive or vegetative,
is seen at _b_ consisting of a short axis bearing crowded bud-scales.
The leaves are crowded and according to Maslen have a phyllotaxis of
⁸⁄₂₁: the lamina is linear like that of _Cordaites_ with 16 collateral
bundles in the petiole. The presence of a meristematic band at the
base of the lamina affords evidence of a deciduous habit. The large
size of the pith is a striking feature with its central tissues in
the form of transverse diaphragms and a narrower peripheral zone
of solid parenchyma (fig. 483, A, _a_). The secondary wood of the
stele is composed of tracheids with 2–3 contiguous alternate rows of
bordered pits on the radial walls, but none on the tangential walls.
In the stem shown in fig. 483, A, the secondary wood is preserved
only in patches. Numerous blunt teeth varying in prominence project
into the pith; these consist chiefly of serially disposed centrifugal
tracheids distinguished by their spiral and scalariform structure and
by the medullary rays which are broader than those in the more external
xylem. Further reference is made to these perimedullary strands in the
description of the leaf-traces. The medullary rays are uniseriate and
usually 1–6 cells in depth: beyond the secondary wood is a cambium
and a cylinder of secondary phloem (fig. 483, D, _ph_²) consisting of
tubular elements, presumably sieve-tubes, and elongated secretory sacs.
The pericycle is composed of several rows of rather large and short
cells and has an ill-defined outer boundary. A succession of arcs of
periderm-like tissue and phellogen, which may invade the pericycle
and phloem, forms a prominent feature in the cortex; radially placed
bands of fibres similar to those in _Lyginopteris_ and other genera
occur in the outer cortex. At the edge of the pith the more prominent
projections of xylem are arranged in pairs (fig. 483, B) and as each
pair travels downwards the component strands gradually fuse[717]. Each
bundle of a double trace consists internally of an arc of centripetal
xylem, the elements of which are arranged in rows (fig. 483, B, _cp_),
with a single protoxylem group in the middle of the inner face, _px_.
It is not clear whether any primary centrifugal tracheids are present,
but there are indications that such are occasionally represented.
In most cases the primary xylem of the leaf-traces is exarch, but
the existence of mesarch bundles is not improbable. The bulk of each
foliar bundle is formed of a fan-shaped mass of secondary centrifugal
xylem (fig. 483, B, _cf_) and an island of parenchyma occurs next
the protoxylem. There is no clearly defined boundary between the
outer or centrifugal xylem of the leaf-traces and the tracheids of
the stem-wood; the latter may consist exclusively of tracheids with
bordered pits or the inner rows of the xylem-cylinder may be of the
scalariform or spiral type. Differences shown in transverse sections
of the inner portion of the xylem are due to the circumstance that in
certain parts of the inner face of the secondary wood leaf-traces are
unrepresented, while in other places the dwindled remains of the outer,
centrifugal, portions of a trace are still recognisable. As each double
leaf-trace passes down the pith the bundles fuse and the single strand
retains for a time some centripetal xylem; this gradually disappears
and at a lower level the centripetal xylem also dies out. The space
enclosing the obtuse apices of the bundles shown in fig. 483, B, was
originally occupied by thin-walled tissue which accompanied the trace
in its outward course. In _Mesoxylon Sutcliffii_ the leaf-strands pass
almost horizontally through the secondary wood, bend outwards in the
phloem and follow a steeply ascending course to the leaves. In fig.
483, B, a double leaf-trace is seen at the inner edge of the secondary
wood with the centrifugal xylem, _cf_, continuous with that of the
stele: fig. 483, D, _lt_, shows a leaf-trace in the pericycle where one
of the bundles has divided and the other is tangentially extended and
partially divided. The branching is carried further in the cortex, as
seen in fig. 483, C, where the trace is represented by a curved row of
six bundles, _lt_, and at a higher level further subdivision may occur.
The leaf-bundles are collateral and in the leaf retain both centripetal
and centrifugal tracheids. In the section shown in fig. 483, C, the
oval stele of an axillary shoot is seen at _s_ subtended by the row of
collateral bundles: the stele has a fairly large pith surrounded by a
zone of secondary xylem with broad medullary rays.
[Illustration: Fig. 483. _Mesoxylon Sutcliffii_. Transverse sections
of stem. A. _a_, outer pith; _b_, axillary bud; _x_² secondary xylem.
B. _cp_, _cf_, centripetal and centrifugal xylem; _px_, protoxylem. C.
_lt_, leaf-traces in the cortex; _s_, stele of axillary branch; _ph_²,
secondary phloem. D. Leaf-trace bundles, _lt_, external to the phloem,
_ph_². (A, C, D, sections in the Manchester Collection, 717 _b_; B,
Cambridge Botany School, 530.)]
* * * * *
Among other species of _Mesoxylon_ mention may be made of _M. Lomaxi_
and _M. poroxyloides_. _M. Lomaxi_ Scott and Maslen[718] generally
resembles _M. Sutcliffii_ but shows the following distinctive features:
the leaves are more scattered and less crowded; the twin-bundles of the
leaf-traces fuse immediately on entering the pith, thus appearing for
the most part as single and not double strands in the perimedullary
zone; the centripetal xylem is well developed, the medullary rays are
deeper and the outer cortex has shorter bands of mechanical tissue.
In _Mesoxylon poroxyloides_ Scott and Maslen[719], the twin-bundles
of the traces unite soon after reaching the pith as in _M. Lomaxi_,
the secondary tracheids have only two rows, or sometimes a single row,
of bordered pits and the tracheids are rather smaller than in _M.
Lomaxi_ (20–40μ as compared with 30–60μ) and the medullary rays are
shallower. There is a particularly broad zone of spiral and reticulate
transitional tracheids at the inner edge of the wood as in _Cordaites_
and in _Dadoxylon Pedroi_ (fig. 476). The leaves of this species are
believed to be represented by the type described by Dr Benson as
_Cordaites Felicis_ (fig. 465)[720], but, as already suggested, it is
very probable that many or possibly nearly all the leaves from British
Coal Measures described as _Cordaites_ may belong to _Mesoxylon_.
The chief interest of the genus _Mesoxylon_ is its close resemblance
in certain characters to _Cordaites_ and _Poroxylon_: the presence
of strands of centripetal xylem in the perimedullary region is an
important feature in which _Mesoxylon_ differs from stems assigned
(under the generic name _Dadoxylon_) to _Cordaites_. _Mesoxylon_
differs from _Poroxylon_ in having a discoid pith like that of
_Cordaites_, but a more important difference is the absence in the
leaf-trace xylem of _Mesoxylon_ of bordered pits of the Araucarian
type, whereas in _Poroxylon_ Araucarian pits occur in both the
centripetal and centrifugal tracheids. In _Poroxylon_ the secondary
xylem is manoxylic; in _Mesoxylon_, as in _Cordaites_, it is pycnoxylic.
=The range of Cordaites and a consideration of other imperfectly known
genera.=
An increased precision in knowledge derived from anatomical
investigation often tends to demonstrate the untrustworthiness
of criteria based on external features previously employed with
confidence. This inevitable though, from the point of view of the
systematist, inconvenient result of intensive study is well illustrated
by the recent discovery of the stems named by Scott and Maslen
_Mesoxylon_[721]. A separation of _Cordaites_ from _Mesoxylon_, which
no doubt extended far beyond the British area, is possible only
if well-preserved petrified material is available. The leaves of
_Mesoxylon_, so far as our imperfect knowledge of them enables us to
express an opinion, are constructed on a plan almost identical with
those of _Cordaites_ and, as already stated, it is almost certain
that many of the impressions referred to _Cordaites_ were borne on
_Mesoxylon_ stems. An additional source of confusion is supplied by
the _Cordaites_-like leaves of _Poroxylon_. It is evident, therefore,
that even within the limits of the Carboniferous and Permian formations
the recognition of true _Cordaites_ leaves must often be attended with
considerable risk of error. Apart from the possible confusion between
the foliage of _Cordaites_ and _Mesoxylon_ there are other difficulties
as regards detached leaves which depart more or less widely from
the typical Cordaitean form. Leaves such as _C. circularis_ (fig.
468, B) and _C. grandifolius_ emphasise the lack of any thoroughly
satisfactory dividing line separating single pinnules of _Cardiopteris_
or _Cyclopteris_ on the one hand and leaves of _Psygmophyllum_
on the other from _Cordaites_. The petrified buds described as
_Dolerophyllum_[722] have been quoted by several authors as examples of
unexpanded shoots of _Cordaites_ though anatomical evidence warrants a
generic separation. In the case of species founded on leaves described
in this chapter as _Cordaites_ it should be remembered that further
research may necessitate an alteration in nomenclature.
Among the species included in _Cordaites_ is _Noeggerathiopsis
Hislopi_[723] (figs. 470–472), a type widely spread in India and in
other parts of Gondwana-Land: if the change of generic name is accepted
it involves the extension of the geographical range of _Cordaites_ from
Northern Europe and North America to the southern botanical province.
We have as yet no proof of the existence of _Cordaites_ in the Arctic
regions. The range in time of _Cordaites_ or of the Cordaitales has
generally been stated to be from the Upper Devonian to the Permian.
It is, however, by no means certain that the genus flourished before
the Carboniferous period, though it is clear that closely allied
types must have lived in pre-Carboniferous floras. The strata in New
Brunswick from which Dawson recorded his supposed Devonian _Cordaites_
have been shown to be Upper Carboniferous in age[724]. As regards the
length of time during which the Cordaitales existed we have no decisive
evidence. In recent years the tendency has been to extend their range
into the Mesozoic era, and there are several pieces of evidence in
favour of this. There is no doubt that considerations of age based on
the arbitrary divisions of the geological scale sometimes insinuate
themselves too thoroughly into questions connected with the duration
of plant-types whether represented by families or genera. We have been
accustomed to regard _Cordaites_ as a genus confined to the Palaeozoic
period, a type which with many others carried on the tradition of
Upper Carboniferous forests to the Permian floras and then made way
for the precursors of Mesozoic types. There is, however, no valid
reason for supposing that _Cordaites_ and other Palaeozoic genera did
not survive as less prominent members in succeeding floras. It must be
admitted that evidence in support of Mesozoic Cordaitales is not above
suspicion, though the probability is that _Cordaites_ or some allied
genera still flourished in the earlier stages of the Mesozoic era.
The data on which this opinion is based cannot be fully discussed in
a general treatise, but a few of the facts may be briefly considered.
Zeiller[725] and other authors have expressed the view that the
Cordaitales were not exclusively Palaeozoic. In addition to _Cordaites_
(_Noeggerathiopsis_) _Hislopi_ recorded from Rhaetic floras, other
possible representatives of the group are illustrated by specimens
included in such genera as _Yuccites_, _Bambusium_ and _Krammera_.
=Pelourdea= gen. nov.
The name _Yuccites_[726] was given to some detached, broad, linear
leaves from the Bunter sandstone of the Vosges which were compared with
the foliage of _Yucca_ and classed among Monocotyledons. The authors
of the genus also described a cylindrical cast as a _Yuccites_ stem,
including both stem and leaves in _Yuccites vogesiacus_. The supposed
stem, as Fliche[727] has shown, is a pith-cast and is appropriately
named by him _Endolepis vogesiacus_. The Vosges leaves are assigned
by this author to the genus _Cordaites_, a change of name which may
eventually be justified though as yet based on insufficient evidence.
There are objections to the institution of a new name in place of
_Yuccites_, but it is undesirable to retain a designation suggesting
false ideas with regard to affinity. A new name _Pelourdea_ (after
M. Pelourde of Paris, whose recent death deprives Palaeobotany of an
able and promising investigator) is therefore proposed for leaves of
the _Yuccites_ type which in form, venation, and spiral phyllotaxis
agree with those of _Cordaites_ but cannot confidently be assigned to
that genus or even to the Cordaitales. For linear leaves, especially
from Jurassic strata, resembling those of _Phoenicopsis_ the name
_Desmiophyllum_[728] is employed: these are very similar to those of
_Pelourdea_; they are characterised by their fairly uniform breadth and
afford no indication of their arrangement on the supporting axis.
_Pelourdea vogesiaca_ (Schimper and Mougeot).
The linear-lanceolate leaves described by Schimper and Mougeot as
_Yuccites vogesiacus_ and transferred by Fliche to _Cordaites_ are
probably specifically identical with specimens described by Mr
Wills[729] from Lower Keuper rocks in Worcestershire. The English
leaves were described by Arber[730] as _Zamites grandis_,—the name
_Zamites vogesiacus_ having been previously used by Schimper and
Mougeot,—on the ground that the supposed leaves were probably pinnae
of a cycadean frond, a view in agreement with an opinion previously
expressed with regard to similar leaves from Stonesfield[731]. A later
discovery by Wills of specimens, on which the drawing reproduced in
fig. 484 is based, of the same type of leaf showing the foliar nature
of the fossils necessitated the abandonment of the pinna-hypothesis,
and the original name _Yuccites vogesiacus_ was resuscitated[732]. The
leaves reach a length of 50 cm. and a maximum breadth of 6·5 cm.; the
lamina is entire, lanceolate or linear-lanceolate, the apex acuminate,
and the lower part rather abruptly contracted and attached by a broad
crescentic base; veins numerous, parallel, and occasionally forked.
Fliche records the occurrence of a small _Artisia_-like pith-cast and
pieces of stem with leaf-scars (4 × 3 mm.) in association with leaves
of _Pelourdea vogesiaca_ in Triassic strata in Lorraine. An imperfectly
preserved specimen described by Fliche as _Cordaianthus Minieri_[733]
resembles an inflorescence of _Cordaites_. It consists of an axis 15
cm. long, the lower part forming a peduncle, and on the upper portion
are linear bracts subtending oblong bodies which may be lateral fertile
shoots.
[Illustration: Fig. 484. _Pelourdea vogesiaca_. Reconstruction of a
foliage-shoot. (After Wills.)]
_Pelourdea hadroclada_ (Halle).
Dr Halle[734] recently published an account of some imperfect
leaves and stem-fragments from the Rhaetic of Scania which he named
_Phyllotenia_ (_?_) _hadroclada_, the generic name provisionally
adopted having been proposed by Salfeld[735] for some rather obscure
remains from the Corallian of Germany. It appears to have escaped
the notice of both authors that Saporta[736] in 1894 had adopted the
designation _Phyllotenia_ for some examples of broad parallel-veined
leaves from Lower Cretaceous rocks in Portugal very similar to
Velenovský’s _Krammera mirabilis_[737]. Some other generic name must
therefore be used. For the Rhaetic species the name _Pelourdea_ would
seem appropriate. The type-specimen consists of an axis 10–12 mm. in
diameter with spirally disposed transversely elongated leaf-scars
bearing sessile linear leaves similar to _Poa-Cordaites_; none of
them are complete, the largest is 6 cm. long and 5–7 mm. broad with
8–12 parallel veins. An examination of the original specimens in the
Stockholm Museum satisfied me that Dr Halle is justified in the opinion
that they may be fragments of some Cordaitalean plant and that he
was well advised to avoid the use of the name _Cordaites_. Salfeld’s
species, _Phyllotenia longifolia_, may be an imperfectly preserved
example of _Phoenicopsis_[738], but the material is too incomplete to
be identified with any degree of confidence.
_Pelourdea Imhofi_ (Heer).
The Triassic leaves from Switzerland described by Heer[739], and more
recently by Leuthardt[740], as _Bambusium Imhofi_, were referred by
Fliche[741] to the genus _Cordaites_. The lamina is ensiform, 25 cm.
long with a maximum breadth of 2·4 cm. Leuthardt’s photograph of
aerial stems and rhizomes of this supposed Monocotyledon are far from
convincing.
_Pelourdea keuperiana_ (Compter).
The leaves from the Lower Keuper of Thuringia assigned by Compter[742]
to _Cordaites_ without adequate evidence resemble those of _P.
vogesiaca_, but there is no evidence as to their manner of attachment;
they are 30–40 cm. long and from 1·5 to 2 cm. broad.
_Pelourdea megaphylla_ (Phillips).
This species was first described by Phillips[743] from the Middle
Jurassic Stonesfield Slate and afterwards referred to _Zamites_[744]:
the leaves bear a striking resemblance to foliage of the type
_Cordaites borassifolius_; the lamina is 30 cm. long and attains a
breadth of 3 cm., the apex is acuminate and slightly contracted towards
the broad concave base. My former comparison of these Stonesfield
leaves with the long pinnae of _Ceratozamia mexicana_ seemed to be
supported by Phillips’s type-specimen of _Palaeozamia longifolia_.
It may be that the supposed pinnae in Phillips’s type are spirally
disposed leaves: if this is the case the specimen may be a fragment
of a _Podozamites_; its specific identity with the larger detached
specimens, though probable, cannot be demonstrated. Some leaves figured
by Zigno[745] from Jurassic rocks of Italy as _Yuccites Schimperianus_
may be identical with _P. megaphylla_.
_Pelourdea mirabilis_ (Velenovský ex Corda +MS.+).
The generic name _Krammera_, suggested by Corda, was employed by
Velenovský[746] for large _Cordaites_-like leaves from the Lower
Cretaceous of Bohemia, for casts of cones regarded by him as stems, and
for fruit-like bodies. The leaves, previously described as _Flabellaria
chamaeropifolia_ Goepp., _Dammara albens_ Presl, etc., bear a close
resemblance to the large broadly linear leaves of _Cordaites_; the
lamina reaches a length of 40 cm. and between the veins occur 1–4 finer
striations. The fossils identified by Velenovský as stems bearing
crowded imbricate scales, which he regarded as the persistent bases
of _Krammera_ leaves, are probably cones; they agree very closely in
size and shape, also in the form of the scales, with cones of _Agathis_
and some other recent Conifers. As the designation _Krammera_ was
instituted primarily for cones and not leaves the name _Pelourdea_ is
substituted for it.
=Niponophyllum.= Stopes and Fujii.
_Niponophyllum cordaitiforme_ Stopes and Fujii.
The generic name _Niponophyllum_[747] was proposed for some petrified
specimens of leaves or possibly leaflets from Upper Cretaceous beds
in Japan which, though not definitely assigned to a group or family,
are considered by the authors of the genus ‘to lie [anatomically]
somewhere between _Cordaites_ and _Cycadeoidea_’ ‘with a closer
similarity to the former than to the latter if we compare the whole
_Cordaites_ leaf with our blade.’ The data on which this conclusion
is based are, however, insufficient to justify a reference of
_Niponophyllum_ to the Cordaitales or indeed to lend any substantial
support to the opinion that the Japanese specimens are anatomically
more akin to _Cordaites_ than to other plants. The type-species is
represented by two specimens of leaf-fragments about 0·4 mm. thick and
from 6 to 9 mm. broad containing from 21 to 33 vascular bundles; the
upper part of the mesophyll is composed of palisade tissue and the
stomata appear to be confined to the lower epidermis. Each bundle is
accompanied by an =I=-shaped girder, and small patches of sclerenchyma
occur next the upper epidermis between the girders; there are no
resin-canals: the vascular bundles are collateral, the xylem is said
to be almost entirely centripetal and exarch, but in the absence of
evidence afforded by longitudinal sections the details of structure
cannot be definitely determined. A comparison is made with Cycadean
leaves and with leaves of Araucarineae and Podocarpeae, also with
_Cordaites_; another type with which _Niponophyllum_ may be compared is
_Desmiophyllum Solmsi_[748].
The genus is interesting as an example of a petrified gymnospermous
type of leaf characterised by the absence of resin-ducts and
transfusion-tracheids, the possession of collateral, apparently
exarch, bundles enclosed in a double sheath; but the data supplied
are insufficient to enable us to allocate the specimens to a position
within the class.
A specimen described by Schenk[749] as _Eolirion primigenium_ from
Lower Cretaceous beds in the Carpathian mountains closely resembles in
habit a foliage-shoot of _Poa-Cordaites_; the leaves are narrow and
linear with obtuse apices and attached, apparently, in a close spiral.
Schenk assigns the plant to the Monocotyledons, but its systematic
position must be left unsettled.
* * * * *
The list of Mesozoic specimens resembling _Cordaites_ leaves might
be extended. Apart from some Triassic and Rhaetic examples which may
well be Cordaitalean, there are many others which, though similar in
form and venation to _Cordaites_, are in all probability more closely
related to _Agathis_ and other genera; the species _Dammarites Bayeri_
recently described by Zeiller[750] from the Upper Cretaceous of
Bulgaria is a case in point. The Araucarian character of the wood of
_Cordaites_ precludes any satisfactory discrimination between Mesozoic
Araucarian stems and those of Cordaitalean species, at least in the
case of such material as is usually available.
=Titanophyllum.= Renault.
_Titanophyllum Grand’Euryi_ Renault. The remarkable leaves on which
this genus and species are founded[751] were discovered in the
Commentry coalfield; they occur as detached specimens and cannot be
correlated with any known stem. Renault suggests that the Autun stems
referred to _Colpoxylon_ may have borne the _Titanophyllum_ leaves,
but this correlation rests only on the dimensions of the stems and
the occurrence of transversely elongated scars on the surface. The
lamina is thick and coriaceous, 70–75 cm. long and 20–25 cm. in
breadth; the veins are parallel but not branched; numerous longitudinal
striations on the upper surface indicate the presence of hypodermal
stereome-strands; stomata are abundant on the lower surface and the
more or less rectangular cells in the neighbourhood of the stomata
appear to be papillose (fig. 485, A, B). The distal region of the
lamina is often torn into strips (fig. 485, A); the approximately
rectangular leaf has a broad elliptical base 9–10 × 3–4 cm.
[Illustration: Fig. 485. _Titanophyllum Grand’Euryi._ A, leaves
¹⁄₃₀ nat. size; B, stomata on the lower surface of the lamina. (After
Renault and Zeiller.)]
Dr White[752] describes a specimen from the Lower Coal Measures of
Missouri as ? _Titanophyllum Brittsii_ which he speaks of as the thick
base of a leaf similar to that described by Renault but, as White says,
no formal diagnosis is possible without more satisfactory material.
Such evidence as is available suggests that _Titanophyllum_ is a type
of Cordaitalean leaf probably closely allied to _Cordaites_.
CHAPTER XXXIV.
CORDAITALES.
C. =PITYEAE.=
=Pitys=. Witham.
This generic name in the form _Pitus_ was first used by Witham[753]
for some petrified pieces of large stems from Lower Carboniferous
strata in the south of Scotland (Berwickshire). In an earlier paper
Witham[754] gives an account of the beds on the banks of the Tweed from
which the specimens of _Pitys_ and other plants were obtained. The name
was revived by Goeppert[755] as a substitute for _Pissadendron_[756]
adopted by Endlicher and Unger: Scott[757] employed the older name in
the account of his investigations, which have added greatly to our
knowledge of Witham’s types. The distinguishing characters of _Pitys_
are: the Araucarian pitting of the secondary xylem, the large pith, the
occurrence of numerous small primary xylem strands of mesarch structure
in the peripheral region of the pith, and the simple nature of the
leaf-traces. Nothing is known of the extrastelar tissues, and beyond
the fact that the species were arborescent we have no information with
regard to the foliar[758] or reproductive organs.
[Illustration: Fig. 486. _Pitys antiqua._ Central region of stem,
showing primary xylem strands as black dots. (Kidston Collection, 598
A.)]
_Pitys antiqua_ Witham.
In 1899 Scott[759] published a preliminary description of some sections
in the possession of Dr Kidston from Lennel Braes (Berwickshire:
Calciferous series) under the name _Araucarioxylon antiquum_, but
in the more complete account the name _Pitys_[760] is adopted. The
following description is based on Scott’s paper and on the examination
of the sections. Fig. 486 represents a diagrammatic sketch of a section
(2·7 × 2·7 cm.) of the central region of a stem which had lost most
of its secondary wood. In some cases the pith reaches a diameter of
3 cm.; it consists of large parenchymatous cells broader than deep,
several of which contain a black substance and are probably secretory
elements: the intercellular spaces are fairly large. Horizontally
extended gaps, due to shrinkage and collapse, occur in the pith and
give to it an appearance not unlike that of _Cordaites_. Numerous small
elliptical strands of primary xylem, 0·15–0·3 mm. in diameter, are
scattered in the peripheral region (fig. 486) at varying distances from
the inner edge of the secondary wood and occasionally, when about to
bend outwards as a leaf-trace, a primary xylem-strand abuts directly
on the secondary xylem. The protoxylem occupies a more or less central
position in each mesarch strand (fig. 487, B, _px_): the centrifugal
tracheids have the Araucarian pitting while the centripetal elements
are spiral. A few parenchymatous cells are associated with the more
central tracheids. A leaf-trace about to bend outwards into the zone of
secondary wood is double, but at a slightly higher level in its course
it assumes the form of a single strand. The foliar bundles are thus
single and not true double traces. Scott recognised, at the extreme
edge of the pith, an association with outgoing leaf-traces of a single
reparatory strand deeper in the medullary tissue. In this species there
is no evidence that an outgoing trace is accompanied by an arc of
secondary xylem, but that such was the case is rendered highly probable
by the discovery of an arc of wood added by the cambium to a leaf-trace
in _Pitys Withami_[761]. The radial disposition of the pith-cells, many
of which appear to be secretory, around each primary xylem-strand (fig.
487, B) is a characteristic feature. A difficult problem, namely the
relation of primary xylem and phloem, is raised by the fact that the
primary strands are composed exclusively of xylem and are in most cases
separated from the secondary wood by several parenchymatous cells.
Scott favours the view that the primary phloem was originally at some
distance from the primary xylem, the cambium being formed nearer to the
phloem, an arrangement foreign to recent Gymnosperms. It is perhaps
conceivable that the primary conducting strands included no true phloem.
[Illustration: Fig. 487. _Pitys antiqua._ A, radial section of
secondary xylem; B, transverse section showing the inner edge of the
secondary wood and two primary-xylem strands with protoxylem, _px_.
(Kidston Coll.)]
The secondary xylem consists of tracheids with 4–5 alternate rows of
hexagonal pits on the radial walls (fig. 487, A) and not infrequently
on the tangential faces. Near the ends of the tracheids the pits are
occasionally more scattered and separate and may be reduced to a single
row[762], but on the whole the pitting is essentially Araucarian. The
medullary rays are generally 4 cells in breadth, but may be 7 cells
broad. In depth the rays extend to 70 cells. As seen in fig. 487, B,
the inner ends of the rays are especially broad owing to the tangential
dilatation of the cells. The innermost secondary tracheids are
characterised by pitting intermediate between spiral and reticulate.
There are no regular rings of growth in the wood.
_Pitys primaeva_ Witham. This species[763], also founded on material
from the Calciferous sandstone of Berwickshire, differs from _P.
antiqua_ in the broader and shorter form and greater breadth of the
medullary rays (fig. 488, A, B), also in the larger tracheids and
in the less crowded arrangement of the bordered pits in which the
circular form sometimes replaces the hexagonal type. The structure
of the pith is not known, but Scott was able to recognise in the
partially preserved pith of a branch indications of primary-xylem
groups and other features pointing to a close resemblance to _P.
antiqua_[764]. A piece of stem originally described by Williamson[765]
as _Lyginodendron_ (?) _anomalum_ from the Lower Carboniferous volcanic
ash of the Isle of Arran would appear to be closely related to, if
not specifically identical with, _P. primaeva_ and, as Scott says, it
should at least be included in the same genus.
[Illustration: Fig. 488. _Pitys primaeva._ A, transverse section of
the secondary xylem; B, tangential section of the secondary xylem.
(From sections of the type-specimen in the Edinburgh University
Botanical Department.)]
_Pitys Withami_ (Lindley and Hutton). The Craigleith Tree.
1831. _Pinites Withami_ Lindley and Hutton, Foss. Flora, Vol. +i.+
Pl. +ii.+
1831. _Pinites medullaris_, Ibid. Pl. +iii.+
1902. _Pitys Withami_ Scott, Trans. R. Soc. Edinb. Vol. +xl.+ p. 354,
Pl. +ii.+ fig. 10: Pl. +vi.+ fig. 21.
This species was founded on some sections cut from an incomplete stem
36 feet long obtained in 1826 from the Calciferous sandstone of the
Craigleith quarry near Edinburgh. The specimen named by Lindley and
Hutton _Pinites medullaris_ is no doubt specifically identical with
the larger stem. In the same year (1831) Witham[766] published an
account of a still larger stem from the same locality, 47 ft long and
5 ft in diameter in the lower part, and in his book the name _Pinites
Withami_ is adopted. A large specimen of this tree is erected in the
grounds of the Natural History Museum, London, and other specimens
are preserved in the Edinburgh Botanic Garden. Goeppert in 1850
referred the species to _Dadoxylon_ and later to _Pitys_[767], while
Brongniart[768] assigned it to his genus _Palaeoxylon_. Scott[769], who
examined Witham’s sections placed it in _Pitys_. The pitting of the
secondary tracheids is often multiseriate, but the medullary rays are
narrower than in _Pitys antiqua_ and _P. primaeva_, rarely exceeding
4 cells in breadth, though still of the manoxylic type. Primary-xylem
strands occur in the peripheral region of the pith agreeing closely
with those of _P. antiqua_. There are no regular and continuous annual
rings though as Witham stated there are concentric markings on the wood
which superficially resemble true rings. The leaf-traces are single
and in their passage through the cylinder of wood an arc of secondary
tracheids is added to the primary elements.
=Archaeopitys.= Scott and Jeffrey.
_Archaeopitys Eastmanii_ Scott and Jeffrey. The genus
_Archaeopitys_[770] has recently been instituted for a specimen of a
stem from the Lower Carboniferous rocks of Kentucky which differs from
_Pitys antiqua_, the type with which it is most closely allied, in the
position and behaviour of the primary vascular strands in the pith. The
type-specimen is a piece of stem 2·7 cm. in diameter including a solid
parenchymatous pith 5·5 mm. broad and a cylinder of secondary wood. The
wood is similar to that of _Cordaites_; the tracheids have 2–3 rows of
pits but for the most part the details of structure are not preserved;
the medullary rays are both uniseriate and multiseriate and not very
deep; the structure is more Cordaitean than Cycadean. A characteristic
feature is the occurrence of about 30 vascular bundles in the medullary
region: these mesarch strands, with the protoxylem near the centre,
are scattered through the pith and several lie on the outer edge in
contact with the secondary xylem or are partially embedded in the
xylem-cylinder. The examination of a series of sections demonstrated
the fusion of perimedullary with medullary strands and the occasional
union of the strands of both regions with one another. It appears that
the perimedullary strands are the leaf-traces while the strands deeper
in the pith are merely branches from the peripheral leaf-trace strands.
In _Pitys antiqua_ the medullary xylem strands are confined to
the outer zone of the pith and constitute the leaf-traces: in
_Archaeopitys_, on the other hand, the medullary strands are
scattered through the pith and the leaf-traces are restricted to the
circummedullary region in actual contact with the secondary xylem. In
the Devonian genus _Callixylon_ there are similar strands but they are
confined to the edge of the pith and are usually in contact with the
wood as are the circummedullary strands in _Archaeopitys_. The grouping
of the secondary xylem of _Callixylon_ into wedge-shaped masses at the
inner edge of the cylinder is a characteristic feature; this feature is
less definite in _Archaeopitys_ and absent from _Pitys_.
=Callixylon.= Zalessky.
_Callixylon Trifilievi_ Zalessky. This genus is represented by a
single species[771], originally referred to _Dadoxylon_, founded on
material from Upper Devonian rocks in the Donetz basin, Russia, and
based solely on the anatomical characters of the secondary wood and
central region of an arborescent stem. The wood is pycnoxylic and
of the Araucarian type; the inner portion of the xylem-cylinder is
divided into groups, similar to the regular wedges in a Calamite stem,
consisting of tracheids converging towards an obtuse apex occupied by
a primary xylem strand, fig. 489, A, _a_, _b_. On the radial walls of
the tracheids the bordered pits not infrequently form a single row of
flattened ovals, but more usually there are two or sometimes three
rows of alternate contiguous pits (fig. 489, B): circular and separate
pits also occur. As Zalessky states, the pits do not always occupy the
whole radial face; unpitted patches sometimes interrupt the continuity
of the pitted areas[772]. Similar circular and more scattered pits
are unusually abundant on the tangential walls. There are no complete
rings of growth. The medullary rays are narrow and, except at their
dilated inner ends, uniseriate; usually one or a few cells deep, they
may reach a depth of 12 or more cells. The pits on the radial walls
of the ray-cells are said to be 4–7 in the field. The pith consists
of thin-walled flattened parenchyma frequently elongated in a radial
direction. At the inner edge of the secondary xylem and generally in
contact with it are several anastomosing strands of primary xylem,
mesarch in structure but with the protoxylem nearer the inner edge.
These bundles may be single (fig. 489, A, _a_) or double (fig. 489, A,
_b_, and C) and closely resemble those of _Pitys antiqua_ except in
their closer relation to the secondary wood. The leaf-traces have not
been described, but the occurrence of twin-bundles like those in fig.
489, C, suggests that they were double. The primary-xylem elements
show particularly well transitional forms of pitting connecting the
multiseriate and scalariform types.
_Callixylon_, though conveniently and justly regarded as a distinct
genus, exhibits in its primary xylem a fairly close agreement with
_Pitys_[773]. The above account is based in part on Zalessky’s
description and partly on specimens in Dr Kidston’s possession.
[Illustration: Fig. 489. _Callixylon Trifilievi._ A, C, the inner
margin of the secondary xylem showing strands of primary xylem,
_a_, _b_, and C. B, tracheids of the secondary xylem. (A, C, from
photographs supplied by Prof. Zalessky; B, Cambridge Botany School.)]
Miss Elkins and W. Wieland[774] have recently described some Upper
Devonian wood from Indiana characterised by a grouping of the circular
or elliptical bordered pits in the radial walls of the tracheids
similar to those in _Callixylon Trifilievi_ which they include
together with the Middle Devonian species _Cordaites Newberryi_[775]
in Zalessky’s genus. Though these two American species are comparable
in the discontinuous arrangement of the tracheal pits with the
Russian type the latter is characterised by the presence of primary
xylem-strands, a feature that has not been recognised in the American
stems: it would seem, then, undesirable to adopt the designation
_Callixylon_ in preference to _Dadoxylon_ unless there is evidence as
to similar characters in the primary region of the xylem.
=Coenoxylon.= Zalessky.
_Coenoxylon Scotti_ Zalessky. Prof. Zalessky[776] gave the name
_Coenoxylon_ to a small and incomplete piece of stem of doubtful
provenance but possibly from the Ural Permian beds. The pith, 2 cm.
broad, consists of parenchyma associated in the central region with
numerous large sclerous cells. In one section a sinuous band of
meristematic tissue was observed near the periphery of the pith: the
appearance of this tissue in a photograph given to me by Prof. Zalessky
suggests comparison with occasional strips of similar dividing cells
in the pith of _Lyginopteris_. The secondary wood is composed of
tracheids with 1–2 rows of flattened or hexagonal pits on the radial
walls and narrow uniseriate medullary rays reaching a depth of 15 cells
and with 2–7 oval pits in the field. As in the wood of _Mesopitys
Tchihatcheffi_[777] there are distinct and apparently complete rings of
growth.
It is on the ground of the arrangement and structure of the primary
xylem that Zalessky instituted a new generic name. The primary xylem
forms teeth of variable size which project into the pith from the edge
of the secondary xylem: the prominent portions of the main mass of
primary xylem give off branches, differing considerably in size and
shape, some of which become separated by a comparatively broad band
of parenchyma from the parent xylem-tissue. These bundles anastomose
in their course through the pith and in doing so incorporate between
them patches of parenchyma. The bundles of primary xylem are endarch.
From the centrifugal strands at the periphery of the pith double
leaf-traces are produced which pass almost horizontally through the
secondary wood. As Zalessky points out, the leaf-traces in their dual
nature and in the elongated and narrow form of the tracheal groups,
as seen in tangential section of the secondary wood, bear a close
resemblance to those of _Ginkgo biloba_.
This Russian genus agrees in its double leaf-trace with _Mesoxylon_,
_Mesopitys_, and _Antarcticoxylon_: among recent plants _Ginkgo_ would
seem to be the most closely allied type.
=Parapitys.= Zalessky.
The designation _Parapitys_[778] has been proposed for a single Upper
Carboniferous species characterised by the possession of secondary wood
like that of _Cordaites_, double leaf-traces, and small mesarch primary
xylem-strands. Nothing is known of the leaves or reproductive organs.
_Parapitys Spenceri_ (Scott).
In 1880 Williamson[779] published a short account of a transverse
section of a specimen found by Mr J. Spencer in Upper Carboniferous
strata near Halifax in Yorkshire which afforded evidence of the
occurrence of double leaf-traces. The following description is taken
from Scott’s account[780] of the species, which he named _Dadoxylon
Spenceri_. The parenchymatous pith, 5–6 mm. in diameter, is obtusely
pentagonal, the prominent angles corresponding to the points of exit
of paired leaf-traces like those of _Mesoxylon_, _Ginkgo_, and other
genera. The secondary xylem consists of narrow tracheids with crowded
multiseriate pits on the radial walls and narrow medullary rays
one-cell broad and 1–8 cells deep. In contact with the inner margin
of the secondary wood are a few small mesarch strands of primary
xylem, the protoxylem and some parenchyma occupying a more or less
central position. A leaf-trace about to enter the secondary xylem is
represented by twin-bundles which retain their double nature as they
traverse the stele, but at a lower level the two components fuse and
appear as single bundles at the outer edge of the pith. The division
of a leaf-trace into two before passing out, as in _Poroxylon_,
constitutes a difference from _Lyginopteris_ in which the division
occurs later.
Zalessky’s generic name _Parapitys_ is an appropriate substitute for
_Dadoxylon_ in view of the presence of separate primary xylem strands,
a feature foreign to typical Dadoxylons which agree with recent
Conifers and Cycads in the absence of vascular strands distinct from
the endarch centrifugal wood. As Scott[781] says, _Parapitys_ ‘is best
regarded as a near ally of _Mesoxylon_.’
=Mesopitys.= Zalessky.
_Mesopitys Tchihatcheffi_ (Goeppert). The genus _Mesopitys_ was
instituted by Zalessky for a Permian species founded by Goeppert[782]
on a piece of decorticated stem from the Kousnetzk basin in Siberia
and afterwards more fully described by Goeppert and Stenzel[783].
The structure of the secondary wood led Goeppert to adopt the name
_Araucarites_ for which Kraus[784] substituted _Araucarioxylon_.
A recent investigation of additional material by Zalessky brought
to light the existence of groups of primary xylem abutting on the
secondary xylem and projecting into the pith, characterised by the
occurrence of spiral protoxylem elements on the inner edge. The
recognition of this important feature justified Zalessky in the
adoption of a new generic term. In general anatomical characters
_Mesopitys_ agrees with _Eristophyton Beinertianum_ (Goepp.) but is
distinguished by the more feebly developed primary-xylem groups and by
their endarch structure.
The examination of sections from some of Prof. Zalessky’s material
lent to me by Dr Kidston enables me to confirm Zalessky’s description,
though I am not convinced that the primary xylem-strands are
exclusively endarch: in most of the primary groups the protoxylem is
clearly on the inner edge, but in a few cases there may be a small
amount of centripetal xylem present. The characters of _Mesopitys
Tchihatcheffi_ may be summarised as follows:
Annual rings well defined, varying considerably in breadth; the summer
wood is represented by several rows of narrower tracheids (fig. 490,
A). In the piece of stem shown in the figure the breadth of the wood
from the flattened and crushed pith to the broken outer edge is 6 cm.
The medullary rays are numerous, uniseriate, rarely 2 cells in breadth;
the pits on the radial walls of the ray-cells, 7–10 in the field, are
apparently simple, oval, and oblique: the rays are generally 3–4 cells
in depth but may be deeper. There are 1–3 rows of hexagonal alternate
rows of pits on the radial walls of the tracheids. The primary xylem
consists of groups, varying in size and sometimes reduced to a very
few elements, in contact with the secondary xylem, usually though
probably not invariably endarch. In the two narrow radially elongated
and partially destroyed primary strands shown in fig. 490, B, the
protoxylem, _px_, is on the inner edge. The leaf-trace passes through
the secondary wood as a single strand. In the section reproduced in
fig. 490, A, the crushed and flattened pith measures 9 by 2 mm.; it
consists of thin-walled parenchyma with a few scattered thicker-walled
cells.
[Illustration: Fig. 490. _Mesopitys Tchihatcheffi._ A, transverse
section showing rings of growth in the wood. B, primary xylem with
protoxylem, _px_, and the edge of the secondary xylem, _x²_. (Kidston
collection, 2156.)]
Nothing is known as to the structure of the cortical tissue or leaves.
=Antarcticoxylon.= Seward.
_Antarcticoxylon Priestleyi_ Seward. The specimen on which this
genus was founded was discovered by Mr Raymond Priestley[785] in a
boulder, probably derived from the Upper Beacon sandstone, on the
Priestley Glacier south of 74° S. lat. in the course of the journey
of the Northern Party of Capt. Scott’s second Antarctic Expedition.
The type-specimen is a piece of silicified stem 1 ft long and 3
ins. in diameter; there were no tissues preserved external to the
secondary wood and it is impossible to say what proportion of the
original thickness is represented. Annual rings are clearly marked
at least macroscopically (fig. 491, C) though there is very little
difference between the spring and summer tracheids: the centre of the
compressed stem is occupied by a lighter coloured elliptical area 7
× 2 mm. which superficially resembles a pith, but in the peripheral
region it consists of portions of a cylinder of spiral and scalariform
tracheids, the actual pith being not more than 2–3 mm. in breadth.
The pith consists of lacunar parenchyma separated by horizontal bands
of dark cells containing some secreted substance (fig. 491, F): the
preservation is, however, not sufficiently good to enable one to
describe it in detail. The secondary xylem is of the pycnoxylic type;
the tracheids have either a single row of contiguous and partially
flattened pits on their radial walls or a double row of alternate
polygonal pits; the medullary rays are nearly always uniseriate
(fig. 491, E) and from 1 to 24 cells in depth. At the inner edge of
the secondary wood there was a fairly broad zone of more delicate
tracheids (fig. 491, A, _x_) characterised by spiral or scalariform
bands and by their relatively small diameter. This innermost zone,
which supplies the leaf-traces, is spoken of as the primary xylem; it
appears to be endarch though this cannot be definitely determined.
A characteristic feature of the primary xylem in the perimedullary
region, as also in the leaf-traces on their way through the secondary
wood, is the presence of short and broad tracheids (fig. 491, D, _t_)
with reticulate thickening bands: these short elements may represent
centripetal xylem and are similar to the short tracheids described
by Scott[786] in the sheath of _Mesoxylon Lomaxi_ and to the larger
elements in the stem of _Megaloxylon_[787].
An interesting feature seen in transverse sections of the secondary
wood is the occurrence of light bands concentric with the rings of
growth which are broadest near the long axis of the stem (fig. 491, C).
In their narrower parts these bands are clearly due to the partial
destruction of the secondary tracheids, but in other places crushed
parenchymatous tissue occurs which may be a traumatic phenomenon or
possibly comparable with Nördlinger’s ‘medullary spots[788]’ formed
by local hypertrophy of medullary tissue. Although the structure of
the leaf-traces cannot be definitely determined, it would seem that
each trace passed into the perimedullary region as a single bundle of
relatively large size composed of spiral and scalariform tracheids
narrower than the secondary elements. The traces during their outward
course were accompanied by some parenchymatous tissue continuous with
that in the pith, and the inner spiral tracheids of the trace were
connected with isodiametric reticulate elements. The dimensions of the
leaf-traces point to leaves of fairly large size.
[Illustration: Fig. 491. A–F, _Antarcticoxylon Priestleyi._ A, B,
transverse sections of the xylem; _a_, small tracheids simulating
protoxylem; _x_, xylem at the edge of the pith. C, transverse section
showing leaf-traces, _l_, _a_, _b_. D, leaf-trace with short tracheids,
_t_, in the pith; _s_, sclerous cells. E, tangential section. F, pith
in longitudinal section. G, _Pityosporites antarcticus_; see Vol. +iv.+
(All the sections are in the British Museum.)]
In the structure of the secondary wood _Antarcticoxylon_ agrees on
the whole with an Araucarian stem: the broad zone of xylem composed
of spiral and scalariform tracheids at the edge of the pith is a
feature common to _Mesoxylon_, _Cordaites_, and _Araucaria_. There
is no evidence of the occurrence of double leaf-traces such as
characterise certain Cordaitalean genera and some existing members of
the Araucarineae. In the single nature of the leaf-traces the Antarctic
stem resembles _Mesopitys Tchihatcheffi_ also in the presence of rings
of growth[789], but in _Antarcticoxylon_ the preservation of the
primary xylem is too imperfect to admit of any satisfactory comparison
as regards this important tissue with other types.
The precise age of the Beacon sandstone has not been determined,
but the probability is that the upper beds from which the boulder
containing _Antarcticoxylon_ was derived are not older than the Rhaetic
period. The chief interest of this imperfectly preserved stem with
undoubted Araucarian affinities is its occurrence in the rocks of
Antarctica in association with other remains of comparatively large
stems.
CHAPTER XXXV.
PALAEOZOIC GYMNOSPERMOUS SEEDS.
Seeds are abundantly represented as fossils from Carboniferous to
Post-Tertiary deposits. The importance of fossil and sub-fossil
species in the later geological series has been demonstrated by the
investigations of Mr and Mrs Clement Reid and a few other workers in
this neglected field. In cases where it is possible to assign seeds
to their parent-plants the descriptions of casts, impressions, or
petrifactions are added to the account of vegetative organs; but
it frequently happens that seeds are preserved only as detached
specimens many of which have little or no value as botanical records,
while others that afford striking examples of the possibilities of
petrifaction as a means of preserving the most delicate structures,
are of great importance. In Volume +ii.+ an account was given of such
Palaeozoic seed-bearing organs as _Lepidocarpon_ and _Miadesmia_, and
the genera _Lagenostoma_, _Sphaerostoma_, and _Trigonocarpus_ are
dealt with in this volume under _Lyginopteris_, _Heterangium_, and
_Medullosa_. Certain seeds afford some evidence as to the systematic
position of the parent-plants though insufficient to warrant more than
a surmise as to the nature of the vegetative organs: in several cases
it is only from the resemblance of detached seeds to types that on the
strength of more or less convincing evidence are referred to definite
parent-plants that any conclusions can be drawn with regard to precise
systematic position. In view of the occurrence of several different
types of seeds that retain their morphological features, but cannot be
assigned with any degree of certainty to genera founded on vegetative
organs, a special chapter is devoted to a comparative study of selected
examples with the object of directing attention to data bearing on
evolutionary problems. The chief interest of Palaeozoic seeds to the
botanist lies in the facts they contribute towards the elucidation
of questions connected with the promotion of the megasporangium and
megaspore of the Pteridophyta to the higher stage represented by the
integumented megasporangium (nucellus) and single megaspore that in
the main fulfil the definition of a seed[790]. ‘With the evolution
of the seed,’ as Oliver says, ‘the plant rose at a bound to a higher
plane, and this structure in its perfected form has become the very
centre of the plant’s existence[791].’ We can as yet form a very
partial conception of the successive stages in the adoption of the
seed-habit, but since 1855, the year in which Hooker and Binney[792]
published their paper on the structure of _Trigonocarpus_, ample
proof has been furnished of the importance of Palaeozoic seeds from
the standpoint of affinity between recent Gymnosperms and extinct
seed-bearing plants, and of the _modus operandi_ of evolutionary
tendencies. A cursory examination of Palaeozoic seeds suffices to
demonstrate their resemblance to those of recent Cycads and the seed
of _Ginkgo biloba_; but while it is clearly with these Gymnosperms
that the majority of the seeds described in the following pages are
most closely allied, the extinct types possess many distinguishing
features that throw light on some at least of the factors concerned in
the production of the modern type. In many of the Palaeozoic seeds the
nucellus stands free within the integument, to which it is attached
only in the chalazal region, in contrast to the lateral union between
integument and nucellus in the ovules of recent Cycads. It has been
suggested by Oliver[793] that the seed of the Conifer _Torreya_ affords
a clue to the interpretation of this difference and that the lower part
of the seed in Cycads and _Torreya_ represents a later intercalation
in the basal portion of the ovule, the ancient type having a free
nucellus in contrast to the nucellus of modern seeds which is free
only at the apex. It has been objected[794] that there are no adequate
grounds for assuming the addition of an intercalated zone or of the
elongation of the ovule that this implies, the more probable view
being that the lateral union of nucellus and integument represents
congenital fusion in the ancestral type, a fusion comparable with that
of the coherent petals of a gamopetalous corolla. In the presence of a
pollen-chamber most of the Palaeozoic seeds agree with those of recent
Cycads, but in the extinct forms it is usually a more highly developed
structure. The name pollen-chamber was given by Brongniart[795] to
the pollen-containing cavity in the free region of the nucellus in
the petrified seeds from St Étienne in ignorance of the use of the
same term by Griffith[796] in a posthumous work published in 1852 for
the nucellar chamber in _Cycas_[797]. The genus _Stephanospermum_
(fig. 494, A) illustrates the means by which the pollen-chamber was
liberally supplied with water and thus adapted to the requirements of
fertilisation by motile gametes. The pollen-chamber and its vascular
supply paved the way for siphonogamy, that is the development of a
pollen-tube for the more direct transmission of the male sperms. The
highly developed mantle of tracheal tissue at the periphery of the
nucellus in _Stephanospermum_, represented on a reduced scale by the
separate vascular strands of other seeds, may be compared with the
tracheal investment to the nucellus in the recent Dicotyledonous genus
_Cassytha_[798]. The presence of a nucellar vascular system in several
Palaeozoic seeds is a feature in which they differ from those of recent
Cycads with the exception of _Bowenia_. The retreat of the vascular
supply from the immediate neighbourhood of the pollen-chamber in recent
Cycads may, as Oliver points out, be correlated with the evolution of
the pollen-tube—the substitution of siphonogamy for zoidiogamy. The
diagram reproduced in fig. 492 represents a synthetic type based on
such seeds as _Stephanospermum_ and _Cardiocarpus_ which illustrate an
arrangement of conducting tissue frequently found in Palaeozoic seeds:
the main strand gives off a pair of bundles in the sarcotesta in the
principal plane, as in _Cardiocarpus_[799]; from the tracheal mass in
the chalazal region numerous bundles pass up the nucellus as far as the
floor of the pollen-chamber. The nature of the vascular supply in this
generalised type and in individual genera should be compared with that
in the seeds of recent Cycads[800] described in Chapter +xxviii.+
[Illustration: Fig. 492. ‘A conjectural synthetic type of seed
embodying the characters of such a seed as _Stephanospermum_ with those
of a _Cardiocarpus’_; _n_, nucellus; _pc_, pollen-chamber. (After
Oliver.)]
Recent research has revealed the not unexpected fact that in such
Upper Carboniferous petrified seeds as have been investigated—a
small proportion of the large number produced in the Palaeozoic
forests—there was a remarkable range in the mechanism connected with
pollination and the maturation of the microspores. A comparison of
the genera _Physostoma_, _Lagenostoma_, _Conostoma_, _Trigonocarpus_,
_Stephanospermum_ and others reveals the occurrence of very different
though not unrelated structural features especially in the apical
region of the seed. These seeds, including _Physostoma_, probably the
most archaic type, represent a stage in evolution already far removed
from the starting-point: the diversity of plan recalls the variety in
the form of the chloroplasts in the Green Algae, and in both cases
we are in touch with an experimental phase representing a tentative
advance towards greater efficiency.
In its differentiation into an outer fleshy region, the sarcotesta, a
stony layer, the sclerotesta, and in many cases an inner flesh, the
Palaeozoic seeds resemble recent Cycads: in both extinct and modern
seeds the balance of evidence would seem to be in favour of attributing
a single rather than a double origin to the integument.
Among the numerous types of Palaeozoic seeds are several which
invite comparison with the fruits or carpels, apart from the seeds,
of Angiosperms. Impressions of _Samaropsis_ seeds (figs. 502, B–K;
503; 504) bear a close resemblance to the laterally expanded fruits
of the common Crucifer _Thlaspi arvense_; the ribbed testa of
_Hexagonocarpus_ (fig. 506, H) and other genera recalls the fruit-wall
of _Alstroemeria_; the recently described Lower Carboniferous seed
_Thysanotesta sagittula_ Nath. (fig. 506, F) simulates a carpel of
_Erodium_. These and similar instances of a close parallelism in
external features between organs that are not homologous, though in
themselves of no morphological significance, are at least interesting
as illustrating the plasticity displayed by reproductive structures,
which in the Palaeozoic period marked a morphological achievement
comparable in its importance with the still greater achievement
represented by the highly specialised fruits of the modern Flowering
plants. The range in form and surface-features of Angiospermous
fruits was foreshadowed by Palaeozoic seeds. Structural types and
in some cases, superadded to these, features which may reasonably
be supposed to have facilitated dispersal had been acquired by the
seeds of Palaeozoic plants in forms that in a much later period were
adopted by fruits even to a greater degree than by seeds. Characters
useful in seed-dispersal, that are now shared by fruits and seeds,
are illustrated by the fleshy and possibly edible seeds of extinct
Gymnosperms, the plumes and hairy beak of _Gnetopsis_ (fig. 494,
E) and _Thysanotesta_ (fig. 506, F) suggestive of feathery stigmas
and other appendages. The lacunar sarcotesta of _Aetheotesta_, the
thick endotesta of _Pachytesta_ (fig. 497), and the air-chamber of
_Codonospermum_ (fig. 498), are strictly comparable with aids to
buoyancy in fruits of existing Flowering plants. The mucilage-hairs and
superficial cells in _Physostoma_ (fig. 494, I) and _Stephanospermum_
may be compared with the thick mucilaginous investment of the
megaspores of recent water-ferns and with similar tissues of some
Angiospermous seeds.
The bionomics of Palaeozoic plants is a subject worthy of more
serious attention than it has so far received. The search for
morphological characters that may have facilitated the wanderings
of widely distributed genera and species and a closer investigation
of physiological-anatomical problems presented by the vegetative
organs of petrified plants would not only extend our knowledge of the
morphology of ancient types but would stimulate comparative study
and, incidentally, relieve the dullness of pure description. It may
be argued that we should first establish a more solid foundation
by further observations on living plants; but even at the risk of
allowing speculation too free a hand the attempt is worth making, and
it may be urged that, as in phylogenetic enquiries so in other branches
of botany, facts obtained from plants of other ages may serve to
supply deficiencies in knowledge based only on existing forms. One of
the difficulties inseparable from the study of fossil plants, namely
the identification of impressions and casts with specimens exhibiting
anatomical characters, is particularly well illustrated by seeds. The
description of a genus based on mere external form may sometimes be
extended without great risk of error to include species founded on
anatomical characters, but on the other hand, there are many instances
in which—despite a general resemblance in form and size between
petrifactions and impressions—lack of evidence of generic identity
requires the employment of distinctive names. The determination of
impressions is, as Lesquereux recognised, ‘subject to a great deal of
uncertainty,’ and many of the genera founded on external features are
purely artificial and include species that have no essential features
in common. Moreover in the case of petrified specimens the apparent
absence of an external fleshy layer is often due to destruction before
preservation: as Solms-Laubach[801] points out, it is obviously
impossible to be certain as to the number of integumental layers
in seeds that are not well preserved in all their parts. Goeppert
founded a new genus, _Acanthocarpus_, on a Permian seed described as
_A. xanthioides_[802], because of the occurrence of spinous processes
attached to an obcordate kernel: these apparent spines are in all
probability the remains of a very imperfectly preserved sarcotesta. The
preservation of the central portion of a seed, that is the seed-cavity
with the enclosing shell, conveniently called the nucule, has often led
to an unnecessary multiplication of generic terms. Other examples of
confusion resulting from different states of preservation are quoted in
the accounts of some of the selected types.
Williamson in 1877 pointed out that we learn from the large number
of different kinds of Palaeozoic seeds that ‘there were in the
Carboniferous forests many gymnospermous stems clothed with foliage
of which we have not yet discovered any traces, probably because
these Gymnosperms did not flourish upon the low swampy grounds which
were the homes of the great mass of the coal-producing plants[803].’
Prof. Zeiller[804] has also drawn attention to the numerical excess of
seeds over vegetative organs. This discrepancy has to a large extent
been explained by the discovery that many of the supposed Ferns were
seed-bearing plants, and a further explanation is suggested by the
superiority of seeds over stems and leaves in their adaptation to
dispersal by water.
In 1874 Brongniart[805] described several petrified seeds from material
discovered by Grand’Eury in the St Étienne coal-field, and seven years
later his descriptions were republished[806], with the addition of
several beautifully executed drawings, as a posthumous volume edited by
his distinguished pupil Renault. Williamson’s researches supplied much
additional information, and in recent years the more detailed study of
French and English seeds by Bertrand and particularly by Oliver and
his pupils has further emphasised the interest and importance of this
field of work. Brongniart proposed a two-fold classification of French
seeds: (i) bilaterally symmetrical seeds, more or less flattened in
section, which he believed to be Cordaitean; (ii) radially symmetrical
seeds, circular in transverse section: the latter group he considered
to be less closely allied to recent types. The employment of the
terms Platyspermeae and Radiospermeae, proposed by Oliver[807] for
Brongniart’s divisions, serves a useful purpose if due regard is paid
to the adequacy of the evidence as to symmetry and if it is recognised
that this classification cannot be rigidly employed in all cases.
It was pointed out by Brongniart that the occasional occurrence of
tricarinate seeds of _Ginkgo_ (fig. 631) and _Taxus_ is an exception
to the general rule of bilateral symmetry: seeds of _Cycas_ are
normally bilateral, but radially symmetrical forms also occur[808].
The genus _Conostoma_ (fig. 494, B) represents an intermediate
type which, though almost radially symmetrical, exhibits a slight
tendency towards platyspermy. Evidence recently brought forward by
Nathorst[809] renders probable a connexion of a presumably radiospermic
seed _Lagenospermum Arberi_[810] with the Lower Carboniferous fronds
_Adiantites bellidulus_ Heer, and this furnishes an interesting
illustration of the association of both platyspermic and radiospermic
seeds with the same generic type of foliage. While retaining Radiosperm
and Platysperm as convenient descriptive terms, I have not adopted them
as group-designations on the ground that they do not in themselves
serve as trustworthy criteria of relationship. Attention is called
by Salisbury[811] to the occurrence of bilaterally and radially
symmetrical fruits among British Carices and to a similar mixture in
the family Polygonaceae.
The acquisition of more detailed and accurate knowledge of Palaeozoic
seeds led to an extension of the two-fold division of Brongniart
and Oliver which is based on such characters as the position of the
vascular tissue in relation to the integument and nucellus, the form of
the pollen-chamber, and other features. The division Lagenostomales has
been instituted for _Lagenostoma_ and some other Radiosperms connected
by certain important characters: these seeds may be referred to the
Pteridospermeae though it is only in the case of _Lagenostoma_, and to
a less extent _Sphaerostoma_, that a correlation between vegetative
organs and seeds has been rendered sufficiently probable to justify
an assumption of generic identity. The name Trigonocarpeae[812]
has recently been used for a section of Radiosperms represented by
_Trigonocarpus_, _Stephanospermum_, and other genera. Although the
genus _Stephanospermum_, as Oliver[813] says, may be regarded as
the type-genus of a group of seeds, it is more fitting, as the same
author[814] insists, to adopt a divisional term based on the generic
name of the much more widely spread and more familiar _Trigonocarpus_.
For the sake of uniformity in nomenclature it is proposed to adopt
the name Trigonocarpales instead of Trigonocarpeae to rank with
Lagenostomales.
The Platyspermeae comprise such seeds as _Cardiocarpus_,
_Mitrospermum_, and _Rhabdospermum_, genera characterised by
well-marked anatomical features and probably Cordaitean; it has,
however, been shown that typical Platysperms were also borne on leaves
of Pteridosperms and, as Mrs Arber[815] says, the notion that every
member of the Platyspermeae was necessarily a Cordaitean seed has been
discredited by the discovery of the seeds of _Aneimites_ (_Wardia_)
and _Pecopteris Pluckeneti_[816]. For general purposes it is hardly
necessary to adopt the subdivisions of the Lagenostomales used by
Oliver and Salisbury[817], though as facts accumulate we shall no
doubt be able to make further advances towards a natural system of
classification. The following three divisions of Permo-Carboniferous
seeds include genera founded on petrified specimens and thus
afford valuable morphological data. The groups Lagenostomales and
Trigonocarpales include types belonging to closely related plants, a
relationship clearly expressed in the seed-characters.
I. +Lagenostomales.+
The seeds included in this group are for the most part Radiosperms, but
in its slightly developed bilateral symmetry _Conostoma oblongum_ is a
type transitional between Radiosperms and Platysperms. The testa may
be ribbed and the ribs vary in number. The nucellus (megasporangium)
is united to the integument not only at the base but laterally as
far as the shoulder of the seed up to a level corresponding to the
base of the pollen-chamber (lagenostome) as in all recent Cycads
and in the majority of Conifers. The seeds proper apart from the
cupule are supplied with a single set of vascular bundles; there is
no vascular tissue in the nucellus, a feature no doubt correlated
with the fusion of nucellus and integument[818]. The free portion of
the integument is more or less deeply lobed or, in _Lagenostoma_, it
forms a pyramidal canopy of fused lobes enclosing the lagenostome. The
presence of a tapetal zone surrounding the megaspore is believed to
be a feature characteristic of the group[819]. The testa, wholly or
partially ribbed, is relatively thinner than in the Trigonocarpales and
Cardiocarpales, and in its differentiation agrees less closely with
the testa of recent Cycadean seeds. In _Lagenostoma_ and possibly in
other genera a loose sheath or cupule surrounded the ovule, while in
_Gnetopsis_ a similar envelope enclosed two to four seeds.
The microspores are multicellular and smaller than those of
Trigonocarpales, the average dimensions (_Conostoma_, _Physostoma_,
_Lagenostoma_) being 67μ × 52μ.
Genera. _Physostoma_; _Conostoma_; _Sphaerostoma_; _Lagenostoma_;
_Gnetopsis_.
_Lagenostoma_ may safely be referred to _Lyginopteris_, and
_Sphaerostoma_ with but little risk of error to _Heterangium_: the
parent-plants of the other genera are unknown, but all may be regarded
as the seeds of Pteridosperms and probably of genera more nearly
allied to the Lyginopterideae than to the Medulloseae. The genus
_Lagenospermum_, recently instituted by Nathorst[820], is dealt with in
Chapter +xxxi.+
=Physostoma.= Williamson.
_Physostoma elegans_ Williamson.
The generic name _Physostoma_[821] was applied by Williamson[822] to
a seed from the Lower Coal Measures of Lancashire which he named _P.
elegans_; he afterwards described it as _Lagenostoma physoides_, but
the original name has been revived by Oliver[823] to whom our knowledge
of this type is chiefly due. The specimens figured by Williamson[824]
as _Sporocarpon ornatum_ also belong to _Physostoma elegans_. The
seeds are circular in section, approximately 6 mm. long with a maximum
diameter of 2 mm. The testa has about 10 longitudinal ribs passing in
the apical region into a ring of free lobes or tentacles surrounding
and considerably overtopping the nucellar apex: these tentacles take
the place of a micropylar tube (fig. 494, I; fig. 493, D) and are a
feature ‘in which this seed differs from all other known seeds, fossil
or recent[825].’ A single vascular strand passes through the chalazal
region and divides into 10 bundles, one to each rib and tentacle.
The single integument consists of a few layers of cells, those of
the epidermis being prolonged into clavate mucilaginous hairs, fig.
494, I, _h_, that may reach a length of ·5 mm. and in the living seed
almost covered the whole surface of the testa, being especially long
on the ribs and tentacles. There is no special development of sclerous
tissue, the vascular bundles, _v_, being embedded in parenchyma in
the inner portion of the integument. The nucellus is represented by
a zone rich in secretory cells, and internal to this is a tapetum.
Integument and nucellus are coalescent up to the apical region where
the former splits into 10 tentacles. The nucellar apex has the form of
a tall dome surrounded by a bell-shaped pollen-chamber (fig. 494, I,
_pc_; fig. 493, C, D, _c_) into which it projects like the base of a
wine-bottle. The circular opening of the pollen-chamber overtops the
roof of the dome formed of the secretory tissue of the nucellus and the
carbonised remains of the tapetum: this dark band surrounds the large
megaspore-cavity (fig. 494, I). _Physostoma_ is the only member of the
Lagenostomales in which the megaspore projects into the free nucellar
apex: in other genera intercalary growth has produced a more or less
prominent plinth, the name given to the free portion of the nucellus
between the megaspore and the pollen-chamber. Williamson[826] described
the mammillated apex of the nucellus as pushed up into the base of the
lagenostome which ‘looks like a bladder half full of fluid resting
upon and overhanging the end of a soda-water bottle’: it was this
appearance that suggested the name _Physostoma_. The section reproduced
in fig. 493, D, shows in the centre the limiting tissue of the nucellus
surrounded by the pollen-chamber, _c_, and external to this are the
tentacles with their groups of long hairs: the vascular bundles are
represented by spaces in the more internal small-celled tissue (see
also fig. 494, I). A characteristic feature is the presence of a
tapetum or megaspore-jacket[827] in the nucellus: immediately internal
to the vascular bundles stretching from the chalaza to the apex of the
megaspore-cavity is a layer of delicate cells with secretory sacs,
and this is succeeded by a broad black layer of rather larger cells,
a tissue which was probably in full activity in a younger stage of
development.
[Illustration: Fig. 493. A, _Lagenostoma ovoides_, longitudinal
section of the lagenostome. B, _Lagenostoma Lomaxi_, transverse
section of the lagenostome and canopy; _c_, pollen-chamber; _d_, space
between the nucellus and integument. (A, after Miss Prankerd; B, from
a section in the Manchester Museum, R 1048.) C, _Physostoma elegans_,
longitudinal section showing microspores in the pollen-chamber, _c_.
(From a section in the University College Collection.) D, _Physostoma
elegans_, transverse section of the apical region showing the
tentacles, pollen-chamber, _c_, etc. E, _Telangium Scotti_, transverse
section of sporangia (Manchester Coll. R 1047). F, G, _Stephanospermum
akenioides_. F, section of sclerotesta. G, tracheids from the nucellus.
(University College Coll.)]
A comparable tapetal layer is described by Lang[828] in the ovule of
_Stangeria_: the majority of the sporogenous cells surrounding the
megaspore become disintegrated and are absorbed, but the outermost
zone forms a more definite tapetal layer: as already suggested, this
tissue in _Physostoma_ may be a group-character. No archegonia have
been found, but in a few cases some of the delicate prothallus-tissue
occurs in the interior of the seed. Microspores are often abundant
in the pollen-chamber (fig. 493, C, _c_); in one seed 80 are
recorded. The occurrence of so many microspores suggested to Oliver
that insect-agency may have been responsible for the precision in
pollination that is greater than one would expect in anemophilous
plants. The spores are smaller than those of _Lagenostoma_ (55μ × 45μ)
and in several of them the remains of a cellular tissue are preserved
(fig. 494, N), also some sub-reniform bodies (fig. 494, M) similar to
those described as spermatozoids by Dr Benson in _Lagenostoma_ (fig.
408, D).
The most interesting features of _Physostoma_ are: the absence of
a continuous micropylar tube and its replacement by a circle of
integumental lobes; the apical prolongation of the nucellar apex into
the pollen-chamber, and the presence of long mucilaginous hairs on the
integument. The large pollen-chamber is a character which distinguishes
_Physostoma_ from _Conostoma_ and its form is very different from that
in _Lagenostoma_.
The tentacles of the integument and the form of the nucellar apex are
features consistent with Oliver’s view that _Physostoma_ is the most
primitive of Palaeozoic seeds though, as Burlingame[829] says, the
elaborate form of the encasing envelope marks a considerable advance
beyond the earliest type of megasporangium integument.
A new type of _Physostoma_ has been briefly described by Gordon[830],
without a specific designation, from the Lower Carboniferous beds of
Pettycur (Fife): it was found in association with _Heterangium_ and
_Sphaerostoma ovale_.
We have no knowledge of the plant to which _Physostoma_ belonged,
but the general plan of organisation of the seed points to a near
relationship to _Lagenostoma_ and presumably, as regards the
parent-plant, to a genus related to _Lyginopteris_.
=Conostoma.= Williamson.
This name[831], suggested by the funnel-like pollen-chamber or
lagenostome, was applied by Williamson[832] to some seeds from the
Lower Coal Measures of Lancashire and Yorkshire and from the Lower
Carboniferous beds of Burntisland. The Burntisland seeds, referred by
Williamson to two species, have recently been united and described
by Miss Benson as _Sphaerostoma ovale_[833]. The English species has
been thoroughly investigated by Oliver and Salisbury[834] who have
also described a second species, _C. anglo-germanicum_, from the Coal
Measures of Lancashire and Germany.
_Conostoma oblongum_ Williamson.
This rare type is represented by approximately cylindrical seeds with
an average length of 5 mm. and a maximum breadth of 2·3 mm. borne on
a relatively stout stalk and tapering to a blunt apex characterised
by a canopy of six short lobes (fig. 494, B, C) in marked contrast to
the long tentacles of _Physostoma_. In the basal region the integument
has six prominent ribs which soon die out when traced upwards: a
transverse section through the body of the seed is hexagonal (fig.
494, D), the angles corresponding to the basal ribs, and there is a
slight tendency to platyspermy. The testa has an epidermal mucilaginous
layer which becomes exfoliated through the lifting-up of the cuticle
by the underlying mucilage: below this, at the apex of the seed, is
a cap of fleshy tissue (fig. 494, B, _sa_) which, it is suggested,
may have had a secretory function in connexion with a drop-mechanism
in pollination like that in recent Conifers. No microspores have
been found in the pollen-chamber. The epidermis, called by Oliver
and Salisbury the blow-off layer (fig. 494, B, _m_), together with
the cap of soft tissue constitute a feebly developed sarcotesta. A
sclerotesta consisting of a palisade-layer and a fibrous hypoderm
extends over the main body of the seed below the epidermis; it forms
the basal ribs and increases considerably in breadth at the apical
region to form a sclerous cone penetrated by six strands of parenchyma
enclosing vascular bundles (fig. 494, D) which pass up from the
conducting tissue immediately external to the nucellus. The nucellus
is coalescent with the integument, as in _Physostoma_, as far as the
level of the domical free apex of the nucellus where the tapetal tissue
that lines the seed-cavity passes across the almost flat top of the
central region originally occupied by the megaspore. In some sections
prothallus-tissue was found with an apical ‘tent-pole’ protuberance.
A striking feature of _Conostoma_ is the mechanism for the reception
of the microspores. The free part of the nucellus consists of the
plinth, a broad tapering region originally filled with parenchyma but
in most cases represented only by its epidermis: the plinth, _p_, is
seen in fig. 494, B, to be two-storeyed, the upper and narrower storey
being a space formerly filled by a pad of tissue suspended from the
floor of the superposed lagenostome (pollen-chamber)[835]. The greater
development of the domical plinth is a feature in which _Conostoma_
differs from _Physostoma_. At the apex of the plinth and resting on
a slight depression is a small lagenostome, bowl-shaped in section,
and like the pollen-chamber of _Lagenostoma_, formed as the result of
enzyme-action on the apical papilla of the nucellus (fig. 494, B, B′,
_l′_). The mouth of the lagenostome engages with the micropylar tube by
a projecting flange (fig. 494, B′, _f_) of tissue lining the micropylar
canal and by a second flange (_f′_) at the base of the lagenostome
where the roof of the plinth (fig. 494, B′, _p_) bends downwards and
inwards. The walls of the lagenostome are formed by strong cells with
thickening bands giving them the appearance of tracheids (_l′_),
but the floor of the lagenostome is made of thinner cells which
become disorganised, allowing the microspores to fall into the large
plinth-cavity below (_p_, fig. 494, B), an arrangement comparable
with the two-storeyed pollen-chamber of _Bowenia_[836] and, to a less
extent, with the micropyle of the Conifer _Tsuga_. The microspores are
multicellular and ellipsoidal measuring 75μ × 65μ.
[Illustration: Fig. 494. A, _Stephanospermum akenioides_; _s_,
space between integument and nucellus; _n_, nucellus; _e_, inner
part of testa; _sc_, sclerotesta; _t_, _t_, tracheidal mantle; _pc_,
pollen-chamber; _a_, archegonia; _td_, tracheidal pad. B–D, _Conostoma
oblongum_; _a_, level of the transverse section shown in fig. C; _b_,
level of transverse section D; _m_, lobes of tissue surrounding the
micropyle; _sa_, sarcotesta; _v_, vascular bundles; _p_, plinth. B′,
section of lagenostome and part of the integument; _f_, _f′_, flanges;
_l′_, wall of micropyle-funnel. E, F, G, _Gnetopsis elliptica_;
_t_, tent-pole. F, section of the plumes. G, section through the
lagenostome. H, _Gnetopsis_ from Barnsley, Yorkshire, slightly
enlarged. I, _Physostoma elegans_; _h_, hairs. K, L, _Mitrospermum
compressum_; _cf_, inner flesh; _n_, nucellus and megaspore. L,
transverse section. M, microspores and (?) male gametes of _Physostoma
elegans_. N, microspore of _Physostoma_ showing part of exine and the
internal cells. (A–I, N, M, after Oliver; H, Kidston Coll. No. 1255; K,
L, after Mrs Arber.)]
The species _Conostoma anglo-germanicum_ agrees closely with _C.
oblongum_ in general form and organisation, but it has eight ribs,
four more prominent than the others, and differs also in other
minor characters from the rather shorter seeds of the type-species.
_Conostoma_ differs from _Lagenostoma_ in the absence of the tubular
prolongation of the lagenostome, the micropyle being like that in
recent Gymnosperms. In _Conostoma_ the tracheid-like elements of the
lateral wall of the lagenostome are a characteristic feature, and no
evidence has been found of the existence of a central core of tissue
such as occupies the centre of the seed-apex in _Lagenostoma_. The
long hairs of _Physostoma_ are represented in _Conostoma_ by the much
smaller mucilaginous cells of the epidermis and in _Lagenostoma_ by
the less closely united mucilage-cells of the superficial layer of the
testa.
=Sphaerostoma.= Benson.
As already pointed out in Chapter +xxix.+ where this genus is described
as probably the seed of _Heterangium_, there is a fairly close general
resemblance between _Sphaerostoma_ and _Lagenostoma_. In the presence
of free apical lobes the former genus resembles _Conostoma_, and
while agreeing with _Lagenostoma_ in its annular pollen-chamber it
is peculiar in the retention of an epidermis over the roof of the
pollen-chamber: as in _Lagenostoma_ the seed is enclosed by an outer
integument or cupule.
=Lagenostoma.= Williamson.
An account of this type of seed is included in the description of
_Lyginopteris_[837]. The more striking peculiarities are exhibited by
the pollen-chamber and the free region of the integument: the annular
pollen-chamber (fig. 493, D, _c_; fig. 409) surrounds a central
nucellar cone and is prolonged upwards as a tube engaging with the
micropyle in contrast to the form of the pollen-chamber and the absence
of a tubular prolongation in _Conostoma_. The tentacles of _Physostoma_
and the short apical lobes of _Conostoma_ are replaced by an apical
cone formed by the coalescence of the integument containing nine
cavities originally filled with parenchyma (figs. 409; 493, B). The
presence of a cupule is a characteristic feature of young seeds, but
from negative evidence in the case of most other seeds it is unsafe
to assume that the cupule of _Lagenostoma_ is an exceptional feature.
The nucellus and testa are united as far as the shoulders of the seed
as in the seeds of recent Cycads and in contrast to their lateral
independence in _Trigonocarpus_, _Stephanospermum_, and other genera.
=Gnetopsis.= Renault.
This generic name was given by Renault[838] to some small petrified
seeds from the Stephanian of Grand’ Croix and to impressions from the
Commentry coal-field which he believed to belong to some Gnetaceous
plant. Saporta and Marion[839] and other authors have accepted
these seeds as evidence of the existence of Palaeozoic Gnetales: it
has, however, been shown[840] that _Gnetopsis_ has no claim to such
relationship and is a type of seed closely allied to _Conostoma_.
Renault described three species, afterwards adding three from another
locality[841]; the genus is recorded also from Commentry[842] and
Gard[843]. More recently Depape and Carpentier[844] have described
examples from the Westphalian of Valenciennes which they place in
the Pteridosperms in accordance with the conclusion of Oliver and
Salisbury. _Gnetopsis_ has also been discovered by Mr Hemingway in the
Middle Coal Measures of England[845] (fig. 494, H).
_Gnetopsis elliptica_ Renault.
The seeds of this species, slightly oval in section, occur in groups of
2–4 in a cupular investment (fig. 506, E, p. 359) described by Renault
as an ovary but correlated by Oliver and Salisbury with the cupule
which surrounds the single ovule of _Lagenostoma_. The cupule is lined
with hairs similar to those on the wall of the cupule of _Lagenostoma_.
A characteristic feature of the French seeds is the presence of three
or four long plumes of hairs at the apex (fig. 494, E, F). As seen in
fig. 494, E, a small lagenostome (pollen-chamber) rests on the roof of
a broad plinth precisely as in _Conostoma_, and four vascular bundles,
corresponding to the six bundles in _Conostoma_, pass into the apical
cap of sclerous tissue enclosed by a sarcotesta, _sa_ (fig. 494, E,
G). A ‘tent-pole’ prolongation (fig. 494, E, _t_) occurs at the apex
of the prothallus. Renault described a portion of the integument as
consisting of lacunar tissue which Oliver and Salisbury homologise with
the superficial mucilaginous layer of _Conostoma_: this is seen above
the sclerotesta in the apical region of fig. 494, E, _sa_.
_Gnetopsis anglica_ Kidston +MS.+
This species (fig. 494, H) is represented by seeds from the Middle Coal
Measures near Barnsley, Yorkshire, 4 mm. long with apical appendages
at least 2·2 cm. in length and probably four in number. The appendages
do not show the hairs which form a prominent feature in the French
specimens, but this is probably the result of imperfect preservation:
there are indications of hairs on other specimens in Dr Kidston’s
Collection. The type-specimen, in Dr Kidston’s Collection, was
generously lent to me for examination.
_Gnetopsis_, while agreeing with _Conostoma_ in the more important
features, is distinguished by the apical plumes, the very slight
development of a tent-pole prolongation of the nucellar apex (fig. 494,
E, _t_), the smaller number of vascular bundles, and by the presence of
an enclosing cupule (fig. 506, E). In its slight departure from radial
symmetry _Gnetopsis_ forms a transition between the Radiospermeae and
the Platyspermeae. It is undoubtedly the seed of a Pteridosperm, but
nothing is known as to the nature of the vegetative organs of the
parent-plant.
II. +Trigonocarpales.+
In this group are included radially symmetrical seeds for the most
part belonging to members of the Medulloseae. The peripheral zone of
the nucellus is supplied with vascular tissue and the nucellus is
free within the integument except at the base; it is superior and not
semi-inferior[846] as in recent Cycads and in Lagenostomales. The ovule
of _Myrica Gale_, in which the nucellus stands free within the single
integument, affords an interesting parallel to seeds of this class in
contrast to the usual Angiospermous type with a laterally coalescent
nucellus. In _Myrica Gale_[847] the vascular supply is confined to
the integument. There is a comparatively broad pollen-chamber and in
some types the lateral tissue of the nucellus is prolonged as a tube
within the micropyle. The usually ribbed testa is differentiated into
an outer flesh (sarcotesta), a sclerotesta, and probably in most cases
an endotesta or inner flesh. The ribs of the sclerotesta are in the
majority of genera in multiples of three and in position correspond to
the outer ring of vascular bundles. The presence of lacunar tissue in
the sarcotesta of several genera may be correlated with dispersal by
water. The apical region of the integument is not lobed but extends as
a longer or shorter micropylar tube above the summit of the nucellus.
In the differentiation of the testa, the form of the pollen-chamber,
and in some other features, the seeds of this group present a general
agreement with those of recent Cycads.
The microspores are multicellular and larger than those of the
Lagenostomales: in _Stephanospermum akenioides_ they measure 160μ ×
100μ[848] while in _Aetheotesta_[849] they reach 360μ × 290μ.
Genera. _Trigonocarpus_; _Tripterospermum_; _Ptychotesta_;
_Hexapterospermum_; _Polypterospermum_; _Pachytesta_;
_Stephanospermum_; _Polylophospermum_; _Codonospermum_; _Aetheotesta_;
_Eriotesta_; _Gaudrya_.
=Trigonocarpus.= Brongniart.
A description of the morphological features of _Trigonocarpus
Parkinsoni_ and _T. shorensis_ is given in the chapter on _Medullosa_
(p. 117), as there is good evidence that they are the seeds of that
genus. There is considerable difference in size and to some extent
in the form of casts included in _Trigonocarpus_ and, in the absence
of anatomical data, it is hardly possible to determine the actual
systematic position of many of the specimens so named. Dr Arber[850]
has recently proposed a new generic name _Schizospermum_ for casts
very like those of _T. Parkinsoni_, but distinguished by the splitting
of the shell into three valves, a character which leads him to
conclude that it is the external surface which is preserved and not
a mere cast of the seed-cavity. It is, however, more probable that
the specimens are casts of a split sclerotesta. In _Trigonocarpus
pusillus_[851] the shell is divided into three valves, the dividing
lines being marked by greatly reduced ribs, and in _T. schizocarpoides_
Grand’Eury[852], a species that may not be a true _Trigonocarpus_,
there is also evidence of splitting. Arber points out that the species
_Rhabdocarpus Boschianus_ Berg. is founded on a _Trigonocarpus_
from which the outer flesh has disappeared leaving the shell as the
external covering. _Trigonocarpus_ seeds are widely distributed in
Carboniferous and Permian rocks in Europe and North America: from the
latter continent Newberry[853] has described several different forms
that afford good examples of the abundance and variety of the genus.
Some of the specimens included by Newberry[854] in _Trigonocarpus_
are probably distinct generic types: his species _T. multicarinatus_
may be identical with the ribbed cast shown in fig. 506, A. The
casts described by Lindley and Hutton and by other authors as _T.
Dawesi_[855] are nearly 5 cm. long, and if these are correctly included
in the genus they point to the occurrence of seeds much larger than
the type-species. The French species _Trigonocarpus pusillus_[856]
Brongn., one of the smallest Palaeozoic seeds, from 6·5 to 15 mm. long,
differs from _Trigonocarpus Parkinsoni_ and _T. shorensis_ in the
absence of prominent ribs and in the much feebler development of the
sarcotesta. Specimens of the German type _T. sporites_ Weiss, believed
by some authors to be megaspores, were described by Zeiller[857] from
Valenciennes as seeds: these are from 2·5 to 3·5 mm. long and have
three small ribs. Zeiller quotes the presence of cell-outlines on the
surface as evidence of their seed-nature, but it may be that this
feature represents a sculpturing of the exine of a spore. Typical
_Trigonocarpus_ seeds agree in several morphological characters with
those of recent Cycads. They differ in the lack of a lateral union
between nucellus and integument; the presence of nucellar tracheids,
though a feature shared with _Bowenia_, distinguishes them from the
majority of recent Cycadean seeds. In the comparatively long and fleshy
micropylar tube a seed of _Encephalartos Lehmanni_ presents a fairly
close resemblance to a _Trigonocarpus_. Salisbury has pointed out that
the three species _T. Parkinsoni_, _T. shorensis_, _T. pusillus_ form
a consecutive series illustrating the gradual disappearance of the
secondary ribs that form a prominent feature in _T. Parkinsoni_; but
for a comparison of these with other types of fossil and recent seeds
the reader is referred to Salisbury’s summary[858].
=Tripterospermum.= Brongniart.
The seed on which this genus was founded by Brongniart[859] is clearly
very closely related to _Trigonocarpus_ and, as Oliver[860] says,
the distinguishing character described by the author of the genus is
unimportant. Brongniart describes the type species, _T. rostratum_,
as characterised by the presence of three prominent wings composed of
a testa differentiated into an inner hard tissue and an outer lacunar
tissue. It is, however, hardly possible to say whether the outer soft
tissue was originally flattened in the form of ‘wings’ or pressed down
on to the harder shell. Renault[861] notes the association of seeds
that he refers to this genus with the leaves of _Dorycordaites_, but
apart from the improbability of any connexion between _Tripterospermum_
and _Cordaites_, Renault’s seeds are too imperfect to demonstrate
their identity with Brongniart’s genus. Kidston[862] has described an
impression of a three-winged seed from the coal-field of Staffordshire
as _Tripterospermum ellipticum_, a form described on page 357 as
_Polypterocarpus anglicus_ (fig. 496, B).
=Ptychotesta.= Brongniart.
The type-species of this genus[863], _Ptychotesta tenuis_[864], about
3 cm. long, is characterised by six very prominent flanges or wings
formed by the fissured or folded sclerotesta (fig. 495, B). There is no
information as to the vascular supply or other anatomical details. It
is not at all improbable that there is no real distinction between this
genus and Brongniart’s genus _Hexapterospermum_.
=Hexapterospermum.= Brongniart.
In this genus Brongniart[865] included two species, _Hexapterospermum
stenopterum_ and _H. pachypterum_: the shell is hexagonal in
transverse section, each angle being prolonged as a narrow flange.
In one of the sections figured by Brongniart (fig. 495, E) the
ribs are not fissured: this is said to be a feature distinguishing
_Hexapterospermum_ from _Ptychotesta_, but the occurrence of a
fissured rib in another section suggests that in the structure of
the ribs there is no essential difference between the two genera.
In _Ptychotesta pachypterum_ the testa is prolonged at the chalazal
end as in _Polylophospermum_, and it is possible that there is
no generic difference. Williamson described a cast from the Coal
Measures of Lancashire as _Hexapterospermum_ [= _Hexagonocarpus_]
_Noegerrathi_[866] (fig. 506, H), but in the absence of anatomical
characters it is preferable to avoid the use of Brongniart’s term and
to assign them to Renault’s genus _Hexagonocarpus_[867]. Similarly
the seeds referred by Dr P. Bertrand[868] to _Hexapterospermum_ may
appropriately be included in the genus _Hexagonocarpus_.
[Illustration: Fig. 495. A, _Polypterospermum Renaultii_. B,
_Ptychotesta tenuis_. C, D, _Polylophospermum_ _stephanense_; _sa_,
sarcotesta; _s_, spaces; _v_, vascular bundles. E, _Hexapterospermum
stenopterum_. F, _Diplotesta avellana_. G, _Taxospermum_ _Grüneri_. H,
_Diplotesta Grand’Euryana_. (After Brongniart; C, after Oliver.)]
=Polypterospermum.= Brongniart.
This generic name was proposed for an ovoid seed from St Étienne
described as _Polypterospermum Renaultii_[869]; hexagonal in section
with six deep and sharp flanges at the angles alternating with six
secondary ridges distinguished by their blunter edges and slightly
smaller depth (fig. 495, A). Without further anatomical details it
is hardly possible to say whether or not the species represents a
well-defined generic type, but it is not improbable that a fuller
knowledge would confirm Brongniart’s institution of a new generic
designation. The seeds described by Arber[870] and Kidston[871]
respectively as _Radiospermum ornatum_ and _Polypterospermum ornatum_
are transferred to _Polygonocarpus_ on the ground that they afford no
evidence of anatomical characters of the _Polypterospermum_ type.
=Pachytesta.= Brongniart.
Brongniart[872] established this genus for some unusually large seeds
(fig. 496, A) from the Coal Measures of France reaching a length of
11–12 cm. and resembling in form and size a hen’s egg. Petrified
examples have been described by Brongniart and Renault[873], and
Oliver[874] has given a lucid statement of the more interesting
features of this Permo-Carboniferous genus.
_Pachytesta gigantea_ (Grand’Eury).
In the separation of nucellus and integument _Pachytesta_ agrees with
_Stephanospermum_ and _Trigonocarpus_. There is a double series of
vascular bundles in the outer part of the testa or exotesta (fig. 497,
_ex_) consisting of a spongy tissue bounded externally and internally
by sclerotic layers: the exotesta is succeeded by a broader endotesta
of spongy consistency which Renault suggested may have served as
a floating mechanism, and this is intimately associated with the
nucellus by means of grooves engaging with short ridges (fig. 497,
_nr_) on the surface of the nucellar tissue. The exotesta is divided
into three valves by radial extensions of the sclerotic tissue (_b_,
_c_, fig. 497; at _a_ the exotesta is shown in an unsplit condition).
In connexion with each radial plate are two curved plates of fibrous
tissue which extend towards the grooves in the endotesta (fig. 497,
_t_): as Oliver suggests, these plates may have served a mechanical
purpose for the support of the bulky nucellus. The peripheral region
of the nucellus is supplied by several vascular bundles (fig. 497,
_n_) from the tracheal chalazal disc. The exotesta is regarded by
Oliver as corresponding to the sarcotesta and sclerotesta of other
seeds, and the grooves in the endotesta interlocking with the nucellar
ridges are compared with the interlocking of nucellus and canopy in
_Lagenostoma_, as also with the ruminated endosperm of _Torreya_.
[Illustration: Fig. 496. A, _Pachytesta incrassata_. B,
_Polypterocarpus anglicus_. (A, after Renault; B, after Kidston.)]
[Illustration: Fig. 497. _Pachytesta_. Transverse section of a seed
showing the exotesta, _ex_, with sclerous layers and vascular strands
(black), the endotesta (dotted), the nucellus with its ring of vascular
bundles, _n_, and the prothallus, _p_. The three radial plates in the
exotesta are seen at _a_, _b_, _c_, with the trabeculae, _t_, and
internal to these are the grooves in the endotesta engaging with ribs
on the nucellus, _nr_. (After Oliver.)]
We have no definite information as to the plants which bore
_Pachytesta_, but it is probable that they were members of the
Medulloseae. Grand’Eury[875] believes _Pachytesta_ to be the seed of
_Alethopteris Grandini_, though this view requires confirmation. This
author figures several _Pachytesta_ seeds attached in two oblique rows
to a comparatively slender axis which may be the rachis of a large
compound frond[876]. Renault and Zeiller[877] have figured specimens
of _P. gigantea_ and _P. incrassata_ from Commentry which afford a
good idea of the form of these large seeds; the genus is recorded also
from Gard, Blanzy[878], and other localities. Kidston[879] described a
large oval seed, blunt at each end, from the Middle Coal Measures of
Lancashire as _Carpolithus Wildii_ which he thinks may be allied to
_Pachytesta_, but adds, ‘I do not think we are justified in placing
mere impressions of plants in genera, whose distinctive characters are
derived from their internal organisation, unless there is conclusive
evidence to show their identity.’ On this specimen Arber[880] has
founded a new genus _Megalospermum_, but as the type-specimen shows
no distinctive features other than large dimensions it would seem
preferable to retain the more general designation _Carpolithus_[881].
Another example of a seed that may be generically identical with
_Pachytesta_ is that described by Lesquereux from North American Coal
Measures as _Rhabdocarpus Mansfieldi_ and more recently recorded by
White from Missouri as _Rhabdocarpus (Pachytesta) Mansfieldi_[882].
There is little doubt that this and other species of seeds preserved
as impressions are examples of _Pachytesta_ but, as Kidston says, it
is preferable to reserve the name for specimens showing anatomical
features.
=Stephanospermum.= Brongniart.
The genus _Stephanospermum_, founded by Brongniart[883] on petrified
specimens from French Stephanian beds, affords a good example of
a radiospermic seed without ribs differing in certain well-marked
characters from such seeds as _Lagenostoma_, _Physostoma_, and
_Conostoma_, notably in the complete separation of the nucellus from
the integument and in the possession of a nucellar vascular system. The
descriptions by Brongniart and Renault[884] have been extended by the
thorough investigations of Oliver[885].
_Stephanospermum akenioides_ Brongniart.
This species is represented by ellipsoidal seeds, 10 mm. long with
a maximum breadth of 4–4·5 mm., circular in transverse section.
The integument consists of a thick sclerotesta lined internally by
a thinner soft layer, the endotesta (fig. 494, A, _sc_, _e_), and
in all probability covered by an outer flesh or sarcotesta as in
_Trigonocarpus_, though this tissue is not preserved and is omitted
from the section shown in fig. 494, A. The sclerotesta is composed
of a broad outer band of thick-walled palisade cells—the contracted
contents of which are a striking feature in the silicified seeds (fig.
493, F); these are succeeded by an inner zone of longitudinal fibres.
In the structure of the palisade-layer _Stephanospermum_ bears a close
resemblance to the sporocarp wall of _Pilularia_[886]. In the apical
region the shell forms a circular ridge surrounding a peri-micropylar
trough, a character expressed by the term ‘crown-seed[887]’ employed
by Grand’Eury: the trough sometimes contains partially destroyed
tissue that may be a remnant of a sarcotesta. A _Stephanospermum_
seed, with its apical core and surrounding depression with remnants
of some partially destroyed tissue, may be compared with a fruit of
_Attolia speciosa_ (Palmae) in which a tuft of fibrous tissue picked
out by decay from the mesocarp surmounts the conically pointed apex
of the harder interior of the fruit-wall. The base of the sclerotesta
is perforated by a vascular strand which expands into a tracheal
disc, _td_, fig. 494, A, at the base of the megaspore from which a
continuous mantle 2–3 cells broad, of short spiral and scalariform
tracheids (fig. 493, G), spreads over the whole of the nucellus
immediately below the nucellar epidermis as far as the lower part of
the sides of the pollen-chamber: this mantle forms the floor of the
large domical pollen-chamber excavated out of the nucellar cone (fig.
494, A, _pc_). The fact that in sections of older seeds the tracheal
floor shows signs of splitting and disorganisation led Oliver to
conclude that in the living seed the tracheids underwent a gradual
disintegration prior to fertilisation, thus allowing the passage of
the antherozoids to the egg-cells (fig. 494, A, _a_). The presence of
a continuous tracheal sheath instead of separate vascular bundles is a
special feature in which _Stephanospermum_ differs from _Trigonocarpus_
and other Palaeozoic seeds as well as from those of recent Cycads;
as Oliver suggests, ‘the apparent perfection of the vascular
mantle in _Stephanospermum_ may have proved an obstacle to further
development[888]’ and was not retained by the more successful types. In
its tracheal sheath _Stephanospermum_ resembles the seeds of _Ginkgo_.
The nucellar cone is prolonged as a beak into the micropyle formed by
the tubular integument. The megaspore occupies the central portion
of the seed and in the course of its development it compressed the
megasporangium (nucellus) to such an extent that little more than the
epidermis remains: there is a definite megaspore-membrane surrounding
the prothallus-tissue in which there were probably two archegonia (fig.
494, A, _a_)[889]. The nucellus stands free within the integument from
which it is separated by a space (_s_, fig. 494, A). Microspores are
frequently met with in the pollen-chamber in which they matured after
their introduction through the micropyle, probably with the aid of a
drop of mucilage: they are large oval bodies with an average size of
160μ × 100μ, some reaching over 200μ, in length and, as Renault was
the first to point out, within a finely granulate exospore there are
several thin-walled cells: this statement was not accepted by some
authors but Prof. Oliver’s researches have amply confirmed it, and an
examination of the original preparations convinced me that Renault had
correctly described the structural features. Oliver shows that there
are about 20 cells within each microspore regularly arranged as rows
of five wedge-shaped elements with their pointed ends directed towards
the centre, and he thinks that these cells may have undergone further
division to produce sperm-mother-cells, though there is not such good
evidence of this as in the differently constituted microspores of
_Stephanospermum caryoides_. No trace of pollen-tubes was found and it
is probable that the antherozoids were liberated by the rupture of the
delicate prothallus-tissue. The tracheal sheath afforded an adequate
means of water-supply to the pollen-chamber and this enabled the motile
antherozoids to reach the archegonia.
_Stephanospermum caryoides_ Oliver[890].
This species, founded on a specimen from ., is a larger seed (15·5 ×
12·5 mm.) and more globular than _S. akenioides_; there is a shorter
micropylar beak and a less developed peri-micropylar trough. As in _S.
akenioides_ the nucellus is free from the base and the two species
conform to the same general type of construction. The microspores are
distinguished by the presence of only two internal cells which do not
occupy the whole of the spore-cavity but are surrounded by a large
peripheral cell comparable with the tube-cell in recent microspores,
though there is no proof that a tube was formed: in the case of _S.
akenioides_ Oliver considers that fertilisation was not assisted by
the production of a pollen-tube. The two cells by further division
gave rise to a secondary cell-complex consisting of at least eight
antherozoid-mother-cells. No antherozoids have been found in the
microspores but it is possible that two small bodies, 17μ × 15μ, met
with in a pollen-chamber may represent the nuclei of sperms. Their
small size differentiates them from the much larger male gametes of
Cycads and from the supposed sperms of _Physostoma_ and _Lagenostoma_.
We have no proof as to the nature of the plant which bore seeds of the
_Stephanospermum_ type, but it is significant that the specimens occur
in close association with fragments of _Alethopteris_ and _Myeloxylon_,
a circumstance that favours the view, based on the resemblance of these
seeds to _Trigonocarpus_, that _Stephanospermum_ is the seed of a
member of the Medulloseae.
=Polylophospermum[891].= Brongniart.
The type-species _Polylophospermum stephanense_ Brongn.[892],
founded on partially preserved material from Grand’ Croix, is a
narrow hexagonal seed 15 mm. long. Additional facts as to the
structural features have been contributed by Oliver[893]. The testa
is differentiated into an inner shell (sclerotesta) and an outer
flesh (_sa_, fig. 495, C, D): the sclerotesta has six prominent,
fissured, ribs, one at each angle, and between these are six solid and
less prominent secondary ribs. Oliver states that there is an outer
series of vascular bundles in the sarcotesta, one bundle immediately
external to each secondary rib (fig. 495, C, _v_). In the presence
of two kinds of ribs and in the relation of ribs to tracheal strands
_Polylophospermum_ agrees with _Trigonocarpus Parkinsoni_. Strands of
short tracheids supply the peripheral region of the nucellus and, as in
_Stephanospermum_, reticulate elements extend as far as the floor of
the large pollen-chamber. There was probably no lateral union between
nucellus and integument. A striking feature is the prolongation of the
testa at each end of the seed to form an open chamber surrounding the
micropylar beak and the seed-base (fig. 495, D, _s_, _s_): the apical
chamber, though relatively more prominent, is comparable with that in
_Stephanospermum_, while the basal chamber recalls that in the seed
named by Scott and Maslen _Trigonocarpus Oliveri_[894] but subsequently
removed by Salisbury[895] from that genus. There is no evidence as to
the parent-plant of _Polylophospermum_, but it may be assumed to have
been a Pteridosperm, probably one of the Medulloseae.
[Illustration: Fig. 498. A, B, _Codonospermum_. A, _C. olivaeforme_,
longitudinal section showing the seed-proper and the air-chamber, _s_;
_pc_, pollen-chamber. B, Diagrammatic sketch of a _Codonospermum_
showing the vascular supply, _v_, and the fibrous arcs, _f_, in the
wall of the lower part of the seed. C, _Aetheotesta elliptica_, _s_,
sarcotesta with lacunae; _v_, vascular supply. (After Renault.)]
=Codonospermum[896].= Brongniart.
Our knowledge of this peculiar genus is derived from Brongniart’s
description of the type-species _Codonospermum anomalum_[897]
(fig. 506, B, C) from St Étienne and from Renault’s account of _C.
olivaeforme_[898]. The seeds are globular or ellipsoidal and reach a
length of 2 cm.: the testa is differentiated into an outer flesh and a
sclerotesta and has usually eight ribs. The most striking feature is
the division of the seed into two regions, an upper portion containing
the nucellus and megaspore and a lower portion in the form of an
empty chamber that probably served as a float (fig. 498, A, _s_).
Externally the upper half or seed-proper forms a depressed cupola with
eight slightly developed ribs, separated by a circular transverse
constriction from the basal chamber (fig. 498, B). There is a fairly
large pollen-chamber, _pc_, in which Renault found multicellular
microspores in _C. olivaeforme_. In _C. anomalum_ 16 vascular bundles
(fig. 498, B, _v_) surround the central region of the seed probably
in the peripheral tissue of the nucellus; these bundles unite in the
chalazal region to form a strand that passes up the centre of the empty
chamber. In _C. anomalum_ the testa of the lower half has eight ribs
and corresponding with each rib is a strand of fibrous tissue (fig.
498, B, _f_). In _C. olivaeforme_ the testa is thicker than in _C.
anomalum_ and the lower region of the seed is smooth and circular in
section.
Impressions of _Codonospermum_ are described[899] from Commentry, from
the Loire—the Gard district[900], and by Zeiller[901] from Blanzy.
There is no decisive evidence as to the parent-plant, but some French
authors[902] regard the frequent association of _Codonospermum_ with
leaves of _Dolerophyllum_ as significant.
