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Title: First course in biology
Author: L. H. Bailey
Walter Moore Coleman
Release date: September 10, 2025 [eBook #76851]
Language: English
Original publication: New York: The MacMillan Company, 1908
Credits: Greg Bergquist, Harry Lamé and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.)
*** START OF THE PROJECT GUTENBERG EBOOK FIRST COURSE IN BIOLOGY ***
Transcriber’s Notes
Phrases printed in bold face, italics or small capitals in the
source document have been transcribed between =equal signs= or
_underscores_, or as ALL CAPITALS for this e-text.
More Transcriber’s Notes may be found at the end of this e-text.
FIRST COURSE IN BIOLOGY
[Illustration]
THE MACMILLAN COMPANY
NEW YORK · BOSTON · CHICAGO
ATLANTA · SAN FRANCISCO
MACMILLAN & CO., LIMITED
LONDON · BOMBAY · CALCUTTA
MELBOURNE
THE MACMILLAN CO. OF CANADA, LTD.
TORONTO
[Illustration: KENTISH PLOVER WITH EGGS AND YOUNG (PROTECTIVE
RESEMBLANCE)
From the Exhibit in the British Natural History Museum. (Morgan.)]
FIRST COURSE IN BIOLOGY
BY
L. H. BAILEY
_PART I. PLANT BIOLOGY_
AND
WALTER M. COLEMAN
_PART II. ANIMAL BIOLOGY_
_PART III. HUMAN BIOLOGY_
New York
THE MACMILLAN COMPANY
1909
_All rights reserved_
COPYRIGHT, 1908,
BY THE MACMILLAN COMPANY.
Set up and electrotyped. Published July, 1908. Reprinted
October, 1908; February, September, 1909.
Norwood Press
J. S. Cushing Co.--Berwick & Smith Co.
Norwood, Mass., U.S.A.
PREFACE
The present tendency in secondary education is away from the formal
technical completion of separate subjects and toward the developing
of a workable training in the activities that relate the pupil to his
own life. In the natural science field, the tendency is to attach less
importance to botany and zoology and physiology as such, and to lay
greater stress on the processes and adaptations of life as expressed
in plants and animals and men. This tendency is a revolt against the
laboratory method and research method of the college as it has been
impressed into the common schools, for it is not uncommon for the pupil
to study botany without really knowing plants, or physiology without
knowing himself. Education that is not applicable, that does not put
the pupil into touch with the living knowledge and the affairs of his
time, may be of less educative value than the learning of a trade in a
shop. We are coming to learn that the ideals and the abilities should
be developed out of the common surroundings and affairs of life rather
than imposed on the pupil as a matter of abstract, unrelated theory.
One of the marks of this new tendency in education is the introduction
of unit courses in biology in the secondary schools, in the place of
the formal and often dry and nearly meaningless isolated courses in
botany, zoology, and physiology. This result is one of the outcomes of
the recent nature-study discussions.
The present volume is an effort to meet the need for a simple and
untechnical text to cover this secondary biology in its elementary
phases. The book stands between the unorganized nature-study of the
intermediate grades and the formal science of the more advanced
courses. It is a difficult space to bridge, partly because the subjects
are so diverse, and partly because some teachers do not yet understand
the importance of imparting to beginners a general rather than a
special view point.
Still another difficulty is the lack of uniformity in the practice
of different schools. It is not urged that it is desirable to have
uniformity in all respects, but the lack of it makes it difficult to
prepare a book that shall equally meet all needs. It is hoped, however,
that the present book is fairly adaptable to a variety of conditions,
and with this thought in mind the following suggestions are made as to
its use:
Being in three separate parts, the teacher may begin with plants, or
with animals, or with human physiology.
If a one-year course is desired, the topics that are printed in large
type in Parts II and III may be used, and a choice from the chapters in
Part I.
For three half-year courses, all the parts may be covered in full.
If the course in biology begins in the fall (with the school year),
it may be well to study plant biology two days in the week and animal
biology three days until midwinter; when outdoor material becomes
scarce, human biology may be followed five days in the week; in spring,
plants may be studied three days and animals two days.
If the use of the book is begun at midyear, it will probably be better
to follow the order in the book consecutively.
If it is desired to take only a part of the plant biology, Chapters VI,
XIV, XX, XXIII, XXIV may be omitted, and also perhaps parts of other
chapters (as of X, XII, XIII) if the time is very short. The important
point is to give the pupil a rational conception of what plants are
and of their main activities; therefore, the parts that deal with
the underlying life processes and the relation of the plant to its
surroundings should not be omitted.
If more work is wanted it is best to provide the extra work by means
of the study of a greater abundance of specimens rather than by
the addition of more texts; but the teacher must be careful not to
introduce too much detail until the general subject has first been
covered.
The value of biology study lies in the work with the actual things
themselves. It is not possible to provide specimens for every point in
the work, nor is it always desirable to do so; for the beginning pupil
may not be able to interest himself in the objects, and he may become
immersed in details before he has arrived at any general view or reason
of the subject. Great care must be exercised that the pupil is not
swamped. Mere book work or memory stuffing is useless, and it may dwarf
or divert the sympathies of active young minds.
Every effort should be made to apply the lessons to daily life. The
very reason for knowing plants and animals is that one may live with
them, and the reason for knowing oneself is that he may live his daily
life with some degree of intelligence. The teacher should not be afraid
to make all teaching useful and practical.
In many cases a state syllabus designates just what subjects shall be
covered; the topics may be chosen easily from the text, and the order
of them is usually left largely to the discretion of the teacher.
Finally, let it be repeated that it is much better for the beginning
pupil to acquire a real conception of a few central principles and
points of view respecting common forms that will enable him to tie his
knowledge together and organize it and apply it, than to familiarize
himself with any number of mere facts about the lower forms of life
which, at the best, he can know only indirectly and remotely. If the
pupil wishes to go farther in later years, he may then take up special
groups and phases.
CONTENTS
PAGE
GENERAL INTRODUCTION I xi
PART I. PLANT BIOLOGY
CHAPTER
I. NO TWO PLANTS OR PARTS ARE ALIKE P 1
II. THE STRUGGLE TO LIVE P 4
III. SURVIVAL OF THE FIT P 7
IV. PLANT SOCIETIES P 9
V. THE PLANT BODY P 15
VI. SEEDS AND GERMINATION P 20
VII. THE ROOT--THE FORMS OF ROOTS P 32
VIII. THE ROOT--FUNCTION AND STRUCTURE P 38
IX. THE STEM--KINDS AND FORMS--PRUNING P 49
X. THE STEM--ITS GENERAL STRUCTURE P 59
XI. LEAVES--FORM AND POSITION P 73
XII. LEAVES--STRUCTURE AND ANATOMY P 86
XIII. LEAVES--FUNCTION OR WORK P 92
XIV. DEPENDENT PLANTS P 106
XV. WINTER AND DORMANT BUDS P 111
XVI. BUD PROPAGATION P 121
XVII. HOW PLANTS CLIMB P 129
XVIII. THE FLOWER--ITS PARTS AND FORMS P 133
XIX. THE FLOWER--FERTILIZATION AND POLLINATION P 144
XX. FLOWER-CLUSTERS P 155
XXI. FRUITS P 163
XXII. DISPERSAL OF SEEDS P 172
XIII. PHENOGAMS AND CRYPTOGAMS P 176
XXIV. STUDIES IN CRYPTOGAMS P 182
PART II. ANIMAL BIOLOGY
I. INTRODUCTION A 1
II. PROTOZOANS A 10
III. SPONGES A 17
IV. POLYPS A 22
V. ECHINODERMS A 34
VI. WORMS A 42
VII. CRUSTACEANS A 51
VIII. INSECTS A 63
IX. MOLLUSKS A 97
X. FISHES A 109
XI. BATRACHIANS A 126
XII. REPTILES A 139
XIII. BIRDS A 150
XIV. MAMMALS A 184
PART III. HUMAN BIOLOGY
I. INTRODUCTION H 1
II. THE SKIN AND KIDNEYS H 16
III. THE SKELETON H 28
IV. THE MUSCLES H 39
V. THE CIRCULATION H 51
VI. THE RESPIRATION H 70
VII. FOOD AND DIGESTION H 89
VIII. THE NERVOUS SYSTEM H 117
IX. THE SENSES H 142
X. BACTERIA AND SANITATION H 158
GENERAL INDEX i
GENERAL INTRODUCTION
=PRELIMINARY EXPERIMENTS=
These experiments are inserted for those pupils who have not had
instruction in chemistry and physics, to give them a point of view on
the subjects that follow. At least a general understanding of some
of these subjects is necessary to a satisfactory elementary study of
biology.
=Elements and Compounds.=--The material world is made up of elements
and compounds. An _element_ is a substance that cannot be separated
into two or more substances. A _compound_ is formed by the union of two
or more elements. All the material or substance of which the earth and
its inhabitants is composed is formed of the chemical elements; this
substance taken all together is known as _matter_.
_Carbon_ and _iron_ are examples of elements. Compare a bit of
charcoal, which is one form of carbon, with a new iron nail. Which is
brighter? Heavier for its size? Tougher? More brittle? Harder? More
readily combustible? Resistant to change when left exposed to air
and dampness? There are two other forms of carbon: graphite or black
lead (used in pencils and stove polish); and diamond, which occurs in
crystals and is the hardest known substance. Iron does not have varied
forms like carbon. _Sulfur_ is another element. What is its color? Has
it odor? Taste? Will it dissolve in water? Is it heavy or light? Will
it burn? What is the color of the flame? Of the fumes? _Phosphorus_,
another element, burns so readily that it ignites by friction and is
used in matches. Rub the tip of a match with the finger. What is the
odor of phosphorus? Phosphorus exists in nature only in combination
with other elements. Lead, tin, silver, gold, copper, zinc, nickel,
platinum, are elements.
There are less than eighty known elements; but the compounds formed of
them are innumerable. Carbon is found in all substances formed by the
growth of living things. That there is carbon in sugar, for example,
can easily be shown by charring it on a hot shovel or a stove until its
water is driven off and only charcoal is left. Part of the starch in a
biscuit remains as charcoal when it has been half burned.
=Oxygen and the Air.=--The great activity of pure oxygen in attacking
other substances can be shown by passing into a fruit-jar a lighted
splinter, a piece of lighted magnesium ribbon, an old watch spring (or
a bit of picture wire), the end of which has been dipped in sulfur and
lighted. About one fifth of the air is oxygen and about four fifths
is _nitrogen_ and other inactive gases. Pure nitrogen will quickly
extinguish a lighted splinter thrust into it. It is the oxygen in the
air that supports all forms of burning. Less than one half of one per
cent of the air is an inactive gas called carbon dioxid, a compound of
carbon and oxygen. It is formed not only when wood or coal is burned,
but also by the life processes of animals and plants.
=Favorable and Unfavorable Conditions for Evaporation.=--Pour the same
quantity of water (half a glassful) into three saucers and two bottles.
Place one saucer near a hot stove; place the other two in a cool place,
having first covered one of them with a dish. Place one of the bottles
by the stove and the other by the remaining saucers. After some hours,
examine the saucers and bottles and compare and record the results.
Explain. State three conditions that are favorable to evaporation.
State three ways in which evaporation may be prevented or decreased.
=Tests for Acid, Alkaline, and Neutral Substances.=--For _acid tests_,
use sour buttermilk (which contains _lactic acid_), or _hydrochloric
acid_ diluted in ten parts water, or _strong vinegar_ (which contains
_acetic acid_). Has the acid a characteristic (“sour”) _odor_ and
_taste_ (test it only when very dilute)? Rub dilute acid between the
fingers; how does it feel? Is there any effect on the fingers? Obtain
litmus paper at a druggist’s. Dip a strip of red litmus and of blue
litmus paper into the acid. What result?
For _alkaline tests_, dissolve in a glass of water a spoonful of baking
soda or some laundry soap; or dissolve an inch stick of caustic soda
in a glass of water. Test odor and “feel” of last solution as with the
acid; likewise test effect of alkaline solution on red and blue litmus
paper. Record results. Alkalies are strong examples of a more general
class of substances called _bases_, which have the opposite effect from
acids.
Test pure water. Has it odor? A taste? Test it with red and blue litmus
paper. Water is a _neutral_ substance: that is, it is neither an acid
nor an alkali (or base).
After making appropriate tests, write _ac_, _al_, or _neu_ after each
name in the following list (or write in three columns): vinegar, soda,
saliva, sugar, juice of apple, lemon, and other fruits, milk, baking
powder, buttermilk, ammonia, salt water.
Pour some of the alkaline solution into a dish, gradually add dilute
acid (or sour buttermilk), stirring with glass rod and testing with
litmus until the mixture does not turn red litmus blue nor blue litmus
red. The acid and alkali are then said to have _neutralized_ each
other, and the resulting substance is called a _salt_. The salt may
be obtained by evaporating the water of the solution. Most common
minerals are salts. If the last experiment is tried with soda and sour
buttermilk, the demonstration will show some of the facts involved in
bread making with the use of these substances.
=Test for Starch.=--Starch turns blue with iodine. The color may be
driven away by heat, but will return again as the temperature lowers.
Procure a few cents’ worth of tincture of iodine and dilute it. Get a
half dozen pieces of paper and cardboard, all different, and test each
for starch by placing it over mouth of bottle and tipping the bottle
up. If much starch is present the spot will be blue-black or dark blue;
if little starch, pale blue; if no starch, brown or yellowish.
Make pastes with wheat flour, potato starch, and corn starch. Treat a
little of each with a solution of rather dilute tincture of iodine.
Try grains from crushed rice with the same solution. Are they the same
color? Cut a thin section from a potato, treat with iodine and examine
under the microscope.
=To study Starch Grains.=--Mount in cold water a few grains of starch
from each of the following: potato, wheat, arrowroot (buy at drug
store), rice, oats, corn. Study under microscope the sizes, forms,
layers, fissures, and location of nuclei, and make a drawing of a few
grains of each.
=Test for Grape Sugar.=--Make a thick section of a bit of the edible
part of a pear and place it in a bath of Fehling’s solution. After
a few moments boil the liquid containing the section for one or two
minutes. It will turn to an orange color, showing a deposit of an oxid
of copper and perhaps a little copper in the metallic form. A thin
section treated in like manner may be examined under the microscope,
and the fine particles, precipitated from the sugar of the pear, may
be clearly seen. (_Fehling’s solution_ is made by taking one part each
of these three solutions and two parts of water: (1) Copper sulfate, 9
grams in 250 cubic centimeters of water; (2) sodium hydroxid, 30 grams
in 250 c.c. water; (3) Rochelle salts, 43 grams in 250 c.c. water.)
=Test for Nitrogenous Substances, or Proteids.=--Put a little white
of egg into a test tube and heat slowly. What change takes place in
the egg? Put another part of the white of egg into a test tube and
add dilute nitric acid. Compare the results of the two experiments.
White of egg is an example of a proteid; that is, it is the form of
nitrogen most commonly found in plant and animal tissue, and it can be
formed only by life processes. Do acid and heat harden or soften most
substances? Either of the above tests reveal proteid, if present. Does
cooking tend to soften or toughen lean meat?
Another test for proteid is nitric acid, which _turns proteid_
(and hardly anything else) _yellow_. Proteid when burned has a
characteristic odor; this will be noticed if lean meat or cheese is
charred in a spoon. The offensive odor from decomposing proteid is also
characteristic, whether it comes from stale beans, meat, mushrooms, or
other things containing proteid.
=Test for Fats and Oils.=--Place a little tallow from a candle on
unglazed paper and warm. Hold the paper up to the light and examine it.
What effect has the fat had on the paper? Place a little starch, sugar,
powdered chalk, or white of egg on paper and repeat the experiment; is
the effect the same? Place some of the tallow in a spoon, and heat.
Compare the effect of heat on fat and proteid. Water also makes paper
semi-transparent, but it soon evaporates: fat does not evaporate.
Another test for fats is to mount a thin section of the endosperm of
castor-oil seed in water and examine with high power. Small drops of
oil will be quite abundant. Treat the mount with alcanin (henna root in
alcohol). The drops of oil will stain red. This is a standard test for
fats and oils.
=To make or liberate Oxygen.=--If there is a chemistry class in school,
one of its members will doubtless be glad to prepare some of the gas
called _oxygen_, and furnish several glass jars filled with it to the
biology class. If it is desired to make oxygen, the following method
may be employed: Provide a dry glass flask of three to four ounces
capacity. It should have a glass delivery tube, inserted through a
one-holed rubber stopper, and so bent as to pass under the surface
of water contained in a deep dish. Fill several pint fruit-jars with
water, cover with pieces of stiff pasteboard, and turn mouth downwards
in the dish of water. From one half to two thirds ounces of an equal
mixture of potassium chlorate and manganese dioxid (procured at drug
store) is put in the flask and heated by means of a gas or alcohol
lamp. When the oxygen begins to form, collect some in jars by inserting
the end of delivery tube under the jars as they stand in water.
_Caution_: Remove delivery tube from water before cooling the flask, to
prevent any water being drawn back.
=Oxidation.=--That something besides wood or coal is necessary to a
fire can be shown by shutting off entirely the draught of a stove. Fire
and other forms of combustion depend on a process called _oxidation_.
This consists in the uniting of oxygen with other substances. When wood
decays, the carbon in it oxidizes (unites with oxygen) and _carbon
dioxid gas_ is formed. When wood burns, the oxidation is more rapid.
When iron oxidizes, _iron rust_ is formed. When hydrogen is oxidized,
water is formed. Kerosene oil contains hydrogen, and water is formed
when it is burned. Almost every one has noticed the cloud of moisture
which collects on the chimney when the lamp is first lighted. By
using a chimney which has been kept in a cold place, the moisture
becomes apparent; soon the chimney becomes hot and the water no longer
collects, but it continues to pass into the room as long as the lamp
burns. Fats also contain hydrogen. Hold a piece of cold glass or an
inverted tumbler above the flame of a tallow candle. Does water collect
on it?
Oxidation may be said to be the basis of all life processes for this
reason: oxidation gives rise to heat and sets free energy, and all
living things need heat and energy in order to grow and live. The
heat of animals is very noticeable. The oxidation in plants also
forms a slight amount of heat. In both animals and plants oxidation
is much slower than in ordinary fires. That heat is formed even in
slow oxidation is shown by fires which arise spontaneously in masses
of decaying material. The rotting of wood is not only accompanied by
heat but sometimes by light, as when “fox fire” is emitted. Rub the
end of a match on your finger in the dark. Explain the result. Strike
a match and notice the white fumes which rise for an instant. These
fumes are not ordinary smoke (particles of carbon), but they are oxid
of phosphorus. Why will water (oxid of hydrogen) not burn? Sand is oxid
of silicon. Explain how throwing sand on a fire puts it out. [See also
experiments with candle and breath, in The Principles of Biology.]
=Inorganic and Organic Matter.=--=Test for Minerals.=--The earth
was once in a molten condition, which would have destroyed any
combustible material if any had then existed. Before plants and
animals existed, the earth consisted mostly of incombustible minerals,
known as _inorganic matter_. Substances formed by animals and plants
are _organic matter_, so called because built up by organized or
organ-bearing or living things; starch is an example, being formed in
plants. Organic substances are composed chiefly of carbon, oxygen,
hydrogen, and nitrogen. (See page 1 of “Animal Biology.”) Coal-oil, and
all combustible materials have their origin in life. Hence, burning
to find whether there is an incombustible residue is also a _test for
minerals_. Meat, bread, oatmeal, bone, wood, may be tested for mineral
matter by burning in a spoon held over a hot fire, or flame of gas
or lamp. The substance being tested should be burned until all black
material (which is organic carbon and not a mineral) has disappeared.
Any residue will be _mineral matter_.
=Protoplasm.=--Inside the cells of plants and animals is the _living
substance_, known as _protoplasm_. It is a structureless, nearly or
quite colorless, transparent jelly-like substance of very complex and
unstable composition. Eighty per cent or more is water; the remainder
is proteid, fats, oils, sugars, and salts. Protoplasm has the power of
_growth and reproduction_; it can make _living substance from dead or
lifeless substances_. It has the _power of movement_ within the cell,
and it is influenced (or is irritable) by heat, light, touch, and other
stimuli. When protoplasm dies the organism dies.
=Physics= is the science that treats of the _properties_ and
_phenomena_ (or behavior) of matter or of objects; as of such
properties or phenomena or agencies as heat, light, force, electricity,
sound, friction, density, weight, and the like.
=Chemistry= is the science that treats of the _composition_ of matter.
All matter is made up, as we have seen, of elements. Very few elements
exist in nature in a free or uncombined form. The nitrogen and oxygen
of the air are the leading uncombined elements.
In order to express the chemical combinations clearly, _symbols_ are
used to represent each element, and these symbols are then combined
to represent the proportions of each in the compound. If C stands for
carbon and O for oxygen, the carbon dioxid might be represented by the
formula COO. In order to avoid the repetition of any letter, however, a
number is used to denote how many times the element is taken: thus the
formula always used for carbon dioxid is CO₂. The formula for hydrogen
oxid, or water, is H₂O; that for starch is C₆H₁₀O₅. N stands for
nitrogen; P, for phosphorus; K, potassium; Fe, iron; S, sulfur.
=Biology= is the science that treats of life; that is, of all knowledge
of plants and animals of all kinds. (See page 1, “Animal Biology.”)
HOW A CANDLE BURNS
Some of the foregoing suggestions may be readily explained and
illustrated by simple experiments with a burning candle. The
following directions for such experiments are by G. W. Cavanaugh.
The materials needed for this exercise are: a piece of candle about
two inches long, a lamp chimney (one with a plain top is best), a
piece of white crockery or window glass, a piece of fine wire about
six inches long, a bit of quicklime about half the size of an egg,
and some matches. All of these, with the possible exception of the
quicklime, can be obtained in any household. If you perform the
experiment requiring the lime, be sure that you start with a fresh
piece of quick or stone lime, which can be had of any lime or cement
dealer. During the performance of the following simple experiments,
the pupil should describe what he sees at each step. The questions
inserted in the text are offered merely as suggestions in the
development of the desired ideas. The answers are those which it is
desired the pupils shall reach or confirm by their own observation.
I. _Oxygen_
Light the candle and place it on a piece of blotting paper (_A_). What
do you see burning? Is anything burning besides the candle? The answer
will probably be “no.” Let us see.
Place the lamp chimney over the lighted candle, and partly cover the
top by a piece of stiff paper, as in Fig. A. Ask the pupils to observe
and describe how the flame goes out; _i.e._ that it is gradually
extinguished and does not go out instantly. Why did the flame go out?
The probable thought will be, “Because there was no air.” (If there was
no air within the chimney, some could have entered at the top.)
[Illustration: _A._--THE BEGINNING OF THE CANDLE EXPERIMENT.]
[Illustration: _B._--SUPPLYING AIR UNDERNEATH THE CHIMNEY.]
Place two pencils beside the relighted candle and on them the chimney
(_B_). What is the difference between the way in which the candle burns
now and before the chimney was placed over it? It flickers, or dances
about more. What makes boys and girls feel like dancing about when they
go out from a warm schoolroom? What makes the flame dance or flicker
when the chimney is raised by the pencils? Because it gets fresh air
under the chimney.
Repeat the first experiment, in which the flame grows gradually smaller
till it is extinguished. Why does the flame die out now? Is it really
necessary to have fresh air in order to keep a flame burning?
To prove this further, let the candle be relighted. Place the chimney
over it, now having the top completely closed by a piece of paper.
Have ready a lighted splinter or match, and just as soon as the candle
is extinguished remove the paper from the chimney top and thrust in
the lighted splinter. Why does the light on the splinter go out? What
became of the freshness that was in the air? It was destroyed by the
burning candle.
Evidently there is some decided difference between unburned air and
burned air, since a flame can continue to burn only in air that has the
quality known as freshness. This quality of fresh air is due to oxygen,
represented by O. Why was the splinter put out instantly, while the
candle flame died out gradually? When the splinter was thrust in, the
air had no freshness or oxygen at all, while when the candle was placed
under the chimney, it had whatever oxygen was originally in the air
within the chimney.
Endeavor to have this point clearly understood: that the candle did
not go out as long as the air had any oxygen and that the splinter was
extinguished immediately because there was no oxygen left.
Relight the candle. A former question may now be repeated: Is anything
else burning besides the candle?
When the subject of the necessity of fresh air and consequently of
oxygen for the burning of the candle seems to be understood, the
following questions, together with any others which suggest themselves,
may be asked: What is the reason that draughts are opened in stoves?
Why is the bottom of a “burner” on a lamp always full of holes?
II. _Carbon_
Let us now observe the blackened end of a burned match or splinter.
This black substance is usually known by the name of charcoal. If
handled, it will blacken the fingers. Try this. The same substance is
found on the bottoms of kettles which have been used over a wood fire,
but it is there a fine powder.
Let us see what was burning when the candle was lighted, besides the
oxygen in the air. Relight the candle and hold the porcelain or glass
about an inch above the bright part of the flame. What happens to it
there? Next, lower it directly into the flame (_C_). What is the black
stuff that gets on the glass? Look closely and see whether it is not
deposited here also as a fine powder. Will this deposit from the candle
blacken the fingers?
[Illustration: _C._--THE CARBON (OR SOOT) IS DEPOSITED ON THE GLASS.]
Instead of using the name _charcoal_ for this black substance, let us
call it _carbon_, the better name, because there are several kinds of
carbon, and charcoal is only that kind which is rather light and easily
blackens the hands.
The carbon from the candle flame came mostly from the wax or tallow;
only a very small part came from the wick. It cannot be seen in the
tallow, neither can it be seen in unburned wood, and yet it can be
found when the wood is partly burned.
Why, now, is the glass blackened when held in the flame and not when
held directly above it? It is because the carbon from the candle has
not been completely burned at the middle of the flame; but it is burned
beyond the bright part of the flame. When the glass is held in the
flame, the carbon that is not yet completely burned is deposited on it,
because it is cooler than that in the surrounding flame.
A fine deposit of carbon can be had from any of the luminous parts of
the flame; and it is these thousands of little particles of carbon,
getting white hot, which glow like coals in the stove and make the
light. Just as soon as they are completely burned, there is no more
light, as coals cease to glow when burned to ashes.
III. _Carbon dioxid_
[Illustration: _D._--THE TEST WITH THE SUSPENDED FILM OF LIMEWATER.]
Let us now inquire what becomes of the carbon that we find in the
bright part of the flame and of the oxygen that was in the air in the
lamp chimney. When the candle was extinguished within the chimney,
there was no oxygen left, as shown by the lighted splinter, which was
put out immediately. Neither could any of the particles of carbon be
found except on the wick. Yet they both still exist within the chimney,
but in an entirely different condition. While the candle was burning,
the little particles of carbon that we find ascending in the flame
are joining with the oxygen of the air and making an entirely new
substance. This new substance is a gas and cannot be seen in the air.
Of what two substances is this new substance made? It is CO₂.
Place a bit of quicklime in about half a glass of water on the day
previous to the experiment. When ready for use there will be a white
sediment at the bottom and a thin white scum on the top of the clear
limewater. The pupils should see this white scum, as a question
about it will follow. Make a loop in the end of the piece of wire by
turning it around the point of a lead pencil. Remove the scum from the
limewater with a piece of paper and insert the loop into the clear
water. When withdrawn, the loop ought to hold a film of clear water.
Pass the wire through a piece of cardboard or stiff paper, and arrange
as shown in _D_.
Place the chimney over the lighted candle. Lower the loop into the
chimney and cover the top of the chimney with the paper. Withdraw the
wire two minutes after the candle goes out. Note the cloudy appearance
of the film of water on the wire. The cloudiness was caused by the
carbon dioxid formed while the candle was burning.
Omitting the candle, hang the freshly wetted wire in the empty chimney.
Let the film of limewater remain within the chimney for the same length
of time as when the candle was used. It does not become cloudy now.
The cloudiness in clear limewater is a test or indication that carbon
dioxid is present.
What caused the white scum on the limewater which stood overnight?
How does the CO₂ get into the air? It is formed whenever wood, coal,
oil, or gas is burned.
The amount of CO₂ in ordinary air is very small, being only three parts
in ten thousand. If the limewater in the loop be left long enough in
the air, it will become cloudy. The reason it clouds so quickly when
the candle is being burned is that a large amount of CO₂ is formed.
Besides being made by real flames, CO₂ is formed every time we breathe
out air. Renew the film of water in the loop and breathe against it
gently for two or three minutes.
The presence of CO₂ in the breath may be shown better by pouring off
some of the clear limewater into a clean glass and blowing into it
through a straw.
Why does water put out a fire? The answer is, not alone because it
wets and shuts off the supply of free oxygen, but because it cools
the carbon, which must be hot in order to unite with the oxygen, and
prevents the oxygen of the air from getting as near the carbon as
before.
PLANT BIOLOGY
CHAPTER I
NO TWO PLANTS OR PARTS ARE ALIKE
[Illustration: FIG. 1.--NO TWO BRANCHES ARE ALIKE. (Hemlock.)]
If one compares _any two plants_ of the same kind ever so closely, it
will be found that they _differ from each other_. The difference is
apparent in size, form, color, mode of branching, number of leaves,
number of flowers, vigor, season of maturity, and the like; or, in
other words, all plants and animals _vary from an assumed or standard
type_.
If one compares _any two branches or twigs_ on a tree, it will be found
that they differ in size, age, form, vigor, and in other ways (Fig. 1).
If one compares _any two leaves_, it will be found that they are
unlike in size, shape, color, veining, hairiness, markings, cut of
the margins, or other small features. In some cases (as in Fig.
2) the differences are so great as to be readily seen in a small
black-and-white drawing.
[Illustration: FIG. 2.--NO TWO LEAVES ARE ALIKE.]
If the pupil extends his observation to animals, he will still find the
same truth; for probably _no two living objects are exact duplicates_.
If any person finds two objects that he thinks to be exactly alike, let
him set to work to discover the differences, remembering that _nothing
in nature is so small or apparently trivial as to be overlooked_.
=Variation=, or differences between organs and also between organisms,
is one of the most significant facts in nature.
SUGGESTIONS.--The first fact that the pupil should acquire about
plants is that no two are alike. The way to apprehend this great fact
is to see a plant accurately and then to compare it with another
plant of the same species or kind. In order to direct and concentrate
the observation, it is well to set a certain number of attributes
or marks or qualities to be looked for. 1. Suppose any two or more
plants of corn are compared in the following points, the pupil
endeavoring to determine whether the parts exactly agree. See that
the observation is close and accurate. Allow no guesswork. Instruct
the pupil to measure the parts when size is involved:
(1) Height of the plant.
(2) Does it branch? How many secondary stems or “suckers” from one
root?
(3) Shade or color.
(4) How many leaves?
(5) Arrangement of leaves on stem.
(6) Measure length and breadth of six main leaves.
(7) Number and position of ears; color of silks.
(8) Size of tassel, and number and size of its branches.
(9) Stage of maturity or ripeness of plant.
(10) Has the plant grown symmetrically, or has it been crowded by
other plants or been obliged to struggle for light or room?
(11) Note all unusual or interesting marks or features.
(12) Always make note of comparative vigor of the plants.
NOTE TO TEACHER.--The teacher should always insist on _personal work_
by the pupil. Every pupil should _handle and study the object by
himself_. Books and pictures are merely guides and helps. So far as
possible, study the plant or animal _just where it grows naturally_.
=Notebooks.=--Insist that the pupils make full notes and preserve
these notes in suitable books. Note-taking is a powerful aid in
organizing the mental processes, and in insuring accuracy of
observation and record. The pupil should draw what he sees, even
though he is not expert with the pencil. The drawing should not be
made for looks, but to aid the pupil in his orderly study of the
object; it should be a means of self-expression.
=Laboratory.=--Every school, however small, should have a laboratory
or work-room. This work-room may be nothing more than a table at one
side of the room where the light is good. Here the specimens may be
ranged and studied. Often an aquarium and terrarium may be added.
A cabinet or set of shelves should be provided for a museum and
collection.
The laboratory may be in part out of doors, as a school garden; or
the garden may be at the pupil’s home, and yet be under the general
direction of the teacher.
CHAPTER II
THE STRUGGLE TO LIVE
Every plant and animal is _exposed to unfavorable conditions_. It is
obliged to contend with these conditions in order to live.
[Illustration: FIG. 3.--A BATTLE FOR LIFE.]
No two plants or parts of plants are identically exposed to the
conditions in which they live. The large branches in Fig. 1 probably
had more room and a better exposure to light than the smaller ones.
Probably no two of the leaves in Fig. 2 are equally exposed to light,
or enjoy identical advantages in relation to the food that they receive
from the tree.
Examine any tree to determine under what advantages or disadvantages
any of the limbs may live. Examine similarly the different plants in
a garden row (Fig. 3); or the different bushes in a thicket; or the
different trees in a wood.
The plant meets its conditions by _succumbing to them_ (that is, by
dying), or by _adapting itself to them_.
The tree _meets the cold_ by ceasing its active growth, hardening its
tissues, dropping its leaves. Many herbaceous or soft-stemmed plants
meet the cold by dying to the ground and withdrawing all life into the
root parts. Some plants meet the cold by dying outright and providing
abundance of seeds to perpetuate the kind next season.
[Illustration: FIG. 4.--THE REACH FOR LIGHT OF A TREE ON THE EDGE OF A
WOOD.]
Plants _adapt themselves to light_ by growing toward it (Fig. 4); or by
hanging their leaves in such position that they catch the light; or,
in less sunny places, by expanding their leaf surface, or by greatly
lengthening their stems so as to overtop their fellows, as do trees and
vines.
The adaptations of plants will afford a fertile field of study as we
proceed.
=Struggle for existence= and =adaptation to conditions= are among the
most significant facts in nature.
The sum of all the conditions in which a plant or an animal is placed
is called its =environment=, that is, its surroundings. The environment
comprises the conditions of climate, soil, moisture, exposure to light,
relation to food supply, contention with other plants or animals. _The
organism adapts itself to its environment, or else it weakens or dies._
Every weak branch or plant has undergone some hardship that it was not
wholly able to withstand.