=Aetheotesta.= Brongniart.
_Aetheotesta elliptica_ Renault.
Brongniart instituted the genus _Aetheotesta_[903] for an incomplete
seed (_A. subglobosa_) from Grand’ Croix, and Renault[904] subsequently
founded the species _A. elliptica_ on much better material. The testa
of the elliptical seed, 3 cm. long, consists of an outer region
very thin on the flanks but highly developed at the apex and base
which forms a sarcotesta characterised in the apical region by large
radially disposed spaces, fig. 498, C, _s_; the sclerotesta, composed
of harder tissue, is prolonged as an apical beak. There is a large
pollen-chamber, _pc_, in which Renault found multicellular microspores
(320μ–400μ). In the chalazal region the main vascular supply forms
a cup-like investment, _v_, in the basal portion of the nucellus,
and at a higher level this breaks up into several nucellar strands.
Renault thinks that _Aetheotesta_ is the seed of _Dolerophyllum_, but
there is no proof of any connexion. The presence of large spaces in
the sarcotesta may be interpreted, as Renault suggests, as evidence of
adaptation to dispersal by water.
=Eriotesta.= Brongniart.
Brongniart[905] instituted this genus[906] on an incomplete transverse
section of a seed from Grand’ Croix, 8 mm. in diameter, which he called
_Eriotesta velutina_, characterised by a ribbed and probably octagonal
testa bearing numerous elongated hairs over the whole surface. The
material is, however, too meagre to throw any light on the important
features of the seed.
=Gaudrya.= Grand’Eury.
_Gaudrya trivalvis_ Grand’Eury.
The generic name _Gaudrya_[907] was proposed for two petrified seeds
from the Gard coal-field briefly described as _G. trivalvis_, the
type-species, and _G. lagenaria_. The testa of the former species
shows signs of splitting along three equidistant lines; it consists
of a sarcotesta enclosing an endotesta with six longitudinal ribs:
Grand’Eury speaks of lacunae between the endotesta and nucellus which
he regards as spaces in a tissue which made the seed buoyant and
facilitated dispersal by water. It is not clear whether the nucellus
and integument were originally connected or laterally free: the lacunae
may be the remains of an inner flesh and not spaces in a spongy tissue.
The genus is radiospermic and characterised by a long micropyle and
a broad pollen-chamber. On the available evidence it is difficult to
assign the specimens to their systematic position, but the genus is
probably a member of the Trigonocarpales.
III. +Cardiocarpales.+
Platyspermic seeds for the most part belonging to Cordaitalean plants
and agreeing in their plan of organisation, even more closely than
the seeds of the Trigonocarpales, with those of recent Cycads. The
nucellus is free laterally from the integument and there is a series of
vascular bundles in the nucellus. The testa consists of an outer flesh,
the sarcotesta, which may reach a considerable thickness, a shell
or sclerotesta, and in some genera an endotesta. In seeds preserved
as impressions the sarcotesta often gives them a winged appearance
(_Samaropsis_). The pollen-chamber is relatively small, resembling in
this respect the chamber in recent Cycads. A central prolongation of
the prothallus-tissue in the form of a blunt column or ‘tent-pole’
is a characteristic feature; the same feature occurs in seeds of the
Lagenostomales, but in the Cordaitales it resembles more nearly the
‘tent-pole,’ as it was called by Hirase, in recent Cycadean seeds and
in _Ginkgo_. The presence of two vascular strands in the sarcotesta
in the principal plane of the seeds is a character shared with the
seeds of _Cycas_: the position and course of these bundles are useful
characters for distinguishing different types within the group. The
microspores are multicellular.
Genera. _Cardiocarpus_; _Cyclospermum_; _Cycadinocarpus_;
_Rhabdospermum_; _Mitrospermum_; _Diplotesta_; _Leptocaryon_;
_Taxospermum_; _Compsotesta_. These generic names are all used in the
following pages for seeds known to possess certain anatomical features;
there are also included in the Cardiocarpales the genera _Samaropsis_,
_Cordaicarpus_, and _Rhabdocarpus_, but it is proposed to limit their
use to specimens which furnish no anatomical data and cannot therefore
be assigned with equal confidence to a section of seeds based on
definite morphological characters. It is certain that some at least of
the seeds described under these names would, if preserved as petrified
specimens, be included in one or other of the genera named above.
There is ample proof that some of these seeds were borne on Cordaitean
plants and that the group as a whole represents the seeds of the
Cordaitales[908]. It is, however, certain that some Platyspermic
seeds were produced by Pteridosperms. No little confusion has been
caused by the employment of the same generic names for petrified
seeds and for casts and impressions affording no evidence as to
similarity in anatomical characters. With a view to avoid the risks
necessarily entailed by following this practice it is suggested that
a clearer distinction should be drawn between genera based primarily
on structural features and form-genera. The following notes on the
genera _Cardiocarpus_, _Cordaicarpus_, _Cyclocarpon_, _Cycadinocarpus_,
_Jordania_, and _Samaropsis_, may serve to illustrate some of the
difficulties connected with the terminology of Palaeozoic seeds.
_Cardiocarpus_. Brongniart[909] proposed the name _Cardiocarpon_ in
1828 for Upper Carboniferous seeds described as compressed lenticular,
cordiform or reniform ‘fruits’ with an acute apex: in his later
work[910] he recognised their true morphological nature and gave an
account of some exceptionally well-preserved examples from Grand’
Croix. Brongniart in common with other authors believed _Cardiocarpus_
seeds to belong to Cordaitean plants, a view that in several cases is
based on conclusive evidence. The specimen represented in fig. 501,
D, illustrates the characteristic form of a cast of a _Cardiocarpus_
seed, and the sections shown in fig. 501, A and B, are from an
identical or a very closely allied species. The generic characters
are: (i) the presence of a narrow flattened border or wing surrounding
a platyspermic nucule, (ii) the cordiform base and more or less
pointed apex, (iii) the differentiation of the testa into a sarcotesta
and sclerotesta free from the nucellus except at the base, (iv) the
‘tent-pole’ prolongation of the prothallus (fig. 510, A, _b_) and the
presence of a fairly large pollen-chamber, _pc_, (v) the occurrence of
two sets of vascular bundles, an inner nucellar series and two double
vascular strands (fig. 500, A, _v_, B) which are given off from the
main supply before it reaches the sclerotesta. The term _Cardiocarpus_
as used by Brongniart signifies a type of seed possessing both certain
anatomical and external characters. The proposal is to restrict the
generic appellation to seeds exhibiting definite structural features
agreeing in essentials with _Cardiocarpus sclerotesta_ and _C.
drupaceus_.
_Cordaicarpus_. This name was first employed by Geinitz[911] in the
form _Cordaicarpon_, the type-species being _C. Cordai_ (fig. 502, C)
from the Coal Measures of Germany, a seed referred by the author of
the genus to _Cordaites principalis_ but, as Kidston has pointed out,
there is evidence that this correlation may be incorrect: there is,
however, no doubt as to its Cordaitean parentage. Specimens included
in this genus agree closely with species of _Cardiocarpus_, but they
are usually described as being distinguished by the absence of a flat
border and by a more rounded and less cordate base. In the example
of _Cordaicarpus Cordai_ shown in fig. 502, C, and in other species
assigned by authors to this genus there is a narrow border and the
form of the base is an inconstant character. As Kidston[912] and other
authors point out, there are no definite and constant characters by
which to distinguish _Cardiocarpus_ from _Cordaicarpus_ as regards the
form of the seeds preserved as casts or impressions. A further account
of _Cordaicarpus_ is given on a later page.
_Cordaispermum_. This designation was formerly adopted by Renault[913]
for seeds having the form and anatomical features of _Cardiocarpus_
which there is good reason for attributing to _Cordaites_ or to some
allied genus. In view of the fact that the majority of the seeds under
consideration are undoubtedly Cordaitean there is no need to employ
this additional generic name.
_Cyclocarpon_. Fiedler[914] instituted this term for seeds previously
described by Berger as _Cardiocarpon emarginatum_ (fig. 502, B,
now included in _Samaropsis_) and added a new species _Cyclocarpon
nummularium_. Brongniart[915] subsequently described the structure
of two species, _C. tenue_ and _C. nummulare_, which he referred to
Fiedler’s genus, and Bertrand[916] has shown that these differ from
the genus _Cardiocarpus_ in the recurrent course of the bundles given
off from the chalazal strand as in the genus _Rhabdospermum_ (cf.
fig. 501, E). There are no good grounds for retaining the designation
_Cyclocarpon_ for casts and impressions, as the specimens so named are
indistinguishable from impressions referred to _Cordaicarpus_. The
generic name _Cyclocarpus_, retained by Bertrand only for _C. tenuis_
and _C. nummularis_ simply for anatomical reasons, is now altered to
_Cyclospermum_ on the ground that the designation _Cyclocarpon_ has
been used for impressions affording no information with regard to
anatomical features.
_Cycadinocarpus_. Renault[917] transferred to this genus Brongniart’s
species _Cardiocarpus augustodunensis_ on the ground that the vascular
system exhibits in a greater degree than the other types included
by Brongniart in _Cardiocarpus_ a resemblance to that in recent
cycadean seeds. Bertrand[918] confirms Renault’s account and retains
_Cycadinocarpus augustodunensis_ as a species worthy of generic
distinction. A short account of this seed is given on a later page.
_Jordania_. This name was given by Fiedler[919] to compressed
ovate-cordate seeds characterised by a broad membranous border bearing
a superficial resemblance to the seeds of _Bignonia_. The type-species,
_J. bignoniodes_ (fig. 502, I), from the Coal Measures of Saarbrücken
has the form usually associated with the designation _Samaropsis_,
and as the latter term is generally adopted there are no adequate
reasons for the retention of _Jordania_. The name _Jordania_ has also
been applied, by Schenk[920], to fossil Dicotyledonous wood and was
previously used by Boissier[921].
[Illustration: Fig. 499. _Samaropsis emarginata_, from the
Westphalian series, Yorkshire. (Kidston Coll., 4227; × 2.)]
_Samaropsis_. Goeppert[922] defined _Samaropsis_ as ‘Fructus
samaroideus membranaceus, compressus, margine alatus, monospermus.’ The
type-species, _S. ulmiformis_, from the Permian of Brenau, is a small
seed with a broad wing or border, but a better example of _Samaropsis_
is figured by Goeppert as the wing of an insect[923]. Examples of
the genus are shown in figs. 502, A–H; 503; 504. Seeds included in
_Samaropsis_ differ from those referred to _Cordaicarpus_ in the
presence of a broader and more clearly defined border which in some
cases, as in the genus _Mitrospermum_ (fig. 494, K, L), undoubtedly
represents a lateral wing-like extension of the sarcotesta. In some
instances the wing may be a tangentially expanded integument comparable
with the perianth of _Welwitschia_, and in some Jurassic seeds referred
by Heer[924] to _Samaropsis_ the lateral appendages are probably true
wings. It is advisable to restrict the designation _Samaropsis_
to Palaeozoic seeds. Nucules deprived of the broad border would be
referred to _Cordaicarpus_ as usually employed for impressions. The
generic name _Samaropsis_ serves a useful purpose as a distinctive term
for platyspermic seeds preserved as casts or impressions characterised
by the possession of a wide border or wing broader than in typical
examples of _Cordaicarpus_. The specimen represented in fig. 499
affords a good illustration of the difference between _Samaropsis_ and
_Cordaicarpus_. In this specimen the border clearly consists of two
portions, an inner narrower border (black in the drawing) and an outer
more delicate portion; the former is the impression of the sclerotesta
and the outer represents the fleshy sarcotesta which in the living seed
may have formed a wing. If, as often happens, the seed were preserved
with the narrow border only it would be assigned to _Cordaicarpus_,
many species of which are undoubtedly incomplete _Samaropsis_ seeds.
The seeds described by Lindley and Hutton as _Cardiocarpon acutum_
(fig. 444, p. 171) have been made by Arber[925] the type of a new genus
_Cornucarpus_, the distinguishing feature being the triangular form
and the apical horns of the wing. The seeds figured by Arber[926] from
the Kent coalfield as _Cornucarpus acutus_ are, however, not identical
with the type of Lindley and Hutton, which has the characters of
_Samaropsis_. _Samaropsis_ is widely distributed in Permo-Carboniferous
rocks in Europe and North America and is recorded also from India[927]
(fig. 504), China[928], South Africa[929] (fig. 503), South
America[930] (fig. 502, F, G) and Australia[931]. Some seeds of this
form were certainly borne on Cordaitean plants (cf. fig. 480, A), but
seeds of similar type have been found in organic connexion with the
foliage of Pteridosperms (figs. 442, 445, pp. 167, 172). The Permian
‘cone-scales’ bearing seeds described by Geinitz as _Cardiocarpon
triangulare_[932], represented by well preserved impressions in the
Dresden Museum, appear to be of the _Samaropsis_ type: the same
author referred some _Samaropsis_ seeds to the Conifer _Walchia_, but
Weiss[933] dissents from this correlation as the seeds often occur
in beds in which _Walchia_ is not represented. Renault states that
the seeds of the fertile shoot described by him as _Cycadospadix
Milleryensis_[934] from Autun [= _Strobilites Milleryensis_ (Ren.)]
closely resemble _Samaropsis fluitans_ Daws. as figured by Weiss. The
suggestion by White[935] that _Samaropsis_ seeds were borne on fertile
leaves of _Gangamopteris_ adds a further difficulty to the use of the
generic characters of _Samaropsis_ as criteria of systematic position.
The Permian seeds figured by Goeppert[936] as _Oreodoxites Martianus_
are possibly specimens of _Samaropsis_.
The designation _Samaropsis_, though usually restricted to Palaeozoic
species, is applied by some authors to ‘winged’ seeds from Mesozoic
strata; but as some of the Jurassic seeds[937] so named appear to have
true wings like those of some recent Conifers it is advisable to adhere
to the more limited use of the name.
It is safe to assert that many _Samaropsis_ seeds agreed generally
in structure with Cordaitean seeds such as the petrified examples
described by Brongniart as _Cardiocarpus_. The species _Mitrospermum
compressum_[938] is an example of a petrified seed having the external
features of _Samaropsis_.
=Cardiocarpus.=
This generic title I propose to restrict to petrified seeds exhibiting
the characters described by Brongniart[939] and more recently by
Bertrand[940] in _C. sclerotesta_ and _C. drupaceus_. In general
organisation seeds of this generic type agree with those of recent
Cycads and with the seed of _Ginkgo biloba_, but there are certain
distinguishing features. An important character is afforded by the
course and place of origin of the lower vascular strands from the main
supply at the base of the seed. The outer vascular system consists
of two bundles given off from the main strand, before it reaches
the sclerotesta, which pass up the sarcotesta (fig. 500, B). In
_Rhabdospermum_, on the other hand, the corresponding bundles arise
at a higher level and form recurrent strands which penetrate the
sclerotesta before passing up the fleshy part of the integument (cf.
fig. 501, E).
[Illustration: Fig. 500. _Cardiocarpus drupaceus_ var. _expansus_.
A, transverse section of the testa approximately in the middle of the
seed; _v_, vascular bundles. B, diagrammatic sketch, adapted from
Brongniart’s drawing of the base of the seed showing the sarcotesta,
_sa_, the sclerotesta, _sc_, and the pad of vascular tissue, _d_, at
the base of the nucellus. (After Brongniart.)]
_Cardiocarpus sclerotesta_ Brongniart. The testa is differentiated into
an inner shell and an outer sarcotesta (fig. 501, A; the sclerotesta
is shown in black); there is a well developed pollen-chamber (_pc_)
and below this the prothallus-tissue is prolonged as a blunt and short
tent-pole, _b_, as in _Gingko_ and in several fossil seeds. On each
side of the apical tent-pole the slightly shrunken prothallus shows two
small archegonia, _a_, which in the relatively small size and spherical
form of the egg-cells resemble those of _Ginkgo_. In transverse section
(fig. 501, B) the seed is bi-convex and at each end of the major axis
the sclerotesta forms a small keel. There are two sets of vascular
bundles concerned in the supply of material to the ovule; a lower pair
of bundles given off from the central strand in the sarcotesta (fig.
500, B) which pass to the apical region in the inner tissues of the
sarcotesta in the principal plane (fig. 500, A, _v_), and an inner set
of bundles that pass up the peripheral tissue of the nucellus.
The species described by Brongniart as _Cardiocarpus (Cyclocarpus)
tenuis_ and _C. nummularis_ have been removed by Bertrand[941] from
_Cardiocarpus_ on the ground that the integumental bundles pursue a
course like that in _Rhabdospermum_; it is now referred to the new
genus _Cyclospermum_[942].
[Illustration: Fig. 501. A, _Cardiocarpus sclerotesta_ in longitudinal
section; _pc_, pollen-chamber, _b_, tent-pole, _a_, archegonia. B,
transverse section; _a_, archegonia. D, cast of the same or a similar
type of seed. C, E, _Rhabdospermum cyclocaryon_, longitudinal section
and a diagrammatic sketch of the seed-base; _m_, micropyle; _b_,
tent-pole; _a_, archegonium. (A, B, C, after Brongniart; D, after
Renault and Zeiller; E, adapted from Brongniart.)]
=Cyclospermum.= Gen. nov. (= _Cyclocarpus_ Bertrand).
As stated on a previous page Bertrand[943] re-establishes the
generic name _Cyclocarpus_, founded on impressions without reference
to anatomical characters, for two petrified seeds from St Étienne
described by Brongniart as _Cardiocarpus tenuis_ and _Cyclocarpus
nummularis_[944]. These types differ from _Rhabdospermum_ in the
absence of an apical snout but agree with that genus in the steeply
descending course of the vascular strands in the basal region of the
seed. As stated on a previous page, the name _Cyclospermum_ is proposed
as a substitute for _Cyclocarpus_ because of the employment of the
latter term for impressions.
=Cycadinocarpus.= Schimper[945].
_Cycadinocarpus augustudunensis_ (Brongniart[946]). In the possession
of two sets of vascular bundles this type agrees with _Cardiocarpus_,
but the more internal strands pass up on the inner face of the
sclerotesta without penetrating into the nucellus, a feature in which
_Cycadinocarpus_ agrees with the majority of recent cycadean seeds: the
outer bundles are given off from the main supply after it has entered
the sclerotesta and not before as in _Cardiocarpus_; they follow an
oblique course in the sclerotesta and emerge into the sarcotesta at
the shoulders of the basal curve of the seed. As in _Cardiocarpus_ and
_Rhabdospermum_ the two outer bundles lie in the principal plane of
the seed. There is a pollen-chamber at the apex of the nucellus and
the latter tissue is prolonged as a tent-pole which engages with the
micropyle. In the absence of data as to the course of the vascular
bundles in the chalazal region it would not be possible to distinguish
between this genus and _Cardiocarpus_.
=Rhabdocarpus= Berger and =Rhabdospermum= gen. nov.
It is proposed to restrict the name _Rhabdocarpus_[947] to impressions
and casts of seeds of the type represented by _R. tunicatus_ as figured
by Berger[948] and reproduced in fig. 506, K, the term _Rhabdospermum_
being applied to seeds of similar form in which are shown certain
distinguishing anatomical features. _Rhabdocarpus tunicatus_ Berger
is a species founded on a specimen from the Coal Measures of Silesia
characterised by an outer carbonised testa prolonged apically as a
blunt snout and, as seen in fig. 506, K, covering an apparently ribbed
nucule, but the ‘ribs’ are due to the presence of fibrous strands and
are not ribs in the ordinary sense. The outer tissue shows numerous
longitudinal striations due presumably to the presence of fibrous
elements in the sarcotesta like those shown in the petrified seed
represented in fig. 501, C. The genus is defined by Berger as follows:
‘Semina ovata vel elliptico-oblonga secundum longitudinem parallele
nervosa vel tenuissime striata, putamine (interdum deficiente)
instructa.’ As used by Berger and many other authors _Rhabdocarpus_
includes a miscellaneous collection of seeds often differing widely
from the type-species. Many of the examples correctly referred to
Berger’s genus are platyspermic though a bilateral symmetry is by no
means always clear. Renault and Zeiller[949] in their definition of
_Rhabdocarpus_ include bilateral symmetry as a characteristic feature
and speak of the seeds as oblong or oval with a pointed or truncate
apex and a rounded base. Impressions of _Rhabdocarpus_ differ from
those of _Cardiocarpus_ or _Cordaicarpus_ in their more elongate
form, always longer than broad, and in the absence of a basal sinus.
The seeds found attached to _Neuropteris_ pinnae and, in external
features, agreeing with many specimens included in Berger’s genus, have
been transferred by P. Bertrand[950] and Arber[951] to a new genus
_Neurospermum_[952]. Arber[953] in his recent revision of British seeds
proposes to restrict the name _Rhabdocarpus_ to platyspermic seeds
having a ‘large unsymmetrical nucule enclosed in a large unsymmetrical
wing or sarcotesta,’ that is to forms symmetrical in one plane. In
this category he includes _Rhabdocarpus tunicatus_ Berg. (fig. 506,
K) and _R. subtunicatus_[954] Grand’Eury, but it is not clear on what
grounds Berger’s species is spoken of as symmetrical in only one
plane: in the species _R. Lilleanus_ Arb.[955] the symmetry is hardly
sufficiently well defined to rank as a generic character. In the case
of the _Neuropteris_ seeds the apical snout is slightly curved, thus
giving them an unsymmetrical appearance (cf. fig. 422, p. 114). The
Carboniferous and Permian seeds usually referred to _Rhabdocarpus_
are transferred by Arber to his genus _Platyspermum_[956], a
designation for which it is proposed to substitute Nathorst’s genus
_Holcospermum_[957]. In seeds preserved as more or less flattened
impressions it is practically impossible in many cases accurately to
determine the symmetry: as fig. 506, A, shows, casts indistinguishable
from some examples of _Platyspermum_ are radially symmetrical.
Brongniart[958] extended the original definition of _Rhabdocarpus_ to
include certain anatomical characters, and these have been more fully
defined by Bertrand[959]. It is for seeds showing these anatomical
features that the name _Rhabdospermum_ is now proposed. This course is
followed on the ground that it is advisable to avoid confusion between
petrified specimens and impressions which in spite of superficial
resemblance may not be closely related. In some cases it is practically
certain that an impression of the _Rhabdocarpus_ type is generically
identical with a seed of similar form showing the anatomical structure
of _Rhabdospermum_, but unless identity is established a distinct
terminology is preferable. The use of the generic name _Rhabdospermum_
carries with it an implication of platyspermy, but under _Rhabdocarpus_
may be included seeds which are radiospermic and platyspermic. Some
seeds agreeing with _Rhabdospermum_ are referred by Grand’Eury[960]
to _Poroxylon_, and it is probable that _Rhabdospermum_ like
_Cardiocarpus_ is a Cordaitean seed. On the other hand _Rhabdocarpus_
may well include species, apart from those transferred to
_Neurospermum_, that belong to Pteridosperms. A species, _Rhabdocarpus
Oliveri_, recently described by Kidston[961] from the Staffordshire
coalfield is an example of a radiospermic seed which may be assigned
to a Pteridosperm. The type-specimen is an ovate seed 4 cm. long and 2
cm. broad agreeing in form and surface-features with _Rhabdocarpus_ as
already defined, but the evidence it affords of internal structure is
insufficient to determine its position with regard to genera founded on
anatomical characters. Other examples of _Rhabdocarpus_ are described
by Lesquereux[962] and White[963] from American Coal Measures, by
Grand’Eury[964] from the Loire, by Renault[965] from Autun, and by many
other authors.
=Rhabdospermum.= Gen. nov.
The platyspermic seeds included in this genus agree in size and form
with impressions assigned to _Rhabdocarpus_ and as regards the main
features conform anatomically to _Cardiocarpus_; they were probably
borne on Cordaitean plants. Fig. 501, C, represents a longitudinal
section of the species _Rhabdospermum cyclocaryon_ described
by Brongniart as _Rhabdocarpus cyclocaryon_: the sarcotesta is
particularly well developed in the apical region; at the apex a portion
of the micropyle is seen at _m_ and near the nucellus are pieces of
the sclerotesta shown in black. The presence of anastomosing fibres
near the surface is a characteristic feature: these, as Bertrand points
out, do not form a hypodermal tissue in the strict sense as they may
be separated by some of the thin-walled parenchyma of the sarcotesta
from the epidermis. The sclerotesta is only partially preserved but the
inner portion forms a dark line enclosing the nucellus, the superficial
tissue of which is separated from the shrunken prothallus represented
by the almost spherical dotted region: the remains of an archegonium
are seen at _a_ (fig. 501, C) and the characteristic tent-pole apex
of the prothallus is shown at _b_. While in shape and in the general
plan of organisation _Rhabdospermum_ agrees with _Cardiocarpus_, the
vascular system in the chalazal region constitutes a distinguishing
feature. In _Rhabdospermum_ the main vascular strand passes through
the sclerotesta, _e_, _e′_, fig. 501, E, before giving off two bundles
which bend back (‘faisceaux récurrents’), traverse the shell, and then
pass up the sarcotesta in correspondence with the feebly developed
lateral keels as far as the micropyle, while in _Cardiocarpus_ (fig.
500, B) the bundles are given off before the main strand reaches the
sclerotesta. Similar recurrent bundles occur also in _Mitrospermum_
(fig. 494, K)[967].
=Mitrospermum.= A. Arber.
_Mitrospermum compressum_ (Williamson). Mrs Arber[968] proposed the
name _Mitrospermum_[969], suggested by the peculiar form of the
seed-base, as a substitute for _Cardiocarpon_ for Williamson’s species
_C. compressum_[970] from the Lower Coal Measures of Lancashire. The
seed is platyspermic and there is some evidence that it split into two
valves along the principal plane (the longer axis of the section, fig.
494, L). The diagrammatic and partially restored longitudinal section
reproduced in fig. 494, K, shows the main features: a sarcotesta, _sa_,
covers the surface of the testa as a thin layer except at the edges
of the flattened sides where it forms a wing-like border; preserved
as an impression the seed would be assigned to _Samaropsis_. The
sclerotesta, _sc_, has a pointed apex which surrounds the lower third
of the micropyle and a broad base perforated by the chalazal vascular
strand. There was probably a narrow inner flesh as in _Trigonocarpus_
and recent Cycadean seeds (fig. 494, K, _cf_). The nucellus was free
from the integument except at the base, as in _Trigonocarpus_ and
_Stephanospermum_ (fig. 494, K, _n_): internal to the shrivelled
remains of the inner flesh there was a nucellar tapetum surrounding the
megaspore. Details as to the pollen-chamber are lacking though there
are indications that it resembled that of some species of Cordaitean
seeds. The main vascular supply passes through the sclerotesta and then
forms a low cushion of short reticulate elements below the base of the
nucellus from which two bundles are given off (fig. 494, K, _v_) in the
principal plane. The course of the bundles which pierce the sclerotesta
led Mrs Arber to remove this seed from _Cardiocarpus_, as recently
defined by Bertrand[971], since in that genus the integumental bundles
have their origin below the sclerotesta. In the course of the vascular
bundles _Mitrospermum_ is intermediate between _Rhabdospermum_ and
_Taxospermum_.
This genus is founded on a detached seed, but its resemblance to
undoubted Cordaitean species favours its attribution to that group
though, as Mrs Arber points out, some markedly platyspermic seeds are
known to have been borne on fern-like fronds and _Mitrospermum_ may
belong to some genus of Pteridosperms.
=Diplotesta.= Brongniart.
_Diplotesta Grand’Euryana_ Brongniart. The generic name _Diplotesta_,
suggested by Grand’Eury, was given by Brongniart[972] to a Grand’ Croix
seed which he compared with that of the Conifer _Cephalotaxus_. The
type-specimen is elliptical and platyspermic (fig. 495, H, p. 322),
and differs from _Taxospermum_ in the cordate form of the seed-cavity,
also in the more restricted union of nucellus and testa. The testa
is differentiated into a sarcotesta (_sa_) and sclerotesta, and the
latter forms two feebly developed keels in the principal plane: a
characteristic feature shared with _Mitrospermum_ is the splitting
of the shell into two equal valves (fig. 495, F). Fig. 495, H, shows
the contracted cylindrical nucellus and the pollen-chamber: the
sarcotesta (_sa_) is only partially preserved. _Diplotesta_ differs
from _Cardiocarpus_ in the course of the integumental vascular bundles
which are of the type illustrated by _Rhabdospermum_, _Taxospermum_,
and _Cyclocarpus_, but from these genera it is distinguished by the
dehiscence of the shell, also by its form and certain anatomical
features as described by Brongniart and Bertrand[973].
In this genus Bertrand includes Brongniart’s species _Sarcotaxus
avellana_ (fig. 495, F), a correlation suggested by the latter author.
=Leptocaryon.= Brongniart.
Brongniart[974] founded this genus for a single species, _Leptocaryon
avellana_, represented by a Grand’ Croix specimen 12 × 10 mm., which
he believed to be related to _Taxus_. _Leptocaryon_ differs from
_Taxospermum_ in the structure of the testa, but resembles it in
external features. Bertrand[975] in his revision and extension of
Brongniart’s account says that the sections throw no light on the
nature of the vascular supply, and it is therefore impossible to form a
satisfactory opinion as to the relationships of the genus. Renault[976]
referred this genus to the Cordaitales, but we have no evidence as to
the parent-plant.
=Taxospermum.= Brongniart.
Brongniart[977] gave this name to a small elliptical seed, 15×9 mm.,
recalling in external features the seed of _Taxus_, a genus to which
he believed the Grand’ Croix species to be related. The type-species
_Taxospermum Grüneri_ (fig. 495, G) has a comparatively thin testa
characterised by the absence of a sub-chalazal pad formed by the
swelling of the sclerotesta. The nucellus is attached by a broad
base to the testa and the two regions appear to be connected for
a short distance on the flanks[978]; in this feature the seed is
comparable with that of the Conifer _Torreya_ and differs from the
other platysperms, _Diplotesta_, _Rhabdospermum_, etc. Bertrand[979]
states that the main vascular strand extends from the hilum to the
chalaza before giving off the two opposite bundles which ‘follow the
floor of the shell-cavity, and on reaching the flanks traverse the
shell obliquely from below upwards[980].’ In the course and position
of the integumental bundles _Taxospermum_ differs from _Cardiocarpus_,
_Cycadinocarpus_, and _Rhabdospermum_. In this genus Bertrand includes
_Sarcotaxus angulosus_ Brongn. and _S. olivaeformis_ Brongn.[981]
=Compsotesta.= Bertrand ex Brongniart +MS.+
_Compsotesta Brongniarti_ Bertrand. The generic name
_Compsotesta_[982], though adopted by Brongniart for some incomplete
specimens from Grand’ Croix, was not published either by him or
Renault: it has recently been revived by Bertrand[983] in his account
of the anatomical details of Brongniart’s sections. This seed appears
to be closely allied to the polypterous forms _Ptychotesta_ and
_Hexapterospermum_: the testa consists of a sarcotesta differentiated
into two zones the outer of which contains vascular bundles in
correspondence with the ribs, and an inner shell. There is a nucellar
vascular supply and the nucellus is free on the flanks as in
_Stephanospermum_ and _Trigonocarpus_.
=Samaropsis.= Goeppert.
The characters of this Permian and Carboniferous genus have already
been described: the name has reference only to superficial features
especially the samara-like ‘wing,’ and connotes no special anatomical
features.
_Samaropsis fluitans_ (Dawson). The species described by Dawson[984]
as _Cardiocarpum fluitans_ from Carboniferous strata in Nova Scotia,
is represented by oval seeds with a fairly broad border usually
showing an apical notch. Fig. 502, A, is a copy of Dawson’s figure:
the apparent absence of an apical sinus in the ‘wing’ is probably
due either to an error in interpretation or to some imperfection in
the specimen. As fig. 502, A, shows, the type-specimens are far from
satisfactory, and it may be that they are not specifically identical
with the more complete specimens from European strata referred to
Dawson’s species. Zeiller[985] points out that seeds of this species
vary considerably in size, but there is always in well-preserved
examples a bifid beak at the apex. Seeds of similar form though not
specifically identical are described from the Coal Measures of Missouri
as _Cardiocarpon (Samaropsis) Branneri_ Fairch. and White[986]. Good
examples of _S. fluitans_ are figured by Weiss[987] from the Coal
Measures of Saarbrücken and the species is widely distributed in Upper
Carboniferous beds generally.
_Samaropsis bicaudata_ Kidston. This species (fig. 502, E) originally
described[988] from Lower Carboniferous rocks in Scotland as
_Cardiocarpus bicaudata_ and subsequently assigned to _Samaropsis_, is
characterised by a greater development of the flat wing-like border
which is divided into two long tapering basal lobes. Seeds of similar
form are figured by Lesquereux[989] from Pennsylvania as _Cardiocarpus_
(_Ptilocarpus_) _bicornutus_.
_Samaropsis_ (_Samarospermum_) _moravica_ (Helmhacher). This type[990]
(fig. 502, H) is characterised by the great length of the wing-like
border and on that account it was transferred by Arber to a new genus.
It was originally described by Helmhacher from the Permian of Moravia
as _Jordania moravica_ and the type-specimen has been refigured by
Zeiller[991] who records the species from Upper Carboniferous and
Permian rocks in France: it is recorded also from several localities
in Germany[992]. Seeds figured by Potonié[993] from the Permian of
Thuringia as _Samaropsis Crampii_ (Hartt) are undoubtedly examples of
_S. moravica_: the true _S. Crampii_ has recently been well illustrated
by Dr Stopes[994] from the Westphalian of New Brunswick. The species is
recorded by Arber[995] from the Kent coalfield.
_Samaropsis emarginata_ (Goeppert and Barger).
The seed represented in fig. 502, B, from the Lower Coal Measures
of Kilmarnock, Scotland[996], affords a good example of the genus:
the species was originally described by Berger as _Cardiocarpon
emarginatum_ and it was on this type that Fiedler founded the
genus _Cyclocarpon_[997]. It has been referred by many authors to
_Cardiocarpon_ and might be regarded as a type intermediate between
_Cordaicarpus_, as used in this chapter, and _Samaropsis_, though the
breadth of the border is more in keeping with the latter designation.
The figured specimen is 1·6 cm. long and 1·4 cm. broad; the nucule has
a slightly cordate base and shows several faint converging ribs which
are too inconspicuous to be represented in a natural-size drawing.
A narrow median groove in the apical region shows the position of a
vascular strand. The species is recorded from several countries:
similar though specifically distinct seeds, described by Dawson
as _Cardiocarpon cornutum_, have recently been re-described by Dr
Stopes[998] from the Westphalian of New Brunswick where they occur in
association with the leaves of _Cordaites Robbii_ Daws.
[Illustration: Fig. 502. A, _Samaropsis fluitans_. B, _Samaropsis
emarginata_. C, D, _Cordaicarpus Cordai_. E, _Samaropsis bicaudata_.
F, _Samaropsis Seixasi_. G, _Samaropsis barcellosa_. H, _Samaropsis
moravica_. I, _Samaropsis bignonioides_. K, _Samaropsis Newberryi_. (A,
after Dawson; B, R. K. 1576; C, R. K. 1899; D, R. K. 4647; E, after
Kidston; F, G, after White; H, after Zeiller; I, after Fiedler; K, R.
K. 2313. All nat. size.)]
_Samaropsis Newberryi_ Andrews.
This species was originally described by Andrews[999] from the Coal
Measures of Ohio: the specimen shown in fig. 502, K, was sent to Dr
Kidston by Mr Claypole. The whole seed is 5 cm. wide and 3·5 cm. in
depth; it is characterised by a short and relatively broad nucule
surrounded by a very broad and flat border showing faintly marked
radially disposed lines and in places some irregularly distributed
pits. The apex is emarginate and there is a broad and deep sinus in
the sarcotesta in the chalazal region. The seed resembles _Samaropsis
alata_ Kidst.[1000] and _S. Baileyi_ (Daws.)[1001] but it differs from
these in the greater breadth of the ‘wing’ and in the form of the
nucule.
The seed described by Fiedler[1002] as _Jordania bignonioides_
(fig. 502, I) agrees closely with _S. alata_ Kidst. but is probably
specifically distinct.
_Samaropsis barcellosa_ (White).
White[1003] described this species (fig. 502, G) from
Permo-Carboniferous rocks in Brazil (Rio Grande do Sul) as
_Cardiocarpon barcellosum_. The nucule is said to be cordate but, as
seen in the figure, there is no clear indication of a basal sinus: the
presence of a relatively broad ‘wing,’ as White says, entitles the seed
‘to a place in the _Samaropsis_ section of the genus.’ The author of
the species compares it with seeds described from Westphalian rocks in
Ohio[1004] and Pennsylvania[1005]. It is interesting to find a type
which is common in both Europe and North America in the western portion
of Gondwana Land. Seeds of similar form are recorded also from India,
South Africa, and Australia[1006].
_Samaropsis Seixasi_ (White).
This Brazilian species from the same beds is described by White as
_Gangamopteris_ (_Samaropsis_) _Seixasi_[1007]: it is characterised by
a small ovate nucule 8–10 mm. long and 5 mm. broad, in some specimens
surrounded by a complete ‘wing’ extending above the apex and below the
base, giving the seed an appearance similar to that of _Samaropsis_
(_Samarospermum_) _moravica_ while sometimes, as in the example shown
in fig. 502, F, the broad border is preserved only at the sides.
These seeds are abundant in the Santa Catharina beds, where they were
discovered by Dr Esdras do Prado Seixas, in association with leaves of
_Gangamopteris_, and White thinks that they were borne on the fertile
leaves of that genus which he has named _Arberia_[1008]. Although
there is as yet no proof of a connexion between _Gangamopteris_ and
seeds of this or any other type it is almost certain that it was a
seed-producing plant.
_Samaropsis Leslii_ sp. nov.
[Illustration: Fig. 503. _Samaropsis Leslii_. From Vereeniging, S.
Africa. (Mr Leslie’s Collection; nat. size.)]
The seed on which this species is founded was discovered by Mr T. N.
Leslie in the Ecca beds (Permo-Carboniferous) of Vereeniging, South
Africa, a locality from which the same geologist has obtained leaves of
_Cordaites_, _Psygmophyllum_, _Glossopteris_ and other genera[1009].
In the slightly cordate base and tapered apex (fig. 503) the nucule
agrees closely with those of European examples, but the Vereeniging
type is distinguished by its larger dimensions and by the wider border
indicating a thick sarcotesta continued basally into a stout stalk. The
apex is emarginate and a median rib marks the position of a vascular
strand. There is no evidence as to the nature of the parent-plant.
_Samaropsis indica_ (Zeiller).
Prof. Zeiller[1010] described this species as _Cardiocarpus indicus_
from the Karharbari (Lower Gondwana) beds of India. An examination of
the type-specimens enables me to confirm the accuracy of the original
account. The platyspermic seed is 5·5 cm. long and 4·5 cm. broad;
a cordate nucule is enclosed by a flat border similar to that of
_Samaropsis Leslii_ but narrower especially on the sides of the nucule.
At the apex there is a deep sinus extending to the nucule, and at the
base a fairly broad band of carbonaceous matter shows the position of
the chalazal vascular strand. The seed is characterised by its large
size and by its almost orbicular form: it occurs as a detached specimen
in beds containing _Cordaites_ (_Noeggerathiopsis_) and _Glossopteris_.
A species from Arkansas described by Lesquereux[1011] as _Cardiocarpus
ingens_ [= _Cordaicarpus ingens_ (Lesq.)] affords another example of a
large seed similar to _C. indicus_ and, except in its more orbicular
form, to _Samaropsis Leslii_.
_Samaropsis Milleri_ (Feistmantel).
[Illustration: Fig. 504. _Samaropsis Milleri._ (Indian Geological
Survey, Calcutta; nat. size.)]
An examination of the type-specimen from the Calcutta Museum enables
me to amplify the original description in an important particular. The
species was found in Lower Gondwana (Katharbari) beds in India and
referred by Feistmantel[1012] to the genus _Carpolithes_. Arber[1013],
who tentatively employed the generic name _Cardiocarpus_ in place
of _Carpolithes_, suggests that the seeds may be radiospermic, as
Feistmantel’s drawings show only a very narrow border to the nucule.
The specimen reproduced in fig. 504 was figured by Feistmantel without
any indication of a definite sarcotesta or wing, but as seen in the
drawing the ovate cordate sclerotesta is surrounded on one side and at
the base by an outer envelope: this is clearly seen at the apex where
it shows a rounded termination sloping downwards towards the micropyle
precisely as in _Samaropsis indica_ (Zeill.). The border is narrow at
the sides and broader at the base as in _S. Leslii_. The seed is 4·5
cm. long and 2·3 cm. broad, differing from _S. indica_ in its rather
smaller size and in the slightly narrower nucule. Though there is no
decisive evidence as to the parent-plant the occurrence of a specimen
of this species partially covered by a scale-leaf of a type[1014]
very similar to that which is generally recognised as belonging to
_Glossopteris_ suggests the possibility that the seeds may belong to
that genus. Scale-leaves of _Glossopteris_ are described in Volume
+ii.+, but it may be added here that leaves similar in form to those
from India, Australia, and elsewhere are figured by Geinitz[1015]
from the Altai Mountains as _Trigonocarpus_? _actaeonelloides_: the
specimens are represented with the basal scar at the apex.
=Cordaicarpus.= Geinitz.
In view of the fact that the generic names _Cardiocarpus_,
_Cordaicarpus_, and other designations have been applied to casts
and impressions which cannot be distinguished by any constant or
important feature it is proposed to adopt the name _Cordaicarpus_
for platyspermic seeds, preserved as casts or impressions, having
a comparatively narrow border enclosing an ovate or cordate-ovate
nucule; the base is either rounded or cordate. The choice between
_Cordaicarpus_ and _Samaropsis_ depends on the breadth of the border.
_Cordaicarpus_, though more suggestive of a Cordaitean alliance, may in
some cases be a Pteridosperm seed.
_Cordaicarpus Cordai_ (Geinitz). Lenticular seeds more or less
orbicular or broadly ovate (fig. 502, C, D), often slightly cordate at
the base of the nucule and with a broadly acute apex: the border is
narrow or sometimes hardly represented as in the seeds described by
Berger as _Rhabdocarpus ovoides_, a species similar to but more oval
than _Cordaicarpus Cordai_. The latter species[1016] occurs in several
coalfields in Britain, France, Germany, and elsewhere. Fig. 502, C,
shows a good example from the Middle Coal Measures of Yorkshire, 9 mm.
long by 8 mm. broad; on the very slightly cordate nucule are several
faint ribs converging towards the base and apex and between them
fine striations, characters too indistinct to be reproduced in the
natural-size drawing. The flat border represents the sclerotesta. The
seed shown in fig. 502, D, from the Westphalian series of Warwickshire
belongs to the same species or is a closely allied type: the faint
suggestion of reticulation on its surface might be regarded as a reason
for referring it to _C. areolatus_ Boul.[1017], a form characterised
by a reticulation on the testa, described by Zeiller[1018] and other
authors. This reticulation is, however, in some cases at least, formed
by crumpling and splitting of the superficial carbonised film into more
or less regular meshes: the figured specimen occurs with several other
seeds of the same type, most of which have a smooth surface. Dr Kidston
tells me that a recent critical examination of seeds in his collection
leads him to regard some specimens (_e.g._ fig. 502, D) previously
referred by him to _C. Cordai_ as identical with _Carpolithes
membranaceus_ Goepp.[1019]
[Illustration: Fig. 505. _Cordaicarpus Cordai._ Cuticle of the testa.
(Kidston Collection.)]
The photograph reproduced in fig. 505 shows the result of chemically
treating the carbonised cuticle of a seed of _Cordaicarpus Cordai_, a
method little used as yet in the case of Palaeozoic plants but which
may be useful in distinguishing seeds which cannot be satisfactorily
separated by microscopic features. The superficial cells have very
thick walls and present an appearance similar to that of the sclerous
cells in the testas of some petrified specimens.
The larger seed shown in fig. 501, D, from Commentry, described by
Renault and Zeiller[1020] as _Cardiocarpus sclerotesta_, is another
example of _Cordaicarpus_ as now defined.
IV. +Miscellaneous Seeds.+
In this section are included genera based on characters of
comparatively little morphological importance; their claim to treatment
under a common heading is that we know little or nothing of their
anatomical features or of the parent-plants.
i. _Ribbed seeds._
The seeds represented by the following genera possess ribs or
flanges usually in multiples of three; the transverse section may be
triangular, hexagonal, or polygonal. The symmetry is generally radial,
but it is difficult to determine whether a slight departure from the
radiospermic form is an original feature or the result of pressure.
Some of the ribbed seeds with which we are now concerned are no doubt
closely allied to _Trigonocarpus_ and should be included in the
Trigonocarpales, but others may well be distinct forms.
Genera: _Hexagonocarpus_, _Decagonocarpus_, _Polypterocarpus_,
_Rhynchogonium_, _Boroviczia_, _Diplopterotesta_, _Musocarpus_,
_Holcospermum_.
=Hexagonocarpus.= Renault.
This generic name is adopted by Renault[1021] for casts from Commentry
which, while probably identical with Brongniart’s _Hexapterospermum_,
afford no confirmatory anatomical evidence. The species _Hexagonocarpus
crassus_[1022] is represented by casts or nucules characterised
by six well-defined ribs and grooves with a length of nearly 3
cm. In this genus may be included the cast from the Coal Measures
of Lancashire described by Williamson[1023] as _Hexapterospermum
Noeggerathi_ (fig. 506, H), and another British example is afforded
by _Hexagonocarpus Hookeri_ Kidst.[1024], a rare fossil in the South
Staffordshire coalfield. It is impossible confidently to assign these
ribbed casts to genera founded on petrified specimens as they almost
certainly belong to different types, but the employment of the name
_Hexagonocarpus_ may conveniently be used for casts or impressions of
seeds with six longitudinal ribs differing in their relatively broader
and less prominent form from the wing-like flanges of _Polypterocarpus_
(cf. fig. 496, B). The seeds described by Dr P. Bertrand[1025] as
_Hexapterospermum modestae_, and believed by him to belong to a plant
with _Neuropteris_ fronds, should be included in _Hexagonocarpus_ as we
have no definite knowledge of their anatomical features.
=Decagonocarpus.= Renault.
This name, proposed by Renault[1026], is applied to seeds without
petrified tissues characterised by ten ribs; an example is afforded
by _Decagonocarpus olivaeformis_ from the Commentry coalfield, an
elliptical seed which bears a close resemblance to _Holcospermum
sulcatum_ (fig. 506, A) except in the smaller number of ribs.
=Polypterocarpus.= Grand’Eury.
Grand’Eury[1027] adopted this generic name for seeds from St Étienne
characterised by the presence of three, six, or more deep wings
or flanges. The term _Pterospermum_ has recently been proposed by
Arber[1028] for a seed from the Coal Measures of Staffordshire, which
he names _P. anglicum_: the type-species of the genus has three deep
wings, one from each angle. For the same seed Kidston[1029] proposed
the name _Tripterospermum ellipticum_, but as Arber’s account was
published first his specific name has priority. _Pterospermum_ had,
however, been previously used for a genus of Sterculiaceae, and partly
on this account but mainly because Grand’Eury’s genus _Polypterocarpus_
is available the latter designation is adopted. In _Polypterocarpus
anglicus_ (fig. 496, B) the flanges project slightly beyond the apex
of the seed and there is a small notch at the base; the nucule is 5
cm. long and 1 cm. broad. While it is not improbable that this seed
is generically identical with Brongniart’s _Tripterospermum_[1030],
it is safer, in the absence of structural details, to employ the less
committal term. There is no information with regard to the nature of
the parent-plants of species of _Polypterocarpus_. The English seed
from the Middle Coal Measures of Derbyshire and the Staffordshire
coalfield described by Arber[1031] as _Radiospermum ornatum_ and by
Kidston[1032] as _Polypterospermum ornatum_ affords another example of
_Polypterocarpus_ as the generic name is here employed.
=Rhynchogonium.= Heer.
Heer[1033] proposed this generic name for some globose, ovate, or
oblong ‘fruits’ from Lower Carboniferous strata in Spitzbergen,
including also fragments of ‘leaves’ which without satisfactory
evidence he believed to belong to the same plant. The supposed
fruits are clearly seeds, and Nathorst regards the ‘leaves’ as
portions of a Fern rachis. Heer described four species, but these
have since been reduced to two, and indeed it is probable that only
one type, _Rhynchogonium costatum_, is represented. Nathorst[1034]
compares Heer’s seeds with a Lower Carboniferous species described
by Young[1035] as _Trigonocarpum gloagianum_, the resemblance of
which to the Spitzbergen seeds was pointed out by Kidston. A seed of
_Rhynchogonium costatum_ is about the size of a hazel-nut and may
reach a length of 21 mm.; it is ovate, with a broad rounded base,
and in the upper third is tapered and conical, the sides of the
characteristic snout being distinguished from the smooth surface of
the rest of the seed by the presence of eight ribs converging towards
the apex (506, G). Zalessky[1036] recorded closely allied seeds from
Lower Carboniferous beds in Northern Russia, assigning them to a new
genus _Boroviczia_, the type-species being _B. Karpinskii_; he adduced
arguments in favour of Heer’s interpretation of the fossils as fruits
but, according to Nathorst, this view has been abandoned. In his recent
memoir on the Culm flora of Spitzbergen Nathorst[1037] discusses the
morphological nature of _Rhynchogonium_ seeds and describes additional
specimens. Without the aid of petrified examples it is hardly possible
to determine the true nature of the fossils.
[Illustration: Fig. 506. A, _Holcospermum sulcatum_. B, C,
_Codonospermum anomalum_. D, _Diplopterotesta spitzbergensis_ (×
3). E, _Gnetopsis elliptica_ (cupule). F, _Thysanotesta sagittula_.
G, _Rhynchogonium costatum_. H, _Hexagonocarpus Noeggerathi_. I,
_Boroviczia Karpinskii_. K, _Rhabdospermum tunicatum_. (A, Kidston
Collection; B, after Grand’Eury; C, after Renault and Zeiller; D, F,
G, after Nathorst; E, after Renault; H, after Williamson; I, after
Zalessky; K, after Berger.)]
Some specimens of _Rhynchogonium sulcatum_ in Dr Kidston’s collection
show the original surface-features: the carbonised integument is
divided in the upper region into linear lobes separated from one
another at their origin by fairly wide sinuses, a type of integument
suggesting comparison with _Physostoma_. This species was originally
described by Lindley and Hutton as _Carpolithes sulcata[1038]_ from
Lower Carboniferous rocks at Newhaven in Scotland and has recently been
figured by Zalessky[1039] from specimens in the Kidston collection
from the Lower Calciferous sandstone of Midlothian. Nothing definite
can be said as to the parent-plant, but it is significant that in
Midlothian _Rhynchogonium sulcatum_ occurs in a bed full of isolated
pinnules of a _Cardiopteris_ almost to the exclusion of any other
fossils[1040].
The seed figured by Nathorst[1041] from the Culm of Spitzbergen as
_Lagenospermum? glandiforme_ agrees closely with _Rhynchogonium_
and _Boroviczia_, and it is impossible to decide whether the lobed
appearance is due to the presence of a cupule or to the divisions of an
integument.
=Boroviczia.= Zalessky.
The specimens from Lower Carboniferous beds in Russia[1042] on which
this genus was founded are perhaps unnecessarily separated from
_Rhynchogonium_; they are ovate and beaked, 10 mm. long with a maximum
breadth of 6 mm. The type-species, _Boroviczia Karpinskii_ (fig. 506,
I), is represented both by specimens in which the cast is complete
and by others in which the apical snout of the integument is split
into separate lobes identical in form and apparently in number with
those of _Rhynchogonium_. Nathorst[1043], who retains the generic name
and describes two additional species from Spitzbergen, points out
that in Boroviczia the tapered apex is more sharply differentiated
from the broader basal portion, a difference hardly worthy of generic
recognition. If _Boroviczia_ is retained as a genus distinct from
_Rhynchogonium_ it should include the seeds described by Young as
_Trigonocarpum gloagianum_.
=Diplopterotesta.= Nathorst.
_Diplopterotesta spitzbergensis_ (Heer). Heer[1044] included in
_Samaropsis_ some seeds, described as _Samaropsis spitzbergensis_, from
Lower Carboniferous strata in Spitzbergen which differ considerably
from typical examples of the genus. These have recently been made the
type of a new genus _Diplopterotesta_[1045]: they are platyspermic
seeds nearly twice as long as broad, 6–9 × 3·5–5 mm., characterised
by a thin sclerotesta expanded throughout the length of the seed into
two prominent transversely striated wing-like ribs or flanges (fig.
506, D). At the apex, which is broad in contrast to the pointed basal
end of the seed, the sclerotesta forms a crown of eight lobes about
the flat summit of the seed-body. As Nathorst points out, this species
closely resembles the Carboniferous seeds figured by Grand’Eury[1046]
as _Polypterocarpus_, but in the latter type there are more than two
wings. Nathorst’s figures, one of which is reproduced in fig. 506, D,
suggest a difficulty in determining the number of the flanges, which
would seem to be more than two, but this appearance is regarded by
Nathorst as misleading and he believes that except at the apex there
are only two wings.
=Musocarpus.= Brongniart.
Brongniart[1047] proposed this name for two species, _M. prismaticus_
and _M. difformis_, from French Coal Measures, but gave no description
of the specimens. The type-species, described from the Loire by
Grand’Eury as _Musocarpus prismaticus_[1048], is an ovate seed nearly
3 cm. long with six longitudinal ribs, three being more prominent
than the others, and characterised by a ribbed prolongation of
the base of uniform diameter spoken of as a carpophore, which was
apparently articulated to the lower part of the seed-proper from which
it was easily detached by a natural absciss-layer. Nothing is known
of the structure or of the affinity of the genus. Some specimens
in Dr Kidston’s collection from Westphalian beds in Lanarkshire
are closely allied to or perhaps identical with _M. prismaticus_.
In the presence of a distinct basal region _Musocarpus_ resembles
_Codonospermum_[1049], though without any knowledge of the anatomy of
the former type it is impossible to say whether or not this resemblance
has any morphological importance.
=Holcospermum.= Nathorst.
_Holcospermum sulcatum_ (Sternberg). The cast reproduced in fig. 506,
A, affords a good example of a form of seed recorded under several
generic names and not uncommon in Upper Palaeozoic rocks in Europe
and North America, which in most cases cannot be assigned to a genus
implying the possession of certain anatomical characters. This type
was figured by Sternberg[1050] from the Coal Measures of Radnitz as
_Carpolites sulcatus_. Some ‘fruits’ collected on the beach near
Newhaven, Midlothian, from the Calciferous Sandstone series, are
figured by Lindley and Hutton[1051] as _Carpolithes sulcata_, but
as already stated these have been transferred[1052] to the genus
_Rhynchogonium_. Several authors have referred specimens of the type
now included in _Holcospermum_ to _Rhabdocarpus_, but that genus, as
stated on a previous page, is restricted to seeds agreeing in form
with _R. tunicatus_. Renault[1053] instituted the genus _Colpospermum_
for a partially petrified seed from Commentry agreeing externally with
_Carpolites sulcatus_ Sternb. and regarded by him as specifically
identical, characterised by longitudinal ribs which represent folds
of the testa, the intervening grooves being occupied by an irregular
reticulum formed by occasionally anastomosing smaller ribs. The generic
name _Colpospermum_ should therefore be reserved for ribbed seeds
showing the anatomical features described by Renault and Zeiller:
its application to Sternberg’s species is inadvisable on the ground
that we have no information with regard to the morphological nature
of the ribbing. More recently Arber[1054] has proposed the name
_Platyspermum_, a name previously applied to a Cruciferous plant,
for Stephanian and Permian seeds formerly assigned to Berger’s genus
_Rhabdocarpus_, which are symmetrical in two planes. In this genus
he includes _Platyspermum sulcatum_ and among other species _P.
Kidstoni_ founded on a seed originally identified by Kidston[1055] as
_Rhabdocarpus multistriatus_ Sternb. which, though probably a distinct
species, is of the same general type as _C. sulcatus_ Sternb.
The cast represented in fig. 506, A, from the Middle Coal Measures of
Yorkshire is 3·5 cm. long and has 18 regular longitudinal ribs: it is
radially symmetrical and does not conform in this respect to Arber’s
definition of _Platyspermum_. In many cases, _e.g._ the flattened seed
figured by Kidston as _Rhabdocarpus multistriatus_, it is impossible to
determine the symmetry of the seed. The old generic name _Carpolites_,
_Carpolithes_ or _Carpolithus_ has been used in a very wide sense and
does not connote any well-defined features; it should be reserved,
in the form _Carpolithus_ as used by Linnaeus, for seeds that cannot
be assigned to a systematic position or which do not exhibit any
distinctive characters worthy of emphasis by the institution of a
special name. The generic term _Holcospermum_, recently proposed
by Nathorst[1056], is a suitable name for this type of seed; as
defined by the author, it includes seeds that may be radiospermic or
platyspermic. Specimens of the type-species, _H. dubium_[1057],from
the Lower Carboniferous beds of Spitzbergen, agree closely in size
and shape with some examples of _Rhynchogonium_ and _Boroviczia_, but
they are distinguished by prominent ribs extending the whole length
of the cast. In some seeds similar to _H. sulcatum_ the ribs form
sharp ridges, but the difference between rounded and sharp ridges is
often determined by the method of preservation: a specimen deprived of
its outer flesh would form a cast more sharply ribbed than a seed in
which the sarcotesta had been moulded on to the ribbed sclerotesta.
On the other hand some ribs are formed by blunt sclerotestal folds as
in _Colpospermum_: both types of ribbing are included in the genus
_Holcospermum_.
ii. _Other Genera._
=Malacotesta.= Williamson.
This generic name was instituted by Williamson[1058] for a petrified
seed from the Coal Measures of Lancashire which he named _Malacotesta
oblonga_: the type-specimen is a small seed 6–7 mm. long characterised
by a thick fleshy integument. The structure is however insufficiently
known to admit of a satisfactory comparison of the imperfectly
preserved specimen figured by Williamson with other types.
=Thysanotesta.= Nathorst.
Nathorst[1059] founded this genus on a single seed from the Lower
Carboniferous plant-beds of Spitzbergen which exhibits features
sufficiently distinctive to justify its recognition as the type of a
separate genus.
_Thysanotesta sagittula_ Nathorst. The type-specimen is a long and
narrow seed, 20 mm. long, ovate below and prolonged apically into a
slender beak, 8 mm. in length, which probably represents a micropylar
tube; the beak bears numerous stiff hairs (fig. 506, F). The seed
closely resembles a carpel of _Erodium_ without the horizontal part
of the awn. There is no evidence as to the nature of the parent-plant
but the species affords an interesting example of a Palaeozoic seed
apparently adapted for wind-dispersal, or possibly the bristles may
have served the same purpose as in the fruits of _Erodium_. Attention
is called elsewhere[1060] to the frequent resemblance of Palaeozoic
seeds such as _Thysanotesta_ to fruits of recent flowering plants.
=Carpolithus.= Linnaeus.
Nathorst[1061] has pointed out that this generic name was employed by
Linnaeus for fossil fruits: in the form _Carpolites_ (Sternberg) or
_Carpolithes_[1062] it has been widely used and differently defined
by authors, usually in a comprehensive sense including fossil seeds
from both Palaeozoic and Mesozoic strata which cannot be assigned to
a definite position in the plant-kingdom. It is desirable to adopt
some designation for seeds from strata of different ages which do not
exhibit any features sufficiently distinctive to justify the creation
of a special genus. By employing such a name as _Carpolithus_, without
attempting to define its characters within prescribed limits, for casts
or impressions of seeds which are not distinguished by any striking
characters and cannot be allocated to any particular section of
seed-bearing plants the unnecessary multiplication of generic titles
is avoided: when any additional data are obtained differentiating
particular types from other forms of _Carpolithus_ the provisional
term should be superseded by some distinctive generic name. Among
seeds from the Coal Measures there are several examples of both large
and small types without any regular ribs or lacking such features
as serve to distinguish the genera already described, which are
appropriately included in _Carpolithus_. The two species _Carpolithus
Wildii_ Kidst.[1063] and _C. bivalvis_ Goepp.[1064] are two examples
of seeds from Upper Carboniferous rocks which it is desirable to refer
to this comprehensive genus pending further discoveries as to their
morphological features. The Jurassic species _C. conicus_ Lind. and
Hutt.[1065] is another type which it has been customary to include in
_Carpolithus_.
(_Microspermum._ Arber.)
The generic name _Microspermum_ has recently been proposed by
Arber[1066] for some Westphalian seeds described by Carpentier[1067]
from the North of France as _Carpolithes? samaroides_ and for similar
fossils from the Middle Coal Measures of Nottingham. The supposed seeds
are small, ovate or pyriform bodies, 5–12 mm. long and 2·5–6 mm. broad,
with one extremity broadly rounded and the other acute: one side is
keeled, the other grooved, and a large foramen occurs near the broader
end and on the grooved surface. Arber emphasises the fact that the
specimens are symmetrical in one plane only. As the author of the genus
points out the morphological nature of the fossils is not thoroughly
established, nor is the parent-plant known. In view of the ill-defined
characters of the specimens so far discovered it is hardly desirable
to institute a new generic name implying their seed-nature; moreover
_Microspermum_ has previously been employed for a genus of Compositae.
An examination of specimens leads me to doubt their seed-nature and it
would seem more likely that they are foliar organs, possibly bracts
which originally bore seeds or sporangia.
* * * * *
An examination of some of the specimens of supposed Permian seeds for
which Geinitz[1068] proposed the generic name _Guilelmites_ convinced
me that they are inorganic structures, probably nodules in shale
smoothed and rounded by slickensiding.
CHAPTER XXXVI.
CYCADOPHYTA.
The term Cycadophyta, suggested by Nathorst[1069], is used in a
comprehensive sense to include both recent Cycads and the much
larger number of extinct types which it is customary to speak of
as Cycadean plants or fossil Cycads. The designation ‘Cycads’ in
the case of the majority of the fossil forms is, however, open to
criticism on the ground that they differ too widely from existing
genera to be associated with them in one class. It would be pedantic
and inconvenient to give up the almost universal practice of extending
the term Cycad beyond the limits defined by the characters of
recent species. The important point is to adopt some classification
which gives expression to our views as to the degree of affinity
between recent and extinct types. In a considerable number of cases,
especially impressions of presumably Cycadean fronds and stems that
occur without any fertile shoots, it is impossible to determine the
degree of relationship to modern types. It was with a view to a
rational group-designation for such fossils that Nathorst proposed
the term Cycadophyta, including in it the two classes Cycadales and
Bennettitales. The Cycadales comprise the recent genera and such
extinct types as may legitimately be included in the same class, but
as we shall see later there are hardly any fossil species that can be
assigned to this section on thoroughly satisfactory grounds. The term
Bennettitales is used by Engler, Nathorst, and several other authors as
a class-designation for a large number of Mesozoic Cycads agreeing in
their more important morphological characters with the Lower Cretaceous
stems on which Carruthers[1070] founded the genus _Bennettites_,
placing it in a new tribe, the Bennettiteae. Some authors have followed
Carruthers in the use of the family-name Bennettiteae for a subdivision
of the Cycadales equal in rank to the Cycadaceae, while others, wishing
to give greater emphasis to the difference between the extinct and
recent plants, prefer to adopt the class-name Bennettitales. Carruthers
regarded _Bennettites_ as occupying the same position in relation to
other Cycads as _Taxus_ holds with regard to the cone-bearing members
of the Coniferae. The adoption of Bennettitales is intended to convey
the impression that the class is more distantly related to the recent
Cycads than is implied by the analogy of _Taxus_. Nathorst[1071], as
the result of his discovery of certain reproductive organs associated
with some Rhaetic fronds described as _Dioonites spectabilis_, proposed
a third subdivision, the Dioonitales, but he subsequently[1072]
restored the fronds to their original designation _Nilssonia
pterophylloides_, and on further examination found that the supposed
microspore-bearing organs were seeds. _Nilssonia pterophylloides_
would therefore find a more natural place in the class Nilssoniales
instituted by Thomas[1073].
BENNETTITALES.
=Cycadeoidea.= Buckland.
In 1827 Buckland[1074] proposed the generic name _Cycadeoidea_ for
some petrified stems from the Purbeck beds in the Isle of Portland and
published a description of two species, _Cycadeoidea megalophylla_
and _C. microphylla_. Brongniart[1075] considered Buckland’s term
_Cycadeoidea_ inappropriate and proposed in its place _Mantellia_, the
type-species being _Mantellia nidiformis_ Brongn., the Portland stem
which Buckland a month or two later called independently _Cycadeoidea
megalophylla_. Subsequently Brongniart[1076] withdrew _Mantellia_ as
it had been previously used by Parkinson for a sponge and substituted
_Cycadites_. Some years later Carruthers[1077] revived _Mantellia_
for a type of Cycadean stem from Portland though one species,
apparently indistinguishable from those referred to _Mantellia_, he
named _Bennettites portlandicus_. There is no adequate reason for the
retention of the generic name _Mantellia_. The close resemblance of the
short and thick stems (12–30 cm. in height) described by Buckland to
those of some recent Cycads was recognised by Robert Brown and Loddiges
and the former suggested to Buckland the inclusion of the fossils in
a new family Cycadeoideae. It was this suggestion that led Buckland
to adopt _Cycadeoidea_ as a generic name. In a later account of the
Portland stems Buckland[1078], in deference to Brongniart’s opinion,
substituted Brongniart’s name _Cycadites_ for _Cycadeoidea_. It is
noteworthy that no reference is made in the original description to
the occurrence of lateral shoots among the persistent petiole-bases
that encase the Portland stems, but in a later account such shoots
are represented in one of the figured stems and are compared with the
buds occasionally produced on stems of _Cycas_[1079]. The subsequent
researches of Carruthers[1080] demonstrated the reproductive nature
of precisely similar lateral shoots in the stem on which he founded
the genus _Bennettites_. The generic name _Echinostipes_ given by
Pomel[1081], who had a passion for instituting new nomenclature, to
Buckland’s Portland stems has not been adopted: his genus _Crossozamia_
proposed for certain stems and fronds was revived by Carruthers[1082]
but has not been generally used. A further complication in the
nomenclature of Cycadean stems was introduced by Saporta’s
institution[1083] of _Bulbopodium_ and _Cylindropodium_: in the former
genus he included the small ovoid stem figured by Lindley and Hutton
as _Cycadeoidea pygmaea_[1084] and two French Jurassic species which
might reasonably be assigned to _Cycadeoidea_. To _Cylindropodium_ were
referred some large French stems from Jurassic strata: an examination
of the type-specimens in Paris convinced me that they are typical
forms of _Cycadeoidea_. As Ward[1085] has pointed out, both Saporta’s
genera may be merged in _Cycadeoidea_. Fliche and Zeiller[1086] also
include the small globular stems named by Saporta _Bulbopodium_ in
the older genus _Cycadeoidea_: one such type from the Portlandian of
Boulogne is described by these authors as _Cycadeoidea pumila_. Saporta
also proposed the name _Platylepis_[1087], the type-species being
_Cycadeoidea micromyela_ Mor., from the Lias of Calvados, which has
recently been investigated by Lignier[1088] who wisely adopts Morière’s
designation. Another unnecessary generic name is _Schizopodium_ given
by Morière to a stem, _S. Renaulti_[1089], regarded by Lignier as
indistinguishable specifically from _C. micromyela_.
The two names _Cycadeoidea_ and _Bennettites_ have been used by
authors for stems which are unquestionably generically identical
and as is often the case much confusion has been caused through the
failure of palaeobotanists to arrive at an agreement. Lester Ward, a
staunch advocate of the rule of priority, repeatedly pointed out that
Buckland’s name _Cycadeoidea_ should take precedence of _Bennettites_
on the ground that stems for which these genera were instituted are
clearly of the same type, and he added that the older genus, though
abandoned by its author, cannot be given up without violating the
inexorable rules of priority. On the other hand it has been urged that
the genus _Bennettites_ as defined by Carruthers is characterised
by the possession of (i) fertile shoots bearing strobili and (ii)
vegetative organs exhibiting certain anatomical characters. Buckland’s
species of _Cycadeoidea_, though bearing lateral shoots, are not well
enough preserved to afford definite information as to the morphological
features of the strobili, nor have we satisfactory data with regard
to the degree of resemblance between the vegetative features of
_Bennettites_ and the Portland stems. Carruthers laid stress on the
elliptical section of the stele in _Bennettites_ in contrast to the
cylindrical cylinder of Buckland’s _Cycadeoidea_ trunks. Subsequent
research has shown that this difference is not in itself a valid
criterion either of generic or specific rank but, as Wieland says, it
is an open question to what extent the stem structure of _Cycadeoidea_
and _Bennettites_ agrees. The probability is that were our knowledge
of the Portland stems less incomplete, they would be found to possess
no anatomical features inconsistent with this generic union. Granting
the correctness of this view, the adoption of the later generic term
would be a reasonable course to follow on the ground that it stands
for stems showing well preserved structure, while _Cycadeoidea_ was in
the first instance applied to stems showing only partially preserved
stumps of strobili, and the name was not retained by its author. Graf
Solms-Laubach[1090] and some other authors have used _Bennettites_ for
Cycadean stems possessing strobili of known structure such as those of
_Bennettites Gibsonianus_, reserving _Cycadeoidea_ for similar stems
but without strobili sufficiently well preserved to afford evidence of
morphological characters. This practice I followed in 1895[1091], but
my usage of the two generic names has not been consistent, the name
_Cycadeoidea_ being afterwards employed[1092] in a more comprehensive
sense. The investigation of the reproductive shoots of American Lower
Cretaceous and Upper Jurassic Cycadean stems[1093] has demonstrated the
practical identity of their ovulate strobili with those of the English
_Bennettites_. It is clear that the American stems as well as numerous
specimens from Italy and other European localities are generically
inseparable from _Bennettites_. The adoption of _Cycadeoidea_ by
Wieland, following Ward, has naturally strengthened the claim of
Buckland’s genus at least so far as wide usage is concerned, and with
some reluctance I propose to fall in with this terminology and for
the sake of convenience to give up the use of _Bennettites_. Among
Mesozoic Cycadean stems agreeing with those of recent genera in habit
and in the presence of an armour of persistent leaf-bases are several
which afford no evidence either of the occurrence of fertile shoots
or of lateral shoots with terminal flowers. To such stems the name
_Cycadeoidea_ has been applied, the designation _Bennettites_ being
restricted to stems with lateral fertile shoots: this practice of
treating the absence of reproductive shoots as a characteristic feature
of _Cycadeoidea_ is regarded by Wieland as illogical and artificial;
and if, as seems probable, he is correct in believing that the majority
of the Mesozoic Cycadean plants culminated their vegetative period by
prolific development of flowers, the absence of flowering branches
would be contingent on a certain stage of development and not a generic
character. Dr Stopes[1094] has recently published facts with regard
to the anatomical features of Cycadean stems which have a bearing
on the vexed question of nomenclature, but are more important from
a morphological point of view as they indicate a closer agreement
between certain types of Lower Cretaceous stems and those of _Cycas_
and other recent genera, in which successive rings of vascular tissue
are developed, than has previously been recognised. In her diagnosis of
_Cycadeoidea_ she includes the following statement: ‘In its internal
anatomy the trunk shows two or more (up to eight are recorded) zones
of secondary wood, the zones composed of distinct series of tracheids
each more or less regularly arranged in radial sequence.’ It is
claimed that the addition of this character constitutes for the first
time a clear distinction between _Cycadeoidea_ and _Bennettites_. Dr
Stopes states that the two stems on which Buckland founded the genus
_Cycadeoidea_ are lost and adds that Buckland’s type has certain
anatomical features which are not found in _Bennettites_. Buckland
in his description of _C. microphylla_ states that there are ‘two
laminated circles’ in the stem instead of the usual single cylinder,
a character suggestive of _Cycas_. In the original figure of this
species there are no indications of any lateral fertile shoots though,
as Dr Stopes says, many of the Portland stems undoubtedly possessed
such flowers. This author makes no reference to Buckland’s later
description of _C. microphylla_: in this it is stated that the stem
bears numerous buds rising from the axillae of petioles, and these
are shown in the illustration[1095]. Without access to the actual
specimen it is impossible to say whether or not the two ‘laminated
circles’ described and figured by Buckland[1096] are two distinct
cylinders or parts of one cylinder separated by the infiltration of
some inorganic substance. In his description of _Cycadeoidea Yatesii_
Carruthers spoke of the occurrence of two cylinders of wood, and this
was confirmed in a subsequent account of the type-specimen[1097]. Dr
Stopes gives a fuller account of Carruthers’ type and re-confirm a
the existence of two vascular cylinders; she also describes a new
species, _C. buzzardensis_[1098] (fig. 578), in which there are 3–8
or more cylinders. Neither of these stems affords any evidence of the
possession of fertile shoots; they agree closely with stems of the
_Bucklandia_ type in their comparatively slender habit and differ in
this respect from Buckland’s Portland species. The occurrence of more
than one vascular cylinder in the stems _Cycadeoidea_ (= _Bucklandia_)
_Yatesii_ and _C._ (= _Bucklandia_) _buzzardensis_ suggests the
possibility that this feature was characteristic of other species
included in _Bucklandia_.
It is clear that some at least of the stems referred to the genus
_Bucklandia_ bore flowers of the _Williamsonia_ type[1099], and it is
not improbable that the stems described by Dr Stopes as _Cycadeoidea
Yatesii_ and _C. buzzardensis_ (fig. 578) possessed fertile shoots
comparable with those of the Middle Jurassic species _W. gigas_.
Dr Stopes’s contribution, while establishing a close agreement in
anatomical features between some Lower Cretaceous stems and those of
_Cycas_, does not warrant the further conclusion that these stems
were in other morphological characters closely allied to modern
Cycads. The main features of _Cycadeoidea_ may be summarised as
follows: The principal trunk is generally unbranched (fig. 507)
and identical in habit with some species of _Macrozamia_, _Dioon_,
and _Encephalartos_ (cf. figs. 379, 382); in some species, _e.g._
_Cycadeoidea Marshiana_, _C. superba_[1100], _C. nana_[1101], the
plant is represented by several approximately equal, thick, tuberous
stems, in some cases easily separated from one another: a similar
clustered habit is exhibited by certain forms of _Encephalartos_. The
size of a _Cycadeoidea_ trunk varies from a few centimetres in length
with a diameter of similar dimensions, as in _C. pumila_, to over a
metre long as in _C. gigantea_ (fig. 535), or as much as 3–4 metres in
_C. Jenneyana_ with a diameter of about half a metre. The surface is
covered with persistent leaf-bases, exactly as in many recent Cycads,
embedded in a thick mass of ramental scales which often stand out as
a prominent reticulum, the petioles having partially decayed before
the penetration of the mineralising solution through their harder
tissues (fig. 507). On the conical terminal bud preserved in some
stems (fig. 536) the foliage-leaves are replaced by linear scales.
The leaf-bases often show the vascular bundles which form a simpler
system than in the majority of recent species, their arrangement being,
as Wieland says, more Fern-like; they form a series of collateral
strands following the outline of the petiole-base[1102] with a U-shaped
invagination in the middle of the upper face (fig. 517, A). Beyond the
structure of the bundles at the base of the fronds and in the cortex
of the stem our knowledge of the anatomy of the vascular supply of
the rachises is very meagre. At the petiole-base each bundle consists
either entirely of radial rows of centrifugal scalariform tracheids and
medullary rays usually one-cell broad (fig. 519, B) or of centrifugal
and centripetal xylem in varying proportions. The ground-tissue is
well supplied with large secretory canals and in the larger leaf-bases
there is a considerable development of periderm at the surface (fig.
517, B) as in recent Cycads. The ramenta formed from the epidermal
cells consist in most species of fairly broad scales one-cell thick
at the edges and broader in the middle; in _Cycadeoidea nigra_[1103]
they are generally one-cell thick throughout and similar ramenta are
common in _C. Gibsoniana_ (fig. 517, B). In _C. micromyela_ unicellular
hairs replace the scaly ramenta, but transitional forms occur between
hairs and scales. In _Williamsonia scotica_ (fig. 562) and in an Indian
species of that genus the ramenta are exclusively long hairs as in
recent Cycads, the scale-form of the ramenta in _Cycadeoidea_ being a
Fern-character. The degree of development of the ramental tissue varies
in different species; in _C. Stilwelli_ and _C. excelsa_ it is feebly
developed while in _Cycadeoidea micromyela_ the ramenta almost cover
the exposed leaf-base armour. The exceptional abundance of the ramental
scales is a striking characteristic of some American stems referred
to a separate genus, _Cycadella_[1104]. In the abundance of the
ramental tissue, in the compact structure of the well protected cones,
and in the thickly cuticularised epidermis of the bracts and leaves
_Cycadeoidea_ exhibits xerophilous characters in a very high degree.
[Illustration: Fig. 507. _Cycadeoidea marylandica._ The first
American stem to be described. On the side of the stem shown in the
photograph there are about 30 young strobili scattered among the
leaf-bases. (After Wieland; ¼ nat. size.)]
[Illustration: Fig. 508. _Cycadeoidea Wielandi._ Transverse sections
of the secondary xylem of the stem. A, the middle region; B, the inner
edge of the xylem. (After Wieland; × 100.)]
With very few exceptions the stems of _Cycadeoidea_ so far described
afford no satisfactory evidence of the presence of more than one
vascular cylinder in the main stem: in this respect _Cycadeoidea_
agrees with such recent Cycads as _Dioon_, _Ceratozamia_, and
_Stangeria_. In the stem of C. _Jenneyana_ the secondary vascular
tissue reaches a considerable thickness and shows signs of ‘rings’
in the xylem, but these are probably the result of some periodic
interference with the uniform growth and not an indication of more
than one xylem-cylinder. The secondary xylem (figs. 508, 509) consists
only of centrifugal tracheids with some spiral elements on the inner
edge; though manoxylic, _Cycadeoidea_ has more compact wood than that
of recent Cycads; the medullary rays are 1–2 cells broad except near
the perimedullary region where they are broader and the individual
cells are tangentially stretched (fig. 508, B). The tracheids are
scalariform, but in _C. micromyela_, an exceptional type, some of the
xylem-elements have 1–2 rows of separate bordered pits (fig. 538). The
phloem (fig. 518, B) is characterised by an alternation of thick-walled
elements and thinner cells[1105]. From the main stele branches are
given off to supply the flowering shoots in the form of a cylindrical
stele like that of the primary axis, and each leaf-trace arises as
a single bundle which, in the form of a U-shaped strand (fig. 519,
A), pursues a straight course to the leaf-base (fig. 510) where it
breaks up into several branches (fig. 538, B). Both leaf-trace and
peduncle stele are given off from the lower edge of a medullary ray.
In the parenchymatous cortex large secretory canals (fig. 518, B) are
a conspicuous feature, and accessory cortical steles similar to those
in _Cycas_ occasionally occur (fig. 511). The large pith consists of
parenchyma and secretory canals, and internal periderm[1106] may be
present; no medullary bundles have been discovered.
[Illustration: Fig. 509. _Cycadeoidea Wielandi._ Tangential section
of secondary xylem of the stem. (After Wieland; × 100.)]
[Illustration: Fig. 510. _Cycadeoidea_ sp. A piece of stem showing
(A) the persistent leaf-bases in side-view and at _b_ the scars where
the bases have broken off, and (B) the inner face of the same piece
with the exposed leaf-traces passing into the leaves; one of the traces
is seen at _t_ in fig. A. (From a specimen in the British Museum; ½
nat. size.)]
[Illustration: Fig. 511. _Cycadeoidea Gibsoniana._ Stele in the
cortex. (British Museum, 8406.)]
[Illustration: Fig. 512. _Cycadeoidea ingens._ Transverse section of
a young frond, above the tip of the rachis, embedded in ramenta. The
rachis is situated on the upper side of the two ranks of pinnae. The
arrow points towards the axis of the stem. (After Wieland; × 4.)]
The correlation of the numerous fronds[1107] preserved in Mesozoic
strata with their parent-stems is seldom possible. It is known that
leaves of the _Zamites_ type were borne on stems (_Bucklandia_)
agreeing with _Cycadeoidea_ in certain features but differing in the
habit of the fertile shoots (fig. 542), and there is evidence that
similar stems bore _Ptilophyllum_ and _Dictyozamites_ fronds[1108];
but only unexpanded leaves have been found in actual connexion with
_Cycadeoidea_ stems. Wieland[1109] discovered young pinnate fronds,
agreeing in the form of the pinnae with _Zamites_ and with some forms
of _Encephalartos_, embedded in a thick mass of ramental scales in the
terminal bud of a stem: the rachises were erect and the two-ranked
pinnae imbricate and folded inwards (fig. 512), the vernation being
like that of _Dioon_ and not circinate as in _Cycas_ and Ferns. The
mesophyll of the leathery pinnae is differentiated into palisade
and lacunar parenchyma, and the bundles are said to be ‘mesarch’
though on this point more information is desirable. Each bundle is
surrounded by a sheath of thick-walled cells and the same tissue
forms =I=-shaped girders as in similar recent leaves. In one species,
_Cycadella ramentosa_[1110], the rachis of a young frond found among
the leaf-bases had a broad U-shaped vascular strand.
In most _Cycadeoidea_ stems a characteristic feature is the occurrence
of reduced leaves, or bracts, arranged spirally about a cone which
sometimes projects slightly beyond the general level of the persistent
leaf-bases, or the cones may be fully developed yet still more or less
hidden within the armour of petiole-bases (fig. 517, C). These cones,
or flowers, are borne at the apex of lateral axillary shoots, and it
is characteristic of the genus that they never project more than a
very short distance beyond the truncate stumps of the old leaf-bases.
The axis of a flowering branch bears numerous linear, hairy, bracts
(figs. 513; 514, _b_) which with their thick felt of ramenta constitute
an efficient protective investment. The summit of a fertile shoot
forms a rounded hemispherical cushion (fig. 514), or the receptacle
may be more elongate and conical (fig. 513) and in some species
pyriform[1111]. The flowers are generally bisporangiate, but the fact
that in flowers with mature microsporophylls the ovules are small and
apparently immature (fig. 513) makes it difficult to determine whether
the megasporophylls are merely immature or functionless as in the
male flower of _Welwitschia_ (cf. fig. 818). It would seem, however,
that in most cases the flowers were bisexual[1112] (fig. 513). A
remarkable feature is the enormous number of flowers on a single stem;
in _Cycadeoidea Dartoni_[1113], 54 cm. long and 35 cm. broad, 500–600
flowers were counted on one side. On the other hand the large stem of
_C. gigantea_ (fig. 536) shows no flowers. All the flowers on a single
trunk are approximately in the same stage of development: it would
seem, as Wieland points out, that after a vegetative period of some
considerable duration the plant produced a large crop of flowers, and
it is conceivable that as in _Corypha_ and some other recent Flowering
plants this supreme effort set a limit to the plant’s existence. In
the development of flowers from the old stem _Cycadeoidea_ affords a
striking example of cauliflory.
[Illustration: Fig. 513. _Cycadeoidea._ Restoration of an unexpanded
bisporangiate strobilus with some of the hairy bracts removed. Compare
_Cycadeoidea dacotensis_, figs. 529, 530. (After Wieland; _ca_ nat.
size.)]
[Illustration: Fig. 514. Ovulate strobilus of _Cycadeoidea_.
Longitudinal section showing the pith, _m_, stele, _x_, _p_, and
cortex, _c_, of the stem, the ovulate strobilus with bracts, _b_,
seeds, _s_, etc., enclosed by foliage-leaves, _l_; _a_, insertion of
leaves on the stem; _d_, insertion of disc of microsporophylls. (After
Wieland.)]
The structure of the flowers is one of the most obvious differences
between _Cycadeoidea_ and recent Cycads (_cf._ figs. 393, 394).
The bisexual flowers of the fossil stems are comparatively small,
not exceeding a few centimetres in length, like a hen’s egg or a
medium-sized pear and in marked contrast to the male and female
cones of modern Cycads (_cf._ figs. 393, 394). A verticil of pinnate
microsporophylls is attached by a circular collar formed of the
concrescent bases of the sporophylls to the lower portion of the
receptacle; each pinnule bears several shortly-stalked synangia
divided into loculi containing microspores usually with smooth walls
and similar, except in their larger size, to those of modern Cycads
(fig. 532). Sections of some microspores figured by Wieland[1114]
show what appear to be cells in the spore-cavity, but they are larger
than ordinary prothallial cells and their true nature is doubtful. We
lack information both as regards the nature of the male gametes and
the tissue formed on the germination of the spores. The free portions
of the microsporophyll-whorl may consist of as many as 20 pinnate
sporophylls, but the number is generally smaller; these are much longer
than the ovulate part of the flower and in an immature state the ends
of the sporophylls are bent inwards and downwards (fig. 513) between
the bracts and the receptacle. After expanding and shedding the spores
the whole male disc is thrown off leaving a narrow rim below the
hemispherical or conical receptacle (fig. 514, _d_). The sterile distal
end of a microsporophyll is generally slightly expanded and spathulate;
in _C. colossalis_[1115] it bears a pair of wing-like appendages (fig.
533).
The upper part of the receptacle is covered with two kinds of organs
which together form a layer of uniform depth; these are believed to be
homologous, foliar structures; the majority are sterile and have the
form of slender long and narrow appendages (fig. 514) each normally
with a single axial vascular strand. These so-called interseminal
scales increase in breadth in the apical region and form polygonal
summits less than a millimetre in breadth or exceeding 2 mm. The
low pyramidal apices of the interseminal scales give a mosaic-like
appearance to the surface of the ovulate receptacle (fig. 515). In
the lower part of the receptacle these sterile sporophylls are the
only appendages, but over the greater part of the receptacle they
are intermixed with a smaller number of similar appendages which
bear a single terminal orthotropous ovule (fig. 514, _s_). Each
ovule-bearing organ or megasporophyll (seed-stalk) is surrounded by
5—6 interseminal scales, and the narrow cylindrical micropylar tubes
are readily distinguished from the sterile sporophylls in surface-view
(figs. 516, 564). The seeds appear to be exalbuminous and the embryo
is dicotyledonous (figs. 516, 521, 523)[1116]. The seeds are very
small in comparison with those of living Cycads. The structure of
the megasporophylls, both sterile and fertile, is described in more
detail in the account of _Cycadeoidea Morierei_ and other forms. Fig.
516 represents a longitudinal section of one of the smallest seeds
of _Cycadeoidea_, between 3 and 4 mm. long; an embryo occupies the
greater part of the seed-cavity: the micropylar tube is formed of
three layers, a strong inner palisade-layer, a thin middle layer, and
an outer palisade-tissue, the interior of the tube being filled with
parenchyma; at the shoulder of the seed above the root-end of the
embryo the surface of the testa is characterised by 5–6 wings formed
by the radial extension of palisade-cells. After the shedding of the
spores and the abscission of the microsporophylls the flowering shoot
probably increased slightly in length, thus pushing the ripening seeds
beyond the ends of the surrounding leaf-bases. The ripe flowers were
eventually cut off by an absciss-layer immediately below the receptacle
(figs. 521, C, _a_; 522, _a_), large cup-like depressions being left
on the surface of the stem (fig. 534). The ovulate cone on which the
species _Cycadeoidea Morierei_ is founded probably represents the
condition of a naturally detached flower of a _Cycadeoidea_. It is
possible that the detached flowers freed from their encircling bracts
may have been edible, the small seeds being dispersed by animal agency.
[Illustration: Fig. 515. _Cycadeoidea_ sp. Surface-view of a young
ovulate strobilus showing the swollen ends of interseminal scales
grouped about the circular micropyles. (After Wieland; × 10.)]
[Illustration: Fig. 516. _Cycadeoidea Dartoni._ Longitudinal section
of seed with embryo. (After Wieland; × 19.)]
* * * * *
The splendid petrified stem, _Cycadeoidea etrusca_ Cap.[1117], one
of the treasures of the Bologna Museum, was found on a tomb 20 miles
west of that city where it was doubtless placed by the Etruscans
who obtained it from the Upper Jurassic scaly clays in the Apennine
Hills. It was in an imperfectly preserved flower of this fossil
that Graf Solms-Laubach discovered some microspores, but it was not
until Wieland’s examination of the more complete American stems that
information was obtained as to the spore-bearing organs. Another
Italian stem, _Cycadeoidea montiana_ Cap., was described in 1753 as
a ‘congeries of barnacles[1118].’ The specimen named by Goeppert
_Raumeria Reichenbachiana_[1119] was described in the middle of the
eighteenth century as a mass of _Hippurites_ or coral cups: this
was found in a swamp in Galicia and is now one of the most striking
objects in the Dresden Museum; a brief account of it is given on page
409. In 1859 Tyson discovered two large trunks in the Potomac beds of
Maryland for which Fontaine subsequently proposed the name _Tysonia
marylandica_[1120], but as Ward pointed out the species is clearly a
_Cycadeoidea_ (fig. 507). In 1894 Lester Ward[1121] recorded several
additional stems from Tyson’s locality. It is, however, from the Black
Hills of Dakota, an isolated spur of the Rocky Mountains, formed of
older rocks encircled by Lower Cretaceous strata[1122], that the
greatest number of Cycadean trunks have been obtained: the magnificent
collection now in the Yale Museum is largely due to the energy and
munificence of the late Prof. Marsh. From the Upper Jurassic beds in
Carbon Co., Wyoming[1123], several stems have been collected, and a
preliminary study of their external features led Ward to institute 20
species of a new genus _Cycadella_. Stems have also been discovered
in the Freezout Hills of Wyoming and additional specimens have been
found in the Potomac formation of Maryland. The discovery of over
1000 specimens of Cycadean stems in the Lower Cretaceous and Upper
Jurassic beds of a few localities in the United States bears striking
testimony to the abundance of these extinct Gymnosperms during the
latter part of the Mesozoic era. It is perhaps true that, as Lester
Ward wrote, ‘Cycads are to the vegetable kingdom what Dinosaurs are
to the animal, each representing the culmination in Mesozoic times of
the ruling Dynasties in the life of their age[1124].’ Although the
number of stems obtained from European countries is relatively small,
the abundance of specimens in the Upper Jurassic strata of the Isle
of Portland and Northern Italy and their occurrence in Belgium[1125],
France, Germany, Austria, Poland, India and elsewhere, together with
an abundance of Cycadean fronds in practically all Jurassic and Lower
Cretaceous plant-bearing beds, demonstrate the dominant position of
the Bennettitales. The occurrence of the genus _Williamsonia_ in
many European localities as well as in India, Afghanistan, and other
countries, and the not infrequent occurrence of stems assigned to
_Bucklandia_, _Yatesia_, _Cylindropodium_, and other genera furnish
evidence of the rich development of the Bennettitales in later Jurassic
and Lower Cretaceous floras. Wieland’s recent discovery[1126] of
numerous Cycadean fronds, _Williamsonia_ flowers, and stems in Liassic
rocks in Mexico shows that the group had already assumed an important
position in the early part of the Jurassic period.
The memoir by Carruthers[1127] on British Cycadean stems contains the
first account of the morphological features of Bennettitalean flowers
based on petrified material. In 1891 Solms-Laubach contributed an
important paper on the Bennettitean flower and several years later
Lignier[1128] contributed additional data derived from a careful
study of a well preserved strobilus[1129] from the Gault of Normandy.
Wieland’s researches[1130] added very greatly to our knowledge,
particularly with regard to the morphology of the microsporophylls.
Among the earlier descriptions of the reproductive organs of the
Bennettitales is Buckland’s account[1131] of a specimen from the
Inferior Oolite of Charmouth, Dorset (fig. 560), which he referred to
the genus _Podocarya_ (= _Williamsonia Bucklandi_[1132]): a thorough
examination of the type-specimen, which unfortunately cannot be found,
would probably furnish many important facts.
{ _Cycadeoidea_ (_Bennettites_) _Gibsoniana_ (_Carruthers_).
{ _Cycadeoidea_ (_Bennettites_) _Saxbyana_ (_Brown_).
These two species serve to illustrate the type of stem for which
Carruthers instituted the tribe Bennettiteae and the genus
_Bennettites_. _Bennettites Gibsonianus_ is the most important of the
five species described by Carruthers[1133], as it was from its fertile
shoots that information was first obtained as to the nature of the
ovulate strobili of the Bennettitales. _B. Saxbyanus_[1134], originally
described as _Cycadites Saxbyanus_ from a specimen found by Mr Saxby
at Bonchurch in the Isle of Wight and represented by Wealden examples
from Brook Point, is chiefly interesting for the clear preservation
of the anatomical features of the stem. Three other species were also
described by Carruthers; they are: _Bennettites maximus_ Carr., a large
stem similar to _B. Saxbyanus_, in the Museum of the Geological Survey;
_B. portlandicus_ from the Lower Purbeck of the Isle of Portland, in
the collection of the Geological Society; and _B. Peachianus_, a piece
of a compressed stem, in the British Museum, from the Upper Jurassic of
Helmsdale in N.E. Scotland.
[Illustration: Fig. 517. _Cycadeoidea Gibsoniana._ A, transverse
section of petiole showing vascular bundles and ramenta; B, portion of
A enlarged showing periderm and ramenta. C, tangential section of stem
with leaf-bases, ramenta (black) and two flowers, 1, 2. (A, slightly
enlarged, Manchester Collection, R, 1069; C, after Carruthers.)]
_Cycadeoidea (Bennettites) Gibsoniana._
This species was founded on a petrified portion of a large stem of
Lower Greensand age discovered by Mr Gibson in Luccomb Chine in the
Isle of Wight: the type-specimen is represented by pieces of the
original block in the British Museum and in one of the Museums at the
Royal Gardens, Kew. The following description is based partly on the
published accounts and in part on an examination of sections in the
British Museum, the Manchester University Museum, and in Dr Scott’s
collection.
The elliptical form of the stem and vascular cylinder as seen in
transverse section, regarded by Carruthers[1135] as a feature
characteristic of the genus, has no morphological significance and is
in part at least due to compression. In the large pith, the armour of
persistent petiole-bases separated by dense ramental scales (fig. 517,
A, B), and in habit, _Cycadeoidea Gibsoniana_ agrees generally with
the stems of many recent Cycads, but the resemblance of the vegetative
organs is in marked contrast to the differences exhibited by the
reproductive shoots. The pith consists of parenchyma with scattered
secretory ducts but no medullary vascular bundles. In the pith of
_Cycadeoidea Peachiana_ there are patches of tissue superficially
resembling vascular strands, but these are probably bands of internal
phloem like those described by Solms-Laubach[1136] in some Italian
stems. In none of the English stems are there any clear indications of
the occurrence of more than one cambium in the stele. The secondary
xylem is entirely centrifugal with some smaller crushed elements,
presumably protoxylem, at the inner edge where the medullary rays are
especially broad. The xylem is of the manoxylic type (fig. 518, A)
as in recent Cycads; though the medullary rays, 1–2 cells broad, are
rather smaller than in recent species. The tracheids are scalariform
as in _Stangeria_ (fig. 397). As in recent Cycads there is a broad
cylinder of secondary phloem (fig. 518, B)[1137] composed of alternate
layers of thick-walled and thinner elements—sieve-tubes and parenchyma:
traces of lateral sieve-plates occur on some of the elongated elements.
Each leaf-trace arises as a single strand from the lower edge of a mesh
formed by the large inner end of a medullary ray: on emerging into
the inner cortex the trace has the form of a U-shaped strand (fig.
519, A, _lt_) which passes direct to the petiole, following a steeply
ascending course in _Cycadeoidea Saxbyana_ and almost horizontal in _C.
Gibsoniana_. Before entering the base of a leaf the trace breaks up
into several collateral strands and these form a simple pattern as
seen in a tangential section of the leaf-bases (fig. 517, A, C), the
central bundles on the upper side forming a U-shaped involution. There
is no indication of any girdling of the foliar bundles. The arrangement
of the petiolar bundles is simpler and more Fern-like than in the
majority of existing Cycads. Each vascular bundle consists in the
petiole-base mainly of centrifugal secondary xylem and medullary-ray
tissue (fig. 519, B); a group of centripetal tracheids is usually
recognisable internal to the protoxylem: the structure is of the
mesarch type with a variable amount of centripetal xylem, and agrees
generally with that in recent Cycads.
[Illustration: Fig. 518. _Cycadeoidea Gibsoniana._ A, secondary xylem
of stem; B, secondary phloem and part of the cortex with secretory
ducts, _s_. (A, B, British Museum, 13206.)]
[Illustration: Fig. 519. _Cycadeoidea Gibsoniana._ A, transverse
section of the vascular cylinder of stem, with leaf-trace, _lt_; _c_,
cambium, _px_, protoxylem. B, vascular bundle of petiole. (British
Museum.)]
The comparatively narrow cortex is composed of parenchyma with
scattered secretory sacs (fig. 518, B, _s_), and occasionally an
elliptical vascular strand (fig. 511) is present which is probably
cauline as are the similar strands in _Cycas_. The persistent
petiole-bases are covered with ramental scales which form a dense
interfoliar packing: these frequently consist of a single layer of
fairly thick-walled cells or, as seen in transverse section, of
spindle-like scales one-cell thick at the edges and 2–3 cells broad in
the middle (fig. 517, B).
[Illustration: Fig. 520. _Cycadeoidea Gibsoniana._ Ground-tissue of
bract. (British Museum. 41388.)]
The presence of fertile shoots, presumably axillary, is one of the most
striking features of Bennettitean stems. The branching is monopodial
and not sympodial as in most recent Cycads. The nearest approach to
the method of branching in _Cycadeoidea_ is afforded by some stems
of _Macrozamia_ recently described by Chamberlain[1138]. It is not
improbable that some of the flowering branches of _Cycadeoidea_
were branched. Solms-Laubach[1139] states that he observed certain
characters in the secondary axes of _Cycadeoidea Gibsoniana_ which led
him to suspect that there may have been fascicled systems of fertile
shoots emerging in a body or in close proximity to one another between
the leaf-bases of the stem. An example of a branched flowering shoot
is described in _Williamsonia scotica_[1140]. A fertile shoot agrees
in structure with the main axis and Scott[1141] states that the phloem
is particularly well developed, a feature by no means unusual in
fertile branches. These lateral shoots (fig. 514) bear numerous linear
bracts each with three collateral vascular bundles, and ground-tissue
composed of thick-walled cells characterised by scalariform pitting
(fig. 520): secretory sacs are abundant. The hypodermal stereome is
especially developed on the inner face of the bracts. The apex of a
lateral shoot has the form of a rounded cushion (figs. 514; 521, A, C)
similar to the receptacle of many Composites, and on this are borne the
sporophylls. It is characteristic of _Cycadeoidea_ that the flowers
project very slightly beyond the surface of the stem and the peduncles
are not exposed except in tangential sections through the leaf-base
armour (fig. 517, C, 1, 2). On the fall of the flower or ripe ‘fruit,’
which is effected by an absciss-layer (figs. 521, C, _a_; 522, _a_),
a cup-like scar is left on the stem (_cf._ fig. 534). This method of
flower-production suggests comparison, _mutatis mutandis_, with the
phenomenon of cauliflory in certain recent Flowering plants; it is one
of the distinguishing features between _Cycadeoidea_ and stems bearing
longer fertile shoots with flowers of the _Williamsonia_ type.
[Illustration: Fig. 521. _Cycadeoidea (Bennettites) Gibsoniana._
A, C, longitudinal sections; _a_, absciss-layer; _b_, bracts; _pr_,
‘pericarp’; _s_, scales, sterile and fertile. B, transverse section
of female flower; _i_, interseminal scales; _m_, megasporophylls. D,
transverse section of seed showing the testa, _t_, separated by a
space, _sp_, from the embryo. E, embryo; _r_, radicle. (A, B, D, E,
after Solms-Laubach; C, section in the British Museum.)]
Fig. 517, C, shows a tangentially cut surface of a portion of the stem
of _Cycadeoidea Gibsoniana_ with two axillary fertile shoots; one,
1, is cut across below the receptacle and shows the axis surrounded
by bracts while the other, 2, is seen at a higher level, above the
receptacle, where the section has exposed the numerous sporophylls.
The rounded surface of the receptacle is covered with a dense cluster
of long slender appendages, seed-stalks and interseminal scales, the
latter being much more numerous than the former (fig. 521, A, B). These
organs are believed to be homologous foliar structures, the seed-stalks
being megasporophylls and the interseminal scales abortive or potential
sporophylls (see also figs. 562, 563). Fig. 514 shows the form of a
single flower from an American stem closely allied to _Cycadeoidea
Gibsoniana_.
[Illustration: Fig. 522. _Cycadeoidea Gibsoniana._ Longitudinal
section of flower showing half the receptacle with part of the
absciss-layer, _a_. (British Museum.)]
[Illustration: Fig. 523. _Cycadeoidea Gibsoniana._ Seed with embryo.
(British Museum, 41388.)]
The megasporophylls are more or less polygonal in transverse section:
there is a central concentric vascular strand surrounded by a thick
cortex (fig. 527): at its upper end the sporophyll bears a single
orthotropous seed containing a dicotyledonous embryo (figs. 521, D, E;
523). The vascular strand pierces the base of the testa and expands
to form a shallow cup of tracheal tissue in the chalaza; there are no
bundles in the single integument. The testa (fig. 521, D, _t_) consists
of three regions, a median layer of rather large rectangular or
palisade-cells with an inner and outer tissue composed of much smaller
cells. The testa is prolonged distally as a slender cylindrical column
or micropylar tube at the base of which it becomes broader owing to
the increase in breadth of the middle or palisade layer. A nucellar
beak projects as a cone into the base of the micropylar tube. No
pollen-chamber has been found. It is noteworthy that the micropyle is
closed in the ripe seeds. Internal to the testa there is a crushed
membrane separated from the embryo by a space (fig. 521, D, _sp_): this
is the remains of the nucellus and, as Solms-Laubach points out, there
is no proof that any endosperm was present in the ripe seeds[1142].
The embryo consists of a short axis, the conical radicle and the very
short apex of the epicotyl, also two equal cotyledons each with a
few vascular bundles (fig. 521, D). The long interseminal scales, as
seen in transverse section in the lower part of a flower between the
sporophylls, appear as compressed polygonal organs (fig. 521, B, _i_)
with an axial vascular strand surrounded by parenchyma and limited by
a strong epidermis; they pass up between the seed-stalks, _m_, and in
the distal end become considerably enlarged (figs. 514, 515), gradually
expanding to form a truncate or slightly pyramidal apex (figs. 553,
563). The swollen peltate apices of adjacent scales form a continuous
covering to the flower interrupted, except in the lower sterile part
of the flower, by symmetrically disposed cylindrical micropylar tubes
(fig. 515). The peripheral interseminal scales form a homogeneous
parenchymatous tissue which springs from below the edge of the
receptacle (fig. 521, A, B, _pr_) and the individuality of the scales
composing this ‘pericarp’ is indicated by occasional invaginations of
the epidermal layer which marks the boundary of the polygonal areas.
The structure of the megasporophylls and scales is more fully described
in the case of _Cycadeoidea (Bennettites) Morierei_[1143].
The flowers of _Cycadeoidea Gibsoniana_ appear to be unisexual and
ovulate: in view of the discovery by Wieland of numerous bisexual
fertile shoots on American species of _Cycadeoidea_ it would be
reasonable to regard the apparently unisexual flowers of the English
species as originally bisexual but preserved at a stage subsequent to
the loss, by abscission, of the disc of microsporophylls. Fig. 514
shows a flower of an American _Cycadeoidea_ practically identical with
those of _C. Gibsoniana_, but the remains of the staminate disc are
clearly seen at _d_ below the swollen apex of the flowering axis. In
the photograph of half of the same region in _C. Gibsoniana_ reproduced
in fig. 522 there is no indication of any similar trace of a whorl of
microsporophylls. Admitting the fact that a shrivelled remnant of the
persistent base of a whorl of microsporophylls might easily escape
observation, it is difficult to believe that any fertile leaves ever
existed in the flower represented in figs. 521, 522. It is equally
difficult to regard the specimen represented in fig. 561 as other than
a true unisexual (ovulate) flower.
_Cycadeoidea (Bennettites) Morierei_ (Saporta and Marion).
The name _Bennettites_ was adopted by Lignier for this species which
was founded on a detached flower from the Gault[1144] of Vaches-Noires,
Normandy. It was first described by Morière[1145], then by Saporta and
Marion[1146], who named it _Williamsonia Morierei_, and it has since
been thoroughly investigated by Lignier[1147]. There is no evidence as
to the nature of the parent-stem though Morière suggested a possible
connexion with _Zamia Brongniarti_ Mor. (figured by Saporta[1148]
as _Fittonia Brongniarti_) from the same locality. There can be no
reasonable doubt that _Bennettites Morierei_ was borne on a lateral
branch of a stem of the _Cycadeoidea_ type: it is constructed on
essentially the same plan as the flowers of _Cycadeoidea (Bennettites)
Gibsoniana_, and in both cases there is no indication of the presence
of microsporophylls. The type-specimen is 5·5 cm. long and 3·5
cm. broad, ovoid, and characterised by a depressed cushion-like
receptacle as in _Cycadeoidea Gibsoniana_. The enveloping bracts
with their ramental scales agree generally in structure with those
of the English species and, except as regards the ramenta, with
_Williamsonia scotica_: numerous stomata occur on the lower surface;
the ground-tissue consists of thick-walled parenchyma and the narrow
pit-canals simulate the scalariform bands in _Cycadeoidea Gibsoniana_
(_cf._ fig. 520). The pitted sclerous cells in the bracts of _W.
scotica_ are of the same type. There is an anastomosing system of
secretory canals, also several vascular bundles like those in _C.
Gibsoniana_ but more numerous; the latter are composed of a group of
phloem-elements abutting externally on fibres, a well-defined cambium,
and radially disposed scalariform tracheids: internal to the protoxylem
is a group of elements considered by Lignier to be centripetal xylem.
From the branching and slightly divergent course of the bundles in the
upper part of the bracts Lignier concluded that these organs represent
the basal portions of leaves originally provided with a terminal limb.
It may be that the small lateral appendages to some of the bracts of
_Williamsonia scotica_ (fig. 561, _l_) afford support to this view.
_Megasporophylls_ (seed-stalks and seeds). These organs, 3–4·5 cm. long
and approximately 1·5 mm. in diameter, are in most cases imperfectly
preserved. In transverse section and at a level of 1 cm. above the
receptacle a stalk bearing an atrophied seed shows the following
features: an epidermis with very thick internal walls encloses a
parenchymatous ground-tissue with an axial conducting strand. At a
higher level the epidermal cells have walls of uniform thickness, and
a hypodermal layer of cells with coloured contents is differentiated
from the ground-tissue (fig. 524, D, _ac_). As the seed-base is
approached the epidermal cells tend to separate from one another and
divide longitudinally, the compact epidermal layer being replaced
by an envelope of tubular, dissociated, cells (fig. 524, D, _Et_).
Similar tubular elements occur in the seed-stalks of _Cycadeoidea
Gibsoniana_. A fully developed seed-stalk bearing a complete seed cut
across in the middle region shows the following features: a concentric
vascular strand surrounded by thin-walled parenchyma and the coloured
hypodermal layer (fig. 524, D, _ac_), the whole being enclosed in the
tubular envelope of epidermal origin (_Et_) which is more strongly
developed than in the stalks of imperfect seeds: there may be as many
as 10–12 tubular cells on one radius. When traced downwards towards
the receptacle the tubular envelope decreases in breadth, though
the cells become more numerous and smaller, until in the immediate
neighbourhood of the receptacle the tubular tissue is transformed into
a compact parenchyma of large cells each of which corresponds to a
group of tubes formed by the septation of the cells. Traced upwards
this thin-walled parenchyma gradually passes into thick-walled tubes,
and near the seed-base the tubular envelope is reduced to two layers,
an inner consisting of relatively small cells with sinuous radial walls
(the folded layer of Lignier) and an outer tubular layer. Lignier
describes an interesting abnormality, a bifid seed-stalk enclosed in a
common epidermis which he compares with the occasional branching of the
seed-stalks of _Ginkgo biloba_.
[Illustration: Fig. 524. _Cycadeoidea (Bennettites) Morierei._
A. Transverse section of the micropylar tube containing the apex of
the nucellus; _Ei_, inner epidermis; _Tf_, ground-tissue; _e_,
outer epidermis with the thickening of the walls shown in a few of
the cells.
B. Transverse section of the upper part of the micropylar tube;
lettering as in fig. A.
C. Transverse section at the level of the wings formed by the fibrous
layer and corresponding to the angles of the seed, approximately at
the level _cp_ in fig. 525; _cn_, nucellar cavity; _Ei_, inner
epidermis of seed-coat; _cf_, fibrous layer of wings, _f_, which
extend across the fleshy layer, _tch_, to the radial layer _ar_
(_cf._ fig. 525); _at_, tubular layer; _Ee_, epidermis of adjacent
scale detached from the other tissues, _ase_, along the line of
fracture _d_; _EE_, epidermis of two adjacent scales.
D. Transverse section of peduncle; _tr_, tracheids; _ac_, coloured
subepidermal layer; _Et_, tubular epidermis, double in places;
_EE_, epidermis formed from neighbouring scales. (From Prof.
Lignier’s drawings; A, B, D, × 118; C, × 90.)]
_Seeds._ The seeds (figs. 525, 526), 6–7 × 2·5–3 mm., are tetragonal or
pentagonal in the upper half (fig. 527, 1, 2), the angles being formed
by thick but not very prominent wings of tissue (fig. 524, C, _cf_);
they are orthotropous and have a single integument (figs. 525, 526).
The tubular layer forming the outer portion of a seed-stalk near the
seed-base is prolonged over the surface of the testa as a discontinuous
covering in the form of isolated or small groups of tubes, giving a
striated appearance to the seeds. This layer though apparently a part
of the seed is derived from the neighbouring interseminal scales of
which it is the epidermal layer; it consists of elongated cells and
scattered stomata[1149]. The folded layer persists only in the lower
part of the seed, being replaced by a layer of radially extended cells
(radial layer; _ar_, figs. 524, C; 525, _ar_; 527, _c_) in the upper
region of the seed. In the micropylar region both the tubular and
folded layers undergo further change; the external, tubular, layer
forms a kind of epidermis (_at_, figs. 524, 525), the subepidermal
layer, consisting of the radially elongated cells (figs. 524, 525,
_ar_; 527, _c_). The superficial layer assumes a different aspect in
the micropylar region, its cells being thicker walled, as are also
those of the subepidermal layer (fig. 524, A and B). The micropylar
canal (figs. 524, 525, _cm_) is cylindrical in the lower part but at
the apex is reduced to a long and narrow slit bounded by an internal
epidermis of radially stretched cells which in the lower portion of
the tube are thinner walled and isodiametric. The rest of the testa is
differentiated into two regions; an outer fleshy region immediately
internal to the folded (or radial) layer and an inner fibrous region
next the nucellus, which is one-layer broad between the wings but
opposite the wings it extends radially outwards across the fleshy
tissue to the radial layer (figs. 524, C; 525; 527): in the winged
portion of the seed this tissue forms the inner fibrous portion of the
wings but in the lower part of the seed below the wings it forms a
single layer of uniform breadth finally spreading out as a basal cup
in the chalazal region where it is pierced by the vascular strand. The
fleshy portion of the testa forms one layer in the proximal part of
the seed and becomes several layers wide between the fibrous wings
in the upper part. This fleshy tissue appears to be derived from the
coloured, subepidermal, layer of the seed-stalk, while the internal
parenchyma is regarded by Lignier as the equivalent of the fibrous
layer of the testa. In the micropylar tube the fibrous layers are
replaced by 2–3 layers of sclerous cells (fig. 524, A, B). The testa
has no vascular supply: the concentric strand of the seed-stalk passes
through the fibrous tissue at the base of the seed and reaches the
base of the nucellus (fig. 525). The nucellar apex extends into the
lower part of the micropyle (fig. 525, _n_), and in some cases Lignier
noticed an axial canal formed by the breaking-down of the cells which
abutted below on a cavity above the embryo, probably the remains of
a pollen-chamber (figs. 525, 527). No microspores have been found.
Two dark spots shown at _co_, fig. 525, may represent archegonia but
this is doubtful, especially as the seed contains a well-developed
embryo. The nucellus is free from the testa only in the apical region
and a dicotyledonous embryo occupies the interior without any trace of
endosperm. Lignier points out that in some seeds containing embryos the
nucellar beak is not completely perforated: in this fact and in the
absence of microspores in the micropylar canals he is inclined to see
evidence of parthenogenesis[1150].
[Illustration: Fig. 525. _Cycadeoidea (Bennettites) Morierei._
Section of a seed and adjacent interseminal scales. _tm_, micropylar
tube; _n_, nucellar beak in the micropylar canal, _cm_; _cp_,
pollen-chamber; _co_, archegonia (?); _em_, position of the embryo;
_ch_, chalaza; _dn_, remains of the nucellus; _af_, fibrous layer
passing below into the shell, _cq_, and the peduncle, _Tf_; _tch_,
fleshy layer; _ar_, radial and tubular layers represented in the
peduncle by the tubular envelope _at_; _Ec_, swollen ends of the
interseminal scales. (From a drawing kindly supplied by Prof. Lignier;
× 10.)]
[Illustration: Fig. 526. _Cycadeoidea (Bennettites) Morierei._
Longitudinal section of a seed and interseminal scales. (From a
photograph supplied by Prof. Lignier.)]
In several respects the seeds of _Cycadeoidea_ agree with those of
_Gnetum_: reference should be made to the account of the seed of
_Gnetum africanum_ in Chapter +lii.+ and to the papers referred to in
the footnote[1151].
_Interseminal scales._ The young seed-stalks agree very closely
with the interseminal scales: each seed-stalk is surrounded by 5–6
scales (fig. 527) as in other Bennettitean flowers (fig. 564).
For the greater part of their length the interseminal scales are
compressed, but above the seeds, where they are free from pressure
(fig. 526), they become much thicker and form a covering (‘pericarp’)
as in _Cycadeoidea Gibsoniana_. In its upper region an interseminal
scale consists of an epidermis with strongly thickened inner walls,
hypodermal thick-walled cells and parenchymatous ground-tissue with
a single axial bundle. In the lower part the scale is more flattened
and the thick-walled hypoderm is replaced by thin-walled parenchyma.
Some of the scales at the periphery of the receptacle where there are
no seed-stalks are broader and may have six vascular bundles; this,
Lignier suggested, might be regarded as evidence of the reduction of
the interseminal scales from leaves possessing a terminal limb; but a
further examination of scales at the periphery of the flower led him
to the conclusion that the distal swelling of the scales is solely due
to the hypertrophy of conjunctive tissue and is not the result of the
modification of a reduced limb[1152]. The morphological value of the
interseminal scales and seed-stalks has not been definitely settled,
though the probability is that they are homologous organs and foliar.
Solms-Laubach[1153] suggested that both may be axial, the seed-stalks
representing axes ending in a flower reduced to a single ovule; or,
he adds, the seed-stalks may just as well be carpels, though in that
case we should have the unusual phenomenon of terminal seeds. The
interseminal scales may be aborted seed-stalks crushed between the
latter; or if the seed-stalks are axes, the scales may be foliar. He is
inclined to see in the scales the bracts and prophylls of seed-stalks
to which must be added such bracteoles, preceding the seed or flower,
as may happen to spring from the seed-stalks. Pearson[1154], on the
assumption that the seed-stalks are axial structures, institutes a
comparison between _Welwitschia_ and _Bennettites_ and regards each
flower of _Welwitschia_ as a much reduced Bennettitean strobilus.
Lignier believes the interseminal scales to be leaves borne on the
swollen apex (receptacle) of an axis of the second order, while the
seed-stalks are fertile leaves of a unifoliar bud of the third order
possibly axillary though not necessarily so to the interseminal scales.
My own view, influenced by the examination of the immature flower of
_Williamsonia scotica_, is that the seed-stalks (megasporophylls) and
scales are homologous, the former being sporophylls and the latter
sterile foliage leaves, the whole flower, as Wettstein[1155] says,
consisting of a conical axis bearing numerous fertile and sterile
carpels enclosed by a perianth of bracts. Worsdell[1156], who shares
Čelakovsky’s opinion that sporophylls were originally radially
symmetrical organs bearing a terminal sporangium, regards the flowers
of _Cycadeoidea Gibsoniana_ and other species as more primitive
than those of recent Cycads: he does not see any justification for
the view that the Bennettitalean flowers are in advance of those of
existing Cycadean plants as regards a supposed tendency towards the
Angiospermous type. He maintains that _Bennettites_ ‘shows absolutely
no indication of such an advanced structure in its essential organs,
the sporophylls, which remain primitively radial in structure, bearing
the ovules in a terminal position.’
[Illustration: Fig. 527. _Cycadeoidea Morierei._ Transverse section
of interseminal scales and seeds near the apex of the latter; seeds 1
and 2 show the pollen-chamber, _a_; the fibrous layer, _b_, forming
wings and extending across the fleshy tissue; _c_, the radial layer;
seeds 3 and 4 are aborted. (After Lignier.)
The letters _a_, _b_, _c_, in this figure correspond to _cp_, _cf_, and
_ar_ in figs. 525, 526.]
_Cycadeoidea dacotensis_ (McBride).
McBride[1157] first described this Lower Cretaceous species from the
Black Hills of South Dakota as _Bennettites dacotensis_, the generic
name _Cycadeoidea_ being adopted by Ward[1158] who distinguished
some of McBride’s specimens as _Cycadeoidea McBridei_. The stem is
elliptical in section, 32 cm. long and 45 cm. in girth: owing to the
partial decay of the petiole-bases the ramental reticulum forms a
prominent feature. Numerous flowers, all of which are approximately
at the same stage of development, project like conical buttons above
the general level of the stem-surface[1159]. The bisporangiate flowers
consist of a conical receptacle bearing interseminal scales and
megasporophylls, the whole being surrounded by spirally disposed
bracts (fig. 529). A whorl of 18 or 19 nearly mature microsporophylls
is attached to the base of the receptacle (figs. 528, 530); each
microsporophyll has a strong rachis extending beyond the apex of the
flower-axis and bent inwards and downwards with the distal end tucked
between the ascending rachis and the receptacle. The slender pinnules,
in two alternate series, are bent downwards and bear synangia in rows.
A transverse section just below the ovulate portion of the cone shows
a continuous ring of tissue encircling the receptacle with vascular
bundles parallel to the surface (fig. 530, _A_, _m_); at a higher level
the bundles fall into groups preparatory to the breaking up of the
disc into separate microsporophylls. Immediately above the apex of the
central cone the coherent basal portion of the verticil of sporophylls
is replaced by the separate rachises which in section have the form
of isosceles triangles (fig. 530, _B_). Each microsporophyll is
approximately 10 cm. long; the longest pinnule being 1·5 cm. in length
and bearing two lateral series of synangia, 10 in each row. At maturity
the microsporophylls probably spread out and the whole whorl was thrown
off leaving an annular rim (fig. 514, _d_) such as is often seen at the
base of older ovulate strobili. The immaturity of the ovules in this
(fig. 528) and other specimens led to the suggestion that the strobili
of _Cycadeoidea_ were protandrous. The synangia (fig. 531) are several
times broader than long and similar in size to those of the Fern
_Marattia_. In each synangium are two rows of elongated loculi (fig.
532) containing oval microspores usually with a smooth exine and rather
larger than those of recent Cycads. The synangium-wall is composed of a
palisade-layer of thick-walled cells and a layer of smaller and thinner
cells: the palisade-layer is narrowest at the apex where dehiscence
occurs and broadest at the base where the hypodermal tissue is more
abundant and forms a short thick pedicel. The two rows of loculi are
bounded by flattened cells and there are 10–20 loculi in each of the
two rows: dehiscence of the individual loculi occurs in the middle of
the inner wall.
[Illustration: Fig. 528. _Cycadeoidea dacotensis._ Longitudinal
section through a bisporangiate strobilus; _s_, folded microsporophylls
with synangia; _o_, receptacle bearing short megasporophylls and
interseminal scales; _a_, eroded surface of bracts; _r_, ramenta
between the bracts and leaf-bases; _l_, leaf-base; _c_, cortex of stem;
_t_, vascular cylinder of peduncle. (After Wieland; nat. size.)]
[Illustration: Fig. 529. _Cycadeoidea dacotensis._ Transverse
sections of a young ovulate strobilus. A, near the summit of the
strobilus 2 cm. below the surface of the armour of leaf-bases, showing
numerous bracts surrounding the receptacle and embedded in a mass of
ramenta, also sections of some leaf-bases with vascular bundles. B,
in this section, 2·5 cm. below A, the peduncle of the strobilus is
seen with a cylinder of vascular bundles; _b_, a bract belonging to an
adjacent strobilus. (After Wieland; nat. size.)]
[Illustration: Fig. 530. _Cycadeoidea dacotensis._ Transverse
sections through a bisporangiate strobilus. A, showing the receptacle
with its interseminal scales and ovules, the continuous disc of
microsporophylls, _m_, with vascular bundles, and the separate (_m′_)
infolded portions of the microsporophylls with some synangia; bracts
and ramenta. B, this section, cut above the apex of the receptacle,
shows the microsporophylls and synangia. (After Wieland.)]
[Illustration: Fig. 531. _Cycadeoidea dacotensis._ Synangia exposed
by weathering and showing the radially disposed loculi. (After Wieland;
× 6.)]
_Cycadeoidea Marshiana_ Ward.
[Illustration: Fig. 532. _Cycadeoidea dacotensis._ Synangium in
longitudinal section showing the thick pedicel, the line of dehiscence,
and two loculi with a few microspores. (After Wieland; × 40.)]
This Lower Cretaceous Black Hills species[1160] affords an admirable
example of a method of branching exhibited by some stems: as shown in
Wieland’s photographs[1161] there may be five or six large and massive
trunks all in the same stage of fructification, differing but little
in size and forming a cluster resembling independent plants growing in
close proximity to one another. There is apparently no central or major
axis and the habit is therefore very different from that of a branching
_Bucklandia_. _Cycadeoidea Marshiana_ bore large ovulate pyriform
strobili projecting slightly beyond the leaf-bases; they are 5 cm. long
with a maximum diameter of 3·5 cm. and have an elongated receptacle
bearing short scales and sporophylls. The apical bud of one of the
trunks shows particularly well in transverse section the dense ramental
packing between the bud-scales[1162]. Similar clusters of short and
thick trunks occur in _Cycadeoidea superba_ and other American species.
In the small bisporangiate flowers of this species[1163] the
microsporophylls, 11 or 12 in the verticil, are characterised by
the presence of a ventral furrow which, as Wieland suggests, may be
comparable on a much simpler scale with the winged sporophylls of
_Cycadeoidea colossalis_ (fig. 533). The disc splits up at a distance
of 1 cm. above the apex of the receptacle into the microsporophylls,
each of which is 5·5 cm. long and bears two rows of pinnules which
in the middle region have a length of 1 cm.; a microsporophyll is
elongate, elliptical, and acuminate. In this species as in some others
there is a brush of sterile scales at the apex of the receptacle.
_Cycadeoidea colossalis_ Ward.
Wieland[1164] has recently described some interesting features in the
microsporophylls of a bisporangiate flower assigned to this Lower
Cretaceous species from the Black Hills illustrating a departure from
the usual type. The hairy bracts extend considerably above the apex
of the flower-proper; in fig. 533, A, a transverse section above
the receptacle, they are shown grouped about a circle of V-shaped
structures, converging towards a central point, which are the sterile
prolongations of the ten rachises of the free portions of the staminate
disc. Each rachis is divided by a deep ventral furrow into a pair
of wings (fig. 533, B, C), and it is these pairs of wings that form
the V-shaped structures in fig. 533, A. The wings form a dome-like
group above the flower-apex (fig. 533, D, E). The synangia are borne
in two rows on the concrescent disc and on the free sporophylls,
which in this type are much simpler than in other species and agree
in the absence of pinnules with some forms of _Williamsonia_ (_cf._
fig. 556). The receptacle is pyriform and bears very short scales and
seed-stalks; from its apex several interseminal scales are prolonged
as a terminal brush, a feature of interest in connexion with flowers
of _Williamsonia_. Wieland compares the wings of the microsporophylls
to the two horns on the distal surface of the corresponding organs of
_Ceratozamia_ and draws a comparison between them and the canopy of
some Palaeozoic seeds, but it is doubtful whether homologies can be
established between these elaborate sporophylls and the integuments of
Pteridosperm seeds[1165].
_Cycadeoidea Reichenbachiana_ (Goeppert).
Goeppert referred this species to his genus _Raumeria_[1166], a generic
name retained by Carruthers though, as Solms-Laubach[1167] points
out, the abundance of lateral fertile shoots among the leaf-bases
shows it to be essentially similar to _Cycadeoidea Gibsoniana_.
The type-specimen in the Dresden Museum is a splendid example of
a fossil cycadean stem; it is probably of Lower Cretaceous age,
but was found in Galicia as an isolated specimen. It consists of a
portion of a cylindrical trunk similar in habit to _C. gigantea_,
·5 met. high and about the same in diameter. The pith, according to
Schuster[1168], is 13 cm. in diameter and the xylem 8 cm. broad. There
are many flowering shoots some of which are represented by cup-like
depressions, the base of the cup consisting of the cylindrical axis
and the sides bearing the impress of the encircling bracts (fig.
534). Goeppert compared these lateral shoots with the buds frequently
produced on the stems of _Cycas_. It is interesting to find that some
of the cups correspond very closely in size with _Williamsonia_
flowers, another indication of the very close agreement between the
_Williamsonia_ and _Bennettites_ types of strobili. Some flowers
still in place show 16 bipinnate microsporophylls that were petrified
before the synangium-bearing fronds unfolded[1169]. The ramental
scales and other tissues figured by Schuster are of the usual type. A
second specimen found as a boulder in Silesia and named by Goeppert
_Raumeria Schulziana_ may, as he suggests, be a younger example of _C.
Reichenbachiana_. Another Galician stem, probably also Lower Cretaceous
in age, is described by Raciborski[1170] as _Cycadeoidea Niedźwiedzkii_.
[Illustration: Fig. 533. _Cycadeoidea colossalis._ Diagrammatic
restorations of the bisporangiate flower. A, transverse section above
the receptacle showing the bracts (black), a petiole with vascular
bundles, ramenta, and (1–10) the wings of the microsporophylls. B, C,
longitudinal section of flower showing the receptacle with the small
megasporophylls, the staminate disc with winged microsporophylls
and synangia, and the terminal brush of interseminal scales
(indicated by the arrow in B). The megasporophylls and synangia are
represented larger than the actual size. D, this shows on one side
the dome-like arrangement of the microsporophylls and, on the right,
a microsporophyll in side-view. E, longitudinal section as far as the
plane _T_ surmounted by the apex of the collection of microsporophylls,
_c_; _s_, microsporophyll with synangia; _A_, recurved apex of
microsporophyll; _B_, bracts; _D_, insertion of disc; _L_, outer bracts
next the petiole bases. (After Wieland; _ca._ nat. size.)]
[Illustration: Fig. 534. _Cycadeoidea Reichenbachiana._ Cup-like
cavity on the stem showing the axis and surrounding bracts of a lateral
fertile shoot. (After Schuster, from a block kindly supplied by Prof.
Rothpletz.)]
_Cycadeoidea gigantea_ Seward.
This species is founded on a large stem from the Upper Purbeck series
of the Isle of Portland[1171] where it was discovered in a shaly clay
17 ft above the great Dirt bed which yielded the trunks described
by Buckland and other authors (fig. 535). The stem (fig. 554) is 1
met. 18 cm. high and has a maximum diameter of 1 met. 7 cm. It is the
tallest fossil Cycadean stem so far found in a single piece though
_Cycadeoidea Jenneyana_ probably reached a greater height. The stem
is elliptical in section (fig. 537), a form due in part at least
to compression. The only tissues preserved are in the superficial
region of the persistent leaf-bases. As the result of decay before
mineralisation many of the petiole-bases are represented by cavities or
meshes in a prominent reticulum of silicified ramental scales. Towards
the apex the leaf-bases are smaller and a conical bud surrounded by
linear scale-leaves occupies the summit: an irregular cap of ramental
scales forms the apex of the terminal bud. In section the bud would no
doubt present an appearance like that shown in Wieland’s photograph
of the terminal cone of _C. Marshiana_[1172]. There is a striking
resemblance both in the ramental cap and in the form of the protective
scales between the fossil stem and such a Cycad as _Encephalartos
Altensteinii_[1173]. A remarkable feature of _C. gigantea_ is the
absence of any fertile shoots among the leaf-bases. In one tangential
section a small bud was found, but it affords no evidence of the
presence of any reproductive organs. A similar bud is described by
Lignier[1174] in the stem of _C. micromyela_. The absence of lateral
flowers is, however, hardly a sufficient reason for separating this
stem generically from other species of _Cycadeoidea_: negative evidence
in this case is of doubtful value. While it is possible that the
strobili were terminal as in most recent Cycads, it is more probable
that they were lateral. The surface-features, though not perfect,
are for the most part sufficiently well preserved to enable one to
recognise the bract-encircled axes of strobili were any present. If as
Wieland believes, and he is probably correct, the production of flowers
was the culminating event in the life of these Cycadean plants, the
absence of fertile shoots is merely an expression of immaturity. It is,
however, difficult to understand how lateral branches could find their
way to the surface among the crowded and cork-covered leaf-bases of the
stem. The absence of flowers may be due to some unfavourable external
conditions. The petioles consist of parenchymatous ground-tissue with
many secretory sacs and in some cases twelve partially preserved
vascular bundles: the xylem consists of radial rows of centrifugal
tracheids and medullary rays, but it is not possible to say whether
any centripetal xylem was present. A fairly thick band of phelloderm
and periderm, apparently subepidermal in origin, forms the peripheral
tissue, and in places epidermal cells with attached ramenta are
clearly preserved. The ramenta are of the type characteristic of the
majority of fossil Cycadean stems. Stomata were found showing a pair of
guard-cells and apparently two subsidiary cells: the epidermal cells
have straight walls.
[Illustration: Fig. 535. Section of the quarry in the Isle of
Portland in which _Cycadeoidea gigantea_ was found.]
[Illustration: Fig. 536. _Cycadeoidea gigantea._ (The original is in
the British Museum; ⅛ nat. size.)]
[Illustration: Fig. 537. _Cycadeoidea gigantea._ Transverse section
of the stem.]
[Illustration: Fig. 538. _Cycadeoidea micromyela._ A, tracheids from
the stele. B, course of the vascular bundles at the base of a leaf.
C, section of a leaf-trace entering the stele; _m_, _l_, median and
lateral lobes of the trace. (After Lignier.)]
_Cycadeoidea micromyela_ Morière.
This Liassic species from Normandy has been fully investigated by
Lignier[1175]; originally referred to the Conifers, it was afterwards
described by Morière[1176] as _Cycadeoidea micromyela_. As regards
external features the stem is of the usual _Cycadeoidea_ type:
Saporta[1177] assigned it to the genus _Platylepis_. The secondary
xylem consists of tracheids with bordered pits on the radial walls
arranged as single contiguous rows, resembling scalariform pitting, or
as 1–2 rows of separate circular pits (fig. 538, A), a type different
from that of the great majority of Mesozoic species. The uniseriate
medullary rays are 7–20 cells deep, a character recalling the compact
wood of Indian _Williamsonia_ stems. Ramental scales are for the most
part replaced by long unicellular hairs like those of _Williamsonia
scotica_ and some Indian stems. Lignier states that true ramenta
occur on the young leaves and in older fronds become transformed by
separation of the cells into long tubes. Each leaf-trace arises as a
single bundle dividing into three as it leaves the stele and eventually
splits up into several collateral bundles (fig. 538, B, C). The stele
is elliptical. No fertile shoots are preserved: a single axillary
bud is described which agrees very closely with that in _Cycadeoidea
gigantea_.
[Illustration: Fig. 539. _Cycadeoidea Jenneyana_ (?). Longitudinal
section of an ovulate strobilus, showing the pyriform receptacle with
vascular supply, the long interseminal scales and megasporophylls, and
a few of the surrounding bracts. (After Wieland; × 1½ nat. size.)]
_Cycadeoidea Jenneyana_ Ward.
The stems of this species, from the Black Hills of Dakota[1178],
resemble those of _Cycadeoidea gigantea_ and _C. Reichenbachiana_ in
their thick columnar form but differ from the former in the presence
of bisporangiate flowers associated with the leaf-bases. This species
probably reached a length of 3–4 met. A striking feature[1179] is the
unusual thickness of the xylem-cylinder, which shows clear indications
of concentric rings, probably the expression of seasonal changes during
the production of secondary conducting tissue by a single cambium.
Similar concentric rings have been described in the stems of the
recent Cycad _Dioon spinulosum_[1180]. Fig. 539 represents an ovulate
strobilus referred to this species by Wieland.
_Cycadeoidea pumila_ Fliche and Zeiller.
This French Portlandian species[1181] affords a good example of a very
small bulbiform trunk, 3·5–4 by 2·5–3 cm., superficially resembling
a Pine-cone: the leaf-bases are, however, less uniform in size and
shape than Abietineous cone-scales; there are also indications of
interpetiolar ramenta and a small lateral, presumably fertile, branch.
A stem of similar form is described by Saporta[1182] from Corallian
beds in France as _Bulbopodium micromerum_, and _Cycadeoidea nana_
Ward[1183] from Dakota is another example of a small Zamia-like
Mesozoic stem. A small tuberous stem, 8 × 7·5 cm., was described by
Lindley and Button from Lyme Regis as _Cycadeoidea pygmaea_[1184]; no
flowers are shown in the drawing, but occasional irregularities in the
arrangement of the leaf-bases may be due to the presence of lateral
fertile shoots.
=Cycadella.= Ward.
This generic name was instituted by Lester Ward[1185] for some
petrified stems from Jurassic beds in Wyoming of relatively small size,
bulbous or more or less spherical, and characterised by the presence
of a thick layer (5–15 mm.) of dense ramental tissue. The unusually
vigorous development of the ramental scales is an interesting feature,
though it is perhaps questionable whether it is worthy of generic
recognition. The flowers of _Cycadella_, though less than those of most
_Cycadeoidea_ stems, are of the same type. In a later account of the
genus Ward[1186] describes a few additional species and in _Cycadella
ramentosa_ he notes the preservation of young fronds. The fronds are
small and bear a few pinnae: the xylem is said by Wieland[1187] to
be mesarch, but in the absence of more details the foliar bundles
cannot be fully described. In some Cycadellas young flowers, less than
1 cm. in diameter, are preserved, those of _Cycadella wyomingensis_
(7 mm. in diameter) being the smallest bisporangiate strobili so far
recorded. The French species, _Cycadeoidea micromyela_ Mor., resembles
_Cycadella_ in the profuse development of ramental tissue which may
cover the surface of the stem.
=Amphibennettites.= Fliche.
This generic name was instituted[1188] for two species founded on very
imperfectly preserved ‘fruits’ of Lower Cretaceous (Albian) age from
the Argonne which, though in close agreement with _Bennettites_ as
represented by _B. Gibsonianus_ and _B. Morierei_, are referred to a
separate genus on the ground that the preservation is not such as to
establish their generic identity with those species and because of
certain distinctive features.
_Amphibennettites Bleicheri_ Fliche. The ovulate strobili are
sub-elliptical, 3·5 × 3 cm., with several elliptical pits close to
the surface originally occupied by seeds borne on short stalks and
larger than the seeds of other species of _Cycadeoidea (Bennettites)_.
Interseminal scales occur between the seeds. The second species,
_Amphibennettites Renaulti_, is rather larger and more conical: the
seeds reach a length of 11 mm. greater than that of any of the American
seeds described by Wieland. In neither species is there any indication
of an involucre of bracts. The preservation of the specimens leaves
much to be desired, but it would seem that the Argonne fossils agree
in their main characters with Bennettitean strobili and it is doubtful
whether a distinctive generic name is necessary. The occurrence of
seeds over the whole surface, a feature that suggested the name
_Amphibennettites_, may be only apparent and the result of cutting
the cone transversely. It is worthy of note that one of Fliche’s
sections[1189] bears a close resemblance to an Araucarian cone, and in
the absence of structure the two types of cone might easily be confused.
[Illustration: Fig. 540. _Vectia luccombensis._ Transverse section
showing the alternation of fibres, _s_¹, _s_², and radial pairs
of pitted elements, _v_¹ and _v_²; _m_, medullary-ray cells; _a_,
parenchyma cell between four thin-walled elements; _sp_, pits between
adjacent fibres; _l_, much reduced lumen of fibre. (After Stopes.)]
=Vectia.= Stopes. Genus _incertae sedis_.
_Vectia luccombensis_ Stopes.
The generic name _Vectia_ has been given by Dr Stopes[1190] to some
petrified secondary phloem discovered by her at Luccomb Chine in the
Isle of Wight: the fossil is from Aptian beds. The mass of phloem
is 26 mm. in breadth and consists of regularly alternating bands
of thin-walled sieve-tubes and very thick fibres associated with a
little parenchyma (fig. 540). To the naked eye the specimen presents
an appearance suggestive of rings of growth but this is due to the
presence of bands of 2–3 narrow cells which are probably cork. The
whole is penetrated by uniseriate medullary rays. A striking feature
is the regular alternation of single rows of fibres with two bands
of sieve-tubes; in places the two bands of sieve-tubes are separated
by 2–4 rows of very flat, presumably, cork-cells, and similar bands
may be adjacent to or pass obliquely across the fibres. The elongated
elements described as sieve-tubes, though thin in comparison with the
fibres, have thickened walls and on their radial faces are single
rows of circular pits, often in pairs; these are almost certainly
sieve-areas which have lost the finer pitting of the sieve-plates.
The fibres are more or less square in transverse section and have
excessively thick walls, the lumen being reduced to a small hole.
Parenchymatous cells (fig. 540, _a_) occupy the angles between the
sieve-tubes and occasionally stretch tangentially between a pair of
tubes: these are compared by Dr Stopes to companion-cells, but their
manner of occurrence hardly justifies the interesting suggestion that
they may be precursors of the Angiosperm companion-cells. The medullary
rays may be as wide as the elements which they traverse; they are
characterised by their wavy walls, as seen in radial longitudinal
sections; no pitting was noticed. A remarkable feature of the specimen
is its considerable breadth: it is pointed out that in a giant stem
of _Sequoia_ with a girth of over 40 ft the secondary phloem does not
exceed 3–4 mm. in breadth. The great thickness of the phloem in the
fossil suggests comparison with the corresponding tissue in recent and
fossil Cycadean stems, and the alternation of hard and soft phloem is
a feature exhibited also by _Cycadeoidea Gibsoniana_ (fig. 518, B). Dr
Stopes concludes that the phloem is in the main similar to that in some
Cupressineae, Taxineae, and Taxodineae. It is noteworthy that similar
phloem with sieve-tubes and fibres associated with cork is described by
Graf Solms-Laubach[1191] from Upper Jurassic beds in Franz Josef Land.
The systematic position of _Vectia_ cannot be definitely determined,
but I believe that it is more closely allied to Cycadean than to
Coniferous phloem.
* * * * *
+Note.+ It is unfortunate that Mr Wieland’s second volume dealing
with American Cycads [Wieland (16)] did not come into my hands until
nearly the whole of this volume was in type. Students will find in it
many additions to our knowledge of _Cycadeoidea_ and _Williamsonia_,
much theoretical discussion that is suggestive and interesting, useful
summaries of our knowledge of fossil Cycads, and many beautiful
photographic plates illustrating the morphology of American species of
_Cycadeoidea_.
CHAPTER XXXVII.
BENNETTITALES (_continued_).
=WILLIAMSONIA.= Carruthers.
This genus was first figured by Young and Bird[1192] from specimens
obtained from Lower Estuarine beds near Whitby: these authors compared
the fossils to the head of an Artichoke (_Cynara integrifolia_), ‘the
covering or calyx consisting of numerous lanceolate and striated
leaves’ (fig. 544). In 1840 Williamson[1193] noticed the association
with fronds of _Zamia gigas_ Lind. and Hutt. of ‘a remarkable fossil,
apparently connected with the fructification of a _Cycas_,’ and some
years later Yates[1194] expressed the opinion that the fructifications
figured by Young and Bird probably belonged to the plants which
bore the fronds known as _Zamites gigas_. Leckenby[1195] figured
some leaves of _Palaeozamia pecten_ (= _Ptilophyllum pecten_) in
close association with a small flower of _Williamsonia_ which was
subsequently recognised as a whorl of microsporophylls. In 1870 two
papers of exceptional interest were published, one by Williamson[1196]
who was the first to attempt an exhaustive account of the genus, and
the other by Carruthers[1197] who proposed the name _Williamsonia_,
thus associating ‘with a group of the most characteristic Yorkshire
fossils two men (father and son) who have largely contributed to the
exposition of Yorkshire geology.’ Carruthers instituted a new tribe
Williamsonieae for the genus _Williamsonia_, the type-species being
_Williamsonia gigas_: the specific name had been previously given by
Lindley and Hutton to the fronds (_Zamia gigas_) of the plant which
was believed to have borne the flowers for which the new designation
was proposed. Two other species, _Williamsonia hastula_ and _W.
pecten_, were assigned to the new genus. The conclusion arrived at by
Williamson as to a connexion between _Zamites gigas_ and _Williamsonia_
flowers was, however, not accepted by Saporta[1198], who figured and
described several exceptionally good specimens from the Yorkshire coast
which formed part of the Yates collection in the Paris Natural History
Museum. In 1897 a short account was published[1199] of the Yates
specimens, an examination of which convinced me of the correctness of
Williamson’s views as to an organic connexion between stems, peduncles,
flowers, and fronds. During a visit to Paris several photographs were
taken, but these were not published: similar photographs have since
been reproduced by Wieland[1200] and reduced copies from two negatives
in my possession are shown in figs. 541, 542. The restoration by
Williamson in his well-known memoir is probably correct so far as the
general habit of the plant is concerned, though the flowers which
he speaks of as male are now known to be ovulate. The position of
the male organs, whether borne separately or on the same axis as the
megasporophylls, has not been definitely settled.
In 1891 the Marquis of Saporta thus introduced his discussion on
Williamsonia,—‘avec les _Williamsonia_ nous abordons un des problèmes
les plus difficiles, un des sujets des plus controversés, mais
aussi les plus curieux, peut-être même le plus remarquable de tous
ceux que nous offre l’ensemble des plantes jurassiques.’ Wieland’s
investigations have placed us in possession of many important
facts with regard to the closely allied flowers of _Cycadeoidea_
and have enabled us considerably to extend our knowledge beyond
the stage represented by the work of Carruthers, Williamson, and
other authors; and more recently Nathorst’s important discoveries
have demonstrated the close agreement between _Williamsonia_ and
_Bennettites (Cycadeoidea)_. Several problems still remain unsolved.
Having regard to the deficiency of the data concerning the morphology
of the _Williamsonia_ type of flower and the wider question as to
a phylogenetic relationship that some botanists believe to exist
between the Bennettitales and the Angiosperms, Saporta’s words
are still pertinent. Wieland’s discoveries in Mexico[1201] have
furnished additional evidence of the wide geographical distribution
of the _Williamsonia_ type of flower in the Jurassic period, and it
may be confidently asserted that the Bennettitales, including both
_Williamsonia_ and _Cycadeoidea_, occupied a dominant position in the
floras of the world during the stage of plant-development immediately
preceding the evolution and rapid spread of the Angiosperms, the
present dominant class.
There has been considerable uncertainty among authors with regard to
the application of the name _Williamsonia_. In former accounts of the
genus the name was employed by me both for leaves and flowers on the
ground that Williamson was correct in his opinion as to the connexion
between _Williamsonia gigas_ and _Zamites gigas_. The type of frond to
which the latter term is applied is by no means uncommon in Jurassic
strata though it is not always associated with flowers, and the
use of the generic term _Williamsonia_ is therefore not invariably
justifiable. Nathorst[1202] has recently reiterated his opinion that it
is inadvisable to employ the name _Williamsonia_ except for the flowers
or the complete plant and strongly urges palaeobotanists to retain
the provisional genus _Zamites_ when the fronds only are in question.
While agreeing with the contention that the greatest care should be
exercised to avoid the use of generic names implying a correlation of
vegetative and reproductive organs that rests on any evidence short of
demonstration, it may be suggested that the better plan is to add the
name _Williamsonia_ in parentheses after _Zamites_ or _Ptilophyllum_
in cases where there is no reason to doubt that the fronds belong to a
_Williamsonia_ plant.
_Williamsonia gigas_ (Williamson).
The species selected for a rather detailed description is still
imperfectly known, but it is particularly interesting as the type on
which the first scientific account of the genus was based. The name
_Williamsonia gigas_ is now generally employed for the flowers which
bore megasporophylls as the essential organs: they may have been
bisporangiate,—a view that seems to me the more probable,—but this
has not been demonstrated. There are very few cases in which fronds of
_Zamites gigas_ occur in organic connexion with stems, and we cannot
with safety employ other than a provisional generic term for fossil
stems which it is believed bore flowers of the _Williamsonia_ type.
For the imperfectly preserved piece of stem shown in fig. 541 the
name _Williamsonia (Bucklandia) gigas_ is employed, as there is no
reasonable doubt that in addition to the fronds of _Zamites gigas_ it
bore peduncles (fig. 541, _a_), with _Williamsonia_ flowers. This and
other stems found in close association with _Williamsonia_ flowers in
England, India, and Mexico are of the type known as _Bucklandia_[1203];
but it would in most instances be unwise to add _Williamsonia_ even as
a subordinate title. Casts of stems in close association with fronds
and flowers are not uncommon in
collections of plants from the Yorkshire coast; the surface-features
are of the type shown in fig. 576, rhomboidal or lozenge-shaped bases
of petioles as described under the genus _Bucklandia_[1204]. The stem
reproduced in fig. 541, about 5 cm. broad, is imperfectly preserved and
the leaf-bases are not clearly seen. Saporta’s figure[1205] conveys
but a poor idea of the actual specimen. To one side of the stem, 5 cm.
from the lower, broken, end, are attached the petioles of two clearly
preserved fronds of _Zamites gigas_, and above these is part of a third
frond apparently in its original position. The main axis is prolonged
obliquely upwards to the left as a branch, _a_, 3 cm. broad and 14 cm.
long, covered with hairy bracts and bearing distally several narrow,
linear-lanceolate, scale-leaves. This branch is undoubtedly a fertile
shoot or peduncle. A specimen figured (from a drawing) by Saporta[1206]
as a peduncle of a _Williamsonia_ flower and reproduced in fig. 542 is,
in surface-features, identical with the branch _a_ shown in fig. 541,
but at the apex it bears a bud covered with linear bracts identical
with those of _Williamsonia gigas_. This bud is almost certainly a
young flower. Similar peduncles are described by Williamson, and he
speaks of one which is bifurcated: this specimen is probably that
reproduced in fig. 543 and now in the Leeds Museum: at the base the
axis is 3·5 cm. in diameter; the two divergent arms bear numerous
bracts identical with those of _Williamsonia gigas_ and in addition
are a few shorter ovate scales recalling those figured by Nathorst as
probably belonging to _Williamsonia pecten_. The Leeds specimen is
from the Lower sandstone and shale near Scarborough. Similar branched
peduncles are represented in the Whitby Museum and in the National
Collection. Wieland[1207] has also figured a peduncle bearing a
‘typical fruit bud’ of _Williamsonia gigas_ similar to that reproduced
in fig. 542. These specimens fully justify Williamson’s restoration
published in his paper of 1870.
[Illustration: Fig. 541. _Williamsonia gigas._ Fronds (_Zamites
gigas_) and flowering shoot, _a_, attached to a stem (_Bucklandia_).
(Yates Collection, Paris; nat. size.)]
[Illustration: Fig. 542. _Williamsonia gigas._ Flowering shoot and
flower-bud. (Yates Collection, Paris.)]
In a former account of this species[1208] the opinion was expressed
that the flowers described by Williamson as male were ovulate and
constructed on the plan of those of _Bennettites Gibsonianus_
Carr. This conclusion has since been confirmed by Nathorst[1209]
who succeeded in obtaining excellent preparations of the cuticular
membranes of interseminal scales and micropylar tubes (fig. 545),
demonstrating their very close agreement with those of the flowers of
_Cycadeoidea_.
[Illustration: Fig. 543. _Williamsonia gigas._ Two peduncles, B and
C, with imperfectly preserved bracts. Diameter of axis, A, 3·5 cm.
(From a specimen in the Leeds Museum; nat. size.)]
One of Williamson’s ‘carpellary discs’ has been shown by Nathorst to be
a verticil of microsporophylls bearing synangia, but both this author
and Lignier[1210] think that the two specimens figured by Williamson as
carpellary discs are distinct organs, one being a staminate whorl and
the other a sterile infundibuliform organ. My own view is that both are
of the same nature and consist of microsporophylls.
[Illustration: Fig. 544. _Williamsonia gigas._ Portion of a flower
showing the protective bracts, the annular zone formed by numerous
sterile sporophylls and interseminal scales, and the large central
cavity originally occupied by the receptacle. (From a specimen in the
Williamson collection, Cambridge Botany School; nat. size.)]
[Illustration: Fig. 545. _Williamsonia gigas._ Micropylar tube.
(After Nathorst.)]
Fig. 544 represents the usual form in which the flowers of _W. gigas_
are found; it consists of linear bracts covered with hairs identical
with those on the peduncles shown in figs. 541–543; they surround a
pyriform axis and form what Williamson called an involucrum. The base
of the fossil is characterised by an annular zone formed of crowded,
radially disposed, narrow ridges now known to be casts of interseminal
scales. At the outer edge of this annular area impressions of the
peltate ends of interseminal scales are not infrequently preserved.
Fig. 545 is a photograph of one of Nathorst’s preparations showing
the very great similarity between a micropylar tube of _W. gigas_ and
the corresponding structures in _Cycadeoidea_. The small micropylar
tubes are surrounded by 5–6 polygonal expanded apices of interseminal
scales as in _Cycadeoidea_ (fig. 515; _cf._ also fig. 563), and the
apex of each peltate distal end projects slightly as a central papilla
composed of more strongly cuticularised cells. In most specimens the
megasporophylls and interseminal scales (sterile megasporophylls) are
preserved only as an annular zone at the base of the receptacle (fig.
548, _as_), but it is clear from some specimens of _W. gigas_ and other
species figured by Saporta[1211], Nathorst[1212], and Krasser[1213]
that originally the whole surface of the pyriform axis was beset with
these organs which fell off, presumably, when the seeds had reached
maturity. No satisfactory examples of seeds have been found in English
specimens. Krasser has described some specimens of _Williamsonia_
from Jurassic rocks in Sardinia to which he assigns some associated
seeds, but, as he admits, there is no proof of any connexion. In some
cases a funnel-like depression is seen at the upper end of a strobilus
of _W. gigas_ (fig. 546, B, C, _a_) identical in the occurrence of
radially disposed ridges with the annular zone at the base and due to
the preservation of interseminal scales and aborted megasporophylls in
the upper part of the receptacle: in this region also the impressions
of polygonal apices of the scales are sometimes found. The probability
is that while the greater part of the armour of scales and seeds was
thrown off, at the upper and lower end of the receptacle some sterile
megasporophylls and scales remained (fig. 548, _as_, _dl_).
[Illustration: Fig. 546. _Williamsonia gigas._ A, apical portion
of flower. B, cast of A; _a_, persistent interseminal scales. C,
flower in longitudinal section. C′, interseminal scales from the base.
(Williamson Collection, Botany School, Cambridge.)]
Williamson regarded the funnel-shaped depression as the impression of
the lower surface of a laterally expanded portion of the axis of the
flower, and to this expansion he gave the name lenticular disc (figs.
546, 547, _a_). It is, however, much more likely that the apparent
extension of the axis is due to the preservation of the sterile
zone of armour which formed a cluster of appendages, the impressions
of which are seen on the sides of the funnel-like depression, the
receptacle being prolonged as a slender axis (fig. 547, C). The next
point to consider is the form of the axis beyond the level of the
collar of sterile armour. Williamson described the axis as spreading
out to form the lenticular disc and then prolonged as a narrow conical
pyramidal axis which is slightly extended horizontally immediately
below a terminal mammilla: the apical mammilla he designated the
corona (fig. 547, C, _r_). As already stated, the lenticular disc
is probably not an expanded part of the axis but the result of the
preservation of a spreading mop-like cluster of interseminal scales.
This is the view expressed by Lignier[1214] who kindly furnished
the block from which fig. 548 is reproduced. The lower face of
Williamson’s lenticular disc is characterised by a series of spoke-like
radiating ridges (fig. 547, A′) between which are less distinct
radially disposed lines, and at the periphery there are impressions
(fig. 547, A′′), continuous with some of the radiating ridges, of the
terminal shields of interseminal scales. In fig. 547, drawn from one
of the original specimens described by Williamson, these features are
shown at A′ and B: fig. A′ represents the circular area, which is
at right-angles to the axis of the flower, in surface-view. In the
centre of this circular area is a depression ending in a short papilla
surrounded by a narrow basal rim: this feature is shown on a cast of
the specimen represented in fig. 547, B. In this case Williamson’s
corona is seated on a very short axis whereas in fig. 547, C, also from
one of Williamson’s specimens, the corona forms the apex of a longer
pyramidal axis. Wieland[1215] regarded the circular area seen in fig.
547, A, as the impression of the apical portion of a bisporangiate
strobilus, the ridges marking the edges of the incurved distal portions
of microsporophylls bent over the apex of the ovulate cone (_cf._ fig.
513), and he interpreted the polygonal depressions at the periphery
(fig. 547, A′′) as those of sori, an interpretation entirely different
from that of Lignier. The latter author[1216] in part reasserted his
opinion but modified it as regards the meaning of the ridges on the
circular area, agreeing so far with Wieland as to consider them as
having been formed by the folded-over rachises of microsporophylls
attached as a concrescent collar to the base of the ovulate cone. This
interpretation does not, however, explain the relation between the
radial striations on the circular area and the polygonal impressions
at its periphery. Wieland still dissents from Lignier’s opinion and
suggests that the circular area has not been demonstrated to belong
to the apical end of a flower. Fig. 547 shows that its position is
apical. Fig. 548 represents Lignier’s view as to the nature of the rim
surrounding the apical mammilla: he suggested that several interseminal
scales borne at the apical region of the receptacle were concrescent
and formed linear bracts the edges of which are represented by the main
ridges in fig. 547, A′. These concrescent scales bent upwards and were
closely applied to or perhaps concrescent with the pyramidal axis and
were then prolonged as a wide infundibuliform apparatus (Williamson’s
carpellary disc). This organ was, however, easily detached, and the rim
seen at _r_ in fig. 547, C, represents its narrow broken base. With
this view I am in general agreement; but while Lignier regards the
funnel-like appendage as sterile and considers that similar organs,
but with a large central cavity at the base of the funnel, may have
been microsporophyll-discs which were borne below the ovulate strobilus
in the position occupied by the microsporophylls in _Cycadeoidea_
(fig. 528)—my inclination is to see in the terminal appendage a
whorl of concrescent microsporophylls. This view lacks the support
of demonstration. It is obvious from Williamson’s specimens and from
others described by Saporta, Nathorst, and Lignier that the receptacle
of _Williamsonia gigas_ was not so simple in its termination as that
of the flowers of _Cycadeoidea_. In _Cycadeoidea dacotensis_ Wieland
showed that the apex of the receptacle bore a tuft of long interseminal
scales, and it is readily conceivable that these apical appendages
were still further developed in some _Williamsonia_ flowers to form a
whorl of concrescent leaves borne on the prolonged apex of the axis.
There is little doubt as to the homology of interseminal scales and
microsporophylls, and there is no difficulty in supposing that while in
some flowers the foliar organs assumed the form of interseminal scales
of unusual length, in other species they became microsporophylls.
[Illustration: Fig. 547. _Williamsonia gigas._ A, flower in
longitudinal section, showing, especially on the left side,
interseminal scales and megasporophylls and a pyriform cavity
representing the central axis (nat. size). A′, the under surface of
the apical region. A′′, interseminal scales from A′. B, cast of A′.
C, apical region of another specimen; _a_, interseminal scales; _c_,
column; _r_, ridge. (Williamson Collection, Botany School, Cambridge.)]
[Illustration: Fig. 548. _Williamsonia gigas._ Restoration showing
an ovulate strobilus bearing a terminal infundibuliform appendage.
Lignier, to whom the restoration is due, points out that the apical
portion of the axis at _dl_ should be represented as straight and not,
as in the figure, horizontally expanded. _bi_, bracts; _as_, persistent
interseminal scales forming the annular zone; _r_, receptacle; _cs_,
caducous megasporophylls and interseminal scales; _dl_, persistent
interseminal scales, an extension of which formed the large funnel-like
appendage, _at_; _ap_, apex of the receptacle. (After Lignier.)]
It is noteworthy that the radiating ridges on the circular area
shown in fig. 547, A′, agree in position and approximately at
least in number with those on the sides of the cupular disc of
the microsporophyll-verticil of _Williamsonia whitbiensis_[1217].
Nathorst describes a specimen seen in a private collection in which
an infundibuliform appendage appeared to be preserved in situ at the
apex of a flower of _Williamsonia gigas_ (_cf._ fig. 548, _at_).
Thomas[1218], in his description of _Williamsoniella_, compares
the radial ridges on the apical sterile portion of a flower of
_Williamsonia gigas_ to the ridges on his _Williamsoniella_ which are
formed by the tips of infolded microsporophylls.
[Illustration: Fig. 549. _Williamsonia gigas._ A, diagrammatic
drawing showing the position of the synangia, at _S_, and part of the
staminate disc. B, a single synangium; × 6. (After Thomas.)]
_Williamsonia gigas_ (Microsporophylls).
[Illustration: Fig. 550. _Williamsonia gigas._ Side-view of an
incomplete staminate disc showing the basal cup torn at the lower end
and part of one of the free microsporophylls. (Diagrammatic drawing,
after Thomas; nat. size.)]
In the course of an examination of the _Williamsonia_ specimens (from
Yorkshire) in Paris in July of last year (1914) Mr Thomas[1219]
found a specimen previously overlooked, which is undoubtedly either
a male flower or, as I am inclined to think, the staminate disc of a
bisporangiate flower of _Williamsonia gigas_. The nature of the matrix
shows that it came from the neighbourhood of Whitby. It consists
of an urn-shaped organ formed of the concrescent bases of 18–20
microsporophylls each 7–8 mm. wide; the cup is 5–6 cm. broad, the
base being torn but tapered (fig. 549) as though originally prolonged
downwards into a stalk as in _W. spectabilis_. Along the middle line
of each sporophyll is a series of depressions, probably the same in
nature as those on _W. whitbiensis_ described by Nathorst, though it
is not clear whether, in this case at least, they represent aborted
synangia. Some reniform synangia (fig. 549, B) occur in the rock just
above the cup. The sporophylls spread outwards from the base and then
curve inwards, bending outwards again as they become free. A portion
of a microsporophyll is shown in fig. 550 bearing segments projecting
inwards as in _W. spectabilis_ (fig. 551). This specimen, which occurs
in association with female flowers, is regarded by Mr Thomas as part
of a unisexual flower. He discusses the possibility of its connexion
with an ovulate receptacle and expresses the opinion that if it were
borne at the upper end of a bisporangiate flower the whole would be
top-heavy and the arrangement uneconomical. On the other hand if, as
suggested on page 434, the flowers were bisexual the staminate disc,
which reached maturity before the ovules, may have been thrown off,
as in _Cycadeoidea_, before the seeds were ripe. The form of the disc
resembles that of the Indian specimen described on another page as
_Williamsonia_ sp., _cf._ _W. setosa_ Nath.; it does not, I venture to
think, afford an argument against the view that the microsporophyll-cup
of some _Williamsonia_ flowers was attached near the apex of the
receptacle and was formed of modified foliar organs homologous with
those which, in the ovulate portion of the flower, constitute the
interseminal scales and megasporophylls.
A further consideration of the microsporophylls of _Williamsonia_ will
be found in a later section of this chapter.
_Williamsonia spectabilis_ Nathorst.
This species[1220], the first example of undoubted microspore-bearing
organs referred to _Williamsonia_, was founded on material discovered
by Prof. Nathorst in the Lower Estuarine series of Whitby; it has also
been obtained from beds of the same age at Marske in the Cleveland
district of Yorkshire[1221]. _Williamsonia spectabilis_, though
indubitably a male organ, has not been found attached to a stem, and
there is no decisive evidence as to its connexion with a particular
species of frond. Nathorst believes that it belongs to the plant which
bore the leaves known as _Ptilophyllum pecten_, an opinion based
chiefly on association. The more complete specimens consist of a broad
funnel-shaped organ prolonged below into a slender stalk and divided at
the margin into several linear-lanceolate segments (microsporophylls)
the apices of which were rolled inwards like young fern-fronds (figs.
551, 552). The synangia agree closely in form and in such structural
features as can be made out from cuticular preparations with those
described by Wieland in American species of _Cycadeoidea_; they are
slightly reniform, 5–6 mm. long and 2 mm. broad and divided into
several loculi by transverse partitions (fig. 552). The microspores,
58–65_µ_ in length, are rather narrow, ovate and very similar to those
described by Solms-Laubach[1222] in _Cycadeoidea etrusca_. The synangia
are attached in two rows to slender lateral segments which appear to
be given off from the upper face near the median line of the broad
linear sporophylls (fig. 565, A). Nathorst points out that the position
of the fertile pinnae brings the sporophylls into close relation with
the vegetative fronds of _Ptilophyllum pecten_ and other Cycadean
fronds in which the pinnae are attached to the upper face of the
rachis. While the longer pinnae in the middle portion of a sporophyll
bear several synangia, those near the base and apex are shorter and,
in the proximal region nearer the broad cup formed by the coherent
bases of the sporophylls, occur singly, thus approaching the condition
characteristic of _W. whitbiensis_ (fig. 565, B) in which they are
sessile on the simple microsporophylls. It is noteworthy that in some
specimens figured by Nathorst there is a tendency of the lower part
of the cup to break away from the coherent bases of the sporophylls
(fig. 551)[1223], and it is not unlikely that some of the impressions
described as infundibuliform appendages are incomplete examples of
_Williamsonia spectabilis_.
[Illustration: Fig. 551. _Williamsonia spectabilis_ and leaves of
_Ptilophyllum pecten_. (After Nathorst; ⅚ nat. size.)]
[Illustration: Fig. 552. _Williamsonia spectabilis._ Restoration of
an almost mature male flower. (After Thomas; approximately nat. size.)]
[Illustration: Fig. 553. _Williamsonia Leckenbyi._ Surface-view and
in section.
(Restoration after Nathorst.)]
_Williamsonia Leckenbyi_ Nathorst.
This species, founded on specimens from the Middle Estuarine
beds exposed on the Yorkshire coast at Cloughton Wyke[1224], is
characterised by the almost spherical form of the strobilus, 4·5–5 cm.
in diameter. The relatively small receptacle is covered by a thick
mass of megasporophylls and interseminal scales except in the lower
part which bears only sterile scales. Nathorst believes that the seeds
were very small, but no undoubted examples have been found. A specimen
in the British Museum, figured in 1900[1225], shows the surface-view
of an impression of the base of the flower; a small circular raised
boss occupies the centre—the scar of the receptacle—and surrounding
this is a reticulum formed by the impression of the distal ends of the
interseminal scales. The uniform nature of the reticulum, the meshes
of which are all of the same type, shows that in the basal region of
the flower the organs borne on the receptacle were all sterile as in
_Cycadeoidea (Bennettites) Morierei_. Except in the smaller diameter
of the receptacle this specimen is practically identical with that of
_Williamsonia Carruthersi_ Sew. reproduced in fig. 559. The form of
the strobilus is shown in Nathorst’s restoration[1226] represented
in fig. 553. The interseminal scales have broad peltate distal ends
characterised by a patch of lighter and thinner-walled cells at the
apex (fig. 554); the micropylar tubes are slightly expanded at the
summit and their epidermal cells are papillose as in _Williamsonia
scotica_ (_cf._ fig. 563, B). Nathorst in 1909 adopted the name
_Williamsonia pecten_ Carr.[1227] for the specimens originally referred
to _W. Leckenbyi_ as well as for microsporophylls that he believed
to belong to the same plant as the ovulate strobili: but in a later
paper[1228] he restricts the name _Williamsonia pecten_ to the male
strobili, reserving _W. Leckenbyi_ for the ovulate forms, as there is
no proof that both were borne on the same plant. From the evidence
at present available it is reasonable to regard _W. Leckenbyi_ as a
unisexual flower. In all probability the fronds known as _Ptilophyllum
pecten_ are the foliage of the parent-plant of _W. Leckenbyi_, though
in the absence of proof it is advisable to retain both names.
[Illustration: Fig. 554. _Williamsonia Leckenbyi._ Micropyle and
interseminal scale.
(After Nathorst.)]
_Williamsonia whitbiensis_ Nathorst.
Under this name Nathorst[1229] described some interesting specimens of
microsporophylls formerly attributed by him to _Williamsonia pecten_,
but the discovery of additional material led him to distinguish the
Whitby (Lower Estuarine) fossils as _W. whitbiensis_, retaining the
name _W. pecten_ for the type originally figured by Leckenby[1230]
from the Middle Estuarine series at Cloughton Wyke on the Yorkshire
coast. In the type-specimen, 8–10 cm. in diameter, there are 15
linear segments coalescent basally into a thick cup differing from
that of _W. spectabilis_ in the absence of a stalk (figs. 555, 556).
A more important distinctive feature is the production of synangia
on the simple sporophylls (figs. 556, B; 565, B) and not on special
fertile segments as in _W. spectabilis_ (fig. 552). The inner face of
each sporophyll, as seen in impressions, shows two regular rows of
small depressions, one on each side of the median line; these become
gradually smaller towards the base of the cup-like disc (figs. 555,
556). On the actual carbonised surface of the inner face of the cup
small and transversely elongated projections take the place of the
depressions and these show the same decrease in size when traced from
the free segments to the cupular organ. Nathorst obtained microspores
only from the larger projections and none from the smaller, a
circumstance which may indicate that only the upper and larger synangia
were fully developed[1231].
[Illustration: Fig. 555. _Williamsonia whitbiensis._ (After Nathorst;
⅚ nat. size.)]
[Illustration: Fig. 556. _Williamsonia whitbiensis._ A, male flower.
B, sporophyll with synangia. (After Nathorst.)]
This species is especially interesting as throwing light on the nature
of one of the specimens (from the Whitby Museum) figured by Williamson
as a ‘carpellary disc[1232]’: the ‘seeds’ of Williamson are no doubt,
as Nathorst believes, synangia, while the smaller pairs of markings
figured by Williamson represent rudimentary synangia and not ‘abortive
ovules.’ Though the specific identity of Williamson’s specimen and
_Williamsonia whitbiensis_ is not certain, the latter is undoubtedly a
closely allied form of a microsporophyll-verticil. A specimen figured
in 1900 as a flower of _Williamsonia pecten_[1233], designated by
Nathorst _Williamsonia_ sp., is a very similar if not an identical
type; it consists of a fairly deep basal cup the surface of which is
characterised by the presence of several regular ridges between which
are pairs of small depressions containing carbonaceous matter. In the
light of Nathorst’s researches it is clear that this is an incomplete
example of a whorl of microsporophylls. The base of the disc is
incomplete, but it is certain from the small size of the basal hole
with torn edges that the cup could not have been attached to the base
of a receptacle as are the microsporophylls in Wieland’s bisporangiate
flowers of _Cycadeoidea_. The specimens referred by Nathorst to
_Williamsonia pecten_[1234] (Leck. _ex parte_) are similar to those
described as _W. whitbiensis_, but differ in the texture of the cup and
in the degree of cuticularisation of the synangial walls. The synangia
of _W. pecten_ are of the usual reniform type and multicellular as in
_W. spectabilis_.
_Williamsonia setosa_ Nathorst.
The distinguishing features of this species[1235], founded on material
collected by Dr Halle from Lower Estuarine beds at Whitby, are (i)
the greater number of linear sporophylls which bear numerous bristles
or stout hairs, (ii) the loose coherence of the contracted proximal
portion of the linear segments, and (iii) a narrower basal disc in
place of the deeper cup of other species. One of the specimens referred
to this species, formerly regarded by Nathorst as an infundibuliform
organ of an ovulate strobilus of _W. gigas_[1236], bears a striking
resemblance to an Indian fossil described by Feistmantel from
India[1237].
+Indian species of Williamsonia (Flowers).+
Several specimens of _Williamsonia_ have been described from the
Rajmahal and other Jurassic series in India, some of which exhibit a
close agreement with _Williamsonia gigas_. It is, however, noteworthy
that no fronds of the _Zamites gigas_ type have been discovered in
Indian beds; on the other hand the association of fronds of the
same type as _Ptilophyllum pecten_ with Williamsonian strobili is
significant, as also the occurrence of stems apparently identical in
surface-features with English and Mexican species.
_Williamsonia_ sp.
Oldham and Morris[1238] figured a specimen from the Rajmahal Hills
consisting of a circular disc enclosed by a zone of ‘closely packed
tubes,’ the basal portion of an ovulate Williamsonia strobilus,
which they regarded as a pressed mass of young leaves ‘probably
related to _Palaeozamia_’ [_Ptilophyllum_]. The figured specimen
shows that the radially disposed ‘tubes’ surrounding the circular
area are interseminal scales some of which are seen at the periphery
in surface-view as small polygonal areas as in English specimens.
Feistmantel[1239] refigured this specimen and referred it to
_Williamsonia gigas_ though on insufficient grounds. To the same
species Feistmantel[1240] assigns two other specimens from the
Rajmahal series, one of which consists of several narrow linear
bracts partially enclosing a strobilus with a portion of the annular
zone at the base in which the seminiferous scales are shown in
longitudinal-view and a few in apical-view.
_Williamsonia_ sp. _cf._ _Williamsonia setosa_ Nathorst.
[Illustration: Fig. 557. _Williamsonia_ sp. A, whorl of
microsporophylls; _s_, synangia (?). C, side-view of the basal portion
of A. B, part of a microsporophyll enlarged. (Indian Geological Survey;
A, nat. size.)]
A third example from the same locality (fig. 557) is described
by Feistmantel[1241] as part of one of Williamson’s ‘carpellary
discs[1242],’ a comparison that is fully justified. The accompanying
drawing has been carefully made from the actual specimen: portions of
10 very hairy bracts radiate in a horizontal plane from a continuous
lamina with a wrinkled and ridged surface bent sharply back at
right-angles to the bracts and forming a double curve as seen in the
sectional view (fig. 557, C). The form assumed by the vertical part
of the disc is, I believe, the result of compression. Wieland[1243]
regards this fossil as a whorl of microsporophylls originally attached
to the lower portion of the receptacle of a bisexual flower. Close to
the edge of one of the bracts is an imperfectly preserved structure
(fig. 557, B, _s_) which may represent two alternately arranged rows of
synangia belonging to one of the hairy bracts; but we have no evidence
as to the position of the microsporophylls on the flower-axis. The
central space enclosed by the crushed concrescent portion of the disc
is large enough to have embraced a receptacle but, on the other hand,
the portion preserved may have broken off from a proximal cup like
that of _W. spectabilis_[1244], which, as Nathorst’s specimens show,
is sometimes broken across near the upper edge of the basal funnel.
This specimen is spoken of by Feistmantel as _Williamsonia gigas_. It
is impossible to say whether these Rajmahal specimens belong to one
species, and they are therefore provisionally designated _Williamsonia_
sp. and _Williamsonia_ sp. _cf._ _W. setosa_.
_Williamsonia microps_ Feistmantel.
This species is based on a compressed ovate strobilus surrounded by
linear bracts and a portion of the cylindrical axis[1245]. It is
possible that this smaller, bud-like, specimen may be a younger example
of the species referred by Feistmantel to _Williamsonia gigas_.
_Williamsonia Blandfordi_ Feistmantel.
Founded on a small strobilus enclosed by linear bracts, from the
Jurassic rocks of Cutch[1246], very similar to _Williamsonia pecten_;
as seen in fig. 558, drawn from the original specimen, the flower is
associated with a _Ptilophyllum_ frond indistinguishable from some
examples of _Ptilophyllum pecten_.
_Williamsonia indica_, sp. nov.
This name is proposed for some imperfect specimens described by
Feistmantel from the Godaveri district and named by him _Williamsonia_
sp. _cf._ _Williamsonia gigas_[1247]. They differ from _Williamsonia
gigas_ in the larger size of the bracts which reach a length of 13 cm.
and may be compared with those of a large specimen recorded from Mexico
as _Williamsonia Cuauhtemoc_[1248].
[Illustration: Fig. 558. _Williamsonia Blandfordi_ and _Ptilophyllum_
frond.
(Geological Survey of India; nat. size.)]
It is almost certain that some at least of the Indian flowers were
borne on stems with the foliage known as _Ptilophyllum acutifolium_, an
inference based not only on the almost constant association of flowers
and fronds but also on the juxtaposition of both kinds of organs with
stems precisely similar to those described from England and Mexico.
Though none of the specimens are sufficiently well preserved to afford
much information as to structural features, Miss Bancroft[1249] has
shown that the bracts of one of the examples assigned by Feistmantel
to _W. gigas_ are similar anatomically to those of _Williamsonia
scotica_ and are clothed with simple hairs. The important point is
the very close correspondence between the Indian and English types of
_Williamsonia_, as regards flowers, fronds, and stems.
+British Specimens.+
_Williamsonia Carruthersi_ Seward.
[Illustration: Fig. 559. _Williamsonia Carruthersi._ A, unexpanded
flower. A′, the reticulate lamellae projecting from the face of a
bract. B, the basal portion of a larger and expanded flower showing the
impressions of the interseminal scales and the base of the receptacle.
(British Museum, A, V. 3177; B, V. 3201.)]
This species was founded on several specimens from Wealden beds on
the Sussex coast none of which afford information as to anatomical
structure[1250]. It is not improbable that more than one species is
represented. The ovulate cone, 6 cm. long, is surrounded by several
linear bracts (fig. 559, A) and in shape resembles _Bennettites
Morierei_ Lign.; the bracts are broken across near the base, as is
frequently the case in _Williamsonia gigas_, exposing an annular zone
formed by persistent interseminal scales. From the inner face of some
of the bracts project slender radiating plates (fig. 559, A′) which
no doubt mark the boundary of the superficial and relatively large
interseminal scales, like those forming the so-called pericarp in
_Bennettites Gibsonianus_. The receptacle appears to have been conical,
a feature recalling _Bennettites_ rather than _Williamsonia_. The
saucer-like impression shown in fig. 559, B, is practically identical
with the corresponding portion of _Williamsonia Leckenbyi_: the centre
is occupied by a raised area, the basal part of the receptacle, on
which a series of peripheral prominences represents the vascular
strands; the sides of the saucer show very clearly the reticulum formed
by the distal ends of interseminal scales. One reason for assigning
this species to _Williamsonia_ rather than to _Bennettites_ (or
_Cycadeoidea_) is the occurrence in the same bed of a peduncle 12 cm.
long and 3 cm. broad which probably belonged to the parent-plant of
the cone. The surface of the peduncle shows spirally disposed scars of
bracts crowded at the distal end and more widely separated in the lower
portion.
_Williamsonia Bucklandi_ (Unger).
In 1837 Buckland[1251] gave an account of a ‘unique and beautiful
fossil fruit’ from Inferior Oolite beds at Charmouth in Dorsetshire
and stated that the type-specimen was in the Oxford Museum. Professor
Sollas kindly searched for the specimen some years ago but without
success. Buckland considered that the fruit was related to the
Pandanaceae and described it as follows: ‘The size of this fruit is
that of a large orange, its surface is occupied by a stellated covering
or epicarpium, composed of hexagonal tubercles, forming the summits
of cells, which occupy the entire circumference of the fruit. Within
each cell is contained a single seed, resembling a small grain of rice
more or less compressed, and usually hexagonal. When the epicarpium
is removed, the points of the seeds are seen, thickly studded over
the surface of the fruit. The bases of the cells are separated from
the receptacle by a congeries of foot-stalks formed of a dense mass
of fibres, resembling the fibres beneath the base of the seeds of the
modern _Pandanus_.’ At the suggestion of Robert Brown he called the
‘fruit’ _Podocarya_, the specific name _Bucklandi_ being afterwards
given by Unger[1252]. Brongniart[1253] called attention to the
resemblance of Buckland’s specimen to _Williamsonia_, and that name
has been adopted by Saporta[1254], Nathorst, and other authors[1255].
Sowerby’s drawings illustrating the original description, one of which
is reproduced in fig. 560, show that this unusually fine specimen is
an ovulate Bennettitean strobilus very similar in its thick conical
receptacle to some of Wieland’s species of _Cycadeoidea_, _e.g._ _C.
dacotensis_ (fig. 528): the armour of scales and megasporophylls agrees
exactly with that of some species of _Williamsonia_ from Yorkshire
and with the flowers of _Cycadeoidea_. Though included in the genus
_Williamsonia_ it would not be out of place in _Cycadeoidea_.
[Illustration: Fig. 560. _Williamsonia Bucklandi._ (After Buckland; ⅚
nat. size.)]
_Williamsonia scotica_ Seward.
The type-specimen was found by Hugh Miller near Cromarty (N.E.
Scotland) and figured as a cone of peculiar form[1256]; it was obtained
from a limestone nodule probably derived from Upper Jurassic rocks.
The fossil is 11 cm. long and has a maximum breadth of 6 cm. (fig.
561): numerous linear bracts cover the surface and in the lower portion
many of them are broken. A noteworthy feature is the absence of any
clean-cut base, a fact pointing to fracture rather than a natural
abscission of the fertile axis. The following description may serve
to give a general idea of the salient characters. Flowering shoot
ovoid, covered with linear bracts some of which are prolonged above
the conical apex as slender tapered organs and two of them bear a few
short lateral appendages (fig. 561, _l_), probably reduced leaflets,
near their distal ends. The cylindrical axis, completely hidden by
bracts, 1·5 cm. in its widest part, bears in the lower or sterile
region bracts and long hairs and in the upper part interseminal scales
and immature megasporophylls which together form a narrow band (fig.
562, _S_) 2 mm. broad extending over the incompletely preserved and
conical apex, as in some of the American examples of _Cycadeoidea_.
The strobilus was probably borne at the apex of a lateral branch given
off from a stem covered with persistent petiole-bases: there is no
evidence that this was the case, but the appearance of the ovoid cone
suggests comparison with those of _Williamsonia gigas_ which were
terminal on fairly long branches and not partially hidden among the
bases of fronds as in _Cycadeoidea_. It is, however, possible that the
cone of _Williamsonia scotica_ is a lateral structure: this suggestion
is based on the occurrence of a small branch or bud, which may be the
apex of the whole fertile shoot, given off from the cone-axis but only
revealed in transverse sections. The interseminal scales, 2 mm. long
and 0·23 mm. broad at the truncate distal end (fig. 563), are polygonal
in section and arranged as rosettes of 5–6 around each megasporophyll
(fig. 564, a section tangential to the peripheral layer of scales and
sporophylls). The megasporophylls, equal in length to the scales,
consist of a cylindrical axis bearing a terminal megasporangium, an
undifferentiated nucellus, enclosed in a single integument prolonged
as a micropylar tube above the conical end of the nucellus (fig. 563,
B, C, _a_). Fig. 562 represents a transverse section through the cone
showing the cylindrical axis with its compact covering layer (fig. 563,
A, _s_) of sterile and fertile appendages, and beyond this sections
of the enveloping bracts embedded in a dense felt of long hairs. The
tissue of the axis, though very imperfectly preserved, shows occasional
groups of secretory sacs and a few patches of scalariform tracheids:
there is evidence of the occurrence of peripheral conducting tissue
in the lower portion of the axis such as occurs in the peduncles of
American species of _Cycadeoidea_ described by Wieland. The bracts
nearer the axis are more shrivelled than those farther away, the
result of the feebler development of hypodermal stereome in the more
internal bracts. Sunken stomata occur on the lower surface of some of
the bracts: several collateral bundles are present in each and large
secretory ducts are abundant. The numerous hairs on the bracts and the
sterile region of the cone are outgrowths of epidermal cells; most of
them consist of a short basal cell and a very long thick-walled tubular
hair reaching a length of several centimetres. In some cases the basal
cell bears a group of short cells each of which is the starting-point
of a long hair: this is worthy of notice from the point of view of
comparison with the ramenta of other Bennettitalean flowers. The short
proximal cell of a hair is surrounded by a cuticular ring like a
rounded base-moulding where it rests on the epidermis: this has been
aptly compared to the dark rings that form a striking feature of the
cuticular membrane of _Ptilophyllum_ leaflets[1257].
[Illustration: Fig. 561. _Williamsonia scotica._ Strobilus in
surface-view; _l_, bract with short lateral appendages. (Royal Scottish
Museum, Edinburgh; ¾ nat. size.)]
[Illustration: Fig. 562. _Williamsonia scotica._ Transverse
section; _S_, scales and megasporophylls; _a_, bract showing detached
superficial tissue on the inner side. (_ca._ × 2.)]
[Illustration: Fig. 563. _Williamsonia scotica._ Megasporophylls
and interseminal scales in longitudinal section. A, part of the axis
showing the attachment, _s_, of a scale and megasporophyll. B, apex of
micropylar tube showing funnel-shaped cavity and papillose epidermal
cells on the integument and on the adjacent scale; _a_, apex of
nucellus. C, upper part of a scale and megasporophyll; _a_, apex of
nucellus. (A, _ca._ × 20; B, C, × 100.)]
[Illustration: Fig. 564. _Williamsonia scotica._ Transverse section
near the distal end of a micropylar tube and the surrounding polygonal
interseminal scales. (_ca._ × 100.)]
In the examination of the type-specimen the first section cut was
transverse to the axis (fig. 562), and this happened to traverse the
lowest part of the fertile region of the receptacle, as was shown by
the fact that in the next lower section the axis bore only bracts
and hairs. It is clear that the sterile portion of the receptacle
passed abruptly upwards into the fertile region, and it is extremely
unlikely that any microsporophylls were borne at the base of that
portion of the cone-axis which produced the scales and megasporophylls.
The cone was, in all probability, unisexual. On the analogy of the
cones shown in figs. 513, 514, one would expect to find between the
sterile and fertile regions either a verticil of microsporophylls or
the remains of an annular disc from which the effete sporophylls had
been detached. There is no trace of any such disc, and the fact of
the immaturity of the megasporophylls renders it unlikely that were
the cone bisexual the microsporophylls would have been detached. As
previous records show, there is nothing improbable in the occurrence
of a unisexual Bennettitean flower. These remarks are made in view
of an opinion expressed by Dr Wieland that the bracts with lateral
appendages (fig. 561, _l_), to which allusion has been made, are
microsporophylls and that if the cone had been sliced longitudinally
the presence of a microsporophyll-disc would have been discovered.
The latter possibility has already been considered, and as regards
the former there is nothing in the structure of the small lateral
appendages of the longest bracts to indicate that they were connected
with spore-production. It is not unlikely that the bracts with small
outgrowths (fig. 561, _l_) correspond to the more leaf-like bracts of
_Wielandiella_ and _Williamsoniella_. The two sets of organs spoken of
as interseminal scales and megasporophylls are probably homologous,
foliar, structures; in the one case leaves transformed into cylindrical
organs bearing terminal integumented and undifferentiated megasporangia
and, in the other, sterile or sterilised sporophylls. The polygonal
truncate distal end of an interseminal scale is flat or slightly
concave and covered by a thick epidermis, and on the sides of the
scale many of the surface-cells are strongly papillose (figs. 563,
564). The rest of the interseminal scale consists mainly of elongated
cells, which in the lower portion of the axis of the scale assume a
tubular form, presumably immature conducting elements: in one scale
only was any tracheal tissue found and that was represented by 2–3
scalariform tracheids. The scales appear to arise from the axis like
the bracts as superficial outgrowths, and probably in a later stage of
development the centre of each scale would be occupied by a vascular
strand. The megasporophylls bear a close resemblance to the scales,
but in transverse section they appear as smaller and circular organs
each the centre of a group of polygonal interseminal scales precisely
as in other Bennettitean flowers (fig. 564; _cf._ fig. 515). The
proximal part of a megasporophyll consists of a column of parenchyma
(fig. 563, A, _s_) extending through half of the length; from this
column is detached a narrow cylinder of small crushed cells which
most likely represents the remains of tissue that originally occupied
the space surrounding the axial column. At a higher level the axial
column becomes broader and its short cells more elongated and slightly
divergent towards the sloping sides of the conical nucellus. The loose
cylinder of tissue is attached to the nucellar cone and prolonged
beyond its apex as a broad integument enclosing a very small micropyle
(fig. 563, C). The apex of the integument has the form of a shallow
funnel: its epidermal cells are papillose (fig. 563, B, C) and the
presence of short transversely elongated cells is a characteristic
feature of the tissue lining the micropylar canal. The bracts agree
generally with those of _Cycadeoidea Gibsoniana_, _Cycadeoidea
Morierei_, and the American species. The ground tissue is composed of
sclerenchyma comparable with the scalariform elements in the bracts
of _Cycadeoidea Gibsoniana_ (_cf._ fig. 520). It is in the possession
of long hairs like those on the leaves of _Dioon_ and other recent
Cycads that _Williamsonia scotica_ differs from previously described
flowers in all of which the fern-like ramental scales are a conspicuous
feature. It is interesting to find that similar hairs are substituted
for scales in some Indian stems described by Miss Bancroft[1258].
Lignier[1259] mentions the occurrence of long unicellular hairs on
_Cycadeoidea micromyela_ (p. 415), a Jurassic French species, but
the ramenta are in part multicellular lamellae and the presence of
transitional forms suggests a possible derivation of hairs from scales
both in fossil species and in recent Cycads. The megasporophylls and
interseminal scales are much shorter than in _Cycadeoidea Gibsoniana_
and other species in which the axis of the cone forms a depressed
receptacle (_cf._ fig. 521, A, C), but they correspond closely with
those of several American species. In _Cycadeoidea Gibsoniana_ and _C.
Morierei_ the distal ends of the interseminal scales are much broader
and their diameter greatly exceeds that of the micropylar tubes, 2·8
mm. as compared with 0·25 mm., whereas in _Williamsonia scotica_
the scales are 0·23 mm. broad and the micropylar tubes 0·15 mm. The
mummified micropylar tubes of _W. pecten_ bear a striking resemblance
in form and in the papillose epidermal cells to those of the Scotch
species.
There are two additional points suggested by the structure of the
fertile region, namely the possibility that the megasporophylls are
arrested rather than immature organs and, secondly, the method of
pollination. In regard to the first there would seem to be no adequate
reason for doubting the correctness of the view that the sporophylls
are potentially perfect ovules which were petrified at a comparatively
early stage in development. The dense woolly covering investing the
surface of the scales and megasporophylls recalls an inflorescence
of _Aesculus hippocastanum_ in its winter-fur and hardly suggests a
collection of ovules accessible to microspores. In all probability at a
later stage the protecting bracts with their felt of hairs would bend
outwards leaving exposed the receptive micropyles.
+Microsporophylls.+
In view of the association of microsporophylls and ovulate strobili
in the flowers of _Cycadeoidea_ described by Wieland, most of which
are bisexual, it is reasonable to expect a similar association in the
flowers of _Williamsonia_ which agree closely in the essential features
of both micro- and mega-sporophylls with those of _Cycadeoidea_. It is,
therefore, surprising that in no single case have the microsporophylls
attributed to _Williamsonia_ been found in actual connexion with a
receptacle bearing interseminal scales and megasporophylls. The same
statement holds good with regard to the Williamsonias discovered
in Mexico. Nathorst believes that the microsporophylls on which he
has founded several species are unisexual flowers with the possible
exception of _W. pyramidalis_[1260]. This species, found by Dr Halle
at Cloughton Wyke, is represented by a small ovulate strobilus
characterised by a conical receptacle with a blunt mucronate apex: with
it is associated a microsporophyll bearing synangia. The orientation
of the two specimens is such as to suggest an original connexion.
As Nathorst says, there is, however, no proof that the two belong
to one flower. Wieland[1261], though believing that the existence
of bisporangiate Williamsonia flowers is ‘reasonably certain,’
agrees with Nathorst’s conclusion as to the unisexual character of
_W. spectabilis_ and _W. pecten_. On the other hand, he regards the
microsporophyll-verticil which was first described by Williamson as
a carpellary disc, then named by Nathorst[1262] _W. bituberculata_
and afterwards identified as a microsporophyll-disc closely allied
to _W. whitbiensis_, as the staminate part of _W. gigas_. This view
is, in my opinion, impossible to reconcile with the nature of the
specimen. If, as Wieland suggests, it is the staminal collar split
off from the base of a large ovulate cone like that of _Williamsonia
gigas_, one would expect to find a central space in the middle of the
cupular base large enough to embrace the receptacle. Neither in this
specimen nor in several other forms of microsporophyll-verticils is
there such a central space. It is clear that the discs described as
_W. spectabilis_, _W. whitbiensis_, and other species were not borne
as concrescent collars on a stout axis as are the corresponding organs
in _Cycadeoidea_. The Indian specimen reproduced in fig. 557 and the
very closely allied type _W. setosa_ are incomplete at the centre and
may possibly have been borne at the base of an ovulate bisporangiate
strobilus, but there is no definite evidence that this was the case.
Moreover, in _W. spectabilis_ the lower part of the cup (fig. 551)
easily splits away from the rest of the staminate disc, and this may
explain the central space in the specimen shown in fig. 549, A. If _W.
spectabilis_, to take one example, is a complete flower there are
certain difficulties which are not easily explained: as Nathorst has
shown, in this type there is a short stalk, but in _W. whitbiensis_
the base of the funnel has no stalk and there is no interruption of
the stout lamina at the centre or any indication of a scar. Nathorst
compares the funnel-like region of _W. whitbiensis_ to a kind of
cupule which became detached after flowering[1263]. But a cupule is
supported on an axis and, though no scar is apparent on some of the
more complete specimens, it is obvious that the verticil must have been
supplied with vascular tissue from some axial organ. This brings us to
the consideration of a morphological point which cannot be definitely
answered. Nathorst has previously raised the question—is it possible
that the microsporophylls were attached to the upper part of an ovulate
strobilus; were the flowers bisexual and epigynous? He believes the
answer to be in the negative. Reference has already been made to the
probable occurrence at the apex of the receptacle of _Williamsonia
gigas_ of a funnel-like organ of the type described by Williamson as
‘carpellary disc[1264],’ a term under which Nathorst[1265] believes
that Williamson included two different things,—staminate discs
borne on separate, unisexual, flowers, and sterile organs called
by Lignier[1266] the infundibuliform apparatus. The latter, it is
believed, were attached to the apex of an ovulate strobilus as shown
in fig. 548, comparable in position with the leaves at the summit of
an inflorescence of _Ananas_. A comparison of the fossils regarded as
infundibuliform appendages with some of the microsporophyll-verticils
shows that they are identical in form, the only difference being
that on the former there are no synangia. This fact can hardly be
regarded as negative evidence fatal to the morphological identity of
these sterile and fertile organs. The available evidence, though far
from complete, is favourable to the view that in some _Williamsonia_
flowers, _e.g._ _W. gigas_, the microsporophylls were produced at the
apex of the axis in the position shown in fig. 548. To cite a rough
analogy,—in _Cycadeoidea_ the flower was hypogynous as in _Erica_; in
_Williamsonia_ epigynous as in _Vaccinium_. This view does not exclude
the possibility of the existence of unisexual flowers in some species,
but the evidence in favour of a separation of the sexes is by no means
decisive. Another difficulty is the absence of protective bracts in the
case of the microsporophylls, a striking contrast to the bract-enclosed
ovulate strobili of _Williamsonia_ or to the bract-covered flowers
of _Cycadeoidea_. Were the microsporophylls borne on a separate axis
general considerations would lead us to expect the association of
bracts with the essential organs. The fact that no such association has
been recorded is a fact favourable to the view that the flowers were
bisporangiate.
[Illustration: Fig. 565. A, _Williamsonia spectabilis_,
microsporophyll; B, _W. whitbiensis_, section of sporophyll; C, _W.
mexicana_. (A, B, after Nathorst; C, after Wieland.)]
The student is warned that the opinion expressed with regard to the
position of the microsporophylls is contrary to that which is held by
several palaeobotanists[1267].
_Williamsonia mexicana_ Wieland.
This species is one of the numerous types discovered by Wieland in
Mexico[1268]. It is distinguished by the deep campanulate concrescent
portion of the whorl of microsporophylls and by the ten short free
lobes which bear two rows of lateral synangia (fig. 565, C). Among
the British forms _Williamsonia whitbiensis_ would appear to be the
most closely allied type. _W. mexicana_ occurs in association with
_Otozamites_ fronds, as is the case with an Italian specimen figured by
Zigno[1269], but in the Mexican species there is no conclusive evidence
of organic connexion.
+Other species of Williamsonia.+
_Williamsonia Haydeni_ Seward.
A Jurassic species from Afghanistan[1270] founded on a single specimen
of a flattened broadly-oval flower similar to _W. gigas_ but smaller
and enclosed by narrow linear bracts. An interesting feature is the
occurrence of a funnel-shaped depression at the apex showing radiating
lines on its surface as in the _Williamsonia_ represented in fig. 546,
A. In all probability these lines denote the persistence of a collar
of interseminal scales on the upper part of the elongated conical
receptacle. An examination of the carbonaceous material revealed
the presence of some short rods agreeing in size and shape with the
interseminal scales of other species.
_Williamsonia Otozamitis_ (Zigno).
Zigno[1271] instituted the generic name _Blastolepis_ for some
specimens from the Jurassic rocks of north Italy which he referred to
three species, _B. falcata_, _B. acuminata_, and _B. Otozamitis_. These
are true Williamsonias closely allied to _W. gigas_. An examination of
the type-specimen of _B. Otozamitis_ in the Padua collection led me
to the conclusion that Zigno was correct in representing the ovulate
strobilus, which shows an annular area like that in specimens of _W.
gigas_, as being in organic connexion with an _Otozamites_ frond.
Wieland has recently discovered species of _Williamsonia_ in Mexico
that he correlates with _Otozamites_ leaves.
_Williamsonia_ sp. Seward.
Though by no means satisfactory as a trustworthy record of the genus,
the specimens so designated from the Kimmeridgian of Scotland[1272] are
probably imperfect examples of the genus.
_Williamsonia oregonensis_ Fontaine.
The type-specimen from Jurassic rocks in Oregon[1273] consists of a
stout axis bearing several contiguous linear bracts forming a more or
less spherical cluster 5 cm. broad. The form suggests a _Williamsonia_,
but the evidence is hardly decisive.
_Williamsonia Forchammeri_ Nathorst.
A Bornholm species[1274] from Lower Jurassic strata represented by
an annular zone surrounding a central area, probably a portion of an
ovulate strobilus.
_Williamsonia minima_ Saporta.
This Upper Jurassic species from Portugal[1275] consists of a number of
small bracts or leaves attached to a central axis and is of no value as
evidence of the occurrence of _Williamsonia_.
_Williamsonia problematica_ (Newberry).
This species was first described from the Amboy clays as _Palaeanthus_
(_Williamsonia_) _problematica_[1276] and compared to a Composite
inflorescence with long ray-florets. More recently Hollick[1277] has
referred to this species specimens from the Cretaceous of Long Island
and Martha’s Vineyard, but none of them afford conclusive evidence of
Williamsonian affinity. Some of the examples, as suggested by Hollick,
agree fairly closely with _Williamsonia cretacea_ Heer.
_Williamsonia Smockii_ Newberry.
The curious urn-like bodies from the Amboy clays[1278] on which this
species is based are not unlike the capsules of a _Papaver_ but bear no
real resemblance to a _Williamsonia_.
_Williamsonia Riesii_ Hollick.
A species from the Cretaceous rocks of Martha’s Vineyard[1279] referred
to _Williamsonia_ on rather slender grounds and represented by
imperfect material.
_Williamsonia_ (?) _phoenicopsoides_ Ward.
This fossil from the Cretaceous of the Black Hills, Dakota[1280], is
much too imperfect to be accepted as a record of _Williamsonia_.
_Williamsonia elongata_ Lesquereux.
This species, founded on part of a conical receptacle with some
appendages superficially resembling those of _Williamsonia_[1281], is
too incomplete to be determined with any confidence. The type-specimen
is from Cenomanian beds in Kansas.
_Williamsonia virginiensis_ Fontaine.
This is undoubtedly a true member of the genus; it is characterised by
narrow ovate bracts bearing conspicuous hairs surrounding the base of
a receptacle which shows a portion of an annular zone of interseminal
scales[1282].
_Williamsonia_ (?) _gallinacea_ Ward.
This species from the Potomac beds[1283] is of no value as a record of
_Williamsonia_.
_Williamsonia_ (?) _Bibbinsi_ Ward.
The imperfectly preserved specimen from the Potomac series so named
by Ward[1284] is probably part of an Abietineous cone as stated by
Berry[1285] who includes Ward’s type with other specimens referred to
_Abietites macrocarpus_ Font.
_Williamsonia cretacea_ Heer.
Two specimens, figured by Heer[1286] from the Lower Cretaceous of
Greenland, on which this species is founded, consist of an axis covered
with small scale-leaves and at the broad apex bearing numerous narrow
linear bracts forming a more or less spherical cluster 3·8 cm. in
breadth. The species resembles _W. problematica_ (Newb.).
_Williamsonia recentior_ Dawson.
The specimens from the Middle Cretaceous of Canada figured by
Dawson[1287] under this name are very imperfect and of no botanical
value.
[Illustration: Fig. 566. _Wielandiella angustifolia._ (After
Nathorst.)]
=WIELANDIELLA.= Nathorst.
The specimens on which this genus is founded were originally described
by Nathorst from Höör in Scania as _Williamsonia angustifolia_[1288]:
in a second paper[1289] a restoration of the plant was published (fig.
566). The examination of additional specimens from the Rhaetic of
Bjuf and of cuticular preparations led to the establishment of a new
genus _Wielandia_[1290] for which _Wielandiella_[1291] was afterwards
substituted, _Wielandia_ having been previously employed for an
existing plant. _Wielandiella_ agrees in the general morphology of
its bisporangiate flowers with _Cycadeoidea_, but differs widely from
nearly all other members of the Bennettitales in the repeatedly forked
slender stem which is in marked contrast to the vegetative axis of any
recent Cycad. Among recent Cycads with terminal strobili an indication
of a primitive dichasium is afforded by the occurrence of an aborted
bud in a stem of _Dioon edule_ described by South and Compton[1292];
but in the habit of the stem _Wielandiella_ is far removed from any
recent Cycadean type. The microsporophylls are smaller and simpler than
in _Williamsonia_ or _Cycadeoidea_ and the foliage-leaves are of the
_Anomozamites_ type (_cf._ fig. 615).
[Illustration: Fig. 567. _Wielandiella angustifolia._ Branched stem
and receptacle. (After Nathorst.)]
_Wielandiella angustifolia_ Nathorst.
In an account of this species in 1902 Nathorst described two types of
strobilus, male and female, but a re-investigation of the material led
to a modification of the earlier conclusions. The stem is slender,
rarely exceeding 1·5 cm. in breadth, repeatedly branched as a dichasial
system with a fertile shoot in the forks formed by the equal and
widely divergent branches. Nathorst’s restoration, as he points out,
may exaggerate the regularity of the branching, but an examination of
the original specimens in the Stockholm Museum convinced me that the
habit represented in fig. 566 is substantially correct. The method of
branching is similar to that in the inflorescences of Gnetalean plants
and recalls some _Gleichenia_ fronds. The surface of the thicker pieces
of stem shows fine longitudinal striae, while transverse striations
like those on the axis of a _Heterangium_ frond characterise the
more slender specimens. Closely set polygonal leaf-scars cover the
stem for a short distance below each bifurcation and the surface of
the short and relatively stout peduncles of the strobili (fig. 567).