SUGGESTIONS.--The pupil should study any plant, or branch of a plant,
with reference to the position or condition under which it grows, and
compare one plant or branch with another. With animals, it is common
knowledge that every animal is alert to avoid or to escape danger,
or to protect itself. =2.= It is well to begin with a branch of a
tree, as in Fig. 1. Note that no two parts are alike (Chap. I). Note
that some are large and strong and that these stand farthest towards
light and room. Some are very small and weak, barely able to live
under the competition. Some have died. The pupil can easily determine
which ones of the dead branches perished first. He should take note
of the position or place of the branch on the tree, and determine
whether the greater part of the dead twigs are toward the center of
the tree top or toward the outside of it. Determine whether accident
has overtaken any of the parts. =3.= Let the pupil examine the top of
any thick old apple tree, to see whether there is any struggle for
existence and whether any limbs have perished. =4.= If the pupil has
access to a forest, let him determine why there are no branches on
the trunks of the old trees. Examine a tree of the same kind growing
in an open field. =5.= A row of lettuce or other plants sown thick
will soon show the competition between plants. Any fence row or weedy
place will also show it. Why does the farmer destroy the weeds among
the corn or potatoes? How does the florist reduce competition to its
lowest terms? what is the result?
CHAPTER III
THE SURVIVAL OF THE FIT
The plants that most perfectly meet their conditions are able to
persist. _They perpetuate themselves._ Their offspring are likely to
inherit some of the attributes that enabled them successfully to meet
the battle of life. _The fit_ (those best adapted to their conditions)
_tend to survive_.
Adaptation to conditions depends on the fact of variation; that is,
if plants were perfectly rigid or invariable (all exactly alike) they
could not meet new conditions. Conditions are necessarily new for every
organism. _It is impossible to picture a perfectly inflexible and
stable succession of plants or animals._
=Breeding.=--_Man is able to modify plants and animals._ All our common
domestic animals are very unlike their original ancestors. So all our
common and long-cultivated plants have varied from their ancestors.
Even in some plants that have been in cultivation less than a century
the change is marked: compare the common black-cap raspberry with its
common wild ancestor, or the cultivated blackberry with the wild form.
[Illustration: FIG. 5.--DESIRABLE AND UNDESIRABLE TYPES OF COTTON
PLANTS. Why?]
By choosing seeds from a plant that pleases him, the breeder may be
able, under given conditions, to produce numbers of plants with more
or less of the desired qualities; from the best of these, he may again
choose; and so on until the race becomes greatly improved (Figs. 5,
6, 7). This process of continuously choosing the most suitable plants
is known as =selection=. A somewhat similar process proceeds in wild
nature, and it is then known as =natural selection=.
[Illustration: FIG. 6.--FLAX BREEDING.
_A_ is a plant grown for seed production; _B_, for fiber production.
Why?]
[Illustration: FIG. 7.--BREEDING.
_A_, effect from breeding from smallest grains (after four years),
average head; _B_, result from breeding from the plumpest and heaviest
grains (after four years), average head.]
SUGGESTIONS.--=6.= Every pupil should undertake at least one simple
experiment in selection of seed. He may select kernels from the best
plant of corn in the field, and also from the poorest plant,--having
reference not so much to mere incidental size and vigor of the plants
that may be due to accidental conditions in the field, as to the
apparently constitutional strength and size, number of ears, size
of ears, perfectness of ears and kernels, habit of the plant as to
suckering, and the like. The seeds may be saved and sown the next
year. Every crop can no doubt be very greatly improved by a careful
process of selection extending over a series of years. Crops are
increased in yield or efficiency in three ways: better general care;
enriching the land in which they grow; attention to breeding.
CHAPTER IV
PLANT SOCIETIES
In the long course of time in which plants have been accommodating
themselves to the varying conditions in which they are obliged to grow,
_they have become adapted to every different environment_. Certain
plants, therefore, may live together or near each other, all enjoying
the same general conditions and surroundings. These aggregations of
plants that are adapted to similar general conditions are known as
=plant societies=.
Moisture and temperature are the leading factors in determining
plant societies. The great geographical societies or aggregations
of the plant world may conveniently be associated chiefly with the
moisture supply, as: _wet-region societies_, comprising aquatic and
bog vegetation (Fig. 8); _arid-region societies_, comprising desert
and most sand-region vegetation; _mid-region societies_, comprising
the mixed vegetation in intermediate regions (Fig. 9), this being the
commonest type. Much of the characteristic scenery of any place is due
to its plant societies. Arid-region plants usually have small and hard
leaves, apparently preventing too rapid loss of water. Usually, also,
they are characterized by stiff growth, hairy covering, spines, or a
much-contracted plant-body, and often by large underground parts for
the storage of water.
Plant societies may also be distinguished with reference to latitude
and temperature. There are _tropical societies_, _temperate-region
societies_, _boreal_ or _cold-region societies_. With reference to
altitude, societies might be classified as _lowland_ (which are chiefly
wet-region), _intermediate_ (chiefly mid-region), _subalpine_ or
_mid-mountain_ (which are chiefly boreal), _alpine_ or _high-mountain_.
The above classifications have reference chiefly to great geographical
floras or societies. But there are _societies within societies_. There
are small societies coming within the experience of every person who
has ever seen plants growing in natural conditions. There are roadside,
fence-row, lawn, thicket, pasture, dune, woods, cliff, barn-yard
societies. _Every different place has its characteristic vegetation._
Note the smaller societies in Figs. 8 and 9. In the former is a
water-lily society and a cat-tail society. In the latter there are
grass and bush and woods societies.
[Illustration: FIG. 8.--A WET-REGION SOCIETY.]
=Some Details of Plant Societies.=--Societies may be composed of
_scattered and intermingled plants_, or of dense _clumps_ or _groups
of plants_. Dense clumps or groups are usually made up of one kind of
plant, and they are then called =colonies=. Colonies of most plants
are transient: after a short time other plants gain a foothold amongst
them, and an intermingled society is the outcome. Marked exceptions to
this are grass colonies and forest colonies, in which one kind of plant
may hold its own for years and centuries.
In a large newly cleared area, plants usually _first establish
themselves in dense colonies_. Note the great patches of nettles,
jewel-weeds, smart-weeds, clot-burs, fire-weeds in recently cleared
but neglected swales, also the fire-weeds in recently burned areas,
the rank weeds in the neglected garden, and the ragweeds and May-weeds
along the recently worked highway. The competition amongst themselves
and with their neighbors finally breaks up the colonies, and _a mixed
and intermingled flora is generally the result_.
[Illustration: FIG. 9.--A MID-REGION SOCIETY.]
In many parts of the world the _general tendency of neglected areas is
to run into forest_. All plants rush for the cleared area. Here and
there bushes gain a foothold. Young trees come up; in time these shade
the bushes and gain the mastery. Sometimes the area grows to poplars or
birches, and people wonder why the original forest trees do not return;
but these forest trees may be growing unobserved here and there in
the tangle, and in the slow processes of time the poplars perish--for
they are short-lived--and the original forest may be replaced. Whether
one kind of forest or another returns will depend partly on the kinds
that are most seedful in that vicinity and which, therefore, have
sown themselves most profusely. Much depends, also, on the kind of
undergrowth that first springs up, for some young trees can endure more
or less shade than others.
[Illustration: FIG. 10.--OVERGROWTH AND UNDERGROWTH IN THREE
SERIES,--trees, bushes, grass.]
Some plants _associate_. They grow together. This is possible largely
because they diverge or differ in character. Plants associate in two
ways: _by growing side by side_; _by growing above or beneath_. In
sparsely populated societies, plants may grow alongside each other.
In most cases, however, there is _overgrowth_ and _undergrowth_: one
kind grows beneath another. Plants that have become adapted to shade
are usually undergrowths. In a cat-tail swamp, grasses and other
narrow-leaved plants grow in the bottom, but they are usually unseen
by the casual observer. Note the undergrowth in woods or under trees
(Fig. 10). Observe that in pine and spruce forests there is almost no
undergrowth, partly because there is very little light.
On the same area the societies may _differ at different times of the
year_. There are spring, summer, and fall societies. The knoll which is
cool with grass and strawberries in June may be aglow with goldenrod in
September. If the bank is examined in May, look for the young plants
that are to cover it in July and October; if in September, find the
dead stalks of the flora of May. What succeeds the skunk cabbage,
hepaticas, trilliums, phlox, violets, buttercups of spring? What
precedes the wild sunflowers, ragweed, asters, and goldenrod of fall?
=The Landscape.=--To a large extent the _color of the landscape_ is
determined by the character of the plant societies. Evergreen societies
remain green, but the shade of green varies from season to season;
it is bright and soft in spring, becomes dull in midsummer and fall,
and assumes a dull yellow-green or a black-green in winter. Deciduous
societies vary remarkably in color--from the dull browns and grays of
winter to the brown greens and olive-greens of spring, the staid greens
of summer, and the brilliant colors of autumn.
The _autumn colors_ are due to intermingled shades of green, yellow,
and red. The coloration varies with the kind of plant, the special
location, and the season. Even in the same species or kind, individual
plants differ in color; and this individuality usually distinguishes
the plant year by year. That is, an oak which is maroon red this autumn
is likely to exhibit that range of color every year. The autumn color
is associated with the natural maturity and death of the leaf, but it
is most brilliant in long and open falls--largely because the foliage
ripens more gradually and persists longer in such seasons. It is
probable that the autumn tints are of no utility to the plant. _Autumn
colors are not caused by frost._ Because of the long, dry falls and the
great variety of plants, the autumnal color of the American landscape
is phenomenal.
=Ecology.=--The study of the relationships of plants and animals to
each other and to seasons and environments is known as =ecology= (still
written _œcology_ in the dictionaries). It considers the habits,
habitats, and modes of life of living things--the places in which they
grow, how they migrate or are disseminated, means of collecting food,
their times and seasons of flowering, producing young, and the like.
SUGGESTIONS.--One of the best of all subjects for school instruction
in botany is the study of plant societies. It adds definiteness and
zest to excursions. =7.= Let each excursion be confined to one or two
societies. Visit one day a swamp, another day a forest, another a
pasture or meadow, another a roadside, another a weedy field, another
a cliff or ravine. Visit shores whenever possible. Each pupil should
be assigned a bit of ground--say 10 or 20 ft. square--for special
study. He should make a list showing (1) how many kinds of plants
it contains, (2) the relative abundance of each. The lists secured
in different regions should be compared. It does not matter greatly
if the pupil does not know all the plants. He may count the kinds
without knowing the names. It is a good plan for the pupil to make a
dried specimen of each kind for reference. The pupil should endeavor
to discover why the plants grow as they do. Note what kinds of plants
grow next each other; and which are undergrowth and which overgrowth;
and which are erect and which wide-spreading. _Challenge every plant
society._
CHAPTER V
THE PLANT BODY
=The Parts of a Plant.=--Our familiar plants are made up of several
distinct parts. The most prominent of these parts are _root_, _stem_,
_leaf_, _flower_, _fruit_, _and seed_. _Familiar plants differ
wonderfully in size and shape_,--from fragile mushrooms, delicate
waterweeds and pond-scums, to floating leaves, soft grasses, coarse
weeds, tall bushes, slender climbers, gigantic trees, and hanging moss.
=The Stem Part.=--In most plants there is a _main central part or
shaft_ on which the other or _secondary parts_ are borne. This main
part is the =plant axis=. Above ground, in most plants, the main plant
axis bears the _branches_, _leaves_, and _flowers_; below ground, it
bears the _roots_.
The rigid part of the plant, which persists over winter and which is
left after leaves and flowers are fallen, is the =framework= of the
plant. The framework is composed of both root and stem. When the plant
is dead, the framework remains for a time, but it slowly decays. The
dry winter stems of weeds are the framework, or skeleton of the plant
(Figs. 11 and 12). The framework of trees is the most conspicuous part
of the plant.
=The Root Part.=--The root bears the stem at its apex, but otherwise it
normally _bears only root-branches_. The stem, however, _bears leaves_,
_flowers_, _and fruits_. Those living surfaces of the plant which are
most exposed to light are _green or highly colored_. The root tends to
grow _downward_, but the stem tends to grow _upward toward light and
air_. The plant is anchored or fixed in the soil by the roots. Plants
have been called “earth parasites.”
=The Foliage Part.=--The _leaves precede the flowers_ in point of
time or life of the plant. _The flowers always precede the fruits and
seeds._ Many plants die when the seeds have matured. The whole mass of
leaves of any plant or any branch is known as its _foliage_. In some
cases, as in crocuses, the flowers seem to precede the leaves; but the
leaves that made the food for these flowers grew the preceding year.
[Illustration: FIG. 11.--PLANT OF A WILD SUNFLOWER.]
[Illustration: FIG. 12.--FRAMEWORK OF FIG. 11.]
=The Plant Generation.=--The course of a plant’s life, with all the
events through which the plant naturally passes, is known as the
plant’s =life-history=. The life-history embraces various stages,
or epochs, as _dormant seed_, _germination_, _growth_, _flowering_,
_fruiting_. Some plants run their course in a few weeks or months, and
some live for centuries.
The entire life-period of a plant is called a =generation=. It is the
whole period from birth to normal death, without reference to the
various stages or events through which it passes.
A generation begins with _the young seed_, not with germination. _It
ends with death_--that is, when no life is left in any part of the
plant, and only the seed or spore remains to perpetuate the kind. In a
bulbous plant, as a lily or an onion, the generation does not end until
the bulb dies, even though the top is dead.
When the generation is of only one season’s duration, the plant is
said to be =annual=. When it is of two seasons, it is =biennial=.
Biennials usually bloom the second year. When of three or more seasons,
the plant is =perennial=. Examples of annuals are pigweed, bean, pea,
garden sunflower; of biennials, evening primrose, mullein, teasel; of
perennials, dock, most meadow grasses, cat-tail, and all shrubs and
trees.
=Duration of the Plant Body.=--Plant structures which are more or
less soft and which die at the close of the season are said to be
=herbaceous=, in contradistinction to being =ligneous= or =woody=. A
plant which is herbaceous to the ground is called an =herb=; but an
herb may have a woody or perennial root, in which case it is called an
=herbaceous perennial=. Annual plants are classed as herbs. Examples
of herbaceous perennials are buttercups, bleeding heart, violet,
water lily, Bermuda grass, horse-radish, dock, dandelion, golden rod,
asparagus, rhubarb, many wild sunflowers (Figs. 11, 12).
Many herbaceous perennials have _short generations_. They become weak
with one or two seasons of flowering and gradually die out. Thus,
red clover usually begins to fail after the second year. Gardeners
know that the best bloom of hollyhock, larkspur, pink, and many other
plants, is secured when the plants are only two or three years old.
Herbaceous perennials which die away each season to bulbs or tubers,
are sometimes called =pseud-annuals= (that is, _false annuals_). Of
such are lily, crocus, onion, potato, bull nettle, and false indigo of
the Southern states.
True annuals reach old age the first year. Plants which are normally
perennial _may become annual in a shorter-season climate by being
killed by frost_, rather than by dying naturally at the end of a
season of growth. They are climatic annuals. Such plants are called
=plur-annuals= in the short-season region. Many tropical perennials
are plur-annuals when grown in the north, but they are treated as true
annuals because they ripen sufficient of their crop the same season in
which the seeds are sown to make them worth cultivating, as tomato, red
pepper, castor bean, cotton. Name several vegetables that are planted
in gardens with the expectation that they will bear till frost comes.
[Illustration: FIG. 13.--A SHRUB OR BUSH. Dogwood osier.]
Woody or ligneous plants are usually longer lived than herbs. Those
that remain low and produce several or many similar shoots from the
base are called =shrubs=, as lilac, rose, elder, osier (Fig. 13). Low
and thick shrubs are =bushes=. Plants that produce one main trunk and a
more or less elevated head are =trees= (Fig. 14). All shrubs and trees
are perennial.
[Illustration: FIG. 14.--A TREE. The weeping birch.]
Every plant makes an effort _to propagate, or to perpetuate its kind_;
and, as far as we can see, this is the end for which the plant itself
lives. _The seed or spore is the final product of the plant._
SUGGESTIONS.--=8.= The teacher may assign each pupil to one plant in
the school yard, or field, or in a pot, and ask him to bring out the
points in the lesson. =9.= The teacher may put on the board the names
of many common plants and ask the pupils to classify into annuals,
pseud-annuals, plur-annuals (or climatic annuals), biennials,
perennials, herbaceous perennials, ligneous perennials, herbs,
bushes, trees. Every plant grown on the farm should be so classified:
wheat, oats, corn, buckwheat, timothy, strawberry, raspberry,
currant, tobacco, alfalfa, flax, crimson clover, hops, cowpea, field
bean, sweet potato, peanut, radish, sugar-cane, barley, cabbage, and
others. Name all the kinds of trees you know.
CHAPTER VI
SEEDS AND GERMINATION
[Illustration: FIG. 15.--PARTS OF THE BEAN.
_R_, cotyledon; _O_, caulicle; _A_, plumule; _F_, first node.]
The seed contains a _miniature plant_, or =embryo=. The embryo usually
has three parts that have received names: the stemlet, or =caulicle=;
the seed-leaf, or =cotyledon= (usually 1 or 2); the bud, or =plumule=,
lying between or above the cotyledons. These parts are well seen in the
common bean (Fig. 15), particularly when the seed has been soaked for a
few hours. One of the large cotyledons--comprising half of the bean--is
shown at _R_. The caulicle is at _O_. The plumule is shown at _A_. The
cotyledons are attached to the caulicle at _F_: _this point may be
taken as the first node or joint_.
=The Number of Seed-leaves.=--All plants having _two seed-leaves_
belong to the group called =dicotyledons=. Such seeds in many
cases split readily in halves, _e.g._ a bean. Some plants have
only _one_ seed-leaf in a seed. They form a group of plants called
=monocotyledons=. Indian corn is an example of a plant with only one
seed-leaf: a grain of corn does not split into halves as a bean does.
Seeds of the pine family contain more than two cotyledons, but for our
purposes they may be associated with the dicotyledons, although really
forming a different group.
These two groups--the dicotyledons and the monocotyledons--represent
two great natural divisions of the vegetable kingdom. The dicotyledons
contain the woody bark-bearing trees and bushes (except conifers), and
most of the herbs of temperate climates except the grasses, sedges,
rushes, lily tribes, and orchids. The flower-parts are usually in fives
or multiples of five, the leaves mostly netted-veined, the bark or
rind distinct, and the stem often bearing a pith at the center. The
monocotyledons usually have the flower-parts in threes or multiples of
three, the leaves long and parallel-veined, the bark not separable, and
the stem without a central pith.
Every seed is _provided with food_ to support the germinating
plant. Commonly this food is starch. The food may be stored _in the
cotyledons_, as in bean, pea, squash; or _outside the cotyledons_, as
in castor bean, pine, Indian corn. When the food is outside or around
the embryo, it is usually called =endosperm=.
[Illustration: FIG. 16.--EXTERNAL PARTS OF BEAN.]
=Seed-coats; Markings on Seed.=--The embryo and endosperm are inclosed
within a covering made of two or more layers and known as the
=seed-coats=. Over the point of the caulicle is a minute hole or a
thin place in the coats known as the =micropyle=. This is the point at
which the pollen-tube entered the forming ovule and through which the
caulicle breaks in germination. The micropyle is shown at _M_ in Fig.
16. The scar where the seed broke from its funiculus (or stalk that
attached it to its pod) is named the =hilum=. It occupies a third of
the length of the bean in Fig. 16. The hilum and micropyle are always
present in seeds, but they are not always close together. In many cases
it is difficult to identify the micropyle in the dormant seed, but its
location is at once shown by the protruding caulicle as germination
begins. Opposite the micropyle in the bean (at the other end of the
hilum) is an elevation known as the =raphe=. This is formed by a union
of the funiculus, or seed-stalk, with the seed-coats, and through it
food was transferred for the development of the seed, but it is now
functionless.
Seeds differ wonderfully in size, shape, color, and other
characteristics. They also vary in longevity. These characteristics are
_peculiar to the species or kind_. Some seeds maintain life only a few
weeks or even days, whereas others will “keep” for ten or twenty years.
In special cases, seeds have retained vitality longer than this limit,
but the stories that live seeds, several thousand years old, have been
taken from the wrappings of mummies are unfounded.
=Germination.=--The embryo is not dead; it is only dormant. _When
supplied with moisture, warmth, and oxygen (air), it awakes and grows:
this growth is_ =germination=. The embryo lives for a time on the
stored food, but gradually the plantlet secures a foothold in the soil
and gathers food for itself. _When the plantlet is finally able to
shift for itself, germination is complete._
=Early Stages of Seedling.=--The germinating seed first _absorbs
water, and swells_. The starchy matters gradually become soluble. The
seed-coats are ruptured, the caulicle and plumule emerge. During this
process the seed _respires freely, throwing off carbon dioxid_ (CO₂).
The caulicle usually elongates, and from its lower end roots are
emitted. The elongating caulicle is known as the =hypocotyl= (“below
the cotyledons”). That is, the hypocotyl is that part of the stem of
the plantlet lying between the roots and the cotyledon. _The general
direction of the young hypocotyl, or emerging caulicle, is downwards._
As soon as roots form, it becomes fixed and its subsequent growth
tends to raise the cotyledons above the ground, as in the bean. When
cotyledons rise into the air, germination is said to be =epigeal=
(“above the earth”). Bean and pumpkin are examples. When the hypocotyl
does not elongate greatly and the cotyledons remain under ground, the
germination is =hypogeal= (“beneath the earth”). Pea and scarlet runner
bean are examples (Fig. 48). When the germinating seed lies on a hard
surface, as on closely compacted soil, the hypocotyl and rootlets may
not be able to secure a foothold and they assume grotesque forms. (Fig.
17.) Try this with peas and beans.
[Illustration: FIG. 17.--PEA. Grotesque forms assumed when the roots
cannot gain entrance to the soil.]
The first internode (“between nodes”) above the cotyledons is
the =epicotyl=. It elevates the plumule into the air, and _the
plumule-leaves expand into the first true leaves of the plant_. These
first true leaves, however, may be very unlike the later leaves in
shape.
[Illustration: FIG. 18.--COTYLEDONS OF GERMINATING BEAN SPREAD APART TO
SHOW ELONGATING CAULICLE AND PLUMULE.]
=Germination of Bean.=--The common bean, as we have seen (Fig. 15),
has cotyledons that occupy all the space inside the seed-coats. When
the hypocotyl, or elongated caulicle, emerges, the plumule-leaves have
begun to enlarge, and to unfold (Fig. 18). The hypocotyl elongates
rapidly. One end of it is held by the roots. The other is held by the
seed-coats in the soil. It therefore takes the form of a loop, and the
central part of the loop “comes up” first (_a_, Fig. 19). Presently
the cotyledons come out of the seed-coats, and the plant straightens
and the cotyledons expand. These cotyledons, or “halves of the bean,”
persist for some time (_b_, Fig. 19). They often become green and
probably perform some function of foliage. Because of its large size,
the Lima bean shows all these parts well.
[Illustration: FIG. 19.--GERMINATION OF BEAN.]
[Illustration: FIG. 20.--SPROUTING OF CASTOR BEAN.]
[Illustration: FIG. 21.--GERMINATION OF CASTOR BEAN.
Endosperm at _a_.]
[Illustration: FIG. 22.--CASTOR BEAN.
Endosperm at _a_, _a_; cotyledons at _b_.]
[Illustration: FIG. 23.--GERMINATION COMPLETE IN CASTOR BEAN.]
=Germination of Castor Bean.=--In the castor bean the hilum and
micropyle are at the smaller end (Fig. 20). The bean “comes up”
with a loop, which indicates that the hypocotyl greatly elongates.
On examining germinating seed, however, it will be found that the
cotyledons are contained inside a fleshy body, or sac (_a_, Fig. 21).
This sac is the endosperm. Against its inner surface the thin, veiny
cotyledons are very closely pressed, absorbing its substance (Fig. 22).
The cotyledons increase in size as they reach the air (Fig. 23), and
become functional leaves.
[Illustration: FIG. 24.--SPROUTING INDIAN CORN.
Hilum at _h_; micropyle at _d_.]
[Illustration: FIG. 25.--KERNEL OF INDIAN CORN.
Caulicle at _b_; cotyledon at _a_; plumule at _p_.]
[Illustration: FIG. 26.--INDIAN CORN.
Caulicle at _c_; roots emerging at _m_; plumule at _p_.]
[Illustration: FIG. 27.--INDIAN CORN.
_o_, plumule: _n_ to _p_, epicotyl.]
=Germination of Monocotyledons.=--Thus far we have studied
dicotyledonous seeds; we may now consider the monocotyledonous group.
Soak kernels of corn. Note that the micropyle and hilum are at the
smaller end (Fig. 24). Make a longitudinal section through the narrow
diameter; Fig. 25 shows it. The single cotyledon is at _a_, the
caulicle at _b_, the plumule at _p_. The cotyledon remains in the seed.
The food is stored both in the cotyledon and as endosperm, chiefly the
latter. The emerging shoot is the plumule, with a sheathing leaf (_p_,
Fig. 26). The root is emitted from the tip of the caulicle, _c_. The
caulicle is held in a sheath (formed mostly from the seed-coats), and
some of the roots escape through the upper end of this sheath (_m_,
Fig. 26). The epicotyl elongates, particularly if the seed is planted
deep or if it is kept for a time confined. In Fig. 27 the epicotyl has
elongated from _n_ to _p_. The true plumule-leaf is at _o_, but other
leaves grow from its sheath. In Fig. 28 the roots are seen emerging
from the two ends of the caulicle sheath, _c_, _m_; the epicotyl has
grown to _p_; the first plumule-leaf is at _o_.
[Illustration: FIG. 28.--GERMINATION IS COMPLETE.
_p_, top of epicotyl; _o_, plumule-leaf; _m_, roots; _c_, lower roots.]
In studying corn or other fruits or seeds, the pupil should note
how the seeds are arranged, as on the cob. Count the rows on a corn
cob. Odd or even in number? Always the same number? The silk is the
style: find where it was attached to the kernel. Did the ear have any
coverings? Explain. Describe colors and markings of kernels of corn;
and of peas, beans, castor bean.
=Gymnosperms.=--The seeds in the pine cone, not being inclosed in
a seed-vessel, readily fall out when the cone dries and the scales
separate. Hence it is difficult to find cones with seeds in them after
autumn has passed (Fig. 29). The cedar is also a gymnosperm.
[Illustration: FIG. 29.--CONES OF HEMLOCK (ABOVE), WHITE PINE, PITCH
PINE.]
Remove a scale from a pine cone and draw it and the seeds as they lie
in place on the upper side of the scale. Examine the seed, preferably
with a magnifying glass. Is there a hilum? The micropyle is at the
bottom or little end of the seed. Toss a seed upward into the air. Why
does it fall so slowly? Can you explain the peculiar whirling motion
by the shape of the wing? Repeat the experiment in the wind. Remove
the wing from a seed and toss it and an uninjured seed into the air
together. What do you infer from these experiments?
[Illustration: FIG. 30.--MUSKMELON SEEDLINGS, with the unlike
seed-leaves and true leaves.]
SUGGESTIONS.--Few subjects connected with the study of plant-life
are so useful in schoolroom demonstrations as germination. The pupil
should prepare the soil, plant the seeds, water them, and care for
the plants. =10.= Plant seeds in pots or shallow boxes. The box
should not be very wide or long, and not over four inches deep.
Holes may be bored in the bottom so it will not hold water. Plant
a number of squash, bean, corn, pine, or other seeds about an inch
deep in damp sand or pine sawdust in this box. The depth of planting
should be two to four times the diameter of the seeds. Keep the sand
or sawdust moist but not wet. If the class is large, use several
boxes, that the supply of specimens may be ample. Cigar boxes and
chalk boxes are excellent for individual pupils. It is well to begin
the planting of seeds at least ten days in advance of the lesson,
and to make four or five different plantings at intervals. A day
or two before the study is taken up, put seeds to soak in moss or
cloth. The pupil then has a series from swollen seeds to complete
germination, and all the steps can be made out. Dry seeds should be
had for comparison. If there is no special room for laboratory, nor
duplicate apparatus for every pupil, each experiment may be assigned
to a committee of two pupils to watch in the schoolroom. =11.= Good
seeds for study are those detailed in the lesson, and buckwheat,
pumpkin, cotton, morning glory, radish, four o’clock, oats, wheat.
It is best to use familiar seeds of farm and garden. Make drawings
and notes of all the events in the germination. Note the effects
of unusual conditions, as planting too deep and too shallow and
different sides up. For hypogeal germination, use the garden pea,
scarlet runner or Dutch case-knife bean, acorn, horse-chestnut.
Squash seeds are excellent for germination studies, because the
cotyledons become green and leafy and germination is rapid. Its
germination, as also that of the scarlet runner bean, is explained in
“Lessons with Plants.” Onion is excellent, except that it germinates
too slowly. In order to study the root development of germinating
plantlets, it is well to provide a deeper box with a glass side
against which the seeds are planted. =12.= Observe the germination of
any common seed about the house premises. When elms, oaks, pines, or
maples are abundant, the germination of their seeds may be studied in
lawns and along fences. =13.= When studying germination, the pupil
should note the differences in shape and size between cotyledons and
plumule-leaves, and between plumule-leaves and the normal leaves
(Fig. 30). Make drawings. =14.= Make the tests described in the
introductory experiments with bean, corn, the castor bean, and other
seed for starch and proteids. Test flour, oatmeal, rice, sunflower,
four o’clock, various nuts, and any other seeds obtainable. Record
your results by arranging the seeds in three classes, 1. Much starch
(color blackish or purple), 2. Little starch (pale blue or greenish),
3. No starch (brown or yellow). =15.= _Rate of growth of seedlings
as affected by differences in temperature._ Pack soft wet paper to
the depth of an inch in the bottom of four glass bottles or tumblers.
Put ten soaked peas or beans into each. Cover each securely and set
them in places having different temperatures that vary little. (A
furnace room, a room with a stove, a room without stove but reached
by sunshine, an unheated room not reached by the sun.) Take the
temperatures occasionally with a thermometer to find difference in
temperature. The tumblers in warm places should be covered very
tightly to prevent the germination from being retarded by drying
out. Record the number of seeds which sprout in each tumbler within
1 day; 2 days; 3 days; 4 days, etc. =16.= _Is air necessary for the
germination and growth of seedlings?_ Place damp blotting paper in
the bottom of a bottle and fill it three fourths full of soaked
seeds, and close it tightly with a rubber stopper or oiled cork.
Prepare a “check experiment” by having another bottle with all
conditions the same except that it is covered loosely that air may
have access to it, and set the bottles side by side (why keep the
bottles together?). Record results as in the preceding experiment.
=17.= _What is the nature of the gas given off by germinating seeds?_
Fill a tin box or large-necked bottle with dry beans or peas, then
add water; note how much they swell. Secure two fruit-jars. Fill one
of them a third full of beans and keep them moist. Allow the other
to remain empty. In a day or two insert a lighted splinter or taper
into each. In the empty jar the taper burns: it contains oxygen. In
the seed jar the taper goes out: the air has been replaced by carbon
dioxid. The air in the bottle may be tested for carbon dioxid by
removing some of it with a rubber bulb attached to a glass tube (or
a fountain-pen filler) and bubbling it through lime water. =18.=
_Temperature._ Usually there is a perceptible rise in temperature
in a mass of germinating seeds. This rise may be tested with a
thermometer. =19.= _Interior of seeds._ Soak seeds for twenty-four
hours and remove the coat. Distinguish the embryo from the endosperm.
Test with iodine. =20.= _Of what utility is the food in seeds?_ Soak
some grains of corn overnight and remove the endosperm, being careful
not to injure the fleshy cotyledon. Plant the incomplete and also
some complete grains in moist sawdust and measure their growth at
intervals. (Boiling the sawdust will destroy molds and bacteria which
might interfere with experiment.) Peas or beans may be sprouted on
damp blotting paper; the cotyledons of one may be removed, and this
with a normal seed equally advanced in germination may be placed on a
perforated cork floating in water in a jar so that the roots extend
into the water. Their growth may be observed for several weeks. =21.=
_Effect of darkness on seeds and seedlings._ A box may be placed
mouth downward over a smaller box in which seedlings are growing.
The empty box should rest on half-inch blocks to allow air to reach
the seedlings. Note any effects on the seedlings of this cutting off
of the light. Another box of seedlings not so covered may be used
for a check. Lay a plank on green grass and after a week note the
change that takes place beneath it. =22.= _Seedling of pine._ Plant
pine seeds. Notice how they emerge. Do the cotyledons stay in the
ground? How many cotyledons have they? When do the cotyledons get
free from the seed-coat? What is the last part of the cotyledon to
become free? Where is the growing point or plumule? How many leaves
appear at once? Does the new pine cone grow on old wood or on wood
formed the same spring with the cone? Can you always find partly
grown cones on pine trees in winter? Are pine cones when mature on
two-year-old wood? How long do cones stay on a tree after the seeds
have fallen out? What is the advantage of the seeds falling before
the cones? =23.= _Home experiments._ If desired, nearly all of the
foregoing experiments may be tried at home. The pupil can thus make
the drawings for the notebook at home. A daily record of measurements
of the change in size of the various parts of the seedling should
also be made. =24.= _Seed-testing._--It is important that one know
before planting whether seeds are good, or able to grow. A simple
seed-tester may be made of two plates, one inverted over the other
(Fig. 31). The lower plate is nearly filled with clean sand, which
is covered with cheese cloth or blotting paper on which the seeds
are placed. Canton flannel is sometimes used in place of sand and
blotting paper. The seeds are then covered with another blotter or
piece of cloth, and water is applied until the sand and papers are
saturated. Cover with the second plate. Set the plates where they
will have about the temperature that the given seeds would require
out of doors, or perhaps a slightly higher temperature. Place 100
or more grains of clover, corn, wheat, oats, rye, rice, buckwheat,
or other seeds in the tester, and keep record of the number that
sprout. The result will give a percentage measure of the ability of
the seeds to grow. Note whether all the seeds sprout with equal vigor
and rapidity. Most seeds will sprout in a week or less. Usually such
a tester must have fresh sand and paper after every test, for mold
fungi are likely to breed in it. If canton flannel is used, it may be
boiled. If possible, the seeds should not touch each other.
[Illustration: FIG. 31.--A HOME-MADE SEED-TESTER.]
NOTE TO TEACHER.--With the study of germination, the pupil will need
to begin dissecting.