Though for the most part confined to the region of false dichotomy,
leaf-scars occasionally occur on other parts of the stem. Small
fronds, 7–8 cm. long, agreeing closely with _Anomozamites minor_
Brongn., occur in the same beds at Bjuf, and the striking resemblance
between their long linear and winged petioles and the transversely
striated bracts enclosing the strobili of _Wielandiella_ amply
justifies Nathorst’s conclusion that _Wielandiella_ bore fronds of the
_Anomozamites_ form[1293]. Small scars marking the position of bracts
occur immediately below each strobilus and occasionally form narrow
zones between the larger foliage leaf-scars. The strobili are met with
in two forms representing two states of preservation and, probably,
different ages. In one form the strobilus consists of a small pyriform
axis separated from the peduncle by an annular swelling characterised
by parallel striations (fig. 567), the so-called palisade-ring. From
this ring Nathorst obtained many microspores scattered and in groups
on the surface of short sporophylls, 2·5–3 mm. in length. It is these
sporophylls which form the parallel striations; they occur as a circle
of rather broad linear organs with irregularly toothed distal ends and
an epidermis of papillose cells. The oval microspores, 32–42μ long,
vary in size and, as Nathorst says, this may indicate immaturity. The
precise mode of occurrence of the spores has not been ascertained, but
they were probably produced in sporangia on the surface of the small
microsporophylls. These strobili have in all probability lost the
female organs which were borne on the pyriform axis, and the inference
is that the strobili were protogynous. Thomas[1294] compares the ring
at the base of the flower-axis from which spores were obtained by
Nathorst to the whorl of microsporophylls of _Williamsoniella_, but
in _Wielandiella_ the sporophylls are greatly reduced and possibly
functionless. _Wielandiella_ may be intermediate between the bisexual
_Williamsoniella_ and the unisexual _Williamsonia scotica_. In the
second form of strobilus the pyriform axis is hidden and the specimens
consist of a central ovate body, approximately 3 cm. long, surrounded
by several linear bracts (fig. 568, A). The carbonised surface of the
central region revealed on chemical treatment a fairly regular pattern
formed by the contiguous polygonal ends of interseminal scales arranged
round smaller cylindrical micropylar tubes which project beyond the
level of the scales (fig. 568, B). This arrangement agrees closely with
that of the corresponding organs in _Williamsonia_ and _Cycadeoidea_
(_cf._ figs. 515, 564). In _Wielandiella_ the micropylar tubes are of
uniform diameter and the cells of the epidermis have smooth walls in
contrast to the micropylar tubes of _Williamsonia_ (fig. 563). The
strobilus in this state, before the scales and ovules have become
detached from the axis, may be described as a small _Williamsonia_, but
the habit of the stem is in itself a sufficient reason for the use of a
distinctive generic name[1295].
[Illustration: Fig. 568. _Wielandiella angustifolia._ A, conical
receptacle with bracts. B, surface-view of scales and micropylar tubes.
(After Nathorst; A, ¾ nat. size.)]
A second species, _Wielandiella punctata_, described by Nathorst[1296]
from Scania is founded on pieces of forked stems associated
with fragments of a palisade-ring formed of contiguous segments
(microsporophylls) with microspores 58μ in length. Fronds of
_Anomozamites minor_ occur in the same beds.
Mr Hamshaw Thomas[1297] described some specimens from the Middle
Jurassic beds of Marske in Yorkshire which he suggested might be pieces
of a _Wielandiella_ stem. Additional material was subsequently found
and this enabled Thomas to produce evidence in favour of connecting the
branched vegetative axis with bisporangiate strobili and the fronds of
_Taeniopteris vittata_. For the stems and flowers the new designation
_Williamsoniella_ has been proposed. Further research will no doubt
show that the _Wielandiella_ type of stem was not exceptional in
Rhaetic and Jurassic floras.
Nathorst[1298] suggests the possibility that some specimens from the
Solenhofen Slates described by Thiselton-Dyer[1299] as _Condylites
squamatus_ may be allied to _Wielandiella_. The generic name
_Condylites_ was suggested by the elbow-like branching of stems which
bore imperfectly preserved and apparently terminal cones; the surface
of the branches is covered with the scars of leaves. The resemblance to
_Wielandiella_ is, however, slight and it would seem more probable that
the Solenhofen fossils are Coniferous, though, as Nathorst says, the
supposed scale-like ‘leaves’ may be scars of Cycadean fronds.
Wieland[1300] records the occurrence in Mexico of stems similar to
those of _Wielandiella_ associated with some _Otozamites_ fronds.
=WILLIAMSONIELLA.= Thomas.
This genus was instituted for specimens discovered by Mr Hamshaw
Thomas[1301] in the Middle Estuarine series of the Middle Jurassic
plant-bed at Gristhorpe on the Yorkshire coast, and the genus is
recorded also from the Cleveland district in the same county.
_Williamsoniella_ occurs in those parts of the Gristhorpe bed where
fronds of _Taeniopteris vittata_ are abundant.
_Williamsoniella coronata_ Thomas.
The type-species is represented by fertile shoots consisting of a
central axis bearing both megasporophylls and microsporophylls (figs.
569, 571, A). Below its crown-like sterile apex the pyriform peduncle
is covered with small interseminal scales and ovules similar to those
of _Williamsonia_: this portion is 6 mm. in diameter and 1 cm. long.
A whorl of separate cuneate microsporophylls forms a hypogynous ring
below the basal interseminal scales: each sporophyll is attached by
a narrow base (fig. 570) and bears 5–6 reniform synangia containing
microspores. The flower is thus bisexual: it affords no conclusive
evidence of the occurrence of any covering bracts like those of most
Bennettitalean flowers. In young specimens the microsporophylls are
closely packed round the axis (fig. 571, B). The flower-stalks reach
a length of 3·5 cm. and are 3 mm. in diameter. Fig. 571, C, shows a
receptacle from which the sporophylls have fallen: the microsporophylls
having been no doubt attached to the collar-like swelling at the base.
Towards the apex the axis becomes broader and at _s_ a few interseminal
scales are left: above these is the apical disc (corona) characterised
by longitudinal ribs. An apical disc is reproduced in fig. 572; it
has the form of a royal crown 1–2 mm. high with 12–16 vertical ridges
separating flat surfaces formed by the pressure of microsporophyll
apices in the unexpanded flower. The corona is surmounted by a small
conical elevation which represents the apex of the fertile axis. An
apical view of an unexpanded flower is shown in fig. 571, B; the
tips of 12 sporophylls are closely pressed against the corona which
probably consists in part at least of fused interseminal scales. The
microsporophylls were shed after the dehiscence of the synangia. Each
sporophyll is flattened on the sides and thicker on the curved outer
edge; the synangia, usually in two rows of three, are borne on the
sloping sides (figs. 569, 570). The surface of a microsporophyll is
covered with small rounded projections which produce a characteristic
appearance. The form of a microsporophyll in section is shown in fig.
570: the synangia are similar in shape to those of _Cycadeoidea_ and
_Williamsonia_ (_cf._ figs. 531, 549, etc.) but there are no external
indications of septa like those seen in some other types. On macerating
some specimens it was found that the spores occur in about 20 groups.
The circular or elliptical spores are 0·02 mm. in diameter. The walls
of the epidermal cells of the microsporophylls are straight: the
stomata, which show the features characteristic of the Bennettitales,
agree closely with those of _Taenopteris vittata_.
[Illustration: Fig. 569. _Williamsoniella coronata._ Vertical section
of the flower showing the pyriform axis with small megasporophylls and
interseminal scales and the microsporophylls with synangia. (After
Thomas; × 2.)]
[Illustration: Fig. 570. _Williamsoniella coronata._ Diagrammatic
sketch of a microsporophyll in section and in side-view. (After Thomas;
× 3.)]
[Illustration: Fig. 571. _Williamsoniella coronata._ A, flower
showing two microsporophylls and the central axis with megasporophylls.
B, apical view of an unexpanded flower. C, flower-axis showing the
shallow grooves made by the infolded microsporophylls, which have
fallen, and a few megasporophylls, _s._ (After Thomas; A, × 1⅓; B, C, ×
3.)]
[Illustration: Fig. 572. _Williamsoniella coronata._ Apical disc with
megasporophylls and interseminal scales at the base. (After Thomas; ×
3.)]
The interseminal scales associated with the ovules and covering the
pyriform axis above the microsporophylls are more or less flattened
and hexagonal and the micropylar tubes often project far beyond
the scales. Each micropyle-tube is surrounded by 5–6 interseminal
scales (_cf._ fig. 564). The ovules differ from those of _Cycadeoidea
Gibsoniana_ in the absence of a distinct pedicel and agree with the
corresponding organs of _Williamsonia scotica_[1302]. In the absence of
epidermal papillae the micropylar tubes resemble those of _Wielandiella
angustifolia_. As already stated, the flowers appear to be without
protective bracts, but in the shale from which the specimens were
obtained a few bract-like organs were discovered consisting of a
lanceolate lamina 1·5 cm. long, and 2–3 mm. broad near the base,
and some showed a small oval lamina at the apex with a midrib and
dichotomously branched lateral veins. These bracts with the terminal
lamina are regarded by Thomas as almost certainly reduced leaves of the
_Taeniopteris vittata_ type: they are represented in the restoration
(fig. 573) as occurring at the base of the flower-peduncle. Stomata
were found on the bracts exactly like those on the microsporophylls,
and this affords a strong argument in support of the view that
_Williamsoniella_ belongs to the plant which bore _Taeniopteris_
fronds. There is a close parallelism between the bracts accompanying
_Williamsoniella_ flowers and those described by Nathorst in connexion
with _Wielandiella_[1303]. It seems reasonable to regard the bracts as
serving the purpose of bud-scales.
[Illustration: Fig. 573. _Williamsoniella coronata._ Restoration
of part of a plant: the upper leaves are represented only by the
petiole-bases. (After Thomas; _ca._ ⅜ nat. size.)]
An important point is the constant association with the flowers of
_Taeniopteris vittata_ fronds, a species described in Vol. +ii.+ and by
most palaeobotanists regarded as a Fern frond. _Taeniopteris_ leaves
occasionally show a clean-cut base[1304] and in specimens described
by Thomas there are two small humps on the surface of the proximal
end of the petiole which represent vascular bundles. Humps of similar
size occur on the leaf-scars of stems which are believed to have borne
both _Taeniopteris_ leaves and _Williamsoniella_ flowers. Fragments
of the stems were found in association with flowers: they are 7 mm.–2
cm. in diameter and frequently forked and there is evidence that the
flowers were borne at the forks, the shoot forming a dichasial system.
The habit of the plant is represented in fig. 573 reproduced from Mr
Thomas’s paper.
_Williamsoniella Lignieri_ (Nathorst).
This species described by Nathorst as _Williamsonia_? _Lignieri_ from
Whitby is regarded by Thomas as a _Williamsoniella_. The stomata on
the microsporophylls agree with those of _Taeniopteris_ and the spores
obtained from Nathorst’s flower-buds are like those of _Williamsoniella
coronata_. Evidence is adduced by Thomas in favour of regarding _W.
Lignieri_ as bisexual and not unisexual as Nathorst supposed.
In habit _Williamsoniella_ resembles _Wielandiella_: in the latter
genus the foliage-leaves were confined to portions of the stem near
the forks, while in _Williamsoniella_ they were more uniformly
scattered: _Wielandiella_ bore leaves of the _Anomozamites_ form while
_Williamsoniella_ flowers are always associated with _Taeniopteris_
fronds. The much greater spore-output of _Williamsonia_ may, it is
suggested by Thomas, be correlated with the unisexual nature of the
flowers of that species. The microsporophylls of _Williamsoniella_
differ in their more reduced form from the pinnate microsporophylls of
_Williamsonia_, _e.g._ _W. spectabilis_, and agree more closely with
those of _Wielandiella_. The microsporophylls of _Williamsoniella_
are free and not connate at the base as in _Cycadeoidea_ and
_Williamsonia_. In its pyriform axis _Williamsoniella_ resembles
_Williamsonia gigas_ and differs from _Williamsonia Leckenbyi_ in
the possession of a sterile apical corona: _Williamsoniella_ has
megasporophylls and microsporophylls both of which appear to be
functional, while in _Cycadeoidea_ fully developed microsporophylls
occur in association with megasporophylls which are immature and must
have matured much later than the microsporophylls. The new genus
agrees with _Williamsonia_ in its general features, but the flowers
are smaller and are characterised by the considerable reduction and
simplification of the male organs.
=CYCADOCEPHALUS.= Nathorst.
This genus was founded[1305] on a specimen from the Lower Rhaetic
of Scania, at first regarded as a megastrobilus and on further
examination[1306] found to be a collection of microsporophylls
resembling those of _Williamsonia_ and _Cycadeoidea_. The type-species
is _Cycadocephalus Sewardi_, and a second species, _C. minor_, was
subsequently discovered by Dr Halle at a slightly higher horizon in
the Rhaetic series. Prof. Nathorst’s most recent account of the genus
affords a striking illustration of the possibilities of the method,
which he has employed with conspicuous success, of investigating
carbonised fossils by means of cuticular preparations.
[Illustration: Fig. 574. _Cycadocephalus Sewardi._ A, surface-view;
_a_, appendages. B, the same specimen, after the removal of some
of the microsporophylls, showing the appendages. C, section of a
microsporophyll showing the attachment of appendages. D, section of an
appendage. (After Nathorst. A, B, ¾ nat. size.)]
_Cycadocephalus Sewardi_ Nathorst.
The type-specimen consists of an oval cluster of 16–18 linear
microsporophylls, 9 cm. long, springing from a small circular disc
formed of their concrescent and narrow bases. The whole flower (fig.
574) exclusive of the peduncle is 10 cm. long and 7 cm. broad. The
portion of the comparatively slender peduncle that is preserved shows
no trace of leaf-scars. In the middle of each linear microsporophyll
is a keel-like midrib and on either side of this is a series of linear
appendages (fig. 574) 2–3 cm. long lying in a radial direction towards
the centre of the flower. These appendages were originally thought to
be seeds (fig. 574, _a_), but it was suggested by Wieland that they
might be synangia, the circle of leaves being the male portion of a
bisexual flower of the _Cycadeoidea_ type. Nathorst’s more complete
investigation of the specimen confirmed the first of these suggestions,
but there is no evidence that there was an ovulate receptacle in the
centre of the flower. The appendages are attached by a rather broad and
slightly cordate base and are represented by a thin carbonised cuticle
of rectangular cells showing in one case a row of imperfectly preserved
stomata: on this are numerous groups of tetrahedral microspores, about
55μ in diameter, which show a more or less well marked arrangement in
rows transverse to the long axis of the thin laminae. It is clear from
Nathorst’s researches that the groups were enclosed in loculi bounded
by thin-walled cells[1307], the loculi being in transverse rows on
each side of a midrib. Nathorst speaks of the appendages as synangia
characterised by the large number of the sporogenous compartments,
and he compares them especially to the fertile leaflets of _Danaea
elliptica_ as described by Bower[1308], each appendage being comparable
with a revolute _Danaea_ pinnule in which the edges of the lamina
are united. This is illustrated by the section of an appendage (fig.
574, D) reproduced from Nathorst’s restoration of a _Cycadocephalus_
microsporophyll. From a morphological point of view it would seem more
appropriate to speak of the appendages as highly modified pinnules
rather than synangia. The second species, _C. minor_, agrees closely
except in its smaller size with the type-species. Nathorst regards
_Cycadocephalus_ as a unisexual flower differing from those of
_Williamsonia_ and from the microsporophyll-verticils of _Cycadeoidea_
in the structure of the synangia and in the tetrahedral form of the
spores, though the latter feature he considers to be of secondary
importance, as both bilateral and radial spores occur in recent
Marattiaceae. He includes the genus in the Bennettitales but suggests
that it should be referred to a separate family as an indication of
the possession of characters which mark it off from _Williamsonia_,
_Weltrichia_, _Wielandiella_, and _Cycadeoidea_.
=WELTRICHIA.= Braun.
The name _Weltrichia_ was given by Braun[1309] to some Rhaetic fossils
discovered by Weltrich near Culmbach in Franconia which represent
funnel-shaped structures, the lower part having the form of an
incomplete cup made of the concrescent bases of about 20 broadly
linear segments which in the upper part are separate lanceolate
lobes each with a midrib and slightly curved inwards at the apex.
The whole, nearly 10 cm. long and 9 cm. in diameter at the upper
edge, is very similar to the specimen of _Williamsonia spectabilis_
reproduced in fig. 551. Braun described three species, but he realised
the possibility that the different forms may be different stages in
the development of a single type _Weltrichia mirabilis_. He assigned
the genus to the Rhinantheae. Saporta[1310] drew attention to the
resemblance of Braun’s species to some examples of _Williamsonia_ from
Yorkshire which he considered to be portions of a sterile appendage
borne at the apex of the flower. Some account is given of two types
of funnel-like structures connected with _Williamsonia_ flowers on a
previous page[1311]: one of these has been shown by Nathorst to be
a whorl of microsporophylls, and it is with this that _Weltrichia_
agrees. An important feature of _Weltrichia_ is the occurrence of short
linear segments, 5–8 mm. long, attached to the inner face of each of
the free portions of the linear lobes: the lobes, or more correctly
the free apical portions of the fertile leaves, and their slender
appendages are compared by Nathorst[1312] to the microsporophylls and
relatively long synangia-bearing appendages of _Cycadocephalus_. These,
presumably fertile, segments of _Weltrichia_ project in the flattened
impressions beyond the edges of the free lobes of the campanulate
flower and look like marginal teeth, though they are actually
attached on each side of the midrib and originally extended, as in
_Cycadocephalus_, towards the centre of the funnel-shaped flower. The
examination of one of the type-specimens acquired by Nathorst[1313] for
the Stockholm Museum enabled him to confirm his earlier conclusion that
_Weltrichia_ represents the male portion of a flower, whether unisexual
or bisexual cannot be definitely determined, of a Bennettitalean
plant. There is, as Nathorst states, a close agreement in plan between
_Weltrichia_, _Cycadocephalus_, and _Williamsonia_, and indeed it is
not clear in what respects _Weltrichia_ is sufficiently distinct from
_Cycadocephalus_ to be retained as a separate genus. Our knowledge
of _Weltrichia_ is, however, less complete than in the case of
_Cycadocephalus_ and _Williamsonia_. It is noteworthy that Braun’s
specimens and those on which _Cycadocephalus_ was founded were obtained
from Rhaetic rocks. An account of _Weltrichia_ has also been published
by Schuster[1314] who differs from Nathorst in his interpretation of
the type-specimens: he considers that another fossil described by
Braun and named by him _Palaeoxyris microrhombea_ is the central,
female, portion of a _Weltrichia_ flower, a view that is not supported
by any substantial evidence. The specimens referred by Braun to
_Palaeoxyris_ and afterwards transferred by Schimper[1315] to the genus
_Lepidanthium_ are too obscurely preserved to be determined with any
degree of confidence, and their connexion with _Weltrichia_ is purely
hypothetical. With _Weltrichia_ Schuster also connects the fronds
known as _Otozamites brevifolius_ Braun and some impressions of stems,
combining all in a restoration of a complete _Weltrichia_ plant which
rests more on imagination than on fact. Attention has elsewhere[1316]
been called to some wholly misleading and incorrect statements made by
Schuster which vitiate the value of his descriptions.
Saporta[1317] described a species of _Weltrichia_, _W. Fabrei_. from
French Rhaetic strata at Mende (Lozère) which bears at least a close
superficial resemblance to _Williamsonia spectabilis_, and the same
author founded another species, _Weltrichia oolithica_, on a drawing by
Zigno of a specimen from Jurassic rocks in Italy; but this appears to
be too imperfect for accurate identification.
All that can be said as to the nature of _Weltrichia_, as illustrated
by the type-species, is that it represents a Rhaetic example of a
verticil of microsporophylls very similar to those of _Williamsonia_
and _Cycadocephalus_, if not generically identical with the latter form.
CHAPTER XXXVIII.
CYCADOPHYTA.
+I. Cycadean Stems other than Cycadeoidea.+
Most of the stems now under consideration are represented by casts
or impressions and afford no information with regard to anatomical
characters. They are in many cases more slender and less tuberous than
typical Cycadeoideas, and a few are characterised by an irregular
form of branching, as is shown in some specimens of pith-casts from
Wealden strata in Tilgate Forest figured by Mantell[1318] and now in
the British Museum. The genus _Wielandiella_[1319] (fig. 566) is an
altogether distinct type represented by flowers as well as vegetative
organs. Several generic names have been proposed for Cycadean stems
agreeing with those of many recent Cycads in the possession of an
armour of persistent leaf-bases, but distinguished from _Cycadeoidea_
in the absence of any fertile lateral shoots intercalated among the
petiole-bases. It is, however, impossible in most cases to give any
satisfactory definition by which these genera can be distinguished
from one another; the characters employed by Carruthers[1320],
Saporta[1321], and other authors are of comparatively little
importance as trustworthy criteria and to a large extent are merely
the expression of different states of preservation or of differences
in age. Attention has elsewhere been called to the absence of any
clear dividing line between stems referred to _Bucklandia_, _Yatesia_,
_Fittonia_ and _Cylindropodium_. The species _Cycadeoidea gigantea_
described on a previous page affords an instructive example of the
difficulty of drawing a generic distinction between certain types of
Cycadean stems: in habit, in the form and structure of the leaf-bases,
and in the ramenta this species is identical with other species of
_Cycadeoidea_, but it differs in the absence of lateral fertile shoots,
a feature that may have no morphological significance. It has already
been pointed out that the absence of flowers intercalated among the
leaf-bases may simply mean that the plant had not reached the stage of
flower-production, or their absence may be due to some unfavourable
conditions. Similarly the stems for which Saporta proposed the generic
name _Clathropodium_ agree in every respect with _Cycadeoidea_ except
in the absence, apparent or real, of lateral flowering branches.
Such types as _Clathropodium foratum_ Sap. and _C. sarlatense_
Sap.[1322], the latter probably from Upper Jurassic beds and the
former from an unknown locality, should be included in the genus
_Cycadeoidea_. The stem referred by Saporta to his genus _Platylepis_
as _P. micromyela_[1323] was originally assigned to _Cycadeoidea_ and
more recently Lignier has wisely adopted the original generic name.
The generic term _Bolpopodium_, also instituted by Saporta[1324], is
applied to small tuberous stems which appear to be identical with the
_Cycadeoidea_ type.
Having regard to the meagre data supplied by casts of stems preserved
in various stages of defoliation, and in view of the impossibility
of drawing other than purely arbitrary generic distinctions, it is
preferable to employ one generic name in a liberal sense for stems
that there is good reason to regard as plants that cannot reasonably
be referred to _Cycadeoidea_. The name _Bucklandia_ is thus employed,
and a few examples are described in illustration of the external
features of stems that are undoubtedly Cycadean but in most cases
readily distinguished from _Cycadeoidea_. There are substantial grounds
for stating that plants which bore flowers of the _Williamsonia_
type possessed stems having the characters of _Bucklandia_. It
should, however, be remembered that we cannot always draw a clearly
defined distinction between flowers included in _Williamsonia_ and
_Bennettites_, or _Cycadeoidea_, particularly when they are represented
only by detached ovulate strobili as in _Cycadeoidea_ (_Bennettites_)
_Morierei_ and _Williamsonia scotica_.
=BUCKLANDIA.= Presl.
_Bucklandia_ was proposed by Presl[1325] for a plant described by
Mantell[1326] from the Wealden of Tilgate Forest and compared by him
to the Euphorbiaceae and arborescent Ferns; the same generic name was
given by Robert Brown in 1832 to a recent member of the Hamamelidaceae.
Stokes and Webb[1327] referred the same fossil to _Clathraria_, a name
applied by Brongniart[1328] to certain types of Sigillarian stems and
afterwards adopted by him for the Tilgate Forest species, _C. Lyelli_.
Presl ‘with remarkable discrimination’ recognised the Cycadean nature
of the specimen. Carruthers[1329] in his definition of _Bucklandia_
includes a statement as to the nature of the carpellary leaves and
suggests that a cone associated with the stems may be a staminate
strobilus: the cone is undoubtedly a megastrobilus of an Araucarian
plant and there is no evidence with regard to the nature of either the
male or female reproductive organs in the material that he describes
though, as already pointed out, there are reasons for believing
that _Williamsonia_ flowers were borne on branches of _Bucklandia_
stems. The flowering shoots were not short and intercalated among
the petiole-bases as in _Cycadeoidea_ with the strobili barely
projecting beyond the surface of the leaf-base armour, but they formed
comparatively long branches, sometimes forked, at the apex of the main
stem (_cf._ figs. 541–543).
_Bucklandia_ is usually represented by casts, from Rhaetic to Lower
Cretaceous strata, differing from _Cycadeoidea_ in the absence of
numerous axillary short fertile shoots, in the more slender form and
greater length of the stems, and in the less uniform size of the
persistent leaf-bases which assume various forms. Some of the specimens
reach a length of 4 feet and afford evidence of occasional branching:
the surface is covered with leaf-bases preserved as imbricate, broad,
and obtuse or truncate scales (fig. 575), or as slightly convex
polygonal areas in some cases showing a tendency towards an irregular
zonal arrangement of larger and smaller leaf-bases (fig. 576). Within
the armour of leaf-bases there may be a cast of the large pith the
surface-features of which are practically identical with the cast of
a recent pith reproduced in fig. 398. Casts of the pith preserved as
separate fossils are included in the genus _Cycadeomyelon_.
There is evidence of the occurrence of more than one zone of vascular
tissue in a stem from Lower Greensand beds of Bedfordshire described by
Carruthers as _Yatesia Morrisii_[1330] (= _Bucklandia Yatesii_), and
Dr Stopes[1331] has recently described a species, _B. buzzardensis_
(fig. 578), with several zones of conducting tissue. This feature has
not so far been satisfactorily demonstrated in _Cycadeoidea_. An Indian
species, _Bucklandia indica_, shows that the secondary xylem is more
compact than in typical _Cycadeoidea_ stems, and the tracheids have
multiseriate pitting.
Two long and narrow stems figured by Nathorst from the Rhaetic of
Scania as _Bucklandia Saportana_[1332] differ from other species in
the irregular arrangement of the leaf-bases which in certain regions
are crowded as in the typical example of the genus shown in fig. 576,
but in the intervening portions of the stem they are few in number
and widely separated by the finely striated bark. This type, though
similar to some specimens of English, Mexican, and Indian Bucklandias
in the zonal differences in the leaf-bases, represents an extreme case
of the alternation of smaller and crowded and larger and scattered
leaf-scars. It is by no means unlikely that _Bucklandia Saportana_
forms a transition between _Bucklandia_ and the stem of _Wielandiella_
described by Nathorst from the same region: in _Wielandiella_ the
leaf-scars are concentrated at the region of forking but a few occur
elsewhere: in _B. Saportana_ there is no evidence of branching and in
this respect it differs from _Wielandiella_.
_Bucklandia anomala_ (Stokes and Webb).
This species, from Wealden beds in Sussex, was first described by
Stokes and Webb[1333] as _Clathraria anomala_, and the same type was
figured by Mantell and other authors as _Clathraria Lyelli_. The
specimens referred by Carruthers to _Bucklandia anomala_ and _B.
Mantelli_[1334] do not exhibit any well defined specific differences,
and there would seem to be no reason for retaining both specific
names. The petiole-bases are usually sub-rhomboidal in form and convex
or flat, but in some stems more of each petiole is preserved and the
surface is covered with broad imbricate scales (fig. 575) similar
to some of the detached scales described under the generic name
_Cycadolepis_. Pith-casts occur both in connexion with the _Bucklandia_
stems and as detached specimens. The leaf-bases often show an irregular
zonation of smaller and larger rhomboidal areas. The pith-cast in the
lower part of the specimen from the Wealden of Cuckfield in Sussex
shown in fig. 575 is 5 × 3·5 cm. in diameter.
[Illustration: Fig. 575. _Bucklandia anomala._ (British Museum, No.
V. 3690; rather less than natural size.)]
_Bucklandia Ruffordi_ Seward.
This species, from the Wealden beds on the Sussex coast[1335], was
originally described as _Fittonia Ruffordi_, but in the absence of
any well defined distinctive features that can be regarded as of
morphological significance it is better to include it in _Bucklandia_.
The species affords a good example of a long and narrow type of stem,
one specimen reaching a length of nearly 80 cm. with a breadth of
about 10 cm.; the surface is covered with persistent leaf-bases 1·7
cm. in depth with a scar agreeing in size and shape with the base of
a frond of _Otozamites Goeppertianus_ (Dunk.)[1336] found in the same
beds. There is no indication of any alternation of large and small
leaf-bases, and the species is characterised by the uniform size and
relatively greater depth in a vertical direction of the leaf-base
areas. In all probability the stem bore fertile branches similar to
those of _Williamsonia gigas_ with flowers of the _Williamsonia_ type:
the fronds may have been those known as _Otozamites Goeppertianus_, but
this has not been demonstrated. A stem described by Carruthers from the
Lias of Lyme Regis as _Yatesia gracilis_[1337] and afterwards included
by me in _Cycadeoidea_[1338] is very similar to _B. Ruffordi_ in its
long and narrow form and in the shape of the leaf-bases; it should be
transferred to _Bucklandia_ as _B. gracilis_ (Carr.).
_Bucklandia Milleriana_ Carruthers.
This species was founded on a cast from Lower Oolite beds at Brora
in Sutherlandshire[1339] characterised by leaf-bases very similar to
those of _B. anomala_ but smaller. Casts from the same locality were
named by Carruthers _Yatesia crassa_ and _Y. Joassiana_[1340], but an
examination of specimens in the Dunrobin Museum leads me to regard
these forms as indistinguishable from _B. Milleriana_. The specimen
reproduced in fig. 576 from the Great Oolite of Brora illustrates the
external characters of a typical stem and shows the variation in the
size of the leaf-bases. A portion of the pith-cast is exposed in the
lower part of the stem.
[Illustration: Fig. 576. _Bucklandia Milleriana._ Brora, Scotland.
(Manchester Museum, L. 7229. _ca._ ½ nat. size.)]
_Bucklandia Yatesii_ (Carruthers).
This type from the Lower Greensand of Bedfordshire (fig. 577) was
described by Carruthers as _Cycadeoidea Yatesii_ and subsequently
named _Yatesia Morrisii_[1341]. Ward expressed the opinion that the
name should be _Yatesia Yatesii_, but as _Bucklandia_ is now used
to include _Yatesia_ this combination is fortunately avoided. The
stem is cylindrical, 20–30 cm. long and 12 cm. in diameter, covered
with rhomboidal leaf-bases separated from one another by a ramental
reticulum. There are two concentric vascular cylinders as stated by
Carruthers. In a recent account of this species Dr Stopes[1342] adds
further details: the xylem-cylinders are 5–8 mm. wide and the tracheids
occur in single rows or there may be bands 4–5 elements broad; the
circular bordered pits are uniseriate or in two alternate series.
The medullary rays are broad but the cells are not preserved. The
pith-cast is of the usual Cycadean type.
[Illustration: Fig. 577. _Bucklandia Yatesii._ Type-specimen in the
British Museum.]
The type-specimen was presented by the Cirencester College to the
British Museum.
_Bucklandia buzzardensis_ (Stopes).
[Illustration: Fig. 578. _Bucklandia buzzardensis._ Rough sketch of a
block of wood showing parts of at least eight concentrically arranged
rings of secondary wood. (After Stopes; × ⅔.)]
This species, from Lower Greensand beds at Leighton Buzzard and
believed to be derived from Wealden strata, is described by Dr
Stopes[1343] as _Cycadeoidea buzzardensis_. Though agreeing generally
with _B. Yatesii_, the stem is specifically separated on the ground
that the petiole-bases are more expanded laterally and because of the
occurrence of several vascular cylinders (fig. 578), sometimes as many
as eight, each with a maximum diameter of 1 cm. Dr Stopes thinks it
possible that _B. buzzardensis_ is an older form of _B. Yatesii_.
_Bucklandia squamosa_ (Brongniart).
Sternberg first described this species as _Conites Bucklandi_[1344] and
regarded it as a cone bearing large imbricate cone-scales; it was named
by Brongniart _Bucklandia squamosa_[1345] and Carruthers[1346] retained
this designation. The type-specimen, in the Oxford Museum, from the
Stonesfield Slate is 18 cm. long, showing in the lower part a cast
of the pith. The surface of the stem is covered with thick imbricate
petiole-bases very like those on the stem of a recent _Encephalartos_.
_Bucklandia_ (_Fittonia_) _squamata_ (Carruthers).
Carruthers[1347] founded the genus _Fittonia_ on a single specimen from
the Wealden beds of the Isle of Wight, separating it from _Bucklandia_
on the ground of the occurrence on a portion of the stem of large
imbricate leaf-bases which are at first reflexed and then ascending;
the stem is also broader and more tuberous than most species of
_Bucklandia_. The type-specimen, in the Museum of the Geological Survey
(Jermyn street), bears a close resemblance to a trunk of a recent
_Encephalartos_, but the part of the stem from which the imbricate
stumps have fallen is practically identical with a _Bucklandia_.
As in certain recent Cycads the surface-features probably changed
with the age of the plant; when the foliage-leaves were first shed
a portion of the ascending petiole remained on the stem, and at a
later stage this was cut off leaving a clean-cut rhomboidal scar like
those on the _Bucklandia_ shown in fig. 576. The difference between
_Fittonia_ and _Bucklandia_ may, therefore, be a question of age. While
substituting _Bucklandia_ for _Fittonia_ as the generic name the latter
designation is added in parentheses to denote the possession of certain
features which, though possibly of generic value, are not regarded as
sufficiently important morphologically to warrant generic recognition.
The type-specimen of Saporta’s species _Fittonia insignis_[1348],
in the Paris Museum, from the Oxfordian of Poitiers, appears hardly
distinguishable from _F. squamata_ Carr. Another type with broader
imbricate petiole stumps is described by Saporta from the Portlandian
near Boulogne as _Fittonia Rigauxi_[1349].
[Illustration: Fig. 579. _Bucklandia indica._ A, side-view showing
the leaf-bases and attached petioles of _Ptilophyllum_, also (to the
left) a fragment of a detached _Ptilophyllum_ leaf. B, transverse
section showing the pith, xylem cylinder, cortex, and sections of
petioles. (British Museum; nat. size.)]
_Bucklandia indica_ sp. nov.
Oldham and Morris[1350] and subsequently Feistmantel[1351] described
some specimens of Cycadean stems from the Rajmahal Hills of India
of Lower Jurassic age: the latter author regarded them as stems of
_Williamsonia_ because of their association with flowers of that
type, a conclusion fully justified by the evidence. Feistmantel also
called attention to the resemblance of the Indian stems to specimens
described from British strata as _Bucklandia_ and _Yatesia_. Although
the Indian examples are very similar to stems from Mexico discovered
by Wieland[1352] and to some of the English types, it seems desirable
to refer to them under a specific name and I therefore suggest the
institution of the specific name _indica_, the type-specimen being that
represented in fig. 579. This specimen is particularly interesting
because it affords some information as to anatomical features and
is one of the few fossil stems preserved in organic connexion
with leaves (fig. 579, B). A short account of it was published in
1900[1353] and more recently Miss Bancroft[1354] has made a fuller
investigation of this and other Indian specimens. The stem shown in
fig. 579 from the Rajmahal Hills, and now in the British Museum, bears
fronds of _Ptilophyllum cutchense_ Morr., a type that appears to be
indistinguishable from _P. pecten_; and with similar stems from the
same beds are associated flowers of _Williamsonia_. Miss Bancroft
describes a bract-covered shoot which agrees very closely with those of
English stems reproduced in figs. 541, 542. In addition to the evidence
based on close association, there is the more important argument
furnished by the discovery of ramental hairs like those on the bracts
of _Williamsonia scotica_ and of anatomical characters in the bracts
similar to those in the Scotch strobilus. The persistent leaf-bases
are far from uniform in size; in this respect and in their form they
agree closely with those on _Bucklandia_ stems from English and Mexican
localities. The secondary wood is more compact than in recent Cycads or
in _Cycadeoidea_, though it resembles that of _Cycadeoidea micromyela_;
the medullary rays are uniseriate and the tracheids have multiseriate
bordered pits on their radial walls instead of the scalariform pitting
in the majority of _Cycadeoidea_ stems. Secretory canals are abundant
in the parenchymatous ground-tissue; the cambium and phloem are not
preserved[1355].
The transparent nature of the silicified material rendered very
difficult the examination of the tissues, but enough was discovered
to show that these Indian stems are characterised by certain
features, the more compact nature of the secondary xylem and the
presence of multiseriate pitting, which distinguish them from the
_Cycadeoidea_ type. Further knowledge of the anatomical features of the
_Williamsonia_ (_Bucklandia_) stems from other localities might enable
us to recognise these or other peculiarities as constant distinguishing
characters of _Bucklandia_ in contrast to the Cycadeoidea stems which
bore the _Bennettites_ type of flower.
=Cycadeomyelon.= Saporta.
Casts of the pith-cavity of Cycadean stems, like that shown in fig. 575
projecting beyond the armour of leaf-bases, are occasionally found as
separate fossils and cannot always be referred to a particular species
of stem. For such detached casts Saporta[1356] instituted the name
_Cycadeomyelon_: they are characterised by their comparatively large
diameter and by the possession of surface-features similar to those
on the corresponding cast from a recent Cycadean stem shown in fig.
398, namely spirally disposed, more or less prominent, lozenge-shaped
areas formed by the sand or mud filling the cavities left on the decay
of the parenchyma of the broad medullary rays of a manoxylic stem.
Occasionally a slit at the lower end of a medullary ray area marks the
position of the leaf-trace bending outwards from the lower angle of the
mesh in the xylem-lattice[1357]. Lignier figures part of a pith-cast of
_Cycadeomyelon Apperti_[1358] in which each medullary-ray area has a
circular depression and not a slit extending from the lower angle: this
may indicate that the surface shown on the cast is slightly external to
the inner edge of the stele and in a plane where the leaf-traces were
embedded in the parenchyma of the rays and free from the xylem-cylinder.
Large and branched examples of _Cycadeomyelon_ were figured by some
of the earlier authors from English Wealden beds as species of
_Clathraria_[1359] and in many cases these are undoubtedly pith-casts
of _Bucklandia_ stems: a similar cast is figured under this name by
Schenk from the Wealden of North Germany. From Liassic beds in Normandy
Lignier figures two species of _Cycadeomyelon_, _C. Apperti_ and _C.
densecristatum_. The surface-features of _Cycadeomyelon_ resemble
those of the Palaeozoic genus _Tylodendron_ (see Vol. +iv.+), but in
the latter genus the nodal swellings are a characteristic peculiarity.
Though medullary casts of this type are of no great botanical
importance and their specific distinctions are of little value, it is
safe to assume that broad medullary casts with comparatively large
lozenge-shaped areas belong to Cycadean stems, while narrower specimens
with smaller lozenges are more likely to be pith-casts of Coniferous
stems.
Lester Ward[1360] instituted the genus _Feistmantelia_ for some Lower
Cretaceous casts from the Black Hills which he compared with an
Indian fossil from Cutch described by Feistmantel as ‘the stem of a
Coniferous plant[1361],’ and with pith-casts figured by Stokes and Webb
as _Clathraria anomala_. It is impossible to determine the systematic
position of such imperfect specimens as that on which Ward founded his
species _F. oblonga_: they may, as Hollick and Jeffrey[1362] suggest,
be casts of the bark of some Conifer; there is certainly no good reason
for connecting them with Cycads.
=COLYMBETES.= Stopes.
_Colymbetes Edwardsi_ Stopes. This genus[1363] is founded on the
inner portion of a petrified trunk which was probably cylindrical
and more than 12 cm. in diameter, consisting of a pith, 7·5 cm. in
diameter, and part of a vascular cylinder of remarkable structure.
The type-specimen is of Aptian age and may have come from Leighton
Buzzard (Bedfordshire). The pith (fig. 580, _p_) consists of large
parenchymatous cells and numerous secretory canals: the perimedullary
zone, _pm_, is characterised by the occurrence of loosely disposed
tracheids in groups and radial rows pursuing a sinuous longitudinal
course in the accompanying parenchyma. The tracheids in this region
are small in diameter and have oval, scalariform, or circular pits.
Abutting on the perimedullary zone is the secondary xylem the inner
edge of which forms bays, and this is composed of alternating zones of
vertical and horizontal tracheids (fig. 580, _y₁_–_x₅_; fig. 581) with
bordered, scalariform, pits on their walls traversed by medullary rays
generally biseriate and from 4 to 30 cells deep. The disposition of
the tracheids is such as to render transverse and radial longitudinal
sections practically identical in appearance; the first zone of
secondary xylem with its bayed inner edge consists of vertically
running elements; this is succeeded by a zone in which the tracheids
pursue a horizontal course, and beyond this second zone is another
band of vertical elements (fig. 581). ‘Where the one zone passes
into the next, a curving of the elements is frequently evident, and
in a few cases it is quite possible to trace a single radial series
of tracheids through an angle of 90° running in the same section,
first as a transverse and then as a vertical series. One and the same
medullary ray also can sometimes be followed, first in transverse and
then in radial longitudinal section, which later again turns to true
transverse. The inference is therefore drawn that there was but a
single cambium, which had periodic changes of direction.’ Leaf-traces
(fig. 580, _lt_) are large and numerous; they are spirally disposed
and pass nearly straight through successive xylem-zones: each trace
consists of a small-celled ground-tissue including stone-cells and
patches of tracheids in more or less regular radial rows. Tangential
sections of the wood show that the tracheids follow a sinuous course
forming loops enclosing numerous medullary rays.
[Illustration: Fig. 580. _Colymbetes Edwardsi_. Transverse section
showing ten alternating zones of wood outside the perimedullary zone,
_pm_; _y₁_, _y₂_, etc., vertically running xylem series; _x₁_, _x₂_,
etc., horizontally running xylem series; _p_, pith; _lt_, leaf-traces.
(After Stopes; × 2.)]
[Illustration: Fig. 581. _Colymbetes Edwardsi._ Diagram of stem in
transverse (A) and radial longitudinal (B) section. _p_, pith; _pm_,
perimedullary xylem; _b_, bays of first, vertically running, secondary
xylem; _x₁_, _x₂_, etc., zones of horizontally running secondary
xylem cut transversely in the radial and radially in the transverse
section of the stem; _y₁_, _y₂_, etc., longitudinally running xylem
cut transversely in the transverse and longitudinally in the radial
section. (After Stopes.)]
As the pith and xylem are the only tissues preserved it is on their
structure that any speculation as to affinity must be based. The close
arrangement of the leaf-traces (about 1 cm. apart), as Dr Stopes says,
indicates small leaf-bases, assuming that each leaf received a single
trace. In some respects the xylem and medullary rays resemble those of
Cycads, and the author of the genus includes it in the Cycadophyta; but
as she points out there are many peculiar features, and it is clearly
impossible to assign the new type to a more precisely defined position.
The possibility of any purely mechanical explanation of the course of
the tracheids in the alternating zones is ruled out by the straight
course of the outgoing leaf-traces, and it would seem that the cambium
must have turned over at right-angles at regular intervals during the
growth of the stem.
=Cycadolepis.= Saporta.
This name was used by Saporta[1364] for linear-lanceolate scales from
Upper Jurassic rocks in France which he compared with bud-scales of
recent Cycads. The imperfect scale described as _Cycadolepis villosa_
bears a striking resemblance to the hairy bracts of _Williamsonia_
and may well belong to that genus. Saporta’s term may be usefully
employed in a more extended sense, including not only lanceolate
scales but larger and much broader scales resembling the flattened
petiole-bases on stems of _Macrozamia_, _Encephalartos_, and some
other recent genera, as well as detached carpellary scales, other
than _Cycadospadix_, and microsporophylls which cannot be assigned
to a particular stem. Two qualifying subgeneric terms have been
proposed[1365]:
i. _Cycadolepis_ (_Dory-Cycadolepis_). Scales more or less
linear-lanceolate like those described by Saporta and a specimen
from Jurassic rocks of India named by Feistmantel[1366] _Cycadolepis
pilosa_. This type of _Cycadolepis_ may be identical with the bracts of
_Williamsonia_ flowers, though in the absence of any definite evidence
of such affinity the provisional generic name is more appropriate.
ii. _Cycadolepis_ (_Eury-Cycadolepis_). Broadly oval or orbicular thick
scales (figs. 582, 583), the broadest part being frequently nearer the
distal than the proximal end. These larger scales though usually found
as detached fossils have in one instance been obtained attached to an
imperfectly preserved stem.
[Illustration: Fig. 582. _Cycadolepis_ (_Eury-Cycadolepis_) sp. From
the Wealden beds of Sussex. (Brit. Mus. No. V. 2799.)]
[Illustration: Fig. 583. _Cycadolepis_ (_Eury-Cycadolepis_) sp. Scale
from the Wealden beds of Sussex. (British Museum, No. V. 2131_a_; nat.
size.)]
_Eury-Cycadolepis_ sp.
This type of scale, represented by specimens from the Wealden of
Sussex[1367] (figs. 582, 583), reaches a length of 13 cm. and a breadth
of 7 cm. and is sometimes almost orbicular. The lamina is convex
but shows no definite venation and bears a close resemblance to the
scale-like petiole-stumps on an old stem of _Macrozamia_. On some of
the smaller specimens (fig. 583) several forked veins extend vertically
from the broad base. Since these specimens were first described
additional examples have been discovered in the Wealden beds of Sussex,
some of which are attached to a piece of stem[1368] in such a manner
as to give support to the view that they are leaf-bases very similar
to those on such fossil stems as _Bucklandia_ (_Fittonia_) _Rigauxi_
(Sap.)[1369] and _B._ (_Fittonia_) _squamata_ (Carr.)[1370]. One
partially carbonised scale yielded pieces of cuticle showing numerous
stomata similar to those of recent Cycads and the outlines of very
thick-walled epidermal cells[1371].
_Eury-Cycadolepis Jenkinsiana_ (Tate).
The large and approximately orbicular or broadly ovate scales
so named are believed to be identical with Tate’s _Cyclopteris
Jenkinsiana_[1372] from the Uitenhage series of Cape Colony (Wealden).
The scales reach a length of 12 cm. and were attached by a broad base;
the lamina, which may be strongly bent as though folded over some
immature organ as a protective bract, shows numerous repeatedly forked
veins of the _Cyclopteris_ type and several anastomosing and irregular
lines between the veins suggesting that the scales were tomentose.
+II. Reproductive Organs of Cycadean Plants other
than those of the Bennettitales.+
The fact that practically all known Cycadean stems bore flowers
either of the _Bennettites_ or _Williamsonia_ type prepares us for
the scarcity of reproductive organs like those of recent Cycads. No
specimens have been discovered in a petrified state affording any
evidence of their close affinity to the cones, sporophylls, or seeds
of the Cycadales. Such genera as _Cycadospadix_, _Androstrobus_,
and _Zamiostrobus_, as the following descriptions show, are founded
on material that is too imperfect to throw much light on their true
morphological nature. The probability is that some at least of the
specimens included in these genera are the reproductive organs of
Cycadean plants more closely allied to the existing Cycads than to
the Bennettitales. Among the numerous fossil seeds referred to such
genera as _Cycadeospermum_ and _Cycadinocarpus_ there are but few
that can confidently be assigned to the Cycadales rather than to the
Ginkgoales or Coniferales. While the seeds of the Bennettitales are
clearly distinguished by their much smaller size from those of modern
Cycads, many of the latter agree in size and form with those of some
other Gymnosperms and in the absence of anatomical details could
not easily be identified as fossils. Some of the examples included
in the miscellaneous collection described by authors as species of
_Carpolithus_ or _Carpolithes_ agree closely in external features with
the seeds of modern Cycads, but it is seldom possible to accept them as
undoubted records of Cycadalean plants.
The general conclusion is that such meagre evidence as we possess
affords strong confirmation of the conclusion based on stems and
foliage from Jurassic and Cretaceous strata, namely that the present
representatives of the Cycadophyta are a relatively late product of
evolution, though retaining in their anatomical features many survivals
from a remote antiquity. The occurrence of Cycadean characteristics in
the vegetative organs of the Medulloseae and the recurrence of what may
be called the Cycadean seed-plan, with certain more or less striking
peculiarities reminiscent of earlier stages of evolution, in several
types of Palaeozoic seeds such as _Cycadinocarpus_, _Stephanospermum_,
_Lagenostoma_ and others bear testimony to the antiquity of the
Cycadean stock.
=CARPOLITHUS[1373].= Linnaeus.
This generic name, as Nathorst[1374] has recently pointed out, was
used by Linnaeus in 1768 for ‘Phytolithus fructus’ and has therefore
priority over Sternberg’s genus _Carpolites_ employed in 1825. Lester
Ward[1375] attributes _Carpolithus_ to Stokes and Webb (1824) and
states that in the plural form the name was used by Walch in 1771.
_Carpolithus_ is a convenient term to apply to fossil seeds that cannot
be assigned to a particular group of plants and which do not exhibit
any peculiarities of form sufficiently striking to deserve generic
recognition. Pomel[1376] proposed the genus _Ulospermum_ but it never
came into general use. Schimper’s genus _Cycadinocarpus_ and Saporta’s
_Cycadeospermum_ (preferable in its morphological implication),
though useful in the case of detached seeds of undoubted Cycadean
affinity, can seldom be employed without an admission that they may
imply a relationship that cannot be absolutely established. In the
great majority of cases the better plan is to be content with the more
non-committal term _Carpolithus_ with the addition of a family-name
when there are reasonably good grounds for a more definite reference.
No useful purpose would be served by attempting a complete survey of
the numerous casts and impressions of supposed Cycadean seeds recorded
in palaeobotanical literature, but a few types are briefly described as
examples of specimens with fairly well defined characters, which are in
all probability Cycadean.
_Carpolithus conicus_ (Cycadales?) Lindley and Hutton.
[Illustration: Fig. 584. _Carpolithus conicus._ The type-specimens in
the Manchester Museum; nat. size. (_a_, No. 361; _b_, _c_, No. 360.)]
[Illustration: Fig. 585. _Carpolithus conicus._ From a specimen in
the Malton Museum; nat. size.]
The original specimen figured by Lindley and Hutton[1377] from the
Coralline Oolite of Malton, Yorkshire, as _Carpolithes conica_
and now in the Manchester Museum, is represented in fig. 584. A
second ‘species,’ _Carpolithus Bucklandi_ Lind. and Hutt. ex Will.
+MS.+[1378], from the same locality is no doubt specifically identical
with _C. conicus_. The seeds are conical, broadly truncate at one
end, presumably the base, and tapered to a blunt apex; the broad end
is characterised by the presence of three ridges or in some specimens
by a single median ridge illustrating an oscillation between the
radiospermic and platyspermic form similar to that in _Ginkgo biloba_.
As usually obtained the seeds are probably nucules or casts showing the
surface-features of the inner wall of the sclerotesta, the sarcotesta
having been destroyed before fossilisation: the irregular marginal
teeth at the truncate end suggest casts of vascular bundles in the
integument. The scattered tubercles on the sides of some of the seeds
(fig. 584, _a_) are probably casts of holes in the shell bored by
insects and comparable with those occasionally preserved on the casts
of _Trigonocarpus_. A specimen in the Malton Museum shown in fig. 585
which may be an example of this species illustrates the occurrence
of an internal cast enclosed by the remains of a thick testa. These
Jurassic casts resemble the seeds of _Macrozamia Fraseri_, but it is
impossible to determine their systematic position with confidence.
_Carpolithus_ sp. (Cycadales?) Seward.
An unusually well preserved specimen from the Wealden beds of the
Sussex coast described under this name in 1895[1379] consists of a
kernel and mould, 1·8 × 1·1 cm. The mould from which the kernel is
readily removed is lined with a thin structure representing part of the
testa and between this and the surrounding rock is a layer of coal.
On the surface of the kernel, probably the cast of the seed-cavity,
a reticulum of narrow grooves indicates the course of the vascular
bundles over the surface of the nucellus.
_Carpolithus_ (Cycadales?) _Pomelii_ (Saporta).
The specimen from the Upper Corallian of Châteauroux (Indre) on
which this species was founded by Saporta[1380] under the name
_Cycadeospermum Pomelii_ is a large ovate cast, 5·5 cm. long and 3·5
cm. broad, closely resembling some of the larger recent Cycadean seeds:
it cannot be accepted as a true record of the group without reservation.
Saporta describes other species of _Cycadeospermum_ but none of them
are of any real importance from a botanical point of view: the same
remark applies to the seeds referred by Fontaine[1381] from Potomac
beds to the same genus, also to many other recorded examples of seeds
that afford no decisive evidence of affinity.
Some specimens described by Compter[1382] from the Lettenkohle of
Apolda (Thuringia) as Cycadean fruits—too imperfect to be determined
with accuracy—furnish an additional illustration of the slender
foundation on which many of the records of supposed Cycadean
reproductive organs are based.
=CYCADOSPADIX.= Schimper.
This name was proposed by Schimper[1383] for some French Jurassic
fossils, described by Pomel[1384] as _Crossozamia Hennocquei_ and
_C. Moraeana_, on the ground that they bear a close resemblance to
the megasporophylls of _Cycas_. Their occasional association with
_Otozamites_ fronds suggested a reference to the same parent-plant, but
such data as we have point to _Otozamites_ fronds having been borne
by plants with the _Williamsonia_ type of flower. Schenk[1385], who
figured a specimen of _Cycadospadix_ from France as the inflorescence
of a Cycad, expresses the more probable opinion that it belonged
to a plant with _Cycadites_ fronds. A Permian species described by
Renault as _Cycadospadix Milleryensis_ is now transferred to the genus
_Strobilites_[1386].
_Cycadospadix Pasinianus_ Zigno.
This species, first described from Jurassic strata in Northern
Italy[1387], is recorded also from the Kimmeridgian of France[1388] and
Scotland[1389]. Zigno’s figures give a fairly accurate representation
of the type-specimens in the Padua Museum. The megasporophylls, almost
identical in shape with those of some recent species of _Cycas_ (figs.
381; 392, A–C), consist of a broadly lanceolate or triangular limb
with deeply laciniate sides terminating a pedicel, or the distal
expansion may be preserved without the stalk from which it was no
doubt easily detached as in certain recent Cycads (_cf._ fig. 392, A).
In the specimen from Scotland there are no clear indications of veins
in the lamina, which may have been woolly as in _Cycas_. In some of
the specimens figured by Saporta[1390] and now in the École des Mines,
Paris, the stalk is absent, but in pedicellate examples scars occur
on the sides of the narrow axis and casts of seeds are found in the
same beds. A good example of _Cycadospadix Hennocquei_ is figured by
Saporta from a drawing supplied by Schimper showing two seed-scars
near the base of the lamina: the same specimen, as figured by Saporta
and Marion[1391], bears a seed, but this is presumably a partial
restoration. The occurrence of _Cycadites rectangularis_ Brauns at
Hettange in association with _Cycadospadix_ strengthens the conclusion,
based on the form of the megasporophylls, that some of the Jurassic
Cycads bore megasporophylls very similar to those of existing species
of _Cycas_.
_Cycadospadix integer_ Nathorst.
This Rhaetic species from the south of Sweden[1392] was instituted
for an imperfect broadly lanceolate lamina recalling the distal end
of the megasporophyll of a _Cycas_: the discovery of a more complete
example[1393] justifies Nathorst’s use of the name _Cycadospadix_,
though without further evidence one hesitates to regard the species as
a thoroughly trustworthy record of a Cycadean fertile leaf. The species
is characterised by the entire margin of the broad and relatively short
and thick terminal limb borne on a broad stalk with alternate lateral
projections presumably marking the position of the seeds.
These species of _Cycadospadix_ are particularly interesting as
evidence—though not amounting to demonstration—of the production
by some Jurassic and Rhaetic plants of fertile leaves agreeing
closely with those of _Cycas_. It would seem from the abundance of
Bennettitalean flowers and the very scanty remains of fertile leaves
or cones like those of modern Cycads that the existing type was
exceptional in Mesozoic floras.
=BEANIA.= Carruthers.
_Beania gracilis_ Carruthers.
[Illustration: Fig. 586. _Beania gracilis._ (After Carruthers; ½ nat.
size.)]
The generic name _Beania_[1394] was given to a branched fertile shoot
(fig. 586) from the Middle Jurassic beds at Gristhorpe, Yorkshire,
characterised by loosely disposed sporophylls bearing two sessile
seeds: each sporophyll is given off at a wide angle from a fairly stout
axis and the seeds are borne on the adaxial side of a peltate distal
expansion. Carruthers compared the type-species with a cone of _Zamia_
with which it agrees in the general plan of construction but differs
in the more open habit and in the longer and more slender seed-bearing
pedicels. The same type of shoot was figured by Lindley and
Hutton[1395] as _Sphaereda paradoxa_. _Beania_ is generally regarded as
a Cycadean reproductive shoot, but there is no doubt that the majority
of Jurassic Cycadophyta possessed flowers of the _Bennettites_ types,
and it is clear that _Beania_ differs considerably from _Bennettites_
and _Williamsonia_. Another suggestion is that _Beania_ may belong to
some member of the Ginkgoales[1396]: though very different from the
normal ovuliferous shoot of a _Ginkgo_, it resembles some abnormal
forms (_e.g._ fig. 631, D) in which the ovules occur on elongated
pedicels, but they are borne singly and the micropyle is directed
outwards, while in _Beania_ the ovules are attached in pairs to the
inner face of a distal expansion. There is no conclusive evidence in
support of either interpretation, though the general agreement between
the Jurassic type and the cones of recent Cycads would seem to favour
the inclusion of _Beania_ among the Cycadophyta.
A specimen described by Nathorst[1397] from Upper Jurassic rocks in
the North of Scotland as _Beania Carruthersi_ closely resembles the
type-species, differing chiefly in its smaller size and in the rather
closer arrangement of the sporophylls. The seed-like bodies borne
in pairs on the adaxial side of the terminally expanded pedicels
are covered with small granulations which Nathorst thinks may be
clusters of microspores, the apparent seeds being ‘antherangia.’ The
granulations are, however, very similar to those on the larger detached
seed-like bodies originally described by Nathorst from Rhaetic beds
in Sweden as _Antherangiopsis rediviva_[1398]: subsequent examination
of that species demonstrated that the granulations are due to the
presence of resinous bodies in the tissues of true seeds[1399], and
it is not improbable that a similar interpretation may hold for the
surface-features in the supposed male organs of _Beania Carruthersi_.
Pending further evidence it may be suggested that _Beania Carruthersi_
is like _B. gracilis_ a seed-bearing shoot. The Rhaetic specimens
described by Nathorst as _Stenorrachis scanicus_[1400] are similar in
habit to _Beania_ but differ in the forking of the sporophylls (fig.
656) and in the absence of any terminal swelling on which the seeds are
borne: Nathorst considers that _Stenorrachis_ may be the female organ
of a _Nilssonia_ and it is not improbable that that genus and _Beania_
are closely allied types. We have no definite information with regard
to the reproductive organs of the Nilssoniales: the closer resemblance
which their fronds bear in the structure of the epidermal cells to
those of recent Cycads is consistent with the view that their fertile
shoots were also more like those of existing types. It is, however,
still an unsettled point whether _Beania_ is more closely allied to
the Cycadophyta or to the Ginkgoales, but the balance of opinion is in
favour of the former alliance.
=Zamiostrobus.= Endlicher.
=Cycadeostrobus.= Carruthers.
Though instituted by Endlicher[1401] for a cone figured by Lindley
and Hutton as _Zamia macrocephala_[1402] which is almost certainly
Abietineous and has no claim to be included in the Cycadales, the genus
_Zamiostrobus_ has been adopted by many authors for Cycadean ovulate
cones, not only such as are believed to be closely allied to those of
_Zamia_ but for Cycadean cones generally. Carruthers[1403] suggested
_Cycadeostrobus_ as a more suitable name on the ground that it is less
limited in its implication of affinity; but, as Fliche points out,
Endlicher’s generic name has been widely adopted in a comprehensive
sense as standing for Cycadean megastrobili, excluding the supposed
_Cycas_-like megasporophylls, included under _Cycadospadix_.
Many of the specimens described as species of _Zamiostrobus_ are of
little or no value as records of Cycadean plants, _e.g._ _Zamiostrobus
orientalis_ Heer[1404] from the Jurassic beds of Amurland. A
Lower Cretaceous (Albian) species described by Fliche[1405] as
_Zamiostrobus Loppineti_, though not entirely satisfactory, is more
likely to belong to the Cycadales. The type-specimen is an elliptical
strobilus, 5·5 cm. × 3·2 cm., consisting of an axis bearing at
right-angles numerous small, contiguous, peltate megasporophylls
each with two small seeds on the lower surface. The figures given
by Fliche are, however, not convincing. An examination of specimens
in the British Museum, from Wealden and Jurassic rocks, described
by Carruthers as species of _Cycadeostrobus_, convinced me that
several are undoubtedly Araucarian cones[1406]. Solms-Laubach[1407]
called attention to the Araucarian appearance of _Cycadeostrobus
Brunonis_, a cone from an unknown locality, and this with other
species, _e.g._ _C. elegans_, _C. sphaericus_, _C. truncatus_, etc.,
may safely be referred to _Araucarites_. The specimen figured by
Lindley and Hutton[1408] as _Zamia crassa_ from the Inferior Oolite
of Towcester (Northamptonshire) affords no satisfactory evidence of
Cycadean affinity. The Lower Cretaceous Bohemian specimens described
by Corda[1409] and Velenovský[1410] as _Microzamia gibba_ should not
be included in a genus implying Cycadean affinity: though Velenovský
states that the megasporophylls bear a pair of seeds his illustrations
do not afford any satisfactory evidence of this Cycadean character.
Similarly the fossil regarded by Carruthers[1411] as probably a male
flower of _Bucklandia_ is almost certainly an Araucarian cone. A small
cone from the Lower Miocene of Armissan (Aude) named by Schimper
_Zamiostrobus Saportana_ and figured by Saporta and Marion[1412] may,
as Solms-Laubach says, be Cycadean, but we have no information with
regard to the internal structure or as to the presence or position of
the seeds.
=Androstrobus.= Schimper.
Schimper[1413] instituted this genus for ‘amenta, cycadeacea
antherifera, cylindrica, e squamis imbricatis, latere postico antheras
sessiles ferentibus efformata.’ It may conveniently be applied to
fossils which resemble the male cones of recent Cycads sufficiently
to justify the use of a name implying relationship. As so defined,
_Androstrobus_ is used in a more restricted sense than the word
suggests, just as _Masculostrobus_[1414] has been employed for fossils
that are believed to be the corresponding organs of Conifers. Among
the few species assigned to Schimper’s genus reference may be made to
_A. Balduini_ Sap., originally named by Schimper _A. zamioides_, from
the Upper Bathonian of Etrochy, and _A. Guerangeri_ (Brongn.), another
French type[1415]. Heer’s species _A. sibirica_[1416] of Jurassic age
is represented by a slender axis bearing numerous appendages which in
surface-view have the form of polygonal discs: there are no indications
of microsporangia and the evidence of Cycadean affinity is far from
convincing. Nathorst’s Rhaetic species _A. borealis_[1417] is no more
satisfactory as a record of a Cycadean strobilus. A fossil from the
Lower Cretaceous of Bohemia described as _Zamites familiaris_ and
regarded by Corda[1418] and Carruthers[1419] as a male flower of a
Cycad though not above suspicion may be included in _Androstrobus_.
Under the name _Fričia nobilis_ Velenovský[1420] described some cones
from the Lower Cretaceous plant-beds of Bohemia which he regards
as male strobili of some Cycadean plant: the cone, as shown in
Velenovský’s restoration, is 10 cm. long and 5 cm. in diameter; it
bears a close superficial resemblance to a large cone of _Zamia_ and
consists of a stout axis bearing contiguous peltate, hexagonal, scales
gradually contracted towards the proximal end, similar to those of
_Androstrobus_. The evidence on which this species is identified as a
male cone rests on the occurrence of numerous pits on the surface of
the scales; but no spores or sporangia were found and the pits as shown
in the published figures do not present the appearance of scars of
sporangia.
The Rhaetic specimen originally named by Nathorst _Androstrobus Scotti_
and afterwards transferred to the genus _Lycostrobus_ was described in
Volume +ii.+[1421]
_Androstrobus Nathorsti_ Seward.
The type-specimens were obtained from the Wealden beds of Sussex: they
were referred to the genus _Androstrobus_ on evidence which cannot
be regarded as decisive[1422]. A fairly stout axis, 6·5 cm. long,
bearing spirally disposed sub-triangular scales hexagonal in section
and attached to the axis by a broad base; the scales, or sporophylls,
are 1–1·5 cm. long and gradually tapered towards a pointed or slightly
rounded apex. Near the proximal end of some of the sporophylls there
are regularly arranged polygonal depressions which may be impressions
of microsporangia. The regular disposition of the depressions is a
striking feature and in contrast to the less regular reticulum exposed
after the removal of the sporangia from the microsporophyll of a recent
Cycad. An examination of the cuticular membrane of the microsporophylls
shows that the epidermal cells have thick and straight walls[1423],
characters consistent with the supposed Cycadean affinity of the
strobilus.
CHAPTER XXXIX.
CYCADOPHYTAN FRONDS.
Occasional reference is made to Cycadean fronds in the account of
flowers and stems but it is seldom that genera or species founded
on leaves can be definitely correlated with particular types of
reproductive organs or stems. As in the case of Ferns and Pteridosperms
so also with detached leaves believed to be Cycadean, a large number
of generic names have been employed for impressions which afford no
information with regard to anatomical characters except, in some
of the more favourably preserved specimens, a few facts as to the
epidermal cells. Though association often suggests original connexion
it is inadvisable except in well established cases to extend to fronds
generic terms based on reproductive shoots. The designation _Zamites_
has long been used for fronds that are clearly not closely related to
recent species of _Zamia_, and were it not an old established genus
the significance of which is not likely to be misunderstood, it would
be wiser to substitute for it some name implying no affinity with
any existing type. On the other hand the employment by some authors
of such generic names as _Encephalartos_ and _Ceratozamia_ is not
warranted by the evidence furnished by the imperfect material. Prof.
Newberry[1424] described as _Encephalartos_? _denticulatus_ a piece
of a frond from Rhaetic beds in Honduras characterised by lanceolate
pinnae (30 × 6 mm.) gradually narrowed towards the acute apex and
abruptly contracted at the base: the method of attachment of the pinnae
appears to agree with that in the genus _Zamites_. In this case there
is no valid reason for assuming a relationship with _Encephalartos_
or with any recent type. An impression from Lower Cretaceous, Dakota,
beds in Kansas described as _Encephalartos cretaceus_ Knowlt. ex Lesq.
ms.[1425] consists of a piece of lamina, 9 × 4 cm., obovate-oblong and
with a cuneate base, a serrate margin and thick diverging veins: the
specimen is too incomplete to serve as a record of any Cycadean genus.
The generic name _Encephalartopsis_ was applied by Fontaine[1426]
to some imperfect pinnae from the Potomac beds characterised by a
linear-elliptical lamina with a spinous margin and slightly diverging
and occasionally anastomosing veins. The figured examples of the
type-species, _E. nervosa_, suggest pinnae like those of _Ctenis_; but
in the absence of a rachis the method of attachment of the segments
cannot be ascertained. Saporta[1427] named a specimen from the Miocene
flora of Koumi, Greece, _Encephalartos Gorceixianus_ because of its
resemblance in habit to some species of the recent genus; but the
designation _Zamites_ would be more appropriate. Ettingshausen recorded
an imperfect impression of a pinna from Tertiary rocks in Styria as
_Ceratozamia Hofmanni_[1428] although it is by no means certain that
the fragment is even Cycadean. The genus _Taeniopteris_ was described
in the second volume of this book as probably a Pteridophyte, though
of uncertain systematic position: it has, however, been shown by
Mr Thomas[1429] that the Jurassic species _T. vittata_ was almost
certainly borne on a stem with reproductive organs constructed on the
Bennettitalean plan. Further research may enable us to fix the position
of other species but as yet _T. vittata_ is the only representative of
the genus which there is good reason for assigning to the Bennettitales.
It is undoubtedly true that Cycadean plants, using the term in a wide
sense to include the Bennettitales as well as the Cycadales, bulked
largely in Upper Triassic, Rhaetic, Jurassic-Wealden floras; the
Bennettitales probably reached their maximum development as regards
wealth of form and geographical range in the latter part of the
Jurassic period and in the earliest phase of the Cretaceous epoch. In
Triassic floras Cycadean plants are represented almost solely by fronds
but the very close resemblance between Keuper species and forms that
in Jurassic rocks are found in association with fertile shoots leaves
little doubt as to the affinity of Keuper and Rhaetic species.
The evidence obtained from Permo-Carboniferous strata is much more
meagre, at least as regards Cycadean leaves: the occurrence of certain
morphological Cycadean features is revealed by petrified vegetative
organs of Palaeozoic plants, and the Cycadean plan of organisation is
conspicuous in many Carboniferous and Permian seeds. The discovery
of frond-impressions identical in external characters with Mesozoic
genera may be accepted as a substantial indication that genera already
existed possessing foliage of the Cycadean type, though we have no
certain information with regard to the nature of the other organs of
the parent-plants. A few examples of Palaeozoic species are included
among those selected in illustration of the different genera, namely
_Plagiozamites Planchardi_, _Sphenozamites Rochei_, _Pterophyllum
Fayoli_, _P. Cambryi_: among other recorded instances of Palaeozoic
species are _Pterophyllum Cottaeanum_ Gutb.[1430], a Permian type
similar in habit to _Ctenis_ but without anastomosing veins, a
feature in which it resembles _Pseudoctenis_; the Carboniferous
species _Pterophyllum inflexum_ Eich.[1431] from the Altai mountains,
transferred by Zeiller to _Dioonites_; _P. blechnoides_ Sand.[1432]
from the Stephanian of Oppenau; _Pterophyllum Grand’Euryanum_[1433]
from Upper Carboniferous beds in France, and _P. gonorrachis_
Goepp.[1434] from Silesia. An examination of the type-specimens of the
Carboniferous species _Cycadites gyrosus_ Goepp. and _C. taxodinus_
Goepp.[1435] in the Breslau Museum led me to regard the material as too
imperfect to determine.
A conclusion that is forced upon us by a consideration of the
geological range of Cycadean fronds is that at the close of the
Wealden period, a period very closely linked in the character of
the vegetation with the preceding Jurassic floras, there appears
to have been a relatively sudden decrease in the number of members
of the Cycadophyta: the decline in the fortunes of Cycadean plants
is coincident with the rise and remarkably rapid extension of the
Angiosperms. From Middle and Upper Cretaceous and from Tertiary beds
very few Cycadean remains have been obtained and many of them are
represented by fragmentary fossils that afford no definite evidence
of affinity to recent genera. The antiquity of the Cycadales, that
is the section represented by existing Cycads, cannot be determined;
but it would seem probable that if the Cycads apart from the
Bennettitales existed in Jurassic and Lower Cretaceous floras they
occupied a very subordinate position in comparison with the extinct
Bennettitales. There are no data pointing to any widespread occurrence
of the Cycadales in the Northern Hemisphere in Tertiary times at all
comparable with the geographical range of Tertiary ancestors of the
solitary survivor of the Ginkgoales.
The following records of Tertiary Cycadean fronds illustrate
the paucity of the records. Reference has already been made to
_Encephalartos Gorceixianus_ Sap. of Miocene age, a species that has
no claim to be regarded as an example of the recent South African
genus. The specimen described by Saporta and Marion as ? _Zamites
palaeocenicus_[1436] from the Eocene of Gelinden is too imperfect to
serve as a trustworthy record. A more satisfactory species, similar in
habit to _Zamites gigas_, is that on which Saporta founded the species
_Zamites epibius_[1437] from Lower Miocene beds at Bonnieux (Vaucluse),
France. Another Tertiary species is mentioned by Krasser[1438] from
Pliocene strata in Brazil as _Zamia praecedens_ Krass. ex Ett.
+MS.+ Ettingshausen has described a Tertiary species from New South
Wales, either Lower Miocene or Upper Eocene in age, as _Anomozamites
Muelleri_[1439], characterised by truncate segments with simple veins
and set obliquely to the rachis.
While certain form-genera of fronds can only be referred to the
Cycadophyta, in other cases it is possible to assign fronds to a
section of this comprehensive group characterised by a particular type
of fertile shoot and by certain well defined epidermal features.
The investigation of the cuticular structure of various Cycadean fronds
by Nathorst[1440] and especially by Mr Thomas[1441] has supplied a
basis of classification which affords the best criterion of affinity so
far available. The majority of fronds are placed in the Bennettitales
while the three genera _Ctenis_, _Nilssonia_, and _Ctenopteris_ (or
_Ptilozamites_[1442]) are placed in the Nilssoniales.
I. =Bennettitales.= Epidermal cells characterised by sinuous walls and
generally rectangular; the cuticle is thin; the stomata, confined to
the lower surface of the pinnae, tend to be arranged at right-angles
to the veins and are on a level with the epidermis or very slightly
depressed; two large laterally placed subsidiary cells more or less
surround the guard-cells and these are provided with thickenings of a
definite shape (figs. 594, 609).
Genera: _Ptilophyllum_, _Zamites_, _Otozamites_, _Dictyozamites_,
_Pterophyllum_ and _Anomozamites_, _Taeniopteris_, _Pseudocycas_.
II. =Nilssoniales.= Epidermal cells with straight walls, not sinuous,
irregular in form, rounded, hexagonal, or rectangular; the stomata are
below the level of the epidermis; the cuticle may be thin or thick.
There is no regular arrangement of the stomata; the guard-cells are
surrounded by 6–8 subsidiary cells (fig. 625) which often form an
overarching canopy; thickening lamellae like those on the guard-cells
of the Bennettitales are seldom present.
Genera: _Nilssonia_, _Ctenis_, _Ctenopteris_.
It is a noteworthy fact that the representatives of the smaller group,
the Nilssoniales, in their cuticular features, are more akin than the
Bennettitales to modern Cycads. Until definite evidence is obtained as
to the nature of the reproductive organs of _Nilssonia_, _Ctenis_, and
_Ctenopteris_ it is impossible to say how closely these genera agree
in essential characters with existing members of the Cycadales. If, as
has been suggested, the fertile shoots known as _Beania_[1444] belong
to _Nilssonia_ their resemblance in plan of construction to the cones
of recent genera, much greater than in the case of the flowers of the
Bennettitales, is in accordance with the evidence of the epidermal
characters.
Reference was made in the second Volume of this book to several genera
founded on fronds which through lack of evidence as to the nature of
the reproductive organs cannot be assigned with certainty either to
Ferns or Cycads: it was stated that the genera _Ptilozamites_ and
_Ctenopteris_ are probably Cycadean, and the structure of the epidermal
cells in the latter genus lends support to this view[1445]. Among other
genera of doubtful position not included in the following descriptions
of fronds is _Zamiopsis_ of Fontaine[1446] founded on large compound
fronds from the Potomac formation: the venation and form of the pinnae
are more Fern-like than in _Ctenopteris_, but in general habit the
two genera are not very dissimilar. The generic name Zamiopsis is
misleading as the species bear no resemblance to _Zamia_ or _Zamites_.
+I. Bennettitales.+
=PTILOPHYLLUM.= Morris.
The generic name _Ptilophyllum_ was instituted in 1840 for some
specimens of pinnate fronds from Cutch: in this genus Morris[1447]
included with the Indian leaves the English Jurassic species
_Pterophyllum pecten_ Lind. and Hutt.[1448] (figs. 587, etc.) and
some other forms. He defined _Ptilophyllum_ as follows: ‘Fronds
pinnate; pinnae closely approximated, linear, lanceolate, more or
less elongate, imbricate at the base, attached obliquely; base
semicircular or rounded; veins equal, slender, parallel.’ Morris adds
that he instituted a new genus in preference to _Zamites_ because
of the ‘oblique insertion of the pinnae and their overlapping each
other at the base.’ In a later paper Morris[1449] states that the
pinnae of _Ptilophyllum_ fronds are ‘sometimes auriculed in the upper
and sometimes in the lower part’ of the base of the lamina. In his
catalogue[1450] he adopted Endlicher’s genus _Palaeozamia_ instead of
_Ptilophyllum_. Without discussing the generic nomenclature adopted
by various authors for the Indian types and similar fronds it is
important to refer briefly to the treatment of Morris’s species by
Oldham and Morris and by Feistmantel. In the first of the series of
Memoirs on Gondwana floras[1451] _Ptilophyllum_ is retained for a
section of _Palaeozamia_ together with _Otozamites_ and _Sphenozamites_
as other sectional subdivisions: in the subgenus _Ptilophyllum_ are
included _Palaeozamia acutifolia_ and _P. cutchensis_ (fig. 588, A,
C), also _P. affinis_, _P. rigida_, and _P. bengalensis_. The last
species is in all probability an _Otozamites_: _P. affinis_ and _P.
rigida_ are almost certainly indistinguishable from _P. cutchensis_.
Feistmantel[1452] dealt in detail with the genus _Ptilophyllum_: he
wrote, ‘with Schimper and Schenk I therefore look upon this genus
as an Indian type especially characterised by its ... more or less
slender leaves, angustate towards the apex and base, and petiolate,
with regularly adfixed leaflets.... The leaflets are equal to each
other, for the most part elongate linear, and _auriculate and free
at the upper angle at the base_, but adfixed at the lower angle, and
each is decurrent behind the upper angle of the leaflet next below it,
thus the leaflets are almost imbricate. The veins are rather numerous,
simple, and forked, and more or less divergent[1453].’ Feistmantel
distinguishes certain varieties of _P. cutchense_ (fig. 588, A, C),
none of which appear to be well defined. A specimen from the Rajmahal
Hills with unusually long pinnae, the frond having a breadth of 8 cm.,
is described as _Ptilophyllum acutifolium_ var. _maximum_[1454], but
it differs in no important feature from the smaller and commoner form.
The next point to be considered is the variability of certain species
referred by Feistmantel to _Otozamites_. He figures specimens from the
Jabalpur group as _O. Hislopi_ Feist. ex Old. +MS.+, _O. gracilis_
(Kurr), _O. angustatus_ Feist. (fig. 588, B) and _O. distans_[1455]. An
examination of the figured specimens leads me to regard _O. Hislopi_
and _O. gracilis_ as identical with the _Ptilophyllum_ fronds: the
pinnae exhibit no distinguishing features and there is no reason for
a specific, still less a generic, separation. _Otozamites angustatus_
is indistinguishable from _Otozamites_ sp. as figured from the
Madras coast and from _Ptilophyllum cutchense_, _P. cutchense_ var.
_curvifolium_ and var. _minimum_. The drawings reproduced in fig. 6_a_,
Pl. +x.+ of the Madras flora[1456] and in fig. 8_a_, Pl. +vi.+ of the
Jabalpur flora[1457] showing auriculate bases are inaccurate: in all
the fronds named the pinnae are straight with rounded edges precisely
as in _Ptilophyllum_. The conclusion forced upon me by a comparison
of the actual specimens is that the Indian fronds are not separable
into well-defined species and should all be included in _Ptilophyllum
cutchense_. Moreover in this comprehensive species should be included
the specimens described by Feistmantel as _Otozamites Hislopi_ (fig.
589), _O. angustatus_, and _O. gracilis_. It may well be that a more
detailed investigation of the numerous forms comprised in this protean
species, particularly if specimens are obtained from which cuticular
preparations can be made, may lead to the recognition of additional
species or well-defined varieties. The resemblance between the various
forms of _P. pecten_ from the Jurassic strata of Yorkshire and those
of _P. cutchense_ from India is very striking, and at least in many
cases no specific separation is possible so far at least as the form of
the fronds and pinnae is concerned. The occasional close association
of _Ptilophyllum_ fronds and _Williamsonia_ flowers is an important
agreement between the English and Indian fronds (fig. 590).
[Illustration: Fig. 587. _Ptilophyllum pecten._ (British Museum, V.
3795; ¼ nat. size.)]
[Illustration: Fig. 588. _Ptilophyllum pecten._ A, C, specimens
figured by Feistmantel as _Ptilophyllum cutchense_. B, Feistmantel’s
_Otozamites angustatus_. (⅚ nat. size; Calcutta Museum.)]
[Illustration: Fig. 589. _Ptilophyllum pecten._ A frond figured by
Feistmantel as _Otozamites Hislopi_. A, ⅚ nat. size; B, enlarged
(Calcutta Museum).]
In the first part of the Catalogue of Jurassic plants from Yorkshire
the opinion was expressed[1458], based on an examination of Morris’s
type-specimen of _Ptilophyllum cutchense_ and of a large number
of English and other fronds identical with or closely allied to
_Pterophyllum pecten_ Lind. and Hutt., that the Indian and European
fronds belong to the same genus. In a later paper[1459] it was
maintained that _P. cutchense_ and _P. acutifolium_ are probably
identical with the English type, and a drawing was published—reproduced
in fig. 591—of Morris’s type-specimen. Dr Halle[1460] has discussed
the genus _Ptilophyllum_ and his investigations lead him to a
different conclusion; he, like Zeiller and some other authors, employs
_Ptilophyllum_ in Feistmantel’s sense. The pinna-base is said to agree
in its asymmetrical form with that in _Otozamites_, while it differs
from the symmetrical base of _Zamites_ pinnae. In _Ptilophyllum_ both
edges of the pinna-base are said to bend down in joining the rachis; at
the upper corner the base thus becomes rounded and for some distance
free from the rachis; it is also sometimes a little auriculate; at the
lower edge the pinna is decurrent on the upper surface of the rachis.
In a subsequent paper Halle[1461] repeats the view that the decurrence
of the pinnae by their lower edges is an important distinguishing
feature of _Ptilophyllum_, thus agreeing with Feistmantel whose
illustrations appear to be confirmatory. The drawings in Feistmantel’s
memoirs are, however, misleading and in some cases incorrect. An
examination of a photograph of Morris’s type-specimen of _P. cutchense_
led Halle to conclude that the two edges of the pinna-base bend
downwards on joining the rachis as described by Feistmantel. This
feature is not shown in the drawing reproduced in fig. 591: it is
clear that either the drawing is incorrect or that there has been some
mistake in the interpretation of the photograph. Through the courtesy
of Dr Halle I have been able to examine the actual print: when viewed
in its correct position the two edges of the pinnae appear to bend
down as described by Halle, but if it is examined in the reverse
position the lower angle of the pinnae is seen to be slightly rounded
as in fig. 591, the apparent decurrence being due to a confusion
between the appressed lower edge of one pinna, which is faintly shown,
and the stronger downward trend of the upper edge of the pinna next
below. The upper edges of the pinnae are more prominent because they
are less appressed to the rachis while the lower half of the base
is closer to the rachis and is frequently, though not in Morris’s
specimen, overlapped by the upper edge of the next lower pinna. A
re-examination of the type-specimen in the British Museum confirms this
interpretation. The pinnae of _Ptilophyllum_ are characterised by their
attachment to the upper face of the rachis which they almost completely
cover; the upper angle is rounded and in a few cases auriculate
(fig. 592); the lower angle of the base is slightly rounded and not
infrequently hidden by the imbrication of the adjacent pinna; it is
occasionally auriculate (fig. 593). The pinnae are attached by nearly
the whole base, but the upper angle is free. The veins are parallel,
sub-parallel or, especially in the proximal portion of the lamina,
oblique. The pinnae are linear, varying considerably in relation of
length to breadth and in the form of the apex; they are straight or
more or less falcate. The epidermal cells of such _Ptilophyllum_
fronds as have been examined are characterised by strongly looped or
sinuous walls; the stomata, confined to the lower surface, are roughly
circular and the guard-cells are at right-angles to the veins and not
appreciably sunk. Fig. 594 represents the appearance of a stoma in
surface-view: ‘on either side of the central slit-like pore are two
elliptical or hemispherical structures; they are somewhat flattened
when they abut on the pore, and have rounded ends.... Between these
and the subsidiary cells lie two other thickened patches, more or
less hemispherical in shape, and apparently overlying the central
structures.’ On the analogy of similar appearances in recent Cycads Mr
Thomas[1462] interprets the two pairs of thickened patches as belonging
to the upper and lower sides of the highly inclined guard-cells. This
author calls special attention to the abundance on some of the fronds
included in the aggregate species _P. pecten_ of regular rows of
circular hair-scars preserved as small annulate projections, ·03–·04
mm. in diameter. A comparison of the cuticles of different forms of
_Ptilophyllum pecten_ enabled Thomas to recognise more than one type:
for one of these the name _Ptilophyllum hirsutum_ is proposed. It is
by such work as this that we may hope to discover differentiating
characters.
[Illustration: Fig. 590. _Ptilophyllum pecten_ (_P. cutchense_) and
_Williamsonia Blanfordi_. [Drawn from a specimen figured by Feistmantel
(76²) Pl. +xii.+ fig. 6.]]
[Illustration: Fig. 591. Part of the type-specimen of _Ptilophyllum
cutchense_ Morris. (British Museum; × 3.)]
[Illustration: Fig. 592. _Ptilophyllum pecten._ (Manchester Museum,
Williamson Coll. 3726.)]
[Illustration: Fig. 593. _Ptilophyllum pecten._ From the Lower
Estuarine beds, Cleveland, Yorkshire. (After Thomas; nat. size.)]
[Illustration: Fig. 594. _Ptilophyllum pecten_; stoma. (After Thomas
and Bancroft.)]
The different forms of _Williamsonia_ flowers found in association
with fronds of the _Ptilophyllum_ habit also point to the inclusion
of more than a single species under the group-species _P. pecten_. As
additional evidence is obtained further analysis will be possible,
but in dealing with impressions which include specimens transitional
from one form of frond to another, the most convenient and to my
mind the most logical course is to treat a species as an aggregate-
or group-species. Some authors believe that the two fronds described
by Phillips as _Cycadites pecten_ and _C. pectinoides_ are distinct
species[1463], but there would seem to be no adequate reason for this
view. The fronds described by Heer[1464] from the Lower Cretaceous of
Greenland as species of _Zamites_ and similar leaves from Graham Land
included in that genus by Halle[1465] are in my opinion inseparable
from _Ptilophyllum_, and this applies equally to _Otozamites Hislopi_
(Old.) (fig. 589) and _O. abbreviatus_ as figured by Feistmantel
and by Halle. The nomenclature of Cycadean fronds having the habit
of _Ptilophyllum pecten_ is a great difficulty: after carefully
reconsidering the whole question and comparing Feistmantel’s figured
specimens with the large series of English fronds the conclusion
reached is that the characters exhibited by ordinary impressions do not
admit of any satisfactory grouping under well-defined specific types.
In the first place, as already indicated, the use by some authors of
the generic names _Ptilophyllum_, _Otozamites_, and _Zamites_ creates
a false impression of the degree of difference between the numerous
forms of frond agreeing more or less closely with the specimens
on which were founded the species _Ptilophyllum acutifolium_, _P.
cutchense_, _P. pecten_, and _P. pectinoides_ (figs. 587, 591, 595,
etc.). In his important memoir on the Jurassic flora of Graham Land
Halle[1466] discusses the limitation of _Ptilophyllum_, _Zamites_,
and _Otozamites_. He employs _Zamites_ for fronds with linear pinnae
attached to the upper face of the rachis by a base which is more
or less, but often very little, rounded and always asymmetrical,
with or without a basal callosity: fronds of the type _Z. gigas_ he
includes in the section _Euzamites_, while _Z. borealis_ and similar
forms (fig. 597) are referred to a second section, _Subzamites_. It
is in the sense of Halle’s section _Euzamites_ that the generic name
_Zamites_ is employed in this chapter. On the other hand the fronds
grouped by Halle as _Subzamites_ have pinnae with the basal angles of
the lamina very slightly rounded precisely as in _Ptilophyllum_ as
seen in fig. 596 (_cf._ fig. 598 which represents fronds referred by
Halle to _Zamites_); and they are not distinguished by any feature of
generic importance from _Ptilophyllum_ as defined on page 519. The
species _Zamites pusillus_, _Z. Anderssoni_, and _Z. antarcticus_ (fig.
598) described by Halle from Graham Land as well as Heer’s Arctic
forms[1467] _Z. borealis_ (fig. 597), _Z. speciosus_, _Z. brevipennis_,
and others are transferred to _Ptilophyllum_ as types agreeing very
closely with _P. pecten_ and in some cases not clearly distinguishable
from it even specifically.
_Otozamites_ is the name employed by Halle for fronds with pinnae
having contracted, asymmetrical and auriculate, bases, the anterior
lobe being more developed than the posterior. The asymmetry of the
pinna-base is considered an essential feature. As Halle states it
is very difficult in some instances to draw a distinction between
_Otozamites_ and _Ptilophyllum_. As used in this chapter _Otozamites_
signifies fronds with pinnae characterised by an auriculate base, a
lamina usually broader than in _Ptilophyllum_, and by more spreading
veins (fig. 604). The not infrequent occurrence of auriculate pinnae on
fronds (fig. 603, A) which cannot be separated from typical examples of
_P. pecten_ illustrates the narrow dividing line as regards the form
of the pinna-base between _Ptilophyllum_ and _Otozamites_. The Indian
species _O. Hislopi_ (fig. 589) and _O. abbreviatus_, to which Halle
refers some Antarctic fronds, cannot be distinguished from the English
_P. pecten_ or Feistmantel’s and Morris’s Indian fronds described as
_P. cutchense_ and _P. acutifolium_: these forms are therefore included
in _Ptilophyllum_.
_Ptilophyllum_ (_Williamsonia_) _pecten_ (Phillips).
This designation is employed in a wide sense for a group of fronds
exhibiting a considerable range in size, in the relative breadth and
length of the linear pinnae, and in other features. Under _P. pecten_
are included (i) the English fronds from Yorkshire first described
by Phillips[1468] as _Cycadites pecten_ and _C. pectinoides_, the
former from the Middle shale, the latter from the Lower shale of the
Yorkshire coast, together with the Stonesfield slate specimens named
by Sternberg[1469] _Polypodiolites pectiniformis_ (fig. 595) and by
Brongniart[1470] and Lindley and Hutton[1471] _Zamia pectinata_; (ii)
the Indian specimens already considered and (iii) numerous examples
recorded under different names from Jurassic strata in many countries.
Fronds from the Yorkshire coast named by Brongniart[1472] _Zamia
Goldiei_, though regarded by some authors as examples of _Otozamites_,
are probably referable to _P. pecten_. Andrae’s _Pterophyllum
rigidum_[1473] (fig. 596) from Steierdorf is almost certainly a form
of _Ptilophyllum pecten_. The specimen shown in fig. 587 is one of the
few examples of fronds apparently preserved in their original position
attached in a cluster to a _Williamsonia_ (_Bucklandia_) type of stem.
The range in size and form of the pinnae is illustrated in figs. 588,
592, 593.
[Illustration: Fig. 595. _Ptilophyllum pecten._ The specimen figured
by Sternberg as _Polypodiolites pectiniformis_. (Oxford Museum; ⅚ nat.
size.)]
[Illustration: Fig. 596. _Ptilophyllum pecten._ Andrae’s
_Pterophyllum rigidum_ from Steierdorf, Banat. (British Museum, No.
41438; nat. size.)]
Fronds linear, tapering gradually towards the base and apex, often
characterised by a marked uniformity in breadth. The pinnae, short or
comparatively broad or long and narrow, are straight or more or less
falcate; the apex is obtuse or acute or the upper margin of the lamina
may be almost straight and the lower edge curved abruptly upwards
at the apex; the pinnae are usually attached obliquely to the rachis
but may be almost at right-angles; with the exception of the upper
angle, the whole of the base is attached to the frond-axis; the base
of the lamina may be symmetrical, both angles being slightly rounded,
or asymmetrical, the upper or less frequently the lower corner being
auriculate (figs. 592, 593). There is no basal callosity on the lamina
nor is there a median sinus. The veins are more or less spreading at
the base but for the most part parallel. The features of the epidermal
cells and stomata are mentioned in the general account of the genus.
Fertile shoots of plants with this type of frond are described
under _Williamsonia_. Very little is known of the stems which bore
_Ptilophyllum_ fronds, but as stated on page 488 Indian specimens show
leaves of _Ptilophyllum cutchense_ attached to a piece of stem (fig.
579) having the characters of _Bucklandia_ and characterised by a
xylem-cylinder denser than in recent Cycads; the structure of the wood
at least in the Indian stem is rather pycnoxylic than manoxylic.
The fronds grouped under _Ptilophyllum pecten_ are very widely
distributed in Jurassic floras; they are recorded from many
localities in Europe, from Turkestan[1474], India, Graham Land[1475],
Patagonia[1476], and elsewhere.
As thus defined this ‘species,’ or more correctly this group of forms,
undoubtedly includes more than one species in the strict sense, but
without additional data it is maintained that the recognition of
clearly defined specific types or varieties is beyond our power.
It may be urged that in view of the wide geographical range of the
_Ptilophyllum pecten_ type of frond and the admitted probability that
several species in the narrower sense are represented, distinctive
specific names should be retained even though under such designations
are included forms that, so far as can be seen from impressions,
exhibit no constant distinguishing features. My purpose is to emphasise
the futility of attempting to found well-marked species on the
available material. The student must decide for himself what course
to pursue, whether to retain such a specific name as _cutchense_ for
the Indian fronds or to employ that and other specific names as
designations of geographical types differing in no clearly defined
or constant characters from examples of the English _Ptilophyllum
pecten_. A comparative examination of the cuticular membranes in the
comparatively few cases where that is possible would probably furnish a
basis for a satisfactory subdivision of the group-species.
The names _Ptilophyllum Anderssoni_, _P. boreale_, and _P. antarcticum_
are retained for certain forms selected from a number of closely allied
types partly on the ground that these fronds exhibit some more or less
well-marked distinctive characters and in part as a recognition of the
existence of geographical forms.
_Ptilophyllum boreale_ (Heer).
Heer[1477] described numerous well-preserved impressions of pinnate
fronds from the Lower Cretaceous plant-beds of Kome, Greenland, which
he referred to several species of _Zamites_ though the differences
between them are hardly of specific rank. An inspection of several
of the figured specimens in the Stockholm Museum showed that Heer’s
drawings are in the main accurate. _Zamites borealis_ (fig. 597) is
characterised by small linear pinnae attached to the upper face of
the rachis, the stoutness of which is a noteworthy feature; the veins
are parallel and simple. In the shape of the pinnae, including the
base-characters, this species agrees closely with _P. pecten_. The
slightly falcate or straight pinnae are 1·7–2 mm. broad and reach
a length of 15 mm.; in _Z. speciosum_ Heer, probably specifically
identical with _P. boreale_, the pinnae are relatively longer, and in
_Z. brevipennis_ Heer they resemble the shorter pinnae of some of the
narrow fronds of _P. pecten_.
A preparation of the cuticle of a pinna of _P. boreale_ made by
Mr Thomas from a specimen in the Stockholm Museum shows a marked
difference between the upper and lower epidermis: the cells on the
upper surface of the lamina have very thick and sinuous walls precisely
as in _P. pecten_, but the cells are often broader than long and not
elongated parallel to the long axis of the pinna; those of the lower
epidermis are thinner and less clearly preserved: the stomata, which
appear to be like those of _P. pecten_, are scattered and not in rows.
[Illustration: Fig. 597. _Ptilophyllum boreale_ (Heer). Drawn from
one of the specimens from the Lower Cretaceous beds at Ekkorfat,
Greenland, figured by Heer. (Stockholm Museum; nat. size and a few
pinnae enlarged.)]
_Ptilophyllum antarcticum_ (Halle).
The fronds from the Jurassic rocks of Graham Land, described by Halle
as _Zamites antarcticus_[1478], are very similar to some forms of _P.
pecten_ and to _P. boreale_ and other Greenland forms; the linear
subacute pinnae are attached to the upper face of the rachis at a wide
angle and the base of the lamina is truncate and may be very slightly
constricted. The veins are dense, as many as 5 in 1 mm., and they are
occasionally forked near the base (fig. 598, A).
[Illustration: Fig. 598. A, A′, _Ptilophyllum antarcticum_. B, _P.
Anderssoni_. (After Halle.)]
_Ptilophyllum Anderssoni_ (Halle).
This Graham Land species (fig. 598, B), referred by Halle to
_Zamites_[1479], is of the same general type as _P. pecten_, but
is characterised by a coarser venation and by the wider angle of
attachment of the pinnae.
_Ptilophyllum Dunkerianum_ (Goeppert).
Goeppert[1480] proposed the name _Pterophyllum Dunkerianum_ for some
specimens from the Wealden of North Germany which were afterwards
figured by Dunker[1481]. Miquel[1482] included the species in his genus
_Dioonites_ and this name has been adopted by other authors. Attention
has been drawn to the inconsistent use of the title _Dioonites_[1483],
and I have previously employed the name in a sense similar to that in
which it has been adopted by Nathorst, that is for fronds with long
and narrow pinnae without any basal constriction and not auriculate,
attached more or less at right-angles to the upper face of the
rachis; but so defined _Dioonites_ differs in no essential particular
from forms of _Ptilophyllum_ or from fronds referred by authors
to Schimper’s genus _Ctenophyllum_. The name _Ctenophyllum_[1484]
was instituted for certain fronds differing in some points from
_Otozamites_ and _Dioonites_. One such type is _Ctenophyllum_
(_Ptilophyllum_) _pecten_ (Lind. and Hutt.): this is quoted in Zittel’s
_Handbuch_ as a typical representative of the genus. Schimper followed
Feistmantel in his definition of _Ptilophyllum_, a definition which
is not in accordance with the characters of the fronds on which it
was founded by Morris. Fontaine, on the other hand, has applied
_Ctenophyllum_ to fronds of a different type which are now included in
the genus _Pseudoctenis_. There would seem to be no adequate ground for
the retention of _Ctenophyllum_ as a generic designation.
The Wealden species _P. Dunkerianum_ is characterised by the following
features: rachis fairly stout, pinnae approximate, linear 2–3 mm. broad
and reaching a length of 11 cm. or more, gradually narrowed towards the
apex, attached in two almost contiguous rows to the upper face of the
frond-axis: the lower margin of the lamina may be slightly decurrent,
_e.g._ in the apical part of the frond or very slightly broadened and
bluntly rounded. The pinnae are attached at right-angles or, near the
apex, obliquely; veins 5–6, parallel. The epidermal cells as figured
by Schenk[1485] have very sinuous walls and are identical with those
of the English and Indian forms of the group-species _P. pecten_; the
stomata are confined to the lower surface. If Schenk’s drawings of the
stomata are correct they differ from those of other species of the
genus in their simpler structure; there are no subsidiary cells and
the guard-cells show no cuticularised bands. In habit this species
resembles _Encephalartos Ghellinckii_ Lehm. (fig. 382). The superficial
resemblance of the narrow linear pinnae to those of _Cycadites_ led
Dunker and Schenk to refer to that genus some specimens which have
since been described as identical with _P. Dunkerianum_.
=ZAMITES.= Brongniart.
In the first instance the generic name _Zamites_ was used in addition
to _Zamia_ for certain pinnate fronds including species[1486],
such as _Z. Bechei_, which are now regarded as typical examples of
_Otozamites_. Subsequently Brongniart gave up _Zamia_ for fossil fronds
and applied _Zamites_ to fronds with entire pinnae, not truncate at the
apex and not decurrent but slightly constricted at the base. Braun’s
two genera _Podozamites_ and _Pterozamites_ were relegated to the
position of subgenera. The name _Podozamites_ has been employed by
Schenk[1487] for specimens now included in _Zamites_, and _Zamites_ is
used by him[1488] for some fossils which are examples of _Podozamites_
as generally understood. Goeppert’s definition[1489] of _Zamites_
includes fronds with pinnae of the _Otozamites_ type, and this author
pertinently compares _Zamites_ with recent _Encephalartos_ leaves.
Pomel[1490] proposed the name _Crossozamia_ for certain fronds of the
_Zamites_ type, but this genus with several others instituted by the
same author has not been adopted. Bornemann[1491] described _Zamites_
as comprising species with a greater or less resemblance to the fronds
of recent Zamias.
As defined below, _Zamites_ fronds may be compared with those of
some species of _Encephalartos_, _Ceratozamia_, and _Macrozamia_.
There has been considerable difference of opinion with regard to
the range of form in the pinnae that it is advisable to include in
_Zamites_. The name _Zamiophyllum_ was proposed by Nathorst[1492]
for a Wealden species, described by Ettingshausen as _Pterophyllum
Buchianum_ (fig. 601, A–C), characterised by a decrease in the breadth
of the linear pinnae towards the point of attachment and, according
to Nathorst’s description, by the lateral attachment of the pinnae.
An examination of specimens of this type from English rocks[1493]
enabled me to show that the pinnae are attached to the upper face
of the rachis. Zeiller[1494] has also included _Zamiophyllum_ in
_Zamites_, but Halle’s recent definition[1495] of the latter genus
excludes fronds of the _Zamiophyllum_ type. Schimper instituted the
name _Glossozamites_[1496] for fronds bearing pinnae with rounded and
slightly contracted bases and borne on grooves on the upper surface
of the rachis (fig. 601, F). In venation the pinnae agree with those
of _Otozamites_ but the base is not auriculate. Kurr’s Liassic
species _Pterophyllum oblongifolium_[1497] included by Schimper in
_Glossozamites_ is probably an _Otozamites_. Another species referred
to this genus is Schenk’s _Podozamites Zitteli_[1498] from the Urgonian
of Austria (fig. 601, F): in this species the slightly falcate pinnae
with obtuse apices have rounded and not auriculate bases and there is
some evidence of a basal callosity. This species agrees so closely
with such a typical _Zamites_ as _Z. gigas_ that it is difficult to
see on what grounds the retention of _Glossozamites_ is desirable.
A Portuguese specimen referred by Saporta[1499] to _Glossozamites_,
_G. brevis_, is founded on a single specimen very like a leaflet of
_Otozamites Klipsteinii_ (Dunk.); and _G. parvifolia_ Yok.[1500] from
China has no claim to be included among Cycadean fronds. Feistmantel’s
_Glossozamites Stoliczkanus_[1501] is almost certainly a leaf of
_Cordaites_. For certain fronds originally described as _Zamites_
Zeiller[1502] has instituted the genus _Plagiozamites_. An important
question as to the type of frond which may conveniently be included
in the genus _Zamites_ was raised by the application of this name by
Heer to some Lower Cretaceous fronds from Greenland, _Z. borealis_ (=
_Ptilophyllum boreale_, fig. 597), and others which differ in the form
of the pinnae from species usually regarded as typical of the genus.
Halle[1503] accepts the Greenland species as examples of _Zamites_
though he distinguishes them by a sectional name _Sub-Zamites_; he
defines _Zamites_ as including fronds with pinnae attached to the
upper face of the rachis with a contracted and always symmetrical base
though in some cases the basal contraction is exceedingly small; there
is a more or less distinct basal callosity. He recognises two types,
(i) _Eu-Zamites_, _e.g._ _Zamites gigas_ (fig. 599), in which the
pinnae are strongly contracted basally and have a callosity, and (ii)
_Sub-Zamites_, _e.g._ _Z. borealis_[1504], etc., in which the pinnae
are not so broadly rounded at the base and retain the same breadth to
the point of insertion where they are ‘very rapidly and very little
contracted,’ with or without a basal callosity. The basal callosity
in these forms is not shown in many of the pinnae and is at most but
a slight rounding of the angles of the truncate base. The specimens
referred by Halle to _Sub-Zamites_ do not appear to differ in any
feature worthy of generic rank from _Ptilophyllum_.
In the following definition _Zamites_ is employed in a sense more or
less in accordance with Brongniart’s usage but with the inclusion of
such forms as _Z. Buchianus_, the type of Nathorst’s _Zamiophyllum_,
and the exclusion of Heer’s Arctic and Halle’s Antarctic fronds
referred by them to _Zamites_.
Fronds broadly lanceolate reaching a length of over 60 cm.; pinnae
more or less oblique or at right-angles to the rachis (fig. 599),
attached to the upper surface but not completely covering it, linear
or linear-lanceolate, acuminate or obtuse, usually abruptly contracted
at the rounded base and more rarely _(e.g._ _Z. Buchianus_, fig. 601)
gradually tapering to the proximal end, with or without a callosity
at the symmetrical base; veins divergent at the base, simple or
dichotomously branched, for the most part parallel to the edges of the
lamina and slightly divergent in the apical region. The presence of a
basal callosity, such as is best seen in the pinnae of recent species
of _Macrozamia_, is not a feature of great importance and cannot be
easily recognised in many impressions. In the process of fossilisation
the pinnae are often flattened against the surface of the rachis and
this may produce transverse wrinklings of the lamina suggestive of a
basal thickening. In some cases stems of the _Bucklandia_ type occur
in connexion with _Zamites_ fronds (fig. 541). An account of these
stems, and of inflorescences of _Williamsonia_ which were borne by
some at least of the plants with _Zamites_ leaves is given in Chapter
+xxviii.+ In such examples of _Zamites_ as have been examined the
epidermal cells have sinuous walls and the stomata[1505], confined to
the lower face of the lamina, occur in rows with their long axis at
right-angles to that of the pinnae.
_Zamites_ ranges from Rhaetic to Lower Cretaceous strata.
_Zamites truncatus_ Zeiller.
A Rhaetic species from Tonkin[1506] characterised by oval linear pinnae
given off at a wide angle, alternate and not contiguous; apex obtusely
truncate, gradually narrowed to a cuneate base which is rounded or
elliptical and has a more or less definite callosity. The pinnae vary
from 3 to 5 cm. in length and from 5 to 13 mm. in breadth.
_Zamites gigas_ (Lindley and Hutton).
The specific name _gigas_ is retained in preference to that of
_Mantelli_ employed by Brongniart[1507] on the ground that he
afterwards discarded it in favour of the designation proposed by
Lindley and Hutton[1508], and because their name has been generally
adopted.
Fronds large, exceeding 60 cm.; broadly linear lanceolate; the
comparatively slender rachis bears alternate linear lanceolate pinnae
with a rounded and usually slightly swollen base and an acuminate apex.
At the apex of the frond the pinnae are narrow and linear (fig. 599)
and almost parallel to the rachis; in the lower part they are shorter
and relatively broader and attached approximately at right-angles. The
numerous veins diverge from the centre of the base but for the most
part are parallel to the edge of the lamina. The form of the epidermal
cells and the structure of the stomata have recently been described by
Mr Thomas. The external features of the stem (fig. 541) are described
under the genus _Williamsonia_. In the case of fronds of this type
from English Jurassic rocks it would be legitimate to speak of them as
_Williamsonia gigas_, but in view of the fact that such fronds usually
occur as detached specimens and without any associated flowers it is
advisable, as Nathorst maintains, to retain the non-committal genus
_Zamites_.
[Illustration: Fig. 599. _Zamites gigas_. (British Museum, V.
2723_a_; ½ nat. size.)]
This type of frond is widely distributed in Jurassic strata. The
occurrence of many forms agreeing generally with the type-specimen
but differing from it in features that are not constant or of real
morphological importance renders accurate specific delimitation very
difficult. Species that appear to be indistinguishable from _Zamites
gigas_ by any well-marked characters are, _Zamites Feneonis_[1509]
Brongn., _Z. Moreaui_[1510] Brongn., _Z. Renevieri_[1511] Heer, and
_Z. claravallensis_[1512] Sap.; similarly _Z. Schmiedelii_ And.[1513]
is probably identical with _Z. gigas_. The Lower Cretaceous species
_Zamites bohemicus_[1514] Vel. and _Z. iburgensis_[1515] Hos. and von
d. Marck represent very similar forms.
_Zamites recta_ (Tate).
[Illustration: Fig. 600. _Zamites recta_. (Uitenhage series, S.
Africa.)]
This species was originally described by Tate[1516] as _Palaeozamia_
(_Otozamites_) _recta_ from Wealden strata in South Africa and
subsequently transferred to _Zamites_[1517]; it bears a very close
resemblance to _Z. gigas_. The fronds bear alternate linear pinnae
attached to the upper face of the rachis by a slightly contracted
and swollen base. The lamina has an acuminate asymmetrical apex and
the upper edge is slightly falcate; the larger pinnae are over 6
cm. long and nearly 1 cm. broad; the veins are frequently forked as
they converge towards the base of the lamina. No clear evidence of
association of these fronds in the Uitenhage series of South Africa
with _Williamsonia_ flowers has been discovered, but a specimen[1518]
in the Tate collection in the British Museum may be a badly preserved
cluster of bracts belonging to a _Williamsonia_. The rachis of this
species shows some peculiar features in the form of two rows of
alternate cushions in some partially decayed specimens. One of these is
shown in fig. 600; the cushions are raised oval projections with a flat
top, and pieces of the rachis without pinnae might easily be mistaken
for a Coniferous stem.
_Zamites Carruthersi_ Seward.
A species founded on specimens from the Wealden of Sussex[1519] and
recorded from Kimmeridge beds in Scotland[1520], characterised by
linear or linear-elliptical pinnae attached obliquely to the outer
part of the upper surface of the rachis, somewhat abruptly narrowed
at the proximal end but slightly broadened at the actual base (fig.
601, D, E). The pinnae appear to have been caducous and, as in fig.
601, D, the position of an absciss-layer is occasionally visible. In
habit the fronds bear a close resemblance to those of _Encephalartos
longifolius_ Lehm. The veins diverge from the base and are for the most
part parallel, though divergent at the bluntly rounded apex. If, as
may be the case, a specimen figured by Hugh Miller[1521] from Scotland
as _Zamites_ and subsequently named by Richards[1522] _Podozamites
Milleri_ is identical with _Z. Carruthersi_, the specific name
_Milleri_ has priority.
[Illustration: Fig. 601. A–C, _Zamites Buchianus_. D, E, _Zamites
Carruthersi_. F, _Zamites Zitteli_. (A–C after Seward; British Museum;
A, V. 2363; B, V. 2123_a_; C, V. 2227; F, after Schenk.)]
_Zamites Buchianus_ (Ettingshausen).
[Illustration: Fig. 602. _Zamites Buchianus_. (British Museum, V.
2120; ⅙ nat. size.)]
A Wealden and Lower Cretaceous species[1523] (figs. 601, A–C; 602)
represented in several European localities, also in North America
and Japan, reaching a length of over 70 cm.; in habit very similar
to _Ceratozamia mexicana, Macrozamia Macleayi_ and some other recent
Cycads. The rachis has a fairly broad median groove on the upper
surface; pinnae alternate, opposite or sub-opposite, from 3 to 20 cm.
long and from 1·5 to 2 cm. broad, linear, generally narrowed towards
the base, but in the more slender segments the reduction in breadth
is less obvious; attached obliquely to the rachis, slightly thickened
and broadened at the base (fig. 601, C), separated from the rachis
by a distinct absciss-layer and leaving an elliptical scar; usually
inclined at about 45° but the angle varies considerably in different
parts of a frond (fig. 602); apices generally tapering to a point, or
more or less obtusely rounded; veins numerous, parallel, and not as
a rule prominent. It is by no means unlikely that specimens figured
by Goeppert[1524] and some other authors as _Pterophyllum saxonicum_
or _Dioonites saxonicus_ are examples of this species. Fontaine[1525]
speaks of _Dioonites Buchianus_ as one of the most widely distributed
and characteristic members of the Potomac flora and it is described
from Japan by Yokoyama[1526] and Nathorst[1527]. This type appears to
be especially characteristic of Wealden strata.
=OTOZAMITES.= Braun.
Braun[1528] proposed the name _Otozamites_ for certain Mesozoic fronds
formerly included in _Zamites_, one of his types being _Otozamites
obtusus_ (Lind. and Hutt.) (fig. 603, B) originally regarded by
Brongniart as a Fern and named _Filicites Bucklandi_[1529]. The
auriculate form of the base of the pinnae and the spreading veins were
emphasised in the definition of the genus. As in the case of many other
Cycadean fronds the limits of the genus are not always easy to define,
but as described below the genus is on the whole fairly distinctive.
It is a very widely spread Jurassic type and extends from Triassic to
Lower Cretaceous rocks. The supposed Cretaceous species from Greenland,
_O. groenlandica_ Heer[1530], is probably not a plant-impression but a
polished groove in the rock.
Fronds pinnate, reaching a length of 50 cm. or more in some species;
pinnae alternate, separate or contiguous and imbricate, attached by
a portion of the base to the upper surface of the rachis, long and
narrow (fig. 603, A), broadly oval or almost orbicular, apex acute
or obtuse, base auriculate and asymmetrical[1531], the anterior lobe
being more prominent than the posterior edge of the lamina which is
usually rounded. The veins radiate from the base and pass obliquely
with occasional branching to the edge of the pinna; in the more
linear pinnae the veins may be parallel or nearly so. Zigno[1532]
figured a piece of an _Otozamites_ frond from Jurassic Italian strata
in connexion with a _Williamsonia_ and the actual specimen in the
Padua Museum amply justifies the impression produced by the published
drawing. Wieland’s investigations[1533] in Mexico have brought to light
many cases of association of _Otozamites_ fronds and _Williamsonia_
flowers.
[Illustration: Fig. 603. A, _Otozamites Goeppertianus_. B,
_Otozamites obtusus_ (= _O. Bechei_); type-specimen. (A, British
Museum, V. 2360; B, Oxford Museum.)]
The structure of the epidermis is partially described by Schenk[1534]
and more fully by Thomas[1535]: the epidermal cells have sinuous
walls and the stomata, apparently confined to the lower surface,
have guard-cells with hemispherical or spindle-shaped thickened
patches like those of some _Zamites_ fronds. In one species, _O.
Feistmanteli_ Zig., Thomas found about 100 stomata in 1 sq. mm. of
lamina forming almost contiguous lines between the veins. In the
account of the genus _Ptilophyllum_ reference is made to the occurrence
of pinnae with asymmetrical and auriculate bases, and it is only by
the comparison of a large number of specimens that a distinction can
be drawn between fronds that should be assigned to _Otozamites_ and
forms of _Ptilophyllum_ which exhibit a well-marked tendency towards
the _Otozamites_ type of pinna (_cf._ figs. 592, 593). The variation
in the form of the apices of pinnae and the relative position of the
pinnae in different parts of the same frond are features worthy of
notice in the determination of species[1536]. The different appearance
presented by an _Otozamites_ frond as viewed from the upper and lower
face is illustrated in fig. 604. There are no recent Cycads in which
the segments have auriculate bases, but in this feature as in the
sinuous epidermal walls _Otozamites_ agrees with some species of the
Fern _Aneimia_, _e.g._ _A. rotundifolia_ Schrad. (fig. 223, Vol. +ii.+
p. 288).
[Illustration: Fig. 604. _Otozamites Bechei._ A specimen in the Bristol
Museum seen from below (A) and above (B). M. S.]
_Otozamites Bechei_ Brongniart.
There is considerable confusion in the nomenclature of this species
described by Brongniart[1537] from Jurassic strata as _Filicites_
_Bechei_: in it Brongniart included a specimen from the Lias of
Axminster (Dorsetshire) previously figured by De la Beche as a fossil
Fern. It was on the Axminster specimen that Lindley and Hutton founded
the species _Otopteris obtusa_[1538], and as there is no doubt as to
the specific identity of their type-specimen (fig. 603, B) and De
la Beche’s fossil, Brongniart’s designation has prior claim[1539].
_Otozamites Bechei_ is, perhaps, best regarded as a comprehensive type
or a group-species in which numerous _Otozamites_ fronds described
by authors, on inadequate grounds, as distinct species may well be
included. Fronds agreeing generally with _O. Bechei_ were very widely
spread in Rhaetic and Jurassic floras.
Specimens from the Middle Jurassic rocks of Yorkshire have been
described as _Otozamites obtusus_ var. _ooliticus_[1540] to denote
a slight difference in the form of the pinnae from the Liassic
fronds from Dorsetshire; but the distinctive features of the variety
_ooliticus_ are unimportant and hardly worthy of consideration in a
general account of the species interpreted in a wide sense.
Fronds pinnate; pinnae usually more or less falcate, occasionally
straight and with parallel sides, attached obliquely to the upper side
of the rachis; imbricate or separate, the upper edge of the base of the
lamina strongly auriculate, the lower edge rounded; apex obtuse; veins
strongly divergent especially in the lobed base and extending obliquely
to the upper and lower edge of the lamina.
The specimen, from the Lias of Lyme Regis, drawn in outline in fig.
605, is an almost perfect frond: the pinnae are obtusely pointed,
slightly falcate, and there is a prominent lobe on the upper edge of
the base of the laminae.
The Jurassic species _Otozamites graphicus_[1541] (Leck. ex Bean
+MS.+), _O. vicetinus_ Zig.[1542], _O. Hennocquei_[1543] (Pom.),
_O. recurrens_ Sap., _O. Terquemi_[1544] Sap., _O. linearis_[1545]
Halle, are some of many examples of fronds agreeing closely with
_O. Bechei_, or in the case of _O. Terquemi_ with _O. graphicus_.
The fronds described by Halle from Graham Land as _O. linearis_
afford a good illustration of the range of variation in the pinnae: a
characteristic feature is the considerable length, exceeding 20 cm., of
the narrow linear fronds. The impressions from the Kome (Cretaceous)
beds of Greenland described by Heer as _Glossozamites Schenkii_[1546]
are probably closely allied to _O. Bechei_. The Rhaetic species _O.
Bucklandi_ Schenk[1547], _O. indosinensis_ Zeill.[1548], and _O.
Polakii_ Krass[1549], illustrate older examples of closely allied
types. Zeiller records _Otozamites_ pinnae similar to those of _O.
indosinensis_ from Rhaetic beds in Persia[1550].
_Otozamites Beani_ (Lindley and Hutton).
[Illustration: Fig. 605. _Otozamites Bechei._ (British Museum, 40672;
⅔ nat. size.)]
Founded on a specimen in the Scarborough Museum from the Middle
Jurassic of Yorkshire[1551] which is indistinguishable from Leckenby’s
type-specimen of _Otopteris mediana_[1552] in the Sedgwick Museum,
Cambridge. Long and narrow fronds exceeding 20 cm. in length,
characterised by the broadly oval, deltoid or sub-orbicular pinnae,
separate or partially imbricate and attached by a broad auriculate
base; apex bluntly rounded; veins numerous and spreading from the base
of the lamina. The pinnae, which may be 3·5 cm. long and nearly 2 cm.
broad, are narrower and longer in the distal part of the frond (fig.
606).
The Italian Jurassic species _Otozamites molianus_ Zig.[1553],
recorded also from Bornholm, is a very similar type. The generic name
_Cyclozamia_ suggested by Pomel for this form of frond has not been
adopted though it is applied by Schimper to _O. Bunburyanus_ Zig.
_Otozamites Bunburyanus_ Zigno.
A Jurassic species[1554] similar in the long and narrow form of the
frond to _O. Beani_ but distinguished by the much smaller segments
and by their more orbicular lamina (fig. 606, B). In habit the
fronds agree closely with the Fern _Nephrolepis Duffi_. Leckenby’s
species, _Otopteris tenuata_[1555], is probably the same as Zigno’s _O.
Bunburyanus_, the type-specimen of which in the Padua Museum consists
of a long and narrow frond with leaflets not exceeding 8 cm. in length;
the rachis is hidden by the imbricate auriculate bases of the leaflets.
Feistmantel[1556] refers to this species some pieces of very narrow
fronds with overlapping pinnae from Upper Gondwana beds in India. A
still smaller form is described by Möller[1557] from Bornholm as _O.
tenuissimus_, and _O. Bunburyanus_ is recorded from the same flora. _O.
Feistmanteli_ Zig.[1558] agrees in the form of the frond and in its
short and broad pinnae with _O. Bunburyanus_.
[Illustration: Fig. 606. A, _Otozamites Beani_. B, _Otozamites
Bunburyanus_.]
[Illustration: Fig. 607. _Otozamites bengalensis_. (Indian Geological
Survey, Calcutta; ⅔ nat. size.)]
_Otozamites bengalensis_ (Oldham and Morris).
This Indian species from the Rajmahal Hills[1559] and specimens of
the same type from the Cutch flora described as _O. contiguus_ Feist.
afford another illustration of long and narrow fronds with short and
relatively broad pinnae. The drawings published by Oldham and Morris
accurately represent the specimens: the longest frond is 21 cm. long
and neither end is complete (fig. 607); it is 9 mm. broad at the
narrower end and 1·5 cm. at the broader end. The rachis is represented
by a deep and broad groove; the actual bases of the leaflets are
not preserved, but their position shows that they were attached to
the upper face: this is clearly seen in the specimen described by
Feistmantel as _O. contiguus_ which shows also that the lamina is
auriculate at the upper edge of the base. The pinnae vary in shape;
the smaller ones are characterised by a strongly curved lower margin
and the upper edge is slightly curved or straight, while the larger
leaflets have more parallel edges and blunter rounded apices: the
latter form is well shown in the specimens unnecessarily distinguished
by Oldham and Morris as var. _obtusa_.
_Otozamites Klipsteinii_ (Dunker).
This Wealden species, first described by Dunker as _Cyclopteris
Klipsteinii_[1560], is remarkable for the large pinnae. The rachis is
fairly stout; the broadly oval or oblong pinnae vary considerably in
size and in the relation of breadth to length, in rare cases reaching
a length of over 8 cm. and a breadth of 2·4 cm.; apex obtuse, base
slightly auriculate and asymmetrical; veins numerous, radiating from
the point of attachment to the margin of the lamina. The occurrence
of finer lines between the more prominent veins may indicate the
presence of hypodermal stereome strands. Fig. 608 illustrates the
striking variation in the size of the pinnae on a single frond and
their attachment to the upper face of the rachis. In the breadth of
the segments _O. Klipsteinii_ resembles _O. Beani_ (Lind. and Hutt.),
_O. decorus_ Sap.[1561], _O. lagotis_ Brongn.[1562] and two species
from South Russia described by Thomas[1563] as _O. Izuimensis_ and
_O. giganteus_. The pinnae of _O. giganteus_ exceed 10 cm. in length
and 3 cm. in breadth, thus surpassing the largest segments of _O.
Klipsteinii_. Some pinnae from the Jurassic flora of Oregon made by
Fontaine the type of a new species, _O. oregonensis_[1564], may be
fragments of _O. Klipsteinii_. Nathorst[1565] records the occurrence in
Lower Cretaceous or Wealden beds in Spitzbergen of Cycadean leaflets
very like those of _O. Klipsteinii_.
_Otozamites Goeppertianus_ (Dunker).
This Wealden species, named by Dunker[1566] _Pterophyllum
Goeppertianum_, agrees in habit with some of those to which
reference is made under _O. Bechei, e.g. O. linearis_ Halle, and
represents a type of the genus with unusually narrow pinnae (fig.
603, A). The auriculate form of the lamina is feebly developed; the
linear-lanceolate pinnae are occasionally falcate and have acute
apices; as in many other species they were apparently deciduous. It is
by no means easy to distinguish some of these fronds from specimens
included in _Ptilophyllum pecten_.
[Illustration: Fig. 608. _Otozamites Kliptsteini_. (British Museum,
V. 3709; nat. size.)]
=DICTYOZAMITES.= Oldham.
This generic name was instituted[1567] for pinnate fronds from the
Rajmahal series of India, assigned by Feistmantel to a Lower Jurassic
horizon, but probably nearer in age to the Middle Jurassic series.
Morris, joint author with Oldham of the Memoir on the Rajmahal plants,
adopted the name _Dictyopteris_. _Dictyozamites_ agrees very closely
with _Otozamites_ but is readily distinguished by the anastomosing
veins (fig. 609), while the absence of a midrib differentiates it
from the Palaeozoic genus _Dictyopteris_. The genus is recorded also
from Jurassic strata in England, Bornholm, Japan[1568], Korea[1569],
and from a locality 60 nautical miles N.W. of Cape Horn in Tierra
del Fuego[1570]: the specimens from these localities differ only in
unimportant details from the Indian type. _Dictyozamites_ is confined
to Jurassic floras and appears to be especially characteristic
of Middle Jurassic floras. In India[1571] fronds occur in close
association with stems of the _Bucklandia_ type and, although there
is no proof of any connexion with stems or flowers, it is probable
that the fronds of this generic type were borne on stems similar to
those of _Bucklandia_ and that the flowers were constructed on the
_Williamsonia_ plan.
_Dictyozamites falcatus_ (Morris).
Morris[1572] described this Rajmahal species under the names
_Dictyopteris falcata_ and _D. falcata_ var. _obtusa_; the specimens
were included by Feistmantel under the designation _Dictyozamites
indicus_, the original term _falcata_ being discarded without adequate
reason. An examination of several of the figured fronds enables me
to confirm the accuracy of the published drawings and to extend the
description in a few particulars. Fronds pinnate of the habit of
_Otozamites_; pinnae comparatively thick, broadly linear, alternate,
varying considerably in size and in the form of the apex which may
be obtuse or acute. The pinnae are attached by the middle part of
the lamina only; the upper edge of the base is slightly rounded or
auriculate; the lower angle is generally more definitely lobed. The
imbricate bases completely cover the upper face of the comparatively
slender rachis. The longest pinna seen on an Indian frond is 6 cm. with
a breadth of 2 cm. Some of the pinnae on magnification exhibit a finely
tuberculate appearance, due no doubt to the presence of papillae on
the epidermal cells like those on the pinnae of English and Bornholm
specimens. This species is recorded by Yokoyama[1573] from Japan as
_D. falcatus_ var. _distans_, and a similar form, referred by him to a
distinct species, _D. grossinervis_, may be more appropriately named
_D. falcatus_ var. _grossinervis_[1574]. The Indian type occurs also in
Jurassic rocks of Korea, and Halle has discovered some _Dictyozamites_
leaves in Tierra del Fuego[1575] which he describes as _Dictyozamites_
sp. _cf._ _D. falcatus_: this record is of special interest from a
phytogeographical point of view.
_Dictyozamites Johnstrupi_ Nathorst.
This species[1576], from rocks usually spoken of as Liassic but not
improbably Middle Jurassic in age, differs from _D. falcatus_ in the
slightly more falcate form of the pinnae and in the more strongly
auriculate upper angle of the base of the lamina. The stomata[1577]
are confined to the lower epidermis and the strongly cuticularised
guard-cells frequently lie at right-angles to the course of the veins.
The epidermal cells have very sinuous walls (fig. 609, C) and in the
middle of each is a prominent papilla.
_Dictyozamites Hawelli_ Seward.
This Middle Jurassic type from Marske[1578], Yorkshire, differs from
_D. falcatus_ in the relatively broader segments, their straighter form
(fig. 609, B), and in the attachment to the rachis being slightly below
the middle of the pinna base. Fig. 609, A, shows the base of a pinna
and an oval scar similar to those on the rachis of some recent Cycads
(_cf._ fig. 387). The epidermis is like that in _D. Johnstrupi_ and as
in that species the stomata are confined to the lower surface. There
are approximately 120 stomata per square millimetre; each with two
subsidiary cells (fig. 609, C) of elongated form, and the guard-cells
have small thickened outgrowths or papillae as in _D. Johnstrupi_.
The epidermal features are described under _D. Johnstrupi_ and _D.
Hawelli_ (fig. 609, C): a fuller account of those in the latter species
will be found in the paper by Mr Thomas and Miss Bancroft.
[Illustration: Fig. 609. _Dictyozamites Hawelli._ (A, B, British
Museum; C, after Thomas and Bancroft.)]
=PTEROPHYLLUM.= Brongniart.
The name _Pterophyllum_ was first applied by Brongniart[1579] to some
fronds from the Lias of Höör, which he named _P. majus_ and _P. minus_,
species subsequently removed by Nathorst[1580] to Schimper’s genus
_Anomozamites_. Brongniart[1581] defined _Pterophyllum_ fronds, _e.g._
_P. Jaegeri_ (fig. 610), as pinnate, bearing pinnules of almost equal
breadth attached by the whole width of the base and with a truncate
apex; veins slender, equal, simple and slightly arched. There has been
considerable confusion and laxity in regard to the application of the
name _Pterophyllum_ and in many cases no clear distinction has been
recognised between this genus and _Nilssonia_. In _Nilssonia_ the
distinctive feature is the complete absence of any rachis uncovered
by the lamina on the upper face of well-preserved specimens, while
in _Pterophyllum_ the continuity of the lamina is broken by a greater
or less breadth of rachis in the middle line of the frond; the lamina
does not cover the rachis but is attached laterally, or at least the
two laminae of the frond, whether entire or deeply dissected, do not
meet in the middle of the rachis. A specimen from the Cretaceous of
Greenland described by Heer as _Pterophyllum concinnum_[1582] and now
in the Stockholm Museum is probably a piece of a _Nilssonia_; the
rachis is not exposed on the surface of the frond. In _Nilssonia_ the
veins are with few exceptions simple; in _Pterophyllum_ they are often
branched especially near their origin from the rachis: in _Nilssonia_
the segments are of unequal breadth; in _Pterophyllum_ they are
usually equal. It has been the practice of several authors to follow
Schimper[1583] in the employment of the generic name _Anomozamites_
for fronds with a more or less entire or irregularly pinnatisect
lamina which bear a very close resemblance to _Nilssonia_ except that
a portion of the rachis is exposed on the upper face. Potonié[1584]
used _Pterophyllum_ in a wider sense including both fronds with equal
pinnae and those of the _Anomozamites_ type: this more extended use
of _Pterophyllum_ is adopted by Zeiller[1585] who prefers to retain
_Anomozamites_ only as a sub-genus. It is in this sense that the
following definition is framed.
[Illustration: Fig. 610. _Pterophyllum Jaegeri._ From the Keuper of
Lunz; part of a frond 23·5 cm. long and incomplete. (British Museum, V.
1044; nat. size.)]
Fronds pinnate; pinnae linear, attached by the whole base, which may be
enlarged; the apex is truncate, rounded, or occasionally pointed; the
veins are simple or dichotomously branched and parallel to the edge of
the lamina. In some fronds (sub-genus _Anomozamites_) the segments are
unequal (fig. 615), short, broad and truncate, and the lamina may be
entire or divided into a few very unequal segments. The surface of the
rachis is never completely covered by the lamina on the upper face of
the frond and is often characterised by transverse wrinklings, possibly
due to the presence of ramental scales.
Some interesting xerophilous features have recently been described by
Halle[1586] in the lamina of _Pterophyllum (Anomozamites) marginatum_,
a Rhaetic species figured by Schenk and Nathorst from Franconia and
Scania. The pinnae were thick and succulent. Stomata are confined
to the lower surface and the edges of the upper face of the lamina
form a rounded curve causing the thick upper cuticle to abut on the
thinner stomatiferous lower cuticle, thus producing in impressions the
appearance of thickened margins.
There is no satisfactory evidence as to the nature of the reproductive
organs or stems of the plants which bore fronds of the type represented
by _P. Jaegeri_ (fig. 610) and other forms with equal segments. A
stem referred by Heer[1587] and by Leuthardt[1588] to _Pterophyllum_
was not found in connexion with leaves, and there is the same absence
of any convincing evidence in the case of the imperfect specimens
from the Keuper of Basel believed by Leuthardt to be male and female
inflorescences. On the other hand leaves of _Anomozamites_ are known
to have been borne on comparatively slender stems with dichasial
branching, and the reproductive shoots are of the same general type
as those known as _Bennettites_. This discovery is due to Nathorst
who founded the genus _Wielandiella_[1589] on fertile stems with
_Anomozamites_ fronds. Mr Thomas[1590] has recently obtained evidence
from Yorkshire Jurassic material pointing to a similar connexion
between _Anomozamites_ fronds and _Wielandiella_ stems. _Pterophyllum_
is further distinguished from _Nilssonia_ by the folded walls of the
epidermal cells and by the presence of two crescentic subsidiary
cells (fig. 611, A) instead of the ring of cells which surrounds the
guard-cells in _Nilssonia_ (fig. 611, B). Schenk[1591] figured a few
pieces of cuticle from fronds referred to _Pterophyllum_ in which
the walls are more or less sinuous, but the cells of _Pterophyllum
crassinerve_ Goepp.[1592] appear to have straight walls: this species
is, however, probably a _Nilssonia_. The stoma represented in fig.
611, A, is from the lower epidermis of _Pterophyllum_ (_Anomozamites_)
_Nilssoni_ (Phill.)[1593].
_Pterophyllum_ extends from Upper Carboniferous to Lower Cretaceous
strata and is especially characteristic of Keuper and Rhaetic floras.
A possible representative of the sub-genus _Anomozamites_ is described
by Ettingshausen from Tertiary beds in New South Wales as _Anomozamites
Muelleri_[1594].
[Illustration: Fig. 611. A, _Pterophyllum Nilssoni_; B, _Nilssonia
mediana_. (After Thomas and Bancroft.)]
_Pterophyllum Fayoli_ Renault and Zeiller.
This species[1595] was founded on a large frond from the Commentry
coalfield with a stout rachis bearing linear pinnae, attached along
a narrow groove on its outer edge, reaching a length of 12 cm. and a
breadth of 1 cm.; adjacent pinnae are united at the base. The apices
are pointed and there are 10–12 unbranched veins in the lamina. Fig.
612 shows a small piece of the large specimen in the Natural History
Museum, Paris.
_Pterophyllum_ sp. Arber.
The only representative of a Carboniferous frond of Cycadean habit
discovered in Britain is that recorded by Arber[1596] from Westphalian
strata at a depth of 1834 ft at Barfreston in Kent. A fairly stout
rachis bears incomplete pinnae the longest of which is slightly more
than 1 cm. in length and 1–1·5 cm. broad; each segment, very slightly
contracted at the base, has 3–4 occasionally forked veins. Arber
compares the fragments with _Pterophyllum blechnoides_ Sand. from
Germany[1597].
_Pterophyllum Cambryi_ Renault.
This Permian species from Autun[1598] is similar to _P. Fayoli_, but
differs in the more slender rachis and in the finer venation of the
linear, acute, pinnae. The pinnae in Renault’s specimen reach a length
of 4·8 cm. and are from 3·5–4 mm. broad; they are slightly confluent at
the base and the veins occasionally fork.
[Illustration: Fig. 612. _Pterophyllum Fayoli_. (From the
type-specimen, Paris; ⅓ nat. size.)]
Among other Palaeozoic species are _Pterophyllum Grand’Euryanum_ Sap.
and Mar.[1599] discovered by Grand’Eury in the Coal Measures of France,
_P. blechnoides_ Sand.[1600] from the Upper Coal Measures of Oppenau
and recorded by Geinitz[1601] from the Middle Permian of Germany, _P.
Cottaeanum_ Gutb.[1602], a similar type, also from Permian rocks,
but with coarser venation. The specimens figured by Geinitz as _P.
blechnoides_ and _P. Cottaeanum_ are in the Dresden Museum: the former
species is represented by a good impression on shale which shows the
generic characters very clearly.
_Pterophyllum Jaegeri_ Brongniart.
Brongniart[1603] founded this species (fig. 610) on material from the
Keuper of Stuttgart. The fronds are characterised by the relatively
narrow parallel-sided pinnae with rounded or truncate apices and little
or no basal contraction; the pinnae may be contiguous or separate.
There are 14–16 veins in each pinna. Leuthardt[1604], who figures
several examples of this species from Keuper strata at Basel, speaks
of the breadth-index of the pinnae as 12, a term employed to denote
the relation of the breadth to the length of a segment. _Pterophyllum
longifolium_[1605] is a very similar Keuper type: in this species
the pinnae are rather shorter and broader than in _P. Jaegeri_ and
contracted at the base; the apex is truncate or obtuse. The differences
between these species is, however, very trifling. The imperfectly
preserved fossils figured by Leuthardt[1606] as the inflorescences
of _Pterophyllum_ have not been found in connexion with fronds and
their nature is problematical. This and other species are recorded by
Krasser[1607] from the Lunz beds in Austria.
_Pterophyllum Bronni_ Schenk.
A Keuper species[1608] from Raibl in Carinthia distinguished by its
large pinnae, 15 cm. or more in length and 0·5 cm. broad, and by their
almost digitate disposition on the rachis. The fronds appear to be
relatively short: the upper pinnae are highly inclined while the lower
are given off at an obtuse angle; they are obcuneate or more or less
oblanceolate, with a truncate asymmetrical apex and rounded angles; the
base is slightly contracted. Arber[1609] has figured some specimens
from the Munich Museum in one of which there are five spreading pinnae
and a portion of the rachis; one pinna is undoubtedly attached and
the others, though probably in place, are not in actual connexion
with the axis. There is a close resemblance between this species
and _Sphenozamites Rogersianus_ Font.[1610]: in the American type
the fronds must have been 1 met. long; the leaflets, 19 × 9 cm., are
elliptical, broadest near the apex and attached by the middle of the
rounded base. Between the divergent and forked veins there is a fine
granulation probably due to the presence of papillae. _Pterophyllum
Bronni_ and _P. Rogersianum_ might be placed in Schimper’s genus
_Macropterygium_[1611], though another Raibl species, originally
described by Schenk as _Pterophyllum giganteum_[1612] and referred by
Schimper to _Macropterygium_, has much longer and relatively narrow
pinnae and agrees more closely with _Pterophyllum_ as the genus is
usually defined. In order to emphasise the distinctive features of
_Pterophyllum Bronni_ and Fontaine’s Virginian species they may
conveniently be spoken of as _Pterophyllum (Macropterygium) Bronni_ and
_Pterophyllum (Macropterygium) Rogersianum_.
[Illustration: Fig. 613. _Pterophyllum Braunianum._ (A, nat. size; B,
enlarged; after Schenk.)]
_Pterophyllum Braunianum_ Goeppert.
In this Rhaetic species[1613] (fig. 613) the narrow linear pinnae,
contiguous or more or less distant, are 1–2 mm. broad and may exceed 5
cm. in length though they are usually shorter; they are attached more
or less at right-angles to the sides of a transversely wrinkled rachis.
The base of the lamina is broadened and the veins are parallel, simple
or forked. The epidermal cells have sinuous walls.
_Pterophyllum Tietzei_ Schenk.
A Rhaetic species founded[1614] on specimens from Persia and described
also by Zeiller[1615] from Tonkin represented by fronds 1 met. long
and at least 15 cm. broad. The segments, 3–7 cm. long and 8–18 mm.
broad, are often set at right-angles to the rachis; the edges are
parallel but the lower edge bends upwards at the apex. The veins are
simple or forked and approximately 0·3 mm. apart.
_Pterophyllum Bavieri_ Zeiller.
This Rhaetic species from Tonkin[1616] and Persia[1617] is interesting
as affording an example of a frond with exceptionally narrow and
contiguous pinnae. The frond is narrow and lanceolate, 15–20 cm. long
with pinnae normal to the rachis, ·5–1 mm. broad and 7–25 mm. long
attached by the whole base which is sometimes slightly enlarged. The
veins are simple or forked, ·15–·25 mm. apart: the apices of the
segments are rounded or truncate and the form of the whole is similar
to that of _Pterophyllum aequale_ but narrower.
_Pterophyllum_ (_Anomozamites_) _inconstans_ Braun.
In habit this Rhaetic species[1618] resembles _Nilssonia compta_.
The linear-lanceolate fronds, as described by Zeiller[1619] in his
Tonkin memoir, attain a length of 20 cm. and a breadth of 4 cm. The
rachis, characterised by numerous transverse ridges, bears alternate
or sub-opposite leaflets often at right-angles; they are almost
rectangular and hardly longer than broad, attached by the whole of the
base, which may be broadened, to the upper face of the rachis, but
the lamina does not cover the whole of the rachis as in _Nilssonia_.
The pinnae vary in breadth on the same frond and occasionally the
lamina is continuous as in some forms of _Nilssonia_. Schenk[1620]
figures examples from the Rhaetic of Franconia in which the lamina
is very irregularly dissected and may be entire for a considerable
distance. The epidermal cells have slightly sinuous walls. A similar
type is represented by _Pterophyllum_ (_Anomozamites_) _Schenki_
Zeill.[1621], but the segments are contracted basally and become
wider towards the apex where, as in _P. inconstans_, the edges are
parallel. Feistmantel’s species _Platypterygium_ _Balli_[1622], though
superficially similar to _Pterophyllum_, appears to agree more closely
with _Pseudoctenis_.
[Illustration: Fig. 614. A, B, _Pterophyllum Nathorsti_; A from below;
B from above. C, _Nilssonia tenuicaulis_. (A, B, Gunn Collection,
British Museum; C, Arber Coll. Sedgwick Museum, 539; nat. size.)]
_Pterophyllum Nathorsti_ Seward.
This species, founded on a specimen in the Sedgwick Museum, Cambridge,
from the Middle Jurassic beds of Yorkshire, was formerly referred to
the genus _Dioonites_[1623], but since the Yorkshire specimens were
supplemented by material from Kimmeridge strata in Scotland[1624]
affording more definite information with regard to the attachment of
the pinnae it has been transferred to _Pterophyllum_. Pinnae laterally
attached to the rachis which in some specimens shows a transverse
wrinkling, narrow, linear, 3–4 mm. wide and reaching a length of 9 cm.
The base of the segments is slightly expanded; the apex is acuminate
or bluntly pointed: there are approximately three veins in 1 mm. of
lamina. This type (fig. 614, A, B) is similar to _Pterophyllum aequale_
Brongn. as figured by Zeiller[1625] from the Rhaetic of Tonkin and
agrees closely with some of the large Rhaetic specimens referred by
Schenk to _P. Braunianum_. The Jurassic fronds from Oregon described
by Fontaine[1626] as _Ctenophyllum angustifolium_ are similar forms
and a specimen from the Wealden of Germany included by Schenk in
_P. Dunkerianum_[1627] should probably be included in this species.
Other closely allied forms are represented by _P. distans_ Old. and
Morr.[1628] and _P. Footeanum_ from India.
[Illustration: Fig. 615. _Pterophyllum_ (_Anomozamites_) _Nilssoni_.
(British Museum, 39,306; nat. size.)]
[Illustration: Fig. 616. _Pterophyllum_ (_Anomozamites_)
_Lyellianum_. (Geological Survey Museum, 6396; nat. size.)]
_Pterophyllum_ (_Anomozamites_) _Nilssoni_ (Phillips).
The type-specimen, from the Jurassic beds on the Yorkshire coast
and now in the York Museum, was described by Phillips[1629] as
_Aspleniopteris Nilssoni_ and placed in _Pterophyllum_ by Lindley and
Hutton and many other authors[1630]. The fronds are linear; the lamina
may be almost entire or divided into unequal deep truncate segments;
the veins are simple or dichotomously branched (fig. 615). The leaves
are very similar to those of _Nilssonia_; they were probably borne
on stems similar to those described by Nathorst as _Wielandiella_.
Reference is made to the structure of the epidermal cells in the
account of the genus.
_Pterophyllum_ (_Anomozamites_) _Lyellianum_ (Dunker).
This Wealden species, originally referred by Dunker[1631] to
_Pterophyllum_, was afterwards transferred to _Anomozamites_[1632]. The
fronds, in habit resembling the larger Rhaetic species _P. Braunianum_
Goepp., are characterised by the narrow linear pinnae of almost equal
breadth attached approximately at right angles; there is a narrow line
of rachis separating the two rows of segments (fig. 616).
{=CYCADITES.= Sternberg.
{=PSEUDOCYCAS.= Nathorst.
The generic name _Cycadites_ was first used by Sternberg[1633] though
it has since been shown that the specimens for which he proposed it
belong to other genera. As employed by Brongniart[1634] and other
authors _Cycadites_ stands for fossil fronds agreeing in habit with
the pinnate leaves of recent species of _Cycas_ (fig. 387, A); the
presence of a single median in the linear pinnae is generally regarded
as an essential feature. _Cycadites_ may be defined as follows: Fronds
pinnate; pinnae alternate or opposite, linear entire, with a midrib
and no lateral veins, attached to the rachis by the entire base, the
lower margin of which may be slightly decurrent or narrowed near the
point of attachment. Epidermal cells with straight walls and stomata
agreeing in structure with those of the recent genus. As thus defined,
including the characters of the epidermal cells, the genus has no
representatives; but the generic name should also be applied, as
Miss Holden[1635] has recently suggested, to fronds of the _Cycas_
form which afford no information with regard to the structure of the
epidermis. The resemblance of _Cycadites_ fronds to those of _Cycas_,
coupled with the fact that impressions superficially resembling
megasporophylls of the recent genus are recorded from Mesozoic strata,
was considered sufficient justification for the employment of a name
implying close affinity to or even generic identity with _Cycas_. A
fuller knowledge of the epidermal characters of some of the fronds
hitherto included in _Cycadites_ has necessitated the substitution of a
new genus for _Cycadites_. An examination by Nathorst[1636] of Heer’s
Lower Cretaceous Greenland species _Cycadites Steenstrupi_ and of
other fronds showed that the epidermal cell-walls are sinuous and the
stomata arranged differently from those of _Cycas_. For these and other
reasons Nathorst proposed a new name _Pseudocycas_. He also pointed out
that the pinnae in the fossil fronds have as a rule a double ‘midrib.’
Nathorst’s discovery raised the question whether other fronds described
as _Cycadites_ should be transferred to _Pseudocycas_. Miss Holden’s
investigation of other supposed Mesozoic representatives of _Cycas_
leads to the conclusion that ‘it is not impossible that all Mesozoic
specimens of _Cycadites_ will turn out to be _Pseudocycas_.’ This
observer shows that _Cycadites Saportae_ Sew. and _C. Roemeri_ Schk.
agree in the sinuous walls of the epidermal cells with _Pseudocycas_;
and so far no species of _Cycadites_, in which it was possible to
examine the cuticular membrane, has been found that does not conform
to Nathorst’s definition of _Pseudocycas_ at least as regards the
structure of the epidermal cells. Nathorst defined _Pseudocycas_ in the
following sense: Fronds similar to those of _Cycadites_ and _Cycas_
but with pinnae characterised by a double ‘midrib,’ the stomata being
confined or almost confined to the groove between the two ‘midribs.’
Nathorst also notes that in _Pseudocycas_ the bases of the pinnae are
not contracted as is often the case in _Cycadites_ and _Cycas_, but
this is a feature of secondary importance. Miss Holden has, however,
expressed the opinion that the double ‘midrib’ is an untrustworthy
character and that the stomata are not always arranged as in the fronds
examined by Nathorst. Nathorst states that in _Pseudocycas Steenstrupi_
and _P. insignis_ the midrib though usually double may be single: the
same variation occurs in _P. Saportae_. Miss Holden found that an
impression made from a pinna of _Cycas siamensis_ showed a double line
on the upper face and a single rib on the lower; that is _Pseudocycas_
and _Cycas_ characters occur on a single pinna. On drying, the ridge on
the lower face of the lamina collapses and a groove is formed bounded
by two ridges.
In a recently published and interesting paper on ‘Some Xerophytic
Leaf-structures in Mesozoic Plants,’ Dr Halle[1637] makes some
important additions to our knowledge of _Pseudocycas_. He agrees
with Miss Holden’s views with regard to the use of the generic names
_Pseudocycas_ and _Cycadites_, but dissents from her interpretation
of the median groove as the result of shrinkage of a midrib. Part
of the evidence presented by Halle is based on the structure of the
leaf-cuticle as shown in microtome sections[1638]. He found that a
distinct median groove is always present on the pinnae of _Pseudocycas
insignis_ and other species. If the groove were due to collapse of
the tissue of a true median rib the presence of stomata—which in _P.
insignis_ are confined to the middle line of the lamina—below the vein
would be an unusual feature. He found no indication of a median vein
or of any vascular tissue. All that is revealed by an examination
of the cuticle is that the lamina has a well-defined groove bounded
by prominent ridges, and in _Pseudocycas Roemeri_ the groove is
deeper and is formed by the bending-back of the lamina. The stomata
are practically confined to the groove and in _P. insignis_ and _P.
Steenstrupi_ an additional protection against excessive transpiration
was afforded by elongated papillae.
In the sinuous walls of the epidermal cells and in the structure of the
stomata _Pseudocycas_ agrees with the Bennettitalean type as defined
by Thomas and Bancroft[1639]. The ‘midrib’ of the pinnae marks the
position of a pronounced groove and we have no information with regard
to the venation. As Halle says, protection against drought is afforded
by ‘other means than those usual among existing Cycads,’ which provide
against excessive transpiration by the sinking of the individual
stomata below the surface. The epidermal features of _Pseudocycas_
afford a striking example of the danger of basing conclusions on mere
impressions and they further emphasise the great difference between
Mesozoic Cycadean fronds and those of recent genera.
We have no knowledge of the nature of the reproductive organs of the
plants which bore _Pseudocycas_ fronds, but the agreement of the
stomata and epidermal cells with those in some Bennettitalean types
favours the inclusion of the genus in that class. It has previously
been pointed out that the impression figured by Heer[1640] in close
association with the Greenland specimens of _Pseudocycas Steenstrupi_
as a carpellary leaf of the _Cycas_ type is much too imperfect to
be identified and has no claim, as an examination of the actual
specimen in the Copenhagen Museum convinced me, to be compared with a
megasporophyll of _Cycas_. This view is shared by Nathorst.
In some cases the name _Cycadites_ has been applied to fragments
that might equally well belong to Conifers or other plants, and not
infrequently a careful examination of fossils referred to _Cycadites_
shows that the pinnae afford no evidence of a true midrib. Casts
of revolute pinnae like those of the recent species _Encephalartos
Ghellinckii_ (fig. 382) would present an appearance closely resembling
a strong midrib. Heer’s Siberian Jurassic species _Cycadites
sibiricus_[1641] is probably a piece of a _Taeniopteris_ or _Nilssonia_
frond, and _C. gramineus_ Heer[1642] should be referred to _Taxites_.
An examination of the Indian fronds described by Oldham and Morris and
Feistmantel as species of _Cycadites_ leads me to discard all of them
as trustworthy records of the genus: in _Cycadites confertus_[1643]
and _C. Blandfordianus_[1644] there appear to be several veins in
the pinnae and not a single midrib. _Cycadites constrictus_[1645]
is almost certainly a Conifer as Nathorst has also suggested. No
satisfactory example of _Cycadites_ has been described from Palaeozoic
strata; Goeppert’s _Cycadites gyrosus_[1646] is founded on material
too imperfect to determine, and an examination of his Culm species _C.
taxodinus_ in the Breslau Museum led me to refer it to a Conifer. The
specimens figured[1647] by Zeiller from Lower Gondwana rocks in India
as _Cycadites_? sp. are portions of linear leaves or leaflets 5 mm.
broad with a median rib but they can hardly be accepted as evidence of
the presence of a Cycadean plant.
[Illustration: Fig. 617. _Pseudocycas insignis._ From the Lias of
Höör. A, ⅚ nat. size; B, _ca._ × 2. (After Nathorst.)]
_Pseudocycas insignis_ Nathorst.
The fronds of this Cenomanian species from the West of Greenland reach
a breadth of 16 cm.; the rachis, 1 cm. broad, has two parallel ridges
on the upper surface and to these are attached at a wide angle the
broad bases of narrow linear pinnae reaching a length of 9 cm. and a
breadth of 2–3 mm. (fig. 617). The pinnae are thick and separate and
each has a double ‘midrib’ consisting of two parallel lines (fig.
617, B) which are occasionally replaced by one. The so-called double
‘midrib’ represents the two prominent ridges bordering the groove. The
stomata, confined to the median groove, are approximately circular and
the short epidermal cells have sinuous walls[1648].
_Pseudocycas Steenstrupi_ (Heer).
Nathorst refers this species, described by Heer as _Cycadites_, from
the Cenomanian of Greenland, to _Pseudocycas_ on the ground that the
epidermal cells are like those of _P. Steenstrupi_ and the stomata
are confined to a median groove. Heer figures an impression in close
association with the frond of this species which he identifies, without
any adequate reason, as a carpellary leaf like that of a _Cycas_.
_Pseudocycas Saportae_ (Seward).
It has recently been shown by Miss Holden that this Wealden English
species[1649] has the epidermal characters of _Pseudocycas_. In
external form it agrees closely with _Cycadites tenuisectus_ Sap.[1650]
from Lower Cretaceous rocks in Portugal, but nothing is known of
the epidermal features of the latter type. The rachis is broad and
flattened and bears alternate or sub-opposite pinnae of uniform breadth
attached at right-angles or obliquely to its upper surface (fig. 618).
The pinnae are 6–7 cm. long and about 1 mm. broad; their bases are
slightly expanded and the apices sharply pointed. Miss Holden[1651]
finds that the median rib is sometimes double and that the middle
region of the lamina is covered with stomata; the epidermal cells have
sinuous walls and stomata occasionally occur on each side of the main
median stomatal area. Dr. Halle[1652] of Stockholm, who has examined
cuticular preparations made from English specimens, confirms Miss
Holden’s observations as regards the stomata, but he shows that there
is no evidence of the existence of a midrib in the strict sense, the
appearance of a single or double median vein being due to the presence
of a dorsal stomatiferous groove, the edges of which would produce an
impression on the matrix of a double vein or, if the groove became
narrower, the impression would suggest a single midrib.
[Illustration: Fig. 618. _Pseudocycas Saportae._ From the Wealden,
near Hastings. (British Museum, V. 2777; ⅕ nat. size.)]
_Pseudocycas Roemeri_ (Schenk).
This Wealden species recorded from North Germany[1653] and the Sussex
coast[1654] has broader pinnae laterally attached to the rachis. Miss
Holden describes the stomata as covering the whole lower surface of the
pinnae except over the midrib. This description must be revised in the
light of Halle’s results obtained from an examination of the cuticle of
the type-specimen of the species in the Berlin Museum. He finds that
the edges of the pinnae are strongly revolute and thus form a deep
dorsal canal which is almost closed[1655], a form of lamina, as seen in
section, very similar to that of an _Empetrum_ leaf. The stomata are
confined to the groove. It may be that the specimen examined by Miss
Holden is specifically distinct or, as Halle also suggests, the cuticle
obtained from the English fossil may not represent the whole surface
but only the walls of the canal with possibly a portion of the cuticle
of the outer dorsal surface. This type of leaf described by Halle
is similar to that of _P. insignis_ with the xerophilous character
intensified.
_Cycadites Saladini_ Zeiller.
This species was founded by Zeiller[1656] on fronds from the Rhaetic of
Tonkin reaching a length of 40 cm. and 2–8·5 cm. broad with a rachis
3–4 mm. wide bearing contiguous linear pinnae 1·5–4·5 cm. long and
1·5–3 mm. broad with a more or less contracted base and a rounded or
obtusely pointed apex. The pinnae are attached almost at right-angles
or at an angle of 60°–80°. There is a clearly defined midrib.
It is not improbable that were the structure of the epidermal
cells known this species would be found to be another example of
_Pseudocycas_.
_Cycadites rectangularis_ Brauns.
This species[1657], first recorded from Rhaetic strata in Germany,
differs in the narrower and more acutely pointed pinnae from _C.
Saladini_. Miss Holden describes the midrib as double, but until
specimens are found which admit of an examination of the cuticles it is
impossible to decide whether it should be transferred to _Pseudocycas_.
The species is widely distributed in Rhaetic and Jurassic strata and
specimens are recorded from the Lias of Lyme Regis on the south coast
of England.
_Cycadites Renaulti_ Lignier.
This species, from the Middle Lias of Normandy[1658], is founded
on fronds 2·2–2·6 cm. broad with a rachis 3 mm. in breadth bearing
laterally-inserted pinnae almost at right-angles 11–12 mm. long and
1·25–1·50 mm. broad; it is very similar to _C. rectangularis_ which
occurs in the same beds.
II. +Nilssoniales.+
=NILSSONIA.= Brongniart.
This genus[1659] was named after the Swedish naturalist Nilsson who
had figured certain plants from the Lias of Höör referred by Fries to
the Ferns: these were named by Brongniart _Nilssonia brevis_ and _N.
elongata_ and classed with the Cycads. The type-specimens of the latter
species are regarded by Nathorst as a form of _N. brevis_. The history
of the genus is fully discussed in Nathorst’s able monograph[1660].
_Nilssonia_, founded on fronds which with one exception are known only
as casts or impressions, may be thus defined: Fronds with circinate
vernation, at least in the type-species _Nilssonia brevis_ (fig. 619,
C, D), similar in shape to the leaves of _Scolopendrium vulgare_ and
_Polypodium irioides_ and to such unusual forms of _Cycas_ fronds as
those reproduced in figs. 384, 387, I[1661], in which the laminae of
the pinnae are concrescent and form a continuous or deeply cut lamina.
They may reach a length of 60 cm. and a breadth of 10 cm. and some
specimens are known in which the leaf is less than 1 cm. in width. The
lamina is occasionally entire, but in the great majority of cases it
is more or less deeply cut into segments of unequal breadth varying
considerably in size and shape even in the same species, usually deep
and truncate and sometimes long and narrow (_e.g. N. pterophylloides_,
fig. 619, B). An important distinguishing feature is the attachment
of the lamina to the upper face of the rachis which it covers: the
extension of the lamina over the surface of the frond axis and the
rare occurrence of branching of the veins are characters in which
_Nilssonia_ differs from _Taeniopteris_. The veins are given off at
right-angles or obliquely from a very narrow groove occupying the
median line of the rachis; they are nearly always simple and in some
of the more fleshy leaves, _e.g. N. brevis_, they are seldom visible.
The surface of the lamina may be smooth or transversely corrugated. The
rachis forms a prominent rib on the under surface of the frond (fig.
620, A) and may be continued beyond the lamina as a short petiole.
Epidermal cells polygonal or rectangular, with straight walls in
contrast to the sinuous walls of _Taeniopteris_; some of the cells bear
strongly cuticularised papillae, possibly the bases of hairs (compare
the hairs on the fronds of _Acrostichum crinitum_, a Fern with leaves
similar in shape to some of the large entire fronds of _N. orientalis_
though relatively broader and with anastomosing veins). Stomata usually
confined to the lower epidermis and not very numerous; guard-cells
of rounded contour and without any special thickening surrounded by
6–8 accessory cells with thickened walls (fig. 611, B) forming a
chimney slightly raised over the stomatal pore[1662]. In _Nilssonia_
the guard-cells do not exhibit that regularity of orientation which
characterises the stomata of _Ptilophyllum_, _Otozamites_, and other
Bennettitalean fronds. Little is known of the anatomy of the leaves: in
a petrified leaf of _N. orientalis_[1663] from Upper Cretaceous rocks
in Japan there is no palisade-tissue and small groups of sclerenchyma
occur above and below the veins. The xylem appears to be centripetal,
but the preservation is far from satisfactory. A few secretory canals
were found near the edge of the leaf. We have no certain knowledge of
the reproductive organs. The small circular projections figured by
Schenk[1664] on some leaves of _Nilssonia polymorpha_ as sporangia
have no claim to be so regarded. In the description of _N. brevis_
reference is made to some seeds discovered by Nathorst which may belong
to that species. Nathorst suggests the possibility that the Rhaetic
fossil _Stenorrachis scanicus_ Nath. may be the seed-bearing shoot of a
_Nilssonia_, either _N. brevis_ or _N. polymorpha_, and if this surmise
is correct it almost necessarily involves the genus _Beania_[1665]
which has been tentatively referred to the Ginkgoales though without
any convincing evidence to support such connexion. Nothing is known of
the stems: the occasional occurrence of leaves converging towards a
common support points to a Cycadean habit. It is possible, as Nathorst
suggests, that the Rhaetic species _Bucklandia Saportana_[1666] may be
the stem of a _Nilssonia_.
[Illustration: Fig. 619. A, seed (_Nilssonia_?); B, _Nilssonia
pterophylloides_; C, D, _Nilssonia brevis_; E, _N. polymorpha_. (A–D ⅚
nat. size; E, slightly enlarged; after Nathorst.)]
_Nilssonia_ is especially characteristic of Jurassic and Rhaetic
floras; it occurs also in Triassic beds and extends into Cretaceous
floras.
Nathorst instituted the genus _Nilssoniopteris_[1667] for some
specimens from the Yorkshire coast which he believed to be examples of
_Nilssonia tenuinervis_ on the ground that the veins are dichotomously
branched and the epidermal cells have sinuous walls. Mr Hamshaw
Thomas[1668] has, however, shown by an examination of the specimens in
the Stockholm Museum that they belong to _Taeniopteris vittata_, and
Prof. Nathorst agrees with this conclusion. The name _Nilssoniopteris_
must therefore be abandoned. Miquel[1669] proposed the name _Hisingera_
for some _Nilssonia_ fronds, but it has not been adopted.
_Nilssonia polymorpha_ Schenk.
Linear fronds varying considerably in breadth and in the degree
of dissection of the lamina, which may be entire; the margin may
show broad and shallow crenulations or there may be a few narrow
and deep sinuses cutting the otherwise entire lamina into long and
narrow segments. More usually the lamina is divided to the rachis
into numerous truncate segments traversed by parallel, simple, veins
extending from a narrow groove in the middle of the rachis on the
upper surface of the frond (fig. 619, E). The veins run in very narrow
grooves in the generally flat but occasionally corrugated lamina[1670].
This species agrees very closely in habit with _N. compta_ and _N.
brevis_ and, as Nathorst points out, it is in some cases almost
impossible to distinguish _Nilssonia polymorpha_ from _N. brevis_.
Some of the fronds from the Rhaetic of Franconia described by Schenk
as _N. polymorpha_ are examples of _N. brevis_. In _N. polymorpha_ the
distal ends of the segments are blunter, the lamina is much less folded
and when folds or corrugations occur they are less regular than in _N.
brevis_. The epidermal cells are polygonal and have thick, straight,
walls: oval or circular papillae occur both on the lamina and rachis.
The stomata, confined to the lower surface, are between the veins and
each is accompanied by a ring of subsidiary cells (_cf._ fig. 611, B).
_N. polymorpha_ is a member of Rhaetic floras and is recorded also from
Liassic rocks at Höör[1671].
[Illustration: Fig. 620. A, B, _Nilssonia brevis_; A, section of
the frond; B, section of the lamina parallel to the rachis. C, _N.
saighensis_. (A, B, after Nathorst.)]
_Nilssonia brevis_ Brongniart.
This species[1672] (fig. 619, C, D), one of those from Höör on
which the genus was founded, has been very fully investigated by
Nathorst[1673] whose researches have cleared up many obscure features.
The young fronds are circinate like those of Ferns and _Cycas_. The
linear fronds agree generally in habit with those of _N. polymorpha_
and _N. compta_, but the lamina is thicker and is characterised by
regular transverse corrugations; the veins are very rarely visible
except in young leaves which have not reached their full thickness.
The fronds may be 50 cm. long and vary in breadth from 1·5 to 12 cm.;
the petiole is very short or the frond may be sessile. Between the
regular grooves on the upper surface the lamina is more or less convex;
seen from below the grooves are represented by ridges and between each
pair of ridges there are parallel folds, sometimes three (fig. 620,
B) or as many as six; and where the segments are narrow, that is the
strips of lamina between two grooves (or ridges), there may be only
a single fold which gives the appearance of linear segments with a
single midrib as in _Cycadites_, a misleading resemblance of special
interest in reference to the _Nilssonia_ fronds described by Oldham and
Morris[1674] and by Feistmantel[1675] as _Cycadites rajmahalensis_.
Owing to the fleshy nature of the leaf the difference between the
upper and lower side is particularly well marked in this species. The
lamina may be more or less entire, but is usually divided by deep
sinuses extending to the rachis into truncate or distally tapered
segments varying in breadth (fig. 619, C, D), the narrow segments being
characterised by a more pointed apex than in _N. polymorpha_. The
structure of the stomata and epidermal cells is of the type described
in the definition of the genus. Strongly cuticularised papillae,
incorrectly described by Schenk[1676] in _N. polymorpha_ as stomata,
occur on some of the epidermal cells: these may be the bases of hairs.
In some preparations Nathorst found patches of a resinous substance,
an interesting discovery in view of the occurrence of secretory canals
in the petrified leaf of _Nilssonia orientalis_ described by Dr
Stopes[1677].
[Illustration: Fig. 621. _Nilssonia rajmahalensis_ (= _Cycadites
rajmahalensis_). (Indian Geological Survey, Calcutta; nat. size.)]
_Nilssonia brevis_ occurs in Upper Rhaetic and Lower Liassic strata.
_Nilssonia pterophylloides_ Nathorst.
A Rhaetic Scanian species originally referred by Nathorst[1678] to
_Nilssonia_ but later removed by him to _Dioonites_[1679] and in
1909 reinstated in _Nilssonia_[1680] on the ground that the lamina
covers the upper face of the rachis. The segments are fairly uniform
in breadth and linear; they reach 10 cm. in length and are usually
5–7 mm. broad; the lamina is slightly tapered towards the apex (fig.
619, B). There are 3–10 parallel grooves on the upper face of the
segments and between each pair is a single unbranched vein. In close
association with portions of three fronds of this species Nathorst
found several oval bodies, 1 cm. × 7 mm., which he at first regarded
as ‘antherangia’ comparable with the sporocarps of the Hydropterideae,
but an examination of the carbonised tissue demonstrated that the small
rounded bodies contained in each of the ‘antherangia,’ originally
believed to be pollen-sacs, are grains of resin internal to a cuticle
of thick-walled cells and probably formed by secretory sacs in a fleshy
tissue. Internal to the resin-bodies is a second cuticle which may be
the remains of a nucellus, the outer cuticle and the resin belonging
to the sarcotesta. Nathorst’s careful examination of these fossils
shows that they are seeds (fig. 619, A) and were probably borne on
plants of _N. pterophylloides_, though an accidental association is not
improbable.
_Nilssonia compta_ (Phillips).
Broadly linear fronds varying considerably in size and in the breadth
and number of the truncate segments. In some cases the fronds exceeded
40 cm. in length and had a breadth of 9 cm. (fig. 622). The veins are
simple, parallel, and fairly prominent and the lamina shows clearly
the attachment to the upper surface of the rachis which is covered
by it as in all species of the genus[1681]. The structure of the
epidermis and stomata has recently been described by Thomas[1682].
Brongniart mentioned in the _Prodrome_ a species from the Lower Oolite
of Yorkshire under the name _Pterophyllum Williamsonis_[1683], but in
a later work this is given as a synonym of _N. compta_. _Nilssonia
compta_ bears a close resemblance in habit to _N. polymorpha_; it
agrees also with the large fronds described from the Upper Gondwana
of India as _Pterophyllum princeps_[1684]. Since attention was first
called to this similarity an examination of several of the figured
specimens has convinced me that the Indian fronds are either identical
with or at least closely allied to the European leaves. The apparent
lateral attachment of the lamina in the drawings published by Oldham
and Morris and Feistmantel is due to imperfect preservation; the
lamina ends in two raised ridges, and the discovery of a specimen
in which the lamina completely covers the rachis confirmed the
impression made by the other specimens. The Amurland Jurassic species
_Nilssonia Schmidtii_[1685] Heer though probably not identical with
_N. compta_ is a very similar type; it was originally described by
Heer as _Anomozamites Schmidtii_ and transferred by Nathorst[1686] to
_Nilssonia_: the veins are occasionally forked near the rachis and are
rather farther apart (·5 mm.) than in _N. compta_ and the segments are
broader and deeper than in the English species. _Nilssonia nipponensis_
Yok.[1687] a Jurassic species recorded from Japan and North America is
another similar type.
[Illustration: Fig. 622. _Nilssonia compta._ (Whitby Museum; nat.
size.)]
_Nilssonia orientalis_ Heer.
In this Jurassic and Lower Cretaceous species, founded on material from
Jurassic rocks in Siberia[1688], the lamina is generally entire. The
fronds exhibit a wide range in size and shape; they may have the form
of very narrow linear leaves barely 1 cm. across or may reach a breadth
of nearly 10 cm. The leaves from Middle Jurassic British strata named
by Nathorst _N. tenuinervis_[1689] are probably identical with Heer’s
type, and _N. Johnstrupi_[1690] Heer from the Lower Cretaceous of
Greenland may also be referred to _N. orientalis_.
The veins are at right-angles or oblique to the rachis and are very
numerous, three or more in a breadth of 1 mm.[1691] A species recently
described by Halle[1692] from Graham Land as _N. taeniopteroides_
agrees closely in habit with _N. orientalis_: in the southern form
the frond may have a length of 40–50 cm. and a breadth of 3 cm. The
entire lamina of _N. taeniopteroides_ tapers gradually towards the
base and is more rapidly narrowed in the distal region; the petiole is
at least 6–7 cm. long: the simple or branched veins, 15–20 in 1 cm.,
are given off from the axis at a wide angle. The more crowded veins in
_N. orientalis_ constitute one of the few features in which it differs
from Halle’s species, but the fact that the degree of closeness of the
veins is inconstant within the same species renders this distinction of
doubtful value. Halle compares his species also with _N. densinervis_
(Font.) originally described as _Platypterigium densinerve_ from
the Potomac beds[1693] and afterwards transferred by Berry[1694] to
_Nilssonia_ and considered by him to be identical with Fontaine’s
_Platypterigium Rogersianum_. An examination of some of Fontaine’s
specimens in the Washington Museum led me to refer the fronds to
_Nilssonia_[1695].
It is impossible to speak with confidence as to the absolute
specific identity of _N. orientalis_ Heer, _N. Johnstrupi_ Heer,
_N. taeniopteroides_ Halle, and some similar forms; but it is clear
that the linear fronds of this type characterised by an entire or
occasionally pinnatisect lamina were widely distributed in Jurassic
and Lower Cretaceous strata and persisted to the Upper Cretaceous
series in Japan. This form of frond is recorded from England, Scotland,
North America, Greenland, Spitzbergen[1696], Siberia, Russia,
Afghanistan[1697], Japan[1698], Graham Land, and elsewhere. Reference
has already been made to a petrified specimen of _N. orientalis_
described by Dr Stopes from Japan[1699].
Specimens described by Salfeld[1700] from the Corallian of Germany as
_Taeniopteris_ sp. may be _N. orientalis_; Bartholin’s _N. polymorpha_
from Bornholm, Velenovský’s Lower Cretaceous _N. bohemica_ and
Yokoyama’s _N. ozvana_ from Japan are other examples of fronds which
may be identical with _N. orientalis_[1701].
_Nilssonia tenuicaulis_ (Phillips).
This Jurassic species, while agreeing generally in habit with _N.
compta_, is characterised by the narrow and numerous linear segments
with a more acuminate apex. The fronds reached a length of more than
20 cm.[1702] Leckenby’s name _Pterophyllum medianum_[1703] was given
to a specimen from the Yorkshire coast and now in the Sedgwick Museum,
Cambridge, which, with _Pterophyllum angustifolium_, is clearly
identical with _Cycadites tenuicaulis_ Phillips. The specific name
_mediana_ frequently used[1704] for this type should be given up in
favour of the older term _tenuicaulis_. A species of similar habit is
described but not figured by Krasser[1705] as _N. Sturii_ from the Lunz
beds. _N. tenuicaulis_ is fairly common in the Middle Jurassic beds
near Scarborough and is recorded from the Kimmeridgian of Scotland
under the name _N. mediana_ (fig. 614, C)[1706].
_Nilssonia princeps_ (Oldham and Morris).
Oldham and Morris speak of _Pterophyllum princeps_[1707] as one of
the commonest plants in the Rajmahal beds in India. The fronds are
characterised by their large size and by the very broad oblong and
distally truncate pinnae with parallel and occasionally branched
veins. In the specimens figured by Oldham and Morris and Feistmantel
the pinnae are cut off at their bases (fig. 623), which form ridges
parallel to the rachis: this feature is not clearly shown in the
published drawings. By breaking some pieces of rock from a slab
containing figured specimens other pieces were found in which the
laminae of the bases of segments meet in the middle of the upper face
of the rachis. The pinnae vary in breadth from 1 cm. to 3·5 cm. and
reach a length of 8 cm.; the distal end is truncate, the lower edge
being strongly curved: the segments are slightly broadened at the base.
The veins are prominent and parallel, from 0·5 to 0·8 mm. apart. The
Rajmahal fronds described as _Pterophyllum Morrisianum_[1708] appear
to be indistinguishable from this species.
[Illustration: Fig. 623. _Nilssonia princeps._ (Slightly reduced;
Indian Geological Survey, Calcutta.)]
_Nilssonia Schaumburgensis_ (Dunker).
This species, first described as _Pterophyllum Schaumburgense_[1709]
from the Wealden of Germany, affords a good illustration of a small
type of frond closely resembling the much larger species _N. compta_.
Examples from English Wealden rocks seldom exceed 1 cm. in breadth and
are often much narrower; the linear lamina is almost entire or divided
into short and broad truncate segments of unequal breadth: the veins
are parallel and simple. For figures of this species, recorded from
different European localities and from Japan, reference should be made
to the accounts by Schenk[1710], Nathorst, Yokoyama, Yabe, and Fontaine.
=CTENIS.= Lindley and Hutton.
The genus _Ctenis_[1711] was founded on a piece of pinnate frond
from the Middle Jurassic rocks of the Yorkshire coast previously
figured by Phillips as _Cycadites sulcicaulis_. Lindley and Hutton
regarded the plant as probably Cycadean and proposed to apply the name
_Ctenis_ to all leaves having the general characters of Cycadeae, but
with ‘the veins connected by forks or transverse bars.’ While many
authors have accepted _Ctenis_ as a Cycadean genus, by others[1712]
it has been placed among the Ferns, on the ground that some small
circular elevations on the lamina of the segments of certain species
are believed to be sori or sporangia. Since Ettingshausen[1713]
and Schenk[1714] first noticed this feature Raciborski[1715] has
figured several examples from Poland and Staub[1716] records similar
circular bodies on a Liassic Hungarian species. In no single instance
have sporangia been found. Nathorst[1717] proposed the designation
_Anthrophyopsis_ (because of the resemblance of the lamina in form
and venation to the leaves of the Fern _Anthrophyum_) for some
Rhaetic specimens from Scania, but as they were subsequently found
to be segments of a pinnate frond he adopted the name _Ctenis_. An
example in the Manchester Museum[1718] (fig. 624) from Yorkshire,
mentioned by Nathorst in an early paper as probably a new species of
_Anthrophyopsis_, afforded good preparations of the cuticle (fig.
625) which revealed the existence of circular elevations on the outer
walls of the epidermal cells: these may explain the nature of some at
least of the supposed sporangia. The walls of the epidermal cells
are straight. The name _Ctenis_ is applied to pinnate fronds which
are probably Cycadean though we have no evidence as to the nature of
the stem or the reproductive organs. _Ctenis_ fronds are among the
largest Cycadean leaves from Mesozoic floras; in _Ctenis hungarica_
Staub the frond is said to have reached a length of 2 met. and in other
species the dimensions exceed those of most pinnate leaves. The stout
rachis bears linear or broad-oblong pinnae attached at a wide angle
and varying considerably in size and shape; the pinnae are attached
by the whole base which is usually broadened and decurrent but in a
few cases slightly contracted (_e.g._ _C. Zeyschneri_ Rac.[1719]). For
some fronds bearing broad and basally narrowed segments Raciborski
proposed the name _Ctenidiopsis_ in distinction from _Euctenis_ which
he applies to the typical forms. The pinnae may be long and narrow
reaching a length of over 12 cm., or short and broad: in some cases the
frond would be more correctly described as deeply pinnatisect; the apex
of the segments is acute, bluntly rounded or truncate. Several veins
pass into the base of each pinna and pursue a course approximately
parallel to the edge of the lamina; a characteristic feature is the
occasional occurrence of oblique cross-connexions between the veins.
It is possible that in some species the pinnae had spinous margins
as in the pinnae of uncertain affinity figured by Fontaine[1720] as
_Encephalartopsis nervosa_ from the Potomac series. Our knowledge of
the epidermal cells is very meagre: in the specimen represented in fig.
625 the epidermal cells have straight walls and a central papilla. The
genus extends from Triassic to Upper Jurassic rocks.
[Illustration: Fig. 624. _Ctenis_ sp. Single pinna. (Manchester
Museum, No. 53.)]
[Illustration: Fig. 625. _Ctenis_ sp. The epidermis of the pinna
shown in fig. 624. A, surface-view; _p_, papillae; _s_, stomata. B,
side-view. (Manchester Museum, No. 53.)]
_Ctenis lunzensis_ Stur.
This species, first recorded by Stur from the Lunz Upper Triassic
flora, has recently been examined by Krasser[1721] and compared with
the Jurassic species _Ctenis sulcicaulis_ (Phill.) (= _C. falcata_
Lind. and Hutt.) and _C. Potocki_ Rac. No figures or detailed
descriptions have been published.
_Ctenis fallax_ Nathorst.
This Scanian Rhaetic type[1722], including _Anthrophyopsis
crassinervis_, _A. Nilssoni_, and probably _A. obovata_ Nath., is
characterised by very large obtusely pointed pinnae reaching at least
20 cm. in length and over 3 cm. in breadth. The veins are often 2 mm.
apart and form long polygonal meshes. Nathorst figures small circular
patches on the surface of the lamina. Raciborski[1723], on slender
evidence, refers a fragment from the Jurassic of Cracow to this species.
_Ctenis hungarica_ Staub.
A species[1724] characterised by very large fronds reaching 2 met.,
bearing broad linear pinnae almost at right-angles and attached to the
rachis by decurrent bases, attaining a length of 21 cm. and a breadth
at the base of the lamina of 3·5 cm. and 4 cm. a short distance from
the acute apex. The veins are parallel to the edge of the lamina, but
Staub does not appear to have seen distinct anastomoses. It is not
improbable that Staub’s species may be identical with _C. asplenioides_
(Ett.) from the Lias of Hungary, specimens of which are preserved in
the École des Mines, Paris.
_Ctenis asplenioides_ (Ettingshausen).
This species was first described by Ettingshausen[1725] from Liassic
strata in Austria as _Taeniopteris asplenioides_ and compared by him to
large simple fronds of _Asplenium nidus_ but distinguished by a deeply
dissected lamina. Schenk[1726] found that the veins anastomose and
adopted the name _Ctenis_. In habit very similar to _C. sulcicaulis_,
but the pinnae are much broader, exceeding 4 cm., and the veins are
3–5 mm. apart. Only the basal part of the segments is figured by
Ettingshausen. Specimens in the École des Mines, Paris, from Hungary
have pinnae nearly 40 cm. long and 2·5 cm. in breadth, the parallel
veins being connected by a few oblique branches. Both Ettingshausen
and Schenk speak of small circular sori on the lower epidermis,
though these are not figured nor were any sporangia obtained. This
species and other examples of large _Ctenis_ fronds are described by
Raciborski from Lower Jurassic rocks in Poland. He figures part of a
leaf of _C. Zeyschneri_[1727] 40 cm. long bearing alternate pinnae
approximately 10 cm. long and nearly 4 cm. broad, characterised by
obtuse apices, a decurrent lamina, and anastomosing veins closer
together (16–24 per 1 cm.) than those of _C. asplenioides_. In one
Polish specimen, _C. remotinervis_[1728], with pinnae 5 cm. broad the
lamina is represented in the upper part of the frond as continuous over
the face of the rachis, and—if the drawing is accurate—the frond in
this respect differs from typical examples of _Ctenis_ and agrees with
_Nilssonia_. A species of _Ctenis_ with broad pinnae is described by
Yokoyama[1729] from the Jurassic of China as _C. Kaneharai_.
_Ctenis sulcicaulis_ (Phillips).
This type[1730] is more familiar under the name _Ctenis falcata_
given to it by Lindley[1731], but if we follow Lester Ward[1732] in
strict observance of the rule of priority, a course from which I have
frequently deviated on the ground of long usage, the less familiar
designation must be adopted. Fronds pinnate; long and tapered linear
pinnae sometimes exceeding 12 cm. in length and 1 cm. in breadth
attached obliquely or almost at right-angles to a fairly broad rachis
(fig. 626). The lamina is broadest at the base and the lower margin is
strongly decurrent, tapering distally to an acute apex. The parallel
and frequently anastomosing veins diverge slightly in the basal region
of the pinnae. Though usually separate to the base, the laminae of
adjacent pinnae may be continuous as in a pinnatisect leaf[1733]. This
species is recorded also from North America, and fronds of similar
habit are figured by Fontaine[1734] from the Jurassic of Oregon as
_Ctenis orovillensis_: a fragment recorded from Jurassic rocks in
Afghanistan as _Ctenis_ sp. may belong to _C. sulcicaulis_[1735].
_Ctenis latifolia_ (Brongniart).
This species[1736], originally referred to _Taeniopteris_, was
transferred to _Ctenis_ as the result of the discovery of anastomosing
veins in the type-specimen in the Oxford Museum. The segments are
shorter and broader than in _C. sulcicaulis_ and very similar to those
of _C. orovillensis_ Font.
[Illustration: Fig. 626. _Ctenis sulcicaulis._ (British Museum, V.
9012.)]
_Ctenis_ sp.
The pinna shown in fig. 624 from the Jurassic beds in Yorkshire[1737]
is interesting as one of the few examples of the preservation of the
cuticular membrane. The straight or curved walls of the epidermal
cells agree with those of recent Cycads except _Stangeria_, and each
cell bears a large central papilla that gives to the lamina the finely
punctate appearance which has been regarded as evidence of sporangia.
The gaps in the cuticle probably mark the position of sunken stomata.
=PSEUDOCTENIS.= Seward.
This genus[1738] was established for certain pinnate fronds agreeing
in habit with _Ctenis sulcicaulis_ but distinguished by the almost
complete absence of any cross-connexions between the veins. Some of
the forms with narrow pinnae closely resemble species of _Zamites_,
the distinguishing feature being the decurrent lower margin of the
leaflets. Though such fronds might not unreasonably be included in
_Ctenis_, it is more convenient on the analogy of the occasional
occurrence of _Glossopteris_ fronds with very few anastomoses to employ
a distinctive designation.
[Illustration: Fig. 627. _Pseudoctenis eathiensis._ (British Museum,
No. V. 2744; ½ nat. size.)]
_Pseudoctenis eathiensis_ (Richards).
Some of the specimens on which this species[1739] is founded were
originally figured by Miller[1740] from Upper Jurassic strata in
Scotland and afterwards named by Richards[1741] _Zamites eathiensis_.
The general appearance of the fronds is very like that of _Ctenis
sulcicaulis_; the pinnae vary in breadth from about 3 mm. to 1·5 cm.;
they are attached at right-angles or, in the apical region, may be
almost parallel to the rachis. The longest pinna recorded is 17 cm.
and the lamina tapers to a slender apex; the veins are parallel and
occasionally forked, but cross-connexions are rare. The partially
petrified rachis of one specimen showed hypodermal stereome and some
secretory canals as in recent Cycads. The specimen from Wealden rocks
near Hastings (fig. 627), originally described as _Zamites_ sp.[1742],
is probably specifically identical with _Pseudoctenis eathiensis_.
The South African Wealden species, originally described by Tate as
_Palaeozamia Rubidgei_[1743], agrees closely with _Pseudoctenis_ and is
probably an example of that genus. This type bears a close resemblance
in the form of the frond to _Ctenophyllum grandifolium_ Font.[1744]
and _C. Wardi_[1745] Font. from American Trias and Jurassic rocks
respectively. _Pseudoctenis crassinervis_ Sew.[1746] is another Scotch
form with coarser veins.
A frond very similar in habit to _P. eathiensis_ is represented by
_Pseudoctenis ensiformis_ Halle[1747] from the Jurassic strata of
Graham Land originally referred by Nathorst to _Pterophyllum_. An
examination of the type-specimen in the Stockholm Museum revealed its
resemblance to the Scotch species _P. eathiensis_: a single anastomosis
was noticed in one of the pinnae. The broadly ensiform obtuse pinnae,
reaching a length of 7 cm. with a maximum breadth of 3 cm. at their
expanded bases, vary in breadth and are attached at right-angles to a
slender rachis. The veins, 1–1·5 mm. apart, are parallel and strong.
The varying breadth of the pinnae irrespective of their position on the
rachis is a distinctive feature. Halle draws attention to a resemblance
of this Antarctic species to _Ctenophyllum latifolium_ Font. a Potomac
type referred by Berry[1748] to the genus _Ctenopsis_ on the rather
slender ground that the veins are arranged in pairs. Berry in a
footnote expresses the opinion that _Ctenopsis_ is very closely related
to or possibly identical with _Pseudoctenis_.
If the bases of the pinnae in the specimen of _P. ensiformis_ figured
by Halle are complete, as they appear to be, the frond agrees very
closely with _Pterophyllum Carterianum_ Old. and Morr.[1749] from
India. A comparison of the Rajmahal specimen with Halle’s figure
leads me to regard the two fronds as probably identical. The veins in
the Indian species, which should also be referred to _Pseudoctenis_,
are prominent and from ·5 to 1 mm. apart; the base of the lamina is
slightly broadened and the veins curve downwards towards the rachis
in the lower decurrent portion. The other Indian type, _Pterophyllum
Morrisianum_[1750], with which Halle compares his species is, however,
not a _Pseudoctenis_ but should be included in _Nilssonia_ and is
probably identical with _Pterophyllum princeps_ Old. and Morr.
_Pseudoctenis Lanei_ Thomas.
This species[1751], recently described from Middle Jurassic beds at
Marske, Yorkshire, has narrower linear lanceolate pinnae. The linear
pinnae reach a length of 10 cm. and a breadth of 9 mm. The veins
are numerous, 10 in a breadth of 6 mm., and only one cross-vein was
noticed. In the decurrent lower edge of the laminae the fronds are
identical with _Ctenis sulcicaulis_. A very good example of this
species[1752] in the York Museum is reproduced by Mr Thomas in his
account of Cleveland Jurassic plants.
_Pseudoctenis Balli_ (Feistmantel).
A species described originally by Feistmantel[1753] as _Anomozamites
Balli_ from the Barakar group of the Damuda series and afterwards
transferred to the genus _Platypterygium_, characterised by broadly
linear segments of unequal breadth attached obliquely or at
right-angles to a slender rachis. The apices of the segments though
usually imperfect appear to be truncate; the bases of the pinnae
are decurrent by their lower edge. The veins are approximately 3
per millimetre; they are generally forked at the base and in one or
two places show cross-connexions. In the middle of the frond the
narrow rachis is exposed but in the apical region it is covered by
the laminae. The occurrence of two divergent pinnae at the apex of
the frond is a feature met with also in _Ctenis sulcicaulis_. This
description is based on an examination of the specimens figured by
Feistmantel.
III. +Cycadean Fronds which cannot be assigned to a family-position.+
=SPHENOZAMITES.= Brongniart.
This name was proposed by Brongniart[1754] as a subgenus of
_Otozamites_ denoting pinnate fronds bearing leaflets without an
auriculate base: he suggested that the subgenus might eventually be
raised to generic rank and this was done by Zigno[1755] though in too
wide a sense. In the case of _Otozamites Beani_ (Lind. and Hutt.),
quoted by Brongniart in illustration of _Sphenozamites_, the latter
designation is inapplicable as the pinnae are auriculate. Another
species, _Zamites undulatus_ Sternb., to which Brongniart applied his
new subgeneric term, is probably identical with _Otozamites acuminatus_
(L. and H.)[1756].
Although the distinction between _Sphenozamites_ and _Otozamites_ is
often ill defined the former name may be conveniently adopted for
pinnate fronds similar to those of _Zamia Skinneri_ and some species
of _Encephalartos_ characterised by leaflets of an asymmetrical,
obovate, or rhomboidal form with a contracted or cuneate base and
numerous branched divergent veins. Nothing is known of the structure or
reproductive organs of _Sphenozamites_, and the genus, though serving
a useful descriptive purpose, is founded solely on form, and in the
absence of other data it would be rash to assume that its use implies
close natural affinity. In the case of many other genera of Cycadean
fronds there is additional evidence of relationship, but this is not
the case with _Sphenozamites_. The pinnae resemble those of such recent
Cycadean fronds as _Zamia Skinneri_ and _Z. muricata_. The genus ranges
from Lower Permian to Jurassic rocks.
_Sphenozamites Rochei_ Renault.
This species[1757], from the Lower Permian of the Autun district, is
founded on a pinnate frond bearing alternate pinnae, 2·5 × 1 cm., with
an asymmetrical oblong lamina attached obliquely near the edge of
the rachis with a cuneate base slightly decurrent below and a broadly
rounded apex; the veins dichotomise once or twice as they diverge
from the narrow base (fig. 628). The pinnae resemble the leaflets of
_Noeggerathia foliosa_ Sternb. and are similar in shape to those of the
Jurassic species _Sphenozamites Geylerianus_ Zig.
[Illustration: Fig. 628. _Sphenozamites Rochei._ (After Renault; nat.
size.)]
[Illustration: Fig. 629. _Sphenozamites Belli._ (Oxford Museum; nat.
size.)]
_Sphenozamites Belli_ Seward.
This Middle Jurassic species from Stonesfield[1758] is founded on
detached pinnae possibly identical with a specimen figured by Buckman
as _?Naiadea obtusa_[1759]. The pinnae are wedge-shaped, tapering
gradually to an acute apex and attached by a narrow base: the leaflet
shown in fig. 629 is 9 cm. long; the veins are numerous and more
divergent than in some leaves of similar form referred to the genus
_Podozamites_. With this species may be compared several Italian
Jurassic specimens described by Zigno[1760] as four distinct species
but more appropriately assigned to a single type _S. Geylerianus_.
An examination of Zigno’s fronds in the Padua Museum, which he named
_S. Rossii_, leads me to regard the irregularly serrate edge of the
pinnae as the result of tearing of an originally entire lamina and
to compare the specimens with _Otozamites Beani_ (L. and H.). An
imperfect ovoid pinna recalling _S. Belli_ is figured by Newberry
from the Rhaetic of Honduras as _Sphenozamites robustus_[1761]. A
French Upper Jurassic species figured by Saporta as _Sphenozamites
latifolius_ bears a very close resemblance in the form of the leaflets
to the Wealden plant _Sewardia latifolia_[1762]. Kurtz records the
occurrence of _Sphenozamites_, _S. Geinitzianus_, from Rhaetic strata
in Argentina[1763], but I have not seen any figures of this species.
=PLAGIOZAMITES=. Zeiller.
The name _Plagiozamites_ was proposed by Zeiller[1764] for some pinnate
fronds and detached leaflets from the Stephanian of Commentry and the
Lower Permian of the Vosges. The better preservation of the Vosges
material enabled him to recognise certain features which led to the
substitution of _Plagiozamites_ for _Zamites_, the name originally
employed by Renault for the Commentry specimens. _Plagiozamites_ bears
a superficial resemblance to _Zamites_ and _Otozamites_ and differs
but little from _Sphenozamites_ and _Noeggerathia_; it stands for
pinnate fronds bearing ovate pinnae with a sub-amplexicaul oblique
attachment to the rachis as is clearly shown in the species _P.
Planchardi_ (Ren.)[1765]. In the case of Palaeozoic fronds assigned to
the Cycadophyta on the ground of the resemblance of their pinnae to
those of undoubted Cycadean species, it is particularly important to
recognise the fact that decisive evidence as to systematic position is
lacking. We know nothing of the stem, the reproductive organs, or the
epidermal and stomatal characters of _Plagiozamites_, and it is by no
means certain that the genus is a true representative of the group in
which it is provisionally included.
_Plagiozamites Planchardi_ (Renault).
Fronds pinnate; pinnae ovate-lanceolate reaching 5 cm. in length and
1·6 cm. in breadth, inserted obliquely on the rachis, but not along
a line parallel to the long axis of the rachis as in _Zamites_, and
partially embracing it: the edge of the lamina is finely denticulate;
veins slightly divergent and occasionally branched. The leaflets are
narrow and more acute than those of _Noeggerathia_ and _Sphenozamites
Rochei_ Ren. _Plagiozamites_ is recorded from the Stephanian of
Commentry, the Coal Measures of Manchuria[1766], and the Lower Permian
of the Vosges. Renault described six species of _Zamites_ from
Commentry all, except _Z. carbonarius_, based on detached pinnae.
The type-specimen of _Z. carbonarius_ consists of a piece of stout
rachis bearing ovate acute pinnae, 2·2 × 1 cm. Potonié[1767], who
refers a piece of pinnate frond from the Permian of Thuringia to
_Z. carbonarius_, includes the other species of Renault under that
name. Whether or not the differences in the venation and form of the
pinnae are of specific significance cannot be definitely settled
without better material, but the important point is that these
Permo-Carboniferous fronds are sufficiently distinct from _Zamites_
to be placed in a separate genus. _Plagiozamites carbonarius_ is
recorded also by Zalessky[1768] from the Permian of Manchuria though
the examples figured do not afford satisfactory evidence of the
mode of insertion of the segments on the rachis. _P. Planchardi_
has recently been recorded from the Coal Measures of Maryland; the
discovery is interesting both on phytogeographical grounds and as
the first satisfactory record of a Palaeozoic Cycadophyte from North
America[1769].
=Cycadorachis.= Saporta.
The employment of this generic name may serve a useful purpose if used
for specimens, whether preserved as petrifactions or impressions,
believed to be portions of Cycadean frond-axes, but which in the
absence of pinnae cannot be assigned to one of the recognised genera
of fronds. Saporta[1770] describes two species from Kimmeridgian beds
in France, _Cycadorachis abscissa_ and _C. armata_: the first may be
the winged base of a Cycadean petiole, but it agrees equally well with
the broad base of an Osmundaceous leaf and should not be referred to
a genus implying affinity with a particular class. The other species,
_C. armata_, is probably a piece of a spinous axis like that of the
Wealden plant _Sewardia latifolia_ (Sap.). A fragment figured by Fliche
and Bleicher[1771] from the Jurassic of Nancy as _C. tuberculata_ is
another example of a fossil which cannot be referred with any certainty
to the Cycads.
Dr Stopes[1772], inadvertently overlooking the previous institution
of _Cycadorachis_, has recently proposed the name _Cycadeorachis_ for
pinnately branched rachises of Cycadean fronds which, ‘while indicating
the general character of the frond, do not show the shape of the pinnae
well enough to be associated with any of the many foliage-genera.’
LIST OF WORKS REFERRED TO IN THE TEXT
(+Volumes III. and IV.+)
[_With a few exceptions this list does not include books and papers
given in the Bibliographies in volumes I. and II._]
The following are some of the Bibliographies which students will
find useful for additional references:—Geological Literature added
to the Geological Society’s Library, published from time to time
by the Society; Prof. Zeiller’s lists in the ‘Revue Générale de
Botanique’ (Paris); lists given by Arber in the ‘Progressus Rei
Botanicae’ (Leiden), vol. +i.+ Heft i. p. 218, 1907; Jongman’s ‘Die
Palaeobotanische Literatur’ (Jena), 1910–13; also the International
Catalogue of Scientific Literature (Botany and Geology). For the
Literature dealing with Cretaceous plants the student should refer to
Dr Marie Stopes’ ‘Cretaceous Flora’ +i.+ and +ii.+ (British Museum
Catalogues, 1913, 1915).
The dates of books published in parts given in the footnotes to this
volume are as a rule those of the concluding part. For the dates of
separate parts of books relating to Palaeozoic floras the student is
referred to Prof. Zeiller’s valuable list at the end of the ‘Flore
Fossile du Bassin Houiller de Valenciennes.’ Useful bibliographies of
the writings of Saporta, Heer, and Ettingshausen have been compiled by
Zeiller (96), Malloizel and Zeiller (N.D.), and Krasser (97).
=Aase, Hannah C.= (15) Vascular anatomy of the megasporophylls of
Conifers. _Botanical Gazette_, vol. +lx.+ p. 277.
=Affourtit, M. F. A.= and =H. C. C. La Rivière.= (15) On the ribbing of
the seeds of _Ginkgo_. _Annals of Botany_, vol. +xxix.+ p. 591.
=Andersson, J. G.= (10) Die Veränderungen des Klimas seit dem Maximum
der letzten Eiszeit. (Collection of papers published by the Int.
Geol. Congress; edited by J. G. Andersson.) _Stockholm_.
=Andrews, E. B.= (75) Descriptions of Fossil Plants from the Coal
Measures of Ohio. _Geol. Surv. Ohio_.
=Antevs, E.= (14) _Lepidopteris Ottonis_ (Göpp.) Schimp. and
_Anthotithus Zeilleri_ Nath. _K. Svensk._ _Vetenskapsakad. Hand._
Bd. +li.+ No. 7.
—— (14²) The Swedish Species of _Ptilozamites_ Nath. _Ibid._ Bd.
+li.+ No. 10.
=Arber, Agnes.= (See also Robertson, A.) (10) On the structure of the
Palaeozoic seed _Mitrospermum compressum_ (Will.). _Ann. Bot._
vol. +xxiv.+ p. 491.
—— (14) A note on _Trigonocarpus_. _Ibid._ vol. +xxviii.+ p. 195.
=Arber, E. A. Newell.= (02) Notes on the Binney collection
of Coal-Measure Plants. Pt. iii. The type-specimens of
_Lyginodendron oldhamium_ (Binney). _Proc. Camb. Phil. Soc._ vol.
+xi.+ pt. iv. p. 281.
—— (03) On the roots of _Medullosa anglica. Ann. Bot._ vol. +xvii.+
p. 425.
—— (03²) Discussion on Dr Kurtz’s paper (1903). _Quart. Journ. Geol.
Soc._ vol. +lix.+ p. 26.
—— (04) _Cupressinoxylon Hookeri_ sp. nov. a large silicified tree
from Tasmania. _Geol. Mag._ [+v+], vol. +i.+ p. 7.
—— (05) On some new species of _Lagenostoma_, a type of
Pteridospermous seed from the Coal Measures. _Proc. R. Soc._ vol.
+lxxi.+ B, p. 245.
—— (07) On Triassic species of the genera _Zamites_ and
_Pterophyllum_, types of fronds belonging to the Cycadophyta.
_Trans. Linn. Soc._ vol. +vii.+ pt. vii. p. 109.
—— (08) On a new Pteridosperm possessing the _Sphenopteris_ type of
foliage. _Ann. Bot._ vol. +xxii.+ p. 57.
—— (09) On the Fossil Plants of the Waldershare and Fredville series
of the Kent Coalfield. _Quart. Journ. Geol. Soc._ vol. +lxv.+ p.
21.
—— (09²) On the affinities of the Triassic plant _Yuccites
vogesiacus_ Schimp. and Moug. _Geol. Mag._ [+v+], vol. +vi.+ p.
11.
—— (12) On _Psygmophyllum majus_ sp. nov. from the Lower
Carboniferous rocks of Newfoundland, together with a Revision of
the genus and Remarks on its affinities. _Trans. Linn. Soc._ vol.
+vii.+ p. 391.
—— (12²) Fossil Plants from the Kent Coalfield. _Geol. Mag._ [+v+],
vol. +ix.+ p. 97.
—— (13) A preliminary note on the Fossil Plants of the Mount Potts
beds, New Zealand, collected by Mr D. G. Lillie, Biologist to
Capt. Scott’s Antarctic Expedition in the “Terra Nova.” _Proc. R.
Soc._ vol. +lxxxvi.+ p. 344.
—— (13²) The structure of _Dadoxylon Kayi_. _Quart. Journ. Geol.
Soc._ vol. +lxix.+ p. 454.
—— (14) A Revision of the Seed impressions of the British Coal
Measures. _Ann. Bot._ vol. +xxviii.+ p. 81.
—— (14²) On the Fossil Flora of the Kent Coalfield. _Quart. Journ.
Geol. Soc._ vol. +lxx.+ p. 54.
=Arber, E. A. Newell and J. Parkin=. (07) On the origin of Angiosperms.
_Journ. Linn. Soc._ vol. +xxxviii.+ p. 29.
—— (08) Studies on the Evolution of the Angiosperms. _Ann. Bot._
vol. +xxii.+ p. 489.
=Arnoldi, W.= (01) Beiträge zur Morphologie einiger Gymnospermen.
_Bull. Nat. Moscow_, No. 4, 1900.
=Bailey, I. W.= (09) The structure of the wood in the Pineae. _Bot.
Gaz_. vol. +xlviii.+ p. 47.
—— (11) A Cretaceous _Pityoxylon_ with marginal tracheids. _Ann.
Bot._ vol. +xxv.+ p. 315.
=Baily, W. H.= (69) Notice of Plant-remains from Beds interstratified
with the Basalts in the county of Antrim. _Quart. Journ. Geol.
Soc._ vol. +xxv.+ p. 357.
=Bain, F.= and =Sir W. Dawson=. (85) Notes on the Geology and Fossil
Flora of Prince Edward Island. _Canadian Rec. Sci._ vol. +i.+
(1884–85) p. 154.
=Baker, R. T.= and =H. C. Smith=. (10) Research of the Pines on
Australia. _Dpt. Public Instruction_, _Tech. Educ. Ser._ No. 16.
_Sydney_.
=Bancroft, Nellie.= (13) On some Indian Jurassic Gymnosperms and
_Rhexoxylon africanum_, a new Medullosan stem. _Trans. Linn.
Soc._ vol. +viii.+ pt. ii. p. 69.
—— (14) Pteridosperm Anatomy and its relation to that of the Cycads.
_New Phyt._ vol. +xiii.+ p. 41.
=Barber, C. A.= (92) On the nature and development of the corky
excrescences on stems of _Zanthoxylum_. _Ann. Bot._ vol. +vi.+ p.
155.
—— (98) _Cupressionoxylon vectense_; a fossil Conifer from the Lower
Greensand of Shanklin, in the Isle of Wight. _Ann. Bot._ vol.
+xii.+ p. 329.
=Bartholin, C. T.= (94) Nogle i den bornholmske Juraformation
forekommende Planteforsteninger. _Bot. Tidskrift_ (Copenhagen),
Bd. +xix.+ p. 87.
=Bartlett, A. W.= (13) Note on the occurrence of an abnormal
bisporangiate strobilus of _Larix europaea_ DC. _Ann. Bot._ vol.
+xxvii.+ p. 575.
=Bassler, H.= (16) A Cycadophyte from the North American Coal Measures.
_Amer. Journ. Sci._ vol. +xlii.+ p. 21.
=Bayer, A.= (08) Zur Deutung der weiblichen Blüten der Cupressineen
nebst Bemerkungen über _Cryptomeria_. _Beiheft Bot. Cent._ Bd.
+xxiii.+ Abt. +i.+ p. 27.
=Beissner, L.= (91) Handbuch der Nadelholzkunde. _Berlin._
=Bennett, J. J.= and =R. Brown.= (52) Plantae Javanicae rariores.
_London_, 1838–52.
=Benson, Margaret.= (08) On the contents of the pollen-chamber of a
specimen of _Lagenostoma ovoides_. _Bot. Gaz._ vol. +lv.+ p. 409.
—— (12) _Cordaites Felicis_, sp. nov., a Cordaitean leaf from the
Coal Measures of England. _Ann. Bot._ vol. +xxvi.+ p. 202.