=For dissecting=, one needs a lens for the examination of the smaller
parts of plants and animals. It is best to have the lens mounted
on a frame, so that the pupil has both hands free for pulling the
part in pieces. An ordinary pocket lens may be mounted on a wire
in a block, as in Fig. A. A cork is slipped on the top of the wire
to avoid injury to the face. The pupil should be provided with two
dissecting needles (Fig. B), made by securing an ordinary needle
in a pencil-like stick. Another convenient arrangement is shown in
Fig. C. A small tin dish is used for the base. Into this a stiff
wire standard is soldered. The dish is filled with solder, to make
it heavy and firm. Into a cork slipped on the standard, a cross
wire is inserted, holding on the end a jeweler’s glass. The lens
can be moved up and down and sidewise. This outfit can be made for
about seventy-five cents. Fig. D shows a convenient hand-rest or
dissecting-stand to be used under this lens. It may be 16 in. long, 4
in. high, and 4 or 5 in. broad.
Various kinds of dissecting microscopes are on the market, and these
are to be recommended when they can be afforded.
[Illustration: _A._--IMPROVISED STAND FOR LENS.]
[Illustration: _B._--DISSECTING NEEDLE ¹⁄₂ natural size.]
[Illustration: _C._--DISSECTING GLASS.]
[Illustration: _D._--DISSECTING STAND.]
Instructions for the use of the compound microscope, with which
some schools may be equipped, cannot be given in a brief space; the
technique requires careful training. Such microscopes are not needed
unless the pupil studies cells and tissues.
CHAPTER VII
THE ROOT--THE FORMS OF ROOTS
=The Root System.=--The offices of the root are _to hold the plant in
place_, and _to gather food_. Not all the food materials, however, are
gathered by the roots.
[Illustration: FIG. 32.--TAP-ROOT SYSTEM OF ALFALFA.]
[Illustration: FIG. 33.--TAP-ROOT OF THE DANDELION.]
The entire mass of roots of any plant is called its =root system=. The
root system may be annual, biennial or perennial, herbaceous or woody,
deep or shallow, large or small.
=Kinds of Roots.=--A strong leading central root, which runs directly
downwards, is a =tap-root=. The tap-root forms an axis from which the
side roots may branch. The side or spreading roots are usually smaller.
Plants that have such a root system are said to be _tap-rooted_.
Examples are red clover, alfalfa, beet, turnip, radish, burdock,
dandelion, hickory (Figs. 32, 33).
A =fibrous root system= is one that is composed of many nearly equal
slender branches. The greater number of plants have fibrous roots.
Examples are many common grasses, wheat, oats, corn. The buttercup in
Fig. 34 has a fibrous root system. Many trees have a strong tap-root
when very young, but after a while it ceases to extend strongly and the
side roots develop until finally the tap-root character disappears.
[Illustration: FIG. 34.--A BUTTERCUP PLANT, with fibrous roots.]
=Shape and Extent of the Root System.=--The depth to which roots extend
depends on the _kind of plant_, and the _nature of the soil_. Of most
plants the roots extend far _in all directions_ and lie comparatively
_near the surface_. The roots usually radiate from a common point just
beneath the surface of the ground.
_The roots grow here and there in search of food_, often extending much
farther in all directions than the spread of the top of the plant.
Roots tend to spread farther in poor soil than in rich soil, for the
same size of plant. _The root has no such definite form as the stem
has._ Roots are usually very crooked, because they are constantly
turned aside by obstacles. Examine roots in stony soil.
_The extent of root surface is usually very large_, for the feeding
roots are fine and very numerous. An ordinary plant of Indian corn may
have a total length of root (measured as if the roots were placed end
to end) of several hundred feet.
The fine feeding roots are _most abundant in the richest part of the
soil_. They are attracted by the food materials. Roots often will
completely surround a bone or other morsel. When roots of trees are
exposed, observe that most of them are horizontal and lie near the top
of the ground. Some roots, as of willows, extend far _in search of
water_. They often run into wells and drains, and into the margins of
creeks and ponds. Grow plants in a long narrow box, in one end of which
the soil is kept very dry and in the other moist: observe where the
roots grow.
=Buttresses.=--With the increase in diameter, the upper roots often
protrude above the ground and become _bracing buttresses_. These
buttresses are usually largest in trees which always have been exposed
to strong winds (Fig. 35). Because of growth and thickening, the roots
elevate part of their diameter, and the washing away of the soil makes
them to appear as if having risen out of the ground.
[Illustration: FIG. 35.--THE BRACING BASE OF A FIELD PINE.]
=Aërial Roots.=--Although roots usually grow underground, _there are
some that naturally grow above ground_. These usually occur on climbing
plants, the roots becoming _supports_ or fulfilling the office of
tendrils. These aërial roots _usually turn away from the light_, and
therefore enter the crevices and dark places of the wall or tree over
which the plant climbs. The trumpet creeper (Fig. 36), true or English
ivy, and poison ivy climb by means of roots.
[Illustration: FIG. 36.--AËRIAL ROOTS OF TRUMPET CREEPER OR TECOMA.]
[Illustration: FIG. 37.--AËRIAL ROOTS OF AN ORCHID.]
In some plants all the roots are aërial; that is, _the plant grows
above ground_, and the roots gather food from the air. Such plants
usually grow on trees. They are known as _epiphytes_ or _air-plants_.
The most familiar examples are some of the tropical orchids, which are
grown in glass-houses (Fig. 37). Rootlike organs of dodder and other
parasites are discussed in a future chapter.
Some plants bear aërial roots, that may _propagate the plant_ or may
_act as braces_. They are often called =prop-roots=. The roots of
Indian corn are familiar (Fig. 38). Many ficus trees, as the banyan
of India, send out roots from their branches; when these roots reach
the ground they take hold and become great trunks, thus spreading the
top of the parent tree over large areas. The muscadine grape of the
Southern states often sends down roots from its stems. The mangrove
tree of the tropics grows along seashores and sends down roots from the
overhanging branches (and from the fruits) into the shallow water, and
thereby gradually marches into the sea. The tangled mass behind catches
the drift, and soil is formed.
[Illustration: FIG. 38.--INDIAN CORN, showing the brace roots at _oo_.]
=Adventitious Roots.=--Sometimes roots grow from the stem or other
unusual places as the result of some accident to the plant, being
located without known method or law. They are called =adventitious=
(chance) =roots=. Cuttings of the stems of roses, figs, geraniums, and
other plants, when planted, send out adventitious roots and form new
plants. The ordinary roots, or soil roots, are of course not classed as
adventitious roots. The adventitious roots arise on occasion, and not
as a normal or regular course in the growth of the plant.
=No two roots are alike=; that is, they vary among themselves as stems
and leaves do. _Each kind of plant has its own form or habit of root_
(Fig. 39). Carefully wash away the soil from the roots of any two
related plants, as oats and wheat, and note the differences in size,
depth, direction, mode of branching, number of fibrils, color, and
other features. The character of the root system often governs the
treatment that the farmer should give the soil in which the plant or
crop grows.
[Illustration: FIG. 39.--ROOTS OF BARLEY AT _A_ AND CORN AT _B_.
Carefully trace the differences.]
Roots differ not only in their form and habit, but also in color of
tissue, character of bark or rind, and other features. It is excellent
practice to _try to identify different plants by means of their roots_.
Let each pupil bring to school two plants with the roots very carefully
dug up, as cotton, corn, potato, bean, wheat, rye, timothy, pumpkin,
clover, sweet pea, raspberry, strawberry, or other common plants.
=Root Systems of Weeds.=--Some weeds are pestiferous because they seed
abundantly, and others because their underground parts run deep or far
and are persistent. Make out the root systems in the six worst weeds in
your locality.
CHAPTER VIII
THE ROOT.--FUNCTION AND STRUCTURE
=The function of roots is twofold=,--to provide _support or anchorage_
for the plant, and to _collect and convey food_ materials. The first
function is considered in Chapter VII; we may now give attention in
more detail to the second.
The feeding surface of the roots is _near their ends_. As the roots
become old and hard, they serve only as _channels through which food
passes_ and as _hold-fasts or supports_ for the plant. The root-hold of
a plant is very strong. Slowly pull upwards on some plant, and note how
firmly it is anchored in the soil.
[Illustration: FIG. 40.--WHEAT GROWING UNDER DIFFERENT SOIL TREATMENTS.
Soil deficient in nitrogen; commercial nitrogen applied to pot 3 (on
right).]
=Roots have power to choose their food=; that is, they do not absorb
all substances with which they come in contact. They do not take
up great quantities of useless or harmful materials, even though
these materials may be abundant in the soil; but they may take up a
greater quantity of some of the plant-foods than the plant can use to
advantage. _Plants respond very quickly to liberal feeding_,--that is,
to the application of plant-food to the soil (Fig. 40). The poorer the
soil, the more marked are the results, as a rule, of the application of
fertilizers. Certain substances, as common salt, will kill the roots.
=Roots absorb Substances only in Solution.=--Substances cannot be
taken in solid particles. These materials are in solution in the soil
water, and the roots themselves also have the power to dissolve the
soil materials to some extent by means of substances that they excrete.
The materials that come into the plant through the roots are _water
and mostly the mineral substances_, as compounds of potassium, iron,
phosphorus, calcium, magnesium, sulfur, and chlorine. These mineral
substances compose the ash when the plant is burned. The carbon is
derived from the air through the green parts. Oxygen is derived from
the air and the soil water.
[Illustration: FIG. 41.--NODULES ON ROOTS OF RED CLOVER.]
=Nitrogen enters through the Roots.=--All plants must have nitrogen;
yet, although about four fifths of the air is nitrogen, plants are
not able, so far as we know, to take it in through their leaves. It
enters through the roots in combination with other elements, chiefly in
the form of nitrates (certain combinations with oxygen and a mineral
base). The great family of leguminous plants, however (as peas, beans,
cowpea, clover, alfalfa, vetch), _use the nitrogen contained in the
air in the soil_. They are able to utilize it through the _agency of
nodules_ on their roots (Figs. 41, 42). These nodules contain bacteria,
which appropriate the free or uncombined nitrogen and pass it on to the
plant. The nitrogen becomes incorporated in the plant tissue, so that
these crops are high in their nitrogen content. Inasmuch as nitrogen in
any form is expensive to purchase in fertilizers, the use of leguminous
crops to plow under is a very important agricultural practice in
preparing the land for other crops. In order that leguminous crops may
acquire atmospheric nitrogen more freely and thereby thrive better,
_the land is sometimes sown or inoculated with the nodule-forming
bacteria_.
[Illustration: FIG. 42.--NODULES ON VETCH.]
[Illustration: FIG. 43.--TWO KINDS OF SOIL THAT HAVE BEEN WET AND
THEN DRIED. The loamy soil above remains loose and capable of growing
plants; the clay soil below has baked and cracked.]
=Roots require moisture= in order to serve the plant. The soil water
that is valuable to the plant is not the free water, but the _thin
film of moisture which adheres to each little particle of soil_. The
finer the soil, the greater the number of particles, and therefore
the greater is the quantity of film moisture that it can hold. This
moisture surrounding the grains may not be perceptible, yet the plant
can use it. _Root absorption may continue in a soil which seems to be
dust dry._ Soils that are very hard and “baked” (Fig. 43) contain very
little moisture or air,--not so much as similar soils that are granular
or mellow.
=Proper Temperature for Root Action.=--_The root must be warm in order
to perform its functions._ Should the soil of fields or greenhouses be
much colder than the air, the plant suffers. When in a warm atmosphere,
or in a dry atmosphere, plants need to absorb much water from the soil,
and the roots must be warm if the root-hairs are to supply the water as
rapidly as it is needed. _If the roots are chilled, the plant may wilt
or die._
=Roots need Air.=--Corn on land that has been flooded by heavy rains
loses its green color and turns yellow. _Besides diluting plant-food,
the water drives the air from the soil, and this suffocation of the
roots is very soon apparent in the general ill health of the plant._
Stirring or tilling the soil aërates it. Water plants and bog plants
have adapted themselves to their particular conditions. They get their
air either by special surface roots, or from the water through stems
and leaves.
=Rootlets.=--_Roots divide into the thinnest and finest fibrils: there
are roots and there are rootlets._ The smallest rootlets are so slender
and delicate that they break off even when the plant is very carefully
lifted from the soil.
[Illustration: FIG. 44.--ROOT-HAIRS OF THE RADISH.]
_The rootlets, or fine divisions, are clothed with the_ =root-hairs=
(Figs. 44, 45, 46). _These root-hairs attach to the soil particles, and
a great amount of soil is thus brought into actual contact with the
plant._ These are very _delicate prolonged surface cells of the roots_.
They are borne for a short distance just back of the tip of the root.
_Rootlet and root-hair differ._ The rootlet is a _compact cellular
structure. The root-hair is a delicate tubular cell_ (Fig. 45), _within
which is contained living matter (protoplasm); and the protoplasmic
lining membrane of the wall governs the entrance of water and
substances in solution_. Being long and tube-like, these root-hairs are
especially adapted for taking in the largest quantity of solutions; and
they are the principal means by which plant-food is absorbed from the
soil, although the surfaces of the rootlets themselves do their part.
Water plants do not produce an abundant system of root-hairs, and such
plants depend largely on their rootlets.
[Illustration: FIG. 45.--CROSS-SECTION OF ROOT, enlarged, showing
root-hairs.]
[Illustration: FIG. 46.--ROOT-HAIR, much enlarged, in contact with the
soil particles (_s_). Air-spaces at _a_; water-films on the particles,
as at _w_.]
The root-hairs are very small, often invisible. They, with the young
roots, are usually broken off when the plant is pulled up. They are
best seen when seeds are germinated between layers of dark blotting
paper or flannel. On the young roots, they will be seen as a mold-like
or gossamer-like covering. _Root-hairs soon die_: they do not grow into
roots. New ones form as the root grows.
=Osmosis.=--The water with its nourishment goes through the thin walls
of the root-hairs and rootlets by the process of osmosis. If there
are two liquids of different density on the inside and outside of an
organic (either vegetable or animal) membrane, the liquids tend to mix
through the membrane. The _law of osmosis_ is that _the most rapid flow
is toward the denser solution_. The protoplasmic lining of the cell
wall is such a membrane. The soil water being a weaker solution than
the sap in the roots, the flow is into the root. A strong fertilizer
sometimes causes a plant to wither, or “burns it.” Explain.
=Structure of Roots.=--The root that grows from the lower end of the
caulicle is the _first_ or =primary root=. =Secondary roots= branch
from the primary root. Branches of secondary roots are sometimes called
=tertiary roots=. Do the secondary roots grow from the cortex, or from
the central cylinder of the primary root? Trim or peel the cortex from
a root and its branches and determine whether the branches still hold
to the central cylinder of the main root.
=Internal Structure of Roots.=--A section of a root shows that it
consists of a _central cylinder_ (see Fig. 45) surrounded by a layer.
This layer is called the =cortex=. The outer layer of cells in the
cortex is called the =epidermis=, and some of the cells of the
epidermis are prolonged and form the delicate root-hairs. The cortex
resembles the bark of the stem in its nature. The central cylinder
contains many tube-like canals, or “vessels” that convey water and food
(Fig. 45). Cut a sweet potato across (also a radish and a turnip) and
distinguish the central cylinder, cortex and epidermis. Notice the hard
cap on the tip of roots. Roots differ from stems in having no real pith.
=Microscopic Structure of Roots.=--Near the end of any young root or
shoot the cells are found to differ from each other more or less,
according to the distance from the point. _This differentiation takes
place in the region just back of the growing point._ To study growing
points, use the hypocotyl of Indian corn which has grown about one half
inch. Make a longitudinal section. Note these points (Fig. 47): (_a_)
the tapering root-cap beyond the growing point; (_b_) the blunt end of
the root proper and the rectangular shape of the cells found there;
(_c_) the group of cells in the middle of the first layers beneath the
root-cap,--this group is the growing point; (_d_) study the slight
differences in the tissues a short distance back of the growing point.
There are four regions: the =central cylinder=, made up of several rows
of cells in the center (_pl_); the =endodermis=, (_e_) composed of a
single layer on each side which separates the central cylinder from
the bark; the =cortex=, or inner bark, (_e_) of several layers outside
the endodermis; and the =epidermis=, or outer layer of bark on the
outer edges (_d_). Make a drawing of the section. If a series of the
cross-sections of the hypocotyl should be made and studied, beginning
near the growing point and going upward, it would be found that these
four tissues become more distinctly marked, for at the tip the tissues
have not yet assumed their characteristic form. The central cylinder
contains the ducts and vessels which convey the sap.
[Illustration: FIG. 47.--GROWING POINT OF ROOT OF INDIAN CORN.
_d_, _d_, cells which will form the epidermis; _p_, _p_, cells that
will form bark; _e_, _e_, endodermis; _pl_, cells which will form the
axis cylinder; _i_, initial group of cells, or growing point proper;
_c_, root-cap.]
=The Root-cap.=--Note the form of the root-cap shown in the microscopic
section drawn in Fig. 47. Growing cells, and especially those which
are forming tissue by subdividing, are very delicate and are easily
injured. The cells forming the root-cap are older and tougher and are
suited for pushing aside the soil that the root may penetrate it.
=Region of most Rapid Growth.=--The roots of a seedling bean may
be marked at equal distances by waterproof ink or by bits of black
thread tied moderately tight. The seedling is then replanted and left
undisturbed for two days. When it is dug up, the region of most rapid
growth in the root can be determined. Give a reason why _a root cannot
elongate throughout its length_,--whether there is anything to prevent
a young root from doing so.
[Illustration: FIG. 48.--THE MARKING OF THE STEM AND ROOT.]
In Fig. 48 is shown a germinating scarlet runner bean with a short
root upon which are marks made with waterproof ink; and the same root
(Fig. 49) is shown after it has grown longer. Which part of it did not
lengthen at all? Which part lengthened slightly? Where is the region of
most rapid growth?
[Illustration: FIG. 49.--THE RESULT.]
=Geotropism.=--Roots turn toward the earth, even if the seed is planted
with the micropyle up. This phenomenon is called =positive geotropism=.
Stems grow away from the earth. This is =negative geotropism=.
[Illustration: FIG. 50.--THE GRASP OF A PLANT ON THE PARTICLES OF
EARTH. A grass plant pulled in a garden.]
[Illustration: FIG. 51.--PLANT GROWING IN INVERTED POT.]
[Illustration: FIG. 52.--HOLES IN SOIL MADE BY ROOTS, now decayed.
Somewhat magnified.]
SUGGESTIONS (Chaps. VII and VIII).--=25.= _Tests for food._ Examine
a number of roots, including several fleshy roots, for the presence
of food material, making the tests used on seeds. =26.= _Study of
root-hairs._ Carefully germinate radish, turnip, cabbage, or other
seed, so that no delicate parts of the root will be injured. For
this purpose, place a few seeds in packing-moss or in the folds of
thick cloth or of blotting paper, being careful to keep them moist
and warm. In a few days the seed has germinated, and the root has
grown an inch or two long. Notice that, except at a distance of
about a quarter of an inch behind the tip, the root is covered with
minute hairs (Fig. 44). They are actually hairs; that is, root-hairs.
Touch them and they collapse, they are so delicate. Dip one of the
plants in water, and when removed the hairs are not to be seen.
The water mats them together along the root and they are no longer
evident. Root-hairs are usually destroyed when a plant is pulled out
of the soil, be it done ever so carefully. They cling to the minute
particles of soil (Fig. 46). The hairs show best against a dark
background. =27.= On some of the blotting papers, sprinkle sand;
observe how the root-hairs cling to the grains. Observe how they
are flattened when they come in contact with grains of sand. =28.=
_Root hold of plant._ The pupil should also study the root hold. Let
him carefully pull up a plant. If a plant grow alongside a fence or
other rigid object, he may test the root hold by securing a string to
the plant, letting the string hang over the fence, and then adding
weights to the string. Will a stake of similar size to the plant
and extending no deeper in the ground have such firm hold on the
soil? What holds the ball of earth in Fig. 50? =29.= _Roots exert
pressure._ Place a strong bulb of hyacinth or daffodil on firm-packed
earth in a pot; cover the bulb nearly to the top with loose earth;
place in a cool cellar; after some days or weeks, note that the bulb
has been raised out of the earth by the forming roots. All roots
exert pressure on the soil as they grow. Explain. =30.= _Response
of roots and stems to the force of gravity, or geotropism._ Plant a
fast-growing seedling in a pot so that the plumule extends through
the drain hole and suspend the pot with mouth up (_i.e._ in the
usual position). Or use a pot in which a plant is already growing,
cover with cloth or wire gauze to prevent the soil from falling,
and suspend the pot in an inverted position (Fig. 51). Notice the
behavior of the stem, and after a few days remove the soil and
observe the position of the root. =31.= If a pot is laid on one side,
and changed every two days and laid on its opposite side, the effect
on the root and stem will be interesting. =32.= If a fleshy root
is planted wrong end up, what is the result? Try it with pieces of
horse-radish root. =33.= By planting radishes on a slowly revolving
wheel the effect of gravity may be neutralized. =34.= _Region of
root most sensitive to gravity._ Lay on its side a pot containing a
growing plant. After it has grown a few days, wash away the earth
surrounding the roots. Which turned downward most decidedly, the tip
of root or the upper part? =35.= _Soil texture._ Carefully turn up
soil in a rich garden or field so that you have unbroken lumps as
large as a hen’s egg. Then break these lumps apart carefully with
the fingers and determine whether there are any traces or remains
of roots (Fig. 52). Are there any pores, holes, or channels made by
roots? Are the roots in them still living? =36.= Compare another lump
from a clay bank or pile where no plants have been growing. Is there
any difference in texture? =37.= Grind up this clay lump very fine,
put it in a saucer, cover with water, and set in the sun. After a
time it will have the appearance shown in the lower saucer in Fig.
43. Compare this with mellow garden soil. In which will plants grow
best, even if the plant-food were the same in both? Why? =38.= _To
test the effect of moisture_ on the plant, let a plant in a pot or
box dry out till it wilts; then add water and note the rapidity with
which it recovers. Vary the experiment in quantity of water applied.
Does the plant call for water sooner when it stands in a sunny window
than when in a cool shady place? Prove it. =39.= Immerse a potted
plant above the rim of the pot in a pail of water and let it remain
there. What is the consequence? Why? =40.= _To test the effect of
temperature on roots._ Put one pot in a dish of ice water, and
another in a dish of warm water, and keep them in a warm room. In a
short time notice how stiff and vigorous is the one whose roots are
warm, whereas the other may show signs of wilting. =41.= _The process
of osmosis._ Chip away the shell from the large end of an egg so as
to expose the uninjured membrane beneath for an area about as large
as a dime. With sealing-wax, chewing-gum, or paste stick a quill
about three inches long to the smaller end of the egg. After the
tube is in place, run a hat pin into it so as to pierce both shell
and membrane; or use a short glass tube, first scraping the shell
thin with a knife and then boring through it with the tube. Now set
the egg upon the mouth of a pickle jar nearly full of water, so that
the large end with the exposed membrane is beneath the water. After
several hours, observe the tube on top of the egg to see whether the
water has forced its way into the egg and increased its volume so
that part of its contents are forced up into the tube. If no tube is
at hand, see whether the contents are forced through the hole which
has been made in the small end of the egg. Explain how the law of
osmosis is verified by your result. If the eggshell contained only
the membrane, would water rise into it? If there were no water in
the bottle, would the egg-white pass down into the bottle? =42.=
_The region of most rapid growth._ The pupil should make marks with
waterproof ink (as Higgins’ ink or indelible marking ink) on any soft
growing roots. Place seeds of bean, radish, or cabbage between layers
of blotting paper or thick cloth. Keep them damp and warm. When stem
and root have grown an inch and a half long each, with waterproof ink
mark spaces exactly one quarter inch apart (Figs. 48, 49). Keep the
plantlets moist for a day or two, and it will be found that on the
stem some or all of the marks are more than one quarter inch apart;
on the root the marks have not separated. The root has grown beyond
the last mark.
NOTE TO TEACHER.--The microscopic structure of the root can be
determined only by the use of the compound microscope; but a good
general conception of the structure may be had by a careful attention
to the text and pictures and to explanations by the teacher, if such
microscopes are not to be had. See note at close of Chapter X.
CHAPTER IX
THE STEM--KINDS AND FORMS; PRUNING
=The Stem System.=--The stem of a plant is the part that _bears the
buds_, _leaves_, _flowers_, _and fruits_. Its office is _to hold these
parts up to the light and air_; and through its tissues the various
food-materials and the life-giving fluids _are distributed to the
growing and working parts_.
The entire mass or fabric of stems of any plant is called its =stem
system=. It comprises the trunk, branches, and twigs, but not the
stalks of leaves and flowers that die and fall away. The stem system
may be herbaceous or woody, annual, biennial, or perennial; and it may
assume many sizes and shapes.
=Stems are of Many Forms.=--The general way in which a plant grows is
called its =habit=. The habit is the _appearance or general form_.
Its habit may be open or loose, dense, straight, crooked, compact,
straggling, climbing, erect, weak, strong, and the like. The roots and
leaves are _the important functional or working parts_; the stem merely
connects them, and its form is exceedingly variable.
=Kinds of Stems.=--_The stem may be so short as to be scarcely
distinguishable._ In such cases the crown of the plant--that part
just at the surface of the ground--bears the leaves and flowers; but
this crown is really a very short stem. The dandelion, Fig. 33, is an
example. Such plants are often said to be =stemless=, however, in order
to distinguish them from plants that have long or conspicuous stems.
_These so-called stemless plants die to the ground every year._
[Illustration: FIG. 53.--STRICT SIMPLE STEM OF MULLEIN.]
[Illustration: FIG. 54.--STRICT UPRIGHT STEM OF NARROW-LEAVED DOCK.]
[Illustration: FIG. 55.--TRAILING STEM OF WILD MORNING GLORY
(_Convolvulus arvensis_).]
Stems are =erect= when they grow straight up (Figs. 53, 54). They
are =trailing= when they run along on the ground, as melon, wild
morning-glory (Fig. 55). They are =creeping= when they run on the
ground and take root at places, as the strawberry. They are =decumbent=
when they lop over to the ground. They are =ascending= when they lie
mostly or in part on the ground but stand more or less upright at their
ends; example, a tomato. They are =climbing= when they cling to other
objects for support (Figs. 36, 56).
[Illustration: FIG. 56.--A CLIMBING PLANT (a twiner).]
Trees in which the main trunk or the “leader” continues to grow from
its tip are said to be =excurrent= in growth. _The branches are borne
along the sides of the trunk_, as in common pines (Fig. 57) and
spruces. Excurrent means _running out_ or _running up_.
[Illustration: FIG. 57.--EXCURRENT TRUNK. A pine.]
Trees in which the main trunk does not continue are said to be
=deliquescent=. _The branches arise from one common point or from each
other._ The stem is lost in the branches. The apple tree, plum (Fig.
58), maple, elm, oak, China tree, are familiar examples. Deliquescent
means _dissolving or melting away_.
[Illustration: FIG. 58.--DELIQUESCENT TRUNK OF PLUM TREE.]
=Each kind of plant has its own peculiar habit or direction of
growth=; spruces always grow to a single stem or trunk, pear trees are
always deliquescent, morning-glories are always trailing or climbing,
strawberries are always creeping. We do not know why each plant has its
own habit, but the habit is in some way _associated with the plant’s
genealogy or with the way in which it has been obliged to live_.
The stem may be =simple= or =branched=. A simple stem usually grows
from the terminal bud, and side branches either do not start, or, if
they start, they soon perish. Mulleins (Fig. 53) are usually simple. So
are palms.
_Branched stems may be of very different habit and shape._ Some stem
systems are narrow and erect; these are said to be _strict_ (Fig. 54).
Others are _diffuse_, _open_, _branchy_, _twiggy_.
=Nodes and Internodes.=--The parts of the stem at which buds grow
are called =nodes= or =joints= and the spaces between the buds are
=internodes=. The stem at nodes is usually enlarged, and the pith is
usually interrupted. The distance between the nodes is influenced by
the vigor of the plant: how?
[Illustration: FIG. 59.--RHIZOME OR ROOTSTOCK.]
=Stems vs. Roots.=--Roots sometimes grow above ground (Chap. VII); so,
also, _stems sometimes grow underground_, and they are then known as
=subterranean stems=, =rhizomes=, or =rootstocks= (Fig. 59).
=Stems normally bear leaves and buds, and thereby are they
distinguished from roots=; usually, also, they contain a pith. The
leaves, however, may be reduced to mere scales, and the buds beneath
them may be scarcely visible. Thus the “eyes” on a white potato
are cavities with a bud or buds at the bottom (Fig. 60). Sweet
potatoes have no evident “eyes” when first dug (but they may develop
adventitious buds before the next growing-season). The white potato is
a stem: the sweet potato is probably a root.
[Illustration: FIG. 60.--SPROUTS ARISING FROM THE BUDS, or eyes, of a
potato tuber.]
=How Stems elongate.=--_Roots elongate by growing near the tip. Stems
elongate by growing more or less throughout the young or soft part_ or
“between joints” (Figs. 48, 49). But any part of the stem soon reaches
a limit beyond which it cannot grow, or becomes “fixed”; and the new
parts beyond elongate until they, too, become rigid. When a part of the
stem once becomes fixed or hard, it never increases in length: that is,
_the trunk or woody parts never grow longer or higher; branches do not
become farther apart or higher from the ground_.
=Stems are modified in form= by the particular or incidental conditions
under which they grow. _The struggle for light_ is the chief factor
in determining the shape and direction of any limb (Chap. II). This
is well illustrated in any tree or bush that grows against a building
or on the margin of a forest (Fig. 4). In a very dense thicket the
innermost trees shoot up over the others or they perish. Examine any
stem and endeavor to determine why it took its particular form.
=The stem is cylindrical=, _the outer part being bark and the inner
part being wood or woody tissue_. In the dicotyledonous plants, the
bark is usually easily separated from the remainder of the cylinder at
some time of the year; in monocotyledonous plants the bark is not free.
Growth in thickness takes place inside the covering and not on the very
outside of the plant cylinder. It is evident, then, that the covering
of _bark must expand in order to allow of the expansion of the woody
cylinder within it_. The tissues, therefore, must be under constant
pressure or tension. It has been determined that the pressure within a
growing trunk is often as much as fifty pounds to the square inch. The
lower part of the limb in Fig. 61 shows that the outer layers of bark
(which are long since dead, and serve only as protective tissue) have
reached the limit of their expanding capacity and have begun to split.
The pupil will now be interested in the bark on the body of an old elm
tree (Fig. 62); and he should be able to suggest one reason why stems
remain cylindrical, and why the old bark becomes marked with furrows,
scales, and plates.
[Illustration: FIG. 61.--CRACKING OF THE BARK ON AN ELM BRANCH.]
[Illustration: FIG. 62.--PIECE OF BARK FROM AN OLD ELM TRUNK.]
Most woody plants increase in diameter by the addition of an _annual
layer or “ring”_ on the outside of the woody cylinder, underneath the
bark. The monocotyledonous plants comprise very few trees and shrubs in
temperate climates (the palms, yuccas, and other tree-like plants are
of this class), and they do not increase greatly in diameter and they
rarely branch to any extent. Consult the woodpile for information as to
the annual rings.
=Bark-bound Trees=.--If, for any reason, the bark should become so
dense and strong that the trunk cannot expand, the tree is said to be
“bark-bound.” Such condition is not rare in orchard trees that have
been neglected. When good tillage is given to such trees, they may
not be able to overcome the rigidity of the old bark, and, therefore,
do not respond to the treatment. Sometimes the thinner-barked parts
may outgrow in diameter the trunk or the old branches below them.
The remedy is to _release the tension_. This may be done either by
softening the bark (by washes of soap or lye), or by separating it. The
latter is done by slitting the bark-bound part (in spring), thrusting
the point of a knife through the bark to the wood and then drawing
the blade down the entire length of the bark-bound part. The slit is
scarcely discernible at first, but it opens with the growth of the
tree, filling up with new tissue beneath. Let the pupil consider the
ridges which he now and then finds on trees, and determine whether
they have any significance--whether the tree has ever been released or
injured by natural agencies.
[Illustration: FIG. 63.--PROPER CUTTING OF A BRANCH. The wound will
soon be “healed.”]
=The Tissue covers the Wounds and “heals” them.=--This is seen in Fig.
63, in which a ring of tissue rolls out over the wound. This ring of
healing tissue forms most rapidly and uniformly when the wound is
smooth and regular. Observe the healing on broken and splintered limbs;
also the difference in rapidity of healing between wounds on strong and
weak limbs. There is difference in the rapidity of the healing process
in different kinds of trees. Compare the apple tree and the peach.
This tissue may in turn become bark-bound, and the healing may stop.
On large wounds it progresses more rapidly the first few years than it
does later. This roll or ring of tissue is called a =callus=.
=The callus grows from the living tissue of the stem= just about the
wound. It cannot cover long dead stubs or very rough broken branches
(Fig. 64). Therefore, in pruning _the branches should be cut close to
the trunk_ and made even and smooth; _all long stubs must be avoided_.
The seat of the wound should be close to the living part of the trunk,
for the stub of the limb that is severed has no further power in itself
of making healing tissue. The end of the remaining stub is merely
covered over by the callus, and usually remains a dead piece of wood
sealed inside the trunk (Fig. 65). If wounds do not heal over speedily,
germs and fungi obtain foothold in the dying wood and _rot sets in_.
Hollow trees are those in which the decay-fungi have progressed into
the inner wood of the trunk; _they have been infected_ (Fig. 66).
[Illustration: FIG. 64.--ERRONEOUS PRUNING.]
[Illustration: FIG. 65.--KNOT IN A HEMLOCK LOG.]
=Large wounds should be protected= with a covering of paint, melted
wax, or other adhesive and lasting material, to keep out the germs and
fungi. A covering of sheet iron or tin may keep out the rain, but it
will not exclude the germs of decay; in fact, it may provide the very
moist conditions that such germs need for their growth. Deep holes in
trees should be treated by having all the decayed parts removed down to
the clean wood, the surfaces painted or otherwise sterilized, and the
hole filled with wax or cement.
[Illustration: FIG. 66.--A KNOT HOLE, and the beginning of a hollow
trunk.]
=Stems and roots are living=, and they should not be wounded or
mutilated unnecessarily. Horses should never be hitched to trees.
Supervision should be exercised over persons who run telephone,
telegraph, and electric light wires, to see that they do not mutilate
trees. Electric light wires and trolley wires, when carelessly strung
or improperly insulated, may kill trees (Fig. 67).
[Illustration: FIG. 67.--ELM TREE KILLED BY A DIRECT CURRENT FROM AN
ELECTRIC RAILROAD SYSTEM.]
SUGGESTIONS.--_Forms of stems._ =43.= Are the trunks of trees ever
perfectly cylindrical? If not, what may cause the irregularities?