—— (14) _Sphaerostoma ovale_ (_Conostoma ovale_ et _intermedianum_,
Williamson), a Lower Carboniferous ovule from Pettycur,
Fifeshire, Scotland. _Trans. R. Soc._ Edinburgh, vol. +l.+ pt. i.
No. i. p. 1.
=Benson, M.= and =E. J. Welsford=. (09) The morphology of the ovule
and female flower of _Juglans regia_ and of a few allied genera.
_Ann. Bot._ vol. +xxiii.+ p. 623.
=Berger, R.= (48) De fructibus et seminibus ex formatione
lithanthracum. _Diss. Inaug. Vratislaviae._
=Bergeron, J.= (84) Note sur les strobiles du _Walchia piniformis_.
_Bull. soc. géol. France_ [3], Tome +xii.+ p. 583.
=Berridge, E. M.= (11) On some points of resemblance between Gnetalean
and Bennettitean seeds. _New Phyt._ vol. +x.+ p. 140.
—— (12) The structure of the female strobilus in _Gnetum Gnemon_.
_Ann. Bot._ vol. +xxvi.+ p. 987.
=Berridge, Emily M.= and =Elizabeth Sanday=. (07) Oogenesis and
embryogeny in _Ephedra distachya_. _New Phyt._ vol. +vi.+ p. 127.
=Berry, E. W.= (03) The Flora of the Matawan Formation. _Bull. New York
Bot. Gard._ vol. +iii.+ No. 9, p. 45.
—— (05) Additions to the fossil Flora from Cliffwood. _Bull. Torrey
Bot. Club_, vol. +xxxii.+ p. 43.
—— (06) Contributions to the Mesozoic Flora of the Atlantic Coastal
Plain. I. _Ibid._ vol. +xxxiii.+ p. 33.
—— (07) Coastal Plain Amber. _Torreya_, vol. +vii.+ p. 4.
—— (07²) Contributions to the Pleistocene Flora of North Carolina.
_Journ. Geol._ vol. +xv.+ No. 4, p. 338.
—— (08) Some Araucarian remains from the Atlantic Coastal Plain.
_Bull. Torrey Bot. Club_, vol. +xxxv.+ p. 249.
—— (08²) A Mid-Cretaceous species of _Torreya_. _Amer. Journ. Sci._
vol. +xxv.+ p. 382.
—— (09) A Miocene Flora from the Virginian Coastal Plain. _Journ.
Geol._ vol. +xvii.+ p. 19.
—— (09²) Pleistocene Swamp deposits in Virginia. _Amer. Nat._ vol.
+xliii.+ p. 432.
—— (10) A revision of the Fossil Plants of the genus _Nageiopsis_ of
Fontaine. _Proc. U. S. Nat. Mus._ vol. +xxxviii.+ p. 185.
—— (10²) The epidermal characters of _Frenelopsis ramosissimus_.
_Bot. Gaz._ vol. +l.+ p. 305.
—— (10³) Additions to the Pleistocene Flora of New Jersey.
_Torreya_, vol. +x.+ p. 261.
—— (10⁴) Contributions to the Mesozoic Flora of the Atlantic Coastal
Plain. V. North Carolina. _Bull. Torrey Bot. Club_, vol.
+xxxvii.+ p. 181.
—— (11) The Lower Cretaceous deposits of Maryland. (Berry, Clark,
and Bibbin.) _Maryland Geol. Surv._
—— (11²) A Lower Cretaceous species of Schizaeaceae from Eastern
North America. _Ann. Bot._ vol. +xxv.+ p. 193.
—— (11³) The Flora of the Raritan Formation. _Geol. Surv. New
Jersey, Bull._ 3.
—— (11⁴) A Revision of several genera of Gymnospermous plants from
the Potomac group in Maryland and Virginia. _Proc. U. S. Nat.
Mus._ vol. +xl.+ p. 289.
—— (12) The age of the plant-bearing shales of the Richmond
coal-field. _Amer. Journ. Sci._ vol. +xxxiv.+ p. 224.
—— (12²) Notes on the genus _Widdringtonites_. _Bull. Torr. Bot.
Club_, vol. +xxxix.+ p. 341.
—— (12³) Contributions to the Mesozoic Flora of the Atlantic Coastal
Plain. VII. Texas. _Bull. Torrey Bot. Club_, vol. +xxxix.+ p.
387.
—— (12⁴) Pleistocene plants from the Blue Ridge in Virginia. _Amer.
Journ. Sci._ vol. +xxxiv.+ p. 218.
—— (14) The Upper Cretaceous and Eocene floras of South Carolina and
Georgia. _U. S. Geol. Surv. Professional papers_, No. 84.
—— (15) The Mississippi River Bluffs at Columbus and Hickman,
Kentucky, and their Fossil Flora. _Proc. U. S. Nat. Mus._ vol.
+xlviii.+ p. 293.
—— (16) The Geological history of Gymnosperms. _The Plant World_,
vol. +xix.+ p. 27.
=Bertrand, C. E.= (74) Anatomie comparée des tiges et des feuilles chez
les Gnétacées et les Conifères. _Ann. Sci. nat._ [v], vol. +xx.+
p. 5.
—— (83) Note sur le genre _Vesquia_, Taxinée fossile du Terrain
Aachénien de Tournai. _Bull. soc. bot. France_ [3], Tome +v.+ p.
293.
—— (89) Les Poroxylons végétaux fossiles de l’époque houillière.
_Ann. soc. Belg. de Microscopie_, Tome +xiii.+ Fasc. i.
—— (98) Remarques sur la structure des grains de pollen de
_Cordaites_. _Assoc. Franç. pour l’avanc. des Sci. Nantes_
(1898), p. 436.
—— (07) Les caractéristiques du genre _Rhabdocarpus_ d’après les
préparations de la collection B. Renault. _Bull. soc. bot._ [4],
Tome +vii+, p. 654.
—— (07²) Les caractéristiques du genre _Diplotesta_ de Brongniart.
_Bull. soc. bot. France_ [4], tome +vii.+ p. 388.
—— (07³) Les caractéristiques du genre _Leptocaryon_ de Brongniart.
_Ibid._ p. 452.
—— (07⁴) Les caractéristiques du genre _Taxospermum_ de Brongniart.
_Ibid._ p. 213.
—— (07⁵) Remarques sur le _Taxospermum angulosum_. _Compt. rend.
d’assoc. Franç. pour l’avanc. des sci._ (Reims, 1907), p. 410.
—— (08) Les caractéristiques du _Cycadinocarpus angustodunensis_ de
B. Renault. _Bull. soc. bot. France_ [4], tome +viii.+ p. 326.
—— (08²) Les caractéristiques du genre _Cardiocarpus_ d’après les
graines silicifiées étudiées par Ad. Brongniart et B. Renault.
_Ibid._ p. 391.
—— (08³) La spécification des _Cardiocarpus_ de la collection B.
Renault. _Ibid._ p. 454.
—— (09) Sur le genre _Compsotesta_ de Ad. Brongniart. _Ann. Jard.
Bot. Buit._ [2], suppl. 3.
—— (11) Le Bourgeon femelle des _Cordaites_. _Nancy._
=Bertrand, C. E.= et =B. Renault=. (82) Recherches sur les Poroxylons.
_Arch. bot. du Nord de la France_, vol. +ii.+ p. 243.
=Bertrand, P.= (08) Sur les stipes de _Clepsydropsis_. _Compt. Rend._,
Nov. 16, 1908.
—— (11) Structure des stipes _d’Asterochlaena laxa_ Sterzel. _Mém.
soc. géol. Nord_, Tome +vii.+ i.
—— (13) Les Fructifications de Neuroptéridées recueillies dans le
terrain houiller du Nord de la France. _Ann. soc. géol. Nord_,
Tome +xlii.+ p. 113.
—— (14) État actuel de nos Connaissances sur les Genres ‘Cladoxylon’
et ‘Steloxylon.’ _Compt. Rend. de l’assoc. franç. pour
l’Avancement des Sciences_ (Havre, 1914), p. 446.
=Beust, F.= (85) Untersuchung über fossile Hölzer aus Grönland. _Neue
Denksch. allgem. Schweiz. Ges. gesammt. Naturwiss_. Bd. +xxix.+
=Binney, E. W.= (66) On Fossil wood in calcareous nodules found in the
upper foot coal near Oldham. _Proc. Lit. Phil. Soc. Manchester_,
vol. +v.+ p. 113.
=Bleicher and Fliche=. (92) Contribution à l’étude des Terrains
Tertiaires d’Alsace. _Bull. soc. géol. France_ [3], Tome +xx.+ p.
375.
=Bodenbender, W.= (96) Beobachtungen über Devon- und Gondwana-Schichten
in der Argentinischen Republik. _Zeitsch. Deutsch. geol. Ges._
Bd. +xlviii.+ p. 743.
—— (02) Contribucion al Conocimiento de la Precordillera de San Juan
de Mendoza. _Bot. Acad._ _Nac. Cienc. Cordoba_, vol. +xvii.+ p.
203.
=Boodle, L. A.= (15) Concrescent and solitary Foliage-leaves in
_Pinus_. _New Phyt._ vol. +xiv.+ p. 19.
=Boodle, L. A.= and =W. C. Worsdell=. (94) On the comparative anatomy
of the Casuarineae, with special reference to the Gnetaceae and
Cupuliferae. _Ann. Bot._ vol. +viii.+ p. 231.
=Boulay=. (79) Recherches de paléontologie végétale dans le terrain
houiller du Nord de la France. _Ann. soc. scient. Bruxelles_,
ann. iv. pt. 2, 1880.
—— (87) Notice sur la Flore tertiaire des environs de Privas
(Ardiche). _Bull. soc. bot. France_, Tome +xxxiv.+ p. 227.
—— (88) Notice sur les Plantes fossiles des grès tertiaires de
Saint-Saturnin (Marne et Loire). _Journ. Bot. Ann._ 2, p. 921.
=Bower, F. O.= (81) On the germination and histology of the seedlings
of _Welwitschia mirabilis_. _Quart. Journ. Micr. soc._ vol.
+xxi.+ pp. 15, 571.
—— (82) The germination and embryogeny of _Gnetum Gnemon_. _Ibid_.
vol. +xxii.+ [N.S.], p. 277.
—— (84) On the structure of _Rhynchopetalum montanum_. _Journ. Lin.
Soc._ vol. +xx.+ p. 440.
—— (12) Studies in the Phylogeny of the Filicales. II. _Lophosira_,
and its relation to the Cyatheoideae and other Ferns. _Ann. Bot._
vol. +xxvi.+ p. 269.
=Bowerbank, J. S.= (40) History of the Fossil fruits and seeds of the
London Clay. _London_.
=Braun, A.= (75) Die Frage nach der Gymnospermie der Cycadeen.
_Monatsber. K. Preuss. Akad. Wiss. Berlin_, p. 289.
—— (75²) Die Diagnosen dreier im Jahre 1873 von G. Wallis in Neu
Granada entdeckter Cycadeen. _Ibid_. p. 376.
=Braun, C. F. W.= (43) Beiträge zur Petrefactenkunde Bayreuth (Graf zu
Münster), Heft +vi.+ _Bayreuth_.
—— (47) Die Fossile Gewächse aus den Grenzschichten zwischen dem
Lias und Keuper des neu aufgefundenen Pflanzenlagers in dem
Steinbrüche von Veitlahm bei Culmbach. _Flora_, p. 81.
—— (49) Beiträge zur Urgeschichte der Pflanzen. VI. _Weltrichia_
eine neue Gattung fossiler Rhizantheen. _Progr. iii. Jahresber.
K. Kreis-Landwirthsch. und Gewerbschule zu Bayreuth_.
=Brauns, D.= (66) Der Sandstein bei Seinstedt unweit des Fallsteins und
die in ihm vorkommenden Pflanzenreste. _Paleont_. Bd. +ix.+ p. 47.
=Brenchley, Winifred E.= (13) On Branching specimens of _Lyginodendron
Oldhamium_ Will. _Journ. Linn. Soc_. vol. +xli.+ p. 349.
=Bristow, H. W.= (62) The Geology of the Isle of Wight. _Mem. Geol.
Surv. Great Britain_.
=Brongniart, A.= (25) Observations sur les végétaux fossiles renfermés
dans les grès de Hoer en Scanie. _Ann. Sci. nat._ vol. +iv.+ p.
200.
—— (28) Essai d’une Flore du grès bigarré. _Ann. Sci. nat._ vol.
+v.+ p. 435.
—— (33) Notice sur une Conifère fossile du terrain d’eau douce de
l’île d’Iliodroma. _Ann. Sci. nat._ tome +xxx.+ p. 175.
—— (74) Études sur les graines fossiles trouvées à l’état silicifié
dans le terrain Houiller de Saint Étienne. _Ann. Sci. nat._ tome
+xx.+ [5], p. 234.
—— (81) Recherches sur les graines fossiles silicifiées. _Paris_.
=Bronn, H. G.= (58) Beiträge zur triassischen Schiefer von Raibl.
_Neues Jahrb. Min_. p. 129.
=Brooks, F. T.= and =A. Sharples=. (14) Pink disease. _Bull. No._ 21,
_Depart. Agric. Fed. Malay States_.
=Brooks, F. T.= and =W. Stiles=. (10) The structure of _Podocarpus
spinulosus_ (Smith) R. Br. _Ann. Bot._ vol. +xxiv.+ p. 305.
=Buchman, J.= (45) Outline of the Geology of the neighbourhood of
Cheltenham (in collaboration with R. I. Murchison and H. E.
Strickland). _London_.
=Buckland, W.= (28) On the Cycadeoideae, a Family of Fossil Plants
found in the Oolite quarries of the Isle of Portland. _Trans.
Geol. Soc_. [2], vol. +ii.+ p. 395.
—— (37) Geology and Mineralogy considered with reference to Natural
Theology. _London_.
=Burckhardt, C.= (11) Bemerkungen zu einigen Arbeiten von W. Gothan und
A. G. Nathorst. _Cent. Min. Geol.; Paleont_. p. 442.
=Burgestein, A.= (06) Zur Holzanatomie der Tanne, Fichte und Lärche.
_Ber. deutsch. Bot. Ges._ Bd. +xxiv.+ Heft +vi.+ p. 295.
—— (08) Vergleichende Anatomie des Holzes der Koniferen.
_Wiesner-Festschrift, Wien_.
=Burlingame, L.= (08) The staminate cone and male gametophyte of
_Podocarpus. Bot. Gaz._ vol. +xlvi.+ p. 161.
—— (13) The Morphology of _Araucaria brasiliensis. Bot. Gaz._ vol.
+lv.+ p. 97.
—— (15) The Morphology of _Araucaria brasiliensis. Ibid_. vol.
+lix.+ p. 1.
—— (15²) The Origin and Relationships of the Araucarians. _Ibid_.
vol. +lx.+ p. 1.
=Butterworth, J.= (97) Some further investigations of Fossil seeds
of the genus _Lagenostoma_ (Williamson) from the Lower Coal
Measures, Oldham. _Mem. Proc. Manchester Lit. and Phil. Soc._
vol. +xli.+ ix. p. 1.
=Caldwell, O. W.= (07) _Microcycas calocoma. Bot. Gaz._ vol. +xliv.+ p.
118.
=Caldwell, O. W.= and =C. F. Baker=. (07) The identity of _Microcycas
calocoma_. _Ibid_. vol. +xliii.+ p. 130.
=Cambier, R.= et =A. Renier=. (10) _Psygmophyllum Delvali_ n. sp. du
Terrain houiller de Charleroi. _Ann. soc. géol. Belg_. Tome +ii.+
p. 23. (_Mém. in 4to_.)
=Capellini, G.= and =Conte E. Solms-Laubach=. (92) I Tronchi di
Bennettitee dei Musei Italiani. _Mem. Reale Acad. Sci. Istit.
Bologna_ [5], tom. +ii.+ p. 161.
=Carano, E.= (04) Contribuzione alla conoscenza della Morfologia e
dello sviluppo del fascio vascolare delle foglie delle Cicadacee.
_Ann. di Bot_. vol. +i.+ p. 109 (Rome).
=Carpentier, A.= (11) Sur quelques fructifications et inflorescences du
Westphalien du Nord de la France. _Rev. Gén. Bot_. tome +xxiii.+
p. 1.
—— (13) Contribution à l’étude du Carbonifère du Nord de la France.
_Mém. soc. géol. du Nord_, tome +vii.+ ii. p. 1.
=Carruthers, W.= (66) On Araucarian cones from the Secondary beds of
Britain. _Geol. Mag_. vol. +iii.+ p. 249.
—— (66²) On some fossil Coniferous fruits. _Ibid_. vol. +iii.+ p.
534.
—— (67) On _Cycadeoidea Yatesii_ sp. nov. a fossil Cycadean stem
from the Potton sands, Bedfordshire. _Ibid_. vol. +iv.+ p. 199.
—— (67²) On Gymnospermous Fruits from the Secondary rocks of
Britain. _Journ. Bot_. vol. +v.+ p. 1.
—— (67³) On some Cycadean Fruits from the Secondary rocks of
Britain. _Geol. Mag_. vol. +iv.+ p. 101.
—— (68) British Fossil Pandanaceae. _Ibid_. vol. +v.+ p. 153.
—— (69) On _Beania_, a new genus of Cycadean Fruit from the
Yorkshire Oolite. _Ibid_. vol. +vi.+ p. 1.
—— (69²) On some undescribed Coniferous fruits from the Secondary
rocks of Britain. _Ibid_. vol. +vi.+ p. 1.
—— (70) On Fossil Cycadean stems from the Secondary rocks of
Britain. _Trans. Linn. Soc_. vol. +xxvi.+ p. 675.
—— (71) On two undescribed Coniferous fruits from the Secondary
rocks of Britain. _Geol. Mag_. vol. +viii.+ p. 1.
—— (77) Description of a new species of _Araucarites_ from the
Coralline Oolite of Malton. _Quart. Journ. Geol. Soc_. vol.
+xxxiii.+ p. 402.
—— (93) On _Cycas Taiwaniana_, sp. nov. and _C. Seemanni_ R. Br.
_Journ. Bot_. vol. +xxxi.+ p. 1.
=Carter, M. Geraldine=. (11) A Reconsideration of the origin of
Transfusion-tissue. _Ann. Bot_. vol. +xxv.+ p. 975.
=Caspary, R.= and =R. Triebel=. (89) Einige fossile Hölzer Preussens.
_K. Preuss. Geol. Landesanstalt_, Bd. +ix.+ Heft iii. p. 113.
=Čelakovský, L.= (82) Zur Kritik der Ansichten von den Fruchtschuppe
der Abietineen. _Abh. K. böhm. Ges. Wiss. Prag_ [vi], Bd. +ii.+
=Chamberlain, C. J.= (06) The ovule and female gametophyte of _Dioon_.
_Bot. Gaz._ vol. +xlii.+ p. 321.
—— (09) _Dioon spinulosum. Ibid._ vol. +xlviii.+ p. 401.
—— (10) See Coulter and Chamberlain.
—— (10²) Fertilization and embryogeny in _Dioon edule_. _Bot. Gaz._
vol. +l.+ p. 415.
—— (11) The adult Cycad Trunk. _Ibid._ vol. +lii.+ p. 81.
—— (12) Morphology of _Ceratozamia_. _Ibid._ vol. +liii.+ p. 1.
—— (12²) A round-the-world Botanical Excursion. _Pop. Sci. Monthly_,
vol. +lxxxi.+ p. 417.
—— (12³) Two species of _Bowenia_. _Bot. Gaz._ vol. +liv.+ p. 419.
—— (13) _Macrozamia Moorei_, a connecting link between living and
fossil Cycads. _Bot. Gaz._ vol. +lv.+ p. 141.
=Chapman, F.= (09) Jurassic Plant-remains from Gippsland, Pt. ii. _Rec.
Geol. Surv. Victoria_, vol. +iii.+ pt. i. p. 103.
=Chrysler, M. A.= (15) The Medullary rays of _Cedrus_. _Bot. Gaz._ vol.
+lix.+ p. 387.
=Church, A. H.= (14) On the Floral Morphology of _Welwitschia
mirabilis_ (Hooker). _Phil. Trans. R. Soc._ vol. 205, p. 115.
=Cockerell, T. D. A.= (06) The Fossil Flora and Fauna of the Florissant
(Colorado) shales. _Univ. Colorado Series_, vol. +iii.+ No. 3.
—— (08) Description of Tertiary Plants. II. _Amer. Journ. Sci._ vol.
+xxvi+ [4], p. 537.
—— (08²). The Fossil Flora of Florissant, Colorado. _Bull. Amer.
Mus. Nat. Hist._ vol. +xxiv.+ p. 71.
—— (08³) Florissant; a Miocene Pompeii. _Pop. Sci. Monthly_ (Aug.
1908, p. 112).
=Coemans, E.= (66) Description de la flore fossile du premier étage du
terrain Crétacé du Hainaut. _Mém. Acad. R. Belg._, tome +xxxvi.+
=Coker, W. C.= (03) On the gametophyte and embryo of _Taxodium_. _Bot.
Gaz._ vol. +xxxvi.+ p. 1.
—— (09) Vitality of Pine seeds and the delayed opening of cones.
_Amer. Nat._ vol. +xliii.+ p. 677.
=Compter, G.= (94) Die fossile Flora des untern Keupers von
Ostthüringen. _Zeitsch. für Naturwiss._ _Leipzig_, Bd. +lxvii.+
p. 205.
—— (03) Cycadeenfrüchte aus der Lettenkohle von Apolda. _Zeitsch.
für Naturwiss._ _Stuttgart_, Bd. +lxxv.+ p. 171.
=Compton, R. H.= (08) See South and Compton.
=Cowentz, H.= (78) Ueber ein tertiares Vorkommen Cypressenartiger
Hölzer bei Calistoga in Californien. _Neues Jahrb. Min._ p. 800.
—— (82) Fossile Hölzer aus der Sammlung der König. geol.
Landesanstalt zu Berlin. _Jahrb. K. preuss. geol. Land. Bergakad.
Berlin für das Jahr_ 1881, p. 144.
—— (85) Sobre algunos arboles fosiles del Rio Negro. _Bol. Acad.
Nac. Cienc. Cordoba_, tom. +vii.+ p. 575.
—— (86) Die Angiospermen des Bernsteins. _Danzig._
—— (89) Ueber Thyllen und Thyllen-ähnliche Bildungen, vornehmlich im
Hölze der Bernsteinbäume. _Ber. Deutsch. Bot. Ges._ Bd. +vii.+ p.
(34).
—— (92) Untersuchungen über fossile Hölzer Schwedens. _K. Svensk.
Vetenskapsakad. Hand_. Bd. +xxiv.+ No. 13.
—— (01) The past history of the Yew in Great Britain and Ireland.
_Rep._ 71_st Meeting Brit. Assoc._ (_Glasgow_), p. 839.
=Coulter, J. M.= and =C. J. Chamberlain=. (03) The Embryogeny of
_Zamia_. _Bot. Gaz._ vol. +xxxv.+ p. 184.
—— (10) Morphology of Gymnosperms. _Chicago_.
=Cramer, C.= (68) Fossile Hölzer der Arctischen Zone. _Heer’s Foss.
Flor. Arct_. vol. +i.+ p. 167.
=Crié, L.= (89) Beiträge zur Kenntniss der fossilen Flora einiger
Inseln des Südpacifischen und Indischen Oceans. _Pal. Abhand.
(Dames and Kayser)_ (N.F.), Bd. +i.+ Heft ii.
=Daguillon, A.= (90) Recherches morphologiques sur les feuilles des
Conifères. _Rev. Gén. Bot_. tome 11, p. 154.
=Dawson, J. W.= (46) Notices of some Fossils found in the Coal
Formation of Nova Scotia. _Quart. Journ. Geol. Soc_. vol. +ii.+
p. 132.
—— (62) On the Flora of the Devonian period in North-eastern
America. _Ibid_. vol. +xviii.+ p. 296.
—— (63) Further Observations on the Devonian Plants of Maine, Gaspé,
and New York. _Ibid_. vol. +xix.+ p. 458.
—— (63²) Synopsis of the Flora of the Carboniferous Period in Nova
Scotia. _The Canadian Nat. and Geologist_, vol. +viii.+ p. 431.
—— (81) Notes on New Erian (Devonian) plants. _Quart. Journ. Geol.
Soc_. vol. +xxxvii.+ p. 299.
—— (85) On the Mesozoic Floras of the Rocky Mountains Region of
Canada. _Trans. R. Soc. Canada_, sect. +iv.+ p. 1.
—— (90) On new plants from the Erian and Carboniferous, and on the
characters and affinities of Palaeozoic Gymnosperms. _Canadian
Rec. Sci_. vol. +iv.+ p. 1.
—— (93) On new species of Cretaceous plants from Vancouver Island.
_Trans. R. Soc. Canada_, sect. +iv.+ p. 53.
=Dawson, Sir J. W.= and =D. P. Penhallow=. (91) Note on the specimens
of Fossil wood from the Erian (Devonian) of New York and
Kentucky. _The Canadian Rec. Sci_. vol. +iv.+ p. 242.
=Depape, G.= (13) Sur la présence du _Ginkgo biloba_ L. dans le
Pliocène inférieur de Saint-Marcel-d’Ardèche. _Compt. Rend_. vol.
157, p. 957.
=Depape, G.= and =A. Carpentier=. (13) Présence des genus _Gnetopsis_
B. Ren. and R. Zeill. et _Urnatopteris_ Kidst. dans le
Westphalien du Nord de la France. _Ann. soc. géol. du Nord_, tome
+xlii.+ p. 294.
—— (15) Sur quelques graines et fructifications du Westphalien du
Nord de la France. _Rev. Gén. Bot_. vol. +xxvii.+ p. 321.
=Dorety, Helen A.= (08) The embryo of _Ceratozamia_, a physiological
study. _Bot. Gaz_. vol. +xlv.+ p. 412.
—— (08²) The seedling of _Ceratozamia_. _Ibid_. vol. +xlvi.+ p. 205.
—— (09) The extrafascicular cambium of _Ceratozamia_. _Ibid._ vol.
+xlvii.+ p. 149.
—— (09²) Vascular anatomy of the seedling of _Microcycas Calocoma_.
_Ibid._ p. 139.
=Dorrien-Smith, A. A.= (11) A Botanizing expedition to West Australia.
_Journ. R. Hort. Soc._ vol. +xxxvi.+ p. 285.
=Douvillé, H.= et =R. Zeiller=. (08) Sur le terrain houiller du Sud
Oranais. _Compt. Rend._ tome +cxlvi.+ p. 732.
=Drude, O.= (90) Handbuch der Pflanzengeographie. _Stuttgart._
=Dümmer, R.= (12) _Podocarpus formosensis._ _Gard. Chron._ Oct. 19, p.
295.
=Dun, W. S.= (10) Notes on some Fossil plants from the roof of the coal
seam in the Sydney Harbour Colliery. _Journ. Proc. R. Soc. New
South Wales_, vol. +xliv.+ p. 615.
=Duns, J.= (72) On _Cardiocarpon_. _Proc. R. Soc. Edinburgh_, p. 692.
=Dušánek, F.= (13) Spaltöffnungen der Cycadaceen. (Abstract in the
_Bot. Cent._ Bd. +cxxv.+ p. 340.)
=Dusén, P.= (99) Über die Tertiäre Flora der Magellans-Länder. _Wiss.
Ergeb. Schwed. Exped. nach den Magellansländern unter Leitung von
O. Nordenskjöld_, Bd. +i.+ No. iv. p. 87.
—— (08) Über die Tertiäre Flora der Seymour-Insel. _Wiss. Ergeb.
Schwed. Südpolar-Exped._ 1901–03, Bd. +iii.+ Lief. +iii.+ p. 1.
=Duthie, Augusta V.= (12) Anatomy of _Gnetum africanum_. _Ann. Bot._
vol. +xxvi.+ p. 593.
=Eames, A. J.= (13) The Morphology of _Agathis australis_. _Ann. Bot._
vol. +xxvii.+ p. 1.
=Eberdt, O.= (94) Die Braunkohlen Ablagerungen in der Gegend von
Senftenberg. _Jahrb. K. Preuss. Geol. Land. Bergakad. Berlin_,
Bd. +xiv.+ p. 212.
=Eichler, A. W.= (81) Über die weiblichen Blüthen der Coniferen.
_Monatsber. K. Akad. Wiss. Berlin_, p. 1020.
—— (82) Über Bildungsabweichungen bei Fichtenzapfen. _Sitzber. K.
Akad. Wiss. Berlin_, p. 40.
—— (89) Gymnospermae. _Engler and Prantl_; _Die Natürlichen
Pflanzenfamilien_, Teil ii.
=Eichwald, E.= (53–68) Lethaea rossica. _Stuttgart._
=Elkins, Marion G.= and =G. R. Wieland=. (14) Cordaitean wood from the
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=Elwes, H. J.= (12) The Flora of Formosa. _Gard. Chron._ July 13, 1912,
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=Elwes, H. J.= and =A. Henry=. (60) The trees of Great Britain and
Ireland, vol. +i.+ _Edinburgh._
=Endlicher, S.= (40) Genera plantarum secundum ordines naturales
disposita. _Vindobonae_, 1836–40.
—— (47) Synopsis Coniferarum. _Sangalli._
=Engelhardt, H.= (85) Die Tertiärflora des Jesuitengrabens bei
Kundratitz in Nordböhmen. _Nov. Act. K. Leop.-Car. Deutsch. Akad.
Naturforsch._ Bd. +xlviii.+ No. 3, p. 299.
—— (91) Über Tertiärpflanzen von Chile. _Abh. Senckenberg.
naturforsch. Ges_. p. 629.
—— (12) Weiterer Beitrag zur Kenntniss der fossilen Tertiärflora
Bosniens. _Wiss. Mitt. aus Bosnien und der Herzegowina_, Bd.
+xii.+ p. 593.
=Engelhardt, H.= and =F. Kinkelin=. (08) Oberpliocene Flora und Fauna
des Unter-Maintales. _Abh. Senck. Naturforsch. Ges_. Bd. +xxix.+
Heft iii. p. 151.
=Engler, A.= (89) Engler and Prantl; Die Natürlichen Pflanzenfamilien,
Teil +ii.+ Abt. i.
—— (95) Die Pflanzenwelt Öst Afrikas, _etc_. Th. C. _Berlin_.
—— (97) Engler and Prantl; Die Natürlichen Pflanzenfamilien.
Nachtrag zu Teilen +ii–iv.+
=Essner, B.= (86) Ueber den diagnostischen Werth der Anzahl und Höhe
der Markstrahlen bei den Coniferen. _Abh. naturforsch. Ges.
Halle_, Bd. +xvi.+ p. 1.
=Etheridge, R.= (93) On the occurrence of a plant allied to
_Schizoneura_ in the Hawkesbury Sandstone. _Rec. Geol. Surv. New
South Wales_, vol. +iii.+ pt. iii, p. 74.
=Ettingshausen, C. von=. (51) Ueber einige neue und interessante
_Taeniopteris_ Arten aus den Sammlungen des Kais. Hof Mineralien
Cabinetes und der K.k. geol. Reichsanstalt. _Naturwiss. Abh. W.
Haidinger_, vol. +iv.+ p. 95.
—— (52) Beitrag zur näheren Kenntniss der Flora der Wealdenperiode.
_Abh. K.k. geol. Reichs. Wien_, Bd. +i.+ Abth. iii. No. 2, p. 1.
—— (52²) Die Steinkohlenflora von Stradonitz. _Ibid_. Bd. +i.+ Abth.
iii. No. 4.
—— (55) Die Tertiäre Flora von Häring in Tirol. _Ibid_. Bd. +ii.+
Abth. ii. No. 2.
—— (57) Die Fossile Flora von Köflach in Steiermark. _Jahrb. K.k.
geol. Reichs_. Bd. +viii.+ p. 738.
—— (58) Beiträge zur Kenntniss der fossilen Flora von Sotzka in
Untersteiermark. _Sitz. K. Akad. Wiss. Wien_, Bd. +xxviii.+ p.
471.
—— (67) Die Kreideflora von Niederschoena in Sachsen. _Ibid_. Bd.
+lv.+ Abth. i. p. 235.
—— (67²) Die fossile Flora des Tertiär-Beckens von Bilin. _Denksch.
Wiss. Akad. Wien_, Bd. +xxvi.+ p. 79.
—— (70) Beitrag zur Kenntniss der Tertiärflora Steiermarks. _Sitz.
K. Akad. Wien_, Bd. +lx.+ Abth. i. p. 17.
—— (72) Die Fossile Flora von Sagor in Krain. _Denksch. Wiss. Akad.
Wien_, Bd. +xxxii.+ p. 32.
—— (78) Beitrag zur Erforschung der Phylogenie der Pflanzenarten.
_Ibid_. Bd. +xxxviii.+ p. 65.
—— (79) Report on Phyto-Palaeontological Investigations of the
Fossil Flora of Sheppey. _Proc. R. Soc_. vol. +xxix.+ p. 388.
—— (80) Report on Phyto-Palaeontological Investigations of the
Fossil Flora of Alum Bay. _Ibid_. vol. +xxx.+ p. 228.
—— (85) Die Fossile Flora von Sagor in Krain. _Denksch. Wiss. Akad.
Wien_, Bd. +l.+ p. 1.
—— (86) Beiträge zur Kenntniss der Tertiärflora Australiens. _Ibid._
Bd. +liii.+ p. 81.
—— (87) Beiträge zur Kenntniss der Fossile Flora Neuseelands.
_Denksch. K. Akad. Wiss. Wien_, Bd. +liii.+ p. 3.
—— (88) Contributions to the Tertiary Flora of Australia. _Mem.
geol. Surv. N.S.W. Pal._ No. 2.
—— (88²) Die Fossile Flora von Leoben in Steiermark. _Denksch. K
Akad. Wiss. Wien_, Bd. +liv.+ Abth. +i.+ p. 261.
—— (90) Die Fossile Flora von Schoenegg bei Wies in Steiermark.
_Ibid._ Bd. +lvii.+ p. 61.
=Ewart, A. J.= (08) On the longevity of seeds. _Proc. R. Soc.
Victoria_, vol. +xxi.+ (N.S.), pt. i. p. 1.
=Feistmantel, 0.= (72) Beitrag zur Kenntniss der Ausdehnung des
sogennanten Wyřaner Gasschiefers und seiner Flora. _Jahrb. K.k.
geol. Reichs. Wien_, Bd. +xxii.+ p. 289.
—— (76) Notes on the age of some Fossil Floras in India. _Rec. Geol.
Surv. Ind._ vol. +ix.+ pt. iv. p. 115.
—— (76²) Jurassic (Oolitic) Flora of Kach. _Fossil Flora of the
Gondwana System_, pt. i. vol. +ii.+ 1880.
—— (77) Notes on Fossil Floras in India. _Rec. Geol. Surv. Ind._
vol. +x.+ pt. iv. p. 196.
—— (77²) Jurassic (Liassic) Flora of the Rajmahal group in the
Rajmahal hills. _Foss. Flor. Gond. Syst._ vol. +i.+ pt. ii.
—— (77³) Jurassic (Liassic) Flora of the Rajmahal group from
Golapili, near Ellore, S. Godaveri. _Ibid._ pt. iii.
—— (77⁴) Flora of the Jabalpur group (Upper Gondwanas) in the
Son-Narbada region. _Ibid._ vol. +ii.+ pt. ii.
—— (77⁵) Ueber die Gattung _Williamsonia_ Carr. in Indien.
_Palaeontolog. Beit. Palaeontograph._ Suppl. +iii.+ Lief. iii.
—— (79) Upper Gondwana Flora of the outliers on the Madras coast.
_Foss. Flor. Gond. Syst._ vol. +i.+ pt. iv.
—— (79²) The Flora of the Talchir-Karharbari beds. _Ibid._ vol.
+iii.+ pt. i.
—— (80) The Flora of the Damuda-Panchet Divisions. _Ibid._ vol.
+iii.+ pt. ii.
—— (80²) Note on the fossil genera _Noeggerathia_ Sternberg,
_Noeggerathiopsis_ Feist. and _Rhiptozamites_ Schmal. _Rec. Geol.
Surv. India_, vol. +xiii.+ pt. i. p. 61.
—— (80³) Further notes on the correlation of the Gondwana Flora with
other Floras. _Rec. Geol. Surv. Ind._ vol. +xiii.+ pt. iii. p.
190.
—— (81) Palaeontological notes from the Hazáribágh and Lohárdagga
Districts. _Ibid._ vol. +xiv.+ pt. iii. p. 241.
—— (81²) The Flora of the Talchir-Karharbari beds. _Foss. Flor.
Gond. Syst._ vol. +iii.+ pt. i.
—— (81³) The Flora of the Damuda-Panchet Divisions. _Ibid._ vol.
+iii.+ pt. iii.
—— (82) The Fossil Flora of the South Rewah Gondwana Basin. _Ibid_.
vol. +iv.+ pt. i.
—— (86) The Fossil Flora of some of the Coalfields in Western
Bengal. _Ibid_. vol. +iv.+ pl. ii.
—— (89) Übersichtliche Darstellung der geologisch-palaeontologischer
Verhältnisse Süd-Afrikas. Th. i. _Abh. K. böhm. Ges. Wiss_.
[vii], Bd. +iii.+
=Felix, J.= (82) Beiträge zur Kenntniss fossiler Coniferen-Hölzer.
_Engler’s Jahrb_. Bd. +iii.+ p. 260.
—— (84) Die Holzopale Ungarns in Palaeophytologischen Hinsicht.
_Mitt. Jahrb. K. Ung. geol. Anst_. Bd. +vii.+
—— (87) Untersuchungen über fossile Hölzer. _Zeitsch. Deutsch. geol.
Ges_. p. 517.
—— (94) Untersuchungen über fossile Hölzer. _Ibid_. Heft +i.+ p. 79.
—— (96) Untersuchungen über fossile Hölzer. _Ibid_. Heft +ii.+ p.
249.
=Fiedler, H.= (57) Die Fossile Früchte der Steinkohlen-formation.
_Acad. Caes. Leop. Nov. Acta_, Bd. +xxvi.+ p. 239.
=Fliche, P.= (96) Étude sur la flore fossile de l’Argonne
(Albien-Cenomanien). _Bull. soc. sci. Nancy_.
—— (97) Note sur les nodules et bois minéralisés trouvés à St
Parres-les-vaudes (Aube) dans les grès verts infracrétacés. _Mem.
soc. Acad. de l’Aube_, tome +lx.+
—— (99) Note sur quelques fossiles végétaux de l’Oligocène dans les
Alpes Françaises. _Bull. soc. géol. France_ [3], tome +xxvii.+ p.
466.
—— (00) Contribution à la Flore fossile de la Haute-Marne
(Infracrétacée). _Bull. soc. sci. Nancy_.
—— (00²) Note sur un bois fossile de Madagascar. _Bull. soc. géol.
France_ [3], tome +xxviii.+ p. 470.
—— (03) Note sur des bois silicifiés Permiens de la vallée de Celles
(Vosges).
—— (05) Note sur des bois fossiles de Madagascar. _Bull. soc. géol.
France_ [4], tome +v+, p. 346.
—— (10) Flore Fossile du Trias en Lorraine et Franche-Comté avec des
considérations finales par M. R. Zeiller. _Paris_.
=Fliche, P.= and =Bleicher=. (82) Étude sur la flore de l’oolithe
inférieure aux environs de Nancy. _Bull. soc. sci. Nancy_.
=Fliche, P.= and =R. Zeiller=. (04) Note sur une florule Portlandienne
des environs de Boulogne-sur-mer. _Bull. soc. géol. France_ [4],
tome +iv+, p. 787.
=Fontaine, W. M.= (93) Notes on some Fossil plants from the Trinity
Division of the Comanche series of Texas. _Proc. U. S. Nat. Mus_.
vol. +xvi.+ p. 261.
=Foxworthy, F. W.= (11) Philippine Gymnosperms. _Philipp. Journ. Sci_.
(C) _Botany_, vol. +vi.+ No. 3, p. 149.
=Fraine, E. de=. (12) On the structure and affinities of _Sutcliffia_,
in the light of a newly discovered specimen. _Ann. Bot_. vol.
+xxvi.+ p. 1031.
—— (14) On _Medullosa centrofilis_, a new species of _Medullosa_
from the Lower Coal Measures. _Ibid_. vol. +xxviii.+ p. 251.
=Fritel, P. H.= and =R. Vignier=. (11) Étude anatomique de deux bois
Éocènes. _Ann. sci. nat._ [9], tome +xiv.+ p. 63.
=Fujii, K.= (96) On the different views hitherto proposed regarding the
morphology of the flowers of _Ginkgo biloba_. _Bot. Mag. Tokyo_,
vol. +x.+ No. 109, p. 13.
—— (10) Some remarks on the Cretaceous Fossil Flora and the causes
of extinction. _Bot. Mag. Tokyo_, vol. +xxiv.+ No. 284, p. 197.
=Fujioka, M.= (13) Studien über den anatomischen Bau des Hölzes der
japanischen Nadelbäume. _Journ. Coll. Agric. Imp. Univ. Tokyo_,
vol. +iv.+ No. 4, p. 201.
=Gardner, J. S.= (86) A monograph of the British Eocene Flora, vol.
+ii.+ Gymnospermae. _Palaeont. Soc. London._
—— (86²) Second Report of the Committee appointed for the purpose of
reporting on the Fossil Plants of the Tertiary and Secondary beds
of the United Kingdom. Rep. of the 56th Meeting Brit. Assoc.
=Geinitz, H. B.= (42) Charakteristik der Schichten und Petrefacten des
Sächsischen Kreidegebirges. Heft +iii.+ _Dresden und Leipzig._
—— (62) Dyas oder die Zechstein-formation und das Rothliegende, Heft
+ii.+ _Leipzig._
—— (63) Über zwei neue Dyadische Pflanzen. _Neues Jahrb. Min._ p.
525.
—— (71) Über fossile Pflanzen aus der Steinkohlen-Formation am
Altai. _Leipzig._
—— (73) Versteinerungen aus dem Brandschiefer der unteren Dyas von
Weissig bei Pillnitz in Sächsen. _Neues Jahrb. Min._ p. 681.
—— (75) Über neue Aufschlüsse im Brandschiefer der unteren Dyas von
Weissig bei Pillnitz in Sächsen. _Ibid._ p. 1.
—— (80) Nachträge zur Dyas I. _Mittheil. aus dem K. Min.-geol. und
Praehist. Mus. Dresden_, Heft 3.
=Gerry, E.= (10) The distribution of the Bars of Sanio in the
Coniferales. _Ann. Bot._ vol. +xxiv.+ p. 119.
=Geyler, T.= and =F. Kinkelin=. (90) Oberpliocän-Flora aus den
Baugraben des Klärbeckens bei Niederrad _etc._ _Abh. Senck.
Naturforsch. Ges._ Bd. +xv.+ p. 1.
=Gibbs, L. S.= (12) On the Development of the female strobilus in
_Podocarpus. Ann. Bot._ vol. +xxvi.+ p, 515.
=Glück, H.= (02) Eine fossile Fichte aus dem Neckerthal. _Mitt. Grossh.
Bad. geolog. Landesanst._ Bd. +iv.+ Heft iv. p. 399.
=Goc, M. J. le.= (14) Observations on the centripetal and centrifugal
xylems in the petioles of Cycads. _Ann. Bot._ vol. +xxviii.+ p.
183.
=Goebel, K.= (05) Organography of Plants. Pt. ii. _Oxford._
=Goeppert, H. R.= (40) Über die neulichst im Basalttuff des
hohen Seelbachkopfes bei Siegen entdeckten bituminösen und
versteinerten Hölzer, so wie über die der Braunkohlenformation
überhaupt. _Arch. für Min., Geog., etc._ (_Karsten und von
Decken_), Bd. +xiv.+ p. 182.
—— (41) Über den Bernstein.... _Uebersicht der Arbeiten und
Veränderungen der Schles. Ges. für Vaterländ._ _Kultur._
_Breslau._
—— (41²) _Taxites scalariformis_, eine neue Art fossilen Holzes.
_Arch. für Min., Geog., etc._ Bd. +xv.+ p. 727.
—— (44) Ueber die fossilen Cycadeen überhaupt, mit Rücksicht auf die
in Schlesien vorkommenden Arten. _Uebersicht Arbeit. und Veränd.
Schlesisch. Ges. vat. Kult._ 1843, p. 114. _Breslau._
—— (45) F. Wimmer’s Flora von Schlesien nebst einer Uebersicht der
Fossilen Flora Schlesiens von H. R. Goeppert. _Breslau._
—— (45²) Description des végétaux fossiles recueillis par M. P. de
Tchihatcheff en Sibérie. _Voyage scientifique dans l’Altai
oriental_, p. 379. _Paris._
—— (46) Ueber die fossile Flora der mittleren Juraschichten in
Oberschlesien. _Uebers. Arbeit. und Veränd. Schles. Ges. vat.
Kultur im Jahre_ 1845, _Breslau_, 1846, p. 139.
—— (47) Zur Flora des Quadersandsteins in Schlesien. _Nachtrag. Nov.
Act. Ac. Caes. Leop.-Car._ vol. +xxii.+ p. 355.
—— (50) Monographie der fossilen Coniferen. _Natuurkundige Verhand.
Holland. Maatschap. Wetenschappen Haarlem. Leiden._
—— (52) Fossile Flora des Übergangsgebirges. _Nova Acta Caes.
Leop.-Carol. Nat. Cur._ Bd. +XX:I.+ (supplement).
—— (53) Ueber die gegenwärtigen Verhältnisse der Paläontologie in
Schlesien, so wie über fossile Cycadeen. _Denksch. Schles. Ges.
für Vaterländ. Kultur._
—— (65) Die fossile Flora der Permischen Formation. _Palaeont._ Bd.
+ii.+ p. 1.
—— (65²) Über die fossile Kreideflora und ihre Leitpflanzen. _Zeit.
Deutsch. geol. Ges._ Bd. +xvii.+ p. 638.
—— (66) Beiträge zur Kenntniss fossilen Cycadeen. _Neues Jahrb.
Min._ p. 129.
—— (80) Beiträge zur Pathologie und Morphologie fossiler Stämme.
_Palaeontol._ [N.F.], Bd. +viii.+ iii. p. 131.
—— (81) Revision meiner Arbeiten über die Stämme der fossilen
Coniferen, insbesondere der Araucariten, und über die
Descendenzlehre. _Bot. Cent._ Bd. +v.+, +vi.+ p. 378.
=Goeppert, H. R.= and =G. Stenzel=. (81) Die Medulloseae. _Palaeontol._
[N.F.], Bd. +viii.+ p. 113.
—— (88) Nachträge zur Kenntniss der Coniferenhölzer der
Palaeozoischen Formationen. _Abh. K. Preuss. Akad. Wiss. Berlin._
=Gomes, B. A.= (65) Vegetaes Fosseis. Flora fossil do Terrens
Carbonifero das visinhanças dio Porto, serra do Bussaio, e moinho
d’ordem proximo a alcacer do Sal. _Comm. geol. Portugal. Lisbon._
=Gordon, Marjorie.= (12) Ray-tracheids in _Sequoia sempervirens_. _New
Phyt._ vol. +xi.+ p. 1.
+GORDON, W. T.+ (10) On a new species of _Physostoma_ from the Lower
Carboniferous rocks of Pettycur (Fife). _Proc. Camb. Phil. Soc._
vol. +xv.+ pt. +v.+ p. 395.
—— (12) On _Rhetinangium Arberi_, a new genus of Cycadofilices from
the Calciferous sandstone series. _Trans. R. Soc. Edinb._ vol.
+xlviii.+ pt. iv. p. 813.
=Gothan, W.= (05) Zur Anatomie lebender und fossiler
Gymnospermer-Hölzer. _Abh. K. Preuss. geol. Landes._ [N.F.], Heft
+xliv.+ p. 1.
—— (06) Die fossilen Coniferenhölzer von Senftenberg. _Abh. K.
Preuss. Geol. Landesanst. Bergakad._ [N.F.], Heft +xlvi.+ p. 155.
—— (06²) Fossile Hölzer aus dem Bathonien von Russisch-Polen.
_Verhand. K. Russ. Min. Ges. zu St Petersburg_ [ii], Bd. +xliv.+
Lief. i. p. 435.
—— (06³) _Piceoxylon Pseudotsugae_ als fossiles Holz. _Potonié’s
Abbild. und Beschreib. Foss. Pflanz._ Lief. +iv.+ 80.
—— (07) Über die Wandlungen der Hoftüpfelung bei den Gymnospermen im
Laufe der geologischen Epochen und ihre physiologische Bedeutung.
_Sitz. Ges. Naturforsch. Freunde_, No. 2, p. 13.
—— (07²) Die Fossilen Hölzer von König Karls Land. _K. Svensk.
Vetenskapsakad. Hand._ Bd. +xlii.+ No. 10, p. 1.
—— (08) Die Fossile Hölzer von der Seymour- und Snow Hill-Insel.
_Wiss. Ergeb. Schwedis. Südpolar-Exped._ 1901–03, Bd. +iii.+
Lief. viii. _Stockholm._
—— (08²) Die Frage der Klimadifferenzierung im Jura und in der
Kreideformation im Lichte paläobotanischer Tatsachen. _Jahrb. K.
Preuss. Geol. Landes. für_ 1908, Bd. +xxix.+ Th. ii. Heft 2, p.
220.
—— (09) Über Braunkohlenhölzer des rheinischen Tertiärs. _Jahrb. K.
Preuss. geol. Land._ Bd. +xxx.+ Teil i. Heft 3, p. 516.
—— (10) Die Fossile Holzreste von Spitzbergen. _K. Svensk.
Vetenskapsakad. Hand._ Bd. +xlv.+ No. viii.
—— (11) Über einige Permo-Carbonische Pflanzen von der unteren
Tunguska (Sibirien). _Zeitsch. Deutsch. Geol. Ges._ Bd. +lxiii.+
Heft 4, p. 418.
—— (13) Die oberschlesische Steinkohlenflora. Teil +i.+ _K. Preuss.
geol. Landes._ [N.F.], Heft +lxxv.+
=Gourlie, W.= (44) Notice of the Fossil Plants in the Glasgow Museum.
_Proc. Phil. Soc. Glasgow_, vol. +i.+ 1844, p. 105.
=Grand’Eury, C.= (00) Sur les tiges debout, les souches et racines de
_Cordaites_. _Compt. Rend._ tome +cxxx.+ (April 30).
—— (04) Sur les graines des Neuroptéridées. _Compt. Rend._ tome
+cxxxix.+ p. 23.
—— (04²) Sur les graines des Neuroptéridées. _Ibid._ p. 782.
—— (05) Sur les _Rhabdocarpus_, les graines et l’évolution des
Cordaitées. _Ibid._ tome +cxl.+ p. 995.
—— (05²) Sur les graines de _Sphenopteris_, sur l’attribution des
_Codonospermum_ et sur l’extréme variété des ‘graines de
fougères.’ _Ibid._ p. 812.
—— (13) Recherches géobotaniques sur les forêts et sols fossiles et
sur la végétation et la flore houillères, en deux parties et dix
livraisons. Pt. +i.+ Livr. ii., _Paris et Liège._
=Graner=, (94) Die geographische Verbreitung der Holzarten. I. Die
Coniferen. _Forstwissenschaft. Centralblatt, Berlin._
=Griffith, W.= (59) Remarks on _Gnetum_. _Trans. Linn. Soc._ vol.
+xxii.+ pt. iv. p. 299.
=Groom, P.= (10) Remarks on the Oecology of Coniferae. _Ann. Bot._ vol.
+xxiv.+ p. 241.
=Groom, P.= and =W. Rushton=. (13) The structure of the wood of East
Indian species of _Pinus. Journ. Linn. Soc._ vol. +xli.+ p. 457.
=Groppler, R.= (94) Vergleichende Anatomie des Hölzes der Magnoliaceen.
_Biblioth. Bot._ Bd. +vi.+ Heft 31. _Stuttgart._
=Grossenbacher, J. G.= (15) Medullary spots and their cause. _Bull.
Torr. Bot. Club_, vol. +xlii.+ p. 227.
=Guppy, H. B.= (06) Observations of a Naturalist in the Pacific between
1896 and 1899. _London._
=Gutbier, A. von.= (49) Die Versteinerungen des Zechsteingebirges und
Rothliegenden oder des Permischen Systems in Sachsen. _Dresden
and Leipzig._
=Halle, T. G.= (10) A Gymnosperm with Cordaitean-like leaves from the
Rhaetic beds of Scania. _Arkiv för Bot. Upsala_, Bd. +ix.+ No. 14.
—— (12) On the occurrence of _Dictyozamites_ in South America.
_Palaeobot. Zeitsch._ Bd. +i.+ Heft i. p. 40.
—— (13) Some Mesozoic plant-bearing deposits in Patagonia and Tierra
del Fuego and their Floras. _K. Svensk. Vetenskapsakad. Hand._
Bd. +li.+ No. 3.
—— (13²) The Mesozoic Flora of Graham Land. _Wiss. Ergeb. Schwed.
südpolar. Exped._ 1901–03, Bd. +iii.+ Lief. 14, p. 1.
—— See Möller, H. J. and T. G. Halle (13).
—— (15) Some xerophytic leaf-structures in Mesozoic plants. _Geol.
Fören. Stockholm Förhand._ Bd. +xxxvii.+ H. v. p. 493.
=Hallier, H.= (05) Provisional scheme of the Natural (Phylogenetic)
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=Harshberger, J. W.= (98) Water-storage and conduction in _Senecio
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—— (11) Phytogeographic Survey of N. America. (_Die Veget. der
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=Harker, A.= (06) The Geological structure of the Sgurr of Eigg.
_Quart. Journ. Geol. Soc._ vol. +lxii.+ p. 40.
—— (08) The Geology of the small Isles of Inverness-shire. _Mem.
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=Harpe, P. de la.= (62) See Bristow, H. W.
=Hartz, N.= (96) Planteforsteninger fra Cap Stewart i Østgrønland.
_Meddel. om Grønland_, +xix.+ _Copenhagen._
=Hayata, A.= (06) On _Taiwania_, a new genus of Coniferae from the
Island of Formosa. _Journ. Linn. Soc._ vol. +xxxvii.+ p. 330.
—— (07) On _Taiwania_ and its affinity to other genera. _Bot. Mag._
(_Tokyo_), vol. +xxi.+ p. 21.
—— (10) Botanical Survey by the Govt. of Formosa. _Congr. Int. Bot._
(_Bruxelles_), p. 59.
=Heer, O.= (62) On the Fossil Flora of Bovey Tracey. _Phil. Trans. R.
Soc._ vol. +clii.+ p. 1039.
—— (68) i. Die in Nordgrönland, auf der Melville-Insel, im
Banksland, an Mackenzie, im Island und in Spitzbergen entdeckten
fossilen Pflanzen. _Flor. Foss. Arct_. vol. +i.+ _Zürich_.
—— (69) Beiträge zur Kreide-Flora. I. Flora von Moletein in Mähren.
_Neue Denksch. Allgem. Schweiz. Ges. gesammt. Naturwiss_. Bd.
+xxiii.+
—— (71) iii. Die Miocene Flora und Fauna Spitzbergens. _Flor. Foss.
Arct_. vol. +ii.+
—— (71²) Beiträge zur Kreide-Flora. II. Kreide Flora von
Quedlinburg. _Neue Denksch. Allgem. Schweiz. Ges. gesammt.
Naturwiss_. Bd. +xxiv.+
—— (75) ii. Die Kreide-Flora der arctischen Zone. _Flor. Foss.
Arct_. vol. +iii.+
—— (75²) iii. Nachträge zur Miocenen Flora Grönlands. _Ibid_.
—— (76) Flora Fossilis Helvetiae. _Zürich_.
—— (76²) Über Permische Pflanzen von Fünfkirchen in Ungarn. _Mitt.
Jahrb. K. Ung. Geol. Anst_. Bd. +v.+
—— (77) i. Beiträge zur fossilen Flora Spitzbergens. _Flor. Foss.
Arct_. vol. +iv.+
—— (77²) ii. Beiträge zur Jura-Flora Ost Sibiriens und des
Amurlandes. _Ibid_.
—— (78) ii. Beiträge zur fossilen Flora Sibiriens und des
Amurlandes. _Ibid_. vol. +iv.+
—— (81) Contributions à la Flore du Portugal. _Sect. Trav. Geol.
Port_. (_Lisbon_).
—— (81²) Zur Geschichte der Ginkgo-artigen Bäume. _Engler’s Bot.
Jahrb_. Bd. +i.+ p. 1.
—— (82) i. Flora fossilis Grönlandica. _Flor. Foss. Arct_. vol. +vi.+
—— (83) Flora fossilis Grönlandica. _Ibid_. vol. +vii.+
=Helmhacher, R.= (71) _Sitzber. d. K. Böhm. Ges. Wiss_. p. 81.
=Henry, A.= (06) See Elwes and Henry.
=Herzfeld, S.= (10) Die Entwicklungsgeschichte der weiblichen Blüte
von _Cryptomeria japonica_ Don. Ein Beitrag zur Deutung der
Fruchtschuppe der Coniferen. _Sitzber. Akad. Wiss. Wien_, Bd.
+cxix.+ Abt. i. p. 807.
=Hick, T.= (95) On _Kaloxylon Hookeri_ Will. and _Lyginodendron
Oldhamium_ Will. _Mem. Proc. Manchester Lit. Phil. Soc_. [4],
vol. +ix.+ p. 109.
=Hilderbrand, F.= (61) Die Verbreitung der Coniferen. _Rhein. und
Westphal. Verhand_. Bd. +xviii.+ p. 199.
=Hill, T. G.= and =E. de Fraine=. (10) On the seedling structure of
Gymnosperms. IV. _Ann. Bot_. vol. +xxiv.+ p. 319.
=Hirase, S.= (98) Études sur la fécundation et l’embryogenie du _Ginkgo
biloba. Journ. Coll. Sci. Imp. Univ. Tokyo_, vol. +xii.+ p. 103.
=Höhlke, F.= (02) Ueber die Harzbehälter und die Harzbildung bei den
Polypodiaceen und einigen Phanerogamen. _Beiheft Bot. Cent_. Bd.
+xi.+ p. 8.
=Holden, H. S.= (10) Note on a wounded _Myeloxylon. New Phyt_. vol.
+ix.+ p. 253.
=Holden, Ruth=. (13) Some fossil plants from Eastern Canada. _Ann.
Bot_. vol. +xxvii.+ p. 243.
—— (13²) Contributions to the anatomy of Mesozoic Conifers. No. 1.
Jurassic Coniferous wood from Yorkshire. _Ann. Bot_. vol.
+xxvii.+ p. 533.
—— (13³) Cretaceous Pityoxyla from Cliffwood, New Jersey. _Proc.
Amer. Acad. Arts and Sci_. vol. +xvi.+ p. 609.
—— (14) Contributions to the anatomy of Mesozoic Conifers. II.
Cretaceous Lignites from Cliffwood, N. Jersey. _Bot. Gaz_. vol.
+lviii.+ p. 168.
—— (14²) On the relation between _Cycadites_ and _Pseudocycas. New
Phyt_. vol. +xiii.+ p. 334.
—— (15) A Jurassic wood from Scotland. _Ibid_. vol. +xiv.+ p. 205.
—— (15²) On the cuticles of some Indian Conifers. _Bot. Gaz_. vol.
+lx.+ p. 215.
=Hollick, A.= (97) The Cretaceous clay marl exposed at Cliffwood, N. J.
_Trans. N. Y. Acad. Sci_. vol. +xvi.+ p. 124.
—— (04) Additions to the Palaeontology of the Cretaceous formation
on Long Island. No. II. _Bull. N. Y. Bot. Gard_. vol. +iii.+ No.
11, p. 403.
—— (06) The Cretaceous Flora of southern N. Y. and New England. _U.
S. Geol. Surv. Mon_. vol. +l.+
—— (06²) Systematic Palaeontology of the Pleistocene deposits of
Maryland. _Contributions from the New York Bot. Gard_. No. 85.
—— (12) Additions to the Palaeobotany of the Cretaceous formation on
Long Island. _Bull. N. Y. Bot. Gard_. vol. +viii.+ No. 28, p. 154.
=Hollick, A.= and =E. C. Jeffrey=. (06) Affinities of certain
Cretaceous plant-remains commonly referred to the genera
_Dammara_ and _Brachyphyllum. Amer. Nat_. vol. +xl.+ p. 189.
=Holmes, W. H.= (78) Fossil Forests of the Volcanic Tertiary formations
of the Yellowstone National Park. _Ann. Rep. Geol. Geogr. Surv.
U.S.A_. pt. +ii.+ p. 47.
=Hooker, J. D.= (52) _Dacrydium laxifolium. Icones Plant_. vol. +v.+
pl. 815.
—— (60) Flora Tasmanica. _London_.
—— (62) On the Cedars of Lebanon, Taurus, Algeria, and India. _Nat.
Hist. Rev_. p. 11.
—— (63) On _Welwitschia_, a new genus of Gnetaceae. _Trans. Linn.
Soc_. vol. +xxiv.+ p. 1.
=Hooker, J. D.= and =E. W. Binney=. (55) On the structure of certain
limestone nodules enclosed in seams of bituminous coal, with a
description of some Trigonocarpons contained in them. _Phil.
Trans. R. Soc_. vol. +cxlix.+
=Hörich, O.= (06) Potonié’s Abbildungen und Beschreibungen fossiler
Pflanzen-Reste. _Lief_. +iv.+ 69, 70.
=Howse, R.= (88) A catalogue of Fossil Plants from the Hutton
collection. _Nat. Hist. Trans. Northumberland, Durham, and
Newcastle-upon-Tyne_, vol. +x.+
=Hutchinson, A. H.= (14) The male gametophyte of _Abies. Bot. Gaz_.
vol. +lvii.+ p. 148.
—— (15) On the male gametophyte of _Picea canadensis. Ibid_. vol.
+lix.+ p. 287.
=Jeffrey, E. C.= (03) The comparative anatomy and phylogeny of the
Conifers. I. The genus _Sequoia. Mem. Boston Soc. Nat. Hist_.
vol. +v.+ No. 10, p. 441.
—— (04) A fossil _Sequoia_ from the Sierra Nevada. _Bot. Gaz_. vol.
+xxxviii.+ p. 321.
—— (05) The comparative anatomy and phylogeny of the Conifers. The
Abietineae. _Mem. Boston Soc. Nat. Hist_. vol. +vi.+ No. 1.
—— (06) The wound Reactions of _Brachyphyllum_. _Ann. Bot_. vol.
+xx.+ p. 383.
—— (07) _Araucariopitys_, a new genus of Araucarians. _Bot. Gaz_.
vol. +xliv.+ p. 435.
—— (08) Traumatic ray-tracheids in _Cunninghamia sinensis_. _Ann.
Bot_. vol. +xxii.+ p. 593.
—— (08²) On the structure of the leaf in Cretaceous Pines. _Ibid_.
vol. +xxii.+ p. 207.
—— (10) A new _Prepinus_ from Martha’s Vineyard. _Proc. Boston Soc.
nat. Hist_. vol. +xxxiv.+ No. 10, p. 333.
—— (10²) A new Araucarian genus from the Triassic. _Ibid_. vol.
+xxxiv.+ No. 9, p. 325.
—— (10³) On the affinities of _Yezonia. Ann. Bot_. vol. +xxiv.+ p.
769.
—— (11) The affinities of _Geinitzia gracillima_. _Bot. Gaz_. vol.
+l.+ p. 21.
—— (12) The History, Comparative Anatomy and Evolution of the
_Araucarioxylon_ type. _Proc. Amer. Acad. Arts Sci_. vol.
+xlviii.+ No. 13, p. 532.
—— (14) Spore-conditions in hybrids and the mutation hypothesis of
de Vries. _Bot. Gaz_. vol. +lviii.+ p. 322.
=Jeffrey, E. C.= and =M. A. Chrysler=. (06) On Cretaceous _Pityoxyla.
Bot. Gaz_. vol. +xlii.+ p. 1.
—— (06²) The Lignites of Brandon. _Contrib. from the Phanerogamic
Labt. of Harvard Univ_. No. vi.
—— (07) The microgametophyte of the Podocarpineae. _Amer. Nat_. vol.
+xli.+ No. 486, p. 355.
=Jeffrey, E. C.= and =Ruth D. Cole=. (16) Experimental Investigations
on the genus _Drimys. Ann. Bot_. vol. +xxx.+ p. 359.
=Jeffrey, E. C.= and =R. E. Torrey=. (16) _Ginkgo_ and the
microsporangial mechanisms of the seed plants. _Bot. Gaz_. vol.
+lxii.+ p. 281.
=Johnson, T.= (11) A seed-bearing Irish Pteridosperm, _Crossotheca
Höninghausi_ Kidst. _Sci. Proc. R. Dublin Soc_. vol. +xiii.+ p. 1.
—— (12) _Heterangium hibernicum_ sp. nov. a seed-bearing
_Heterangium_ from Co. Cork. _Ibid_. vol. +xiii.+ No. 20.
—— (14) _Ginkgophyllum kiltorkense_ sp. nov. _Ibid_. vol. +xiv.+ p.
169.
=Johnston, R. H.= (86) Fresh contributions to our knowledge of the
Plants of Mesozoic age in Tasmania. _Papers and Proc. R. Soc.
Tasmania_ for 1886, p. 160.
=Johnstrup, M. F.= (83) Recherches sur les fossiles appartenant aux
formations Crétacée et Miocène, sur la côte occidentale du
Grønland. _Medd. om Grønland_, vol. +v.+
=Jones, W. S.= (12) The structure of the Timbers of some common genera
of Coniferous trees. _Quart. Journ. Forestry_, _April_.
—— (13) The minute structure of the wood of _Cupressus macrocarpa_.
_Ibid._
—— (13²) Ray-tracheids in _Sequoia sempervirens_ and their
pathological character. _Lampeter._
=Karsten, G.= (92) Beitrag zur Entwickelungsgeschichte einiger Gnetum
Arten. _Bot. Zeit._ p. 205.
—— (93) Untersuchungen über die Gattung _Gnetum_. I. _Ann. Jard.
Bot. Buitenzorg_, tome +xi.+ p. 195.
—— (93²) Zur Entwickelungsgeschichte der Gattung _Gnetum_. _Cohn’s
Beit. Biol. Pflanz._ +vi.+ p. 337.
=Kershaw, E. M.= (09) The structure and development of the ovule of
_Myrica Gale_. _Ann. Bot._ vol. +xxiii.+ p. 353.
—— (12) Structure and development of the ovule of _Bowenia
spectabilis_. _Ibid._ vol. +xxvi.+ p. 625.
=Kidston, R.= (84) On a new species of _Schützia_ from the Calciferous
sandstone of Scotland. _Ann. Mag. Nat. Hist._ vol. +xiii.+ p. 77.
—— (86) Notes on some fossil plants collected by Mr R. Dunlop,
Airdrie, from the Lanarkshire coal-field. _Trans. Geol. Soc.
Glasgow_, vol. +viii.+ p. 47.
—— (90) The Yorkshire Carboniferous Flora. _Trans. Yorks. Nat.
Union_, pt. +xiv.+
—— (92) Notes on some fossil plants from the Lancashire Coal
Measures. _Trans. Manchester Geol. Soc._ pt. xiii. vol. +xxi.+
—— (04) On the Fructification of _Neuropteris heterophylla_ Brongn.
_Phil. Trans. R. Soc._ vol. +cxcvii.+ p. 1.
—— (04²) On the Fructification of _Neuropteris heterophylla_ Brongn.
_Proc. R. Soc._ vol. +lxxii.+ p. 487.
—— (04³) Some Fossil Plants collected by Mr A. Sinclair from the
Ayrshire coalfield. _Kilmarnock Glenfield Ramblers Soc. Annals_
(1901–04), No. iv. _Kilmarnock._
—— (05) Preliminary Note on the occurrence of Microsporangia in
organic connection with the Foliage of _Lyginodendron_. _Proc. R.
Soc._ vol. +lxxvi.+ p. 358.
—— (11) Les Végétaux houillers recueillis dans le Hainaut Belge.
_Mém. Mus. Roy. d’hist. nat. Belg._ tome +iv.+
—— (14) On the Fossil Flora of the Staffordshire coalfields. Pt.
iii. The Fossil Flora of the Westphalian series of the S. Staffs.
coalfield. _Trans. R. Soc. Edinb._ vol. +l.+ pt. i. p. 73.
=Kidston, R.= and =D. T. Gwynne-Vaughan=. (12) On the Carboniferous
Flora of Berwickshire. Pt. i. _Stenomyelon tuedianum_ Kidst.
_Trans. R. Soc. Edinb._ vol. +xlviii.+ pt. ii. p. 263.
=Kidston, R.= and =W. J. Jongmans=. (11) Sur la Fructification de
_Neuropteris obliqua_ Brongn. _Arch. Neerl. sci. exact. nat._
[+iii.+ B], tome +i.+ p. 25.
=Kirby, J. W.= (64) On some remains of Fishes and Plants from the
‘Upper limestone’ of the Permian series of Durham. _Quart. Journ.
Geol. Soc._ vol. +xx.+ p. 349.
=Kirchner, O.=, =E. T. Loew=, and =C. Schröter=. (06) Die Coniferen und
Gnetaceen Mitteleuropas. _Stuttgart._
=Kirk, T.= (89) The Forest Flora of New Zealand. _Wellington._
=Kirsch, S.= (11) The Origin and Development of resin-canals in
the Coniferae, with special reference to the Development of
Thyloses and their correlation with the Thylosed strands of the
Pteridophytes. _Trans. R. Soc. Canada_, sect. iv. p. 43.
=Kisch, Mabel H.= (13) The Physiological Anatomy of the periderm of
fossil Lycopodiales. _Ann. Bot._ vol. +xxvii.+ p. 281.
=Kleeberg, A.= (85) Die Markstrahlen der Coniferen. (_Inaug. Diss._)
_Bot. Zeit._ Bd. +xliii.+
=Klein, L.= (81) Bau und Verzweigung einiger dorsiventral gebaute
Polypodiaceen. _Nov. Act. K. Leop. Car. Deutsch. Akad.
Naturforsch._ Bd. +xlii.+ No. 7, p. 335.
=Knowlton, F. H.= (89) Description of the fossil woods and lignites
from Arkansas. _Ann. Rep. Geol. Surv. Arkansas_, vol. +ii.+ p.
249.
—— (89²) Fossil wood and Lignite of the Potomac formation. _Bull. U.
S. Geol. Surv._ No. 56.
—— (90) A Revision of the genus _Araucarioxylon_ of Kraus, with the
compiled descriptions and partial synonymy of the species. _Proc.
U. S. Mus._ vol. +xii.+ p. 601.
—— (93) The Laramie and the overlying Livingstone formation in
Montana. Report on the Flora. _Bull. U. S. Geol. Surv._ No. 105.
—— (99) Fossil Flora of the Yellowstone National Park. Monographs.
+xxxii.+ _U. S. Geol. Surv._ pt. ii. chap. +xiv.+
—— (00) Flora of the Montana formation. _Bull. U. S. Geol. Surv._
No. 163.
—— (05) The geology of the Perry basin in South-eastern Maine, with
a chapter on the fossil plants. _U. S. Geol. Surv. Prof. Papers_,
No. 35.
—— (11) The correct technical name for the Dragon tree of the
Kentish Rag. _Geol. Mag._ [v], vol. +viii.+ p. 467.
—— (14) The Jurassic Flora of Cape Lisburne, Alaska. _U. S. Geol.
Surv. Prof. Papers_, No. 85-D, p. 39.
=Kny, L.= (10) Über die Verteilung des Holzparenchyma bei _Abies
pectinata_ DC. _Ann. Jard. Bot. Buit._ [2], Suppl. +iii.+ p. 645.
=Koetlitz, R.= (98) Observations on the geology of Franz Josef Land.
_Quart. Journ. Geol. Soc._ vol. +liv.+ p. 620.
=Kosmovsky, C.= (92) Quelques mots sur les couches à végétaux fossiles
dans la Russie orientale et en Sibérie. _Bull. Soc. Imp. Nat.
Moscou_ [N.S.], tome +v.+ p. 170.
=Kramer, A.= (85) Beiträge zur Kenntniss der Entwickelungsgeschichte
und des anatomischen Baues der Fruchtblätter der Cupressineen und
der Placenten der Abietineen. _Flora_, +xliii.+ p. 519.
=Krasser, F.= (91) Über die fossile Flora der rhätischen Schichten
Persiens. _Sitzber. K. Akad. Wiss. Wien_, Bd. +c.+ Abth. i. p.
413.
—— (97) Constantine Freiherr von Ettingshausen. _Oesterr. bot.
Zeitsch._ Nos. 9 and 10.
—— (03) Konstantin von Ettingshausen’s Studien über die fossile
Flora von Ouricanga in Brasilien. _Sitzber. K. Akad. Wiss. Wien_,
Bd. +cxii.+ Abt. i. p. 852.
—— (05) Fossile Pflanzen aus Transbaikalien der Mongolei und
Mandschurei. _Denksch. K. Akad. Wiss. Wien_, Bd. +lxxviii.+ p.
589.
—— (09) Zur Kenntniss der fossilen Flora der Lunzer Schichten.
_Jahrb. K.k. geol. Reichs. Wien_, Bd. +lix+, Heft i. p. 101.
—— (12) _Williamsonia_ in Sardinien. _Sitzber. K. Akad. Wien_, Bd.
+cxxi.+ Abt. i. p. 944.
—— (13) Die fossile Flora der Williamsonien bergenden Juraschichten
von Sardinien. _Ibid._ Bd. +cxxii.+
=Kraus, G.= (64) Mikroskopische Untersuchungen über der Bau lebenden
Nadelhölzer. _Würzb. Naturwiss. Zeitsch._ Bd. +v.+ p. 144.
—— (66) Über den Bau der Cycadeenfiedern. _Prings. Jahrb._ Bd. +iv.+
p. 305.
—— (83) Beiträge zur Kenntniss fossiler Hölzer. I. Hölzer aus den
Schwefelgruben Siciliens. _Abh. Naturf. Ges. Halle_, Bd. +xvi.+
p. 79.
—— (92) Beiträge zur Kenntniss fossiler Hölzer. _Abh. Naturforsch.
Ges. Halle_, Bd. +xvii.+ p. 67.
—— (96) Physiologisches aus den Tropen. _Ann. Jard. Bot. Buit._ vol.
+xiii.+ p. 217.
=Kräusel, R.= (13) Beiträge zur Kenntniss der Hölzer aus der
Schlesischen Braunkohle. Teil +i.+ (_Inaug. Diss. Breslau._)
_Bot. Cent._ Bd. +cxxiii.+ p. 123.
=Kryshtofovich, A.= (10) Jurassic Plants from Ussuriland. _Mem. Com.
Geol._ [N.S.], Livr. 56.
—— (15) Plant remains from Jurassic lake-deposits of Transbaikalia.
_Mém. Soc. Imp. Russe Mineralog._ [2], +li.+
=Kubart, B.= (08) Pflanzenversteinerungen enthaltende Knollen aus dem
Ostrau-Karwiner Kohlenbecken. _Sitzber. K. Akad. Wiss. Wien_, Bd.
+cxvii.+ Abt. i. p. 573.
—— (11) Corda’s sphaerosiderite aus dem Steinkohlenbecken
Radnitz-Braz in Böhmen nebst Bemerkungen über _Chorionopteris
gleichenioides_ Corda. _Ibid._ Bd. +cxx.+ Abt. i. p. 1035.
—— (11²) _Podocarpoxylon Schwendae_, ein fossiles Holz von Altersee
(Oberösterreich). _Österr. bot. Zeitsch._ No. 5, p. 161.
—— (14) Über die Cycadofilicineen _Heterangium_ und _Lyginodendron_
aus dem Ostrauer Kohlenbecken. _Österr. bot. Zeitsch._ No. +i.+
ii. p. 8.
=Kurtz, F.= (03) Remarks upon Mr E. A. Arber’s communication on the
Clarke collection of Fossil Plants from New South Wales. _Quart.
Journ. Geol. Soc._ vol. +lix.+ p. 25.
=Kutorga, S.= (42) Beitrag zur Palaeontologie Russlands. _Verhand.
Russ.-Kais. Mineral. Ges. St Petersburg._
—— (44) Zweiter Beitrag zur Palaeontologie Russlands. _Ibid._ p. 62.
=Land, W. J. G.= (04) Spermatogenesis and Oogenesis in _Ephedra
trifurca_. _Bot. Gaz._ vol. +xxxviii.+ p. 1.
=Lang, W. H.= (97) Studies in the Development and Morphology of
Cycadean sporangia. I. The microsporangia of _Stangeria
paradoxa_. _Ann. Bot._ vol. +xi.+ p. 421.
—— (00) Studies in the Development and Morphology of Cycadean
sporangia. II. The ovule of _Stangeria paradoxa_. _Ibid._ vol.
+xiv.+ p. 281.
=Lange, T.= (90) Beiträge zur Kenntniss der Flora des Aachener Sandes.
_Zeitsch. Deutsch. geol. Ges._ Bd. +xlii.+ p. 658.
=Laurent, L.= (12) Flore fossile des Schistes de Manat (Puy-de-Dôme).
_Ann. Mus. d’hist. nat. Marseille_ (_Geol._), tome +xiv.+ p. 3.
=Lawson, A. A.= (04) The gametophytes, fertilization, and embryo of
_Cryptomeria japonica_. _Ann. Bot._ vol. +xviii.+ p. 417.
—— (09) The gametophytes and embryo of _Pseudotsuga Douglasii_.
_Ibid._ vol. +xxiii.+ p. 163.
—— (10) The gametophytes and embryo of _Sciadopitys verticillata_.
_Ibid._ vol. +xxiv.+ p. 403.
=Lebour, G. A.= (77) Illustrations of Fossil Plants; being an autotype
reproduction of selected drawings. _London._
=Lesquereux, L.= (74) Contributions to the Fossil Flora of the Western
Territories. Pt. +i.+ The Cretaceous Flora. _Rep. U. S. Geol.
Surv. Territ._ vol. +vi.+
—— (78) On the Cordaites and their related generic divisions, in the
Carboniferous formation of the United States. _Proc. Amer. Phil.
Soc._ (_Philadelphia_), vol. +xvii.+ p. 315.
—— (83) Contributions to the Fossil Flora of the Western
Territories. Pt. iii. The Cretaceous and Tertiary Floras. _U. S.
Geol. Surv. Territ._ vol. +iii.+
—— (91) The Flora of the Dakota group. _Monographs U. S. Geol.
Surv._ vol. +xvii.+
=Leuthardt, F.= (03) Die Keuper Flora von Neuewelt bei Basel. _Abh.
Schweiz. palaeont. Ges._ Bd. +xxx.+ p. 1.
=Lignier, O.= (92) La nervation taenioptéridée de folioles de _Cycas_
et le tissu de transfusion. _Bull. soc. Linn. Normandie_ [4],
vol. +vi.+ fasc. 1.
—— (94) La nervation des Cycadées est dichotomique. _Assoc. Franç.
pour l’avancement de sci._ (_Caen_).
—— (94²) Végétaux Fossiles de Normandie. Structure et affinités du
_Bennettites Morierei_ S. and M. sp. _Mém. soc. Linn. Normand._
tome +xviii.+ p. 1.
—— (95) Végétaux fossiles de Normandie. II. Contributions à la flore
liassique de Ste Honorine-la-Guillaume (Orne). _Ibid._ vol.
+xviii.+
—— (01) _Ibid._ III. Étude anatomique du _Cycadeoidea micromyela_
Mor. _Ibid._ vol. +xx.+ p. 331.
—— (03) Le fruit du _Williamsonia gigas_ Carr. _Mém. soc. Linn.
Normand._ vol. +xxi.+ p. 19.
—— (03²) La Fleur des Gnétacées est-celle intermédiaire entre celle
des Gymnospermes et celle des Angiospermes? _Bull. soc. Linn.
Normand._ [5], vol. +vii.+ p. 55.
—— (04) Notes complémentaires sur la structure du _Bennettites
Morierei_ S. and M. _Bull. soc. Linn. Normand._ [5], vol. +viii.+
p. 3.
—— (06) _Radiculites reticulatus_, radicelle fossile de Séquoinée.
_Bull. soc. bot. France_, tome +vi.+ [iii.], p. 193.
—— (07) Sur un moule litigieux de _Williamsonia gigas_ (L. and H.)
Carr. _Ibid._ [6], vol. 1.
—— (07²) Végétaux fossiles de Normandie. IV. Bois divers (sér. 1).
_Mém. soc. Linn. Normand._ vol. +xxii.+ p. 239.
—— (09) Le _Bennettites Morierei_ (S. and M.) Lignier ne serait-il
pas d’origine infracrétacée? _Bull. soc. Linn. Normand._ [6],
vol. +ii.+ p. 214.
—— (11) Le _Bennettites Morierei_ (S. and M.) Lign. se reproduisait
probablement par parthénogénèse. _Bull. soc. bot. France_ [4],
tome +xi.+ p. 224.
—— (11²) Les “_Radiculites reticulatus_” Lign. soit probablement des
radicelles de Cordaitales. _Assoc. Franç. Avanc. Sci._ +xl.+
(_Dijon_), p. 509. [_See also_ Lignier (06).]
—— (12) Stomates des écailles interséminales chez le _Bennettites
Morierei_ (S. and M.). _Ibid._ tome +xii.+ p. 425.
—— (13) Végétaux fossiles de Normandie. VII. Contributions à la
Flore Jurassique. _Mém. soc. Linn. Normand._ vol. +xxiv.+ p. 69.
—— (13²) Différenciation des tissus dans le Bourgeon végétatif du
_Cordaites lingulatus_ B. Ren. _Ann. sci. nat._ [7], vol. +xvii.+
p. 233.
=Lignier, O.= et =A. Tison=. (11) Les Gnétales sont des Angiospermes
apétales. _Compt. Rend._ Jan. 23.
—— (12) Les Gnétales, leurs fleurs et leur position systématique.
_Ann. sci. nat._ [N.S.].
—— (13) L’ovule tritégumenté des _Gnetum_ est probablement un axe
d’inflorescence. _Bull. soc. bot. France_ [4], tome +xiii.+ p. 64.
—— (13²) Un nouveau Sporange Séminiforme, _Mittagia seminiformis_,
gen. et sp. nov. _Mém. Soc. Linn. Normandie_, tome +xxiv.+ p. 49.
=Lima, W. de.= (88) Flora Fossil de Portugal. Monographia do Genero
_Dicranophyllum_. _Comm. dos Trab. geol. Portugal._
=Lindley, J.= See Murchison and Lyell (29).
=Lingelsheim, A.= (08) Über die Braunkohlenhölzer von Saarau.
_Jahres-Ber. Schles. Ges. Vaterländ. Cultur._ Bd. +lxxxv.+
=Lloyd, F. E.= (02) Vivipary in _Podocarpus_. _Torreya_, +ii.+ p. 113.
=Lomax, J.= (02) On some features in relation to _Lyginodendron
oldhamium_. _Ann. Bot._ vol. +xvi.+ p. 601.
=Lotsy, J.= (99) Contributions to the life-history of the genus
_Gnetum_. _Ann. Jard. Bot. Buit._ [2], vol. +i.+ p. 46.
—— (09) Vorträge über botanische Stammesgeschichte. Bd. +ii.+ _Jena._
—— (11) _Ibid._ Bd. +iii.+
=Ludwig, R.= (61) Fossile Pflanzen aus der ältesten Abtheilung der
Rheinisch-Wetterauer Tertiär-Formation. _Palaeontograph._ Bd.
+viii.+ p. 39.
—— (69) Fossile Pflanzenreste aus den paläolithischen Formation der
Umgegend von Dillenburg, Biedenkopf und Friedberg und aus den
Saalfeldischen. _Ibid._ Bd. +xvii.+ p. 105.
=Lyon, H. L.= (04) The Embryogeny of _Ginkgo_. _Minnesota Bot. Stud._
+xxiii.+ p. 275.
=McBride, T. H.= (93) A new Cycad. _Amer. Geologist_, vol. +xii.+ p.
248.
=Mackie, S. J.= (62) The Dragon Tree of the Kentish Rag. _Geologist_,
vol. +v.+ p. 401.
=McLean, R. C.= (12) Two Fossil prothalli from the Lower Coal Measures.
_New Phyt._ vol. +xi.+ p. 305.
=McNab, W. R.= (70) On the structure of a Lignite from the Old Red
Sandstone. _Trans. Bot. Soc. Edinburgh_, vol. +x.+ p. 312.
=Mahlert, A.= (85) Beiträge zur Kenntniss der Anatomie der
Laubblätter der Coniferen mit besonderer Berücksichtigung des
Spaltöffnungs-Apparates. _Bot. Cent._ Bd. +xxiv.+ p. 54.
=Malloizel, G.= and =R. Zeiller=. (N.D.) Bibliographie et tables
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=Mansell-Pleydell, J. C.= (85) Notes on a cone from the Inferior Oolite
Beds of Sherborne. _Proc. Dorset Nat. Hist. Antiq. Field Club_,
vol. +v.+ p. 141.
=Mantell, G.= (27) Illustrations of the Geology of Sussex. _London._
—— (43) Description of some fossil plants from the chalk formation
of the south-east of England. _Proc. Geol. Soc._ vol. +iv.+ p. 34.
—— (46) Description of some Fossil Fruits from the Chalk formation
of the south-east of England. _Quart. Journ. Geol. Soc._ vol.
+ii.+ p. 51.
=Marion, A. F.= (84) Sur les caractères d’une Conifère tertiaire,
voisine des Dammarées (_Doliostrobus Sternbergi_). _Compt. Rend._
vol. +xciv.+ p. 821.
=Marsh, A. S.= (14) Notes on the Anatomy of _Stangeria paradoxa_. _New
Phyt._ vol. +xiii.+ p. 18.
=Marty, P.= (08) Sur la Flore fossile de Lugarde (Cantal). _Compt.
Rend._ vol. +cxlvii.+ p. 395.
=Maslen, A. J.= (10) See Scott and Maslen.
—— (11) The structure of _Mesoxylon Sutcliffi_ (Scott). _Ann. Bot._
vol. +xxv.+ p. 381.
=Massalongo, A.= (59) Studii sulla Flora Fossile e geologia
stratigrafica del Senigalliese. _Verona._
=Massalongo, A.= and =G. Scarabelli=. (58) Studii sulla Flora Fossile e
geologia stratigrafica del Senigalliese. _Verona._
=Masters, M. T.= (91) Review of some points in the comparative
morphology, anatomy, and life-history of the Coniferae. _Journ.
Linn. Soc._ vol. +xxviii.+ p. 236.
—— (93) Notes on the genera of Taxaceae and Coniferae. _Ibid._ vol.
+xxx.+ p. 1.
—— (00) _Taxodium_ and _Glyptostrobus_. _Journ. Bot._ (February,
1900).
=Matte, H.= (04) Recherches sur l’appareil libéro-ligneux des Cycadées.
_Caen_.
—— (08) Sur le développement morphologique et anatomique des
Cycadacées. _Mém. soc. Linn. Normand_. tome +xxiii.+
=Matthew, G. F.= (10) Revision of the Flora of the Little River group.
_Trans. R. Soc. Canada_, sect. iv. vol. +iii.+ [3], p. 77.
=Mercklin, C. E. von=. (55) Palaeodendrologicon Rossicum. _St
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—— (78) Om _Ginkgo crenata_ Brauns sp. från sandstenen vid Senstedt
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—— (80) Några anmärkningar om _Williamsonia_, Carruthers. _Ibid._
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—— (81) Berättelse, afgifven till Kongl. Vetenskaps-Akad. _Öfver. K.
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—— (02) Beiträge zur Kenntniss einiger Mesozoischen Cycadophyten.
_K. Svensk. Vetenskapsakad. Hand._ Bd. +xxxvi.+ No. 4.
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—— (08²) Paläobot. Mitt. 7. Über _Palissya_, _Stachyotaxus_ and
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—— (09) Paläobot. Mitt. 8. Über _Williamsonia_, _Wielandia_,
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Berücksichtigung Schwedischen Arten. _K. Svensk. Vetenskapsakad.
Hand._ Bd. +xliii.+ No. 12.
—— (10) Excursion C 3. Dépôts fossilifères (plantes) quaternaires de
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Williamsonia-Blüten. _K. Svensk. Vetenskapsakad. Hand._ Bd.
+xlvi.+ No. 4.
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Vetenskapsakad. Hand._ Bd. +xlvi.+ No. 8.
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—— (13²) Die pflanzenführenden Horizonte innerhalb der
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Nachträge zur Pälaozoischen Flora Spitzbergens. _Stockholm._
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—— (15²) Tertiäre Pflanzenreste aus Ellesmere-Land. Rep. second
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=Negri, G.= (14) Sopra alcuni legni fossili del Gebel Tripolitano.
_Boll. Soc. geol. Ital._ vol. +xxxiii.+ p. 321.
=Nestler, A.= (95) Ein Beitrag zur Anatomie der Cycadeenfiedern.
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=Newberry, J. S.= (54) New Fossil Plants from Ohio. _Annals of Science;
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—— (73) Report of the Geological Survey of Ohio, vol. +i.+
—— (88) Rhaetic Plants from Honduras. _Amer. Journ. Sci._ vol.
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=Newberry, J. S.= and =A. Hollick=. (95) The Flora of the Amboy clays.
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=Newton, E. T.= and =J. J. H. Teall=. (97) Notes on a collection
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—— (98) Additional notes on rocks and fossils from Franz Josef Land.
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=Noack, F.= (87) Der Einfluss des Klimas auf die Cuticularisation und
Verholzung der Nadeln einiger Coniferen. _Pringsheim’s Jahrb._
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—— (03) The ovules of the older Gymnosperms. _Ann. Bot._ vol.
+xvii.+ p. 451.
—— (04) Notes on _Trigonocarpus_, Brongn. and _Polylophospermum_,
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—— (05) Über die neuentdeckten Samen der Steinkohlenfarne. _Biolog.
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_Polylophospermum_. _Ann. Bot._ vol. +xxi.+ p. 303.
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Lomaxi_, with a statement of the evidence upon which it is
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=Palibin, J.= (01) Quelques données relatives aux débris végétaux
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=Penhallow, D. P.= (91) See Dawson and Penhallow.
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=Potonié, H.= (88) Die fossile Pflanzen-Gattung _Tylodendron_. _Jahrb.
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—— (96) Ueber Autochthonie von Carbonkohlen-Flötze und der
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—— (02) Fossile Hölzer aus der oberen Kreide Deutsch-Östafrikas. Die
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—— (04) Abbildungen und Beschreibungen fossilen Pflanzen-Reste.
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=Raciborski, M.= (91) Flora Retycka Pólnocnego Stoku Gór
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—— (92) Przyczynek do Flory Retyckiej Polski. _Ibid._ tom. +xxii.+
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—— (92²) _Cycadeoidea Niedźwiedzkii_ nov. sp. _Akad. wiss. Krak.
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=Ratte, F.= (87) Note on two new fossil plants from the Wianametta
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—— (15) The Pliocene Floras of the Dutch-Prussian border. _Meded.
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=Renault, B.= (79) Sur un nouveau groupe de tiges fossiles silicifiées
de l’époque houillière. _Compt. Rend._ tome +lxxxviii.+ p. 35.
—— (80) Sur une nouvelle espèce de _Poroxylon. Compt. Rend._ tome
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—— (80²) Cours de Botanique fossile. Tome +i.+ _Paris._
—— (83) Cours de Botanique fossile. Tome +iii.+
—— (85) Cours de Botanique fossile. Tome +iv.+
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—— (88) Les Plantes fossiles. _Paris._
—— (89) Sur un nouveau genre fossile de tige cycadéenne. _Compt.
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—— (96) Note sur le genre Métacordaite. _Soc. d’hist. nat. d’Autun._
=Renault, B.= and =R. Zeiller.= (85) Sur un nouveau type de Cordaitée.
_Compt. Rend._ vol. +c.+ p. 867.
—— (86) Sur quelques Cycadées houillières. _Ibid._ vol. +cii.+ p.
325.
=Rendle, A. B.= (96) Gymnospermae. The Plants of Milanji, Nyasa-Land,
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—— (04) The Classification of Flowering plants. Vol. +i.+
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=Renier, A.= (07) Trois espèces nouvelles, _Sphenopteris Dumonti, S.
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181.
—— (10) Documents pour l’étude de la paléontologie du terrain
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—— (10²) Paléontologie du Terrain Houiller. _Liège_.
=Renner, O.= (04) Über Zwitterblüthen bei _Juniperus communis. Flora_,
Bd. +xcii.+ p. 92.
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=Robertson, Agnes=. (02) Notes on the anatomy of _Macrozamia
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1.
—— (04) Studies in the Morphology of _Torreya californica_ Torrey.
_New Phyt_. vol. +iii.+ p. 205.
—— (06) Some points in the Morphology of _Phyllocladus alpinus_
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=Rosen, F.= (11) Die biologische Stellung der abessinischen Baumlobelie
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Rosen_, Bd. +x.+ Heft ii. p. 265.
=Rothert, W.= (99) Ueber parenchymatische Tracheiden und Harzgänge im
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=Rushton, W.= (15) Structure of the wood of Himalayan Junipers. _Journ.
Linn. Soc_. vol. +xliii.+ p. 1.
—— (16) The Development of ‘Sanio’s Bars’ in _Pinus Inops. Ann.
Bot_. vol. +xxx.+ p. 419.
=Russow, E.= (72) Vergleichende Untersuchungen der
Leitbündel-Kryptogamen. _Mém. l’Acad. Imp. Sci. St Pétersbourg_
[vii], tome +xix.+ p. 1.
—— (83) Zur Kenntniss des Holzes, insonderheit des Coniferenholzes.
_Bot. Cent_. Bd. +xiii.+ p. 29.
=Salisbury, E. J.= (13) Methods of Palaeobotanical reconstruction.
_Ann. Bot_. vol. +xxvii.+ p. 273.
—— (14) On the structure and relationship of _Trigonocarpus
shorensis. Ann. Bot_. vol. +xxviii.+ p. 39.
=Sanday, Elizabeth=. (07) See Berridge and Sanday.
=Sandberger, F. von=. (64) Die Flora der oberen Steinkohlenformation im
badischer Schwarzwalde. _Verh. Nat. Ver. Carlsruhe_, vol. +i.+ p.
30.
—— (90) Ueber Steinkohlenformation und Rothliegendes im Schwarzwald
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77.
=Sanio, K.= (74) Anatomie der Gemeinen Kiefer (_Pinus silvestris_ L.).
_Pringsheim’s Jahrb_. Bd. +ix.+ p. 78.
=Saporta, G. de=. (62) Études sur la végétation du sud-est de la France
à l’époque Tertiaire. _Ann. Sci. Nat_. tome +xvi.+ [4], p. 309.
—— (62²) _Ibid._ tome +xvii.+ p. 191.
—— (65) _Ibid._ tome +iii.+ [5], p. 5.
—— (65²) _Ibid._ tome +iv.+ p. 5.
—— (68) _Ibid._ tome +ix.+ p. 5.
—— (68²) Note sur la flore fossile des regions arctiques. _Bull.
soc. géol. France_ [2], tome +xxv.+ p. 315.
—— (73) Études sur la végétation du sud-est de la France à l’époque
Tertiaire. _Ann. Sci. nat._ tome +xvii.+ [5], p. 81.
—— (74) Sur la présence d’une Cycadée dans le dépôt Miocène de Koumi
(Eubée). _Compt. Rend._ vol. +lxxviii.+ p. 1318.
—— (75) Sur la découverte de deux types nouveaux de Conifères dans
les schistes Permiens de Lodève (Hérault). _Ibid._ vol. +lxxx.+
p. 1017.
—— (78) Observations sur la nature des végétaux réunis dans le
groupe des _Noeggerathia_; généralités et type du _Noeggerathia
foliosa_ Sternb. _Ibid._ vol. +lxxxvi.+ p. 746.
—— (78²) _Ibid._ Types du _Noeggerathia flabellata_ L. and H. et du
_N. cyclopteroides_ Goepp. _Ibid._ vol. +lxxxvi.+ p. 801.
—— (78³) _Ibid._ Type des _Noeggerathia expansa_ et _cuneifolia_ de
Brongniart. _Ibid._ vol. +lxxxvi.+ p. 860.
—— (78⁴) Sur le nouveau groupe Paléozoique des Dolerophyllées.
_Ibid._ vol. +lxxxvii.+ p. 393.
—— (82) Sur quelques types de végétaux récemment observés à l’état
fossile. _Ibid._ vol. +xliv.+ p. 922.
—— (84) Paléontologie Française. Plantes Jurassiques, tome +iii.+
—— (91) _Ibid._ tome +iv.+ Types Proangiospermiques.
—— (93) Revue des travaux de Paléontologie végétale. _Rev. Gén._
tome +v.+ p. 1.
=Saporta, G. de= and =A. F. Marion=. (76) Recherches sur les végétaux
fossiles de Meximieux. _Arch. Mus. d’hist. nat. de Lyon. Lyon._
—— (78) Révision de la flore Heersienne de Gelinden. _Mém. cour. et
Mém. sav. étrang._ tome +xli.+ (_Acad. roy. sci. etc. Belg._).
—— (85) L’Évolution du Règne végétal. Tome +i.+ Les Phanérogames.
_Paris._
=Saxton, W. T.= (10) Contributions to the life-history of
_Widdringtonia cupressoides_. _Bot. Gaz._ vol. +l.+ p. 31.
—— (10²) Contributions to the life-history of _Callitris_. _Ann.
Bot._ vol. +xxiv.+ p. 557.
—— (10³) Notes on the anatomy of _Widdringtonia_ and _Callitris_.
_S. African Journ. Sci._ p. 282.
—— (10⁴) The development of the embryo of _Encephalartos_. _Bot.
Gaz._ vol. +xlix.+ p. 13.
—— (12) Note on an abnormal prothallus of _Pinus maritima_ L. _Ann.
Bot._ vol. +xxvi.+ p. 943.
—— (13) Contributions to the life-history of _Actinostrobus
pyramidalis_ Miq. _Ann. Bot._ vol. +xxvii.+ p. 321.
—— (13²) The classification of Conifers. _New Phyt._ vol. +xii.+ p.
242.
—— (13³) Contributions to the life-history of _Tetraclinis
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=Schauroth, C. von=. (52) Herr von Schauroth an Herrn Beyrich. _Zeit.
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=Schenk, A.= (67) Ueber die Flora der schwarzen Schiefer von Raibl.
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_Benecke’s Geog.-Pal. Beit_. Bd. +ii.+ _München_.
—— (68²) Beiträge zur Flora der Vorwelt. _Palaeontol_. Bd. +xvi.+ p.
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—— (71) Die fossilen Pflanzen der Wernsdorfer Schichten in der
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—— (80) Ueber fossile Hölzer aus der _Libyschen Wüste. Bot. Zeit_.
Bd. +xxxviii.+ p. 657.
—— (82) Ueber _Medullosa elegans. Engler’s Jahrb_. Bd. +iii.+ p. 156.
—— (82²) Die von dem Gebrüdern Schagintweit in Indien gesammelten
fossilen Hölzer. _Engler’s Bot. Jahrb_. Bd. +iii.+ p. 353.
—— (83) Fossile Hölzer der libyschen Wüste (_Die Libysche Wüste_,
Bd. +iii.+).
—— (89) Ueber _Medullosa_ Cotta. _Abh. K. Sächs. Ges. Wiss_. Bd.
+xv.+ p. 523.
=Schlechtendal, D. von=. (02) _Thuja occidentalis thuringiaca. Zeitsch.
Naturwiss. Stuttgart_. Bd. +lxxv.+ p. 33.
=Schmalhausen, J.= (83) Die Pflanzenreste der Steinkohlenformation am
östlichen Abhange des Ural Gebirges. _Mém. Acad. S. Pétersbourg_,
vol. +xxxi.+ No. 13.
—— (83²) Beiträge zur Tertiär Flora süd-west Russlands. _Palaeontol.
Abh. (Dames and Kayser)_, Bd. +i.+ Heft iv. p. 285.
—— (87) Die Pflanzenreste der Artinskischen und Permischen
Ablagerungen im Osten des Europäischen Russlands. _Mém. Com.
géol. St Pétersbourg_, vol. +ii.+ No. iv. p. 1.
—— (90) Wissenschaftliche Resultate der von der Akad. der Wiss. zur
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=Schneider, W.= (13) Vergleichend-morphologische Untersuchungen über
die Kurztriebe einiger Arten von _Pinus. Flora_ [N.F.], Bd. +v.+
p. 385.
=Schroeter, C.= (80) Untersuchung über fossile Hölzer aus der
arctischen Zone. (Heer’s _Flor. Foss. Arct_. vol. +vi.+ 1882.)
—— (97) Ueber die Vielgestaltigkeit der Fichte (_Picea excelsa_
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=Schuster, J.= (11) Ueber Goeppert’s _Raumeria_ im Zwinger zu Dresden.
_Sitzber. K. Bayer. Akad. Wiss_. p. 489.
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—— (11³) _Pagiophyllum Weismanni_ im unteren Hauptmuschelkalk von
Würzburg. _Geog. Jahresheft_, Bd. +xiii.+ p. 149.
—— (11⁴) Bemerkungen über _Podozamites. Ber. Deutsch. Bot. Ges_. Bd.
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=Schütze, E.= (01) Beiträge zur Kenntniss der Triassischen
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of Cycadaceae. _Ann. Bot_. vol. +xi.+ p. 399.
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vol. +xiii.+ p. 615.
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=Scott, D. H.= and =A. J. Maslen=. (07) The structure of the Palaeozoic
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nov. _Ann. Bot_. vol. +xxi.+ p. 89.
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=Sellards, E. H.= (03) _Codonotheca_, a new type of spore-bearing organ
from the Coal Measures. _Amer. Journ. Sci_. vol. +xvi.+ p. 87.
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=Sernander, R.= (93) Die Einwanderung der Fichte in Skandinavien.
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=Seward, A. C.= (90) _Tylodendron_ Weiss and _Voltzia heterophylla_
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—— (96) A new species of Conifer, _Pinites Ruffordi_, from the
English Wealden formation. _Journ. Linn. Soc_. vol. +xxxii.+ p.
417.
—— (96²) Notes on the geological history of Monocotyledons. _Ann.
Bot_. vol. +x.+ p. 205.
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—— (97²) A contribution to our knowledge of _Lyginodendron. Ann.
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Remarks on European and Eastern Mesozoic Floras. _Quart. Journ.
Geol. Soc_. vol. +lix.+ p. 217.
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=Shaw, F. J. F.= (08) A contribution to the anatomy of _Ginkgo biloba_.
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=Shirley, J.= (98) Additions to the Fossil Flora of Queensland _Geol.
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=Siebold, P. F. von.= (70) Flora Japonica, 1842–70. _Leipzig._
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=Sigrianski, A.= (13) Quelques observations sur l’_Ephedra helvetica_
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=Sinnott, E. W.= (09) Paracedroxylon, a new type of Araucarian wood.
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=Solereder, H.= (99) Systematische Anatomie der Dicotyledonen.
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=Solms-Laubach, Graf zu.= (84) Die Coniferenformen des Deutschen
Kupferschiefers und Zechsteins. _Pal. Abhand._ (_Dames and
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—— (90) Die Sprossfolge der _Stangeria_ und der übrigen Cycadeen.
_Bot. Zeit. Jahrg._ +xlviii.+
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—— (92) See Capellini and Solms-Laubach.
—— (93) Ueber die in den Kalksteinen des Kulm von
Glätzisch-Falkenberg in Schlesien enthaltenen Structur bietenden
Pflanzenreste. _Bot. Zeit. Jahrg._ +li.+ p. 197.
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von La Ternera (Chili). _Neues Jahrb. Min. Beilage_, Bd. +xii.+
p. 581.
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3.
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p. 353.
—— (10) Über die in den Kalksteinen des Culm von
Glätzisch-Falkenberg in Schlesien erhaltenen structurbietenden
Pflanzenreste. IV. _Völkelia refracta_, _Steloxylon Ludwigii_.
_Zeitsch. Bot._ Jahrg. +ii.+ Heft viii. p. 529.
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—— (03) _Ibid._ Jahrg. +liii.+ p. 1.
=Sprecher, A.= (07) Le _Ginkgo biloba_ L. _Genève._
=Squinabol, S.= (92) Contribuzioni alla flora fossile dei terreni
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=Stapf, O.= (89) Die Arten der Gattung _Ephedra_. _Denksch. K. Akad.
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—— (96) On the Flora of Mount Kinabalu in North Borneo. _Trans.
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—— (14) _Encephalartos Hildebrandtii._ _Bull. Miscell. Information_,
_R. Bot. Gard. Kew_, No. 10, p. 386.
=Starr, Anna M.= (10) The microsporophylls of _Ginkgo_. _Bot. Gaz._
vol. +xlix.+ p. 51.
=Staub, M.= (85) _Pinus palaeostrobus_ Etting. in der fossilen Flora
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—— (96) Die Fossilen Ctenis-Arten und _Ctenis hungarica_ n. sp.
_Földtani Közlöny_, vol. +xxvi.+
=Stefani, C. de.= (01) Flore Carbonifere e Permiane della Toscana. _R.
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=Stenzel, G.= (76) Beobachtungen an durchwachsenden Fichtenzapfen.
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—— (88) See Goeppert and Stenzel.
=Sterzel; J. T.= (83) Ueber _Dicksonia Pluckeneti_ (Schloth.). _Bot.
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—— (00) Gruppe verkieselter Araucariten Stämme. _Bericht Naturwiss.
Ges. Chemnitz_, Bd. +xiv.+
—— (03) Ein verkieselter Riesenbaum aus dem Rothliegenden von
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—— (07) Die Karbon- und Rotliegendfloren im Grossherzogtum Baden.
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=Stiles, W.= (08) The anatomy of _Saxegothaea conspicua_ Lind. _New
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—— (12) The Podocarpeae. _Ann. Bot._ vol. +xxvi.+ p. 443.
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=Stopes, Marie C.= (03) On the leaf of _Cordaites_. _New Phyt._ vol.
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vol. +ix.+ p. 235.
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—— (11²) The name of the Dragon tree. _Ibid._ p. 468.
—— (11³) A reply to Prof. Jeffrey’s article on _Yezonia_ and
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—— (14) The “Fern Ledges” Carboniferous Flora of St John, New
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—— (15) Catalogue of the Mesozoic Plants in the British Museum (Nat.
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=Strübing, O.= (88) Die Vertheilung der Spaltöffnungen bei den
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—— (77) Die Culm Flora. Heft ii. _Wien._
=Suzuki, Y.= (10) On the structure and affinities of two new Conifers
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_Bot. Mag. Tokyo_, vol. +xxiv.+ No. 284, p. 183.
=Sykes, M. G.= (10) (See also Thoday, M. G.) The anatomy of
_Welwitschia mirabilis_ Hook. f. in the seedling and adult
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—— (10²) The anatomy and morphology of the leaves and inflorescences
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=Takeda, H.= (13) A theory of transfusion-tissue. _Ann. Bot_. vol.
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—— (13²) Some points in the anatomy of the leaf of _Welwitschia
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=Tate, R.= (67). On the secondary fossils from S. Africa. _Quart.
Journ. Geol. Soc_. vol. +xxiii.+ p. 130.
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=Thibout, E.= (96) Recherches sur l’appareil mâle des Gymnospermes.
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—— (01) The carpophyll of _Encephalartos. Ann. Bot_. vol. +xv.+ p.
548.
—— (01²) Persistence of the leaf-traces in _Araucaria_. _Ibid_. vol.
+xv.+ p. 547.
—— (02) Enumeration of the plants known from China proper, Formosa,
etc. Cycadaceae. _Journ. Linn. Soc_. vol. +xxvi.+ p. 559.
=Thoday, Mary G.= (=Sykes, M. G.=). (11) The female inflorescence and
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Bot_. vol. +xxv.+ p. 1101.
=Thoday, M. G.= and =Emily M. Berridge=. (12) The anatomy and
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=Thomas, F.= (66) Zur vergleichenden Anatomie der
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—— (12) Note on the occurrence of _Whittleseya elegans_ Newb. in
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Phil. Soc_. vol. +xvii.+ pt. iii. p. 256.
—— (13²) The Fossil Flora of the Cleveland district of Yorkshire. I.
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—— (15) On some new and rare Jurassic plants from Yorkshire: The
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vol. +xviii.+ pt. iii. p. 105.
—— (15²) On _Williamsoniella_, a New Type of Bennettitalean Flower.
_Phil. Trans. R. Soc_. vol. 207, p. 113.
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+viii.+ pt. v. p. 155.
=Thompson, W. P.= (10) The origin of ray-tracheids in the Coniferae.
_Bot. Gaz._ vol. +l.+ p. 101.
—— (12) Ray-tracheids in _Abies_. _Ibid._ vol. +liii.+ p. 53.
—— (12²) The anatomy and relationship of the Gnetales. I. The genus
_Ephedra_. _Ann. Bot._ vol. +xxvi.+ p. 1077.
—— (12³) The structure of the stomata of certain Cretaceous
Conifers. _Bot. Gaz._ vol. +liv.+ p. 63.
—— (16) The Morphology and Affinities of Gnetum. _Amer. Journ. Bot._
vol +iii.+ p. 135.
=Thomson, R. B.= (07) The Araucarineae, a Protosiphonogamic method of
Fertilisation. _Science_ [N.S.], vol. +xxv.+ p. 272.
—— (09) On the pollen of _Microcachrys tetragona_. _Bot. Gaz._ vol.
+xlvii.+ p. 26.
—— (13) On the comparative anatomy and affinities of the
Araucarineae. _Phil. Trans. R. Soc._ vol. +cciv.+ p. 1.
—— (14) The spur-shoot of the Pines. _Bot. Gaz._ vol. +lvii.+ p. 362.
=Thomson, R. B.= and =A. E. Allin.= (12) Do the Abietineae extend to
the Carboniferous? _Bot. Gaz._ vol. +liii.+ p. 339.
=Tison, A.= (09) Sur le _Saxegothaea conspicua_ Lind. _Mém. soc. Linn.
Normand._ vol. +xxiii.+ p. 139.
—— (12) Sur la persistance de la nervation dichotomique chez les
Conifères. _Bull. soc. Linn. Normandie_ [vi], vol. +iv.+ p. 30.
—— (12²) See Lignier and Tison.
=Tupper, W. W.= (11) Notes on _Ginkgo biloba_. _Bot. Gaz._ vol. +li.+
p. 374.
=Tuzson, J.= (09) Monographie der fossilen Pflanzenreste der
Balatonseegegend. _Result. der Wiss. Erforsch. des Balatonsees_,
Bd. +i.+ Teil i. _Budapest._
—— (09²) Beiträge zur fossilen Flora Ungarns. _Mitt. Jahrb. K. Ung.
Geol. Reichs._ Bd. +xxi.+ Heft viii. p. 233.
—— (14) Beiträge zur fossilen Flora Ungarns. _Mitt. Jahrb. K.
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=Unger, F.= (45) Synopsis Plantarum Fossilium. _Leipzig_.
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—— (49) Einige interessante Pflanzenabdrücke aus der K.
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—— (51) Die Fossile Flora von Sotzka. _Denksch. K. Akad. Wiss.
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Schiefer von Solenhofen. _Palaeontograph._ Bd. +ii.+ p. 251.
—— (52²) Iconographia plantarum fossilium. Abbildungen und
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Bd. +iv.+ p. 73.
—— (54) Zur Flora des Cypridinenschiefers. _Sitzber. K. Akad. Wiss.
Wien_, Bd. +xii.+ p. 595.
—— (54²) Jurassische Pflanzenreste. _Palaeontograph._ Bd. +iv.+ p.
39.
—— (59) Der versteinerte Wald bei Cairo. _Sitzber. K. Akad. Wiss.
Wien_, Bd. +xxxiii.+ p. 209.
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Bd. +xxvii.+ p. 27.
=Veitch’s= Manual of the Conifers. (00) _London._
=Velenovský, J.= (81) Die Flora aus den Ausgebrannten Tertiären Letten
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—— (87) Neue Beiträge zur Kenntniss der Pflanzen des böhmischen
Cenomans. _Sitzber. K. böhm. Ges. Wiss._ Jahrg. 1886, p. 633.
—— (88) Ueber einige neue Pflanzenformen der böhmischen
Kreideformation. _Ibid._ Jahrg. 1887.
—— (89) Květena Českého Cenomanu. _Abh. K. böhm. Ges. Wiss._ [vii],
Bd. +iii.+
—— (07) Vergleichende Morphologie der Pflanzen. Teil ii. _Prag._
=Vernon, R. D.= (12) On the geology and palaeontology of the
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p. 587.
=Vetters, K. L.= (84) Die Blattstiele der Cycadeen. (Inaug. Diss.)
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=Vierhapper, F.= (10) Entwurf eines neuen Systems der Coniferen. _Jena._
=Ward, L. F.= (85) Synopsis of the Laramie group. _6th Ann. Rep. U. S.
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—— (87) Types of the Laramie Flora. _Bull. U. S. Geol. Surv._
+xxxvii.+
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Rep. U. S. Geol. Surv._ (1887–88).
—— (94) Fossil Cycadean trunks of North America, with a revision of
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vol. +ix.+ p. 75.
—— (94²) Recent discoveries of Cycadean trunks in the Potomac
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+ii.+ No. iii. p. 250.
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Journ. Sci._ vol. +x.+ p. 327.
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Acad. Sci._ vol. +i.+ p. 253.
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40.
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=Weiss, C. E.= (72) Fossile Flora der jüngsten Steinkohlen-formation
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i. p. 1.
=Weiss, F. E.= (12) Report of the 80th meeting (Portsmouth) of the
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—— (13) The root-apex and young root of _Lyginodendron_. _Mem. Proc.
Manchester Lit. Phil. Soc_. vol. +lvii.+ pt. iii.
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=Wernham, H. F.= (11) Floral Evolution; with particular reference to
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=Wettstein, R. V.= (90) Die Omorika-Fichte, _Picea omorica_ (Panc.).
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=Wherry, E. T.= (12) Silicified wood from the Triassic of Pennsylvania.
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=White, D.= (90) On Cretaceous Plants from Martha’s Vineyard. _Amer.
Journ. Sci_. vol. +xxxix.+ p. 93.
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systematic relations. _The Ottawa Naturalist_, vol. +xv.+ No. iv.
p. 98.
=White, D.= and =C. Schuchert=. (98) Cretaceous series of the West
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=Wieland, G. R.= (99) A study of some American Fossil Cycads. Pt. ii.
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+vii.+ p. 305.
—— (02) Notes on living Cycads. I. On the Zamias of Florida. _Ibid_.
vol. +xiii.+ p. 331.
—— (06) American Fossil Cycads. _Washington_.
—— (08) Historic Fossil Cycads. _Amer. Journ. Sci_. vol. +xxv.+ p.
93.
—— (08²) Two new Araucarias from the Western Cretaceous. _Geol.
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—— (09) The Williamsonias of the Mixteca Alta. _Bot. Gaz_. vol.
+xlviii.+ p. 427.
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p. 433.
—— (11²) A study of some American Fossil Cycads. Pt. +v.+ _Ibid_.
vol. +xxxii.+ p. 133.
—— (12) _Ibid_. pt. vi. On the smaller flower-buds of _Cycadeoidea_.
_Ibid_. vol. +xxxiii.+ p. 73.
—— (13) The Liassic Flora of the Mixteca Alta of Mexico, its
composition, age, and source. _Ibid_. vol. +xxxvi.+ p. 251.
—— (14) A study of some American Fossil Cycads. Pt. vii. Further
notes on disk structure. _Ibid_. vol. +xxxviii.+ p. 117.
—— (16) American Fossil Cycads. Vol. +ii.+ Taxonomy. _Washington_.
=Wiesner, J.= (03) Die Rohstoffe des Pflanzenreiches. Bd. +ii.+
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=Wild, G.= (00) On new and interesting features in _Trigonocarpus
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=Williamson, W. C.= (40) On the Distribution of Fossil remains on the
Yorkshire coast from the Lower Lias to the Bath Oolite inclusive.
_Trans. Geol. Soc._ [2], vol. +v.+ p. 223.
—— (51) On the structure and affinities of the plants known as
Sternbergiae. _Manchester Lit. Phil. Soc._ [2], vol. +ix.+ p. 340.
—— (69) On the structure and affinities of some exogens from the
Coal Measures. _Monthly Micros. Journ._ vol. +ii.+ p. 66.
—— (70) Contributions towards the history of _Zamia gigas_ L. and H.
_Trans. Linn. Soc._ vol. +xxvi.+ p. 663.
—— (72) Notice of further researches among the plants of the Coal
Measures. _Proc. R. Soc._ vol. +xx.+ p. 435.
—— (72²) On the structure of the Dicotyledons of the Coal Measures.
_Rep. 41st meeting_ (_Edinburgh_) _of the Brit. Assoc._ p. 111.
—— (74) On the Organisation of the Fossil Plants of the Coal
Measures. VI. _Phil. Trans. R. Soc._ vol. +clxii.+ p. 675.
—— (76) On some fossil seeds from the Lower Carboniferous beds of
Lancashire. _Rep. 45th meeting_ (_Bristol_) _of the Brit. Assoc._
p. 159.
—— (86) On the morphology of _Pinites oblongus_. _Mem. Proc.
Manchester Lit. Phil. Soc._ vol. +x.+ [3], p. 189.
—— (87) On the Organisation of the Fossil Plants of the Coal
Measures. XIII. _Phil. Trans. R. Soc._ vol. 178.
—— (90) _Ibid._ XVII. _Ibid._ vol. +clxxxi.+ p. 89.
=Wiliamson, W. C.= and =D. H. Scott.= (94) The root of _Lyginodendron
oldhamium_ Will. _Proc. R. Soc._ vol. +lvi.+ p. 128.
—— (95) Further observations on the Organisation of the Fossil
Plants of the Coal Measures. III. _Lyginodendron and
Heterangium_. _Phil. Trans. R. Soc._ vol. +clxxxvi.+ p. 703.
=Wills, Lucy.= (14) Plant cuticles from the Coal Measures. _Geol. Mag._
[6], vol. +i.+ p. 385.
=Wills, L. T.= (10) The fossiliferous Lower Keuper rocks of
Worcestershire. _Proc. Geol. Assoc._ vol. +xxi.+ p. 249.
=Winkler, C.= (72) Zur Anatomie von _Araucaria brasiliensis_. _Bot.
Zeit._ Jahrg. +xxx.+ p. 581.
=Witham, H.= (30) On the vegetable fossils from Lennel Braes near
Coldstream, upon the banks of the Tweed in Berwickshire. _Phil.
Mag._ vol. +viii.+ p. 16.
—— (31) Observations on fossil vegetables accompanied by
representations of their internal structure as seen through the
microscope. _Edinb. Journ. Sci._ vol. +v.+ p. 183.
=Worsdell, W. C.= (96) The anatomy of the stem of _Macrozamia_ compared
with that of other genera of Cycadeae. _Ann. Bot._ vol. +x.+ p.
601.
—— (97) On transfusion-tissue, its origin and function in the leaves
of Gymnospermous plants. _Trans. Linn. Soc._ vol. +v.+ [2], p.
301.
—— (98) The vascular structure of the sporophylls of the Cycadaceae.
_Ann. Bot._ vol. +xii.+ p. 203.
—— (98²) The comparative anatomy of certain genera of the
Cycadaceae. _Journ. Linn. Soc._ vol. +xxxiii.+ p. 437.
—— (99) Observations on the vascular system of the female flowers of
Conifers. _Ann. Bot._ vol. +xiii.+ p. 527.
—— (00) The comparative anatomy of certain species of
_Encephalartos_. _Trans. Linn. Soc._ vol. +v.+ pt. xiv. p. 445.
—— (00²) The affinities of the Mesozoic fossil _Bennettites
Gibsonianus_ Carr. _Ann. Bot._ vol. +xiv.+ p. 717.
—— (01) Contributions to the comparative anatomy of the Cycadaceae.
_Trans. Linn. Soc._ vol. +vi.+ pt. ii. p. 109.
—— (01²) The vascular structure of the flowers of the Gnetaceae.
_Ann. Bot._ vol. +xv.+ p. 766.
—— (04) The structure and morphology of the ovule. _Ann. Bot._ vol.
+xviii.+ p. 57.
—— (05) Fasciation, its meaning and origin. _New Phyt._ vol. +iv.+
p. 55.
—— (06) The structure and origin of the Cycadaceae. _Ann. Bot._ vol.
+xx.+ p. 129.
=Wright, W. B.= (14) The Quaternary Ice Age. _London._
=Yabe, H.= (13) Mesozoische Pflanzen von Omoto. _Sci. Rep. of the
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=Yates, J.= (55) Notice of _Zamia gigas_. _Proc. Yorks. Phil. Soc._
vol. +i.+ p. 37.
=Yokoyama, M.= (94) Mesozoic plants from Kozuke, Kii, Awa, and Tosa.
_Journ. Coll. Sci. Imp. Univ. Japan_, vol. +vii.+ pt. iii. p. 201.
—— (05) Mesozoic plants from Nagato and Bitchu. _Ibid._ vol. +xx.+
=Young, J.= (69) _Trans. Nat. Hist. Soc. Glasgow_, vol. +i.+ pl. +iv.+
(No text.)
—— (76) Catalogue of the Western Scottish fossils. _Glasgow._
=Young, Mary S.= (07) The male gametophyte of _Dacrydium_. _Bot. Gaz._
vol. +xliv.+ p. 189.
—— (10) The morphology of the Podocarpineae. _Ibid._ vol. +l.+ p. 81.
=Zalessky, M.= (05) Über Früchte aus den Untercarbon-Ablagerungen
des Mstabeckens in Nord Russland. _Bull. acad. Imp. sci. St.
Pétersbourg_, tome +xxii.+ No. iii. p. 113.
—— (05²) Notiz über die obercarbonische Flora des Steinkohlenreviers
von Jantai in der südlichen Mandshurei. _Verhand. K. Russ. Min.
Ges. St. Pétersbourg_ [2], Bd. +xlii.+ p. 385.
—— (09) Communication préliminaire sur un nouveau _Dadoxylon_
provenant du Dévonien supérieur du bassin du Donetz. _Bull. acad.
Imp. sci. St. Pétersbourg._
—— (10) On the discovery of the calcareous concretions known as coal
balls in one of the seams of the Carboniferous strata of the
Donetz basin. _Ibid._ p. 477.
—— (11) Étude sur l’anatomie du _Dadoxylon Tchihatcheffi_ Goepp. sp.
_Mém. com. géol. St. Pétersb._ [N.S.], Livr. 68, p. 1.
—— (11²) Note préliminaire sur le _Coenoxylon Scotti_, nov. gen. et
sp. _Études Paléobotaniques_, pt. +i.+ _St. Petersburg_.
—— (12) Sur le _Cordaites aequalis_ Goepp. sp. de Sibérie et sur son
identité avec la _Noeggerathiopsis Hislopi_ Bunb. sp. de la Flore
du Gondwana. _Mém. com. géol. St. Pétersb._ [N.S.], Livr. 86.
—— (12²) On the impressions of plants from the coal-bearing deposits
of Sudženka, Siberia. _Bull. soc. Natural. Orel._ pt. +iv.+
—— (13) Flore Gondwanienne du Bassin de la Pétchora. I. Rivière
Adzva. _Bull. soc. Oural. d’amis des Sci. Nat. à Ekatérinebourg_,
vol. +xxxiii.+
=Zang, W.= (04) Die Anatomie der Kiefernadel und ihre Verwendung zur
systematischen Gliederung der Gattung _Pinus_. (Diss. Inaug.)
_Giessen._
=Zeiller, R.= (78) Sur une nouvelle espèce de _Dicranophyllum_. _Bull.
soc. géol. France_ [3], vol. +vi.+ p. 611.
—— (80) Note sur quelques plantes fossiles du terrain permien de la
Corrèze. _Ibid._ vol. +viii.+ [3], p. 196.
—— (96) Le Marquis G. de Saporta, sa vie et ses travaux. _Bull. soc.
géol. France_ [3], vol. +xxiv.+ p. 197.
—— (00) Sur les végétaux fossiles recueillis par M. Villiaume dans
les gîtes charbonneux du Nord-ouest de Madagascar. _Compt. Rend._
Jun. 5.
—— (02) Nouvelles observations sur la flore fossile du bassin de
Kousnetzk (Sibérie). _Ibid._ tome +cxxxiv.+ p. 887.
—— (05) Sur les plantes Rhétiennes de la Perse recueillies par M. J.
de Morgan. _Bull. soc. géol. France_ [4], tome +v.+ p. 190.
—— (05²) Sur quelques empreintes végétales de la formation
charbonneuse supracrétacée des Balkans. _Ann. Mines._
—— (08) See Douvillé and Zeiller.
—— (11) Note sur quelques végétaux infraliasiques des environs de
Niort. _Bull. soc. géol. France_ [4], tome +xi.+ p. 321.
—— (11²) Sur une flore triasique découverte à Madagascar. _Compt.
Rend._ vol. +cliii.+ p. 230.
—— (12) Sur quelques végétaux fossiles de la Grande Oolite de
Marquise. _Bull. soc. acad. Boulogne-sur-mer_, tome +ix.+ p. 5.
—— (N.D.) See Malloizel and Zeiller.
=Zeiller, R.= and =P. Fliche=. (04) Découverte de strobiles de
_Sequoia_ et de Pin dans le Portlandien des environs de
Boulogne-sur-mer. _Compt. Rend._ tome +cxxxvii.+ p. 1020.
=Zeiller, R.= and =L. M. Vidal.= (02) Sobre algunas impresiones
vegetales del Kimeridgense de Santa María de Meyá. _Mem. Real
Acad. Cienc. y Artes Barcelona_, vol. +iv.+ No. 26.
=Zigno, A. de.= (53) Découverte d’une flore Jurassique analogue à celle
de Scarborough dans les couches oolitiques des Alpes Vénitiennes.
_Bull. soc. géol. France_ [2], vol. +x.+ p. 268.
—— (73–85) Flora fossilis formationis Oolithicae. Vol. +ii.+
_Padua_, 1873–85.
=Zopf, W.= (92) Ueber einige niedere Algenpilze (Phycomyceten) und
eine neue Methode ihre Keime aus dem Wasser zu isoliren. _Abh.
Naturforsch. Ges. Halle_, Bd. +xvii.+ p. 79.
ERRATUM
_For_ =Elwes, H. J.= and =A. Henry= (=60=)
_read_ (=06=)
INDEX
_Abies magnifica_ 75
_Acanthocarpus_ 305
_A. xanthioides_ 305
_Acrostichum crinitum_ 568
_Adiantides_ 173
_Adiantites_ 173
_A. bellidulus_ 173, 174, 307
_Aetheotesta_ 304, 319, 331, 332
_A. elliptica_ 138, 330–332
_A. subglobosa_ 331
_Agathis_ 221, 222, 250, 283
_A. australis_ 221
_A. macrophyllus_ 221
_A. vitiensis_ 221
_Alethopteris_ 86, 89, 93, 106, 109, 111, 113, 115, 329
_A. aquilina_ 108
_A. decurrens_ 95
_A. Grandini_ 108, 117, 144, 325
_A. lonchitica_ 93, 108, 117
_A. Serlii_ 117
_Alnus_ 263
_Alstroemeria_ 304
_Amphibennettites_ 418
_A. Bleicheri_ 418
_A. Renaulti_ 418
_Amyelon_ 261
_A. radicans_ 261
Andrews, E. B. 305
_Androstrobus_ 496, 505, 506
_A. Balduini_ 505
_A. borealis_ 505
_A. Guerangeri_ 505
_A. Nathorsti_ 506
_A. Scotti_ 506
_A. sibirica_ 505
_A. zamioides_ 505
_Aneimia rotundifolia_ 539
_Aneimites_ 173
_A. fertilis_ 169, 172
_Angiopteris_ 87, 88, 107
_Anomozamites_ 464, 465, 473, 548–551
_A. Balli_ 586
_A. minor_ 465, 466
_A. Muelleri_ 510, 551
_A. Schmidtii_ 574
_Antarcticoxylon_ 294–299
_A. Priestleyi_ 296–299
_Antherangiopsis rediviva_ 503
_Anthodiopsis Beinertiana_ 126
_Antholithes liliacea_ 264
_Antholithus_ 224, 264
_A. Pitcairniae_ 264
_Anthrophyopsis_ 578, 579
_A. crassinervis_ 581
_A. Nilssoni_ 581
_A. obovata_ 581
_Araucaria_ 222, 250, 251, 299
_A. Bidwillii_ 160
_A. imbricata_ 221
_Araucarioxylon_ 224, 248–250, 295
_A. antiquum_ 285
_A. australe_ 255
_A. Beinertianum_ 199
_A. saxonicum_ 253
_Araucarites_ 240, 295, 504
_A. Beinertianus_ 199
_A. Brandlingii_ 254
_A. Buchianus_ 210
_A. Oldhami_ 245
_A. Tchihatcheffi_ 248
Arber, A. 308, 345, 346
Arber, E. A. N. _Passim_
_Arberia_, 352
_Archaeopitys_ 290
_A. Eastmanni_ 288, 290
_Arctopodium_ 200–204, 207
_A. insigne_ 201
_A. radiatum_, 201
Artis, F. E., 247
_Artisia_, 246–251, 253, 256
_A. alternans_, 248
_A. transversa_, 231, 247
_Aspleniopteris Nilssoni_, 558
_Asplenium nidus_, 581
_Asterochlaena_, 203, 205, 207
_A. kirgisica_, 165
_Asterophyllites_, 261
_Asteropteris noveboracensis_, 203
_Asterotheca_, 168
_Attolia speciosa_, 327
_Aulacopteris_, 106
_Bambusium_, 277
_B. Imhofi_, 280
Bancroft, N., 147, 446, 455, 489
_Beania_, 502, 503, 512, 568
_B. Carruthersi_, 502, 503
_B. gracilis_, 502, 503
_Bennettites_, 367–371
_B. dacotensis_, 403–408
_B. Gibsonianus_, 370, 386, 448. See also _Cycadeoidea
Gibsoniana_
_B. Morierei_, 383, 384, 429, 447. See also _Cycadeoidea
Morierei_
_B. portlandicus_, 368
_B. Saxbyanus_, 386
Benson, M., 54, 55, 61–63, 71, 78–81, 125, 226, 228, 275, 313
Berger, R., 335, 341, 342, 349, 354
Berry, E. W., 575
Bertrand, C. E., 214, 267–269, 306, 340
Bertrand and Renault, 219
Bertrand, P., 110–116, 140, 165, 200–205, 210, 323, 335, 342, 348,
357
_Bignonia_, 336
Binney, E. W., 35, 36, 39, 105
_Blastolepis_, 460
_B. acuminata_, 460
_B. falcata_, 460
_B. Otozamitis_, 460
Boissier, E., 336
_Bolpopodium_, 479
_Boroviczia_, 358, 360, 363
_B. Karpinskii_, 358–360
_Botryoconus_, 264, 265
_Bowenia_, 4, 7–9, 20, 27–29, 87, 139, 315
_B. serrulata_, 27
_B. spectabilis_, 20
_B. spectabilis_ var. _serrata_, 20
Bower, F. O., 12, 196, 475
Braun, A., 12
Braun, F., 475, 477, 537
Brenchley, W. E., 46, 47
Brongniart, A., _Passim_
Brown, R., 368, 448, 480
Buckland, W., 367–371, 448
_Bucklandia_, 372, 368, 408, 425, 426, 478–490, 523, 524, 531,
546
_B. anomala_, 481–483
_B. buzzardensis_, 486
_B. indica_, 488, 489
_B. Mantelli_, 481
_B. Milleriana_, 483, 484
_B. (Fittonia) Rigauxi_, 496
_B. Ruffordi_, 496
_B. Saportana_, 481, 569
_B. (Fittonia) squamata_, 487, 496
_B. squamosa_, 487
_B. Yatesii_, 484–86
Buckman, J., 588
_Bulbopodium_, 368, 369, 479
_B. micromerum_, 417
Bunbury, C. E. F., 240
Burlingame, L., 62, 312
Calamarieae, 190
_Calamopitys_, 190–197, 200, 248
_C. americana_, 193, 200
_C. annularis_, 193, 194, 198, 199
_C. Beinertiana_, 199
_C. Saturni_, 190–194, 198
_Calamopteris_, 190, 196
_C. Hippocrepis_, 196
_Calamosyrix_, 190
Calamoxyleae, 190
_Callipteris_, 109, 142, 169
_Callixylon_, 290–293
_C. Trifilievi_, 291–293
_Calymmatotheca_, 50, 51
_C. acuta_, 67
_C. Stangeri_, 50, 57
Cambier and Renier, 235
_Cardiocarpon_, 264
_C. acutum_, 169, 337
_C. anomalum_, 264
_C. barcellosum_, 351
_C. Branneri_, 348
_C. compressum_, 345
_C. emarginatum_, 335, 389
_C. triangulare_, 338
_Cardiocarpum fluitans_, 348
_Cardiocarpus_, 171, 224, 265, 302, 303, 307, 333–345, 354
_C. angustodunensis_, 336, 341
_C. areolatus_, 355
_C. bicaudata_, 348
_C. (Philocarpus) bicornutus_, 349
_C. cornutus_, 350
_C. drupaceus_, 334, 338
_C. drupaceus_ var. _expansus_, 339
_C. indicus_, 140, 141, 352
_C. ingens_, 353
_C. nummularis_, 339
_C. sclerotesta_, 334, 338–340, 356
_C. tenuis_, 339, 341
_Cardiopteris_, 136, 360
Carpentier, A., 65–67, 81, 110–113, 365
_Carpolites_, 363, 364
_C. sulcatus_, 362
_Carpolithes_, 353, 497
_C. alata_, 118
_C. conica_, 498
_C. granulatus_, 168
_C. Lindleyi_, 264
_C. membranaceus_, 355
_C. Milleri_, 141
_C. nitidulus_, 174
_C. samaroides_, 356
_C. sulcata_, 359, 362
_Carpolithus_, 326, 363–365, 497–500
_C. bivalvis_, 365
_C. Bucklandi_, 498
_C. conicus_, 365, 498, 499
_C. Nathorsti_, 66
_C. Pomelii_, 499
_C. Wildii_, 325, 365
Carruthers, W., _Passim_
_Cassytha_, 302
_Caulopteris Adamsi_, 245
_Cephalotaxus_, 346
_C. pedunculata_, 222
_Ceratozamia_, 6, 9, 10, 19, 24, 28, 409, 507, 529
_Ceratozamia Hofmanni_, 508
_C. mexicana_, 16, 19, 21, 22, 30, 281, 536
_Ceropegia peltata_, 247
Chamberlain, C. J., 9, 29, 391
_Cheilanthites elegans_, 72
Chodat, R., 53, 54, 60, 116, 161
Cladoxyleae, 200–210
_Cladoxylon_, 165, 200–207, 209, 210
_C. dubium_, 201, 202
_C. Kidstoni_, 149, 205, 206, 213
_C. mirabile_, 201–203, 206
_C. taeniatum_, 202, 205
_Clathraria_, 480, 490
_C. anomala_, 481, 491
_C. Lyelli_, 480, 481
_Clathropodium foratum_, 479
_C. sarlatense_, 479
_Clepsydropsis_, 204, 205
_Codonospermum_, 138, 304, 319, 330, 331, 361
_C. anomalum_, 330, 331, 359
_C. olivaeforme_, 330, 331
_Codonotheca_, 67, 124–126, 128
_C. caduca_, 67, 124, 125
_C. pusilla_, 126
_Coenoxylon_, 252, 293, 294
_C. Scotti_, 293
_Colpospermum_, 362, 363
_Colpoxylon_, 109, 142–145, 283
_C. aeduense_, 109, 142, 143
_Colymbetes_, 491–494
_C. Edwardsi_, 491–494
_Compsotesta_, 333, 347
_C. Brongniarti_, 347
Compter, G., 280, 500
_Condylites_, 467
_C. squamatus_, 467
_Conites Bucklandi_, 487
_Conostoma_, 64, 71, 79, 81, 303, 306, 309, 312–317, 326
_C. anglo-germanicum_, 315
_C. intermedianum_, 79
_C. oblongum_, 308, 313–315
_C. ovale_, 79
Corda, A. J., 70, 200, 223, 281, 504, 505
_Cordaianthus_, 142, 220, 224, 264–270
_C. acicularis_, 267
_C. Grand’Euryi_, 268, 269
_C. Lacattii_, 268
_C. Minieri_, 279
_C. Pitcairniae_, 232, 233, 266, 267
_C. Volkmanni_, 266, 267
_C. Williamsoni_, 267, 268
_C. Zeilleri_, 268
_Cordaicarpon_, 334
_C. Cordai_, 334, 335
_Cordaicarpus_, 220, 224, 240, 266, 333, 334, 335, 337, 342,
364
_C. Cordai_, 232, 350, 354, 355
_C. ingens_, 353
_Cordaicladus_, 220, 224, 245
_Cordaioxylon_, 220, 223, 248, 250
_C. Brandlingii_, 254
_Cordaispermum_, 335
Cordaitales, 214–299
Cordaiteae, 219–284
_Cordaites_, 137, 175, 176, 211, 214–217, 219–283
(_passim_), 294, 299, 335
_C. aequalis_, 238, 239, 243
_C. australis_, 240
_C. borassifolius_, 233, 236, 281
_C. circularis_, 139, 237, 276
_C. Clerci_, 239, 243
_C. communis_, 233
_C. crassifolius_, 226, 237
_C. crassus_, 226
_C. Delvali_, 235
_C. Felicis_, 226, 228, 230, 275
_C. gracilis_, 236
_C. grandifolius_, 235, 276
_C. (Noeggerathiopsis) Hislopi_, 238–245, 262
_C. Lacoei_, 237
_C. lancifolius_, 233
_C. linearis_, 236
_C. lingulatus_, 227, 229, 233–235
_C. Mansfieldi_, 232
_C. microstachys_, 236
_C. Newberryi_, 293
_C. Ottonis_, 232
_C. palmaeformis_, 235
_C. principalis_, 226, 229–233, 266, 335
_C. Robbii_, 233, 350
_C. robustus_, 227
_Cordaixylon_, 223
_Cornucarpus_, 337
_C. acutus_, 337
_Corylus colurna_, 60
_Corypha_, 381
Cotta, C. B., 89, 96, 105
Crié, L., 255
_Crossotheca_, 52–54, 113
_C. Hoeninghausi_, 53, 54, 57
_C. Hughesiana_, 52
_Crossozamia_, 368, 500, 529
_C. Hennocquei_, 500
_C. Moraeana_, 500
_Ctenidopsis_, 580
_Ctenis_, 511, 512, 532, 578–583
_C. asplenioides_, 581, 582
_C. falcata_, 532, 580, 582
_C. fallax_, 581
_C. hungarica_, 580, 581
_C. Kaneharai_, 582
_C. latifolia_, 583
_C. lunzensis_, 580
_C. orovillensis_, 582, 583
_C. Potocki_, 580, 582–584
_C. remotinervis_, 582
_C. sulcicaulis_, 580, 582–584, 586, 587
_C. Zeyschneri_, 580, 582
_Ctenophyllum_, 528
_C. angustifolium_, 556
_C. grandifolium_, 585
_C. latifolium_, 585
_C. pecten_, 528
_C. Wardi_, 585
_Ctenopsis_, 585
_Ctenopteris_, 511, 512
_Cyathea_, 88
Cycadales, 1–34
Cycadeae, 8
_Cycadella_, 374, 385, 417, 418
_C. ramentosa_, 379, 417
_C. wyomingensis_, 418
_Cycadeoidea_, 282, 367–417
_C. buzzardensis_, 372, 486
_C. colossalis_, 382, 408–410
_C. dacotensis_, 403–408, 434, 449
_C. Dartoni_, 380, 384
_C. etrusca_, 384, 438
_C. excelsa_, 374
_C. Gibsoniana_, 374, 377, 386–395, 411, 420, 455, 456, 470
_C. gigantea_, 372, 380, 411–416, 478
_C. ingens_, 378
_C. Jenneyana_, 372, 375, 412, 416
_C. McBridei_, 403
_C. Marshiana_, 372, 408, 409, 412
_C. marylandica_, 373
_C. megalophylla_, 367
_C. micromyela_, 369, 374, 376, 415, 418, 456, 488
_C. microphylla_, 367, 371
_C. montiana_, 384
_C. Morierei_, 395–403, 456, 456, 478
_C. nana_, 372
_C. Niedźwiedzkii_, 412
_C. nigra_, 374
_C. Peachiana_, 388
_C. pumila_, 369, 372, 417
_C. pygmaea_, 368, 417
_C. Reichenbachiana_, 409–412, 416
_C. Saxbyana_, 386, 388
_C. Stilwelli_, 374
_C. superba_, 372, 408
_C. Wielandi_, 375, 376
_C. Yatesii_, 371, 372, 484
_Cycadeomyelon_, 481, 490, 491
_C. Apperti_, 490, 491
_C. densicristatum_, 491
_Cycadeorachis_, 591
_Cycadeospermum_, 496, 497
_C. Pomelii_, 499
_Cycadeostrobus_, 503, 504
_C. Brunonis_, 504
_C. elegans_, 504
_C. sphaericus_, 504
_C. truncatus_, 504
_Cycadinocarpus_, 333, 334, 336, 341, 496, 497
_C. angustodunensia_, 326, 341
_Cycadites_, 367, 368, 529, 558–672
_C. Blandfordianus_, 561
_C. confertus_, 561
_C. constrictus_, 561
_C. gramineus_, 561
_C. gyrosus_, 509, 562
_C. pecten_, 520, 522
_C. pectinoides_, 520, 522
_C. rajmahalensis_, 571, 572
_C. rectangularis_, 501, 565, 566
_C. Renaulti_, 566
_C. Roemeri_, 559
_C. Saladini_, 565
_C. Saportae_, 14, 559
_C. sibiricus_, 561
_C. Steenstrupi_, 559
_C. sulcicaulis_, 578
_C. taxodinus_, 509, 562
_C. tenuisectus_, 563, 576
_Cycadocephalus_, 473–477
_C. Sewardi_, 473–475
_Cycadolepis_, 482, 494–496
_C. pilosa_, 494
_C. villosa_, 494
_Cycadorachis_, 590, 591
_C. abscissa_, 590
_C. armata_, 590
_C. tuberculata_, 591
_Cycadospadix_, 141, 494, 500, 501, 504
_C. Hennocquei_, 501
_C. integer_, 501
_C. Milleryensis_, 338
_C. Pasinianus_, 500
_Cycadoxylon_, 185–187
_C. Fremyi_, 186, 187
_C. robustum_, 186, 187
_Cycas_, 4–13, 27, 29, 34, 89, 94, 109, 157, _etc._
_C. angulata_, 21
_C. Beddomei_, 13
_C. Cairnsiana_, 14
_C. circinalis_, 4, 13, 16, 20, 21, 24, 25, 27
_C. media_, 30, 33
_C. Micholitzii_, 13, 14, 33
_C. pectinata_, 21, 22
_C. revoluta_, 5, 7, 10, 22, 27, 30
_C. Ruiminiana_, 21, 22
_C. Rumphii_, 20
_C. Rumphii_ var. _bifida_, 13
_C. siamensis_, 11, 12, 27, 30, 160
_Cyclocarpon_, 334–336, 349
_C. nummularium_, 335
_C. tenue_, 335
_Cyclocarpus_, 340, 346
_C. nummularis_, 341
_Cyclopteris_, 109, 130, 136, 139, 276, 496
_C. Jenksiniana_, 496
_C. Klipsteinii_, 544
_Cyclospermum_, 333, 335, 340, 341
_Cyclozamia_, 541
_Cylindropodium_, 368, 386, 478, 479
_Dadoxylon_, 223, 248–260, 289–295
_D. australe_, 252, 255, 256
_D. Brandlingii_, 251, 254, 260
_D. Buchianum_, 220
_D. Kayi_, 256, 258
_D. materiarum_, 252, 256, 257
_D. medullaris_, 254
_D. meridionale_, 255
_D. Newberryi_, 252
_D. Nicoli_, 255
_D. nummularium_, 255
_D. oldhamium_, 35, 38
_D. ouangonidium_, 252
_D. Pedroi_, 252, 258, 259, 275
_D. permiense_, 259
_D. protopityoides_, 255
_D. Spenceri_, 294
_D. spetzbergense_, 260
_Dammara albens_, 281
_Dammarites Bayeri_, 283
_Danaea elliptica_, 475
_Davallia aculeata_, 48
_D. tenuifolia_, 77
Dawes, J. S., 247
Dawson, Sir J. W., 173, 203, 238, 247, 256, 277, 463
Dawson and Matthew, 252
Dawson and Penhallow, 196
De la Beche, 540
_Decagonocarpus_, 357
_D. olivaeformis_, 357
Depape and Carpentier, 317
_Desmiophyllum_, 236, 278
_D. Solmsi_, 282
_Dicksonites_, 167
_Dicranophyllum_, 246
_Dictyo-Cordaites Lecoi_, 238
_Dictyopteris_, 546
_D. falcata_, 546
_D. Schützii_, 113
_Dictyothalamus_, 127
_D. Schrollianus_, 113, 127
_Dictyoxylon_, 35, 36, 72
_D. Grievii_, 72
_D. oldhamium_, 38
_D. radicans_, 261
_Dictyozamites_, 379, 511, 546–548
_D. falcatus_, 546
_D. falcatus_ var. _distans_, 547
_D. falcatus_ var. _grossinervis_, 547
_D. falcatus_ var. _obtusa_, 546
_D. grossinervis_, 547
_D. Hawelli_, 547, 548
_D. indicus_, 346
_D. Johnstrupi_, 547, 548
_Dioon_, 8, 9, 19, 29, 30, 455
_D. edule_, 10, 15, 16, 19, 27, 28, 34, 464
_D. Purpusii_, 19
_D. spinulosum_, 10, 19, 23, 25, 417
_Dioonites_, 509, 528, 556, 572
_D. Buchianus_, 537
_D. saxonicus_, 537
_D. spectabilis_, 367
_Diplopterotesta_, 360, 361
_D. spitzbergensis_, 359, 360
_Diplotesta_, 265, 333, 346, 347
_D. avellana_, 322
_D. Grand’Euryana_, 322, 346
_Diplotmema_, 77
_D. elegans_, 72
Dolerophylleae, 132
_Dolerophyllum_, 124, 130–139, 229, 237, 276, 331, 332
_D. Berthieri_, 130, 133, 136–138
_D. fertile_, 130, 131, 137, 138
_D. Goepperti_, 132–134, 137, 138
_D. pseudopeltatum_, 136, 137
_Doleropteris_, 136
Doleropteroideae, 132
Dorety, H. A., 30, 162
Dorrien-Smith, A. A., 25
_Dory-Cordaites_, 224, 227, 265, 321
_Dory-Cycadolepis_, 494
Dunker, W., 528, 529, 544, 558
Duns, J., 170
_Echinostipes_, 368
_Edraxylon_, 38, 47
Edwards, W. N., 343
Eichwald, E., 132
Elkins and Wieland, 292
_Encephalartopsis_, 508
_E. nervosa_, 508, 580
_Encephalartos_, 6–10, 14, 23, 28, 29, 34, 158, 372, 487, 507,
508, 529, 587
_E. Altensteinii_, 14, 15, 21, 25, 27, 412
_E. Barteri_, 9, 27, 30, 158
_E. caffer_, 14, 16
_E. cretaceus_, 508
_E. denticulatus_, 507
_E. Fredericki-Guilielmi_, 14, 16
_E. Ghellinckii_, 11, 14, 529, 561
_E. Gorciexianus_, 508, 510
_E. Hildebrandti_, 9
_E. horridus_, 27
_E. Laurentianus_, 14
_E. Lehmanni_, 14, 320
_E. longifolia_, 14, 536
_E. villosus_, 22
Endlicher, S., 285, 503
_Endolepis vogesiacus_, 278
_Eolirion primigenium_, 282
_Eremopteris_, 169–172
_E. artemisaefolia_, 169–171
_E. Macconchii_, 172
_E. Neesii_, 169
_Eriotesta_, 319, 332
_E. vetutina_, 332
_Eristophyton_, 194, 197, 200, 248
_E. Beinertianum_, 199, 295
_E. fasciculare_, 197–199
_Erodium_, 304, 364
Ettingshausen, C. von, 529, 551, 578, 581
_Eu-Cordaites_, 224
_Eu-Ctenis_, 580
_Euphorbia_, 247
_Eury-Cycadolepis_, 494–496
_E. Jenkinsiana_, 496
_Euryphyllum_, 238, 245
_Eu-Zamites_, 521, 531
Feistmantel, O., 240, 443, 445, 494, 514–517, 546, 561, 572, 574,
577, 586
_Feistmantelia_, 139, 491
_F. bengalensis_, 139
_F. oblonga_, 491
Felix, J., 67, 70, 227, 250
Fiedler, H., 123, 335, 336, 349, 351
_Filicites Bechei_, 539, 540
_F. Bucklandi_, 537
_F. (Sphenopteris) elegans_, 72
_F. Pluckeneti_, 166
_Fittonia_, 478, 487
_F. Brongniarti_, 395
_F. insignis_, 487
_F. Rigauxi_, 487
_F. Ruffordi_, 483
_F. squamata_, 487
_Flabellaria_, 223, 233
_F. chamaeropifolia_, 281
Fliche, P., 278, 279, 280, 368, 504
Fontaine, W. M., 385, 500, 508, 578, 580, 582
Fraine, E. de, 95, 96, 149, 153, 155, 161
_Fričia nobilis_, 505
Fries, E., 566
_Fumaria officinalis_, 72
_Gangamopteris_, 258, 338, 352
_G. Seixasi_, 351
_Gaudrya_, 319, 332
_G. lagenaria_, 332
_G. trivalvis_, 332
Geinitz, H. B., 334, 365, 552
Gibbs, L. S., 61
_Ginkgo biloba_, 7, 61, 62, 119, 135, 139, 173, 222, 251, 266,
294, 301, 306, 327, 333, 338, 339, 398, 499, 502
_Gleichenia_, 74, 88
_Glossopteris_, 141, 354
_G. indica_, 140
_Glossozamites_, 530
_G. brevis_, 530
_G. Schenkii_, 541
_G. Stoliczanus_, 530
_Glyptostrobus_, 127
Gnetales, 160
_Gnetopsis_, 304, 309, 314, 317, 318
_G. anglica_, 318
_G. elliptica_, 314, 317, 318, 359
_Gnetum_, 401
_G. africanum_, 401
_G. Gnemon_, 63
Goeppert, H. R., 96, 126, 127, 173, 210, 264, 285, 289, 295, 305,
336, 411, 412, 527
Goeppert and Stenzel, 86, 96, 102, 163, 252, 295
Goldenburg, F., 236
_Gomphostrobus_, 253
Gordon, W. T., 181, 183, 288, 312
Gothan, W., 51, 248–252
Gourlie, W., 36, 37
Grand’Eury, C., _Passim_
Grieve, G., 72
Griffith, W., 28, 302
_Guilelmites_, 365
Halle, T. G., 280, 443, 457, 473, 517, 518, 521, 522, 527, 540,
547, 550, 563, 565, 575
_Haplocalamus_, 190
Heer, O., 174, 280, 336, 358, 360, 462, 520, 525, 530, 541, 549,
563
Helmacher, R., 349
Hemingway, W., 94, 317
_Hemitelia_, 48
_Heterangium_, 51, 70–85, 86–94, 98, 109, 156, 157, 162, 168,
179–183, 193, 194, 214, 309, 312, 316
_H. alatum_, 84
_H. Andrei_, 84
_H. bibractense_, 84
_H. bohemicum_, 84
_H. cylindricum_, 83
_H. Duchartrei_, 83
_H. Grievii_, 71–73, 79–82
_H. hibernicum_, 84
_H. Lomaxi_, 72, 83
_H. minimum_, 83
_H. paradoxum_, 72
_H. polystichum_, 84
_H. punctatum_, 84
_H. Renaulti_, 84
_H. Sturi_, 84, 183
_H. tiliaeoidea_, 71, 81–84
_Hexagonocarpus_, 116, 303, 322, 323, 356
_H. crassus_, 356
_H. Hookeri_, 357
_H. Noeggerathi_, 359
_Hexapterospermum_, 116, 119, 140, 319, 321–323, 348, 356
_H. modestae_, 357
_H. Noeggerathii_, 322, 357
_H. pachypterum_, 321
_H. stenopterum_, 321, 322
Hick, T., 67
_Hierogramma_, 200–204
_H. mysticum_, 201
_Hisingera_, 569
_Holcospermum_, 343, 361–363
_H. dubium_, 363
_H. sulcatum_, 357, 359, 361–363
Holden, H. S., 109
Holden, R., 243, 559, 560, 563, 565
Hollick, A., 461
Hollick and Jeffrey, 491
Hooker, Sir J., 10, 60
Hooker and Binney, 118, 301
Howse, R., 170, 232
_Hysterites Cordaitis_, 233
_Iodes_, 46
Johnson, T., 51, 52, 84
_Jordania_, 334, 336
_J. bignonioides_, 336, 351
_J. moravica_, 347
_Juglans_, 222
_J. regia_, 246
_Kaloxylon_, 67
_K. Hookeri_, 38, 67
_Kalymma_, 190, 192, 194–196
_K. grandis_, 192, 195, 196
_K. striata_, 196
Karsten, G., 30
Kershaw, E. M., 28, 61
Kidston, R., 51–53, 56, 110, 112, 168
Kidston and Gwynne-Vaughan, 185
Klein, L., 145
_Knorria taxina_, 232
Kosmovsky, C., 238
_Krammera_, 277, 281
_K. mirabilis_, 280
Krasser, F., 420, 553, 576, 580
Kraus, G., 28, 210, 295
Kubart, B., 70, 71, 84, 183
Kurtz, F., 589
Kutorga, S., 132
_Lagenidium_, 62
_Lagenospermum_, 64–66, 174, 309
_L. Arberi_, 173, 307
_L. glandiforme_, 360
_L. nitidulum_, 174
_L. oblongum_, 65, 66
_L. Sinclairi_, 57, 64, 66, 81
_Lagenostoma_, 55–66, 71, 81, 116, 122, 125, 160, 173, 303,
307–317, 325, 326, 329, 497
_L. Kidstoni_, 64
_L. Lomaxi_, 51, 55–62, 311
_L. oblonga_, 65
_L. ovoides_, 55, 62–64, 311
_L. physoides_, 62, 301
_L. Sinclairi_, 64, 65
_L. urceolaris_, 65
Leckenby, J., 421
_Lepidanthium_, 477
_Lepidocaryon_, 265, 333, 346, 347
_L. avellana_, 346
_Lepidodendron_, 125, 212, 271
Leslie, T. N., 242, 256
Lesquereux, L., 110, 123, 131, 156, 232, 235, 305, 326
Leuthardt, F., 280, 550, 553
Lignier, O., 34, 63, 217, 229, 247, 386, 415, 428, 432–434, 455
Lindley and Hutton, _Passim_
Linnaeus, 363, 364
_Linopteris_, 86, 109, 113
_L. obliqua_, 111, 113
_Lobelia Rhynchopetalum_, 12
Loddiges, C., 368
Lomax, J., 46, 90
Lotsy, J., 86, 117
_Lycostrobus_, 506
_Lyginodendron_, 36
_L. anomalum_, 289
_L. Landsburgii_, 36, 37
_L. oldhamium_, 38, 70. See also _Lyginopteris oldhamia_
_L. robustum_, 187
_L. Sverdrupi_, 38
Lyginopterideae, 35–85, 89, 162
_Lyginopteris_, 35–70, 74–78, 84, 86–94, 98, 109, 186,
189–191, 194, 198, 214, 273, 293, 295, 309, 316, 369
_L. lacunosum_, 70
_L. oldhamia_, 38–51, 56, 72
_L. tristichum_, 70
_Lygodium_, 88, 180
McBride, T. H., 403
McCoy, Sir F., 240
McLean, R. C., 59
_Macropterygium_, 554
_Macrozamia_, 7, 9, 10, 19, 24, 28, 29, 100, 157, 158, 391,
529, 531
_M. Denisoni_, 16, 28
_M. Fraseri_, 16, 28, 499
_M. gibba_, 504
_M. heteromera_, 19, 27, 33
_M. Macleayi_, 536
_M. Moorei_, 6
_M. Preissii_, 23
_M. spiralis_, 19
_Malacotesta_, 363
_M. oblonga_, 363
Manoxylic, 7
Mantell, G., 478, 480, 481
_Mantellia_, 367, 368
_M. nidiformis_, 367
_Marattia_, 107
_Mariopteris_, 111
Marsh, A. S., 385
_Masculostrobus_, 505
Maslen, A. J., 271
_Matonia_, 88, 190
Matte, H., 30, 159, 160
_Medullosa_, 86–110, 119, 144, 149–157, 161, 164, 165, 183,
190, 196, 207, 209, 319
_M. anglica_, 87–98, 102, 105, 107, 108, 145–158, 161, 180, 219
_M. centrofilis_, 95–97, 157
_M. elegans_, 105–107
_M. gigas_, 100
_M. Leuckarti_, 87, 102–105, 108, 142–145, 154–159, 165
_M. Ludwigii_, 163
_M. porosa_, 89, 92, 157
_M. pusilla_, 94–96
_M. Solmsi_, 92, 148, 157
_M. Solmsi_ var. _gigantea_, 100, 101, 158
_M. Solmsi_ var. _lignosa_, 92
_M. Solmsi_ var. _typica_, 101
_M. stellata_, 87, 89, 96, 97, 100–103, 157, 158, 164
_M. stellata_ var. _corticata_, 92, 99, 100, 158
_M. stellata_ var. _gigantea_, 92, 100
_M. stellata_ var. _lignosa_, 100
_M. stellata_ var. _typica_, 97–99
Medulloseae, 86–165
_Megadendron saxonicum_, 253
_Megalorhachis_, 204
_M. elliptica_, 204
_Megalospermum_, 326
_Megaloxylon_, 175–180, 182, 183, 198, 297
_M. Scotti_, 175–180
_Mesopitys_, 248, 294–296
_M. Tchihatcheffi_, 293–296, 299
_Mesoxylon_, 214, 217, 220, 225, 226, 246, 248, 253, 256, 262,
266, 270–276, 294, 295, 299
_M. Lomaxi_, 274, 275, 297
_M. poroxyloides_, 274, 275
_M. Sutcliffi_, 271–274
_Metacordaites_, 260
_M. Rigolloti_, 254, 260
Mettenius, G., 30
_Microcycas_, 6, 7, 10, 19, 23, 30, 62, 162, 163
_M. Calocoma_, 27
_Microspermum_, 343, 365
Miller, H. 449, 536, 584
Miquel, F. A. W., 528, 569
_Mitrospermum_, 307, 333, 336, 345, 346
_M. compressum_, 314, 338, 345
_Mittagia_, 63, 64
_M. seminiformis_, 63
Morière, J., 369, 395, 415
Morris, J., 264, 512, 514, 528
Mougeot, A., 99
_Musocarpus_, 361
_M. difformis_, 361
_M. prismaticus_, 361
_Myelopteris_, 106, 154
_Myeloxylon_, 89, 93, 96, 99, 105–108, 119, 123, 139, 144,
154, 155, 196,207, 329
_M. Landrioti_, 93, 102, 105, 108
_M. radiatum_, 103, 105, 107, 108
_M. topekense_, 108
_Myrica_, 262
_M. Gale_, 61, 318
_Naiadea obtusa_, 588
Nathorst, A. G., _Passim_
_Nephrolepis Duffi_, 543
Neuropterideae, 87
_Neuropteridophylla_, 86
_Neuropteris_, 56, 86, 89, 106, 109–112, 115, 117, 126, 130,
139, 342, 357
_N. auriculata_, 116
_N. Carpentieri_, 112
_N. gigantea_, 110–113, 116, 140
_N. heterophylla_, 110, 111, 113–117
_N. obliqua_, 115, 116, 124
_N. pseudogigantea_, 112
_N. Schlehani_, 116
_Neuropterocarpus_, 116
_N. Kidstoni_, 114
_Neuropteromedullosa_, 156
_Neurospermum_, 116, 344
_Neurotheca_, 110
Newberry, J. S., 128, 131, 320, 507, 589
_Nilssonia_, 511, 512, 548, 549, 551, 555, 566–578
_N. bohemica_, 576
_N. brevis_, 567–571
_N. compta_, 555, 569, 573, 574, 576, 578
_N. densinervis_, 575
_N. elongata_, 566
_N. Johnstrupi_, 575
_N. mediana_, 551
_N. nipponensis_, 574
_N. orientalis_, 568, 572, 575, 576
_N. ozvana_, 576
_N. polymorpha_, 567–573
_N. princeps_, 576, 577
_N. pterophylloides_, 367, 567, 572, 573
_N. rajmahalensis_, 571
_N. saighensis_, 570
_N. Schaumburgensis_, 578
_N. Schmidti_, 574
_N. Sturii_, 576
_N. taeniopteroides_, 575
_N. tenuicaulis_, 556, 576
_N. tenuinervis_, 569, 575
Nilssoniales, 511, 566–587
_Nilssoniopteris_, 569
_Niponophyllum_, 282, 283
_N. cordaitiforme_, 282
_Noeggerathia_, 589, 590
_N. crassa_, 227
_N. cyclopteroides_, 132
_N. foliosa_, 588
_N. Goepperti_, 132
_N. palmaeformis_, 235, 238
_Noeggerathianthus_, 264
_Noeggerathiopsis_, 220, 238–243
_N. Hislopi_, 238, 241, 276, 277. See also _Cordaites
(Noeggerathiopsis) Hislopi_,
_Odontopteris_, 86, 106, 109
Oldham and Morris, 443, 488, 514, 561, 572, 574, 576, 577
Oliver, F. W., 55, 61–64, 79, 119, 122, 301, 306–309, 321–326, 329
Oliver and Salisbury, 308, 313, 317
Oliver and Scott, 56, 60
_Oreodoxites Martianus_, 338
Osborne, T. G. B., 261, 262
_Otopteris mediana_, 541
_O. tenuata_, 543
_Otozamites_, 460, 467, 500, 511, 514, 517, 521, 522, 528,
530, 537–545, 546, 587, 589
_O. abbreviatus_, 521, 522
_O. angustatus_, 514–516
_O. Beani_, 541–544, 587, 588
_O. Bechei_, 538–541, 544
_O. bengalensis_, 542
_O. bengalensis_ var. _obtusa_, 543
_O. brevifolius_, 447
_O. Bucklandi_, 541
_O. Bunburyanus_, 542, 543
_O. contiguus_, 543
_O. decorus_, 544
_O. distans_, 515
_O. Feistmanteli_, 539, 543
_O. giganteus_, 544
_O. Goeppertianus_, 483, 538, 544
_O. gracilis_, 515, 516
_O. graphicus_, 540
_O. groenlandica_, 537
_O. Hennocquei_, 540
_O. Hislopi_, 515, 516, 521, 522
_O. indosinensis_, 541
_O. Izuimensis_, 544
_O. Klipsteini_, 530, 543, 544
_O. lagotis_, 544
_O. linearis_, 541, 544
_O. molianus_, 541
_O. obtusus_, 537–541
_O. obtusus_ var. _ooliticus_, 540
_O. oregonensis_, 544
_O. Polakii_, 541
_O. tenuissimus_, 543
_O. Terquemi_, 540
_O. vicetinus_, 540
_Ottokaria_, 124, 139–141
_O. bengalensis_, 116, 139, 140
_Pachytesta_, 90, 115–117, 144, 304, 319, 323–236
_P. gigantea_, 323, 325
_P. incrassata_, 324, 325
_Palaeanthus problematica_, 461
_Palaeopitys_, 210
_P. Milleri_, 210
_Palaeospathe aroidea_, 132
_Palaeoxylon_, 100, 289
_Palaeoxyris_, 477
_P. microrhombea_, 477
_Palaeozamia_, 442, 443, 513, 514
_P. acutifolia_, 514
_P. affinis_, 514, 515
_P. bengalensis_, 514
_P. cutchensis_, 514, 515
_P. longifolia_, 281
_P. pecten_, 421
_P. recta_, 534
_P. rigida_, 514, 515
_P. Rubidgei_, 585
_Palmacites_, 118
_Parapitys_, 294, 295
_P. Spenceri_, 294, 295
Parkinson, J., 367
_Paullinia_, 88
Pearson, H. H. W., 28, 402
_Pecopteris Pluckeneti_, 166–168, 171, 308
_P. Sterzeli_, 168
_Pecopteromedullosa_, 156
_Pelourdea_, 277–281
_P. hadroclada_, 280
_P. Imhofi_, 280
_P. keuperiana_, 280
_P. megaphylla_, 281
_P. mirabilis_, 281
_P. vogesiaca_, 278, 279, 281
Penhallow, D. P., 108, 251
Phillips, J., 281, 520, 522, 558, 578
_Phoenicopsis_, 236, 278, 280
_Phylladoderma_, 244
_P. Arberi_, 244
_Phyllocladus_, 122
_Phyllotaenia_, 280
_P. hadroclada_, 280
_P. longifolia_, 280
_Physostoma_, 62, 64, 125, 304, 309–316, 326, 329, 359
_P. elegans_, 62, 309, 311, 314
_Pilularia_, 58, 64, 327
_Pinites_, 35
_P. Brandlingii_, 254
_P. Goepperti_, 210
_P. medullaris_, 289
_P. Withami_, 289
_Pissadendron_, 285
_Pitcairnia_, 264
Pityeae, 285–299
_Pityoxylon chasense_, 251
_Pitys_, 183, 285–289, 290
_P. antiqua_, 285–291
_P. Dayii_, 288
_P. primaeva_, 287–289
_P. Withami_, 286, 289
_Plagiozamites_, 530, 589, 590
_P. carbonarius_, 590
_P. Planchardi_, 509, 589, 590
_Platylepis_, 369, 415, 478
_P. micromyela_, 479
_Platypterygium_, 586
_P. Balli_, 555, 556
_P. densinerve_, 575
_P. Rogersianum_, 576
_Platyspermum_, 114, 343, 362, 363
_P. sulcatum_, 362
_Poa-Cordaites_, 224, 227, 236, 280, 283
_P. tenuifolius_, 236
_Podocarpus_, 61, 262
_Podocarya_, 386, 449
_Podozamites_, 281, 529, 588
_P. Milleri_, 536
_P. Zitteli_, 530
_Polylophospermum_, 319, 322, 329, 330
_P. stephanense_, 322, 329
_Polypodioides pecteniformis_, 522, 523
_Polypodium heracleum_, 145, 190
_P. irioides_, 566
_P. quercifolium_, 145, 190
_Polypterocarpus_, 357, 358, 361
_P. anglicus_, 321, 324, 357
_Polypterospermum_, 319, 323
_P. Renaulti_, 322, 323
Pomel, A., 368, 497, 500, 529, 541
Poroxyleae, 214–219
_Poroxylon_, 83, 142, 214–219, 226, 262, 270, 275, 276, 295,
343
_P. Boysseti_, 214, 218, 219
_P. Duchartrei_, 214
_P. Edwardsii_, 216–219
_P. stephanense_, 217, 219
Potonié, H., 38, 111, 112, 166, 249, 549, 590
_Potoniea_, 113, 116, 117, 128, 129
_P. adiantiformis_, 111, 112, 131
Prankerd, T. L., 62, 63
Priestley, R., 296
_Primula auricula_, 91
Protocycadaceae, 161
Protopityeae, 210–213
_Protopitys_, 207, 209–213, 255
_P. Buchiana_, 210–213
_Psaronius_, 88, 168, 253
_Pseudoctenis_, 528, 556, 584–587
_P. Balli_, 586
_P. crassinervis_, 585
_P. eathiensis_, 584, 585
_P. ensiformis_, 585
_P. Lanei_, 586
_Pseudocycas_, 14, 511, 558–565
_P. insignis_, 560, 562, 565
_P. Roemeri_, 560, 564
_P. Saportae_, 560, 563, 564
_P. Steenstrupi_, 560, 561, 563
_Psygmophyllum_, 276
_P. Delvali_, 235
_P. flabellatum_, 238
_P. majus_, 235
_Pteridotheca Butterworthi_, 54
_Pterispermostrobus_, 66, 67, 126
_P. bifurcates_, 65, 66, 126
_Pterophyllum_, 511, 548–558
_P. aequale_, 556
_P. angustifolium_, 576
_P. Bavieri_, 555
_P. blechnoides_, 509, 552
_P. Braunianum_, 554, 556, 558
_P. Bronni_, 553, 554
_P. Buchianum_, 529
_P. Cambryi_, 509, 552
_P. Carterianum_, 586
_P. concinnum_, 549
_P. Cottaeanum_, 509, 552
_P. crassinerve_, 550
_P. distans_, 557
_P. Dunkerianum_, 527, 528, 557
_P. Fayoli_, 509, 551, 552
_P. Footeanum_, 557
_P. Goeppertianum_, 544
_P. gonorrachis_, 509
_P. Grand’Euryanum_, 509, 552
_P. inconstans_, 555
_P. inflexum_, 509
_P. Jaegeri_, 548–550, 553
_P. longifolium_, 553
_P. Lyellianum_, 557, 558
_P. majus_, 548
_P. marginatum_, 550
_P. medianum_, 576
_P. minus_, 548
_P. Morrisianum_, 578, 586
_P. Nathorsti_, 556
_P. Nilssoni_, 551, 557, 558
_P. oblongifolium_, 530
_P. pecten_, 512, 517
_P. princeps_, 573, 576, 586
_P. rigidum_, 523
_P. Rogersianum_, 554, 575
_P. saxonicum_, 537
_P. Schaumburgense_, 578
_P. Schenki_, 555
_P. Tietzei_, 554, 555
_P. Williamsonis_, 573
_Pterospermum_, 343, 357
_P. anglicum_, 357
_Pterozamites_, 529
_Ptilophyllum_, 379, 512–529, 539
_P. acutifolium_, 446, 517, 521, 522
_P. acutifolium_ var. _maximum_, 515
_P. Anderssoni_, 525, 527
_P. antarcticum_, 525, 527
_P. boreale_, 525–527, 530
_P. cutchense_, 478, 514–517, 521, 522, 524
_P. cutchense_ var. _curvifolium_, 515
_P. Dunkerianum_, 527
_P. hirsutum_, 520
_P. pecten_, 437–440, 443, 445, 512–525
_Ptilozamites_, 511, 512
_Ptychotesta_, 319, 321, 322, 348
_P. pachypterum_, 322
_P. tenuis_, 321, 322
_Ptychoxylon_, 142, 145, 186–190
_P. Levyi_, 187–190
Pychnoxylic, 7
_Pycnophyllum_, 223
_Rachiopteris aspera_, 47
_R. Williamsoni_, 154, 155
Raciborski, M., 412, 578, 581, 582
_Radiculites reticulatus_, 217
_Radiospermum_, 64
_R. ornatum_, 323
Rattray, C., 28
_Raumeria_, 409
_R. Reichenbachiana_, 384, 385
_R. Schulziana_, 412
Reichenbach, —, 253
Reid, Mr and Mrs Clement, 300
Renault, B., _Passim_
Renier, A., 116
_Retinodendron_, 181
_Rhabdocarpos Mansfieldi_, 326
_Rhabdocarpus_, 90, 115, 116, 215, 333, 341–344, 362, 364
_R. Boschianus_, 320
_R. elongatus_, 174
_R. Lilleanus_, 342
_R. Mansfieldi_, 326
_R. multistriatus_, 362, 363
_R. Oliveri_, 344
_R. orientalis_, 174
_R. ovoides_, 354
_R. subtunicatus_, 115, 342
_R. tunicatus_, 115, 341, 342, 362
_Rhabdospermum_, 116, 307, 333, 335, 339–344, 347
_R. cyclocaryon_, 340, 344
_Rhetinangium_, 85, 181–183
_R. Arberi_, 181–183
_Rhexoxylon_, 87, 101, 146–149, 207
_R. africanum_, 146–149
_Rhipidopsis ginkgoides_, 140
_Rhiptozamites Goepperti_, 238, 244, 245
_Rhizo-Cordaites_, 224, 237
_Rhizophidium_, 62
_Rhynchogonium_, 358–363
_R. costatum_, 358, 359
_R. sulcatum_, 358, 360
_Rhynchopetalum montanum_, 12
Richards, J. T., 536, 584
Richter, P. B., 200
Roehl, von, 136
Salisbury, E. J., 122, 307, 320
_Samaropsis_, 168–171, 236, 245, 265–267, 303, 333–338, 345–354
_S. acuta_, 167–171
_S. alata_, 351
_S. Baileyi_, 351
_S. barcellosus_, 350, 351
_S. bicaudata_, 348, 350
_S. bignonioides_, 350
_S. Crampii_, 349
_S. emarginata_, 337, 349, 350
_S. fluitans_, 142, 338, 348, 350
_S. indica_, 352, 353
_S. Leslii_, 352, 353
_S. marginata_, 337
_S. Milleri_, 353
_S. moravica_, 349, 352
_S. Newberryi_, 350
_S. Pitcairniae_, 266
_S. Seixasi_, 350, 351
_S. spitzbergensis_, 360
_S. ulmiformis_, 336
Saporta, G. de, 368, 369, 422, 429, 434, 449, 477–479, 494, 499,
500, 589
Saporta and Marion, 132, 137, 138, 317, 395, 501, 505
_Sarcotaxus_, 265
_S. angulosus_, 347
_S. avellana_, 346
_S. olivaeformis_, 347
Schenk, A., 97, 164, 282, 336, 529, 550, 554, 555, 568, 578, 581
Schimper, W. P., 127, 477, 500, 501, 505, 530, 554
Schimper and Mougeot, 278
_Schizodendron_, 250
_Schizopodium_, 369
_S. Renaulti_, 369
_Schizospermum_, 319
_Schizoxylon_, 200, 203
_S. taeniatum_, 201
Schlotheim, E. F. von, 166
Schmaulhausen, J., 174, 233, 238, 244, 245
Schuster, J., 411, 412, 477
_Schützia_, 124–127
_S. anomala_, 126, 127
_S. Bennieana_, 127
_S. permiensis_, 127
_Scolopteris_, 168
Scott, D. H., _Passim_
Scott and Jeffrey, 191, 196
Scott and Maslen, 119, 122, 330
_Scuto-Cordaites_, 237
_S. Grand’Euryi_, 238
Sellards, E. H., 126
_Senecio praecox_, 287
_Senftenbergia_, 63
_Sequoia_, 217
_Serjania_, 88
_Sewardia latifolia_, 589, 591
Shaw, F. J. F., 160
Shirley, J., 255
_Sigillaria_, 214
_Sigillariopsis_, 214
Solms-Laubach, Graf zu., _Passim_
_Sorocladus stellata_, 110
_Sparganum_, 93, 105, 184, 191
Spencer, J., 294
_Sphaereda paradoxa_, 502
_Sphaerostoma_, 71, 78–81, 307, 309, 316, 319
_S. ovale_, 79, 80, 312, 313
_Sphenophyllum_, 110
_Sphenopteridophylla_, 86
_Sphenopteris_, 109
_S. artemisaefolia_, 169
_S. crithmifolia_, 169, 170
_S. dissecta_, 77, 81
_S. Dubuissonis_, 56
_S. elegans_, 72, 75, 77, 78, 81
_S. Hoeninghausi_, 47–53, 56, 70
_S. Linkii_, 51
_S. obtusifolia_, 81
_S. obtusiloba_, 65
_S. refracta_, 208
_S. Schaumberg-Lippeana_, 66
_Sphenozamites_, 587–589
_S. Belli_, 588, 589
_S. Geinitzianus_, 589
_S. Geylerianus_, 588
_S. robustus_, 589
_S. Rochei_, 509, 587
_S. Rossii_, 588
_Sporocarpon ornatum_, 309
_Stangeria paradoxa_, 8, 9, 12, 16, 19–22, 29, 30, 32, 34,
159, 160, 312, 386
Staub, M., 578
_Steloxylon_, 163–165
_S. Ludwigii_, 163, 164
_Stenomyelon_, 182–185
_S. tuedianum_, 183–185
_Stenorrachis_, 503
_S. scanicus_, 503, 568
Stenzel, G., 165
_Stenzelia_, 106
_Stephanospermum_, 302–304, 307, 323, 326–329, 345, 497
_S. akenioides_, 311, 314, 319, 326–328
_S. caryoides_, 328, 329
Sternberg, C. von, 118, 362, 487, 522, 555
_Sternbergia_, 247
Sterzel, J. T., 105, 167, 168
_Stigmaria_, 193
Stokes and Webb, 480, 481, 491, 497
Stopes, M. C., _Passim_
_Strobilites_, 124, 141, 142, 500
_S. Milleryensis_, 141, 142, 338
Stur, D., 70, 77, 167
_Sub-Zamites_, 521, 530, 531
Sutcliffe, W. H., 149, 161, 162
_Sutcliffia_, 87, 149–156, 182–185
_S. insignis_, 149–156
_S. Williamsoni_, 154
_Syncardia_, 200, 205
_S. pusilla_, 201, 202
_Taeniopteris_, 1, 86, 511, 568, 576, 583
_T. asplenioides_, 581
_T. vittata_, 467, 470, 472, 508, 569
Tate, R., 534
_Taxospermum_, 265, 333, 346, 347
_T. Grüneri_, 322, 347
_Taxus_, 306, 347, 396
_Teconia_, 46
_Telangium_, 54, 55, 125
_T. Scotti_, 54, 311
_Thinouia scandens_, 88
Thiselton-Dyer, W. T., 467
_Thlaspi arvense_, 303
Thoday, Mrs, 28, 160, 161
Thomas, H. H., _Passim_
Thomas and Bancroft, 560
Thomson, R. B., 252, 254
Thomson and Allin, 251
_Thysanotesta_, 304, 364
_T. sagittula_, 304, 314, 359, 364
_Thysopteris elegans_, 65
_Titanophyllum_, 283, 284
_T. Brittsi_, 284
_T. Grand’Euryi_, 283, 284
_Torreya_, 301, 325, 347
_Trigonocarpon_, 117, 118
_Trigonocarpus_, 61, 90, 94, 115–123, 162, 301, 303, 307,
316–329, 345, 499
_T. actaeonelloides_, 354
_T. corrugatus_, 124
_T. Dawesi_, 123, 320
_T. Moyseyi_, 122
_T. multicarinatus_, 320
_T. olivaeformis_, 119
_T. Oliveri_, 122
_T. Parkinsoni_, 118–123, 319–321, 329
_T. pusillus_, 122, 319, 320
_T. rostratum_, 321
_T. schizocarpoides_, 319
_T. shorensis_, 121–124, 319, 320
_T. sporites_, 320
_Trigonocarpum gloagianum_, 358, 360
_Tripterospermum_, 119, 321, 358, 369
_T. ellipticum_, 321, 357
_Tsuga_, 127, 315
_Tylodendron_, 250, 253, 491
Tyson, P., 385
_Tysonia marylandica_, 385
_Ullmannites Beinertianus_, 199
_Ulospermum_, 497
Unger, F., 190, 194, 196, 200, 201, 203, 204, 285, 449
_Vectia_, 419, 420
_V. luccombensis_, 419
Velenovský, J., 281, 504, 505
_Völkelia_, 208–210
_V. refracta_, 208, 209
Vries, H. de, 10
Walch, J. E. J., 497
_Walchia_, 253, 338
Ward, L. F., 368, 369, 385, 409, 417, 491, 497, 582
_Wardia_, 172–174
_W. fertilis_, 171, 172
Warming, E., 25
Warren, E., 256
Watson, D. M. S., 68
Weber and Sterzel, 97, 99, 101, 104, 108
Weiss, C. E., 264, 338
Weiss, F. E., 54, 68
Welsford, E. J., 61
_Weltrichia_, 475–477
_W. Fabrei_, 477
_W. mirabilis_, 476
_W. oolithica_, 477
_Welwitschia_, 160, 161, 336, 380, 403
Wettstein, R. V., 403
White, D., 169, 172, 173, 192, 243, 255, 258, 284, 326
_Whittleseya_, 124–131
_W. brevifolia_, 128
_W. concinna_, 131
_W. elegans_, 128–131
_W. fertilis_, 129, 130
_W. integrifolia_, 131
_W. undulata_, 131
Wieland, G. R., _Passim_
_Wielandia_, 463
_Wielandiella_, 454, 463–467, 472, 473, 478, 481, 550
_W. angustifolia_, 464, 466, 467, 470
_W. punctata_, 446
Wild, G., 119
Williamson, W. C., _Passim_
Williamson and Scott, 42–46, 67, 69, 74, 75, 77
_Williamsonia_, 372, 386, 409, 412, 421–463, 494, 516, 517,
520, 524, 531–534, 538, 546
_W. angustifolia_, 463
_W. Bibbinsi_, 462
_W. bituberculata_, 457
_W. Blandfordi_, 445, 446, 517
_W. Bucklandi_, 386, 448, 449
_W. Carruthersi_, 439, 447, 448
_W. cretacea_, 461, 462
_W. Cuauhtemoc_, 446
_W. elongata_, 462
_W. Forchammeri_, 461
_W. gallinacea_, 462
_W. gigas_, 421–436, 443–447, 451, 457, 460, 472, 483
_W. hastula_, 422
_W. Haydeni_, 460
_W. indica_, 446
_W. Leckenbyi_, 439, 440, 448, 473
_W. Lignieri_, 472
_W. mexicana_, 459, 460
_W. microps_, 445
_W. minima_, 461
_W. Morieri_, 395
_W. oregonensis_, 461
_W. Otozamitis_, 460
_W. pecten_, 422, 426, 440–442, 445, 456
_W. phoenicopsoides_, 462
_W. problematica_, 461, 462
_W. pyramidalis_, 457
_W. recentior_, 463
_W. Riesii_, 461
_W. scotica_, 374, 391, 396, 403, 415, 440, 447, 449–456, 465,
478, 489
_W. setosa_, 436, 443–445
_W. Smockii_, 461
_Williamsonia_ sp., 443–446, 460
_W. spectabilis_, 435–442, 457, 445, 459, 460, 473, 476
_W. virginiensis_, 462
_W. whitbiensis_, 435, 438–442, 457, 458, 460
_Williamsoniella_, 434, 454, 467–473
_W. coronata_, 467–472
_W. Lignieri_, 472
Wills, L. T., 278
Witham, H., 35, 254, 285, 289
Worsdell, W. C., 30, 33, 34, 46, 155, 159, 160, 162, 403
_Xenoxylon phyllocladoides_, 213
Yabe, H., 578
Yates, J., 421
_Yatesia_, 386, 478
_Y. crassa_, 483
_Y. gracilis_, 483
_Y. Joassiana_, 483
_Y. Morrisii_, 484
_Y. vogesiacus_, 277, 278, 483
_Y. Yatesii_, 484
Yokoyama, M., 537, 578, 582
Young, G., 421
Young, J., 358
_Yucca_, 277
_Yuccites_, 277, 278
_Y. Schimperianus_, 281
Zalessky, M., 70, 191, 194, 197, 198, 238, 243, 244, 291–295, 358,
359, 590
_Zalesskya gracilis_, 180
_Zamia_, 11, 12, 16, 24, 30, 62, 139, 507
_Z. angustifolia_, 16
_Z. Brongniarti_, 395
_Z. crassa_, 504
_Z. floridana_, 16, 24, 25
_Z. furfuracea_, 19
_Z. gigas_, 421
_Z. Goldiei_, 522
_Z. integrifolia_, 16, 76
_Z. linifolia_, 16
_Z. Loddigesii_, 5, 16, 18
_Z. macrocephala_, 503
_Z. muricata_, 587
_Z. pectinata_, 522
_Z. praecedens_, 510
_Z. pseudoparasitica_, 19
_Z. pumila_, 9
_Z. pygmaea_, 4
_Z. Skinneri_, 587
_Z. Wallisii_, 16, 17
Zamieae, 8
_Zamiophyllum_, 529–531
_Zamiopsis_, 512
_Zamiostrobus_, 496, 503
_Z. Loppineti_, 504
_Z. orientalis_, 504
_Z. Saportana_, 505
_Zamites_, 281, 378, 379, 507, 512, 517, 520, 521, 525, 527,
529–537, 589, 590
_Z. Anderssoni_, 521
_Z. antarcticus_, 521, 527
_Z. bohemicus_, 534
_Z. borealis_, 521, 525, 530, 531
_Z. brevipennis_, 521, 525
_Z. Buchianus_, 531, 535–537
_Z. carbonarius_, 590
_Z. Carruthersi_, 535, 536
_Z. claravallensis_, 534
_Z. eathiensis_, 584
_Z. epibius_, 510
_Z. familiaris_, 505
_Z. Feneonis_, 533
_Z. gigas_, 422–426, 443, 510, 521, 530–534
_Z. iburgensis_, 534
_Z. Mantelli_, 532
_Z. Moreaui_, 533
_Z. palaeocenicus_, 510
_Z. pusillus_, 521
_Z. recta_, 534
_Z. Renevieri_, 533
_Z. Schmiedelii_, 534
_Zamites_ sp., 585
_Z. speciosus_, 521, 525
_Z. truncatus_, 532
_Z. Zitteli_, 535
Zeiller, R., _Passim_
Zigno, A. de, 281, 460, 587, 588
Zopf, W., 62, 538
FOOTNOTES:
[1] Wieland (06) p. 190.
[2] _Botanical Magazine_, Tab. 1741.
[3] Matte (04) Pl. +xi.+ fig. 185 (_Microcycas_).
[4] Thibout (96).
[5] Thibout (96) Pl. +iv.+ fig. 3. A branched microstrobilus of a
_Macrozamia_ is exhibited in the Botanical Department of the British
Museum.
[6] Pearson (06).
[7] Sohns-Laubach (90); South and Compton (08); Smith, F. G. (07).
[8] Chamberlain (13).
[9] Lang (97); (00).
[10] Chamberlain (09) p. 410.
[11] Caldwell (07).
[12] For figures and references, see Coulter and Chamberlain (10).
[13] Chamberlain (12) p. 11.
[14] Saxton (104).
[15] For an explanation of the occurrence of a single cotyledon in
_Ceratozamia_, see Dorety (08).
[16] Worsdell (00); (01); Chamberlain (11).
[17] μανός, porous, loose in texture; πυκνόϛ, compact.
[18] Sifton (15).
[19] Worsdell (00); (06). See _postea_, Chap. +xxx.+
[20] Worsdell (98²).
[21] For figures, see Mettenius (60) B.; de Bary (84) A.; le Goc (14);
Marsh (14).
[22] Wieland (06) pp. 62, 63.
[23] Matte (04) Pl. +vii.+ fig. 111.
[24] Scott (97); Matte (04) p. 164.
[25] The species _Cycas taiwanensis_ was founded by Mr Carruthers (93)
on material from Formosa, and _C. revoluta_ has also been recorded from
Formosa [Thiselton-Dyer (02) p. 559], but according to Mr Elwes it is
very doubtful whether any native Cycad occurs on the island.
[26] Engler (95) p. 92; Stapf (14).
[27] _Gard. Chron._ June 11, 1904, p. 370.
[28] _Bot. Mag._ 1909, Tab. 8232.
[29] Pearson (06).
[30] Chamberlain (12²).
[31] Chamberlain (06).
[32] Webber (01).
[33] Chamberlain (09).
[34] Hooker, J. D. (91) A. p. 98 (footnote).
[35] Pearson (06).
[36] Prof. de Vries kindly informed me in a letter that this estimate
is not to be regarded as anything more than a rough guess.
[37] Stopes (10).
[38] Caldwell (07).
[39] Bower (84).
[40] Rosen (11).
[41] Seward (95) A. pp. 15 _et seq._
[42] Braun, A. (75).
[43] Thiselton-Dyer (65) B.; _Bot. Mag._ 1909, Tab. 8242.
[44] Thiselton-Dyer (02) p. 560.
[45] _Gard. Chron._ 1904, June 11, p. 370.
[46] Seward (97).
[47] Braun, A. (75²) p. 376.
[48] _Bot. Mag._ 1818, Tab. 1969.
[49] Matte (04) p. 34.
[50] Seward (95) A. p. 5; Robertson (02) fig. 4.
[51] Vol. +ii.+ fig. 287, p. 389.
[52] Chamberlain (09).
[53] Braun, A. (75); Bornemann (56) A. Pl. +x.+
[54] Caldwell (07); Caldwell and Baker (07).
[55] _Bot. Mag._ 1859, Tab. 5121.
[56] Vol. +ii.+ p. 485.
[57] Lignier (94).
[58] Chamberlain (12³).
[59] For information on the anatomy of reproductive shoots, see Thibout
(96); Scott (97); Worsdell (98); Matte (04).
[60] Thiselton-Dyer (01); _Bot. Mag._ 1915, Tab. 8592, 8593. For
instances of monstrous cones, see Miquel (69), Wieland (02).
[61] Chamberlain (09).
[62] Dorrien-Smith (11) p. 287.
[63] Stopes (04) p. 467.
[64] Stopes (04) p. 438, fig. 1; Warming (77) Pl. +iii.+
[65] Chamberlain (06).
[66] Kershaw (12).
[67] Stopes (04).
[68] Oliver (13).
[69] Thoday (Sykes) (11); Sykes (10); Thoday (Sykes) and Berridge (12).
[70] Salisbury (14) p. 72.
[71] Kraus (96).
[72] Pearson (06).
[73] Rattray (13).
[74] Worsdell (96); (01).
[75] See _ante_, p. 5.
[76] Chamberlain (11); Wieland (06).
[77] Pavolini (09); Marsh (14).
[78] Matte (08).
[79] Dorety (08²); (09).
[80] Worsdell (96).
[81] Matte (04) especially pp. 185–202. See also Worsdell (00); (06)
etc.
[82] Matte (04) p. 210.
[83] Worsdell (98²).
[84] Caldwell (07).
[85] Carano (04); le Goc (14); Marsh (14).
[86] Le Goc (14); Marsh (14).
[87] Seward (06).
[88] Robertson (02).
[89] Seward (12²).
[90] Worsdell (98).
[91] Lignier (92).
[92] Nestler (95); Porsch (05); Thomas and Bancroft (13); Dušánek (13).
[93] Binney (66).
[94] Unger (50) A. p. 378.
[95] Williamson (69).
[96] Williamson (73) A.
[97] Gourlie (44).
[98] See page 186.
[99] Solms-Laubach (91) A. pp. 8, 217, 218.
[100] Solms-Laubach (91) A. pp. 8, 217, 218.
[101] Vol. +ii.+ p. 220.
[102] Nathorst (14) Pl. +vii.+ fig. 1.
[103] Nathorst (04) B. p. 11.
[104] Potonié (99) B. p. 171.
[105] Arber, E. A. N. (02).
[106] Williamson and Scott (95).
[107] Williamson and Scott (95) p. 720.
[108] Williamson (90) Pl. +xii.+ fig. 6.
[109] Williamson (90) Pl. +xiii.+ fig. 3, _b._
[110] Williamson and Scott (95) Pl. +xxiii.+ fig. 8.
[111] _Ibid._ p. 722.
[112] Worsdell (06) pp. 140 _et seq._
[113] Lomax (02).
[114] Brenchley (13).
[115] For a description of the method, see Salisbury (13).
[116] Williamson (73) A. p. 403.
[117] Williamson (90).
[118] Vol. +ii.+ p. 299, fig. 232.
[119] Bower (12) Pls. +xxx.+ +xxxiii.+
[120] Höhlke (02).
[121] Williamson (74) Pl. +li.+ fig. 1.
[122] Scott (09) B. fig. 139, p. 375.
[123] Brongniart (28) A. p. 199, Pl. +lii.+ For synonymy, see Kidston
(11) p. 42.
[124] Zeiller (88) A. p. 82, Pl. +vi.+
[125] See also Kidston (06) B, fig. 5, p. 417; Renier (10²), Pls. 60,
70.
[126] Kidston (06) B.
[127] Stur (77) p. 257, Pls. +xxv.+ +xxvi.+
[128] Oliver (05) fig. 6.
[129] Gothan (13) p. 40.
[130] Johnson (11).
[131] Kidston (05).
[132] Kidston (06) B.
[133] Zeiller (83) B.
[134] Gothan (13) p. 49.
[135] Chodat (08) B.
[136] Scott (08) B. p. 292.
[137] Weiss, F. E. (12).
[138] Vol. +ii.+ p. 532.
[139] Scott (09) B. p. 400.
[140] Kidston (06) B.
[141] Benson (04) B.
[142] In his account of the ovule of _Stangeria_ Lang (00) discusses
the possibility of homologising the ovule with a sorus consisting of
one sporangium.
[143] Williamson (77) B. p. 234.
[144] Oliver and Scott (03): (04).
[145] Hörich (06) p. 48.
[146] Kidston (05²) B.
[147] Grand’Eury (05²) B.
[148] Oliver and Scott (04) Pl. +x.+ fig. 28; McLean (12).
[149] Williamson (76).
[150] Oliver (03) p. 462.
[151] Benson (08).
[152] McLean (12).
[153] For figure, see Lotsy (09) p. 714.
[154] Scott (11) p. 105.
[155] Chodat (08) B.
[156] Scott (03).
[157] Scott (09) B. p. 220. See also Oliver (05); Oliver and Scott (04)
p. 231.
[158] Gibbs (12) p. 46.
[159] Oliver (06).
[160] Stopes(05); Prankerd (12).
[161] Sykes (10) p. 219; Thoday (Sykes, M. G.) (11) p. 1124.
[162] Shaw (08).
[163] Benson and Welsford (09) p. 633.
[164] Kershaw (09) p. 359.
[165] Benson (08).
[166] Zopf (92) Pls. +i.+ +ii.+
[167] Burlingame (15).
[168] Williamson (77) B.
[169] Williamson (76) p. 160.
[170] Butterworth (97).
[171] Oliver (09) p. 74.
[172] Prankerd (12).
[173] Vol. +ii.+ p. 364, fig. 270.
[174] Berridge (11).
[175] Lignier (13²).
[176] Nathorst (14) p. 29.
[177] Arber (05).
[178] Oliver (09).
[179] Arber (14) p. 102.
[180] Vol. +ii.+ pp. 294, 295.
[181] Vol. +ii.+ p. 529, fig. 352.
[182] Carpentier (11) p. 3.
[183] See page 66.
[184] Kidston (14) p. 160, Pl. +vii.+ figs. 1, 2.
[185] _Ibid._ p. 161, Pl. +xvi.+ figs. 9, 10.
[186] Grand’Eury (05²) B.
[187] Carpentier (11).
[188] Arber, E. A. N. (08).
[189] Nathorst (08) p. 10, Pl. +ii.+ figs. 19–21.
[190] Stopes (14) p. 74, Pls. +xvii.+ fig. 45, +xxv.+ fig. 69,
text-fig. 15.
[191] See page 124.
[192] Nathorst (14) p. 23, Pl. +xv.+ fig. 43.
[193] Carpentier (13) p. 391.
[194] Williamson (76) B.
[195] Williamson (87) p. 297.
[196] Felix (86) A. p. 51.
[197] Williamson and Scott (94).
[198] Hick (95) p. 114.
[199] Stopes and Watson (08) Pl. +xvii.+ fig. 1.
[200] Weiss, F. E. (13).
[201] Williamson and Scott (95) p. 739.
[202] White (99) B. p. 40.
[203] Felix (86) A.
[204] Zalessky (10).
[205] Kubart (14); (11).
[206] Corda (45) A. Pl. +xvi.+
[207] Kubart (08) fig. 3.
[208] Vol. +ii.+ p. 310, fig. 237, C; p. 311, fig. 238.
[209] Williamson (73) A. p. 403.
[210] Benson (14).
[211] Williamson (72²).
[212] Williamson (73) A.
[213] Williamson (90).
[214] Williamson and Scott (95).
[215] Scott (15).
[216] Scott (15).
[217] Jeffrey (05) Pl. +iii.+ fig. 21.
[218] Kidston (91²) B. p. 49.
[219] Williamson and Scott (95) p. 753.
[220] Williamson and Scott (95) Pl. +xxvii.+ fig. 28.
[221] Stur (77) p. 236, Pls. +xiii.+ +xiv.+
[222] Benson (14).
[223] Oliver (09) p. 111.
[224] Grand’Eury (05²).
[225] Carpentier (11) Pl. +xii.+ fig. 1.
[226] For a fuller description, see Williamson and Scott (95).
[227] Scott (09) B. p. 410; (15).
[228] Scott (15).
[229] Renault (79) B. p. 276, Pl. +xiv.+ figs. 4–8; (96) A. p. 251, Pl.
+lxv.+ figs. 1, 2.
[230] Renault (96) A. pp. 253, 255.
[231] _Ibid._ p. 252, Pl. +lxv.+ figs. 3, 6.
[232] Kubart (14).
[233] Dr. Scott who has seen sections of this species tells me that it
is a striking intermediate form.
[234] Johnson (12).
[235] Scott (15).
[236] Goeppert and Stenzel (81).
[237] Lotsy (09) p. 723.
[238] Zeiller (05) B. p. 725.
[239] Schenck (93) B. Pls. +I–V+, etc.
[240] White, D. (05²) B. p. 389.
[241] Solms-Laubach (97) Pl. +vi.+ fig. 3.
[242] Penhallow (97).
[243] Cotta (32) B. p. 59.
[244] Brongniart (49) A. p. 57.
[245] Scott (99).
[246] Arber, E. A. N. (03).
[247] Renault (76) B.
[248] Arber, E. A. N. (03).
[249] Kidston (05²) B.
[250] Scott (09) B. p. 441 (footnote).
[251] Scott (14).
[252] De Fraine (14).
[253] De Fraine (14) p. 259. See also Kisch (13).
[254] Cotta (32) B. p. 66, Pl. +xiii.+ The well-preserved specimen
figured by Cotta in his Pl. +xiii.+ fig. 2 is in the Dresden Museum.
[255] Goeppert (65) A. p. 209, Pls. +xl.–xliii.+
[256] Goeppert and Stenzel (81).
[257] Weber and Sterzel (96) B.
[258] Schenk (89).
[259] Weber and Sterzel (96) B. p. 51; Schenk (89).
[260] No. V. 8093.
[261] Schenk (82). See also Zeiller (90) B. p. 286.
[262] No. 13767, probably identical with _M. stellata_ var. _lignosa_
Weber and Sterzel.
[263] Mougeot (52) A. p. 36, Pl. +iii.+ figs. 8–10.
[264] Weber and Sterzel (96) B. p. 108.
[265] _Ibid._ p. 56.
[266] Weber and Sterzel (96) B. p. 63.
[267] _Ibid._ p. 66.
[268] Renault (96) A. p. 297; (93) A. Pl. +lxxi.+ figs. 1–6.
[269] Brongniart (49) A. p. 77.
[270] Cotta (32) B. p. 63, Pl. +xii.+ figs. 6, 7.
[271] Schenk (89) p. 339.
[272] Weber and Sterzel (96) B. p. 541, Pls. +ii.+ +iii.+
[273] Goeppert and Stenzel (81) p. 123, Pl. +xvi.+ figs. 13–15;
Solms-Laubach (97); Weber and Sterzel (96) B. p. 79, Pls. +iv.+ +v.+
+ix.+
[274] Goeppert and Stenzel (81) Pl. +iii.+ fig. 15.
[275] Solms-Laubach (97) p. 179.
[276] Scott (99) p. 90.
[277] Weber and Sterzel (96) B. p. 95, Pl. +ix.+
[278] Solms-Laubach (97).
[279] Renault (76) B. p. 7.
[280] Grand’Eury (77) A. p. 122; (90) A. p. 287.
[281] Seward (93).
[282] Penhallow (97).
[283] Williamson (76) B. p. 8.
[284] Zeiller (90) B.
[285] Weber and Sterzel (96) B. p. 102, fig. 26.
[286] Seward (93).
[287] Renault (76) B.
[288] Penhallow (97).
[289] Weber and Sterzel (96) B. p. 139.
[290] Page 142.
[291] Holden, H. S. (10).
[292] Vol. +ii.+ p. 568, fig. 371.
[293] Kidston (87) B.
[294] Bertrand, P. (13) p. 117.
[295] Carpentier (11) p. 10.
[296] Lesquereux (80) A. p. 328, Pl. +xlviii.+
[297] Bertrand, P. (13) p. 120.
[298] Zeiller (99) B. p. 52, Pl. +iv.+ fig. 19.
[299] Carpentier (11) p. 12, Pls +xvi.+ +xvii.+
[300] Carpentier (13) p. 387, Pl. +x.+ figs. 1–6.
[301] Bertrand, P. (13) p. 125.
[302] Kidston (14) p. 108.
[303] _Ibid._ p. 112, Pl. +viii.+ figs. 1–7.
[304] Carpentier (11) p. 13, Pl. +xvi.+ fig. 1.
[305] See page 127.
[306] Renault and Zeiller (88) A. p. 273, Pl. +xxxi.+ figs. 2, 4.
[307] Zeiller (90) B. Pl. +xi.+ fig. 9; (00)² B. p. 108, fig. 83. See
Vol. +ii.+ p. 572.
[308] Bertrand, P. (13) p. 132, Pl. +vi.+ fig. 7.