Do trunks often grow more on one side than the other? =44.= Slit a
rapidly growing limb, in spring, with a knife blade, and watch the
result during the season. =45.= Consult the woodpile, and observe the
variations in thickness of the annual rings, and especially of the
same ring at different places in the circumference. Cross-sections of
horizontal branches are interesting in this connection. =46.= Note
the enlargement at the base of a branch, and determine whether this
enlargement or bulge is larger on long, horizontal limbs than on
upright ones. Why does this bulge develop? Does it serve as a brace
to the limb, and is it developed as the result of constant strain?
=47.= _Strength of stems._ The pupil should observe the fact that
a stem has wonderful strength. Compare the proportionate height,
diameter, and weight of a grass stem with those of the slenderest
tower or steeple. Which has the greater strength? Which the greater
height? Which will withstand the most wind? Note that the grass stem
will regain its position even if its top is bent to the ground. Note
how plants are weighted down after a heavy rain and how they recover
themselves. =48.= Split a cornstalk and observe how the joints are
tied together and braced with fibers. Are there similar fibers in
stems of pigweed, cotton, sunflower, hollyhock?
[Illustration: FIG. 68.--POTATO. What are roots, and what stems? Has
the plant more than one kind of stem? more than two kinds? Explain.]
CHAPTER X
THE STEM--ITS GENERAL STRUCTURE
There are two main types of stem structure in flowering plants, the
differences being based on the arrangement of bundles or strands of
tissue. These types are _endogenous_ and _exogenous_ (page 20). It will
require patient laboratory work to understand what these types and
structures are.
=Endogenous, or Monocotyledonous Stems.=--Examples of endogenous stems
are all the grasses, cane-brake, sugar-cane, smilax or green-brier,
palms, banana, canna, bamboo, lilies, yucca, asparagus, all the cereal
grains. For our study, a cornstalk may be used as a type.
[Illustration: FIG. 69.--CROSS-SECTION OF CORNSTALK, showing the
scattered fibro-vascular bundles. Slightly enlarged.]
A piece of _cornstalk_, either green or dead, should be in the hand of
each pupil while studying this lesson. Fig. 69 will also be of use.
Is there a swelling at the nodes? Which part of the internode comes
nearest to being perfectly round? There is a grooved channel running
along one side of the internode: how is it placed with reference to the
leaf? with reference to the groove in the internode below it? What do
you find in each groove at its lower end? (In a dried stalk only traces
of this are usually seen.) Does any bud on a cornstalk besides the one
at the top ever develop? Where do suckers come from? Where does the ear
grow?
Cut a cross-section of the stalk between the nodes (Fig. 69). Does it
have a distinct bark? The interior consists of soft “pith” and tough
woody parts. The wood is found in _strands_ or _fibers_. Which is more
abundant? Do the fibers have any definite arrangement? Which strands
are largest? Smallest? The firm smooth _rind_ (which cannot properly be
called a bark) consists of small wood strands packed closely together.
Grass stems are hollow cylinders; and the cornstalk, because of the
lightness of its contents, is also practically a cylinder. Stems of
this kind are admirably adapted for providing a strong support to
leaves and fruit. This is in accordance with the well-known law that
a hollow cylinder is much stronger than a solid cylinder of the same
weight of material. Cut a thin slice of the inner soft part and hold
it up to the light. Can you make out a number of tiny compartments or
cells? These cells consist of a tissue called _parenchyma_, the tissue
from which when young all the other tissues arise and differentiate
(Parenchyma = _parent_ + _chyma_, or tissue). The numerous walls of
these cells may serve to brace the outer wall of the cylinder; but
their chief function in the young stalk is to give origin to other
cells. When alive they are filled with cell sap and protoplasm.
[Illustration: FIG. 70.--DIAGRAM TO SHOW THE COURSE OF FIBRO-VASCULAR
BUNDLES IN MONOCOTYLEDONS.]
Trace the _woody strands_ through the nodes. Do they ascend vertically?
Do they curve toward the rind at certain places? Compare their course
with the strands shown in Fig. 70. _The woody strands consist chiefly
of tough fibrous cells that give rigidity and strength to the plant,
and of long tubular interrupted canals that serve to convey sap upward
from the root and to convey food downward from the leaves to the stem
and roots._
Monocotyledons, as shown by fossils, existed before dicotyledons
appeared, and it is thought that the latter were developed from
ancestors of the former. It will be interesting to trace the
relationship in stem structure. It will first be necessary to learn
something of the structure of the wood strand.
[Illustration: FIG. 71.--DIAGRAM OF WOOD STRANDS OR FIBRO-VASCULAR
BUNDLES IN A ROOT, showing the wood (_x_) and bast (_p_) separated.]
=Wood Strand in Monocotyledons and Dicotyledons.=--Each wood strand (or
fibro-vascular bundle) consists of two parts--the bast and the wood
proper. The wood is on the side of the strand toward the center of the
stem and contains large tubular canals that take the watery sap upward
from the roots. The bast is on the side toward the bark and contains
fine tubes through which diffuses the dense sap containing digested
food from the leaves. In the root (Fig. 71) the bast and the wood are
separate, so that there are _two kinds of strands_.
[Illustration: FIG. 72.--PART OF CROSS-SECTION OF ROOTSTOCK OF
ASPARAGUS, showing a few fibro-vascular bundles. An endogenous stem.]
In monocotyledons, as already said, the strands (or bundles) _are
usually scattered in the stem with no definite arrangement_ (Figs. 72,
73). In dicotyledons the strands, or bundles, _are arranged in a ring_.
As the dicotyledonous seed germinates, five bundles are usually formed
in its hypocotyl (Fig. 74); soon five more are interposed between them,
and the multiplication continues, in tough plants, until the bundles
touch (Fig. 74, right). The inner parts thus form a ring of wood and
the outer parts form the inner bark or bast. A new ring of wood or bast
is formed on stems of dicotyledons each year and the age of a cut stem
is easily determined.
[Illustration: _a_
_b_
FIG. 73.--THE SCATTERED BUNDLES OR STRANDS, in monocotyledons at _a_,
and the bundles in a circle in dicotyledons at _b_.]
[Illustration: FIG. 74.--DICOTYLEDONOUS STEM OF ONE YEAR AT LEFT WITH
FIVE BUNDLES, and a Two-year Stem at Right.
_o_, the pith; _c_, the wood part; _b_, the bast part; _a_, one year’s
growth.]
[Illustration: FIG. 75.--FIBRO-VASCULAR BUNDLE OF INDIAN CORN, much
magnified.
_A_, annular vessel; _A′_, annular or spiral vessel; _TT′_,
thick-walled vessels; _W_, tracheids or woody tissue; _F_, sheath of
fibrous tissue surrounding the bundle; _FT_, fundamental tissue or
pith; _S_, sieve tissue; _P_, sieve plate; _C_, companion cell; _l_,
intercellular space, formed by tearing down of adjacent cells; _W′_,
wood parenchyma.]
[Illustration: FIG. 76.--THE DICOTYLEDONOUS BUNDLE OR WOOD STRAND.
Upper figure is of moonseed:
_c_, cambium; _d_, ducts; 1, end of first year’s growth; 2, end of
second year’s growth; bast part at left and wood part at right. Lower
figure (from Wettstein) is sunflower; _h_, wood-cells; _g_, vessels;
_c_, cambium; _p_, fundamental tissue or parenchyma; _b_, bast; _bp_,
bast parenchyma; _s_, sieve-tubes.]
When cross-sections of monocotyledonous and dicotyledonous bundles are
examined under the microscope, it is readily seen why dicotyledonous
bundles form rings of wood and monocotyledonous cannot (Figs. 75
and 76). The dicotyledonous bundle (Fig. 76) has, running across
it, a layer of brick-shaped cells called =cambium=, which cells are
a specialized form of the parenchyma cells and retain the power of
growing and multiplying. The bundles containing cambium are called
_open bundles_. There is no cambium in monocotyledonous bundles (Fig.
75) and the bundles are called _closed bundles_. Monocotyledonous stems
_soon cease to grow in diameter_. The stem of a palm tree is almost as
large at the top as at the base. As dicotyledonous plants grow, the
_stems become thicker each year_, for the delicate active cambium layer
forms new cells from early spring until midsummer or autumn, adding to
the wood within and to the bark without. As the growth in spring is
very rapid, the first wood-cells formed are much larger than the last
wood-cells formed by the slow growth of the late season, and the spring
wood is less dense and lighter colored than the summer wood; hence the
time between two years’ growth is readily made out (Figs. 77 and 78).
Because of the rapid growth of the cambium in spring and its consequent
soft walls and fluid contents, the bark of trees “peels” readily at
that season.
[Illustration: FIG. 77.--WHITE PINE STEM, 5 years old. The outermost
layer is bark.]
=Medullary Rays.=--The first year’s growth in dicotyledons forms a
woody ring which almost incloses the pith, and this is left as a small
cylinder which does not grow larger, even if the tree should live a
century. It is not quite inclosed, however, for the narrow layers
of soft cells separating the bundles remain between them (Fig. 78),
forming radiating lines called =medullary rays= or =pith rays=.
[Illustration: FIG. 78.--ARRANGEMENT OF TISSUES IN TWO-YEAR-OLD STEM OF
MOONSEED.
_p_, pith; _f_, parenchyma. The fibro-vascular bundles, or wood
strands, are very prominent, with thin medullary rays between.]
=The Several Plant Cells and their Functions.=--In the =wood= there are
some parenchyma cells that are still with thin walls, but have lost
the power of division. They are now _storage cells_. There are also
wood fibers which are thick-walled and rigid (_h_, Fig. 76), and serve
to _support_ the sap-canals or _wood vessels_ (or tracheids) that are
formed by the absorption of the end walls of upright rows of cells; the
canals pass from the roots to the twigs and even to ribs of the leaves
and serve to transport the root water. They are recognized (Fig. 79) by
the peculiar thickening of the wall on the inner surface of the tubes,
occurring in the form of spirals. Sometimes the whole wall is thickened
except in spots called _pits_ (_g_, Fig. 76). These thin spots (Fig.
80) allow the sap to pass to other cells or to neighboring vessels.
[Illustration: FIG. 79.--MARKINGS IN CELL WALLS OF WOOD FIBERS.
_sp_, spiral; _an_, annular; _sc_, scalariform.]
[Illustration: FIG. 80.--PITS IN THE CELL WALL.
Longitudinal section of wall at _b_, showing pit borders at _o_, _o_.]
=The cambium=, as we have seen, consists of cells whose function is
_growth_. These cells are thin-walled and filled with protoplasm.
During the growing season they are continually adding to the wood
within and the bark without; hence the layer moves outward as it
deposits the new woody layer within.
[Illustration: FIG. 81.--SIEVE-TUBES, _s_, _s_;
_p_ shows a top view of a sieve-plate, with a companion cell. _c_, at
the side; _o_ shows sieve-plates in the side of the cell. In _s_, _s_
the protoplasm is shrunken from the walls by reagents.]
[Illustration: FIG. 82.--THICK-WALLED BAST CELLS.]
=The bark= consists of inner or _fibrous bark_ or new bast (these
fibers in flax become linen), the _green or middle bark_ which
functions somewhat as the leaves, and the _corky or outer bark_. The
common word “bark” is seen therefore not to represent a homogeneous or
simple structure, but rather a collection of several kinds of tissue,
all separating from the wood beneath by means of cambium. The new
bast contains (1) the _sieve-tubes_ (Fig. 81) which transport the sap
containing organic substances, as sugar and proteids, from the leaves
to the parts needing it (_s_, Fig. 76). These tubes have been formed
like the wood vessels, but they have sieve-plates to allow the dense
organic-laden sap to pass with sufficient readiness for purposes of
rapid distribution. (2) There are also thick-walled _bast fibers_
(Fig. 82) in the bast that serve for _support_. (3) There is also
some parenchyma (parent tissue) in the new bast; it is now in part a
_storage_ tissue. Sometimes the walls of parenchyma cells in the cortex
thicken at the corners and form _brace cells_ (Fig. 83) (collenchyma)
for _support_; sometimes the whole wall is thickened, forming _grit
cells_ or _stone cells_ (Fig. 84; examples in tough parts of pear, or
in stone of fruits). Some parts serve for secretions (milk, rosin,
etc.) and are called _latex tubes_.
[Illustration: FIG. 83.--COLLENCHYMA IN WILD JEWELWEED OR TOUCH-ME-NOT
(IMPATIENS).]
[Illustration: FIG. 84.--GRIT CELLS.]
=The outer bark= of old shoots consists of _corky_ cells that _protect_
from mechanical injury, and that contain a fatty substance (suberin)
impermeable to water and of service to _keep in moisture_. There is
sometimes a cork cambium (or phellogen) in the bark that serves to
extend the bark and keep it from splitting, thus increasing its power
to protect.
=Transport of the “Sap.”=--We shall soon learn that the common word
“sap” does not represent a single or simple substance. We may roughly
distinguish two kinds of more or less fluid contents: (1) _the root
water_, sometimes called mineral sap, that is taken in by the root,
containing its freight of such inorganic substances as potassium,
calcium, iron, and the rest; this root water rises, we have found,
_in the wood vessels_,--that is, in the young or “sapwood” (p. 96);
(2) the _elaborated_ or _organized materials_ passing back and forth,
especially from the leaves, to build up tissues in all parts of the
plant, some of it going down to the roots and root-hairs; this organic
material is transported, as we have learned, _in the sieve-tubes of the
inner bast_,--that is, in the “inner bark.” Removing the bark from a
trunk in a girdle will not stop the upward rise of the root water so
long as the wood remains alive; but it will stop the passage of the
elaborated or food-stored materials to parts below and thus starve
those parts; and if the girdle does not heal over by the deposit of new
bark, the tree will in time _starve to death_. It will now be seen that
the common practice of placing wires or hoops about trees to hold them
in position or to prevent branches from falling is irrational, because
such wires interpose barriers over which the fluids cannot pass; in
time, as the trunk increases in diameter, the wire girdles the tree. It
is much better to bolt the parts together by rods extending through the
branches (Fig. 85). These bolts should fit very tight in their holes.
Why?
[Illustration: FIG. 85.--THE WRONG WAY TO BRACE A TREE. (See Fig. 118).]
=Wood.=--The main stem or trunk, and sometimes the larger branches,
are the sources of lumber and timber. Different kinds of wood have
value for their special qualities. The business of raising wood, for
all purposes, is known as _forestry_. The forest is to be considered
as a crop, and the crop must be harvested, as much as corn or rice is
harvested. Man is often able to grow a more productive forest than
nature does.
=Resistance to decay= gives value to wood used for shingles (_cypress_,
heart of _yellow pine_) and for fence posts (_mulberry_, _cedar_, _post
oak_, _bois d’arc_, _mesquite_).
=Hardness and strength= are qualities of great value in building. _Live
oak_ is used in ships. _Red oak_, _rock maple_, and _yellow pine_ are
used for floors. The best flooring is sawn with the straight edges
of the annual rings upward; tangential sawn flooring may splinter.
_Chestnut_ is common in some parts of the country, being used for
ceiling and inexpensive finishing and furniture. _Locust_ and _bois
d’arc_ (osage orange) are used for hubs of wheels; bois d’arc makes
a remarkably durable pavement for streets. _Ebony_ is a tropical
wood used for flutes, black piano keys, and fancy articles. _Ash_ is
straight and elastic; it is used for handles for light implements.
_Hickory_ is very strong as well as elastic, and is superior to ash for
handles, spokes, and other uses where strength is wanted. Hickory is
never sawn into lumber, but is split or turned. The “second growth,”
which sprouts from stumps, is most useful, as it splits readily.
Fast-growing hickory in rich land is most valuable. The supply of
useful hickory is being rapidly exhausted.
=Softness= _is often important_. _White pine_ and _sweet gum_ because
of their softness and lightness are useful in box-making. “_Georgia_”
or _southern pine_ is harder and stronger than white pine; it is much
used for floors, ceilings, and some kinds of cabinet work. _White
pine_ is used for window-sash, doors, and molding, and cheaper grades
for flooring. _Hemlock_ is the prevailing lumber in the east for
the framework and clapboarding of buildings. _Redwood_ and _Douglas
spruce_ are common building materials on the Pacific coast. _Cypress_
is soft and resists decay and is superior to white pine for sash,
doors, and posts on the outside of houses. _Cedar_ is readily carved
and has a unique use in the making of chests for clothes, as its odor
repels moths and other insects. _Willow_ is useful for baskets and
light furniture. _Basswood_ or _linden_ is used for light ceiling and
sometimes for cheap floors. _Whitewood_ (incorrectly called poplar)
is employed for wagon bodies and often for house finishing. It often
resembles curly maple.
=Beauty of grain and polish= gives wood value for furniture, pianos,
and the like. _Mahogany_ and _white oak_ are most beautiful, although
red oak is also used. Oak logs which are first quartered and then sawn
radially expose the beautiful silver grain (medullary rays). Fig. 86
shows one _mode of quartering_. The log is quartered on the lines
_a_, _a_, _b_, _b_; then succeeding boards are cut from each quarter
at 1, 2, 3, etc. The nearer the heart the better the “grain”: why?
Ordinary boards are sawn tangentially, as _c_, _c_. _Curly pine_,
_curly walnut_, and _bird’s-eye maple_ are woods that owe their beauty
of grain to wavy lines or buried knots. Merely a stump of curly walnut
is worth several hundred dollars. Such wood is sliced very thin for
veneering and glued over other woods in making pianos and other pieces.
If the cause of wavy grain could be found out and such wood grown at
will, the discovery would be very useful. _Maple_ is much used for
furniture. _Birch_ may be colored so as very closely to represent
mahogany, and it is useful for desks.
[Illustration: FIG. 86.--THE MAKING OF ORDINARY BOARDS, AND ONE WAY OF
MAKING “QUARTERED” BOARDS.]
=Special Products of Trees.=--Cork from the bark of the cork oak in
Spain, latex from the rubber and sap from the sugar maple trees,
turpentine from pine, tannin from oak bark, Peruvian bark from
cinchona, are all useful products.
SUGGESTIONS.--_Parts of a root and stem through which liquids rise._
=49.= Pull up a small plant with abundant leaves, cut off the root
so as to leave two inches or more on the plant (or cut a leafy shoot
of squash or other strong-growing coarse plant), and stand it in
a bottle with a little water in the bottom which has been colored
with red ink (eosin). After three hours examine the root; make
cross-sections at several places. Has the water colored the axis
cylinder? The cortex? What is your conclusion? Stand some cut flowers
or a leafy plant with cut stem in the same solution and examine as
before: conclusion? =50.= Girdle a twig of a rapidly growing bush (as
willow) in early spring when growth begins (_a_) by very carefully
removing only the bark, and (_b_) by cutting away also the sapwood.
Under which condition do the leaves wilt? Why? =51.= Stand twigs of
willow in water; after roots have formed under the water, girdle
the twig (in the two ways) above the roots. What happens to the
roots, and why? =52.= Observe the swellings on trees that have been
girdled or very badly injured by wires or otherwise: where are these
swellings, and why? =53.= _Kinds of wood._ Let each pupil determine
the kind of wood in the desk, the floor, the door and window casings,
the doors themselves, the sash, the shingles, the fence, and in the
small implements and furniture in the room; also what is the cheapest
and the most expensive lumber in the community. =54.= How many kinds
of wood does the pupil know, and what are their chief uses?
NOTE TO TEACHER.--The work in this chapter is intended to be
mainly descriptive, for the purpose of giving the pupil a rational
conception of the main vital processes associated with the stem, in
such a way that he may translate it into his daily thought. It is
not intended to give advice for the use of the compound microscope.
If the pupil is led to make a careful study of the text, drawings,
and photographs on the preceding and the following pages, he will
obtain some of the benefit of studying microscope sections without
being forced to spend time in mastering microscope technique. If
the school is equipped with compound microscopes, a teacher is
probably chosen who has the necessary skill to manipulate them and
the knowledge of anatomy and physiology that goes naturally with
such work; and it would be useless to give instruction in such
work in a text of this kind. The writer is of the opinion that the
introduction of the compound microscope into first courses in botany
has been productive of harm. Good and vital teaching demands first
that the pupil have a normal, direct, and natural relation to his
subject, as he commonly meets it, that the obvious and significant
features of the plant world be explained to him and be made a means
of training him. The beginning pupil cannot be expected to know
the fundamental physiological processes, nor is it necessary that
these processes should be known in order to have a point of view
and trained intelligence on the things that one customarily sees.
Many a pupil has had a so-called laboratory course in botany without
having arrived at any real conception of what plants mean, or without
having had his mind opened to any real sympathetic touch with his
environment. Even if one’s knowledge be not deep or extensive, it may
still be accurate as far as it goes, and his outlook on the subject
may be rational.
[Illustration: FIG. 87.--THE MANY-STEMMED THICKETS OF MANGROVE OF
SOUTHERNMOST SEACOASTS, many of the trunks being formed of aërial
roots.]
CHAPTER XI
LEAVES--FORM AND POSITION
Leaves may be studied from four points of view,--with reference (1) to
their _kinds_ and _shapes_; (2) their _position_, or _arrangement_ on
the plant; (3) their _anatomy_, or _structure_; (4) their _function_,
or the work they perform. This chapter is concerned with the first two
categories.
[Illustration: FIG. 88.--A SIMPLE NETTED-VEINED LEAF.]
[Illustration: FIG. 89.--A SIMPLE PARALLEL-VEINED LEAF.]
[Illustration: FIG. 90.--COMPOUND OR BRANCHED LEAF OF BRAKE (a common
fern).]
=Kinds.=--Leaves are =simple= or unbranched (Figs. 88, 89), and
=compound= or branched (Fig. 90). The method of compounding or
branching follows the mode of veining. The veining, or =venation=,
is of two general kinds: in some plants the main veins diverge, and
there is a conspicuous network of smaller veins; such leaves are
=netted-veined=. They are characteristic of the dicotyledons. In
other plants the main veins are parallel, or nearly so, and there is
no conspicuous network; these are =parallel-veined= leaves (Figs.
89, 102). These leaves are the rule in monocotyledonous plants. The
venation of netted-veined leaves is =pinnate= or feather-like when the
veins arise from the side of a continuous midrib (Fig. 91); =palmate=
or =digitate= (hand-like) when the veins arise from the apex of the
petiole (Figs. 88, 92). If leaves were divided between the main veins,
the former would be pinnately and the latter digitately compound.
[Illustration: FIG. 91.--COMPLETE LEAVES OF WILLOW.]
[Illustration: FIG. 92.--DIGITATE-VEINED PELTATE LEAF OF NASTURTIUM.]
[Illustration: FIG. 93.--PINNATELY COMPOUND LEAF OF ASH.]
It is customary to speak of a leaf as compound only when the parts or
branches are completely separate blades, as when the division extends
to the midrib (Figs. 90, 93, 94, 95). The parts or branches are known
as =leaflets=. Sometimes the leaflets themselves are compound, and the
whole leaf is then said to be =bi-compound= or =twice-compound= (Fig.
90). Some leaves are three-compound, four-compound, or five-compound.
=Decompound= is a general term to express any degree of compounding
beyond twice-compound.
[Illustration: FIG. 94.--DIGITATELY COMPOUND LEAF OF RASPBERRY.]
[Illustration: FIG. 95.--POISON IVY. LEAF AND FRUIT.]
[Illustration: FIG. 96.--LOBED LEAF OF SUGAR MAPLE.]
Leaves that are not divided as far as to the midrib are said to be:
=lobed=, if the openings or sinuses are not more than half the depth of
the blade (Fig. 96);
=cleft=, if the sinuses are deeper than the middle;
=parted=, if the sinuses reach two thirds or more to the midrib (Fig.
97);
=divided=, if sinuses reach nearly or quite to the midrib.
The parts are called =lobes=, =divisions=, or =segments=, rather than
leaflets. The leaf may be pinnately or digitately lobed, parted, cleft,
or divided. A pinnately parted or cleft leaf is sometimes said to be
=pinnatifid=.
[Illustration: FIG. 97.--DIGITATELY PARTED LEAVES OF BEGONIA.]
Leaves may have one or all of three parts--=blade=, or expanded
part; =petiole=, or stalk; =stipules=, or appendages at the base of
the petiole. A leaf that has all three of these parts is said to be
=complete= (Figs. 91, 106). The stipules are often green and leaflike
and perform the function of foliage, as in the pea and Japanese quince
(the latter common in yards).
[Illustration: FIG. 98.--OBLONG-OVATE SESSILE LEAVES OF TEA.]
Leaves and leaflets that have no stalks are said to be =sessile= (Figs.
98, 103), _i.e._ sitting. Find several examples. The same is said of
flowers and fruits. The blade of a sessile leaf may partly or wholly
surround the stem, when it is said to be =clasping=. Examples: aster
(Fig. 99), corn. In some cases the leaf runs down the stem, forming a
wing; such leaves are said to be =decurrent= (Fig. 100). When opposite
sessile leaves are joined by their bases, they are said to be =connate=
(Fig. 101).
[Illustration: FIG. 99.--CLASPING LEAF OF A WILD ASTER.]
Leaflets may have one or all of these three parts, but the stalks of
leaflets are called =petiolules= and the stipules of leaflets are
called =stipels=. The leaf of the garden bean has leaflets, petiolules,
and stipels.
[Illustration: FIG. 100.--DECURRENT LEAVES OF MULLEIN.]
The blade is usually attached to the petiole by _its lower edge_. In
pinnate-veined leaves, the petiole seems to continue through the leaf
as a =midrib= (Fig. 91). In some plants, however, the petiole joins the
blade inside or beyond the margin (Fig. 92). Such leaves are said to
be =peltate= or shield-shaped. This mode of attachment is particularly
common in floating leaves (_e.g._ the water lilies). Peltate leaves are
usually digitate-veined.
[Illustration: FIG. 101.--TWO PAIRS OF CONNATE LEAVES OF HONEYSUCKLE.]
=How to Tell a Leaf.=--It is often difficult to distinguish compound
leaves from leafy branches, and leaflets from leaves. As a rule leaves
can be distinguished by the following tests: (1) Leaves are _temporary
structures_, sooner or later falling. (2) Usually _buds are borne in
their axils_. (3) Leaves are usually _borne at joints or nodes_. (4)
They arise on wood of the _current year’s growth_. (5) They have a more
or less _definite arrangement_. When leaves fall, the twig that bore
them remains; when leaflets fall, the main petiole or stalk that bore
them also falls.
[Illustration: FIG. 102.--LINEAR-ACUMINATE LEAF OF GRASS.]
[Illustration: FIG. 103.--SHORT-OBLONG LEAVES OF BOX.]
=Shapes.=--Leaves and leaflets are infinitely variable in shape. Names
have been given to some of the more definite or regular shapes. These
names are a part of the language of botany. The names represent ideal
or typical shapes; there are no two leaves alike and very few that
perfectly conform to the definitions. The shapes are likened to those
of familiar objects or of geometrical figures. Some of the commoner
shapes are as follows (name original examples in each class):
[Illustration]
=Linear=, several times longer than broad, with the sides nearly or
quite parallel. Spruces and most grasses are examples (Fig. 102). In
linear leaves, the main veins are usually parallel to the midrib.
[Illustration]
=Oblong=, twice or thrice as long as broad, with the sides parallel for
most of their length. Fig. 103 shows the short-oblong leaves of the
box, a plant that is used for permanent edgings in gardens.
[Illustration]
=Elliptic= differs from the oblong in having the sides gradually
tapering to either end from the middle. The European beech (Fig. 104)
has elliptic leaves. (This tree is often planted in this country.)
[Illustration]
=Lanceolate=, four to six times longer than broad, widest below the
middle, and tapering to either end. Some of the narrow-leaved willows
are examples. Most of the willows and the peach have oblong-lanceolate
leaves.
[Illustration]
=Spatulate=, a narrow leaf that is broadest toward the apex. The top is
usually rounded.
[Illustration: FIG. 104.--ELLIPTIC LEAF OF PURPLE BEECH.]
[Illustration: FIG. 105.--OVATE SERRATE LEAF OF HIBISCUS.]
[Illustration: FIG. 106.--LEAF OF APPLE, showing blade, petiole, and
small narrow stipules.]
[Illustration]
=Ovate=, shaped somewhat like the longitudinal section of an egg: about
twice as long as broad, tapering from near the base to the apex. This
is one of the commonest leaf forms (Figs. 105, 106).
[Illustration]
=Obovate=, ovate inverted,--the wide part towards the apex. Leaves of
mullein and leaflets of horse-chestnut and false indigo are obovate.
This form is commonest in leaflets of digitate leaves: why?
[Illustration]
=Reniform=, kidney-shaped. This form is sometimes seen in wild plants,
particularly in root-leaves. Leaves of wild ginger are nearly reniform.
[Illustration]
=Orbicular=, circular in general outline. Very few leaves are perfectly
circular, but there are many that are nearer circular than any other
shape (Fig. 107).
[Illustration: FIG. 107.--ORBICULAR LOBED LEAVES.]
[Illustration: FIG. 108.--TRUNCATE LEAF OF TULIP TREE.]
The shape of many leaves is described in combinations of these terms:
as =ovate-lanceolate=, =lanceolate-oblong=.
The shape of the base and apex of the leaf or leaflet is often
characteristic. The base may be =rounded= (Fig. 104), =tapering=
(Fig. 93), =cordate= or heart-shaped (Fig. 105), truncate or squared
as if cut off. The apex may be blunt or =obtuse=, =acute= or sharp,
=acuminate= or long-pointed, =truncate= (Fig. 108). Name examples.
The shape of the margin is also characteristic of each kind of leaf.
The margin is =entire= when it is not indented or cut in any way (Figs.
99, 103). When not entire, it may be =undulate= or wavy (Fig. 92),
=serrate= or saw-toothed (Fig. 105), =dentate= or more coarsely notched
(Fig. 95), =crenate= or round-toothed, =lobed=, and the like. Give
examples.
Leaves often differ greatly in form on the same plant. Observe the
different shapes of leaves on the young growths of mulberries (Fig. 2)
and wild grapes; also on vigorous squash and pumpkin vines. In some
cases there may be simple and compound leaves on the same plant. This
is marked in the so-called Boston ivy or ampelopsis (Fig. 109), a vine
that is used to cover brick and stone buildings. Different degrees of
compounding, even in the same leaf, may often be found in honey locust
and Kentucky coffee tree. Remarkable differences in forms are seen by
comparing seed-leaves with mature leaves of any plant (Fig. 30).
[Illustration: FIG. 109.--DIFFERENT FORMS OF LEAVES FROM ONE PLANT OF
AMPELOPSIS.]
=The Leaf and its Environment.=--The form and shape of the leaf often
have direct relation to the _place in which the leaf grows. Floating
leaves are usually expanded and flat_, and the petiole varies in length
with the depth of the water. _Submerged leaves are usually linear or
thread-like_, or are cut into very narrow divisions: thereby more
surface is exposed, and possibly the leaves are less injured by moving
water. Compare the sizes of the leaves on the ends of branches with
those at the base of the branches or in the interior of the tree top.
In dense foliage masses, the petioles of the lowermost or undermost
leaves _tend to elongate_--to push the leaf to the light.
On the approach of winter the leaf usually ceases to work, and dies.
It may drop, when it is said to be =deciduous=; or it may remain on
the plant, when it is said to be =persistent=. If persistent leaves
remain green during the winter, the plant is said to be =evergreen=.
Give examples in each class. Most leaves fall by breaking off at the
lower end of the petiole with a _distinct joint or articulation_. There
are many leaves, however, that wither and hang on the plant until torn
off by the wind; of such are the leaves of grasses, sedges, lilies,
orchids, and other plants of the monocotyledons. Most leaves of this
character are parallel-veined.
_Leaves also die and fall from lack of light._ Observe the yellow and
weak leaves in a dense tree top or in any thicket. Why do the lower
leaves die on house plants? Note the carpet of needles under the pines.
All evergreens shed their leaves after a time. Counting back from the
tip of a pine or spruce shoot, determine how many years the leaves
persist. In some spruces a few leaves may be found on branches ten or
more years old.
=Arrangement of Leaves.=--Most leaves have a regular _position or
arrangement_ on the stem. _This position or direction is determined
largely by exposure to sunlight._ In temperate climates they usually
hang in such a way that they receive the greatest amount of light. One
leaf shades the other to the least possible degree. If the plant were
placed in a new position with reference to light, the leaves would make
an effort to turn their blades.
_When leaves are_ =opposite= _the pairs usually alternate_. That is, if
one pair stands north and south, the next pair stands east and west.
See the box-elder shoot, on the left in Fig. 110. _One pair does not
shade the pair beneath._ The leaves are in four vertical ranks.
_There are several kinds of_ =alternate= _arrangement_. In the elm
shoot, in Fig. 110, the third bud is vertically above the first. This
is true no matter which bud is taken as the starting point. Draw a
thread around the stem until the two buds are joined. Set a pin at each
bud. Observe that two buds are passed (not counting the last) and that
the thread makes one circuit of the stem. Representing the number of
buds by a denominator, and the number of circuits by a numerator, we
have the fraction ¹⁄₂, _which expresses the part of the circle that
lies between any two buds_. That is, the buds are one half of 360
degrees apart, or 180 degrees. Looking endwise at the stem, the leaves
are seen to be 2-ranked. Note that in the apple shoot (Fig. 110, right)
the thread makes two circuits and five buds are passed: _two-fifths
represents the divergence between the buds_. The leaves are 5-ranked.
[Illustration: FIG. 110.--PHYLLOTAXY OF BOX ELDER, ELM, APPLE.]
_Every plant has its own arrangement of leaves._ For opposite leaves,
see maple, box elder, ash, lilac, honeysuckle, mint, fuchsia. For
2-ranked arrangement, see all grasses, Indian corn, basswood, elm. For
3-ranked arrangement, see all sedges. For 5-ranked (which is one of
the commonest), see apple, cherry, pear, peach, plum, poplar, willow.
For 8-ranked, see holly, osage orange, some willows. More complicated
arrangements occur in bulbs, house leeks, and other condensed parts.
The buds or “eyes” on a potato tuber, which is an underground stem
(why?), show a spiral arrangement (Fig. 111). _The arrangement of
leaves on the stem is known as_ =phyllotaxy= (literally, “leaf
arrangement”). Make out the phyllotaxy on six different plants nearest
the schoolhouse door.
In some plants, several leaves occur at one level, being arranged in a
circle around the stem. Such leaves are said to be =verticillate=, or
=whorled=. Leaves arranged in this way are usually narrow: why?
[Illustration: FIG. 111.--PHYLLOTAXY OF THE POTATO TUBER. Work it out
on a fresh long tuber.]
Although a definite arrangement of leaves is the rule in most plants,
_it is subject to modification_. On shoots that receive the light only
from one side or that grow in difficult positions, the arrangement may
not be definite. Examine shoots that grow on the under side of dense
tree tops or in other partially lighted positions.
[Illustration: FIG. 112.--COWPEA. Describe the leaves. For what is the
plant used?]
SUGGESTIONS.--=55.= The pupil should match leaves to determine
whether any two are alike. Why? Compare leaves from the same plant
in size, shape, color, form of margin, length of petiole, venation,
texture (as to thickness or thinness), stage of maturity, smoothness
or hairiness. =56.= Let the pupil take an average leaf from each of
the first ten different kinds of plants that he meets and compare
them as to the above points (in Exercise 55), and also name the
shapes. Determine how the various leaves resemble and differ. =57.=
Describe the stipules of rose, apple, fig, willow, violet, pea,
or others. =58.= In what part of the world are parallel-veined
leaves the more common? =59.= Do you know of parallel-veined leaves
that have lobed or dentate margins? =60.= What becomes of dead
leaves? =61.= Why is there no grass or other undergrowth under pine
and spruce trees? =62.= Name several leaves that are useful for
decorations. Why are they useful? =63.= What trees in your vicinity
are most esteemed as shade trees? What is the character of their
foliage? =64.= Why are the internodes so long in water-sprouts
and suckers? =65.= How do foliage characters in corn or sorghum
differ when the plants are grown in rows or broadcast? Why? =66.=
Why may removal of half the plants increase the yield of cotton or
sugar-beets or lettuce? =67.= How do leaves curl when they wither? Do
different leaves behave differently in this respect? =68.= What kinds
of leaves do you know to be eaten by insects? By cattle? By horses?
What kinds are used for human food? =69.= How would you describe the
shape of leaf of peach? apple? elm? hackberry? maple? sweet-gum?
corn? wheat? cotton? hickory? cowpea? strawberry? chrysanthemum?
rose? carnation? =70.= Are any of the foregoing leaves compound? How
do you describe the shape of a compound leaf? =71.= How many sizes of
leaves do you find on the bush or tree nearest the schoolroom door?
=72.= How many colors or shades? =73.= How many lengths of petioles?
=74.= Bring in all the shapes of leaves that you can find.
CHAPTER XII
LEAVES--STRUCTURE OR ANATOMY
Besides the =framework=, or system of veins found in blades of all
leaves, there is a soft cellular tissue called =mesophyll=, or =leaf
parenchyma=, and an =epidermis= or skin that covers the entire outside
part.
[Illustration: FIG. 113.--SECTION OF A LEAF, showing the air spaces.
Breathing-pore or stoma at _a_. The palisade cells which chiefly
contain the chlorophyll are at _b_. Epidermal cells at _c_.]
=Mesophyll.=--The mesophyll is _not all alike or homogeneous_. The
upper layer is composed of elongated cells placed perpendicular to the
surface of the leaf. These are called =palisade cells=. These cells
are usually filled with green bodies called =chlorophyll grains=.
The grain contains a great number of chlorophyll drops imbedded in
the protoplasm. Below the palisade cells is the spongy =parenchyma=,
composed of cells more or less spherical in shape, irregularly
arranged, and provided with many intercellular air cavities (Fig. 113).
In leaves of some plants exposed to strong light there may be more than
one layer of palisade cells, as in the India-rubber plant and oleander.
Ivy when grown in bright light will develop two such layers of cells,
but in shaded places it may be found with only one. Such plants as
=iris= and compass plant, which have both surfaces of the leaf equally
exposed to sunlight, usually have a palisade layer beneath each
epidermis.
=Epidermis.=--The outer or epidermal cells of leaves do not bear
chlorophyll, but are usually so transparent that the green mesophyll
can be seen through them. They often become very thick-walled, and are
in most plants devoid of all protoplasm except a thin layer lining the
walls, the cavities being filled with cell sap. This sap is sometimes
colored, as in the under epidermis of begonia leaves. It is not common
to find more than one layer of epidermal cells forming each surface of
a leaf. The epidermis _serves to retain moisture_ in the leaf and as
a general _protective covering_. In desert plants the epidermis, as a
rule, is very thick and has a dense cuticle, thereby preventing loss of
water.
There are various _outgrowths of the epidermis_. =Hairs= are the chief
of these. They may be (1) =simple=, as on primula, geranium, nægelia;
(2) =once branched=, as on wallflower; (3) =compound=, as on verbascum
or mullein; (4) =disk-like=, as on shepherdia; (5) =stellate=, or
star-shaped, as in certain crucifers. In some cases the hairs are
=glandular=, as in Chinese primrose of the greenhouses (_Primula
Sinensis_) and certain hairs of pumpkin flowers. The hairs often
protect the breathing pores, or stomates, from dust and water.
=Stomates= (sometimes called =breathing-pores=) _are small openings
or pores_ in the epidermis of leaves and soft stems that allow the
passage of air and other gases and vapors (_stomate_ or _stoma_,
singular; _stomates_ or _stomata_, plural). They are _placed near the
large intercellular spaces_ of the mesophyll, usually in positions
least affected by direct sunlight. Fig. 114 shows the structure. There
are two =guard-cells= at the mouth of each stomate, which may in most
cases open or close the passage as the conditions of the atmosphere
may require. The guard-cells contain chlorophyll. In Fig. 115 is shown
a case in which there are compound guard-cells, that of ivy. On the
margins of certain leaves, as of fuchsia, impatiens, cabbage, are
openings known as =water-pores=.
[Illustration: FIG. 114.--DIAGRAM OF STOMATE OF IRIS (Osterhout).]
[Illustration: FIG. 115.--STOMATE OF IVY, showing compound guard-cells.]
_Stomates are very numerous_, as will be seen from the numbers showing
the pores to each square inch of leaf surface:
Lower surface Upper surface
Peony 13,790 None
Holly 63,600 None
Lilac 160,000 None
Mistletoe 200 200
Tradescantia 2,000 2,000
Garden Flag (iris) 11,572 11,572
The arrangement of stomates on the leaf _differs with each kind of
plant_. Fig. 116 shows stomates and also the outlines of contiguous
epidermal cells.
[Illustration: FIG. 116.--STOMATES OF GERANIUM LEAF.]
The function or work of the stomates is to _regulate the passage of
gases_ into and out of the plant. The directly active organs or parts
are guard-cells, on either side the opening. One method of opening is
as follows: The thicker walls of the guard-cells (Fig. 114) absorb
water from adjacent cells, these thick walls buckle or bend and part
from each other at their middles on either side of the opening, causing
the stomate to open, when the air gases may be taken in and the leaf
gases may pass out. When moisture is reduced in the leaf tissue,
the guard cells part with some of their contents, the thick walls
straighten, and the faces of the two opposite ones come together, thus
closing the stomate and preventing any water vapor from passing out.
_When a leaf is actively at work making new organic compounds, the
stomates are usually open; when unfavorable conditions arise, they are
usually closed._ They also commonly close at night, when growth (or
the utilizing of the new materials) is most likely to be active. It is
sometimes safer to fumigate greenhouses and window gardens at night,
for the noxious vapors are less likely to enter the leaf. Dust may clog
or cover the stomates. Rains benefit plants by washing the leaves as
well as by providing moisture to the roots.
[Illustration: FIG. 117.--LENTICELS ON YOUNG SHOOT OF RED OSIER
(CORNUS).]
=Lenticels.=--On the young woody twigs of many plants (marked in
osiers, cherry, birch) there are small corky spots or elevations known
as =lenticels= (Fig. 117). They mark the location of some loose cork
cells that function as stomates, for _green shoots_, as well as leaves,
take in and discharge gases; that is, soft green twigs _function as
leaves_. Under some of these twig stomates, corky material may form
and the opening is torn and enlarged: _the lenticels are successors to
the stomates_. The stomates lie in the epidermis, but as the twig ages
the epidermis perishes and the bark becomes the external layer. _Gases
continue to pass in and out through the lenticels_, until the branch
becomes heavily covered with thick, corky bark. With the growth of the
twig, the lenticel scars enlarge lengthwise or crosswise or assume
other shapes, often becoming characteristic markings.
=Fibro-vascular Bundles.=--We have studied the fibro-vascular
bundles of stems (Chap. X). These stem bundles _continue into the
leaves, ramifying into the veins_, carrying the soil water inwards
and bringing, by diffusion, the elaborated food out through the
sieve-cells. Cut across a petiole and notice the hard spots or areas in
it; strip these parts lengthwise of the petiole: what are they?
=Fall of the Leaf.=--In most common deciduous plants, when the season’s
work for the leaf is ended, the nutritious matter may be withdrawn, and
_a layer of corky cells is completed over the surface of the stem where
the leaf is attached. The leaf soon falls._ It often falls even before
it is killed by frost. Deciduous leaves begin to show the surface line
of articulation in the early growing season. This articulation may
be observed at any time during the summer. The area of the twig once
covered by the petioles is called the =leaf-scar= after the leaf has
fallen. In Chap. XV are shown a number of leaf-scars. In the plane
tree (sycamore or buttonwood), the leaf-scar is in the form of a ring
surrounding the bud, for the bud is covered by the hollowed end of
the petiole; the leaf of sumac is similar. Examine with a hand lens
leaf-scars of several woody plants. Note the number of bundle-scars in
each leaf-scar. Sections may be cut through a leaf-scar and examined
with the microscope. Note the character of cells that cover the
leaf-scar surface.
SUGGESTIONS.--_To study epidermal hairs_: =75.= For this study, use
the leaves of any hairy or woolly plant. A good hand lens will reveal
the identity of many of the coarser hairs. A dissecting microscope
will show them still better. For the study of the cell structure, a
compound microscope is necessary. Cross-sections may be made so as to
bring hairs on the edge of the sections; or in some cases the hairs
may be peeled or scraped from the epidermis and placed in water on
a slide. Make sketches of the different kinds of hairs. =76.= It is
good practice for the pupil to describe leaves in respect to their
covering: Are they smooth on both surfaces? Or hairy? Woolly? Thickly
or thinly hairy? Hairs long or short? Standing straight out or lying
close to the surface of the leaf? Simple or branched? Attached to
the veins or the plane surface? Color? Most abundant on young leaves
or old? =77.= Place a hairy or woolly leaf under water. Does the
hairy surface appear silvery? Why? _Other questions_: =78.= Why is
it good practice to wash the leaves of house plants? =79.= Describe
the leaf-scars on six kinds of plants: size, shape, color, position
with reference to the bud, bundle-scars. =80.= Do you find leaf-scars
on monocotyledonous plants--corn, cereal grains, lilies, canna,
banana, palm, bamboo, green brier? =81.= Note the table on page 88.
Can you suggest a reason why there are equal numbers of stomates
on both surfaces of leaves of tradescantia and flag, and none on
upper surface of other leaves? Suppose you pick a leaf of lilac (or
some larger leaf), seal the petiole with wax and then rub the under
surface with vaseline; on another leaf apply the vaseline to the
upper surface; which leaf withers first, and why? Make a similar
experiment with iris or blue flag. =82.= Why do leaves and shoots of
house plants turn towards the light? What happens when the plants
are turned around? =83.= Note position of leaves of beans, clover,
oxalis, alfalfa, locust, at night.
CHAPTER XIII
LEAVES--FUNCTION OR WORK
We have discussed (in Chap. VIII) the work or function of roots and
also (in Chap. X) the function of stems. We are now ready to complete
the view of the main vital activities of plants by considering the
function of the green parts (leaves and young shoots).
=Sources of Food.=--The ordinary green plant has but _two sources
from which to secure food,--the air and the soil_. When a plant is
thoroughly dried in an oven, the water passes off; _this water came
from the soil_. The remaining part is called the =dry substance or dry
matter=. If the dry matter is burned in an ordinary fire, only the
=ash= remains; _this ash came from the soil_. The part that passed off
as gas in the burning _contained the elements that came from the air_;
it also contained some of those that came from the soil--all those (as
nitrogen, hydrogen, chlorine) that are transformed into gases by the
heat of a common fire. The part that comes from the soil (the ash) is
small in amount, being considerably less than 10 per cent and sometimes
less than 1 per cent. _Water is the most abundant single constituent or
substance of plants._ In a corn plant of the roasting-ear stage, about
80 per cent of the substance is water. A fresh turnip is over 90 per
cent water. Fresh wood of the apple tree contains about 45 per cent of
water.
=Carbon.=--_Carbon enters abundantly into the composition of all
plants._ Note what happens when a plant is burned without free access
of air, or smothered, as in a charcoal pit. _A mass of charcoal
remains, almost as large as the body of the plant._ Charcoal is almost
pure _carbon_, the ash present being so small in proportion to the
large amount of carbon that we look on the ash as an impurity. Nearly
half of the dry substance of a tree is carbon. Carbon goes off as _a
gas_ when the plant is _burned in air_. It does not go off alone, but
in combination with oxygen in the form of _carbon dioxid gas_, CO₂.
=The green plant secures its carbon from the air.= In other words, much
of the _solid matter_ of the plant comes from _one of the gases of the
air_. By volume, _carbon dioxid forms only a very small fraction of
1 per cent of the air_. It would be very disastrous to animal life,
however, if this percentage were much increased, for it excludes the
life-giving oxygen. Carbon dioxid is often called “foul gas.” It may
accumulate in old wells, and an experienced person will not descend
into such wells until they have been tested with a torch. If the air
in the well will not support combustion,--that is, if the torch is
extinguished,--it usually means that carbon dioxid has drained into the
place. The air of a closed schoolroom often contains far too much of
this gas, along with little solid particles of waste matters. Carbon
dioxid is often known as carbonic acid gas.
=Appropriation of the Carbon.=--_The carbon dioxid of the air readily
diffuses itself into the leaves and other green parts of the plant._
The leaf is delicate in texture, and when very young the air can
diffuse directly into the tissues. The stomates, however, are the
special inlets adapted for the admission of gases into the leaves and
other green parts. Through these stomates, or diffusion-pores, the
outside air enters into the air-spaces of the plant, and is finally
absorbed by the little cells containing the living matter.
=Chlorophyll= (“leaf green”) is the agent that secures the energy by
means of which carbon dioxid is utilized. This material is contained
in the leaf cells in the form of grains (p. 86); the grains themselves
are protoplasm, only the coloring matter being chlorophyll. _The
chlorophyll bodies or grains are often most abundant near the upper
surface of the leaf, where they can secure the greatest amount of
light._ Without this green coloring matter, there would be no reason
for the large flat surfaces which the leaves possess, and no reason
for the fact that the leaves are borne most abundantly at the ends
of branches, where the light is most available. Plants with colored
leaves, as coleus, have chlorophyll, but it is masked by other coloring
matter. This other coloring matter is usually soluble in hot water:
boil a coleus leaf and notice that it becomes green and the water
becomes colored.
_Plants grown in darkness are yellow and slender, and do not reach
maturity._ Compare the potato sprouts that have grown from a tuber
lying in the dark cellar with those that have grown normally in
the bright light. The shoots have become slender and are devoid
of chlorophyll; and when the food that is stored in the tuber is
exhausted, these shoots will have lived useless lives. A plant that
has been grown in darkness from the seed will soon die, although for a
time the little seedling will grow very tall and slender: why? _Light
favors the production of chlorophyll_, and the chlorophyll is the agent
in the making of _the organic carbon compounds_. Sometimes chlorophyll
is found in buds and seeds, but in most cases these places are not
perfectly dark. Notice how potato tubers develop chlorophyll, or become
green, when exposed to light.
=Photosynthesis.=--_Carbon dioxid diffuses into the leaf; during
sunlight it is used, and oxygen is given off._ How the carbon dioxid
which is thus absorbed may be used in making an organic food is a
complex question, and need not be studied here; but it may be stated
that carbon dioxid and water are the constituents. Complex compounds
are built up out of simpler ones.
_Chlorophyll absorbs certain light rays, and the energy thus directly
or indirectly obtained is used by the living matter in uniting the
carbon dioxid absorbed from the air with some of the water brought up
from the roots. The ultimate result usually is starch._ The process
is obscure, but sugar is generally one step; and our first definite
knowledge of the product begins when starch is deposited in the leaves.
The process of using the carbon dioxid of the air has been known as
carbon assimilation, but the term now most used is =photosynthesis=
(from two Greek words, meaning _light and to put together_).
=Starch and Sugar.=--_All starch is composed of carbon, hydrogen, and
oxygen_ (C₆H₁₀O₅)_ₙ_. The sugars and the substance of cell walls are
very similar to it in composition. All these substances are called
=carbohydrates=. In making fruit sugar from the carbon and oxygen of
carbon dioxid and from the hydrogen and oxygen of the water, _there is
a surplus of oxygen_ (6 parts CO₂ + 6 parts H₂O = C₆H₁₂O₆ + 6 O₂). It
is this oxygen that is given off into the air during sunlight.
=Digestion.=--_Starch is in the form of insoluble granules. When such
food material is carried from one part of the plant to another for
purposes of growth or storage, it is made soluble before it can be
transported._ When this starchy material is transferred from place to
place, it is usually changed into sugar by the action of a diastase.
_This is a process of_ =digestion=. It is much like the change of
starchy foodstuffs to sugary foods by the saliva.
=Distribution of the Digested Food.=--After being changed to the
soluble form, _this material is ready to be used in growth_, either
in the leaf, in the stem, or in the roots. With other more complex
products it is then _distributed throughout all of the growing parts of
the plant;_ and when passing down to the root, it seems to pass more
readily through the _inner bark_, in plants which have a definite bark.
This gradual downward diffusion through the inner bark of materials
suitable for growth is the process referred to when the “descent of
sap” is mentioned. Starch and other products are often _stored in one
growing season to be used in the next season_. If a tree is constricted
or strangled by a wire around its trunk (Fig. 118), the digested food
cannot readily pass down and it is stored above the girdle, causing an
enlargement.
[Illustration: FIG. 118.--TRUNK GIRDLED BY A WIRE. See Fig. 85.]
=Assimilation.=--_The food from the air and that from the soil unite
in the living tissues._ The “sap” that passes upwards from the roots
in the growing season is made up largely of the soil water and the
salts which have been absorbed in the diluted solutions (p. 67). This
upward-moving water is conducted largely through certain tubular canals
of the _young wood_. These cells are never continuous tubes from root
to leaf; but the water passes readily from one cell or canal to another
in its upward course.
The upward-moving water gradually passes to the growing parts, and
everywhere in the living tissues, it is of course in the most intimate
contact with the soluble carbohydrates and products of photosynthesis.
In the building up or reconstructive and other processes it is
therefore available. We may properly conceive of certain of the simpler
organic molecules as passing through a series of changes, gradually
increasing in complexity. There will be formed substances containing
nitrogen in addition to carbon, hydrogen, and oxygen. Others will
contain also sulfur and phosphorus, and the various processes may be
thought of as culminating in =protoplasm=. _Protoplasm is the living
matter in plants._ It is in the cells, and is usually semifluid. Starch
is not living matter. The complex process of building up the protoplasm
is called =assimilation=.
=Respiration.=--_Plants need oxygen for respiration, as animals do._ We
have seen that plants need the carbon dioxid of the air. To most plants
the nitrogen of the air is inert, and serves only to dilute the other
elements; but the _oxygen is necessary for all life_. We know that all
animals need this oxygen in order to breathe or respire. In fact, they
have become accustomed to it in just the proportions found in the air;
and this is now best for them. When animals breathe the air once, they
make it foul, because they use some of the oxygen and give off carbon
dioxid. Likewise, _all living parts of the plant must have a constant
supply of oxygen_. Roots also need it, for they respire. Air goes in
and out of the soil by diffusion, and as the soil is heated and cooled,
causing the air to expand and contract.
The oxygen passes into the air-spaces and is absorbed by the moist
cell membranes. In the living cells it makes possible the formation
of simpler compounds by which energy is released. This energy enables
the plant to work and grow, and the final products of this action are
_carbon dioxid and water_. As a result of the use of this oxygen by
night and by day, plants give off carbon dioxid. _Plants respire; but
since they are stationary, and more or less inactive, they do not need
as much oxygen as animals, and they do not give off so much carbon
dioxid._ A few plants in a sleeping room need not disturb one more than
a family of mice. It should be noted, however, that germinating seeds
respire vigorously, hence they consume much oxygen; and opening buds
and flowers are likewise active.
=Transpiration.=--Much more water is absorbed by the roots than is
used in growth, _and this surplus water passes from the leaves into
the atmosphere by an evaporation process known as_ =transpiration=.
Transpiration takes place more abundantly from the under surfaces
of leaves, and through the pores or stomates. A sunflower plant of
the height of a man, during an active period of growth, gives off a
quart of water per day. A large oak tree may transpire 150 gallons
per day during the summer. For every ounce of dry matter produced, it
is estimated that 15 to 25 pounds of water usually passes through the
plant.
_When the roots fail to supply to the plant sufficient water
to equalize that transpired by the leaves_, =the plant wilts=.
Transpiration from the leaves and delicate shoots is increased by
all of the conditions which increase evaporation, such as higher
temperature, dry air, or wind. The stomata open and close, tending to
regulate transpiration as the varying conditions of the atmosphere
affect the moisture content of the plant. However, in periods of
drought or of very hot weather, and especially during a hot wind, the
closing of these stomates cannot sufficiently prevent evaporation. The
roots may be very active and yet fail to absorb sufficient moisture
to equalize that given off by the leaves. The plant shows the effect
(how?). On a hot dry day, note how the leaves of corn “roll” towards
afternoon. Note how fresh and vigorous the same leaves appear early
the following morning. Any injury to the roots, such as a bruise, or
exposure to heat, drought, or cold may cause the plant to wilt.
Water is forced up by =root pressure= or =sap pressure=. (Exercise 99.)
Some of the dew on the grass in the morning may be the water forced up
by the roots; some of it is the condensed vapor of the air.
_The wilting of a plant is due to the loss of water from the cells._
The cell walls are soft, and collapse. A toy balloon will not stand
alone until it is inflated with air or liquid. In the woody parts of
the plant the cell walls may be stiff enough to support themselves,
even though the cell is empty. Measure the contraction due to wilting
and drying by tracing a fresh leaf on page of notebook, and then
tracing the same leaf after it has been dried between papers. The
softer the leaf, the greater will be the contraction.
=Storage.=--We have said that starch may be stored in twigs to be used
the following year. The very early flowers on fruit trees, especially
those that come before the leaves, and those that come from bulbs, as
crocuses and tulips, are supported by the starch or other food that
was organized the year before. Some plants have very special storage
reservoirs, as the potato, in this case being a thickened stem although
growing underground. (Why a thickened stem? p. 84.) It is well to make
the starch test on winter twigs and on all kinds of thickened parts, as
tubers and bulbs.
=Carnivorous Plants.=--Certain plants capture insects and other very
small animals and utilize them to some extent as food. Such are the
sundew, that has on the leaves sticky hairs that close over the insect;
the Venus’s flytrap of the Southern states, in which the halves of
the leaves close over the prey like the jaws of a steel trap; and the
various kinds of pitcher plants that collect insects and other organic
matter in deep, water-filled, flask-like leaf pouches (Fig. 119).
The sundew and Venus’s flytrap are sensitive to contact. Other plants
are _sensitive to the touch_ without being insectivorous. The common
cultivated sensitive plant is an example. This is readily grown from
seeds (sold by seedsmen) in a warm place. Related wild plants in
the south are sensitive. The utility of this sensitiveness is not
understood.
[Illustration: FIG. 119.--THE COMMON PITCHER PLANT (_Sarracenia
purpurea_) of the North, showing the tubular leaves and the odd,
long-stalked flowers.]
=Parts that Simulate Leaves=.--We have learned that leaves are
endlessly modified to suit the conditions in which the plant is placed.
The most marked modifications are in adaptation to light. On the other
hand, _other organs often perform the functions of leaves_. Green
shoots function as leaves. These shoots may look like leaves, in which
case they are called =cladophylla=. The foliage of common asparagus is
made up of fine branches: the real morphological leaves are the minute
dry functionless scales at the bases of these branchlets. (What reason
is there for calling them leaves?) The broad “leaves” of the florist’s
smilax are cladophylla: where are the leaves on this plant? In most of
the cacti, the entire plant body performs the functions of leaves until
the parts become cork-bound.
=Leaves are sometimes modified to perform other functions than the
vital processes=: they may be tendrils, as the terminal leaflets of pea
and sweet pea; or spines, as in barberry. Not all spines and thorns,
however, represent modified leaves: some of them (as of hawthorns,
osage orange, honey locust) are branches.
[Illustration: FIG. 120.--EXCLUDING LIGHT AND CO₂ FROM PART OF A LEAF]
[Illustration: FIG. 121.--THE RESULT.]
[Illustration: FIG. 122.--TO SHOW THE ESCAPE OF OXYGEN.]
[Illustration: FIG. 123.--TO ILLUSTRATE A PRODUCT OF RESPIRATION.]
[Illustration: FIG. 124.--RESPIRATION OF THICK ROOTS.]
[Illustration: FIG. 125.--TO ILLUSTRATE TRANSPIRATION.]
SUGGESTIONS.--_To test for chlorophyll._ =84.= Purchase about a
gill of wood alcohol. Secure a leaf of geranium, clover, or other
plant that has been exposed to sunlight for a few hours, and, after
dipping it for a minute in boiling water, put it in a white cup with
sufficient alcohol to cover. Place the cup in a shallow pan of hot
water on the stove where it is not hot enough for the alcohol to take
fire. After a time the chlorophyll is dissolved by the alcohol, which
has become an intense green. Save this leaf for the starch experiment
(Exercise 85). Without chlorophyll, the plant cannot appropriate the
carbon dioxid of the air. _Starch and photosynthesis._ =85.= Starch
is present in the green leaves which have been exposed to sunlight;
but in the dark no starch can be formed from carbon dioxid. Apply
iodine to the leaf from which the chlorophyll was dissolved in the
previous experiment. Note that the leaf is colored purplish brown
throughout. The leaf contains starch. =86.= Secure a leaf from a
plant which has been in the darkness for about two days. Dissolve the
chlorophyll as before, and attempt to stain this leaf with iodine.
No purplish brown color is produced. This shows that the starch
manufactured in the leaf may be entirely removed during darkness.
=87.= Secure a plant which has been kept in darkness for twenty-four
hours or more. Split a small cork and pin the two halves on opposite
sides of one of the leaves, as shown in Fig. 120. Place the plant
in the sunlight again. After a morning of bright sunshine dissolve
the chlorophyll in this leaf with alcohol; then stain the leaf with
the iodine. Notice that the leaf is stained deeply except where
the cork was; there sunlight and carbon dioxid were excluded, Fig.
121. There is no starch in the covered area. =88.= Plants or parts
of plants that have developed no chlorophyll can form no starch.
Secure a variegated leaf of coleus, ribbon grass, geranium, or of
any plant showing both white and green areas. On a day of bright
sunshine, test one of these leaves by the alcohol and iodine method
for the presence of starch. Observe that the parts devoid of green
color have formed no starch. However, after starch has once been
formed in the leaves, it may be changed into soluble substances and
removed, to be again converted into starch in certain other parts
of the living tissues. _To test the giving off of oxygen by day._
=89.= Make the experiment illustrated in Fig. 122. Under a funnel
in a deep glass jar containing fresh spring or stream water place
fresh pieces of the common waterweed elodea (or anacharis). Have the
funnel considerably smaller than the vessel, and support the funnel
well up from the bottom so that the plant can more readily get all
of the carbon dioxid available in the water. Why would boiled water
be undesirable in this experiment? For a home-made glass funnel,
crack the bottom off a narrow-necked bottle by pressing a red-hot
poker or iron rod against it and leading the crack around the bottle.
Invert a test-tube over the stem of the funnel. In sunlight bubbles
of oxygen will arise and collect in the test-tube. If a sufficient
quantity of oxygen has collected, a lighted taper inserted in the
tube will glow with a brighter flame, showing the presence of oxygen
in greater quantity than in the air. Shade the vessel. Are bubbles
given off? For many reasons it is impracticable to continue this
experiment longer than a few hours. =90=. A simpler experiment may
be made if one of the waterweeds Cabomba (water-lily family) is
available. Tie a lot of branches together so that the basal ends
shall make a small bundle. Place these in a large vessel of spring
water, and insert a test-tube of water as before over the bundle. The
bubbles will arise from the cut surfaces. Observe the bubbles on pond
scum and waterweeds on a bright day. _To illustrate the results of
respiration_ (CO₂). =91.= In a jar of germinating seeds (Fig. 123)
place carefully a small dish of limewater and cover tightly. Put a
similar dish in another jar of about the same air space. After a
few hours compare the cloudiness or precipitate in the two vessels
of limewater. =92.= Or, place a growing plant in a deep covered jar
away from the light, and after a few hours insert a lighted candle
or splinter. =93.= Or, perform a similar experiment with fresh roots
of beets or turnips (Fig. 124) from which the leaves are mostly
removed. In this case, the jar need not be kept dark; why? _To test
transpiration._ =94.= Cut a succulent shoot of any plant, thrust the
end of it through a hole in a cork, and stand it in a small bottle
of water. Invert over this a fruit jar, and observe that a mist soon
accumulates on the inside of the glass. In time drops of water form.
=95.= The experiment may be varied as shown in Fig. 125. =96.= Or,
invert the fruit jar over an entire plant, as shown in Fig. 126,
taking care to cover the soil with oiled paper or rubber cloth to
prevent evaporation from the soil. =97.= The test may also be made
by placing the pot, properly protected, on balances, and the loss
of weight will be noticed (Fig. 127). =98.= Cut a winter twig, seal
the severed end with wax, and allow the twig to lie several days;
it shrivels. There must be some upward movement of water even in
winter, else plants would shrivel and die. =99.= _To illustrate
sap pressure._ The upward movement of sap water often takes place
under considerable force. The cause of this force, known as _root
pressure_, is not well understood. The pressure varies with different
plants and under different conditions. To illustrate: cut off a
strong-growing small plant near the ground. By means of a bit of
rubber tube attach a glass tube with a bore of approximately the
diameter of the stem. Pour in a little water. Observe the rise of
the water due to the pressure from below (Fig. 128). Some plants
yield a large amount of water under a pressure sufficient to raise a
column several feet; others force out little, but under considerable
pressure (less easily demonstrated). _The vital processes_ (_i.e._,
the life processes). =100.= The pupil having studied roots, stems,
and leaves, should now be able to describe the main vital functions
of plants: what is the root function? stem function? leaf function?
=101.= What is meant by the “sap”? =102.= Where and how does the
plant secure its water? oxygen? carbon? hydrogen? nitrogen? sulfur?
potassium? calcium? iron? phosphorus? =103.= Where is all the starch
in the world made? What does a starch-factory establishment do?
Where are the real starch factories? =104.= In what part of the
twenty-four hours do plants grow most rapidly in length? When is food
formed and stored most rapidly? =105.= Why does corn or cotton turn
yellow in a long rainy spell? =106.= If stubble, corn stalks, or
cotton stalks are burned in the field, is as much plant-food returned
to the soil as when they are plowed under? =107.= What process of
plants is roughly analogous to perspiration of animals? =108.= What
part of the organic world uses raw mineral for food? =109.= Why is
earth banked over celery to blanch it? =110.= Is the amount of water
transpired equal to the amount absorbed? =111.= Give some reasons why
plants very close to a house may not thrive or may even die. =112.=
Why are fruit-trees pruned or thinned out as in Fig. 129? _Proper
balance between top and root._ =113.= We have learned that the leaf
parts and the root parts work together. They may be said to balance
each other in activities, the root supplying the top and the top
supplying the root (how?). If half the roots were cut from a tree,
we should expect to reduce the top also, particularly if the tree is
being transplanted. How would you prune a tree or bush that is being
transplanted? Fig. 130 may be suggestive.
[Illustration: FIG. 126.--TO ILLUSTRATE TRANSPIRATION.]
[Illustration: FIG. 127.--LOSS OF WATER.]
[Illustration: FIG. 128.--TO SHOW SAP PRESSURE.]
[Illustration: FIG. 129.--BEFORE AND AFTER PRUNING.]
[Illustration: FIG. 130.--AN APPLE TREE, with suggestions as to pruning
when it is set in the orchard. At _a_ is shown a pruned top.]
CHAPTER XIV
DEPENDENT PLANTS
Thus far we have spoken of plants with roots and foliage and that
depend on themselves. They collect the raw materials and make them over
into assimilable food. They are =independent=. Plants without green
foliage cannot make food; they must have it made for them or they die.
They are =dependent=. A sprout from a potato tuber in a dark cellar
cannot collect and elaborate carbon dioxid. It lives on the food stored
in the tuber.
[Illustration: FIG. 131.--A MUSHROOM, example of a saprophytic plant.
This is the edible cultivated mushroom.]
_All plants with naturally white or blanched parts are dependent._
Their leaves do not develop. They live on organic matter--that which
has been made by a plant or elaborated by an animal. The dodder,
Indian pipe, beech drop, coral root among flower-bearing plants, also
mushrooms and other fungi (Figs. 131, 132) are examples. The dodder
is common in swales, being conspicuous late in the season from its
thread-like yellow or orange stems spreading over the herbage of other
plants. One kind attacks alfalfa and is a bad pest. The seeds germinate
in the spring, but as soon as the twining stem attaches itself to
another plant, the dodder dies away at the base and becomes wholly
dependent. It produces flowers in clusters and seeds itself freely
(Fig. 133).
[Illustration: FIG. 132.--A PARASITIC FUNGUS, magnified. The mycelium,
or vegetative part, is shown by the dotted-shaded parts ramifying in
the leaf tissue. The rounded haustoria projecting into the cells are
also shown. The long fruiting parts of the fungus hang from the under
surface of the leaf.]
=Parasites and Saprophytes.=--A plant that is dependent on a living
plant or animal is a =parasite=, and the plant or animal on which it
lives is the =host=. The dodder is a true parasite; so are the rusts,
mildews, and other fungi that attack leaves and shoots and injure them.
The threads of a parasitic fungus usually creep through the
intercellular spaces in the leaf or stem and send suckers (or
haustoria) into the cells (Fig. 132). The threads (or the hyphæ) clog
the air-spaces of the leaf and often plug the stomates, and they also
appropriate and disorganize the cell fluids; _thus they injure or
kill their host_. The mass of hyphæ of a fungus is called =mycelium=.