[309] Carpentier (13) p. 375, Pl. +viii.+ fig. 1.
[310] Bertrand, P. (13) p. 135, pl. +vi.+ figs. 2–4.
[311] Kidston (04); (04²); (14) p. 107, fig. 5.
[312] Renault and Zeiller (88) A. Pl. +lxxii.+ fig. 19.
[313] Grand’Eury (90) A. Pl. +vi.+ fig. 6.
[314] Kidston and Jongmans (11).
[315] Grand’Eury (04); (04²).
[316] _Cf._ also _Rhabdocarpus conicus_ and other forms figured by
Renault (93) A. Pl. +lxxxvi.+
[317] Brongniart (74) Pl. +xxi.+; (81) Pls. +ix.–xi.+
[318] See Chapter +xxxv.+
[319] See Chapter +xxxv.+
[320] P. Bertrand (13) p. 129, Pl. +vii.+ figs. 1, 2, 7.
[321] See Chapter +xxxv.+
[322] See page 139.
[323] Arber (14) pp. 93, 103, Pl. +viii.+ fig. 47.
[324] P. Bertrand (13) p. 121.
[325] Grand’Eury (04²) p. 785 (footnote).
[326] Chodat (08) B. p. 33, fig. 15.
[327] Lotsy (09) p. 72.
[328] Grand’Eury (04); (04) B.
[329] Brongniart (28) A. p. 137.
[330] Williamson (77) B.; Scott and Maslen (07) p. 90 (footnote) also
refer to _Trigonocarpon_ as having been used by Brongniart in 1849.
[331] Brongniart (49) A. p. 91.
[332] Lindley and Hutton (35) A. p. 172.
[333] Hooker and Binney (55).
[334] Lindley and Hutton (33) A. Pl. 87.
[335] Wild (00).
[336] Scott and Maslen (07) p. 96.
[337] Scott and Maslen (07).
[338] Arber, A (14).
[339] Oliver (04) p. 97.
[340] Salisbury (14) p. 65.
[341] Arber, E. A. N. (14) p. 95, Pl. +vi.+ fig. 1.
[342] Lindley and Hutton (37) A. Pl. 221; Arber _loc. cit._ p. 95, Pl.
+vi.+ fig. 8.
[343] Fiedler (57) Pl. +xxvii.+ fig. 39.
[344] Lesquereux (80) A. Pl. 85; (84) A. Pl. +iii.+
[345] Salisbury (14).
[346] See page 115.
[347] Renault (96) A. p. 399; (93) A. Pl. +lxxxv.+ fig. 9; Salisbury
(14) p. 66.
[348] Sellards (03) p. 90; (07).
[349] Lesquereux (80) A. p. 93; (84) A. p. 733, Pl. +xciv.+ figs. 1, 2.
[350] Stopes (14) p. 74. See page 66.
[351] Nathorst (14) p. 23. See page 67.
[352] Geinitz (63) p. 525, Pl. +vi.+
[353] Goeppert (65) p. 161, Pls. +XXIII–IV.+ The specimens figured by
Goeppert, which I saw some years ago in the Breslau Museum, do not show
the finer characters very clearly.
[354] Goeppert (65) p. 164, Pls. +XXIV–V.+
[355] Schimper (72) A. p. 358.
[356] Kidston (84) Pl. +v.+ fig. 2.
[357] Renault (96) A. p. 379, fig. 73.
[358] Zeiller in Douvillé and Zeiller (08).
[359] See page 124.
[360] Newberry (54).
[361] Lesquereux (80) A. p. 523, Pl. +iv+; (84). For other references
see Potonié (04).
[362] White, D. (01).
[363] Thomas, H. H. (12); Kidston (14) p. 166.
[364] Renault (93) A. Pl. +lxxii+; (96) A. p. 268. See page 137.
[365] Page 111.
[366] White (01) p. 108.
[367] _Ibid._ p. 104, Pl. +vii.+ figs. 3, 3_a_.
[368] Matthew (10).
[369] Stopes (14) p. 78.
[370] Kidston (14) p. 166, Pl. +xv.+ figs. 1–10.
[371] Saporta (78).
[372] Eichwald (55) Pl. +xviii.+ fig. 18; (60) p. 252.
[373] Goeppert (65) p. 157, Pl. +xxi.+ fig. 4.
[374] Saporta (78²).
[375] Saporta and Marion (85) pp. 16, 68.
[376] Grand’Eury (77) A. p. 192.
[377] Zeiller (00²) B. p. 217.
[378] Kutorga (42).
[379] Unger (50) A. p. 334.
[380] Renault (96) A. p. 262.
[381] No. V. 8114.
[382] A specimen from Orenburg in the Dresden Museum shows the same
surface-features as the British Museum specimen and agrees with the
originals of Goeppert’s figures which are in the Breslau University
Museum.
[383] Renault (96) A. p. 265, fig. 43.
[384] Renault (96) A. p. 262, Pl. +xxii.+ fig. 1.
[385] Grand’Eury (77) A. p. 196, Pl. +xvi+; (90) A. Pl. +viii.+ fig. 1;
Zeiller (06) B. p. 192.
[386] Renault and Zeiller (90) A. p. 556, Pl. +lvii.+
[387] Grand’Eury (04).
[388] Roehl (69) B. Pl. +xvii.+
[389] Saporta and Marion (85) fig. 29.
[390] Renault (96) A, p. 267, Pl. +lxxii.+
[391] Solms-Laubach (91) A. p. 126.
[392] See Chapter +xxxv.+
[393] Zeiller (06) B. p. 227.
[394] Saporta and Marion (85) fig. 37, p. 76.
[395] Schmalhausen (87) Pl. +v.+ figs. 7–9: this specimen, figured as
_Dolerophyllum Goepperti_, is very similar to _Cordaites circularis_
[Grand’Eury (90) A. Pl. +vi.+ fig. 15].
[396] Zeiller (02) B. p. 34, Pl. +iv.+ figs. 9, 10.
[397] Bertrand, P. (13) p. 131, Pl. +vii.+ fig. 6.
[398] Zeiller, _loc. cit._ p. 37.
[399] Feistmantel (79) B. p. 30; (81) A. p. 59, Pl. +xxx.+ fig.
14; (82) B. p. 43, Pl. +xv.+ figs. 5–12. Dr Arber [(05) B. p. 205]
has substituted for _Carpolithes_ the more appropriate designation
_Cardiocarpus_.
[400] Renault (96) A. p. 329; (93) A. Pl. +lxxiii.+
[401] Schimper and Mougeot (44) A. p. 31. Seward (08) B. p. 101.
[402] Brongniart (49) A. p. 60.
[403] Renault (96) A. p. 299; (93) A. Pls. 66, 67.
[404] Grand’Eury (08) B. p. 1242.
[405] Goeppert and Stenzel (81) p. 125; Weber and Sterzel (96) B. p.
79. Solms-Laubach [(97) p. 196] draws attention to the resemblances
between the leaf-scars of _Colpoxylon_ and _Medullosa_.
[406] Klein (81) Pls. +xxii.–xxiv.+
[407] Bancroft (13).
[408] Page 205.
[409] Scott (06).
[410] de Fraine (12).
[411] Scott (06) p. 53.
[412] de Fraine (12).
[413] Reference should be made to the helpful drawings of models of the
vascular system in Miss de Fraine’s paper.
[414] For additional figures of the principal types of _Medullosa_, see
Miss Bancroft’s paper (14).
[415] Lotsy (09) p. 719.
[416] Scott (14) p. 998.
[417] Scott (99) p. 89.
[418] Worsdell (96); (98); (00); (06) etc.
[419] Matte (04); (08). See also Bancroft (14); Dorety (09).
[420] Scott (97).
[421] Worsdell (06).
[422] Shaw (09).
[423] de Fraine (12) p. 1060.
[424] Sykes, M. G. (10²); (10).
[425] Matte (04) Pls. +xv.+ +xvi.+
[426] de Fraine (12).
[427] Scott (06) p. 64.
[428] Chodat (08) B. p. 38.
[429] Worsdell (06) pp. 140 _et seq._
[430] Scott (09) B. p. 464.
[431] For a general summary of ‘Pteridosperm anatomy and its relation
to that of the Cycads’ see Bancroft (14).
[432] See p. 6.
[433] Dorety (09²) p. 144.
[434] Goeppert and Stenzel (81) p. 126, Pl. +xvii.+
[435] Schenk (89) p. 525, Pl. +i.+ figs. 1–16.
[436] Solms-Laubach (96) B. p. 62; (97) p. 197; (10) p. 542, Pl. +iii.+
fig. 9.
[437] P. Bertrand (08); (11) p. 47 (footnote).
[438] In a recent note on _Steloxylon_ to which Dr Scott has drawn my
attention Bertrand records the genus from Saalfeld (Upper Devonian)
and expresses the opinion that _Steloxylon_ may be a condition of
_Cladoxylon_ and not a distinct type—P. Bertrand (14) p. 448.
[439] Vol. +ii.+ p. 576.
[440] Schlotheim (04) A. Pl. +x+, fig. 19.
[441] For synonymy, see Kidston (86) A. p. 125 and Potonié (93) A. p.
81.
[442] Sterzel (83); (86²) B.; Zeiller (06) B. p. 60.
[443] Stur (85) B. p. 293.
[444] Grand’Eury (05).
[445] See also Zeiller (05) B. p. 725.
[446] Grand’Eury (77) A. Pl. +xxxiii.+ fig. 7.
[447] Vol. +ii.+ p. 419, fig. 297.
[448] Zeiller (06) B. p. 63.
[449] For a more complete synonymy, see Kidston (03) B. p. 770.
[450] Brongniart (28²) A. Pls. +xlvi.+, +xlvii.+; Lebour (77) Pls.
+xxxiii.–iv.+
[451] Kidston (14) p. 156; Duns (72).
[452] Howse (88) p. 45.
[453] Arber, E. A. N. (14) p. 97; (09) p. 29, Pl. +i.+ fig. 5.
[454] Kidston (83) B. p. 540, Pl. +xxxii.+ fig. 3.
[455] White refers some fronds from the Missouri Coal Measures to
_Eremopteris_, but their generic identity with the type-species is open
to doubt. White (99) B. p. 16.
[456] White (04) B.
[457] Vol. +ii.+ p. 376.
[458] Goeppert (36²) A. p. 216.
[459] See page 64.
[460] Nathorst (14) p. 30, Pl. +xv.+ figs. 18, 60–68.
[461] Schmalhausen (83) Pl. +iv.+ figs. 13–15.
[462] Heer (77) A. Pl. +v.+ pp. 23–25.
[463] Nathorst (14) p. 30, Pl. +xv.+ fig. 59.
[464] Kidston (86) p. 70, Pl. +iii.+ fig. 6.
[465] Arber, E. A. N. (14) p. 96, Pl. +vi.+ fig. 12.
[466] Seward (99) B.
[467] For additional figures, see Seward (99) B.
[468] Vol. +ii.+ p. 326.
[469] Scott (09) B. p. 476.
[470] Gordon (12). The rich development of secretory tissue suggested
the name _Rhetinangium_ (ῥητίνη, resinous gum): the same prefix had
previously been adopted by Renault in his genus _Retinodendron_
[Renault (96) A. p. 365].
[471] Scott (15).
[472] Page 90.
[473] Kubart (14).
[474] Kidston and Gwynne-Vaughan (12).
[475] Similar to the _Dictyoxylon_ type except in the independent and
not anastomosing course of the stereome strands.
[476] Kidston and Gwynne-Vaughan (12) p. 269.
[477] Renault (96) A. p. 307.
[478] Renault (96) A. p. 308, figs. 55, 56.
[479] Seward (97²).
[480] Scott (00) B. p. 364.
[481] A second band is sometimes present. Scott (00) B. p. 484.
[482] πτύξ, a fold.
[483] Renault (89); (96) A; (93) A. Pl. +lxix.+
[484] Scott (09) B. p. 492.
[485] Klein (81).
[486] Richter and Unger (56) B.
[487] Unger (54) p. 599.
[488] Solms-Laubach (96) B.
[489] Zalessky (11).
[490] Scott and Jeffrey (14).
[491] κάλυμμα, a veil or covering.
[492] White (05²) B. p. 384.
[493] Richter and Unger (56) B. p. 174, Pl. +x.+ figs. 1–3;
Solms-Laubach (96) B. p. 73; Scott (12) p. 1027.
[494] Scott and Jeffrey (14) p. 326.
[495] _Ibid._ p. 317, Pls. 27, 28, 30, 31.
[496] Scott (02).
[497] Scott and Jeffrey (14) p. 328, refer to a specimen over 6 cm. in
diameter: these authors give several excellent figures of _Kalymma_.
[498] Dawson and Penhallow (91).
[499] ἐριστός, to be disputed.
[500] Zalessky (11).
[501] Scott (99²).
[502] Scott (02).
[503] Scott (02) p. 336.
[504] Page 175.
[505] Scott (12) p. 1027.
[506] Tuzson (09).
[507] Unger and Richter (56) B. p. 178.
[508] Scott and Jeffrey (14) p. 364.
[509] Solms-Laubach (96) B.
[510] P. Bertrand (08).
[511] Unger and Richter (56) B. p. 179, Pl. +xii.+ figs. 6, 7;
Solms-Laubach (96) B. p. 52, Pl. +ii.+ figs. 11, 13(?).
[512] Unger and Richter, Pl. +xii.+ figs. 3, 4; Solms-Laubach (96) B.
Pl. +xi.+ fig. 10.
[513] See footnote 3, p. 205.
[514] Solms (96) B. p. 53.
[515] Dawson (81) A. p. 299, Pl. +xii.+ figs. 1–9; Solms-Laubach (91)
A. pp. 173, 188.
[516] This type is represented in the Geological Survey Collection (No.
15871).
[517] For figures, see Solms-Laubach (96) B. Pl. +ii.+
[518] No. 15870. Unger and Richter (56) B. Pl. +vii.+ figs. 19–21.
[519] Page 472, fig. 324.
[520] Solms-Laubach (10) p. 540.
[521] Bertrand, P. (11) p. 47.
[522] Since this account was printed my attention has been drawn by
Dr Scott to a note by Bertrand in which he considerably modifies
his views. He finds that _Hierogramma_ and _Syncardia_ are probably
different states of the _petiole_ of _Cladoxylon_ and while agreeing
with Solms-Laubach’s conclusions he has been able to add important
new facts. Bertrand has now given up the opinion that _Clepsydropsis_
is the petiole of _Cladoxylon_. For further details students should
consult the preliminary note which it is hoped will be followed by a
fully illustrated memoir [Bertrand, P. (14)].
[523] Solms-Laubach (10) p. 537, Pl. +iii.+ figs. 7, 11, 13.
[524] Bancroft (13).
[525] After the late Herr Völkel of Neurode.
[526] Solms-Laubach (10), Pl. +iii.+ figs. 1–4.
[527] Goeppert (52) Pl. +xii.+
[528] Solms-Laubach (91) A. p. 164.
[529] P. Bertrand (08).
[530] The name _Palaeopitys_, with which _Protopitys_ might be
confused, was used by McNab for an imperfect specimen from the Old Red
Sandstone of Scotland described as _Palaeopitys Milleri_; McNab (70).
[531] Kraus (92).
[532] Solms-Laubach (93).
[533] Vol. +ii.+ p. 212, fig. 200, A, B.
[534] See page 206.
[535] In the form of the pits on the tracheids and in the structure of
the medullary rays the English species (as represented in Dr Kidston’s
Collection) agrees very closely with Goeppert’s type.
[536] Gothan (07²) p. 10.
[537] Renault (79) B. p. 272, Pls. +xiii+, +xiv.+
[538] Bertrand and Renault (82); Bertrand, C. E. (89); Renault (96) A.
p. 279, (93) A. Pls. +lxxiv.+ +lxxv+; Scott (09) B. p. 500. See also
Scott and Maslen (10) Maslen (11) p. 409.
[539] Grand’Eury (05).
[540] Lignier (11²).
[541] Renault (80).
[542] Renault (93) A. Pl. +lxxiv.+ fig. 8.
[543] See page 270.
[544] See Vol. +i.+ p. 76, fig. 13.
[545] See Vol. +iv.+
[546] For restorations, see Grand’Eury (77) A. Pl. +d+; good examples
of foliage-shoots are figured by Renault and Zeiller (88) A. Pls.
+lxvi.+ +lxxxi.+; Grand’Eury (90) A. Pl. +lxiv.+; Kidston (02) B. Pl.
+lxiv.+ fig. 2.
[547] Renault (79) B. Pl. +xvi.+ fig. 1; Lignier (13²). Cf.
_Dolerophyllum_, p. 133.
[548] Sternberg (23) A. Pl. +xviii.+
[549] Brongniart (49) A. p. 65.
[550] Unger (50) A. p. 277.
[551] Tuzson (09) p. 18.
[552] Grand’Eury (77) A. p. 257.
[553] Schenk in Schimper and Schenk (90) A. p. 243.
[554] Endlicher (47) p. 298.
[555] Scott (12) p. 1024.
[556] Grand’Eury (05).
[557] Benson (12).
[558] Scott (12) p. 1022.
[559] Grand’Eury (77) A. p. 208.
[560] Grand’Eury (90) A. p. 321.
[561] Renault (79) A. Pl. +xvi.+ fig. 7.
[562] Lesquereux (78) p. 318.
[563] Felix (86) A. Pl. +iii.+ fig. 1.
[564] Renault (79) A. Pl. +xvi.+ fig. 11 bis; Wills, L. (14).
[565] Renault (79) A. Pl. +xvi.+ fig. 5; Stopes (03) Pl. +ix.+ fig. 1;
Lignier (13²).
[566] Benson (12).
[567] Lignier (13²).
[568] Germar (48) B. p. 55, Pl. +xxiii.+
[569] Kidston (93) A. Pl. +iv.+ fig. 16; (02) B. Pl. +lxiv.+ fig. 3.
[570] Kidston (93) A. p. 352.
[571] Lindley and Hutton (33) A. Pl. 95.
[572] Howse (88) p. 112, fig. 7.
[573] Geinitz (55) A. p. 40, Pl. +xxi.+ figs. 7–16.
[574] Kidston (93) A. p. 355.
[575] Lesquereux (80) A. p. 537, Pl. +lxxviii.+
[576] Geinitz (62) p. 148, Pl. +xxxv.+
[577] Sternberg (23) A. Pl. +xviii.+
[578] Corda (45) A. Pl. +xxiv.+ fig. 8.
[579] Feistmantel (72) p. 293.
[580] Lesquereux (78).
[581] White (99) B. p. 260, Pls. +iii.+ +xvi.+ +xlvi.+
[582] Zeiller records the same fungus on leaves of _Cordaites_
(_Noeggerathiopsis_) _Hislopi_ from Tonkin; Zeiller (03) B. p. 151.
[583] Stopes (14) p. 82.
[584] Schmalhausen (87) Pl. +vi.+
[585] Grand’Eury (77) A. p. 218, Pl. +xx.+ figs. 1–4.
[586] Zeiller (06) B. p. 182, Pl. +xlvi.+; Grand’Eury (90) A. Pl.
+vii.+ figs. 1, 2.
[587] Lignier (13²).
[588] Lesquereux (78) p. 318; (80) A. Pl. +lxxvii.+
[589] Cambier and Renier (10); Renier (10²) Pl. 118.
[590] See _postea_.
[591] Goeppert (64) A. Pl. +xxii.+ fig. 2.
[592] Weiss, C. E. (72) p. 199.
[593] Grand’Eury (77) A. Pl. +xviii.+; Renault and Zeiller (88) A. Pl.
+lxvi.+
[594] Weiss, C. E. (72) p. 195.
[595] Kidston (02) B. Pl. +lxiv.+ fig. 2.
[596] Zeiller (80) A. p. 146, Pl. +clxxv.+ fig. 1; Grand’Eury (77) A.
p. 225; (90) A. Pl. +vii.+ fig. 5; Renault and Zeiller (88) A. Pl.
+lxvii.+ figs. 1, 2.
[597] Lesquereux (80) A. p. 539.
[598] Lesquereux (78) p. 322.
[599] Schmalhausen (87) Pl. +vi.+ figs. 4–6.
[600] Grand’Eury (90) A. p. 325, Pl. +vi.+ fig. 15.
[601] Schmalhausen (87) Pl. +v.+ figs. 7–9.
[602] Lesquereux (80) A. p. 535, Pl. +lxxxvii.+ figs. 2–4.
[603] Grand’Eury, _loc. cit._ p. 324, Pl. +iv.+ fig. 14.
[604] Renault and Zeiller (88) A. p. 603, Pl. +lxiii.+ fig. 6.
[605] Dawson (90) p. 3.
[606] Goeppert (45²) p. 7, Pls. +xxvii.+ +xxviii.+
[607] Zalessky (12) p. 36; (12²). See also Gothan (11).
[608] Kosmovsky (92).
[609] Schmalhausen (79) A. p. 32; Zeiller (96) A.
[610] Zeiller (03) B. For other references see Seward (14).
[611] Wieland (13).
[612] McCoy (74) B. Decade +iv.+ p. 22.
[613] Wieland (13).
[614] Newberry (88) p. 350.
[615] Feistmantel (79²) p. 23; (80²).
[616] Bunbury (61) B. p. 334.
[617] Mellor and Leslie (06) B.
[618] White (08) B. p. 549.
[619] Arber (03) B. p. 178, gives references to other authors.
[620] Zeiller (03) B. p. 149, Pl. +xl.+
[621] Zalessky (12).
[622] White (08) B. p. 549.
[623] Seward and Leslie (08) B. p. 120.
[624] Zalessky (13) p. 20, Pl. +ii.+ figs. 4–6.
[625] The results have not yet been published (September, 1915).
[626] Zalessky (13) p. 23, Pls. +i.+ fig. 4; +ii.+ figs. 7, 9; +iii.+
figs. 3, 5–8, 10, 11.
[627] Schmalhausen (79) A. p. 29.
[628] Zeiller (96) A. (02).
[629] Schmalhausen (87) B. p. 37.
[630] Feistmantel (79²) p. 26; Arber (05) B. p. 186.
[631] Feistmantel (82) p. 42, Pl. +xiv.+; White (08) B. Pl. +x+;
Schmalhausen (87) B.
[632] Schmalhausen (87) B. Pls. +v.+, +vii.+
[633] Zeiller (03) B. Pl. +xl.+
[634] Feistmantel (79²) Pl. +xiii.+ fig. 6.
[635] Feistmantel (90) A. Pl. +xxi.+ figs. 1, 2.
[636] Zeiller (02) B. Pl. +vii.+ fig. 6.
[637] Renault (79) B. p. 287.
[638] Renault and Zeiller (88) A. Pl. +lxxi.+
[639] Harshberger (98).
[640] Artis (25) A. Pl. +viii.+
[641] Sternberg (38) A. p. 192. For examples of _Artisia_, see also
Renault and Zeiller (88) A. p. 581, Pl. +lxv.+
[642] Zeiller (06) B. p. 189.
[643] Dawson (46) p. 135.
[644] Williamson (51).
[645] Lignier (95) Pl. +vii.+ fig. 13.
[646] Gothan (05) p. 28.
[647] See page 199.
[648] Renault (79) B. p. 288.
[649] See page 295.
[650] Felix (86) A. p. 56; Knowlton (90); Zeiller (95) B. p. 627;
Penhallow (00) p. 54.
[651] Potonié (02) p. 229.
[652] Gothan (05) p. 13.
[653] Gothan (05) p. 15.
[654] Sterzel (03).
[655] See Chap. +xlv.+
[656] Williamson (77) A. p. 226, Pls. +vii.–ix.+; (80) A. p. 516, Pl.
+xx.+ fig. 16; (83²) A. p. 470.
[657] Thomson and Allin (12); Thomson (13) p. 14.
[658] Penhallow (00) p. 76.
[659] White (08) B. p. 583.
[660] Seward and Ford (06) B. p. 341.
[661] Penhallow (00) p. 64, fig. 12.
[662] See page 293.
[663] Gothan (05) p. 16.
[664] See page 259.
[665] Thomson (13) p. 19.
[666] Arber (05) B. p. 191. See _postea_, p. 255.
[667] An account of this wood is being published by Miss Holden.
[668] Matthew (10) p. 77, Pls. +i.+, +ii.+
[669] Goeppert and Stenzel (88) p. 10.
[670] Penhallow (00) p. 67.
[671] Sterzel (00); (03); (12). See also Goeppert (80).
[672] Goeppert and Stenzel (88) Pl. +ii.+ fig. 14.
[673] Witham (33) A.
[674] Scott (09) B. p. 528, fig. 190. See also Penhallow (00) p. 62,
with references to literature.
[675] Thomson (13) p. 19.
[676] _Ibid._ p. 16.
[677] Felix (86) A. Pl. +v.+ fig. 4.
[678] White (08) B. p. 579, Pl. +xiii.+
[679] _Ibid._ p. 583, Pl. +xiv.+
[680] Arber (05) B. p. 191, figs. 40–43.
[681] Crié (89).
[682] Shirley (98) p. 14; Arber (05) B. p. 201.
[683] Warren (12).
[684] Dawson (63²).
[685] Penhallow (00) figs. 13, 14, 17.
[686] Arber, E. A. N. (13²).
[687] Zeiller (95) B. p. 619, Pl. +ix.+ figs. 8–19.
[688] White (08) B. p. 577.
[689] Renault (96) A. p. 350; (93) A. Pl. +lxxvii.+
[690] Gothan (10) p. 5, Pl. +i.+ figs. 1–3.
[691] Nathorst (11³) p. 222.
[692] Renault (96).
[693] Williamson (72²).
[694] Williamson (74) A. p. 67.
[695] Renault (79) B. p. 294, Pl. +xv.+ figs. 13–17. See also Scott
(09) B. p. 531, fig. 191.
[696] Osborne (09).
[697] Williamson (74) A. Pl. +ix.+ fig. 56.
[698] Mellor and Leslie (06) B.
[699] Brongniart (22) A. Pl. +xiv.+ fig. 7.
[700] Renault and Zeiller (90) A. p. 593.
[701] Lindley and Hutton (33) A. Pl. +lxxxii.+
[702] Morris (40) A. Pl. +xxviii.+ fig. 5.
[703] Carruthers (72³) B.
[704] Goeppert (65) p. 152.
[705] Weiss, C. E. (69) B. p. 201.
[706] Grand’Eury (77) A. p. 299; (90) A. p. 330.
[707] Zeiller (00²) B. p. 211.
[708] See Chap. +xxxv.+
[709] Lindley and Hutton (33) A. Pl. +lxxxii.+; Carruthers (72³) B. p.
7; Kidston (03) B. p. 782; (11) p. 235.
[710] Renault and Zeiller (90) A. p. 592, Pl. +lxxiii.+ fig. 31.
[711] Ettingshausen (52²) p. 5, Pl. +v.+
[712] Renault (79) B. p. 304.
[713] Bertrand, C. E. (11).
[714] Scott and Maslen (10); Scott (12).
[715] Scott (09) B. pp. 511, 526.
[716] Maslen (11).
[717] Maslen (11) Pl. +xxxiii.+ figs. 3–5.
[718] Scott (12) p. 1012, Pls. +lxxxvii.+, +lxxxix.+
[719] Scott (12) p. 1017, Pls. +lxxxviii.+, +xc.+
[720] Benson (12).
[721] See page 270.
[722] See page 132.
[723] See page 238.
[724] Stopes (14); Kidston (02) B. p. 363.
[725] Zeiller (00²) B. p. 213.
[726] Schimper and Mougeot (44) A. p. 42, Pl. +xxi.+
[727] Fliche (10) p. 218, Pl. +xx.+ fig. 2.
[728] See _postea_.
[729] Wills, L. T. (10), p. 296, fig. 26.
[730] Arber (07) Pls. +xvii.–xix.+
[731] Seward (04) B. p. 111.
[732] Arber (09²).
[733] Fliche (10) p. 264, Pl. +xxvii.+ fig. 2.
[734] Halle (10).
[735] Salfeld (09) B. p. 26.
[736] Saporta (94) B. p. 216, Pl. +xxxviii.+
[737] Velenovský (85) B. p. 1, Pls. +i.+, +iv.+
[738] See _postea_.
[739] Heer (76) A. p. 86, Pl. +xxx.+ fig. 10.
[740] Leuthardt (03), p. 6, Pl. +i.+
[741] Fliche (10) p. 175, Pls. +xvi.+, +xvii.+
[742] Compter, G. (94), Pl. +iv.+ fig. 9.
[743] Phillips (71) p. 169.
[744] Seward (04) B. p. 110; Arber, E. A. N. (07) p. 117.
[745] Zigno (85), p. 7, Pl. +xxvi.+
[746] Velenovský (85) B. Pls. +i.–iii.+
[747] Stopes and Fujii (10) p. 16, Pl. +iii.+ figs. 14–16.
[748] See _postea_.
[749] Schenk (71) p. 20, Pl. +vii.+ fig. 4.
[750] Zeiller (05²) p. 17, Pl. +vii.+ figs. 8–11.
[751] Renault and Zeiller (90) A. p. 627, Pl. +lxix.+ figs. 1–4.
[752] White (99) B. p. 271.
[753] Witham (33) A. pp. 37, 71.
[754] Witham (30).
[755] Goeppert (81) p. 403.
[756] Endlicher (47) p. 297.
[757] Scott (02) p. 346.
[758] See footnote p. 288.
[759] Scott (99²); Witham (33) A. Pls. +iii.–viii.+ +xvi.+
[760] Scott (02), p. 346, Pls. +i.+, +ii.+, +v.+, +vi.+
[761] Scott (02) p. 355.
[762] Witham (33) A. Pl. +viii.+ fig. 2.
[763] _Ibid._ p. 39, Pls. +viii.+, +xvi.+; Scott (02) p. 355, Pls.
+ii.+, +vi.+
[764] Since this chapter was written Prof. W. T. Gordon has kindly
supplied the following summary of his unpublished work on the genus
_Pitys_.
‘The re-examination of _Pitys primaeva_ and _P. antiqua_ in the light
of the structure exhibited by numerous specimens of a new species
recently discovered in Haddingtonshire has shown that all three types
are similar as regards the structure of the primary wood. In each
case the primary cylinder is comparable with that in _Archaeopitys
Eastmanii_ [see p. 290], _i.e._, there are medullary as well as
circummedullary xylem-strands. In certain specimens of the new species,
_Pitys Dayii_, the bark and leaves are preserved and thus the details
of leaf-trace emission from the stem have been determined. The leaves
are short and stout and taper gradually to a point, quite distinct from
the long, thin, spatulate Cordaitean foliage. The internal structure of
the leaf renders it easily distinguishable from the _Cordaites_ type
while it tends to accentuate the possible relationship of _Pitys_ with
the Lyginodendreae.’
[765] Williamson (78) A. p. 352, Pl. +xxv.+ figs. 90–92; Williamson and
Scott (95) p. 770; Seward (97²) p. 80.
[766] Witham (31) A.
[767] Goeppert (50) p. 251; (81).
[768] Brongniart (49) A. 77.
[769] Scott (02) p. 354.
[770] Scott and Jeffrey (14) p. 345, Pl. +xxxi.+ figs. 31–36;
text-figs. 4, 5.
[771] Zalessky (09); (11) p. 29, Pl. +iv.+
[772] Zalessky (11) Pl. +iv.+ fig. 3.
[773] Scott (12) p. 1024.
[774] Elkins and Wieland (14).
[775] Penhallow (00) pp. 64, Pl. +xii.+
[776] Zalessky (11²) p. 13, figs. 1–4.
[777] See page 295.
[778] Zalessky (11) p. 28.
[779] Williamson (80) A. p. 516, Pl. +xx.+ fig. 60.
[780] Scott (02) p. 357, Pls. +ii.+, +vi.+
[781] Scott (12) p. 1028.
[782] Goeppert (45²) p. 11, Pls. +xxix.–xxxv.+; Zalessky (11).
[783] Goeppert and Stenzel (88) p. 33, Pls. +v.+, +vi.+
[784] Kraus in Schimper (72) A. p. 381.
[785] Seward (14) p. 17, Pls. +iv.–viii.+
[786] Scott (12).
[787] See page 175.
[788] De Bary (84) A. p. 492; Grossenbacher (15).
[789] See Scott, _Nature_, August 26, 1915.
[790] See Vol. +ii.+ p. 56.
[791] Oliver (06) p. 726.
[792] Hooker and Binney (55).
[793] Oliver (03).
[794] Worsdell (05) p. 58; Salisbury (14) p. 67.
[795] Brongniart (81) p. 31.
[796] For an account of the work of this author see Lang in Oliver (13)
p. 178.
[797] See Scott (09) B. p. 543.
[798] Mirande (05).
[799] For definition of _Cardiocarpus_, see page 338.
[800] See page 25.
[801] Solms-Laubach (91) A. p. 118.
[802] Goeppert (65) p. 177, Pl. +xxvi.+ figs. 27, 28.
[803] Williamson (77) B. p. 262.
[804] Zeiller (88) A. p. 642.
[805] Brongniart (74).
[806] Brongniart (81).
[807] Oliver (04) B. p. 389.
[808] Affourtit and La Rivière (15).
[809] Nathorst (14) p. 32.
[810] See page 173.
[811] Salisbury (14) p. 71.
[812] Salisbury (14).
[813] Oliver (04) B. p. 392.
[814] Oliver (07).
[815] Arber, A. (10) p. 505.
[816] See Chapter +xxxi.+
[817] Oliver and Salisbury (11).
[818] Salisbury (14) p. 67.
[819] Oliver (09) p. 99.
[820] Nathorst (14) p. 29.
[821] φυσάω, to blow; φϋσα, a bladder.
[822] Williamson (76) p. 160; (17) B. p. 241, Pl. +xi.+ figs. 77, 78;
Pl. +xii.+ fig. 79.
[823] Oliver (09); Oliver and Salisbury (11) _passim_; Salisbury (14)
p. 74.
[824] Williamson (80) A. Pl. +xvii.+ figs. 24–28; (83²) A. Pl. +xxxi.+
fig. 27 (called in this case _Sporocarpon anomalum_, no doubt a slip of
the pen).
[825] Oliver (09) p. 75.
[826] Williamson (76) p. 160.
[827] Oliver (09) p. 106.
[828] Lang (00) p. 288.
[829] Burlingame (15) p. 19.
[830] Gordon, W. T. (10).
[831] κώνοϛ, a cone.
[832] Williamson (77) B. p. 241, Pls. +xi.+, +xii.+
[833] Page 79.
[834] Oliver and Salisbury (11).
[835] For a detailed account of the plinth see Oliver and Salisbury
(11).
[836] Page 27.
[837] Page 55.
[838] Renault (84) Pls. +xix.–xxii.+
[839] Saporta and Marion (85) p. 181.
[840] Oliver and Salisbury (11).
[841] Renault (96) A. p. 85, Pl. +xlii.+
[842] Renault and Zeiller (88) A. p. 640, Pls. 72, 82.
[843] Grand’Eury (90) A. Pl. +vi.+ fig. 6.
[844] Depape and Carpentier (13) Pl. +xii.+ figs. 1–3.
[845] Kidston (90) p. 64.
[846] Oliver (02) p. 146.
[847] Kershaw (09).
[848] Oliver (04) B. p. 376.
[849] Renault (96) A. p. 272.
[850] Arber, E. A. N. (14) p. 103, Pl. +viii.+ figs. 48–50.
[851] Brongniart (81) Pl. B. fig. 3.
[852] Grand’Eury (77) A. Pl. +xv.+ fig. 1.
[853] Newberry (73).
[854] _Ibid_. Pl. +xlii.+ fig. 8.
[855] Page 123.
[856] Oliver (04²) B. See also Renault (96) A. p. 398.
[857] Zeiller (88) A. p. 652, Pl. 94, fig. 17.
[858] Salisbury (14).
[859] Brongniart (74) p. 252, Pl. +xxii.+ figs. 6–8.
[860] Oliver (04) B. p. 391.
[861] Renault (96) A. p. 404.
[862] Kidston (14) p. 157.
[863] πτύξ, a plate or fold.
[864] Brongniart (74) p. 253, Pl. +xxii.+ figs. 9–11; (81) p. 26.
[865] _Ibid_. p. 254, Pl. +xxii.+ figs. 12–14; (81) p. 26.
[866] Williamson (77) B. p. 253.
[867] See page 356.
[868] P. Bertrand (13) Pl. +vii.+
[869] Brongniart (74) p. 255, Pl. +xxiii.+ figs. 1–3; (81) p. 27, Pl.
C, figs. 1–3.
[870] Arber, E. A. N. (14) p. 102, Pl. +vii.+ figs. 38–41.
[871] Kidston (14) p. 158, Pl. +x.+ figs. 6, 7; Pl. +xiv.+ figs. 5–9.
[872] Brongniart (74) p. 249, Pl. +xxii.+ figs. 4, 5; (81) Pls.
+xvii.–xxi.+
[873] Renault (96) A. p. 389, Pls. 83, 84.
[874] Oliver (02).
[875] Grand’Eury (04).
[876] Grand’Eury (90) A. Pl. +viii.+ fig. 3; (77) A. Pl. +xvi.+ fig. 5.
[877] Renault and Zeiller (88) A. Pl. 73.
[878] Zeiller (06) B. p. 229.
[879] Kidston (92) p. 8.
[880] Arber, E. A. N. (14) p. 91, Pl. +vii.+ fig. 28.
[881] See page 364.
[882] White (99) B. p. 267; Lesquereux (79) A. Pl. 85, fig. 21.
[883] Brongniart (74) p. 259, Pl. +xxiii.+ figs. 12–15; (81) p. 29, Pl.
+xvi.+
[884] Renault (80²).
[885] Oliver (04) B.
[886] Russow (72) Pls. +iii.+, +iv.+
[887] στέφανοϛ, a crown.
[888] Oliver (04) B. p. 395.
[889] Brongniart (81) Pl. +xvi.+ figs. 4, 6.
[890] _Ibid._ p. 373, Pl. +xlii.+ figs. 17–20; +xliv.+ figs. 36–43.
[891] λόφοϛ, a ridge.
[892] Brongniart (74) p. 256, Pl. +xxiii.+ figs. 6–8; (81) Pl. C, figs.
6–8.
[893] Oliver (04²) B. Pl. +ii.+ figs. 5–10; (07) fig. 1.
[894] Scott and Maslen (07) Pl. +xiii.+ fig. 19.
[895] Salisbury (14).
[896] κώδων, a bell.
[897] Brongniart (74) p. 257, Pl. +xxiii.+ figs. 9–12; (81) p. 28, Pl.
C, figs. 9–12.
[898] Renault (93) A. Pl. +lxxxvii.+; (96) A. p. 393.
[899] Renault and Zeiller (88) A. p. 659, Pl. 83, figs. 10–26.
[900] Grand’Eury (77) A. p. 184, Pl. +xv.+ fig. 5; (90) A. p. 311, Pl.
+iii.+ fig. 6.
[901] Zeiller (06) B. p. 227.
[902] See also Grand’Eury (05²) B.
[903] Brongniart (74) p. 260, Pl. +xxiii.+ pp. 16–18; (81) p. 30.
[904] Renault 96 A. p. 272.
[905] Brongniart (74) p. 256, Pl. +xxiii.+ figs. 4, 5; (81) p. 27, Pl.
C, figs. 4, 5.
[906] ἔριον, wool.
[907] Grand’Eury (90) A. p. 308, Pls. +iv.+ fig. 12, +vi.+ fig. 5.
[908] See page 264.
[909] Brongniart (28) A. p. 87.
[910] Brongniart (74) p. 245 (81).
[911] Geinitz (62) p. 150; Kidston (11) p. 240; Geinitz (55) A. Pl.
+xxi.+ figs. 7–16.
[912] Kidston (94) B. p. 263.
[913] Renault (80²), p. 102.
[914] Fiedler (57) p. 291.
[915] Brongniart (81) Pls. +iv.+, +v.+
[916] Bertrand, C. E. (08²).
[917] Renault (96) A. p. 385.
[918] Bertrand, C. E. (08).
[919] Fiedler (57) p. 288, Pl. +xxviii.+
[920] Schenk (80) p. 660.
[921] Ward (88) p. 802.
[922] Goeppert (65) p. 177, Pl. +xxviii.+ figs. 10, 11.
[923] _Ibid_. fig. 19.
[924] Heer (77) ii. Pl. +xix.+ See also Nathorst (86) Pl. +xxv.+ figs.
10–14.
[925] Arber, E. A. N. (14) p. 97.
[926] Arber, E. A. N. (09) Pl. +i.+ fig. 5.
[927] Feistmantel (79²)
[928] Schenk (83) A. Pl. +xliv.+ fig. 8.
[929] Seward (97²) A.
[930] White (08) B.
[931] Feistmantel (90) A. p. 164.
[932] Geinitz (80) p. 22, Pl. +iii.+ figs. 11–15.
[933] Weiss, C. E. (72) p. 208.
[934] See page 141.
[935] White (08) B. p. 563. See also Vol. +ii.+ p. 517.
[936] Goeppert (65) p. 146, Pl. +xxvi.+ fig. 5.
[937] Heer (77) ii. Pl. +xiv.+
[938] See page 345.
[939] Brongniart (81) p. 20, Pl. +ii.+
[940] Bertrand, C. E. (08²); (08³).
[941] Bertrand, C. E. (08).
[942] This name has been used for a section of a genus of recent
Umbelliferae but not as a generic name (De Candolle’s ‘Prodromus,’ Pars
+iv.+ p. 105, 1830).
[943] Bertrand (08³) p. 454; (08²) p. 392.
[944] Brongniart (81) Pls. +iv.+ +v.+
[945] Schimper (72) A. p. 208.
[946] Brongniart (81) Pl. +iii.+; Bertrand, C. E. (08).
[947] ῥάβδοϛ, a rod.
[948] Berger (48) p. 20, Pl. +i.+ fig. 8.
[949] Renault and Zeiller (88) A. p. 635.
[950] Bertrand, P. (13).
[951] Arber (14) p. 103.
[952] See page 116.
[953] Arber (14) p. 87.
[954] Zeiller (92²) A. Pl. +xv.+ fig. 11.
[955] Arber (14) Pl. +vii.+ fig. 21.
[956] In selecting a generic name for a fossil plant or part of a
plant it has not been the universal practice to avoid the use of a
designation previously employed for a recent plant. It is clearly
in accordance with the Rules adopted by the International Botanical
Congress and with general convenience to avoid the employment of the
same name for two different generic types even if one is known only
in a fossil state. My attention has been called by Mr W. N. Edwards
of the British Museum to the fact that the names _Platyspermum_,
_Microspermum_, and _Pterospermum_ recently proposed by Dr Arber for
Palaeozoic seeds have previously been given to recent flowering plants.
Though I have often neglected to consult the _Index Kewensis_ and the
_Genera Siphonogamarum_ before proposing a ‘new’ generic term, I fully
recognise the importance of avoiding the employment of names in current
use or names which have ‘lapsed into synonymy[966].’
[957] See page 361.
[958] Brongniart (74) p. 246; (81) p. 21, Pls. +ix.–xi.+
[959] Bertrand, C. E. (07).
[960] Grand’Eury (05).
[961] Kidston (14) Pl. +xvi.+ figs. 6–8.
[962] Lesquereux (80) A. p. 574.
[963] White (99) B. p. 267.
[964] Grand’Eury (77) A. Pl. +xv.+
[965] Renault (93) A. Pl. +lxxxvi.+
[966] Règles internationales de la nomenclature botanique adoptées par
le Cong. Internat. Bot. de Vienne, 1905, etc. T. Briquet, Jena, 1912,
p. 37.
[967] See page 314.
[968] Arber, A. (10).
[969] μίτρα, a Persian cap.
[970] Williamson (77) B. p. 257, Pls. +xv.+ +xvi.+
[971] Bertrand, C. E. (08²).
[972] Brongniart (74) p. 247, Pl. +xxi.+ figs. 12–14; (81) p. 21, Pl.
A. fig. 12; Pl. +xiv+; Renault (80²) p. 106, Pl. +xv.+ figs. 12, 13;
Grand’Eury (77) A. p. 239, Pl. +xxvi.+ fig. 27.
[973] Bertrand, C. E. (07²).
[974] Brongniart (74) p. 248, Pl. +xxi.+ fig. 17; (81) p. 22, Pl. A.
fig. 17; Pl. +vi.+
[975] Bertrand, C. E. (07³) compares _Leptocaryon_ with _Diplotesta_ as
regards various structural features.
[976] Renault (80²) p. 108.
[977] Brongniart (74) p. 249, Pl. +xxi.+ figs. 18–20; (81) p. 23, Pl.
A. figs. 18–20; Pl. +xv.+
[978] Oliver (03) p. 457.
[979] Bertrand, C. E. (07⁴).
[980] Bertrand, C. E. (07⁵).
[981] Brongniart (74) p. 247.
[982] κομψόϛ, elegant.
[983] Bertrand, C. E. (09).
[984] Dawson (66) A. p. 165, Pl. +xii.+ fig. 74; Zeiller (06) B. p.
226; Kidston (11) p. 236.
[985] Zeiller (88) A. p. 644.
[986] White (99) B. p. 266, Pls. +lxi.+ fig. 12, +lxxii.+ fig. 3.
[987] Weiss, C. E. (72) Pl. +xviii.+
[988] Kidston (94) B. Pl. +vi.+ fig. 3; (02) B. Pl. +lviii.+ figs. 5, 6.
[989] Lesquereux (80) A. Pl. +lxxxv.+ fig. 51.
[990] Helmhacher (71).
[991] Zeiller (92²) A. Pl. +xv.+ figs. 9, 10.
[992] Geinitz (75) Pl. +i.+ figs. 10, 11; Weiss, C. E. (79) Pl. +iii.+
figs. 17–19.
[993] Potonié (93) A. Pl. +xxxii.+ figs. 12, 13.
[994] Stopes (14) Pl. +xxv.+ fig. 68.
[995] Arber (14) Pl. +vi.+ figs. 19, 20; (14²) Pl. +xi.+ fig. 5.
[996] For synonymy, see Kidston (11) p. 238, Pl. +xxii.+ figs. 3, 3_a_.
[997] Fiedler (57) p. 291.
[998] Stopes (14) p. 89, Pls. +xxi.–xxiii.+
[999] Andrews (75) p. 425, Pl. +xlvi.+ fig. 2.
[1000] Kidston (11) p. 239, Pl. +xii.+ fig. 1.
[1001] Dawson (71) A. Pl. +xix.+ fig. 219; Stopes (14) p. 92.
[1002] Fiedler (57) Pl. +xxviii.+ fig. 36.
[1003] White (08) B. p. 567, Pl. +x.+ fig. 11.
[1004] Newberry (73) Pl. +xliii.+ fig. 8; Lesquereux (80) A Pl.
+lxxxv.+ figs. 36, 37.
[1005] Lesquereux (84) A Pl. +cix.+ figs. 13, 15.
[1006] Seward (97²) A p. 332; Arber (05) B. pp. 206, 207.
[1007] White (08) B. p. 559, Pl. +x.+ figs. 5–8.
[1008] Vol. +ii.+ p. 517.
[1009] Seward and Leslie (08) B.
[1010] Zeiller (02) B. p. 37, Pl. +vii.+ figs. 7, 8; Arber (05) B. p.
205, fig. 44.
[1011] Lesquereux (80) A. Pl. 85, figs. 34, 35.
[1012] Feistmantel (79²) p. 30; (81²) p. 59, Pl. +xxx.+ fig. 14; (82)
p. 43, Pl. +xv.+ figs. 5–12.
[1013] Arber (05) B. p. 205.
[1014] Vol. +ii.+ p. 500.
[1015] Geinitz (71) p. 174, Pl. +iii.+ figs. 10, 11.
[1016] _Ibid._ (55) A. Pl. +xxi.+; Zeiller (88) A. Pl. +xciv.+ fig. 13;
(06) B. p. 224; Kidston (11) p. 240; Arber (14) p. 100.
[1017] Boulay (79) p. 34.
[1018] Zeiller (88) A. Pl. +xciv.+ fig. 12; Kidston (11) Pl. +v.+ figs.
5–7; Arber (14) p. 100.
[1019] Berger (48) Pl. +ii.+ figs. 19, 20.
[1020] Renault and Zeiller (88) A. Pl. +lxxii.+ fig. 3.
[1021] _Ibid._ p. 649.
[1022] _Ibid._ Pl. +lxxii.+ figs. 53–55.
[1023] Williamson (77) B. p. 253, Pl. +xvi.+ figs. 115 _a_, 115 _b_.
[1024] Kidston (14) p. 165.
[1025] Bertrand, P. (13) Pl. +vii.+
[1026] Renault and Zeiller (88) A. p. 651, Pl. +lxxii.+ fig. 56.
[1027] Grand’Eury (77) A. p. 185, Pls. +xv.+, +xvi.+
[1028] Arber (14) pp. 93, 104, Pl. +viii.+ figs. 51, 52.
[1029] Kidston (14) p. 157, Pl. +xiv.+ figs. 1, 2.
[1030] See page 321.
[1031] Arber, _loc. cit._ p. 102.
[1032] Kidston, _loc. cit._ p. 158.
[1033] Heer (77) i. p. 19, Pl. +v.+ figs. 1–11.
[1034] Nathorst (94) A. p. 48, Pl. +iv.+ figs. 7, 8.
[1035] Young (69) Pl. +iv.+ figs. 9, 10; (76) p. 36.
[1036] Zalessky (05).
[1037] Nathorst (14) p. 23, Pl. +xv.+ figs. 44–51.
[1038] Lindley and Hutton (37) A. Pl. 220.
[1039] Zalessky (05).
[1040] For this information I am indebted to Dr Kidston.
[1041] Nathorst (14) p. 32, Pl. +xv.+ fig. 58.
[1042] Zalessky (05).
[1043] Nathorst (14) p. 27, Pl. +v.+ figs. 19–22; Pl. +xv.+ fig.
[1044] Heer (77) i. p. 24, Pl. +v.+ figs. 18–22.
[1045] Nathorst (14) p. 35, Pl. +xv.+ figs. 77–82.
[1046] Grand’Eury (77) A. Pl. +xvi.+ figs. 2–4.
[1047] Brongniart (28) A. p. 137.
[1048] Grand’Eury (77) A. p. 184, Pl. +xv.+ fig. 3.
[1049] See page 330.
[1050] Sternberg (38) A. Pl. +x.+ fig. 3.
[1051] Lindley and Hutton (37) A. Pl. 220.
[1052] Zalessky (05) p. 119.
[1053] Renault and Zeiller (88) A. p. 652, Pl. +lxxii.+ figs. 63–66;
Renault (96) A. p. 400; (93) A. Pl. +lxxxiv.+ fig. 3.
[1054] Arber (14) p. 95, Pl. +vi.+ fig. 11.
[1055] Kidston (88) B. Pl. +xxiii.+ fig. 4.
[1056] Nathorst (14) p. 28.
[1057] _Ibid._ Pl. +xv.+ figs. 53, 54.
[1058] Williamson (77) B. p. 246, Pl. +xiii.+ figs. 88–93.
[1059] Nathorst (14) p. 33. Pl. +xv.+ figs. 69, 70.
[1060] See page 304.
[1061] Nathorst (14) p. 33.
[1062] Seward (95) A. p. 101.
[1063] Kidston (92) p. 8; Arber (14) Pl. +vii.+ fig. 28.
[1064] Kidston (86⁴) B. Pl. +iii.+ figs. 7 _a_–_c_; Berger (48) Pl.
+ii.+ figs. 30, 31.
[1065] See _postea_.
[1066] Arber (14) pp. 90, 100, Pl. +vii.+ figs. 22–27.
[1067] Carpentier (11) p. 7, Pl. +xiv.+ fig. 3.
[1068] Geinitz (62) p. 145, Pl. +xxv.+ figs. 7–9; Goeppert (64) A. p.
145.
[1069] Nathorst (02) p. 3.
[1070] Carruthers (70) p. 694.
[1071] Nathorst (02) p. 23.
[1072] _Ibid._ (09²) pp. 21, 23.
[1073] Thomas and Bancroft (13) p. 196.
[1074] Buckland (27) _Proc. Geol. Soc. London_, Vol. +i.+ No. 8, p. 80;
(28).
[1075] Brongniart (28) A. p. 96.
[1076] _Ibid._ (49) A. p. 59.
[1077] Carruthers (70) p. 678.
[1078] Buckland (37) p. 496, Pls. +lx.+, +lxi.+
[1079] _Ibid._ (28), Pl. +lxi.+ fig. 1. A specimen in the Oxford Museum
may be the original of Buckland’s figure.
[1080] Carruthers (70).
[1081] Pomel (49) p. 16.
[1082] Carruthers (70) p. 690.
[1083] Saporta (75) A. pp. 256, 265, Pls. 118, 119.
[1084] Lindley and Hutton (35) A. Pl. 143.
[1085] Ward (94).
[1086] Fliche and Zeiller (04).
[1087] Saporta (75) A. p. 276, Pl. 120.
[1088] Lignier (01).
[1089] _Ibid._ (13) p. 93.
[1090] Solms-Laubach (91).
[1091] Seward (95) A. p. 139.
[1092] _Ibid._ (04) B. p. 44.
[1093] Wieland (06).
[1094] Stopes (15) p. 309.
[1095] Buckland (37) A. Vol. +ii.+ p. 98, Pl. +lxi.+ fig. 1.
[1096] _Ibid._ (28) Pl. +xlix.+
[1097] Seward (95) A. p. 166.
[1098] Stopes (15) p. 309.
[1099] See page 425.
[1100] Wieland (06) Pls. +vi.–xiii.+
[1101] _Ibid._ (12) p. 88, fig. 10.
[1102] Wieland (06) p. 63, fig. 33.
[1103] See Wieland (06) for additional facts and illustrations.
[1104] See page 417.
[1105] Wieland (06) p. 76; Capellini and Solms-Laubach (92) Pl. +v.+
fig. 6.
[1106] Capellini and Solms-Laubach (92) Pl. +v.+ fig. 2.
[1107] See Chapter +xxxix.+
[1108] See page 489.
[1109] Wieland (99); (06) p. 87.
[1110] Wieland in Ward (05) B. p. 200, Pl. +lxiii.+
[1111] Wieland (14).
[1112] The flowers are frequently described as protandrous but, as Dr
Scott pointed out to me, we have no definite evidence on this point.
[1113] Wieland (11²) p. 134; Coulter and Chamberlain (10) p. 67, fig.
55.
[1114] Wieland (06) p. 160, fig. 84.
[1115] _Ibid._ (14).
[1116] See also Wieland (11²) p. 152, fig. 9.
[1117] Capellini and Solms-Laubach (92); Ward (96) p. 505.
[1118] Ward (96) Pl. +civ.+
[1119] Ward (04); Wieland (08).
[1120] Fontaine (89) B. p. 193, Pls. +clxxiv.–clxxx.+
[1121] Ward (94²).
[1122] For an account of the stratigraphy, see Ward (94³).
[1123] Ward (05) B.
[1124] _Ibid._ (00).
[1125] Coemans (66).
[1126] Wieland (13).
[1127] Carruthers (70).
[1128] Lignier (94²).
[1129] See page 395.
[1130] Wieland (06).
[1131] Buckland (37).
[1132] See page 448.
[1133] Carruthers (70).
[1134] _Ibid._ p. 698; for other references, see Seward (95) A. 139.
[1135] Carruthers (70) Pls. +lvii.+, +lviii.+
[1136] Capellini and Solms-Laubach (92) Pl. +v.+ fig. 2.
[1137] See also Stopes (15) p. 47.
[1138] Chamberlain (13). See Chapter +xxviii.+, page 6.
[1139] Solms-Laubach (91).
[1140] See page 449.
[1141] Scott (09) B, p. 571.
[1142] It is possible that, as Scott suggests, a small patch of
endosperm is represented in a seed of this species figured by him.
Scott (09) B. p. 569, fig. 203, D, _e_.
[1143] See page 396.
[1144] The age was at first believed to be Oxfordian, but Lignier
subsequently (09) referred the rocks to a Lower Cretaceous horizon.
[1145] Morière (69).
[1146] Saporta and Marion (81) A.; (85) p. 244; Saporta (91) p. 168,
Pls. 148, 149.
[1147] Lignier (94²); (04); (09); (11).
[1148] Saporta (75) A. p. 328, Pl. 123.
[1149] Lignier (94) p. 57; (12).
[1150] Lignier (11).
[1151] Berridge (11); Thoday, M. G. (11).
[1152] Lignier (04).
[1153] Solms-Laubach (91).
[1154] Pearson (09).
[1155] Wettstein (11) p. 388.
[1156] Worsdell (00²).
[1157] McBride (93).
[1158] Ward (98) p. 205.
[1159] Wieland (06) p. 185. See Wieland’s description for further
details.
[1160] Ward (98) p. 208.
[1161] Wieland (06) Pls. +vii.–ix.+, +xii.+, +xiii.+
[1162] _Ibid._ Pl. +xix.+ fig. 5.
[1163] _Ibid. passim_; (12).
[1164] Wieland (14).
[1165] This subject is more fully dealt with by Wieland in the Volume
published since the above was written [Wieland (16)].
[1166] Goeppert (53).
[1167] Solms-Laubach (91) A. p. 100.
[1168] Schuster (11). An excellent photograph of the stem is reproduced
in this paper.
[1169] Wieland (08) p. 96.
[1170] Raciborski (92²).
[1171] Seward (97) A.
[1172] Wieland (06) Pl. +xix.+ fig. 5.
[1173] Seward (97) A. figs. 3, 4, pp. 24, 32.
[1174] Lignier (01).
[1175] Lignier (01).
[1176] Morière (69).
[1177] Saporta (75) A. Pl. l.
[1178] Ward (94) p. 87; (98) p. 216.
[1179] Wieland (06) p. 79, Pl. +xiv.+
[1180] Chamberlain (09).
[1181] Fliche and Zeiller (04) p. 789, Pl. +xix.+
[1182] Saporta (75) A. p. 262, Pl. 118.
[1183] Ward (99) B. p. 639, Pls. +clvi.+, +clvii.+
[1184] Lindley and Hutton (35) A. Pl. 143. (I have not seen the actual
specimen.—A. C. S.)
[1185] Ward (00²), Pls. +xiv.–xxi.+
[1186] _Ibid._ (05) B. p. 198, Pls. +xlvi.–lxiii.+
[1187] Wieland (06) p. 101.
[1188] Fliche (96) p. 48, Pl. +v.+ figs. 2, 3; Pl. +xiv.+ fig. 1.
[1189] _Ibid._ Pl. v. fig. 3.
[1190] Stopes (15) p. 247, Pls. +xxiii.–xxv.+, text-figs. 72–75.
[1191] Solms-Laubach (04) p. 12, Pl. +ii.+ figs. 5, 6.
[1192] Young and Bird (22) A. For a fuller account of the history of
our knowledge of _Williamsonia_, see Seward (95) A. p. 146.
[1193] Williamson (40) p. 230.
[1194] Yates (55).
[1195] Leckenby, A. (64). See also Seward (00) B. p. 190.
[1196] Williamson (70).
[1197] Carruthers (70).
[1198] Saporta (91).
[1199] Seward (97⁴).
[1200] Wieland (11).
[1201] Wieland (13).
[1202] Nathorst (13).
[1203] See page 480.
[1204] Williamson (70) Pl. +liii.+ fig. 5; Seward (97⁴).
[1205] Saporta (75) A. Pl. +xi.+ fig. 1.
[1206] _Ibid._ Pl. +xv.+
[1207] Wieland (11) p. 448, fig. 6.
[1208] Seward (95) A. p. 146.
[1209] Nathorst (09) (11).
[1210] Lignier (07).
[1211] Saporta (91) Pl. 248.
[1212] Nathorst (09) Pl. +iii.+
[1213] Krasser (12).
[1214] Lignier (03).
[1215] Wieland (06) p. 152.
[1216] Lignier (07); Wieland (11) p. 462.
[1217] Nathorst (11) Pl. +ii.+
[1218] Thomas (15²).
[1219] Thomas (15).
[1220] Nathorst (09) p. 6, Pls. +i.+, +ii.+; (11) p. 5, Pls. +i.+,
+iii.+; (12).
[1221] Thomas (13²) p. 230, Pl. +xxiv.+ figs. 1–3.
[1222] Capellini and Solms-Laubach (92) Pl. +v.+ fig. 7.
[1223] Nathorst (09) Pl. +i.+ figs. 1–3.
[1224] _Ibid._ (80) p. 39. See also Saporta (91) p. 161, Pl. 248.
[1225] Seward (00) B. p. 201, fig. 35.
[1226] Nathorst (09) p. 14, Pls. +ii.+, +iii.+
[1227] Carruthers (70) p. 694.
[1228] Nathorst (11) p. 19.
[1229] Nathorst (11) p. 9, Pls. +ii.+, +iii.+ See also Nathorst (09) p.
8, Pls. +i.+, +ii.+
[1230] Leckenby (64) A.
[1231] Nathorst (12) p. 7.
[1232] Williamson (70) Pl. +lii.+ fig. 1; Pl. +liii.+ fig. 2.
[1233] Seward (00) B. p. 201, Pl. +ii.+ fig. 7.
[1234] Nathorst (11) p. 19, Pl. +v.+ figs. 1–8; Pl. +vi.+ figs. 1–3.
The name _Palaeozamia pecten_ was applied by Leckenby [Leckenby (64) A.
p. 77, Pl. +ix.+ fig. 47] both to the fronds and an associated flower
which is now recognised as a whorl of microsporophylls. I formerly
employed the name _Williamsonia pecten_ for fronds and flowers, but in
view of Nathorst’s work it is advisable to follow his example and to
use separate names for male and female flowers when there is no proof
that they belong to one type; similarly the fronds may conveniently be
spoken of as _Ptilophyllum pecten_.
[1235] Nathorst (11) p. 17, Pl. +iv.+
[1236] Nathorst (09) Pl. +vii.+ fig. 1.
[1237] See page 444.
[1238] Oldham and Morris (63) B. Pl. +xxxii.+ fig. 2.
[1239] Feistmantel (77²) p. 76; (77⁵) Pl. +ii.+ fig. 5.
[1240] _Ibid._ (77²) Pl. +xliv.+ fig. 2.
[1241] Feistmantel (77²) Pl. +xliv.+ figs. 3, 4.
[1242] Williamson (70) Pl. +lii.+ fig. 1.
[1243] Wieland (11) p. 460, fig. 16 B.
[1244] Nathorst (09) p. 6.
[1245] Feistmantel (77²) Pl. +xli.+ fig. 4; (77) Pl. +i.+ fig. 6; Pl.
+ii.+ fig. 4.
[1246] _Ibid._ (76²) p. 52, Pl. +xii.+ figs. 5–7; (77⁵) Pl. +i.+ figs.
4, 5; Pl. +ii.+ fig. 6.
[1247] Feistmantel (77³) p. 181, Pl. +vii.+ figs. 1–4; (77¹) Pl. +ii.+
figs. 1–3.
[1248] My thanks are due to Mr Wieland for a photograph of this species
that is mentioned but not figured in his paper on the Mexican Flora,
Wieland (13).
[1249] Bancroft (13) p. 76, Pl. +vii.+ figs. 1–5.
[1250] Seward (95) A. p. 157, Pls. +x.+, +xi.+
[1251] Buckland (37) Vol. +i.+ p. 505, Vol. +ii.+ p. 101, Pl. +lxiii.+
figs. 2–10.
[1252] Unger (50) A. p. 327.
[1253] Brongniart (49) A. p. 88.
[1254] Saporta (91) p. 127, Pls. 238, 239.
[1255] For other references, see Seward (04) B. p. 105.
[1256] Miller (57) B. p. 480. For a detailed description and
illustrations, see Seward (12²).
[1257] Thomas and Bancroft (13) p. 184.
[1258] Bancroft (13).
[1259] Lignier (01).
[1260] Nathorst (11) p. 24, Pl. +v.+ figs. 9–11.
[1261] Wieland (11) p. 462.
[1262] Nathorst (09) p. 10; (11) p. 14.
[1263] Nathorst (09) p. 10.
[1264] Williamson (70) Pl. +lii.+: see also Seward (00) B, Pl. +viii.+
fig. 1.
[1265] Nathorst (09) p. 12, fig. 2.
[1266] Lignier (03²) p. 34.
[1267] In addition to the papers already quoted, reference should also
be made to Thomas (15²).
[1268] Wieland (09) p. 430 (the species is here referred to as the ‘El
consuelo _Williamsonia_’); (11) p. 461, fig. 17 C.
[1269] Zigno (85) Pl. +xlii.+
[1270] Seward (12) p. 26, Pl. +iii.+ fig. 44; Pl. +vii.+ fig. 86.
[1271] Zigno (85) p. 173, Pl. +xlii.+ figs. 9–11.
[1272] Seward (11²) p. 691, Pl. +v.+ fig. 99.
[1273] Fontaine in Ward (05) B. p. 118, Pl. +xxix.+ fig. 6.
[1274] Nathorst (80) p. 41, Pl. +viii.+ fig. 7.
[1275] Saporta (94) B. p. 105, Pl. +xix.+ fig. 9.
[1276] Newberry and Hollick (95) p. 125, Pl. +xxxv.+ figs. 1–9.
[1277] Hollick (06) p. 107, Pl. +v.+ figs. 27–32; (12) p. 156, Pl.
+clxiii.+ fig. 4.
[1278] Newberry and Hollick (95) p. 127, Pl. +xxxvi.+ figs. 1–8.
[1279] Hollick (06) p. 107, Pl. +v.+ figs. 25, 26.
[1280] Ward (99) B. p. 668, Pl. +clxii.+ fig. 20.
[1281] Lesquereux (91) p. 87, Pl. +ii.+ fig. 9.
[1282] Fontaine (89) B. p. 273, Pls. 133, 165.
[1283] Fontaine in Ward (05) B. p. 485, Pl. +cvii.+ fig. 4.
[1284] Ward (05) B. p. 554, Pl. +cxv.+ fig. 11.
[1285] Berry (11) p. 405, Pl. +lxvii.+ figs. 1–4.
[1286] Heer (82) B, p. 59, Pls. +xii.+, +xiii.+
[1287] Dawson (85) p. 12, Pl. +iv.+ fig. 1.
[1288] Nathorst (80) p. 50.
[1289] _Ibid._ (88); (02) p. 9, Pls. +i.–iii.+
[1290] _Ibid._ (09) p. 22, Pls. +v.+, +vi.+
[1291] _Ibid._ p. 33.
[1292] South and Compton (08) p. 225, fig. 36.
[1293] For figures of the stem and flowers, see Nathorst (02); (09).
[1294] Thomas (15²).
[1295] Nathorst retains the name _Anomozamites minor_ for the leaves,
restricting _Wielandiella_ to the plant as a whole including strobili
and stems which usually occur in organic union [Nathorst (13)].
[1296] Nathorst (09) p. 25, Pl. +vii.+ figs. 14–22.
[1297] Thomas (13²), p. 239.
[1298] Nathorst (02) p. 16.
[1299] Thiselton-Dyer (72).
[1300] Wieland (11) p. 458.
[1301] Thomas (15²).
[1302] See page 449.
[1303] See page 463.
[1304] Seward (00) B. +xvi.+ fig. 1; Thomas, H. H. (15²) Pl. +xiv.+
fig. 26.
[1305] Nathorst (02) p. 7, Pl. 1.
[1306] _Ibid._ (09) p. 27, Pl. +viii.+; (12²) Pls. +i.+, +ii.+; (12).
[1307] See the photographs reproduced in Nathorst’s latest and most
complete account (12²).
[1308] Bower (97) B.
[1309] Braun (49). (I have not seen this paper.)
[1310] Saporta (91) p. 191, Pls. 253–255.
[1311] See page 428.
[1312] Nathorst (09) p. 28.
[1313] _Ibid._ (11²); (12²).
[1314] Schuster (11²).
[1315] Schimper (72) A. p. 200.
[1316] _Zeitsch. f. Bot._ 1912, p. 456.
[1317] Saporta (91) pp. 204, 206, Pls. 254, 255.
[1318] Mantell (27).
[1319] See page 463.
[1320] Carruthers (70).
[1321] Saporta (75) A. pp. 256 et seq.
[1322] Saporta (75) A. p. 293, Pls. 123, 124.
[1323] See p. 415.
[1324] Saporta (75) A. p. 256.
[1325] Presl in Sternberg (25) A. p. xxxiii.
[1326] Mantell (27).
[1327] Stokes and Webb (24).
[1328] Brongniart (22) A. p. 209; (28) A. p. 128.
[1329] Carruthers (70) p. 682.
[1330] Carruthers (67); (70) p. 688.
[1331] Stopes (15) p. 309. See _postea_, p. 486.
[1332] Nathorst (86) Pl. +xviii.+ fig. 5.
[1333] Stokes and Webb (24) Pls. +xiv.–xvii.+
[1334] Carruthers (70) p. 686, Pl. +liv.+ See also Seward (95) A. p.
123.
[1335] Seward (95) A. p. 132, Pl. +ix.+ fig. 6; (13) p. 101.
[1336] _Ibid._ Pl. +i.+ fig. 2.
[1337] Carruthers (70) p. 689, Pl. +lv.+ fig. 2.
[1338] Seward (04) B. p. 45.
[1339] Carruthers (70) p. 687, Pl. +lv.+ fig. 1.
[1340] Carruthers, p. 689, Pl. +lv.+ figs. 7–9.
[1341] Carruthers (67); (70) p. 688, Pl. +lv.+ figs. 3–6. See also
Seward (95) A. p. 166.
[1342] Stopes (15) p. 299, text-figs. 93–97.
[1343] Stopes (15) p. 309, text-figs. 98–100.
[1344] Sternberg (25) A. Pl. 30.
[1345] Brongniart (28) A. p. 128.
[1346] Carruthers (70) p. 686.
[1347] _Ibid._ (70) p. 690, Pl. +lvi.+
[1348] Saporta (75) A. p. 308, Pls. 125, 126.
[1349] _Ibid._ p. 322, Pl. 127, figs. 1–3.
[1350] Oldham and Morris (63) B. Pl. +xxxiv.+
[1351] Feistmantel (77²) p. 78.
[1352] Wieland (11) p. 440.
[1353] Seward (00) B. p. 194.
[1354] Bancroft (13).
[1355] For illustrations and further details see Bancroft (13).
[1356] Saporta (75) A. p. 331, Pl. 119, fig. 3.
[1357] Lignier (95) p. 11, fig. 1.
[1358] _Ibid._ p. 15, fig. 2.
[1359] Stokes and Webb (24) Pl. +xlv.+; Mantell (27), etc. See Seward
(95) A. pp. 126, 130, etc., for other references.
[1360] Ward (99) B. p. 693, Pl. 169, fig. 19.
[1361] Feistmantel (76²) Pl. +x.+ fig. 2.
[1362] Hollick and Jeffrey (09) B. p. 17.
[1363] Stopes (15) p. 314, Pls. +xxxi.+, +xxxii.+, text-figs. 101–111.
[1364] Saporta (75) A. p. 200, Pl. 114, figs. 4–6.
[1365] Seward (95) A. p. 96.
[1366] Feistmantel (76²) Pl. +vii.+ fig. 5.
[1367] Seward (95) A. p. 98, Pl. +v.+ figs. 2, 6; (03) B. p. 31.
[1368] _Ibid._ (13) p. 101, Pl. +xii.+ figs. 3, 4; Pl. +xiv.+ fig. 6.
[1369] Saporta (75) A. Pl. 127.
[1370] Carruthers (70) Pl. +lvi.+
[1371] I am indebted to Mr Edwards of the Geological Department of the
British Museum for making a preparation of the cuticle.
[1372] Tate (67) Pl. +vi.+ fig. 4; Seward (03) B. p. 29, Pl. +iv.+
figs. 3–6.
[1373] For further reference to this generic name, as applied to
Palaeozoic seeds, see page 364.
[1374] Nathorst (14) p. 33.
[1375] Ward (00) B. p. 363.
[1376] Pomel (49) p. 16.
[1377] Lindley and Hutton (36) A. Pl. 189. See also Seward (04) B. p.
124.
[1378] Lindley and Hutton (36) A. Pl. 189, figs. 3, 5.
[1379] Seward (95) A. p. 105, fig. 7.
[1380] Saporta (75) A. p. 242, Pl. 117, fig. 9.
[1381] Fontaine (89) B. p. 270, Pls. 135, 136.
[1382] Compter, G. (03).
[1383] Schimper (72) A. p. 207, Pl. +lxxii.+ figs. 18–23.
[1384] Pomel (49) p. 13.
[1385] Schenk (67) A. p. 150, Pl. +xxxiii.+ fig. 10.
[1386] See page 141.
[1387] Zigno (85) p. 156, Pl. +xlii.+
[1388] Saporta (91) p. 466, Pl. 298.
[1389] Seward (11²) p. 699, Pl. +vii.+ fig. 18.
[1390] Saporta (75) A. Pl. 116; (91) Pl. 298.
[1391] Saporta and Marion (85) p. 111.
[1392] Nathorst (86) p. 80, Pl. +xvii.+ fig. 7.
[1393] _Ibid._ (02) p. 6, Pl. +i.+ fig. 11.
[1394] Carruthers (69).
[1395] Lindley and Hutton (35) A. Pl. 159.
[1396] Seward and Gowan (00) B. p. 143; Seward (00) B. p. 275, Pl.
+ix.+ fig. 11.
[1397] Nathorst (02) p. 21, Pl. +i.+ figs. 14, 15.
[1398] Nathorst (02) p. 20, Pl. +i.+ figs. 22, 23.
[1399] _Ibid._ (09²) p. 23.
[1400] See Vol. +iv.+
[1401] Endlicher (40) p. 72. See also Schimper (72) A. p. 201.
[1402] Lindley and Hutton (35) A. Pl. 125.
[1403] Carruthers (67³) p. 104.
[1404] Heer (77) +ii.+ p. 47, Pl. +xiii.+ fig. 10.
[1405] Fliche (96) p. 27, Pl. +i.+ fig. 3.
[1406] Seward (95) A. pp. 113 _et seq._; (96) A. p. 215; (04) B. pp.
138, 150.
[1407] Solms-Laubach (91) A. p. 92.
[1408] Lindley and Hutton (35) A. Pl. 136.
[1409] Corda in Reuss (46) B. Pl. +xlvi.+
[1410] Velenovský (85) B. Pl. 6, Pls. +iii.–v.+
[1411] Carruthers (70) Pl. +liv.+ fig. 6.
[1412] Saporta and Marion (85) p. 116, fig. 61, B.
[1413] Schimper (72) A. p. 199.
[1414] See Vol. +iv.+
[1415] Saporta (75) A. p. 209, Pl. 115, figs. 1, 2.
[1416] Heer (77) +ii.+ p. 47, Pl. +iv.+ figs. 14, 15.
[1417] Nathorst (78²) B. p. 49, Pl. +ii.+ figs. 15, 16.
[1418] Corda in Reuss (46) B. p. 86, Pl. +xlix.+ figs. 10, 11.
[1419] Carruthers (67²) p. 6.
[1420] Velenovský (85) B. p. 8, Pl. +iii.+ figs. 1–3, 6, 11.
[1421] Vol. +ii.+ p. 88.
[1422] Seward (95) A. p. 110, Pl. +ix.+ figs. 1–4.
[1423] I am indebted to Mr W. N. Edwards of the British Museum for the
cuticular preparations.
[1424] Newberry (88) p. 346, Pl. +viii.+ fig. 5.
[1425] Lesquereux (91) p. 29, Pl. +i.+ fig. 12.
[1426] Fontaine (89) B. p. 174, Pl. +lxx.+ fig. 4; Pl. +lxxi.+ figs. 3,
4, etc.
[1427] Saporta (74); Saporta and Marion (85) p. 116, fig. 61 C.
[1428] Ettingshausen (88²) p. 272, Pl. +iii.+ fig. 10.
[1429] Thomas, H. H. (15²).
[1430] Gutbier (49) Pl. +viii.+ fig. 7. For a fuller account of
Palaeozoic records, see Seward (95) A. p. 9.
[1431] Eichwald (55) Vol. +i.+ Pl. +xv.+ figs. 5, 6; Zeiller (96) A. p.
474.
[1432] Sandberger (64) Pl. +ii.+ figs. 1–4.
[1433] Saporta and Marion (85) p. 109; Zeiller (06) B. p. 194.
[1434] Goeppert (44) Pl. +i.+ fig. 6.
[1435] _Ibid._ (66) Pl. +ii.+
[1436] Saporta and Marion (78) Pl. +i.+ figs. 4, 5.
[1437] _Ibid._ (85) fig. 61, A, p. 116.
[1438] Krasser (03) p. 852.
[1439] Ettingshausen (86) Pl. +viii.+ figs. 19–21; (88) Pl. +viii.+
figs. 19–21.
[1440] Nathorst (12³) p. 36.
[1441] Thomas and Bancroft (13).
[1442] The genus _Ptilozamites_ described briefly in Volume +ii.+ has
recently been fully investigated by Antevs[1443] who had access to
the rich material in the Stockholm Museum from the Rhaetic beds of
Scania. He thinks that the genus is intermediate between _Anomozamites_
and _Ctenopteris_; its systematic position has not been definitely
established but, as Antevs says, there seems to be no reason why it
should not be a member of the Cycadophyta. In some species, _e.g._
_Ptilozamites fallax_ Nath. and _P. Nilssoni_ Nath., the rachis is
forked, while in _P. Heeri_ Nath. with linear fronds reaching a length
of 53 cm. the rachis is undivided.
[1443] Antevs (14²).
[1444] See page 502.
[1445] Nathorst (08) Pl. +i.+ figs. 3–5; Thomas and Bancroft (13) p.
194, Pl. +xx.+ fig. 12.
[1446] Fontaine (89) B. p. 160, Pls. +lxi.–lxvi.+; Berry (11) p. 354.
[1447] Morris (40) Pl. +xxi.+ figs. 1–4.
[1448] Lindley and Hutton (34) A. Pl. +cii.+
[1449] Morris (41) p. 116.
[1450] _Ibid._ (54) p. 15.
[1451] Oldham and Morris (63) B. p. 27.
[1452] Feistmantel (76²).
[1453] _Ibid._ (76²) p. 42.
[1454] _Ibid._ (77²) Pl. +xl.+ figs. 1, 2.
[1455] _Ibid._ (77²) p. 94, Pls. +v.+ +vi.+
[1456] _Ibid._ (79).
[1457] _Ibid._ (77⁴).
[1458] Seward (00) B. p. 193.
[1459] _Ibid._ (03) p. 227.
[1460] Halle (13²).
[1461] Halle (13²).
[1462] Thomas and Bancroft (13) p. 184.
[1463] Phillips (29) A. Pl. +vii.+ fig. 22; Pl. +x.+ fig. 4.
[1464] Heer (75) +ii.+
[1465] Halle (13²).
[1466] _Ibid._
[1467] Heer (75) +ii.+ Pls. +xiv.–xvi.+
[1468] Phillips (29) A. Pl. +vii.+ fig. 22; Pl. +x.+ fig. 4.
[1469] Sternberg (23) A. Pl. +xxxiii.+ fig. 1. For other references,
see Seward (00) B. p. 190; (04) B. p. 106.
[1470] Brongniart (28) A. p. 94.
[1471] Lindley and Hutton (35) A. Pl. 172.
[1472] Brongniart (28) A. p. 94.
[1473] Andrae (53) A. Pl. +xi.+ fig. 1.
[1474] Seward (07²) p. 29.
[1475] Nathorst (04²) B; Halle (13²).
[1476] Halle (13).
[1477] Heer (75) +ii.+ p. 66, Pls. +xiv.+, +xv.+
[1478] Halle (13²) p. 58, Pl. +vii.+
[1479] _Ibid._ p. 56, Pl. +vii.+
[1480] Goeppert (44) p. 52.
[1481] Dunker (46) A. p. 14, Pl. +ii.+ fig. 3; Pl. +vi.+ fig. 4.
[1482] Miquel (51) p. 212.
[1483] Seward (95) A. p. 38.
[1484] Schimper (70) A. p. 127.
[1485] Schenk (71) B. Pl. +xxxvi.+
[1486] Brongniart (28) A. p. 94.
[1487] Schenk (71) B. p. 8.
[1488] Schenk (67) A. Pls. +xxxvi.+—+vii.+
[1489] Goeppert (44) p. 122.
[1490] Pomel (47) p. 342.
[1491] Bornemann (56) A. p. 54.
[1492] Nathorst (90) A. p. 46.
[1493] Seward (95) A. p. 75.
[1494] Zeiller (03) B. p. 165.
[1495] Halle (13²) p. 55.
[1496] Schimper (72) A. pp. 128, 163.
[1497] Kurr, J. G. (45) B. Pl. +i.+ fig. 5.
[1498] Schenk (71) B. p. 8, Pl. +i.+ fig. 8.
[1499] Saporta (94) B. Pl. +xvi.+
[1500] Yokoyama (94) Pl. +xxi.+ fig. 5.
[1501] Feistmantel (79²) p. 18. This statement is based on an
examination of the specimen.
[1502] Zeiller (94) B. p. 174.
[1503] Halle (13²) p. 55.
[1504] See page 525.
[1505] Thomas and Bancroft (13) p. 184.
[1506] Zeiller (03) B. p. 166, Pl. +xliii.+ figs. 3–6.
[1507] Brongniart (28) A. p. 94. See Seward (00) B. p. 178.
[1508] Lindley and Hutton (38) A. Pl. +clxv.+
[1509] Saporta (75) A. Pls. +LXXXVII–XCII.+
[1510] _Ibid_. Pls. +lxxxiv.+, +lxxxv.+
[1511] _Ibid_. Pl. +xciii.+
[1512] Saporta (75) A. Pl. +xciii.+
[1513] Andrae (53) A. Pl. +ix.+
[1514] Frič and Bayer (01) B. fig. 43, p. 92.
[1515] Hosius and von der March (80) B. Pl. +xliv.+ fig. 202.
[1516] Tate (67) Pl. +v.+ fig. 7.
[1517] Seward (03) B. p. 21, Pls. +iii.+ +v.+
[1518] No. 11117.
[1519] Seward (95) A. p. 86, Pl. +vi.+
[1520] _Ibid_. (11²) p. 694, Pl. +x.+ fig. 43.
[1521] Miller (57) B. fig. 136.
[1522] Richards (84) p. 120.
[1523] Ettingshausen (52) B. p. 21, Pl. +i.+ fig. 1; Seward (95) A. p.
79, Pls. +iii.+, +iv.+, +viii.+
[1524] Goeppert (47) Pl. +xxxviii.+
[1525] Fontaine (89) B. p. 182, Pls. +lxviii.–lxxiv.+, etc.
[1526] Yokoyama (94) p. 223, Pls. +xx.+, +xxiii.+, etc.
[1527] Nathorst (90) A. Pls. +ii.+, +iii.+, +v.+
[1528] Braun in Münster (42) B. p. 36.
[1529] Seward (95) A. p. 56.
[1530] Heer (75) +ii.+ Pl. +xxvi.+ fig. 2; the specimen is in the
Stockholm Museum.
[1531] Halle (13²) p. 55.
[1532] Zigno (85) Pl. +xlii.+ fig. 9.
[1533] Wieland (13).
[1534] Schenk (67) A. Pl. +xxxiv.+ fig. 7.
[1535] Thomas and Bancroft (13) p. 186, Pl. +xix.+ figs. 3, 4.
[1536] Seward (95) A. Pl. +i.+ figs. 1, 2.
[1537] Brongniart (25) Pl. +xix.+ fig. 4; Seward (00) B. p. 219; (04)
B. p. 39.
[1538] Lindley and Hutton (34) A. Pl. +cxxviii.+
[1539] Zeiller (12) p. 6; Halle (13²) p. 63 (footnote).
[1540] Seward (00) B. p. 218.
[1541] Leckenby (64) A. Pl. +viii.+ fig. 5; Seward (00) B. p. 213, Pls.
+i.+, +ii.+
[1542] Zigno (81) Pl. +xxxiii.+ figs. 3, 4.
[1543] Saporta (75) A. PL. 101.
[1544] _Ibid._ Pl. 99.
[1545] Halle (13²) Pl. +vii.+
[1546] Heer (75) +ii.+ Pl. +xvi.+ figs. 5–8.
[1547] Schenk (67) A. Pls. +xxxiii.+, +xxxiv.+
[1548] Zeiller (03) B. Pl. +xliii.+ fig. 1.
[1549] Krasser (91) p. 12.
[1550] Zeiller (05).
[1551] Lindley and Hutton (32) A. Pl. +xliv.+
[1552] Leckenby (64) A. Pl. +x.+ fig. 2.
[1553] Zigno (85) Pls. +xxxv.–xxxvi.+
[1554] Zigno (53) p. 11; Seward (00) B. p. 211.
[1555] Leckenby (64) A. Pl. +ix.+ fig. 3.
[1556] Feistmantel (79) Pls. +vii.+, +xvi.+
[1557] Möller (03) Pl. +i.+
[1558] Zigno (81) Pl. +xxiv.+; Thomas and Bancroft (13) p. 186; Seward
(00) B. p. 221.
[1559] Oldham and Morris (63) B. p. 27, Pl. +xix.+; Feistmantel (76²)
Pl. +vii.+ fig. 4.
[1560] Dunker (46) A. p. 11, Pl. +ix.+ figs. 6, 7; Seward (95) A. p. 60.
[1561] Saporta (75) A. Pls. +cx.+, +cxi.+
[1562] _Ibid._ Pl. +cx.+
[1563] Thomas (11) p. 83, Pls. +v.+, +vi.+
[1564] Fontaine in Ward (05) B. Pl. +xxxviii.+
[1565] Nathorst (13) p. 279.
[1566] Dunker (46) A. p. 14, Pl. +ii.+ fig. 5; Seward (95) A. p. 70,
Pl. +i.+
[1567] Oldham and Morris (63) B. p. 37.
[1568] Seward (03).
[1569] Yabe (05) B. Pl. +ii.+ figs. 2–7.
[1570] Halle (12); (13) p. 9, Pl. +v.+ figs. 29–33.
[1571] Bancroft (13).
[1572] Oldham and Morris (63) B. Pl. +xxiv.+ figs. 1, 2; Feistmantel
(76²) Pls. +iv.–vi.+; (77) Pl. +ii.+
[1573] Yokoyama (89) B, Pl. +vii.+ fig. 10; Pls. +x.+, +xi.+
[1574] Seward (03) p. 217.
[1575] The statement made by me [Seward (11⁴) p. 3] that
_Dictyozamites_ occurs in the Falklands is incorrect.
[1576] Nathorst (89); Möller (03) p. 25, Pl. +v.+
[1577] Nathorst (07²) Pl. +iii.+ figs. 2–8.
[1578] Seward (03); Thomas (13²) p. 238; Thomas and Bancroft (13) p.
186, Pl. +xix.+ figs. 6–8.
[1579] Brongniart (25).
[1580] Nathorst (81) p. 61.
[1581] Brongniart (28) A. p. 95.
[1582] Heer (75) ii. Pl. +xv.+ fig. 11.
[1583] Schimper (72) A. p. 140.
[1584] Potonié (99) B. p. 281.
[1585] Zeiller (03) B. p. 174.
[1586] Halle (15) p. 515, Pl. +xiii.+ figs. 18–20, 22.
[1587] Heer (76) A. Pl. +xxxv.+ fig. 3.
[1588] Leuthardt (03) p. 20.
[1589] See page 463.
[1590] Thomas (13²) p. 237.
[1591] Schenk (67) A. Pls. +xxxvii.–viii.+
[1592] _Ibid_. Pl. +xxxix.+ fig. 7.
[1593] Thomas and Bancroft (13) Pl. +xix.+ fig. 5.
[1594] Ettingshausen (86) Pl. +viii.+ figs. 19–21.
[1595] Renault and Zeiller (88) A. p. 619, Pl. +lxviii.+
[1596] Arber, E. A. N. (12²).
[1597] Sandberger (64) Pl. +ii.+ figs. 1–4.
[1598] Renault (96) A. p. 322, fig. 64.
[1599] Saporta and Marion (85) p. 109, fig. 58 A.
[1600] Sandberger (64) Pl. +ii.+ figs. 1–4.
[1601] Geinitz (73) Pl. +iii.+ fig. 9.
[1602] Geinitz fig. 8.
[1603] Brongniart (28) p. 95.
[1604] Leuthardt (03) p. 14, Pl. +v.+
[1605] _Ibid_. p. 16, Pl. +v.+
[1606] _Ibid_. Pl. +vii.+ fig. 4; Pl. +viii.+ figs. 3–5.
[1607] Krasser (09).
[1608] Schenk (67) Pl. +ii.+ There are some fine examples from the
Raibl beds in the Vienna Geological Survey Collection.
[1609] Arber (07).
[1610] Fontaine (83) B. p. 80, Pls. +xliii.–v.+
[1611] Schimper (72) A. pp. 127, 132.
[1612] Schenk (67) Pl. +ii.+
[1613] Goeppert (44); Schenk (67) A. p. 164, Pl. +xxxviii.+
[1614] Schenk (87) B. p. 6, Pls. +vi.+, +ix.+
[1615] Zeiller (03) B. p. 189, Pl. +xlvii.+ fig. 1.
[1616] Zeiller (03) B. p. 198, Pl. +xlix.+ figs. 1–3.
[1617] _Ibid._ (05) p. 194.
[1618] Braun, F. (43).
[1619] Zeiller (03) B. p. 177, Pl. +xliii.+ fig. 8; Pl. +xliv.+ figs.
1–5.
[1620] Schenk (67) A. Pl. +xxxviii.+ figs. 5–9.
[1621] Zeiller (03) B. Pl. +xliii.+ fig. 7.
[1622] Feistmantel (86) Pl. +ii.+ A. figs. 4–8.
[1623] Seward (00) B. p. 239.
[1624] Seward (11²) p. 694, Pls. +iv.+, +v.+ etc.
[1625] Zeiller (03) B. Pl. +xix.+
[1626] Fontaine in Ward (05) B. Pl. +xxii.+
[1627] Schenk (71) B. Pl. +xxiv.+ fig. 5.
[1628] Oldham and Morris (63) B. Pl. +ix.+; Feistmantel (77³) Pls.
+v.+, +vi.+
[1629] Phillips (29) A. Pl. +viii.+ fig. 4.
[1630] See Seward (00) B. p. 204.
[1631] Dunker (46) A. p. 14, Pl. +vi.+ figs. 1, 2.
[1632] Seward (95) A. p. 91; see also Schenk (71) Pl. +xxxiv.+
[1633] Sternberg (25) A. p. +xxxii.+
[1634] Brongniart (28) A. p. 93. Specimens named by Brongniart
_Cycadites Nilssoniana_ are probably fragments of Dicotyledonous leaves
[Nathorst (81) p. 83].
[1635] Holden, R. (14²).
[1636] Nathorst (07³).
[1637] Halle (15).
[1638] Pls. +xii.+, +xiii.+
[1639] Thomas and Bancroft (13).
[1640] Heer (82) B. Pl. +v.+
[1641] _Ibid._ (78) ii. Pl. +iv.+ fig. 1; Nathorst (97²) p. 387.
[1642] Heer (77) ii. Pls. +viii.+, +xxiii.+, +xxv.+
[1643] Oldham and Morris (63) B. Pls. +vii.+, +viii.+; Feistmantel
(77²) Pl. +xlviii.+ fig. 1; the drawing is very inaccurate.
[1644] Oldham and Morris (63) B. Pl. +ix.+
[1645] Feistmantel (79) Pl. +vii.+ fig. 10; Nathorst (09) p. 5, note 2.
[1646] Goeppert (66).
[1647] Zeiller (02) B. Pl. +vii.+ fig. 4.
[1648] Nathorst (07³) Pls. +i.–iii.+
[1649] Seward (95) A. p 29, Pl. +ii.+ fig. 7; Pl. +vi.+ fig. 5; Pl.
+viii.+ fig. 2.
[1650] Saporta (94) B. p. 171, Pl. +xxxii.+
[1651] Holden, R. (14²).
[1652] Halle (55), p. 502.
[1653] Schenk (71) B. Pl. +xxxii.+ fig. 1.
[1654] Seward (95) A. pp. 2–7.
[1655] Halle (15), Pl. +xii.+ fig. 12.
[1656] Zeiller (03) B. p. 155, Pl. +xli.+
[1657] Brauns (66) p. 56, Pl. +xiv.+ fig. 7; Schenk (67) A. Pl. +xxxv.+
fig. 11; Seward (04) B. p. 37, Pl. +iv.+ fig. 4; Pl. +ii.+ fig. 1.
[1658] Lignier (13) p. 90, Pl. +ix.+ figs. 18, 19.
[1659] Brongniart (25).
[1660] Nathorst (09²).
[1661] Pages 13, 16.
[1662] Nathorst (09²); Thomas and Bancroft (13).
[1663] Stopes (10²).
[1664] Schenk (67) A. Pl. +xxix.+ figs. 1, 2.
[1665] See vol. +iv.+
[1666] Nathorst (86) Pl. +xviii.+ fig. 5.
[1667] _Ibid_. (09²) p. 28.
[1668] Thomas (13²) p. 241; Thomas and Bancroft (13) p. 193.
[1669] Miquel (42) p. 61.
[1670] Schenk (67) A. p. 127, Pls. +xxix.+, +xxx.+; Nathorst (09²) p.
10, Pl. +v.+ figs. 9–13, etc.
[1671] For other references see Nathorst (09²) p. 10.
[1672] Brongniart (25) p. 218.
[1673] Nathorst (09²) p. 12, Pl. +i.+ figs. 2–35, etc.
[1674] Oldham and Morris (63) Pls. +vii.+, +viii.+
[1675] Feistmantel (77³) p. 124.
[1676] Schenk (67) A. Pl. +xxix.+ fig. 10.
[1677] Stopes (10²).
[1678] Nathorst (86) p. 72.
[1679] _Ibid._ (02) p. 18, Pl. +i.+
[1680] _Ibid._ (09²) p. 21, Pls. +vi.+, +vii.+
[1681] Phillips (29) A. p. 148, Pl. +vii.+ fig. 20. See Seward (00) B,
p. 223, Pl. +iv.+ fig. 5; text figs. 39, 40.
[1682] Thomas and Bancroft (13) p. 191.
[1683] A specimen in the Natural History Museum, Paris, labelled _N.
Williamsonis_ is probably that mentioned by Brongniart.
[1684] Oldham and Morris (63) B. Pls. +x.–xiii.+; Feistmantel (77) Pl.
+xlvii.+
[1685] Heer (78) ii. Pls. +xxiii.+, +xxiv.+; Seward (12³) p. 27, Pl.
+ii.+
[1686] Nathorst (97) p. 13.
[1687] Yokoyama (89) B. Pls. +v.+, +vii.+, +xii.+, +xiii.+; Ward (05)
B. Pl. +xvii.+
[1688] Heer (78) ii. p. 18, Pl. +iv.+ figs. 5–9.
[1689] Seward (00) B. p. 230, fig. 41.
[1690] Heer (82) B. Pl. +vi.+
[1691] For figures and references, see Seward (11²) p. 695; Thomas (11)
p. 86.
[1692] Halle (13²) p. 47, Pls. +v.+, +vi.+
[1693] Fontaine (89) B. Pls. +xxx.–xxxv.+
[1694] Berry (11) p. 362, Pls. +lvii.+, +lviii.+
[1695] Seward (00) B. p. 224.
[1696] Nathorst (97) Pl. +i.+ fig. 18.
[1697] Seward (12) p. 30.
[1698] Yokoyama (89) B.; Nathorst (90) A.
[1699] Stopes (10²).
[1700] Salfield (09) B. Pl. +iii.+ figs. 5–7.
[1701] For references, see Seward (12) p. 31.
[1702] Phillips (29) A. p. 148, Pl. +vii.+ fig. 19.
[1703] Leckenby (64) A. p. 77; Seward (00) B. p. 227, Pl. +iv.+ figs.
1–4.
[1704] Seward (00) B. p. 227.
[1705] Krasser (09) p. 120.
[1706] Seward (11²) p. 697.
[1707] Oldham and Morris (63) B. p. 23, Pls. +x.–xiii.+; Feistmantel
(77) Pl. +xlvii.+
[1708] Oldham and Morris (63) B. Pl. +xv.+ fig. 1.
[1709] Dunker (46) A. p. 15, Pl. +i.+ fig. 7, etc.; Seward (95) A. p.
53.
[1710] Schenk (71) B.; Nathorst (90) A.; Yokoyama (94); Fontaine in
Ward (05) B.; Yabe (13).
[1711] Lindley and Hutton (34) A. Pl. +ciii.+; Phillips (29) A. Pl.
+vii.+ fig. 21.
[1712] Zeiller (00) B. p. 115; Krasser (09) p. 113.
[1713] Ettingshausen (51).
[1714] Schenk (68²).
[1715] Raciborski (94) A. Pls. +xvii.–xix.+
[1716] Staub (96).
[1717] Nathorst (86) p. 43.
[1718] Seward (00) p. 21; (00) B. p. 232, figs. 42, 43.
[1719] Raciborski (94) A. Pl. +xvi.+
[1720] Fontaine (89) B. p. 174, Pls. +lxx.–lxxii.+
[1721] Krasser (09) p. 113.
[1722] Nathorst (86) p. 89, Pls. +vii.+, +viii.+, +xi.+, +xix.+
[1723] Raciborski (92) Pl. +ii.+ fig. 2.
[1724] Staub (96)
[1725] Ettingshausen (51) Pls. +xi.+, +xii.+
[1726] Schenk (68²).
[1727] Raciborski (92) Pl. +ii.+ fig. 2.
[1728] _Ibid._ (94) A. Pl. +xviii.+ fig. 2.
[1729] Yokoyama (06) B. Pl. +ix.+
[1730] Phillips (29) A. p. 148, Pl. +vii.+ fig. 21.
[1731] Lindley and Hutton (34) A. Pl. +ciii.+
[1732] Ward (05) B. p. 113.
[1733] Seward (00) B. p. 235, Pl. +viii.+ fig. 2; Zigno (56) A. Pl.
+xxiv.+
[1734] Fontaine in Ward (05) B. Pls. +xxvii.–xxviii.+
[1735] Seward (12) Pl. +iii.+ fig. 43.
[1736] Seward (04) B. p. 115.
[1737] _Ibid._ (00) p. 21.
[1738] Seward (11²) p. 691.
[1739] _Ibid._ p. 792, Pls. +iv.+, +vii.+, +viii.+, +x.+
[1740] Miller (57) B. figs. 133, 135.
[1741] Richards (84) p. 117.
[1742] Seward (95) A. p. 89, fig. 5.
[1743] Tate (67) Pl. +v.+ fig. 3; Seward (03) B. Pl. +v.+ fig. 3.
[1744] Fontaine (83) B. Pls. +xxxix.–xlii.+
[1745] Fontaine in Ward (05) B. Pl. +xxiii.+
[1746] Seward (11²) Pls. +iv.+, +vii.+
[1747] Halle (13²) p. 51, Pl. +vi.+ fig. 8.
[1748] Berry (11) p. 349.
[1749] Oldham and Morris (63) Pl. +xv.+ fig. 4.
[1750] _Ibid._ Pl. +xv.+ fig. 1.; Feistmantel (77) Pl. +xliii.+ fig. 1.
[1751] Thomas (13²) p. 242, Pls. +xxiv.+, +xxvi.+
[1752] _Ibid._ Pl. +xxvi.+
[1753] Feistmantel (86) Pl. +ii.+ A. figs. 4–8.
[1754] Brongniart (49) A. p. 61.
[1755] Zigno (85) p. 105.
[1756] Seward (00) B. p. 215.
[1757] Renault (96) A. p. 327; (93) A. Pl. +lxxxi.+ fig. 1.
[1758] Seward (04) B. p. 119, Pl. +xi.+ fig. 4, text-fig. 12.
[1759] Buckman (45) Pl. +i.+ fig. 2.
[1760] Zigno (85) Pls. +xxxix.+, +xl.+
[1761] Newberry (88) Pl. +viii.+ fig. 14.
[1762] See vol. +iv.+
[1763] Bodenbender (02) p. 40 of the reprint.
[1764] Zeiller (94) B. p. 174, Pls. +viii.+, +ix.+
[1765] Renault and Zeiller (88) A. p. 614, Pl. +lxvii.+ fig. 8.
[1766] Zalessky (05²) p. 401, fig. 13.
[1767] Potonié (93) A. p. 210, Pl. +xxix.+ fig. 5.
[1768] Zalessky (05²) p. 403, figs. 14, 15.
[1769] Bassler (16).
[1770] Saporta (75) A. p. 193, Pl. 114, fig. 3; Pl. 117, fig. 1.
[1771] Fliche and Bleicher (82) p. 21, fig. 4.
[1772] Stopes (15) p. 53.
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