Some of the hyphæ finally grow out of the leaf and produce spores or
reproductive cells that answer the purpose of seeds in distributing the
plant (_b_, Fig. 132).
[Illustration: FIG. 133.--DODDER IN FRUIT.]
A plant that lives on dead or decaying matter is a =saprophyte=.
Mushrooms (Fig. 131) are examples; they live on the decaying matter
in the soil. Mold on bread and cheese is an example. Lay a piece of
moist bread on a plate and invert a tumbler over it. In a few days it
will be moldy. The spores were in the air, or perhaps they had already
fallen on the bread but had not had opportunity to grow. Most green
plants are unable to make any direct use of the humus or vegetable mold
in the soil, for they are not saprophytic. The shelf-fungi (Fig. 134)
are saprophytes. They are common on logs and trees. Some of them are
perhaps partially parasitic, extending the mycelium into the wood of
the living tree and causing it to become black-hearted (Fig. 134).
[Illustration: FIG. 134.--TINDER FUNGUS (_Polyporus igniarius_)
on beech log. The external part of the fungus is shown below; the
heart-rot injury above.]
Some parasites spring from the ground, as other plants do, but they
are _parasitic on the roots of their hosts_. Some parasites may be
_partially parasitic_ and _partially saprophytic_. Many (perhaps
most) of these ground saprophytes are aided in securing their food by
soil fungi, which spread their delicate threads over the root-like
branches of the plant and act as intermediaries between the food and
the saprophyte. These fungus-covered roots are known as =mycorrhizas=
(meaning “fungus root”). Mycorrhizas are not peculiar to saprophytes.
They are found on many wholly independent plants, as, for example,
the heaths, oaks, apples, and pines. It is probable that the fungous
threads perform some of the offices of root-hairs to the host. On the
other hand, the fungus obtains some nourishment from the host. The
association seems to be mutual.
[Illustration: FIG. 135.--BACTERIA OF SEVERAL FORMS, much magnified.]
Saprophytes break down or decompose organic substances. Chief of these
saprophytes are many microscopic organisms known as bacteria (Fig.
135). These innumerable organisms are immersed in water or in dead
animals and plants, and in all manner of moist organic products. By
breaking down organic combinations, _they produce decay_. Largely
through their agency, and that of many true but microscopic fungi,
_all things pass into soil and gas_. Thus are the bodies of plants and
animals removed and the continuing round of life is maintained.
[Illustration: FIG. 136.--AMERICAN MISTLETOE GROWING ON A WALNUT
BRANCH.]
_Some parasites are green-leaved._ Such is the mistletoe (Fig. 136).
They anchor themselves on the host and absorb its juices, but they also
appropriate and use the carbon dioxid of the air. In some small groups
of bacteria a process of organic synthesis has been shown to take place.
=Epiphytes.=--To be distinguished from the dependent plants are those
that grow on other plants without taking food from them. These are
green-leaved plants whose roots burrow in the bark of the host plant
and perhaps derive some food from it, but which subsist chiefly on
materials that they secure from air dust, rain water, and the air.
These plants are =epiphytes= (meaning “upon plants”) or air plants.
Epiphytes abound in the tropics. Certain orchids are among the best
known examples (Fig. 37). The Spanish moss or tillandsia of the South
is another. Mosses and lichens that grow on trees and fences may also
be called epiphytes. In the struggle for existence, the plants probably
_have been driven to these special places_ in which to find opportunity
to grow. Plants grow where they must, not where they will.
SUGGESTIONS.--=114.= Is a puffball a plant? Why do you think so?
=115.= Are mushrooms ever cultivated, and where and how? =116.= In
what locations are mushrooms and toadstools usually found? (There
is really no distinction between mushrooms and toadstools. They are
all mushrooms.) =117.= What kinds of mildew, blight, and rust do
you know? =118.= How do farmers overcome potato blight? Apple scab?
Or any other fungous “plant disease”? =119.= How do these things
injure plants? =120.= What is a plant disease? =121.= The pupil
should know that every spot or injury on a leaf or stem is caused by
something,--as an insect, a fungus, wind, hail, drought, or other
agency. How many uninjured or perfect leaves are there on the plant
growing nearest the schoolhouse steps? =122.= Give formula for
Bordeaux mixture and tell how and for what it is used.
CHAPTER XV
WINTER AND DORMANT BUDS
=A bud is a growing point=, terminating an axis either long or short,
or being the starting point of an axis. _All branches spring from
buds._ In the growing season the bud is active; later in the season it
ceases to increase the axis in length, and as winter approaches the
growing point becomes more or less thickened and covered by protecting
scales, in preparation for the long resting season. This resting,
dormant, or winter body is what is commonly spoken of as a “bud.” A
winter bud may be defined as an _inactive covered growing point_,
waiting for spring.
_Structurally, a dormant bud is a_ =shortened axis= _or_ =branch=,
_bearing miniature leaves or flowers or both, and protected by a
covering._ Cut in two, lengthwise, a bud of the horse-chestnut or other
plant that has large buds. With a pin separate the tiny leaves. Count
them. Examine the big bud of the rhubarb as it lies under the ground in
late winter or early spring; or the crown buds of asparagus, hepatica,
or other early spring plants. Dissect large buds of the apple and pear
(Figs. 137, 138).
[Illustration: FIG. 137.--BUD OF APRICOT, showing the miniature leaves.]
[Illustration: FIG. 138.--BUD OF PEAR, showing both leaves and flowers.
The latter are the little knobs in the center.]
_The bud is protected by firm and dry scales._ These scales are
modified leaves. The scales fit close. Often the bud is protected by
varnish (see horse-chestnut and the balsam poplars). Most winter buds
are more or less woolly. Examine them under a lens. As we might expect,
bud coverings are most prominent in cold and dry climates. Sprinkle
water on velvet or flannel, and note the result and give a reason.
=All winter buds give rise to branches=, _not to leaves alone_; that
is, the leaves are borne on the lengthening axis. Sometimes the axis,
or branch, remains very short,--so short that it may not be noticed.
Sometimes it grows several feet long.
_Whether the branch grows large or not depends on the chance it
has_,--position on the plant, soil, rainfall, and many other factors.
The new shoot is the unfolding and enlarging of the tiny axis and
leaves that we saw in the bud. If the conditions are congenial, the
shoot may form more leaves than were tucked away in the bud. The length
of the shoot usually depends more on the lengths of the internodes than
on the number of leaves.
[Illustration: FIG. 139.--LEAF-SCARS.--Ailanthus.]
=Where Buds are.=--_Buds are borne in the_ =axils= _of the leaves_,--in
the acute angle that the leaf makes with the stem. When the leaf is
growing in the summer, a bud is forming above it. When the leaf falls,
the bud remains, and a scar marks the place of the leaf. Fig. 139 shows
the large leaf-scars of ailanthus. Observe those on the horse-chestnut,
maple, apple, pear, basswood, or any other tree or bush.
Sometimes two or more buds are borne in one axil; the extra ones are
=accessory= or =supernumerary= buds. Observe them in the Tartarian
honeysuckle (common in yards), walnut, butternut, red maple, honey
locust, and sometimes in the apricot and peach.
If the bud is at the end of a shoot, however short the shoot, it is
called a =terminal bud=. _It continues the growth of the axis in a
direct line._ Very often three or more buds are clustered at the tip
(Fig. 140); and in this case there may be more buds than leaf scars.
Only one of them, however, is strictly terminal.
[Illustration: FIG. 140.--TERMINAL BUD BETWEEN TWO OTHER
BUDS.--Currant.]
A bud in the axil of a leaf is an =axillary= or =lateral= bud. Note
that there is normally at least one bud in the axil of every leaf on a
tree or shrub in late summer and fall. The axillary buds, if they grow,
are the _starting points of new shoots the following season_. If a leaf
is pulled off early in summer, what will become of the young bud in its
axil? Try this.
[Illustration: FIG. 141.--A GIGANTIC BUD.--Cabbage.]
_Bulbs and cabbage heads may be likened to buds_; that is, they are
condensed stems, with scales or modified leaves densely overlapping and
forming a rounded body (Fig. 141). They differ from true buds, however,
in the fact that they are condensations of whole main stems rather than
embryo stems borne in the axils of leaves. But bulblets (as of tiger
lily) may be scarcely distinguishable from buds on the one hand and
from bulbs on the other. Cut a cabbage head in two, lengthwise, and see
what it is like.
The buds that appear on roots are unusual or abnormal,--they occur only
occasionally and in no definite order. Buds appearing in unusual places
on any part of the plant are called =adventitious buds=. Such usually
are the buds that arise when a large limb is cut off, and from which
suckers or water sprouts arise.
[Illustration: FIG. 142.--FRUIT-BUD OF PEAR.]
[Illustration: FIG. 143.--THE OPENING OF THE PEAR FRUIT-BUD.]
[Illustration: FIG. 144.--OPENING PEAR LEAF-BUD.]
[Illustration: FIG. 145.--OPENING OF THE PEAR-BUD.]
=How Buds Open.=--_When the bud swells, the scales are pushed apart,
the little axis elongates and pushes out._ In most plants the outside
scales fall very soon, _leaving a little ring of scars_. With terminal
buds, this ring marks the end of the year’s growth: how? Notice peach,
apple, plum, willow, and other plants. In some others, all the scales
grow for a time, as in the pear (Figs. 142, 143, 144). In other plants
the inner bud scales become green and almost leaf-like. See the maple
and hickory.
=Sometimes Flowers come out of the Buds.=--Leaves may or may not
accompany the flowers. We saw the embryo flowers in Fig. 138. The bud
is shown again in Fig. 142. In Fig. 143 it is opening. In Fig. 145 it
is more advanced, and the woolly unformed flowers are appearing. In
Fig. 146 the growth is more advanced.
[Illustration: FIG. 146.--A SINGLE FLOWER IN THE PEAR CLUSTER, as seen
at 7 A.M. on the day of its opening. At 10 o’clock it will be fully
expanded.]
[Illustration: FIG. 147.--THE OPENING OF THE FLOWER-BUD OF APRICOT.]
[Illustration: FIG. 148.--APRICOT FLOWER-BUD, enlarged.]
Buds that contain or produce only leaves are =leaf-buds=. Those which
contain only flowers are =flower-buds= or =fruit-buds=. The latter
occur on peach, almond, apricot, and many very early spring-flowering
plants. The single flower is emerging from the apricot bud in Fig. 147.
A longitudinal section of this bud, enlarged, is shown in Fig. 148.
Those that contain both leaves and flowers are =mixed buds=, as in
pear, apple, and most late spring-flowering plants.
[Illustration: FIG. 149.--FRUIT-BUDS AND LEAF-BUDS OF PEAR.]
_Fruit buds are usually thicker or stouter than leaf-buds. They are
borne in different positions on different plants._ In some plants
(apple, pear) they are on the ends of short branches or spurs; in
others (peach, red maple) they are along the sides of the last year’s
growths. In Fig. 149 are shown three fruit-buds and one leaf-bud on
_E_, and leaf-buds on _A_. See also Figs. 150, 151, 152, 153, and
explain.
[Illustration: FIG. 150.--FRUIT-BUDS OF APPLE ON SPURS: a dormant bud
at the top.]
[Illustration: FIG. 151.--CLUSTER OF FRUIT-BUDS OF SWEET CHERRY, with
one pointed leaf-bud in center.]
[Illustration: FIG. 152.--TWO FRUIT-BUDS OF PEACH with a leaf-bud
between.]
[Illustration: FIG. 153.--OPENING OF LEAF-BUDS AND FLOWER-BUDS OF
APPLE.]
“_The burst of spring_” means in large part the opening of the buds.
_Everything was made ready the fall before. The embryo shoots and
flowers were tucked away, and the food was stored._ The warm rain
falls, and the shutters open and the sleepers wake: the frogs peep and
the birds come.
=Arrangement of Buds.=--We have found that leaves are usually arranged
in a definite order; buds are borne in the axils of leaves: therefore
_buds must exhibit phyllotaxy_. Moreover, branches grow from buds:
branches, therefore, should show a definite arrangement; usually,
however, they do not show this arrangement because _not all the buds
grow and not all the branches live_. (See Chaps. II and III.) It is
apparent, however, that the mode of arrangement of buds determines to
some extent the form of the tree: compare bud arrangement in pine or
fir with that in maple or apple.
[Illustration: FIG. 154.--OAK SPRAY. How are the leaves borne with
reference to the annual growths?]
The uppermost buds on any twig, if they are well matured, are usually
the larger and stronger and they are the most likely to grow the next
spring; therefore, branches tend to be arranged in tiers (particularly
well marked in spruces and firs). See Fig. 154 and explain it.
=Winter Buds show what has been the Effect of Sunlight.=--Buds are
borne in the axils of the leaves, and the size or vigor of the leaf
determines to a large extent _the size of the bud._ Notice that, in
most instances, _the largest buds are nearest the tip_ (Fig. 157). If
the largest ones are not near the tip, there is some special reason for
it. Can you state it? Examine the shoots on trees and bushes.
[Illustration: FIG. 155.--AN APPLE TWIG.]
[Illustration: FIG. 156.--Same twig before leaves fell.]
SUGGESTIONS.--Some of the best of all observation lessons are those
made on dormant twigs. There are many things to be learned, the eyes
are trained, and the specimens are everywhere accessible. =123.=
At whatever time of year the pupil takes up the study of branches,
he should look for three things: the ages of the various parts,
the relative positions of the buds and leaves, the different sizes
of similar or comparable buds. If it is late in spring or early in
summer, he should watch the development of the buds in the axils,
and he should determine whether the strength or size of the bud
is in any way related to the size and vigor of the subtending (or
supporting) leaf. The sizes of buds should also be noted on leafless
twigs, and the sizes of the former leaves may be inferred from the
size of the leaf-scar below the bud. The pupil should keep in mind
the fact of the struggle for food and light, and its effects on the
developing buds. =124.= _The bud and the branch._ A twig cut from
an apple tree in early spring is shown in Fig. 155. The most hasty
observation shows that it has various parts, or members. It seems to
be divided at the point _f_ into two parts. It is evident that the
part from _f_ to _h_ grew last year, and that the part below _f_ grew
two years ago. The buds on the two parts are very unlike, and these
differences challenge investigation.--In order to understand this
seemingly lifeless twig, it will be necessary to see it as it looked
late last summer (and this condition is shown in Fig. 156). The part
from _f_ to _h_,--which has just completed its growth,--is seen to
have its leaves growing singly. In every axil (or angle which the
leaf makes when it joins the shoot) is a bud. The leaf starts first,
and as the season advances the bud forms in its axil. When the leaves
have fallen, at the approach of winter, the buds remain, as seen
in Fig. 155. Every bud on the last year’s growth of a winter twig,
therefore, marks the position occupied by a leaf when the shoot was
growing.--The part below _f_, in Fig. 156, shows a wholly different
arrangement. The leaves are two or more together (_aaaa_), and there
are buds without leaves (_bbbb_). A year ago this part looked like
the present shoot from _f_ to _h_,--that is, the leaves were single,
with a bud in the axil of each. It is now seen that some of these
bud-like parts are longer than others, and that the longest ones are
those which have leaves. It must be because of the leaves that they
have increased in length. The body _c_ has lost its leaves through
some accident, and its growth has ceased. In other words, the parts
at _aaaa_ are like the shoot _fh_, except that they are shorter, and
they are of the same age. One grew from the end or terminal bud of
the main branch, and the others from the side or lateral buds. Parts
or bodies that bear leaves are, therefore, branches.--The buds at
_bbbb_ have no leaves, and they remain the same size that they were
a year ago. They are dormant. The only way for a mature bud to grow
is by making leaves for itself, for a leaf will never stand below it
again. The twig, therefore, has buds of two ages,--those at _bbbb_
are two seasons old, and those on the tips, of all the branches
(_aaaa_, _h_), and in the axil of every leaf, are one season old. It
is only the terminal buds that are not axillary. When the bud begins
to grow and to put forth leaves, it gives rise to a branch, which, in
its turn, bears buds.--It will now be interesting to determine why
certain buds gave rise to branches and why others remained dormant.
The strongest shoot or branch of the year is the terminal one (_fh_).
The next in strength is the uppermost lateral one, and the weakest
shoot is at the base of the twig. The dormant buds are on the under
side (for the twig grew in a horizontal position). All this suggests
that those buds grew which had the best chance,--the most sunlight
and room. There were too many buds for the space, and in the struggle
for existence those that had the best opportunities made the largest
growths. This struggle for existence began a year ago, however,
when the buds on the shoot below _f_ were forming in the axils of
the leaves, for the buds near the tip of the shoot grew larger and
stronger than those near its base. The growth of one year, therefore,
is very largely determined by the conditions under which the buds
were formed the previous year. _Other bud characters._ =125.= It is
easy to see the swelling of the buds in a room in winter. Secure
branches of trees and shrubs, two to three feet long, and stand them
in vases or jars, as you would flowers. Renew the water frequently
and cut off the lower ends of the shoots occasionally. In a week or
two the buds will begin to swell. Of red maple, peach, apricot, and
other very early-flowering things, flowers may be obtained in ten to
twenty days. =126.= The shape, size, and color of the winter buds
are different in every kind of plant. By the buds alone botanists
are often able to distinguish the kinds of plants. Even such similar
plants as the different kinds of willows have good bud characters.
=127.= Distinguish and draw fruit-buds of apple, pear, peach, plum,
and other trees. If different kinds of maples grow in the vicinity,
secure twigs of the red or swamp maple, and the soft or silver maple,
and compare the buds with those of the sugar maple and Norway maple:
What do you learn?
[Illustration: FIG. 157.--BUDS OF THE HICKORY.]
CHAPTER XVI
BUD PROPAGATION
We have learned (in Chap. VI) that plants propagate by means of seeds.
_They also propagate by means of bud parts,--as rootstocks (rhizomes),
roots, runners, layers, bulbs._ The pupil should determine how any
plant in which he is interested naturally propagates itself (or spreads
its kind). Determine this for raspberry, blackberry, strawberry,
June-grass or other grass, nut-grass, water lily, May apple or
mandrake, burdock, Irish potato, sweet potato, buckwheat, cotton, pea,
corn, sugar-cane, wheat, rice.
Plants may be _artificially propagated_ by similar means, as by
_layers_, _cuttings_, and _grafts_. The last two we may discuss here.
=Cuttings in General.=--_A bit of a plant stuck into the ground
stands a chance of growing; and this bit is a_ =cutting=. Plants have
preferences, however, as to the kind of a bit which shall be used, but
_there is no way of telling what this preference is except by trying_.
In some instances this preference has not been discovered, and we say
that the plant cannot be propagated by cuttings.
Most plants prefer that the cutting be made of the =soft= or =growing
parts= (called “wood” by gardeners), of which the “slips” of geranium
and coleus are examples. Others grow equally well from cuttings of the
=hard= or =mature parts= or =wood=, as currant and grape; and in some
instances this mature wood may be of roots, as in the blackberry. In
some cases cuttings are made of tubers, as in the Irish potato (Fig.
60). Pupils should make cuttings now and then. If they can do nothing
more, they can make cuttings of potato, as the farmer does; and they
can plant them in a box in the window.
[Illustration: FIG. 158.--GERANIUM CUTTING.]
[Illustration: FIG. 159.--ROSE CUTTING.]
=The Softwood Cutting.=--The softwood cutting is made from tissue that
is still growing, or at least from that which is not dormant. _It
comprises one or two joints, with a leaf attached_ (Figs. 158, 159).
It must not be allowed to wilt. Therefore, it must be _protected from
direct sunlight and dry air until it is well established; and if it has
many leaves, some of them should be removed, or at least cut in two, in
order to reduce the evaporating surface_. The soil should be uniformly
moist. The pictures show the depth to which the cuttings are planted.
For most plants, the proper age or maturity of wood for the making of
cuttings may be determined by giving the _twig a quick bend: if it
snaps and hangs by the bark, it is in proper condition; if it bends
without breaking, it is too young and soft or too old; if it splinters,
it is too old and woody_. The tips of strong upright shoots usually
make the best cuttings. Preferably, each cutting should have a joint
or node near its base; and if the internodes are very short it may
comprise two or three joints.
_The stem of the cutting is inserted one third or more its length in
clean sand or gravel, and the earth is pressed firmly about it._ A
newspaper may be laid over the bed to exclude the light--if the sun
strikes it--and to prevent too rapid evaporation. The soil should be
moist clear through, not on top only.
[Illustration: FIG. 160.--CUTTING-BOX.]
_Loose sandy or gravelly soil is used._ Sand used by masons is good
material in which to start most cuttings; or fine gravel--sifted
of most of its earthy matter--may be used. Soils are avoided which
contain much decaying organic matter, for these soils are breeding
places of fungi, which attack the soft cutting and cause it to “damp
off,” or to die at or near the surface of the ground. If the cuttings
are to be grown in a window, put three or four inches of the earth
in a shallow box or a pan. A soap box cut in two lengthwise, so that
it makes a box four or five inches deep--as a gardener’s flat--is
excellent (Fig. 160). Cuttings of common plants, as geranium, coleus,
fuchsia, carnation, are kept at a living-room temperature. As long as
the cuttings look bright and green, they are in good condition. It
may be a month before roots form. When roots have formed, the plants
begin to make new leaves at the tip. Then they may be transplanted into
other boxes or into pots. The verbena in Fig. 161 is just ready for
transplanting.
[Illustration: FIG. 161.--VERBENA CUTTING READY FOR TRANSPLANTING.]
It is not always easy to find growing shoots from which to make the
cuttings. The best practice, in that case, is _to cut back an old
plant, then keep it warm and well watered, and thereby force it to
throw out new shoots_. The old geranium plant from the window garden,
or the one taken up from the lawn bed, may be treated this way (see
Fig. 162). The best plants of geranium and coleus and most window
plants are those which are not more than one year old. _The geranium
and fuchsia cuttings which are made in January, February, or March will
give compact blooming plants for the next winter; and thereafter new
ones should take their places_ (Fig. 163).
[Illustration: FIG. 162.--OLD GERANIUM PLANT CUT BACK TO MAKE IT THROW
OUT SHOOTS FROM WHICH CUTTINGS CAN BE MADE.]
[Illustration: FIG. 163.--EARLY WINTER GERANIUM, from a spring cutting.]
=The Hardwood Cutting=.--_Best results with cuttings of mature wood are
secured when the cuttings are made in the fall and then buried until
spring in sand in the cellar._ These cuttings are usually six to ten
inches long. They are not idle while they rest. The lower end calluses
or heals, and the roots form more readily when the cutting is planted
in the spring. But if the proper season has passed, take cuttings at
any time in winter, plant them in a deep box in the window, and watch.
They will need no shading or special care. Grape, currant, gooseberry,
willow, and poplar readily take root from the hardwood. Fig. 164 shows
a currant cutting. It has only one bud above the ground.
[Illustration: FIG. 164.--CURRANT CUTTING.]
=The Graft.=--_When the cutting is inserted in a plant rather than in
the soil, it is a graft_; and the graft may grow. In this case the
cutting grows fast to the other plant, and the two become one. When the
cutting is inserted in a plant, it is no longer called a cutting, but
a =cion=; and the plant in which it is inserted is called the =stock=.
Fruit trees are grafted _in order that a certain variety or kind may
be perpetuated_, as a Baldwin or Ben Davis variety of apple, Seckel or
Bartlett pear, Navel or St. Michael orange.
_Plants have preferences as to the stocks on which they will grow; but
we can find out what their choice is only by making the experiment._
The pear grows well on the quince, but the quince does not thrive
on the pear. The pear grows on some of the hawthorns, but it is an
unwilling subject on the apple. Tomato plants will grow on potato
plants and potato plants on tomato plants. When the potato is the root,
both tomatoes and potatoes may be produced, although the crop will be
very small; when the tomato is the root, neither potatoes nor tomatoes
will be produced. Chestnut will grow on some kinds of oak. In general,
one species or kind is grafted on the same species, as apple on apple,
pear on pear, orange on orange.
_The forming, growing tissue of the stem_ (on the plants we have been
discussing) is the =cambium= (Chap. X), _lying on the outside of
the woody cylinder beneath the bark_. In order that union may take
place, _the cambium of the cion and of the stock must come together_.
Therefore the cion is set in the side of the stock. There are many
ways of shaping the cion and of preparing the stock to receive it.
These ways are dictated largely by the relative sizes of cion and
stock, although many of them are matters of personal preference. The
underlying principles are two: securing _close contact_ between the
cambiums of cion and stock; _covering the wounded surfaces_ to prevent
evaporation and to protect the parts from disease.
On large stocks the commonest form of grafting is the =cleft-graft=.
The stock is cut off and split; and in one or both sides a wedge-shaped
cion is firmly inserted. Fig. 165 shows the cion; Fig. 166, the cions
set in the stock; Fig. 167, the stock waxed. It will be seen that the
lower bud--that lying in the wedge--is covered by the wax; but being
nearest the food supply and least exposed to weather, it is the most
likely to grow: it will push through the wax.
=Cleft-grafting= _is practiced in spring, as growth begins. The cions
are cut previously, when perfectly dormant, and from the tree which it
is desired to propagate._ The cions are kept in sand or moss in the
cellar. Limbs of various sizes may be cleft-grafted,--from one half
inch up to four inches in diameter; but a diameter of one to one and
one half inches is the most convenient size. All the leading or main
branches of a tree top may be grafted. If the remaining parts of the
top are gradually cut away and the cions grow well, the entire top will
be changed over to the new variety.
[Illustration: FIG. 165.--CION OF APPLE.]
[Illustration: FIG. 166.--THE CION INSERTED.]
[Illustration: FIG. 167.--THE PARTS WAXED.]
Another form of grafting is known as =budding=. In this case a single
bud is used, and it is slipped underneath the bark of the stock and
securely tied (not waxed) with soft material, as bass bark, corn
shuck, yarn, or raffia (the last a commercial palm fiber). Budding is
performed _when the bark of the stock will slip or peel_ (so that the
bud can be inserted), and _when the bud is mature enough to grow_.
Usually budding is performed in late summer or early fall, when the
winter buds are well formed; or it may be practiced in spring with buds
cut in winter. In ordinary summer budding (which is the usual mode)
the “bud” or cion forms a union with the stock, and then lies dormant
till the following spring, as if it were still on its own twig. Budding
is mostly restricted to young trees in the nursery. In the spring
following the budding, the stock is cut off just above the bud, so
that only the shoot from the bud grows to make the future tree. This
prevailing form of budding (shield-budding) is shown in Fig. 168.
[Illustration: FIG. 168.--BUDDING. The “bud”; the opening to receive
it; the bud tied.]
SUGGESTIONS.--=128.= Name the plants that the gardener propagates
by means of cuttings. =129.= By means of grafts. =130.= The
cutting-box may be set in the window. If the box does not receive
direct sunlight, it may be covered with a pane of glass to prevent
evaporation. Take care that the air is not kept too close, else the
damping-off fungi may attack the cuttings, and they will rot at the
surface of the ground. See that the pane is raised a little at one
end to afford ventilation; and if the water collects in drops on the
under side of the glass, remove the pane for a time. =131.= Grafting
wax is made of beeswax, resin, and tallow. A good recipe is one
part (as one pound) of rendered tallow, two parts of beeswax, four
parts of rosin; melt together in a kettle; pour the liquid into a
pail or tub of water to solidify it; work with the hands until it
has the color and “grain” of taffy candy, the hands being greased
when necessary. The wax will keep any length of time. For the little
grafting that any pupil would do, it is better to buy the wax of a
seedsman. =132.= Grafting is hardly to be recommended as a general
school diversion, as the making of cuttings is; and the account of it
in this chapter is inserted chiefly to satisfy the general curiosity
on the subject. =133.= In Chap. V we had a definition of a plant
generation: what is “one generation” of a grafted fruit tree, as Le
Conte pear, Baldwin, or Ben Davis apple? =134.= The Elberta peach
originated about 1880: what is meant by “originated”? =135.= How is
the grape propagated so as to come true to name (explain what is
meant by “coming true”)? currant? strawberry? raspberry? blackberry?
peach? pear? orange? fig? plum? cherry? apple? chestnut? pecan?
CHAPTER XVII
HOW PLANTS CLIMB
We have found that plants struggle or contend for a place in which to
live. Some of them become adapted to grow in the forest shade, others
to grow on other plants, as epiphytes, others to _climb to the light_.
Observe how woods grapes, and other forest climbers, spread their
foliage on the very top of the forest tree, while their long flexile
trunks may be bare.
There are several ways by which plants climb, but most climbers may be
classified into four groups: (1) =scramblers=, (2) =root climbers=, (3)
=tendril climbers=, (4) =twiners=.
=Scramblers.=--Some plants rise to light and air _by resting their
long and weak stems on the tops of bushes and quick-growing herbs_.
Their stems may be elevated in part by the growing twigs of the plants
on which they recline. Such plants are scramblers. Usually they are
provided with prickles or bristles. In most weedy swamp thickets,
scrambling plants may be found. Briers, some roses, bed-straw or
galium, bittersweet (_Solanum Dulcamara_, not the _Celastrus_), the
tear-thumb polygonums, and other plants are familiar examples of
scramblers.
=Root Climbers.=--Some plants climb by means of _true roots_. These
roots seek the dark places and therefore enter the chinks in walls and
bark. The trumpet creeper is a familiar example (Fig. 36). The true
or English ivy, which is often grown to cover buildings, is another
instance. Still another is the poison ivy. Roots are distinguished from
stem tendrils by their _irregular or indefinite position_ as well as by
their mode of growth.
[Illustration: FIG. 169.--TENDRIL, to show where the coil is changed.]
=Tendril climbers.=--A slender coiling part that serves to hold a
climbing plant to a support is known as a =tendril=. The free end
swings or curves until it strikes some object, when it attaches itself
and then coils and _draws the plant close to the support_. The spring
of the coil also allows the plant _to move in the wind_, thereby
enabling the plant to maintain its hold. Slowly pull a well-matured
tendril from its support, and note how strongly it holds on. Watch the
tendrils in a wind-storm. Usually the tendril attaches to the support
by _coiling about it_, but the Virginia creeper and Boston ivy (Fig.
170) attach to walls by means of _disks_ on the ends of the tendrils.
[Illustration: FIG. 170.--TENDRIL OF BOSTON IVY.]
Since both ends of the tendril are fixed, when it finds a support, the
coiling would tend to twist it in two. It will be found, however, that
the tendril _coils in different directions_ in different parts of its
length. In Fig. 169, showing an old and stretched-out tendril, the
change of direction in the coil occurred at _a_. In long tendrils of
cucumbers and melons there may be several changes of direction.
Tendrils may represent either _branches_ or _leaves_. In the Virginia
creeper and grape they are branches; they stand opposite the leaves in
the position of fruit clusters, and sometimes one branch of a fruit
cluster is a tendril. These tendrils are therefore homologous with
fruit-clusters, and fruit-clusters are branches.
In some plants tendrils are _leaflets_ (Chap. XI). Examples are the
sweet pea and common garden pea. In Fig. 171, observe the leaf with
its two great stipules, petiole, six normal leaflets, and two or three
pairs of leaflet tendrils and a terminal leaflet tendril. The cobea,
a common garden climber, has a similar arrangement. In some cases
tendrils are _stipules_, as probably in the green briers (smilax).
The _petiole_ or _midrib may act as a tendril_, as in various kinds of
clematis. In Fig. 172, the common wild clematis or “old man vine,” this
mode is seen.
[Illustration: FIG. 171.--LEAVES OF PEA,--very large stipules, opposite
leaflets, and leaflets represented by tendrils.]
=Twiners.=--The entire plant or shoot may wind about a support. Such a
plant is a twiner. Examples are bean, hop, morning-glory, moonflower,
false bittersweet or waxwork (_Celastrus_), some honeysuckles,
wistaria, Dutchman’s pipe, dodder. The free tip of the twining branch
_sweeps about in curves_, much as the tendril does, until it finds
support or becomes old and rigid.
Each kind of plant usually coils _in only one direction_. Most plants
coil against the sun, or from the observer’s left across his front to
his right as he faces the plant. Examples are bean, morning-glory. The
hop twines from the observer’s right to his left, or with the sun.
[Illustration: FIG. 172.--CLEMATIS CLIMBING BY LEAF-TENDRIL.]
SUGGESTIONS.--=136.= Set the pupil to watch the behavior of any
plant that has tendrils at different stages of maturity. A vigorous
cucumber plant is one of the best. Just beyond the point of a young
straight tendril set a stake to compare the position of it. Note
whether the tendril changes position from hour to hour or day to day.
=137.= Is the tip of the tendril perfectly straight? Why? Set a small
stake at the end of a strong straight tendril, so the tendril will
just reach it. Watch, and make drawing. =138.= If a tendril does not
find a support, what does it do? =139.= To test the movement of a
free tendril, draw an ink line lengthwise of it, and note whether the
line remains always on the concave side or the convex side. =140.=
Name the tendril-bearing plants that you know. =141.= Make similar
observations and experiments on the tips of twining stems. =142.=
What twining plants do you know, and which way do they twine? =143.=
How does any plant that you know get up in the world? =144.= Does the
stem of a climbing plant contain more or less substance (weight) than
an erect self-supporting stem of the same height? Explain.
CHAPTER XVIII
THE FLOWER--ITS PARTS AND FORMS
The function of the flower is to _produce seed_. It is probable that
all its varied forms and colors contribute to this supreme end. These
forms and colors please the human fancy and add to the joy of living,
but the flower exists for the good of the plant, not for the good of
man. The parts of the flower are of two general kinds--those that are
directly concerned in the _production of seeds_, and those that act as
_covering and protecting organs_. The former parts are known as the
=essential organs=; the latter as the =floral envelopes=.
=Envelopes.=--The floral envelopes usually bear a close resemblance to
leaves. These envelopes are very commonly of two series or kinds--the
_outer_ and the _inner_. The outer series, known as the =calyx=, is
usually smaller and green. It usually comprises the outer cover of the
flower bud. The calyx is the lowest whorl in Fig. 173.
[Illustration: FIG. 173.--FLOWER OF A BUTTERCUP IN SECTION.]
The inner series, known as the =corolla=, is usually colored and more
special or irregular in shape than the calyx. It is the showy part of
the flower, as a rule. The corolla is the second or large whorl in Fig.
173.
The _calyx_ may be composed of several leaves. Each leaf is a =sepal=.
If it is of one piece, it may be lobed or divided, in which case the
divisions are called =calyx-lobes=.
In like manner, the corolla may be composed of =petals=, or it
may be of one piece and variously lobed. A calyx of one piece, no
matter how deeply lobed, is =gamosepalous=. A corolla of one piece
is =gamopetalous=. When these series are of separate pieces, as in
Fig. 173, the flower is said to be =polysepalous= and =polypetalous=.
Sometimes both series are of separate parts, and sometimes only one of
them is so formed.
_The floral envelopes are homologous with leaves._ Sepals and petals,
at least when more than three or five, are in more than one whorl, and
one whorl stands below another so that the parts overlap. They are
borne on the expanded or thickened end of the flower stalk; this end
is the =torus=. In Fig. 173 all the parts are seen as attached to the
torus. This part is sometimes called the _receptacle_, but this word is
a common-language term of several meanings, whereas torus has no other
meaning. Sometimes one part is attached to another part, as in the
fuchsia (Fig. 174), in which the petals are borne on the calyx-tube.
[Illustration: FIG. 174.--FLOWER OF FUCHSIA IN SECTION.]
=Subtending Parts.=--Sometimes there are _leaf-like parts just
below the calyx_, looking like a second calyx. Such parts accompany
the carnation flower. These parts are =bracts= (bracts are small
specialized leaves); and they form an =involucre=. We must be careful
that we do not mistake them for true flower parts. Sometimes the bracts
are large and petal-like, as in the great white blooms of the flowering
dogwood: here the real flowers are several, small and greenish, forming
a small cluster in the center.
=Essential Organs.=--The essential organs are of two series. The outer
series is composed of the =stamens=. The inner series is composed of
the =pistils=.
_Stamens_ bear the =pollen=, which is made up of grains or spores, each
spore usually being a single plant cell. The stamen is of two parts,
as is readily seen in Figs. 173, 174,--the enlarged terminal part or
=anther=, and the stalk or =filament=. The filament is often so short
as to seem to be absent, and the anther is then said to be _sessile_.
The anther bears the pollen spores. It is made up of two or four parts
(known as sporangia or spore-cases), which burst and discharge the
pollen. _When the pollen is shed, the stamen dies._
The _pistil has three parts_: the lowest, or seed-bearing part, which
is the =ovary=; the =stigma= at the upper extremity, which is a
flattened or expanded surface, and usually roughened or sticky; the
stalk-like part or =style=, connecting the ovary and stigma. Sometimes
the style is apparently wanting, and the stigma is said to be sessile
on the ovary. These parts are shown in the fuchsia (Fig. 174). The
ovary or seed vessel is at _a_. A long style, bearing a large stigma,
projects from the flower. See also Figs. 175 and 176.
[Illustration: FIG. 175.--THE STRUCTURE OF A PLUM BLOSSOM.
_se_, sepals; _p_, petals; _sta_, stamens; _o_, ovary; _s_, style;
_st_, stigma. The pistil consists of the ovary, style, and stigma. It
contains the seed part. The stamens are tipped with anthers, in which
the pollen is borne. The ovary, _o_, ripens into the fruit.]
Stamens and pistils probably are homologous with leaves. A pistil is
sometimes conceived to represent anciently a leaf as if rolled into a
tube; and an anther, a leaf of which the edges may have been turned in
on the midrib.
[Illustration: FIG. 176.--SIMPLE PISTILS OF BUTTERCUP, one in
longitudinal section.]
The pistil may be of _one part or compartment, or of many parts_. The
different units or parts of which it is composed are =carpels=. Each
carpel is homologous with a leaf. Each carpel bears one or more seeds.
A pistil of one carpel is =simple=; of two or more carpels, =compound=.
Usually the structure of the pistil may be determined by cutting
horizontally across the lower or seed-bearing part, as Figs. 177, 178
explain. A flower may contain a simple pistil (one carpel), as the pea
(Fig. 177); _several simple pistils_ (several separate carpels), as
the buttercup (Fig. 176); or a _compound pistil_ with carpels united,
as the Saint John’s wort (Fig. 178) and apple. How many carpels in an
apple? A peach? An okra pod? A bean pod? The seed cavity in each carpel
is called a =locule= (Latin _locus_, a place). In these locules _the
seeds are borne_.
[Illustration: FIG. 177.--PISTIL OF GARDEN PEA, the stamens being
pulled down in order to disclose it; also a section showing the single
compartment (compare Fig. 188).]
[Illustration: FIG. 178.--COMPOUND PISTIL OF A ST. JOHN’S WORT. It has
5 carpels.]
=Conformation of the Flower.=--A flower that has calyx, corolla,
stamens, and pistils is said to be =complete= (Fig. 173); all others
are =incomplete=. In some flowers both the floral envelopes are
wanting: such are =naked=. When one of the floral envelope series is
wanting, the remaining series is said to be calyx, and the flower
is therefore =apetalous= (without petals). The knotweed (Fig. 179),
smartweed, buckwheat, elm are examples.
[Illustration: FIG. 179.--KNOTWEED, a very common but inconspicuous
plant along hard walks and roads. Two flowers, enlarged, are shown at
the right. These flowers are very small and borne in the axils of the
leaves.]
Some flowers lack the pistils: these are =staminate=, whether the
envelopes are missing or not. Others lack the stamens: these are
=pistillate=. Others have neither stamens nor pistils: these are
=sterile= (snowball and hydrangea). Those that have both stamens and
pistils are =perfect=, whether or not the envelopes are missing. Those
that lack either stamens or pistils are =imperfect= or =diclinous=.
Staminate and pistillate flowers are imperfect or diclinous.
[Illustration: FIG. 180.--STAMINATE CATKINS OF OAK. The pistillate
flowers are in the leaf axils, and not shown in this picture.]
[Illustration: FIG. 181.--BEGONIA FLOWERS.
Staminate at _A_; pistillate below, with the winged ovary at _B_.]
When staminate and pistillate flowers are borne on the same plant,
_e.g._ oak (Fig. 180), corn, beech, chestnut, hazel, walnut, hickory,
pine, begonia (Fig. 181), watermelon, gourd, pumpkin, the plant is
=monœcious= (“in one house”). When they are on different plants,
_e.g._ poplar, cottonwood, bois d’arc, willow (Fig. 182), the plant is
=diœcious= (“in two houses”). Some varieties of strawberry, grape, and
mulberry are partly diœcious. Is the rose either monœcious or diœcious?
[Illustration: FIG. 182.--CATKINS OF A WILLOW.
A staminate flower is shown at _s_, and a pistillate flower at _p_. The
staminate and pistillate are on different plants.]
[Illustration: FIG. 183.--FLOWER OF GARDEN NASTURTIUM.
Separate petal at _a_. The calyx is produced into a spur.]
[Illustration: FIG. 184.--THE FIVE PETALS OF THE PANSY, detached to
show the form.]
[Illustration: FIG. 185.--FLOWER OF CATNIP.]
Flowers in which the parts of each series are alike are said to be
=regular= (as in Figs. 173, 174, 175). Those in which some parts are
unlike other parts of the same series are =irregular=. Their regularity
may be in calyx, as in nasturtium (Fig. 183); in corolla (Figs. 184,
185); in the stamens (compare nasturtium, catnip, Fig. 185, sage); in
the pistils. Irregularity is most frequent in the corolla.
=Various Forms of Corolla.=--The corolla often assumes very definite
or distinct forms, especially when gamopetalous. It may have a long
tube with a wide-flaring limb, when it is said to be =funnelform=,
as in morning-glory and pumpkin. If the tube is very narrow and the
limb stands at right angles to it, the corolla is =salverform=, as in
phlox. If the tube is very short and the limb wide-spreading and nearly
circular in outline, the corolla is =rotate= or =wheel-shaped=, as in
potato.
A gamopetalous corolla or gamosepalous calyx is often cleft in such
way as to make two prominent parts. Such parts are said to be =lipped=
or =labiate=. Each of the lips or lobes may be notched or toothed. In
5-membered flowers, the lower lip is usually 3-lobed and the upper one
2-lobed. Labiate flowers are characteristic of the mint family (Fig.
185), and the family therefore is called the Labiatæ. (Literally,
labiate means merely “lipped,” without specifying the number of lips or
lobes; but it is commonly used to designate 2-lipped flowers.) Strongly
2-parted polypetalous flowers may be said to be labiate; but the term
is oftenest used for gamopetalous corollas.
Labiate gamopetalous flowers that are closed in the throat (or entrance
to the tube) are said to be grinning or =personate= (personate means
_masked_, or _person-like_). Snap-dragon is a typical example;
also toadflax or butter-and-eggs (Fig. 186), and many related
plants. Personate flowers usually have definite relations to insect
pollination. Observe how an insect forces his head into the closed
throat of the toadflax.
[Illustration: FIG. 186.--PERSONATE FLOWER OF TOADFLAX.]
The peculiar flowers of the pea tribes are explained in Figs. 187, 188.
[Illustration: FIG. 187.--FLOWERS OF THE COMMON BEAN, with one flower
opened (_a_) to show the structure.]
[Illustration: FIG. 188.--DIAGRAM OF ALFALFA FLOWER IN SECTION:
_C_, calyx; _D_, standard; _W_, wing; _K_, keel; _T_, stamen-tube; _F_,
filament of tenth stamen; _X_, stigma; _Y_, style; _O_, ovary; the
dotted lines at _E_ show position of stamen tube, when pushed upward by
insects. Enlarged.]
=Spathe Flowers.=--In many plants, very simple (often naked) flowers
are borne in dense, more or less fleshy spikes, and the spike is
inclosed in or attended by a leaf, sometimes corolla-like, known as a
=spathe=. The spike of flowers is technically known as a =spadix=. This
type of flower is characteristic of the great arum family, which is
chiefly tropical. The commonest wild representatives in the North are
Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In the former
the flowers are all diclinous and naked. In the skunk cabbage all the
flowers are perfect and have four sepals. The common calla is a good
example of this type of inflorescence.
[Illustration: FIG. 189.--HEAD OF SUNFLOWER.]
=Compositous Flowers.=--The head (anthodium) or so-called “flower” of
sunflower (Fig. 189), thistle, aster, dandelion, daisy, chrysanthemum,
goldenrod, _is composed of several or many little flowers, or_
=florets=. These florets are inclosed in a more or less dense and
usually green _involucre_. In the thistle (Fig. 190) this involucre is
prickly. A longitudinal section discloses the florets, all attached at
bottom to a common torus, and densely packed in the involucre. The pink
tips of these florets constitute the showy part of the head.
[Illustration: FIG. 190.--LONGITUDINAL SECTION OF THISTLE HEAD; also a
FLORET OF THISTLE.]
Each floret of the thistle (Fig. 190) is a complete flower. At _a_ is
the ovary. At _b_ is a much-divided plumy calyx, known as the =pappus=.
The corolla is long-tubed, rising above the pappus, and is enlarged and
5-lobed at the top, _c_. The style projects at _e_. The five anthers
are united about the style in a ring at _d_. Such anthers are said to
be =syngenesious=. These are the various parts of the florets of the
Compositæ. In some cases the pappus is in the form of barbs, bristles,
or scales, and sometimes it is wanting. The pappus, as we shall see
later, assists in distributing the seed. Often the florets are not
all alike. The corolla of those in the outer circles may be developed
into a _long, straplike, or tubular part_, and the head then has the
appearance of being one flower with a border of petals. Of such is
the sunflower (Fig. 189), aster, bachelor’s button or cornflower, and
field daisy (Fig. 211). These long corolla-limbs are called rays. In
some cultivated composites, all the florets may develop =rays=, as in
the dahlia and chrysanthemum. In some species, as dandelion, all the
florets naturally have rays. Syngenesious arrangement of anthers is the
most characteristic single feature of the composites.
[Illustration: FIG. 191.--PETALS ARISING FROM THE STAMINAL COLUMN OF
HOLLYHOCK, and accessory petals in the corolla-whorl.]
=Double Flowers.=--Under the stimulus of cultivation and increased
food supply, flowers tend to become double. True doubling arises in
two ways, morphologically: (1) _stamens or pistils may produce petals_
(Fig. 191); (2) _adventitious or accessory petals may arise in the
circle of petals_. Both of these categories may be present in the
same flower. In the full double hollyhock the petals derived from
the staminal column are shorter and make a rosette in the center of
the flower. In Fig. 192 is shown the doubling of a daffodil by the
modification of stamens. Other modifications of flowers are sometimes
known as doubling. For example, double dahlias, chrysanthemums, and
sunflowers are forms in which the disk flowers have developed rays. The
snowball is another case. In the wild snowball the external flowers
of the cluster are large and sterile. In the cultivated plant all the
flowers have become large and sterile. Hydrangea is a similar case.
[Illustration: FIG. 192.--NARCISSUS OR DAFFODIL. Single flower at the
right.]
SUGGESTIONS.--=145.= If the pupil has been skillfully conducted
through this chapter _by means of careful study of specimens_ rather
than as a mere memorizing process, he will be in mood to challenge
any flower that he sees and to make an effort to understand it.
Flowers are endlessly modified in form; but they can be understood if
the pupil looks first for the anthers and ovaries. How may anthers
and ovaries always be distinguished? =146.= It is excellent practice
to find the flowers in plants that are commonly known by name, and to
determine the main points in their structure. What are the flowers in
Indian corn? pumpkin or squash? celery? cabbage? potato? pea? tomato?
okra? cotton? rhubarb? chestnut? wheat? oats? =147.= Do all forest
trees have flowers? Explain. =148.= Name all the monœcious plants you
know. Diœcious. =149.= What plants do you know that bloom before the
leaves appear? Do any bloom after the leaves fall? =150.= Explain the
flowers of marigold, hyacinth, lettuce, clover, asparagus, garden
calla, aster, locust, onion, burdock, lily-of-the-valley, crocus,
Golden Glow rudbeckia, cowpea. =151.= Define a _flower_.
NOTE TO THE TEACHER.--It cannot be urged too often that _the
specimens themselves_ be studied. If this chapter becomes a mere
recitation on names and definitions, the exercise will be worse than
useless. Properly taught by means of the flowers themselves, the
names become merely incidental and a part of the pupil’s language,
and the subject has living interest.
CHAPTER XIX
THE FLOWER--FERTILIZATION AND POLLINATION
=Fertilization.=--_Seeds result from the union of two elements or
parts._ One of these elements is a cell-nucleus of the pollen-grain.
The other element is the cell-nucleus of an egg-cell, borne in the
ovary. The pollen-grain falls on the stigma (Fig. 193). It absorbs the
juices exuded by the stigma, and grows by sending out a tube (Fig.
194). This tube grows downward through the style, absorbing food as it
goes, and finally reaches the egg-cell in the interior of an ovule in
the ovary (Fig. 195), and =fertilization=, or union of a nucleus of the
pollen and the nucleus of the egg-cell in the ovule, takes place. _The
ovule and embryo within then develops into a seed._ The growth of the
pollen-tube is often spoken of as germination of the pollen, but it is
not germination in the sense in which the word is used when speaking of
seeds.
[Illustration: FIG. 193.--_B_, POLLEN escaping from anther; _A_, pollen
germinating on a stigma. Enlarged.]
[Illustration: FIG. 194.--A POLLEN-GRAIN AND THE GROWING TUBE.]
Better seeds--that is, those that produce stronger and more
fruitful plants--often result when the _pollen comes from another
flower_. Fertilization effected between different flowers is
=cross-fertilization=; that resulting from the application of
pollen to pistils in the same flower is =close-fertilization= or
=self-fertilization=. It will be seen that the =cross-fertilization=
relationship may be of many degrees--between two flowers in the same
cluster, between those in different clusters on the same branch,
between those on different plants. Usually fertilization takes place
only between plants of the same species or kind.
[Illustration: FIG. 195.--DIAGRAM TO REPRESENT FERTILIZATION.
_s_, stigma; _st_, style; _ov_, ovary; _o_, ovule; _p_, pollen-grain;
_pt_, pollen-tube; _e_, egg-cell; _m_, micropyle.]
In many cases there is, in effect, _an apparent selection of pollen_
when pollen from two or more sources is applied to the stigma.
Sometimes the foreign pollen, if from the same kind of plant, grows,
and fertilization results, while pollen from the same flower is less
promptly effective. If, however, no foreign pollen is present, the
pollen from the same flower may finally serve the same purpose.
In order that the pollen may grow, _the stigma must be ripe_. At this
stage the stigma is usually moist and sometimes sticky. A ripe stigma
is said to be =receptive=. The stigma may remain receptive for several
hours or even days, depending on the kind of plant, the weather, and
how soon pollen is received. Watch a certain flower every day to see
the anther locules open and the stigma ripen. When fertilization takes
place, the stigma dies. Observe, also, how soon the petals wither after
the stigma has received pollen.
=Pollination.=--The transfer of the pollen from anther to stigma is
known as =pollination=. The pollen may fall of its own weight on
the adjacent stigma, or it may be carried from flower to flower by
wind, insects, or other agents. There may be =self-pollination= or
=cross-pollination=, and of course it must always precede fertilization.
Usually the pollen is discharged by the bursting of the anthers. The
commonest method of discharge is through a _slit_ on either side of
the anther (Fig. 193). Sometimes it discharges through a _pore_ at the
apex, as in azalea (Fig. 196), rhododendron, huckleberry, wintergreen.
In some plants a part of the anther wall raises or falls as a _lid_,
as in barberry (Fig. 197), blue cohosh, May apple. The opening of an
anther (as also of a seed-pod) is known as =dehiscence= (_de_, from;
_hisco_, to gape). When an anther or seed pod opens, it is said to
_dehisce_.
[Illustration: FIG. 196.--ANTHER OF AZALEA, opening by terminal pores.]
[Illustration: FIG. 197.--BARBERRY STAMEN, with anther opening by lids.]
_Most flowers are so constructed as to increase the chances of
cross-pollination._ We have seen that the stigma may have the power
of choosing foreign pollen. The commonest means of necessitating
cross-pollination is the _different times of maturing of stamens and
pistils in the same flower_. In most cases the stamens mature first:
the flower is then =proterandrous=. When the pistils mature first, the
flower is =proterogynous=. (_Aner_, _andr_, is a Greek root often used,
in combinations, for stamen, and _gyne_ for pistil.) The difference
in time of ripening may be an hour or two, or it may be a day. The
ripening of the stamens and pistils at different times is known as
=dichogamy=, and flowers of such character are said to be dichogamous.
There is little chance for dichogamous flowers to pollinate themselves.
Many flowers are _imperfectly dichogamous_--some of the anthers
mature simultaneously with the pistils, so that there is chance for
self-pollination in case foreign pollen does not arrive. Even when
the stigma receives pollen from its own flower, cross-fertilization
may result. The hollyhock is proterandrous. Fig. 198 shows a flower
recently expanded. The center is occupied by the column of stamens. In
Fig. 199, showing an older flower, the long styles are conspicuous.
[Illustration: FIG. 198.--FLOWER OF HOLLYHOCK; proterandrous.]
[Illustration: FIG. 199.--OLDER FLOWER OF HOLLYHOCK.]
_Some flowers are so constructed as to prohibit self-pollination._
Very irregular flowers are usually of this kind. With some of them,
the petals form a sac to inclose the anthers and the pollen cannot be
shed on the stigma but is retained until a bee forces the sac open;
the pollen is rubbed on the hairs of the bee and transported. Regular
flowers usually depend mostly on dichogamy and the selective power
of the pistil to insure crossing. _Flowers that are very irregular
and provided with nectar and strong perfume are usually pollinated by
insects._ Gaudy colors probably attract insects in many cases, but
perfume appears to be a greater attraction.
[Illustration: FIG. 200.--FLOWER OF LARKSPUR.]
[Illustration: FIG. 201.--ENVELOPES OF A LARKSPUR. There are five wide
sepals, the upper one being spurred. There are four small petals.]
The insect _visits the flower for the nectar_ (for the making of honey)
_and may unknowingly carry the pollen_. Spurs and sacs in the flower
are nectaries (Fig. 200), but in spurless flowers the nectar is usually
secreted _in the bottom of the flower cup_. This compels the insect to
pass by the anther and rub against the pollen before it reaches the
nectar. Sometimes the anther is a long lever poised on the middle point
and the insect bumps against one end and lifts it, thus bringing the
other end of the lever with the pollen sacs down on its back. Flowers
that are pollinated by insects are said to be =entomophilous= (“insect
loving”). Fig. 200 shows a larkspur. The envelopes are separated in
Fig. 201. The long spur at once suggests insect pollination. The spur
is a sepal. Two hollow petals project into this spur, apparently
serving to guide the bee’s tongue. The two smaller petals, in front,
are peculiarly colored and perhaps serve the bee in locating the
nectary. The stamens ensheath the pistils (Fig. 202). As the insect
stands on the flower and thrusts its head into the center, the
envelopes are pushed downward and outward and the pistil and stamens
come in contact with its abdomen. Since the flower is proterandrous,
the pollen that the pistils receive from the bee’s abdomen must come
from another flower. Note a somewhat similar arrangement in the
toadflax or butter-and-eggs.
[Illustration: FIG. 202.--STAMENS OF LARKSPUR, surrounding the pistils.]
In some cases (Fig. 203) the stamens are longer than the pistil in
one flower and shorter in another. If the insect visits such flowers,
it gets pollen on its head from the long-stamen flower, and deposits
this pollen on the stigma in the long-pistil flower. Such flowers are
=dimorphous= (of two forms). If pollen from its own flower and from
another flower both fall on the stigma, the probabilities are that the
stigma will choose the foreign pollen.
[Illustration: FIG. 203.--DIMORPHIC FLOWERS OF PRIMROSE.]
_Many flowers are pollinated by the wind._ They are said to be
=anemophilous= (“wind loving”). Such flowers produce great quantities
of pollen, for much of it is wasted. They usually have broad stigmas,
which expose large surfaces to the wind. They are usually lacking
in gaudy colors and in perfume. Grasses and pine trees are typical
examples of anemophilous plants.
[Illustration: FIG. 204.--FLOWERS OF BLACK WALNUT: two pistillate
flowers at _A_, and staminate catkins at _B_.]
In many cases cross-pollination is insured because the _stamens and
pistils are in different flowers_ (diclinous). Monœcious and diœcious
plants may be pollinated by wind or insects, or other agents (Fig.
204). They are usually wind-pollinated, although willows are often,
if not mostly, insect-pollinated. The Indian corn is a monœcious
plant. The staminate flowers are in a terminal panicle (tassel). The
pistillate flowers are in a dense spike (ear), inclosed in a sheath or
husk. Each “silk” is a style. Each pistillate flower produces a kernel
of corn. Sometimes a few pistillate flowers are borne in the tassel and
a few staminate flowers on the tip of the ear. Is self-fertilization
possible with the corn? Why does a “volunteer” stalk standing alone in
a garden have only a few grains on the ear? What is the direction of
the prevailing wind in summer? If only two or three rows of corn are
planted in a garden where prevailing winds occur, in which direction
would they better run?
[Illustration: FIG. 205.--COMMON BLUE VIOLET. The familiar flowers
are shown, natural size. The corolla is spurred. Late in the season,
cleistogamous flowers are often borne on the surface of the ground. A
small one is shown at _a_. A nearly mature pod is shown at _b_. Both
_a_ and _b_ are one third natural size.]
Although most flowers are of such character as to insure or increase
the chances of cross-pollination, there are some _that absolutely
forbid crossing_. These flowers are usually borne beneath or on the
ground, and they lack showy colors and perfumes. They are known as
=cleistogamous= flowers (meaning “hidden flowers”). The plant has
normal showy flowers that may be insect-pollinated, and in addition
is provided with these simplified flowers. Only a few plants bear
cleistogamous flowers. Hog-peanut, common blue violet, fringed
wintergreen, and dalibarda are the best subjects in the Northern
states. Fig. 205 shows a cleistogamous flower of the blue violet at
_a_. Above the true roots, slender stems bear these flowers, that
are provided with a calyx, and a curving corolla which does not
open. Inside are the stamens and pistils. Late in the season the
cleistogamous flowers may be found just underneath the mold. They never
rise above ground. The following summer one may find a seedling plant,
in some kinds of plants, with the remains of the old cleistogamous
flower still adhering to the root. Cleistogamous flowers usually appear
after the showy flowers have passed. They seem to insure a crop of
seed by a method that expends little of the plant’s energy. The pupil
will be interested to work out the fruiting of the peanut (Fig. 206).
Unbaked fresh peanuts grow readily and can easily be raised in the
North in a warm sandy garden.
[Illustration: FIG. 206.--PODS OF PEANUTS RIPENING UNDERGROUND.]
[Illustration: FIG. 207.--STRUGGLE FOR EXISTENCE AMONG THE APPLE
FLOWERS.]
SUGGESTIONS.--=152.= _Not all the flowers produce seeds._ Note
that an apple tree may bloom very full, but that only relatively
few apples may result (Fig. 207). _More pollen is produced than is
needed to fertilize the flowers_; this increases the chances that
sufficient stigmas will receive acceptable pollen to enable the
plant to perpetuate its kind. At any time in summer, or even in
fall, examine the apple trees carefully to determine whether any
dead flowers or flower stalks still remain about the apple; or,
examine any full-blooming plant to see whether any of the flowers
fail. =153.= Keep watch on any plant to see whether insects visit
it. What kind? When? What for? =154.= Determine whether the calyx
serves any purpose in protecting the flower. Very carefully remove
the calyx from a bud that is normally exposed to heat and sun and
rain, and see whether the flower then fares as well as others. =155.=
Cover a single flower on its plant with a tiny paper or muslin bag
so tightly that no insect can get in. If the flower sets fruit, what
do you conclude? =156.= Remove carefully the corolla from a flower
nearly ready to open, preferably one that has no other flowers very
close to it. Watch for insects. =157.= Find the nectar in any flower
that you study. =158.= Remove the stigma. What happens? =159.=
Which of the following plants have perfect flowers: pea, bean,
pumpkin, cotton, clover, buckwheat, potato, Indian corn, peach,
chestnut, hickory, watermelon, sunflower, cabbage, rose, begonia,
geranium, cucumber, calla, willow, cottonwood, cantaloupe? What have
the others? =160.= On wind-pollinated plants, are either anthers
or stigmas more numerous? =161.= Are very small colored flowers
usually borne singly or in clusters? =162.= Why do rains at blooming
time often lessen the fruit crop? =163.= Of what value are bees in
orchards? =164.= _The crossing of plants to improve varieties or to
obtain new varieties._--It may be desired to perform the operation of
pollination by hand. In order to insure the most definite results,
every effort should be made rightly to apply the pollen which it is
desired shall be used, and rigidly to exclude all other pollen. (_a_)
The first requisite is to remove the anthers from the flower which it
is proposed to cross, and they _must be removed before the pollen has
been shed_. The flower-bud is therefore opened and the anthers taken
out. Cut off the floral envelopes with small, sharp-pointed scissors,
then cut out or pull out the anthers, leaving only the pistil
untouched; or merely open the corolla at the end and pull out the
anthers with a hook or tweezers; and this method is often the best
one. It is best to delay the operation as long as possible and yet
not allow the bud to open (and thereby expose the flower to foreign
pollen) nor the anthers to discharge the pollen. (_b_) The flower
_must next be covered with a paper bag to prevent the access of
pollen_ (Figs. 208, 209). If the stigma is not receptive at the time
(as it usually is not), the desired pollen is not applied at once.
The bag may be removed from time to time to allow of examination
of the pistil, and when the stigma is mature, which is told by its
glutinous or roughened appearance, the time for pollination has come.
If the bag is slightly moistened, it can be puckered more tightly
about the stem of the plant. The time required for the stigma to
mature varies from several hours to a few days. (_c_) When the stigma
is ready, an unopened anther from the desired flower is crushed on
the finger nail or a knife blade, and the pollen is rubbed on the
stigma by means of a tiny brush, the point of a knife blade, or a
sliver of wood. The flower is _again covered with the bag_, which
is allowed to remain for several days until all danger of other
pollination is past. Care must be taken completely to cover the
stigmatic surface with pollen, if possible. The seeds produced by a
crossed flower produce _hybrids_, or plants having parents belonging
to different varieties or species. =165.= One of the means of
securing new forms of plants is by making hybrids. Why?
[Illustration: FIG. 208.--A PAPER BAG, with string inserted.]
[Illustration: FIG. 209.--THE BAG TIED OVER A FLOWER.]
[Illustration: FIG. 210.--FIG. The fig is a hollow torus with flowers
borne on the inside, and pollinated by insects that enter at the apex.]
CHAPTER XX
FLOWER-CLUSTERS
=Origin of the Flower-cluster.=--We have seen that branches arise from
the axils of leaves. Sometimes the leaves may be reduced to bracts and
yet branches are borne in their axils. Some of the branches grow into
long limbs; others become short spurs; _others bear flowers_. In fact,
a flower is itself a specialized branch.
Flowers are usually borne near the top of the plant. Often they
are produced in great numbers. It results, therefore, that flower
branches usually stand close together, forming a cluster. The shape
and arrangement of the flower-cluster _differ with the kind of plant_,
since each plant has its own mode of branching.
[Illustration: FIG. 211.--TERMINAL FLOWERS OF THE WHITEWEED (in some
places called ox-eye daisy).]
Certain definite or well-marked types of flower-clusters have received
names. Some of these names we shall discuss, but the flower-clusters
that perfectly match the definitions are the exception rather than
the rule. The determining of the kinds of flower-clusters is one of
the most perplexing subjects in descriptive botany. We may classify
the subject around three ideas: =solitary flowers=, =centrifugal or
determinate clusters=, =centripetal or indeterminate clusters=.
=Solitary Flowers.=--In many cases flowers are borne singly; they
are separated from other flowers by leaves. They are then said to be
=solitary=. The solitary flower may be either at the end of the main
shoot or axis (Fig. 211), when it is said to be =terminal=; or from
the side of the shoot (Fig. 212), when it is said to be =lateral= or
=axillary=.
[Illustration: FIG. 212.--LATERAL FLOWER OF AN ABUTILON. A greenhouse
plant.]
=Centripetal Clusters.=--If the flower-bearing axils were rather close
together, an open or leafy flower-cluster might result. If the plant
continues to grow from the tip, the older flowers are left farther and
farther behind. If the cluster were so short as to be flat or convex
on top, the outermost flowers would be the older. A flower-cluster
in which the lower or outer flowers open first is said to be a
=centripetal cluster=. It is sometimes said to be an =indeterminate
cluster=, since it is the result of a type of growth which may go on
more or less continuously from the apex.
The simplest form of a definite centripetal cluster is a =raceme=,
which is an open elongated cluster in which the _flowers are borne
singly on very short branches_ and open from below (that is, from
the older part of the shoot) upwards (Fig. 213). The raceme may be
_terminal_ to the main branch; or it may be _lateral_ to it, as in
Fig. 214. Racemes often bear the flowers on one side of the stem, thus
forming a single row.
When a centripetal flower-cluster is long and dense and the flowers
are sessile or nearly so, it is called a =spike= (Fig. 215). Common
examples of spikes are plantain, mignonette, mullein.
[Illustration: FIG. 213.--RACEME OF CURRANT. Terminal or lateral?]
[Illustration: FIG. 214.--LATERAL RACEMES (in fruit) OF BARBERRY.]
[Illustration: FIG. 215.--SPIKE OF PLANTAIN.]
A very _short and dense spike_ is a =head=. Clover (Fig. 216) is a
good example. The sunflower and related plants bear many small flowers
in a very dense and often flat head. Note that in the sunflower (Fig.
189) the outside or exterior flowers open first. Another special form
of spike is the =catkin=, which usually has scaly bracts, the whole
cluster being deciduous after flowering or fruiting, and the flowers
(in typical cases) having only stamens or pistils. Examples are the
“pussies” of willows (Fig. 182) and flower-clusters of oak (Fig. 180),
walnuts (Fig. 204), poplars.
[Illustration: FIG. 216.--HEAD OF CLOVER BLOSSOMS.]
[Illustration: FIG. 217.--CORYMB OF CANDY-TUFT.]
When a loose, elongated centripetal flower-cluster has some primary
branches simple, and others irregularly branched, it is called a
=panicle=. It is a branching raceme. Because of the earlier growth of
the lower branches, the panicle is usually broadest at the base or
conical in outline. True panicles are not very common.
When an indeterminate flower-cluster is short, so that the _top is
convex or flat_, it is a =corymb= (Fig. 217). The outermost flowers
open first. Centripetal flower-clusters are sometimes said to be
corymbose in mode.
When the branches of an indeterminate cluster _arise from a common
point_, like the frame of an umbrella, the cluster is an =umbel= (Fig.
218). Typical umbels occur in carrot, parsnip, caraway and other plants
of the parsley family: the family is known as the Umbelliferæ, or
umbel-bearing family. In the carrot and many other Umbelliferæ, there
are small or secondary umbels, called =umbellets=, at the end of each
of the main branches. (In the center of the wild carrot umbel one often
finds a single, blackish, often aborted flower, comprising a 1-flowered
umbellet.)
[Illustration: FIG. 218.--REMAINS OF A LAST YEAR’S UMBEL OF WILD
CARROT.]
=Centrifugal or Determinate Clusters.=--When the terminal or central
flower opens first, the cluster is said to be =centrifugal=. The
growth of the shoot or cluster is =determinate=, since the length is
definitely determined or stopped by the terminal flower. Fig. 219 shows
a determinate or centrifugal mode of flower bearing.
Dense centrifugal clusters are usually flattish on top because of
the cessation of growth in the main or central axis. These compact
flower-clusters are known as =cymes=. Centrifugal clusters are
sometimes said to be cymose in mode. Apples, pears (Fig. 220), and
elders bear flowers in cymes. Some cyme-forms are like umbels in
general appearance. A head-like cymose cluster is a =glomerule=; it
blooms from the top downwards rather than from the base upwards.
=Mixed Clusters.=--Often the cluster is mixed, being determinate in
one part and indeterminate in another part of the same cluster. The
main cluster may be indeterminate, but the branches determinate. The
cluster has the appearance of a panicle, and is usually so called,
but it is really a =thyrse=. Lilac is a familiar example of a thyrse.
In some cases the main cluster is determinate and the branches are
indeterminate, as in hydrangea and elder.
[Illustration: FIG. 219.--DETERMINATE OR CYMOSE ARRANGEMENT.--Wild
geranium.]
[Illustration: FIG. 220.--CYME OF PEAR. Often imperfect.]
=Inflorescence.=--The mode or method of flower arrangement is known as
the =inflorescence=. That is, the inflorescence is cymose, corymbose,
paniculate, spicate, solitary, determinate, indeterminate. By custom,
however, the word “inflorescence” has come to be used for the
_flower-cluster itself_ in works on descriptive botany. Thus a cyme or
a panicle may be called an inflorescence. It will be seen that even
solitary flowers follow either indeterminate or determinate methods of
branching.
[Illustration: FIG. 221.--FORMS OF CENTRIPETAL FLOWER-CLUSTERS.
1, raceme; 2, spike; 3, umbel; 4, head or anthodium; 5, corymb.]
[Illustration: FIG. 222.--CENTRIPETAL INFLORESCENCE, _continued_.
6, spadix; 7, compound umbel; 8, catkin.]
[Illustration: FIG. 223.--CENTRIFUGAL INFLORESCENCE.
1, cyme; 2, scirpioid raceme (or half cyme).]
=The flower-stem.=--The stem of a solitary flower is known as a
=peduncle=; also the general stem of a _flower-cluster_. The stem of
the individual flower in a cluster is a =pedicel=. In the so-called
stemless plants the peduncle may arise directly from the ground, or
crown of the plant, as in dandelion, hyacinth, garden daisy; this kind
of peduncle is called a =scape=. A scape may bear one or many flowers.
It has no foliage leaves, but it may have bracts.
SUGGESTIONS.--=166.= Name six columns in your notebook as follows:
spike, raceme, corymb, umbel, cyme, solitary. Write each of the
following in its appropriate column: larkspur, grape, rose, wistaria,
onion, bridal wreath, banana, hydrangea, phlox, China berry,
lily-of-the-valley, Spanish dagger (or yucca), sorghum, tuberose,
hyacinth, mustard, goldenrod, peach, hollyhock, mullein, crêpe
myrtle, locust, narcissus, snapdragon, peppergrass, shepherd’s purse,
coxcomb, wheat, hawthorn, geranium, carrot, elder, millet, dogwood,
castor bean; substitute others for plants that do not grow in your
region. =167.= In the study of flower-clusters, it is well to choose
first those that are fairly typical of the various classes discussed
in the preceding paragraphs. As soon as the main types are well fixed
in the mind, random clusters should be examined, for the pupil must
never receive the impression that all flower-clusters follow the
definitions in books. Clusters of some of the commonest plants are
very puzzling, but the pupil should at least be able to discover
whether the inflorescence is determinate or indeterminate. Figures
221 to 223 (from the German) illustrate the theoretical modes of
inflorescence. The numerals indicate the order of opening.
CHAPTER XXI
FRUITS
The ripened ovary, with its attachments, is known as the =fruit=.
_It contains the seeds._ If the pistil is simple, or of one carpel,
the fruit also will have one compartment. If the pistil is compound,
or of more than one carpel, the fruit usually has an equal number
of compartments. The compartments in pistil and fruit are known as
=locules= (from Latin _locus_, meaning “a place”).
[Illustration: FIG. 224.--DENTARIA, OR TOOTH-WORT, in fruit.]
The simplest kind of fruit is a _ripened 1-loculed ovary_. The first
stage in complexity is a ripened _2- or many-loculed ovary_. Very
complex forms may arise by the _attachment of other parts to the
ovary_. Sometimes the style persists and becomes a beak (mustard pods,
dentaria, Fig. 224), or a tail as in clematis; or the calyx may be
attached to the ovary; or the ovary may be embedded in the receptacle,
and ovary and receptacle together constitute the fruit: or an involucre
may become a part of the fruit, as possibly in the walnut and hickory
(Fig. 225), and cup of the acorn (Fig. 226). The chestnut and the beech
bear a prickly involucre, but the nuts, or true fruits, are not grown
fast to it, and the involucre can scarcely be called a part of the
fruit. A ripened ovary is a =pericarp=. A pericarp to which other parts
adhere has been called an accessory or reënforced fruit. (Page 169.)
[Illustration: FIG. 225.--HICKORY-NUT. The nut is the fruit, contained
in a husk.]
[Illustration: FIG. 226.--LIVE-OAK ACORN. The fruit is the “seed” part;
the involucre is the “cup.”]
[Illustration: FIG. 227.--KEY OF SUGAR MAPLE.]
[Illustration: FIG. 228.--KEY OF COMMON AMERICAN ELM.]
Some fruits are =dehiscent=, or split open at maturity and liberate the
seeds; others are =indehiscent=, or do not open. A dehiscent pericarp
is called a =pod=. The parts into which such a pod breaks or splits
are known as =valves=. In indehiscent fruits the seed is liberated by
the decay of the envelope, or by the rupturing of the envelope by the
germinating seed. Indehiscent winged pericarps are known as =samaras=
or =key fruits=. Maple (Fig. 227), elm (Fig. 228), and ash (Fig. 93)
are examples.
=Pericarps.=--The simplest pericarp is a dry, one-seeded, indehiscent
body. It is known as an =akene=. A head of akenes is shown in Fig.
229, and the structure is explained in Fig. 230. Akenes may be seen in
buttercup, hepatica, anemone, smartweed, buckwheat.
[Illustration: FIG. 229.--AKENES OF BUTTERCUP.]
[Illustration: FIG. 230.--AKENES OF BUTTERCUP, one in longitudinal
section.]
A 1-loculed pericarp which dehisces along the front edge (that is, the
inner edge, next the center of the flower) is a =follicle=. The fruit
of the larkspur (Fig. 231) is a follicle. There are usually five of
these fruits (sometimes three or four) in each larkspur flower, each
pistil ripening into a follicle. If these pistils were united, a single
compound pistil would be formed. Columbine, peony, ninebark, milkweed,
also have follicles.
[Illustration: FIG. 231.--FOLLICLE OF LARKSPUR.]
[Illustration: FIG. 233.--CAPSULE OF CASTOR-OIL BEAN AFTER DEHISCENCE.]
[Illustration: FIG. 232.--A BEAN POD.]
A 1-loculed pericarp that dehisces on both edges is a =legume=. Peas
and beans are typical examples (Fig. 232); in fact, this character
gives name to the pea family,--Leguminosæ. Often the valves of the
legume twist forcibly and expel the seeds, throwing them some distance.
The word “pod” is sometimes restricted to legumes, but it is better to
use it generically for all dehiscent pericarps.
A compound pod--dehiscing pericarp of two or more carpels--is a
=capsule= (Figs. 233, 234, 236, 237). Some capsules are of one locule,
but they may have been compound when young (in the ovary stage) and the
partitions may have vanished. Sometimes one or more of the carpels are
uniformly crowded out by the exclusive growth of other carpels (Fig.
235). The seeds or parts which are crowded out are said to be _aborted_.
[Illustration: FIG. 234.--CAPSULE OF MORNING GLORY.]
[Illustration: FIG. 235.--THREE-CARPELED FRUIT OF HORSE-CHESTNUT. Two
locules are closing by abortion of the ovules.]
There are several ways in which capsules dehisce or open. When
they break _along the partitions_ (or septa), the mode is known as
=septicidal dehiscence= (Fig. 236); In septicidal dehiscence the fruit
separates into parts representing the original carpels. These carpels
may still be entire, and they then dehisce individually, usually along
the inner edge as if they were follicles. When the compartments _split
in the middle, between the partitions_, the mode is =loculicidal
dehiscence= (Fig. 237). In some cases the dehiscence is _at the top_,
when it is said to be =apical= (although several modes of dehiscence
are here included). When the _whole top comes off_, as in purslane and
garden portulaca (Fig. 238), the pod is known as a =pyxis=. In some
cases apical dehiscence is by means of a hole or clefts.
[Illustration: FIG. 236.--ST. JOHN’S WORT. Septicidal.]
[Illustration: FIG. 237.--LOCULICIDAL POD OF DAY-LILY.]
The peculiar capsule of the mustard family, or Cruciferæ, is known as
a =silique= when it is distinctly longer than broad (Fig. 224), and
a =silicle= when its breadth nearly equals or exceeds its length. A
cruciferous capsule is 2-carpeled, with a thin partition, each locule
containing seeds in two rows. The two valves detach from below upwards.
Cabbage, turnip, mustard, water-cress, radish, rape, shepherd’s purse,
sweet alyssum, wallflower, honesty, are examples.
[Illustration: FIG. 238.--PYXIS OF PORTULACA OR ROSE-MOSS.]
[Illustration: FIG. 239.--BERRIES OF GOOSEBERRY. Remains of calyx at
_c_.]
[Illustration: FIG. 240.--BERRY OF THE GROUND CHERRY OR HUSK TOMATO,
contained in the inflated calyx.]
[Illustration: FIG. 241.--ORANGE; example of a berry.]
The pericarp may be _fleshy and indehiscent_. A pulpy pericarp
with several or many seeds is a =berry= (Figs. 239, 240, 241). To
the horticulturist a berry is a small, soft, edible fruit, without
particular reference to its structure. The botanical and horticultural
conceptions of a berry are, therefore, unlike. In the botanical sense,
gooseberries, currants, grapes, tomatoes, potato-balls, and even
eggplant fruits and oranges (Fig. 241) are berries; strawberries,
raspberries, blackberries are not.
[Illustration: FIG. 242.--PLUM; example of a drupe.]
A fleshy pericarp containing one relatively large seed or stone is a
=drupe=. Examples are plum (Fig. 242), peach, cherry, apricot, olive.
The walls of the pit in the plum, peach, and cherry are formed from the
inner coats of the ovary, and the flesh from the outer coats. Drupes
are also known as _stone-fruits_.
[Illustration: FIG. 243.--FRUIT OF RASPBERRY.]
[Illustration: FIG. 244.--AGGREGATE FRUIT OF MULBERRY; and a separate
fruit.]
Fruits that are formed by the subsequent union of separate pistils are
=aggregate fruits=. The carpels in aggregate fruits are usually more or
less fleshy. In the raspberry and blackberry flower, the pistils are
essentially distinct, but as the pistils ripen they cohere and form one
body (Figs. 243, 244). Each of the carpels or pistils in the raspberry
and blackberry is a little drupe, or =drupelet=. In the raspberry the
entire fruit separates from the torus, leaving the torus on the plant.
In the blackberry and dewberry the fruit adheres to the torus, and the
two are removed together when the fruit is picked.
=Accessory Fruits.=--When the pericarp and some other part grow
together, the fruit is said to be =accessory= or =reënforced=. An
example is the strawberry (Fig. 245). The edible part is a greatly
_enlarged torus_, and the pericarps are akenes embedded in it. These
akenes are commonly called seeds.
[Illustration: FIG. 245.--STRAWBERRY; fleshy torus in which akenes are
embedded.]
Various kinds of reënforced fruits have received special names. One of
these is the =hip=, characteristic of roses. In this case, the torus is
deep and hollow, like an urn, and the separate akenes are borne inside
it. The mouth of the receptacle may close, and the walls sometimes
become fleshy; the fruit may then be mistaken for a berry. The fruit of
the pear, apple, and quince is known as a =pome=. In this case the five
united carpels are completely buried in the hollow torus, and the torus
makes most of the edible part of the ripe fruit, while the pistils are
represented by the core (Fig. 246). Observe the sepals on the top of
the torus (apex of the fruit) in Fig. 246. Note the outlines of the
embedded pericarp in Fig. 247.
[Illustration: FIG. 246.--SECTION OF AN APPLE.]
[Illustration: FIG. 247.--CROSS-SECTION OF AN APPLE.]
=Gymnospermous Fruits.=--In pine, spruces, and their kin, there is no
fruit in the sense in which the word is used in the preceding pages,
because _there is no ovary_. The ovules are naked or uncovered, in the
axils of the scales of the young cone, and they have neither style nor
stigma. The pollen falls directly on the mouth of the ovule. The ovule
ripens into a seed, which is usually winged. Because the ovule is not
borne in a sac or ovary, these plants are called =gymnosperms= (Greek
for “naked seeds”). All the true cone-bearing plants are of this class;
also certain other plants, as red cedar, juniper, yew. The plants are
monœcious or sometimes diœcious. The staminate flowers are mere naked
stamens borne beneath scales, in small yellow catkins which soon fall.
The pistillate flowers are naked ovules beneath scales on cones that
persist (Fig. 29). Gymnospermous seeds may have several cotyledons.
SUGGESTIONS.--=168.= Study the following fruits, or any five fruits
chosen by the teacher, and answer the questions for each: Apple,
peach, bean, tomato, pumpkin. What is its form? Locate the scar left
by the stem. By what kind of a stem was it attached? Is there any
remains of the blossom at the blossom end? Describe texture and color
of surface. Divide the fruit into the seed vessel and the surrounding
part. Has the fruit any pulp or flesh? Is it within or without the
seed vessel? Is the seed vessel simple or subdivided? What is the
number of seeds? Are the seeds free, attached to the wall of the
vessel, or to a support in the center? Are they arranged in any
order? What kind of wall has the seed vessel? What is the difference
between a peach stone and a peach seed? =169.= The nut fruits
are always available for study. Note the points suggested above.
Determine what the meat or edible part represents, whether cotyledons
or not. Figure 248 is suggestive. =170.= Mention all the fleshy
fruits you know, tell where they come from, and refer them to their
proper groups. =171.= What kinds of fruits can you buy in the market,
and to what groups or classes do they belong? Of which ones are the
seeds only, and not the pericarps, eaten? =172.= An ear of corn is
always available for study. What is it--a fruit or a collection of
fruits? How are the grains arranged on the cob? How many rows do you
count on each of several ears? Are all the rows on an ear equally
close together? Do you find an ear with an odd number of rows? How
do the parts of the husk overlap? Does the husk serve as protection
from rain? Can birds pick out the grains? How do insect enemies enter
the ear? How and when do weevils lay eggs on corn? =173.= _Study a
grain of corn._ Is it a seed? Describe the shape of a grain. Color.
Size. Does its surface show any projections or depressions? Is the
seed-coat thin or thick? Transparent or opaque? Locate the hilum.
Where is the silk scar? What is the silk? Sketch the grain from the
two points of view that show it best. Where is the embryo? Does the
grain have endosperm? What is dent corn? Flint corn? How many kinds
of corn do you know? For what are they used?
[Illustration: FIG. 248.--PECAN FRUIT.]
NOTE TO TEACHER.--There are few more interesting subjects to
beginning pupils than fruits,--the pods of many kinds, forms, and
colors, the berries, and nuts. This interest may well be utilized
to make the teaching alive. All common edible fruits of orchard and
vegetable garden should be brought into this discussion (some of
the kinds are explained in “Lessons with Plants”). Of dry fruits,
as pods, burs, nuts, collections may be made for the school museum.
Fully mature fruits are best for study, particularly if it is desired
to see dehiscence. For comparison, pistils and partially grown fruits
should be had at the same time. If the fruits are not ripe enough to
dehisce, they may be placed in the sun to dry. In the school it is
well to have a collection of fruits for study. The specimens may be
kept in glass jars. _Always note exterior of fruit and its parts:
interior of fruit with arrangement and attachment of contents._
CHAPTER XXII
DISPERSAL OF SEEDS
It is to the plant’s advantage to have its seeds distributed as widely
as possible. _It has a better chance of surviving in the struggle for
existence._ It gets away from competition. Many seeds and fruits are
of such character as to increase their chances of wide dispersal. The
commonest means of dissemination may be classed under four heads:
_explosive fruits_; _transportation by wind_; _transportation by
birds_; _burs_.
[Illustration: FIG. 249.--EXPLOSION OF THE BALSAM POD.]
[Illustration: FIG. 250.--EXPLOSIVE FRUITS OF OXALIS.
An exploding pod is shown at _c_. The dehiscence is shown at _b_. The
structure of the pod is seen at _a_.]
=Explosive Fruits.=--_Some pods open with explosive force and discharge
the seeds._ Even bean and everlasting peas do this. More marked
examples are the locust, witch hazel, garden balsam (Fig. 249), wild
jewel-weed or impatiens (touch-me-not), violet, crane’s-bill or wild
geranium, bull nettle, morning glory, and the oxalis (Fig. 250). The
oxalis is common in several species in the wild and cultivation. One of
them is known as wood sorrel. Fig. 250 shows the common yellow oxalis.
The pod opens loculicidally. The elastic tissue suddenly contracts
when dehiscence takes place, and the seeds are thrown violently.
The squirting cucumber is easily grown in a garden (procure seeds
of seedsmen), and the fruits discharge the seeds with great force,
throwing them many feet.
=Wind Travelers.=--Wind-transported seeds are of two general kinds:
those that are _provided with wings_, as the flat seeds of catalpa
(Fig. 251) and cone-bearing trees and the samaras of ash, elm,
tulip-tree, ailanthus, and maple; and those which have _feathery buoys_
or _parachutes_ to enable them to float in the air. Of the latter kind
are the fruits of many composites, in which the pappus is copious and
soft. Dandelion and thistle are examples. The silk of the milkweed and
probably the hairs on the cotton seed have a similar office, and also
the wool of the cat-tail. Recall the cottony seeds of the willow and
poplar.
[Illustration: FIG. 251.--WINGED SEEDS OF CATALPA.]
=Dispersal by Birds.=--_Seeds of berries and of other small fleshy
fruits are carried far and wide by birds._ The pulp is digested,
but the seeds are not injured. Note how the cherries, raspberries,
blackberries, June-berries, and others spring up in the fence rows,
where the birds rest. Some berries and drupes persist far into winter,
when they supply food to cedar birds, robins, and the winter birds.
Red cedar is distributed by birds. Many of these pulpy fruits are
agreeable as human food, and some of them have been greatly enlarged
or “improved” by the arts of the cultivator. The seeds are usually
indigestible.
=Burs.=--Many seeds and fruits bear spines, hooks, and hairs, which
_adhere to the coats of animals and to clothing_. The burdock has an
involucre with hooked scales, containing the fruits inside. The clotbur
is also an involucre. Both are compositous plants, allied to thistles,
but the whole head, rather than the separate fruits, is transported. In
some compositous fruits the pappus takes the form of hooks and spines,
as in the “Spanish bayonets” and “pitchforks.” Fruits of various kinds
are known as “stick tights,” as of the agrimony and hound’s-tongue.
Those who walk in the woods in late summer and fall are aware that
plants have means of disseminating themselves (Fig. 252). If it is
impossible to identify the burs which one finds on clothing, the seeds
may be planted and specimens of the plant may then be grown.
[Illustration: FIG. 252.--STEALING A RIDE.]
SUGGESTIONS.--=174.= What advantage is it to the plant to have its
seeds widely dispersed? =175.= What are the leading ways in which
fruits and seeds are dispersed? =176.= Name some explosive fruits.
=177.= Describe wind travelers. =178.= What seeds are carried by
birds? =179.= Describe some bur with which you are familiar. =180.=
Are adhesive fruits usually dehiscent or indehiscent? =181.= Do
samaras grow on low or tall plants, as a rule? =182.= Are the cotton
fibers on the seed or on the fruit? =183.= Name the ways in which the
common weeds of your region are disseminated. =184.= This lesson will
suggest other ways in which seeds are transported. Nuts are buried
by squirrels for food; but if they are not eaten, they may grow. The
seeds of many plants are blown on the snow. The old stalks of weeds,
standing through the winter, may serve to disseminate the plant.
Seeds are carried by water down the streams and along shores. About
woolen mills strange plants often spring up from seed brought in the
fleeces. Sometimes the entire plant is rolled for miles before the
winds. Such plants are “tumbleweeds.” Examples are Russian thistle,
hair grass or tumblegrass (_Panicum capillare_), cyclone plant
(_Cycloloma platyphyllum_), and white amaranth (_Amarantus albus_).
About seaports strange plants are often found, having been introduced
in the earth that is used in ships for ballast. These plants are
usually known as “ballast plants.” Most of them do not persist long.=
185.= Plants are able to spread themselves by means of the great
numbers of seeds that they produce. How many seeds may a given elm
tree or apple tree or raspberry bush produce?
[Illustration: FIG. 253.--THE FRUITS OF THE CAT-TAIL ARE LOOSENED BY
WIND AND WEATHER.]
CHAPTER XXIII
PHENOGAMS AND CRYPTOGAMS
The plants thus far studied produce flowers; and the flowers produce
=seeds= by means of which the plant is propagated. There are other
plants, however, that produce no seeds, and these plants (including
bacteria) are probably more numerous than the seed-bearing plants.
These plants propagate by means of =spores=, _which are generative
cells, usually simple, containing no embryo_. These spores are very
small, and sometimes are not visible to the naked eye.
[Illustration: FIG. 254.--CHRISTMAS FERN.--Dryopteris acrostichoides;
known also as Aspidium.]
[Illustration: FIG. 255.--FRUITING FROND OF CHRISTMAS FERN.
Sori at _a_. One sorus with its indusium at _b_.]
Prominent among the spore-propagated plants are _ferns_. The common
_Christmas fern_ (so called because it remains green during winter) is
shown in Fig. 254. The plant has no trunk. The leaves spring directly
from the ground. The leaves of ferns are called =fronds=. They vary
in shape, as other leaves do. Some of the fronds in Fig. 254 are seen
to be narrower at the top. If these are examined more closely (Fig.
255), it will be seen that the leaflets are contracted and are densely
covered beneath with brown bodies. These bodies are collections of
=sporangia= or =spore-cases=.
[Illustration: FIG. 256.--COMMON POLYPODE FERN. Polypodium vulgare.]
[Illustration: FIG. 257.--SORI AND SPORANGIUM OF POLYPODE. A chain
of cells lies along the top of the sporangium, which springs back
elastically on drying, thus disseminating the spores.]
[Illustration: FIG. 258.--THE BRAKE FRUITS UNDERNEATH THE REVOLUTE
EDGES OF THE LEAF.]
[Illustration: FIG. 259.--FRUITING PINNULES OF MAIDENHAIR FERN.]
The sporangia are collected into little groups, known as =sori=
(singular, sorus) or =fruit-dots=. Each sorus is covered with a thin
scale or shield, known as an =indusium=. This indusium separates from
the frond at its edges, and the sporangia are exposed. Not all ferns
have indusia. The polypode (Figs. 256, 257) does not; the sori are
naked. In the brake (Fig. 258) and maidenhair (Fig. 259) the edge of
the frond turns over and forms an indusium. The nephrolepis or sword
fern of greenhouses is allied to the polypode. The sori are in a single
row on either side the midrib (Fig. 260). The indusium is circular or
kidney-shaped and open at one edge or finally all around. The Boston
fern, Washington fern, Pierson fern, and others, are horticultural
forms of the common sword fern. In some ferns (Fig. 261) an entire
frond becomes contracted to cover the sporangia.
[Illustration: FIG. 260.--PART OF FROND OF SWORD FERN. To the pupil: Is
this illustration right side up?]
[Illustration: FIG. 261.--FERTILE AND STERILE FRONDS OF THE SENSITIVE
FERN.]
The sporangium or spore-case of a fern is a more or less globular body
and usually with a stalk (Fig. 257). _It contains the spores. When ripe
it bursts and the spores are set free._
In a moist, warm place _the spores germinate_. They produce a small,
flat, thin, green, more or less heart-shaped membrane (Fig. 262).
This is the =prothallus=. Sometimes the prothallus is an inch or more
across, but oftener it is less than a dime in size. Although easily
seen, it is commonly unknown except to botanists. Prothalli may often
be found in greenhouses where ferns are grown. Look on the moist stone
or brick walls, or on the firm soil of undisturbed pots and beds; or
spores may be sown in a damp, warm place.
[Illustration: FIG. 262.--PROTHALLUS OF A FERN. ENLARGED.
Archegonia at _a_; antheridia at _b_.]
On the under side of the prothallus two kinds of organs are
borne. These are the =archegonium= (containing egg-cells) and the
=antheridium= (containing sperm-cells). These organs are minute
specialized parts of the prothallus. Their positions on a particular
prothallus are shown at _a_ and _b_ in Fig. 262, but in some ferns
they are on separate prothalli (plant diœcious). _The sperm-cells
escape from the antheridium and in the water that collects on the
prothallus are carried to the archegonium, where fertilization of the
egg takes place._ From the fertilized egg-cell a plant grows, becoming
a “fern.” In most cases the prothallus soon dies. The prothallus is the
=gametophyte= (from Greek, signifying the fertilized plant).
The fern plant, arising from the fertilized egg in the archegonium,
becomes a perennial plant, each year producing spores from its fronds
(called the =sporophyte=); but these spores--which are merely detached
special kinds of cells--produce the prothallic phase of the fern plant,
from which new individuals arise. _A fern is fertilized but once in
its lifetime._ The “fern” bears the spore, the spore gives rise to the
prothallus, and the egg-cell of the prothallus (when fertilized) gives
rise to the fern.
A similar =alternation of generations= runs all through the vegetable
kingdom, although there are some groups of plants in which it is very
obscure or apparently wanting. It is very marked in ferns and mosses.
In algæ (including the seaweeds) the gametophyte is the “plant,” as the
non-botanist knows it, and the sporophyte is inconspicuous. _There is
a general tendency, in the evolution of the vegetable kingdom, for the
gametophyte to lose its relative importance and for the sporophyte to
become larger and more highly developed._ In the seed-bearing plants
the sporophyte generation is the only one seen by the non-botanist. The
gametophyte stage is of short duration and the parts are small; it is
confined to the time of fertilization.
The sporophyte of seed plants, or the “plant” as we know it, produces
two kinds of spores--one kind becoming =pollen-grains= and the
other kind =embryo-sacs=. The pollen-spores are borne in sporangia,
which are united into what are called =anthers=. The embryo-sac,
which contains the egg-cell, is borne in a sporangium known as an
=ovule=. _A gametophytic stage is present in both pollen and embryo
sac: fertilization takes place, and a sporophyte arises. Soon this
sporophyte becomes dormant, and is then known as an_ =embryo=. The
embryo is packed away within tight-fitting coats, and the entire body
is the =seed=. When the conditions are right the seed grows, and
the sporophyte grows into herb, bush, or tree. The utility of the
alternation of generations is not understood.
The spores of ferns are borne on leaves; the spores of seed-bearing
plants are also borne amongst a mass of specially developed conspicuous
leaves known as =flowers=, therefore these plants have been known as
the =flowering plants=. Some of the leaves are developed as envelopes
(calyx, corolla), and others as spore-bearing parts, or =sporophylls=
(stamens, pistils). But the spores of the lower plants, as of ferns
and mosses, may also be borne in specially developed foliage, so
that the line of demarcation between flowering plants and flowerless
plants is not so definite as was once supposed. The one definite
distinction between these two classes of plants is the fact that _one
class produces seeds and the other does not_. The seed-plants are now
often called =spermaphytes=, but there is no single coördinate term
to set off those which do not bear seeds. It is quite as well, for
popular purposes, to use the terms =phenogams= for the seed-bearing
plants and =cryptogams= for the others. These terms have been objected
to in recent years because their etymology does not express literal
facts (_phenogam_ signifying “showy flowers,” and _cryptogam_ “hidden
flowers”), but the terms represent distinct ideas in classification.
The cryptogams include three great series of plants--the =Thallophytes=
or algæ, lichens, and fungi; the =Bryophytes= or mosslike plants; the
=Pteridophytes= or fernlike plants.
[Illustration: FIG. 263.--DIAGRAM TO EXPLAIN THE TERMINOLOGY OF THE
FROND.]
SUGGESTIONS.--=186.= _The parts of a fern leaf._ The primary complete
divisions of a frond are called pinnæ, no matter whether the frond
is pinnate or not. In ferns the word “pinna” is used in essentially
the same way that leaflet is in the once-compound leaves of other
plants. The secondary leaflets are called pinnules, and in thrice,
or more, compound fronds, the last complete parts or leaflets are
ultimate pinnules. The diagram (Fig. 263) will aid in making the
subject clear. If the frond were not divided to the midrib, it would
be simple, but this diagram represents a compound frond. The general
outline of the frond, as bounded by the dotted line, is ovate. The
stipe is very short. The midrib of a compound frond is known as
the rachis. In a decompound frond, this main rachis is called the
primary rachis. Segments (not divided to the rachis) are seen at the
tip, and down to _h_ on one side and to _m_ on the other. Pinnæ are
shown at _i_, _k_, _l_, _o_, _n_. The pinna _o_ is entire; _n_ is
crenate-dentate; _i_ is sinuate or wavy, with an auricle at the base;
_k_ and _l_ are compound. The pinna _k_ has twelve entire pinnules.
(Is there ever an even number of pinnules on any pinna?) Pinna _l_
has nine compound pinnules, each bearing several entire ultimate
pinnules. _The spores._--=187.= Lay a mature fruiting frond of any
fern on white paper, top side up, and allow it to remain in a dry,
warm place. The spores will discharge on the paper. =188.= Lay the
full-grown (but not dry) cap of a mushroom or toadstool bottom down
on a sheet of clean paper, under a ventilated box in a warm, dry
place. A day later raise the cap.
CHAPTER XXIV
STUDIES IN CRYPTOGAMS
The pupil who has acquired skill in the use of the compound microscope
may desire to make more extended excursions into the cryptogamous
orders. The following plants have been chosen as examples in various
groups. Ferns are sufficiently discussed in the preceding chapter.
BACTERIA
If an infusion of ordinary hay is made in water and allowed to stand,
it becomes turbid or cloudy after a few days, and a drop under the
microscope will show the presence of minute oblong cells swimming in
the water perhaps by means of numerous hair-like appendages, that
project through the cell wall from the protoplasm within. At the
surface of the dish containing the infusion the cells are non-motile
and are united in long chains. Each of these cells or organisms is a
_bacterium_ (plural, _bacteria_). (Fig. 135.)
Bacteria are very minute organisms,--the smallest known,--consisting
either of separate oblong or spherical cells, or of chains, plates,
or groups of such cells, depending on the kind. They possess a
membrane-like wall which, unlike the cell walls of higher plants,
contains nitrogen. The presence of a nucleus has not been definitely
demonstrated. Multiplication is by the fission of the vegetative
cells; but under certain conditions of drought, cold, or exhaustion
of the nutrient medium, the protoplasm of the ordinary cells may
become invested with a thick wall, thus forming an _endospore_ which
is very resistant to extremes of environment. No sexual reproduction
is known.
Bacteria are very widely distributed as parasites and saprophytes in
almost all conceivable places. _Decay_ is largely caused by bacteria,
accompanied in animal tissue by the liberation of foul-smelling
gases. Certain species grow in the reservoirs and pipes of water
supplies, rendering the water brackish and often undrinkable. Some
kinds of _fermentation_ (the breaking down or decomposing of organic
compounds, usually accompanied by the formation of gas) are due to
these organisms. Other bacteria oxidize alcohol to _acetic acid_, and
produce _lactic acid_ in milk and _butyric acid_ in butter. Bacteria
live in the mouth, stomach, intestines, and on the surface of the
skin of animals. Some secrete gelatinous sheaths around themselves;
others secrete sulfur or iron, giving the substratum a vivid color.
Were it not for bacteria, man could not live on the earth, for not
only are they agents in the process of decay, but they are concerned
in certain healthful processes of plants and animals. We have learned
in Chap. VIII how bacteria are related to nitrogen-gathering.
Bacteria are of economic importance not alone because of their effect
on materials used by man, but also because of the _disease-producing
power_ of certain species. _Pus_ is caused by a spherical form,
_tetanus_ or _lock-jaw_ by a rod-shaped form, _diphtheria_ by short
oblong chains, _tuberculosis_ or “_consumption_” by more slender
oblong chains, and _typhoid fever_, _cholera_, and other diseases
by other forms. Many _diseases of animals and plants_ are caused by
bacteria. Disease-producing bacteria are said to be _pathogenic_.
The ability to grow in other nutrient substances than the natural
one has greatly facilitated the study of these minute forms of life.
By the use of suitable culture media and proper precautions, _pure
cultures_ of a particular disease-producing bacterium may be obtained
with which further experiments may be conducted.
Milk provides an excellent collecting place for bacteria coming
from the air, from the coat of the cow and from the milker. Disease
germs are sometimes carried in milk. If a drop of milk is spread on
a culture medium (as agar), and provided with proper temperature,
the bacteria will multiply, each one forming a colony visible to the
naked eye. In this way, the number of bacteria originally contained
in the milk may be counted.
Bacteria are disseminated in water, as the germ of typhoid fever and
cholera; in milk and other fluids; in the air; and on the bodies of
flies, feet of birds, and otherwise.
Bacteria are thought by many to have descended from algæ by the loss
of chlorophyll and decrease in size due to the more specialized
acquired saprophytic and parasitic habit.
ALGÆ
The algæ comprise most of the green floating “scum” which covers the
surfaces of ponds and other quiet waters. The masses of plants are
often called “frog spittle.” Others are attached to stones, pieces of
wood, and other objects submerged in streams and lakes, and many are
found on moist ground and on dripping rocks. Aside from these, all
the plants commonly known as seaweeds belong to this category; these
latter are inhabitants of salt water.
The simplest forms of algæ consist of a single spherical cell, which
multiplies by repeated division or fission. Many of the forms found
in fresh water are filamentous, _i.e._ the plant body consists of
long threads, either simple or branched. Such a plant body is termed
a _thallus_. This term applies to the vegetative body of all plants
that are _not differentiated into stem and leaves_. Such plants are
known as _thallophytes_ (p. 181). All algæ contain chlorophyll, and
are able to assimilate carbon dioxid from the air. This distinguishes
them from the fungi.
_Nostoc._--On wet rocks and damp soil dark, semitransparent irregular
or spherical gelatinous masses about the size of a pea are often
found. These consist of a colony of contorted filamentous algæ
embedded in the jelly-like mass. The chain of cells in the filament
is necklace-like. Each cell is homogeneous, without apparent
nucleus, and blue-green in color, except one cell which is larger
and clearer than the rest. The plant therefore belongs to the group
of _blue-green algæ_. The jelly probably serves to maintain a more
even moisture and to provide mechanical protection. Multiplication is
wholly by the breaking up of the threads. Occasionally certain cells
of the filament thicken to become _resting-spores_, but no other
spore formation occurs.
[Illustration: FIG. 264.--FILAMENT OF OSCILLATORIA, showing one dead
cell where the strand will break.]
_Oscillatoria._--The blue-green coatings found on damp soil and
in water frequently show under the microscope the presence of
filamentous algæ composed of many short homogeneous cells (Fig. 264).
If watched closely, some filaments will be seen to wave back and
forth slowly, showing a peculiar power of movement characteristic
of this plant. Multiplication is by the breaking up of the threads.
There is no true spore formation.
[Illustration: FIG. 265.--_Strand of Spirogyra_, showing the
chlorophyll bands. There is a nucleus at _a_. How many cells, or parts
of cells, are shown in this figure?]
SPIROGYRA.--One of the most common forms of the green algæ is
spirogyra (Fig. 265). This plant often forms the greater part of the
floating green mass (or “frog spittle”) on ponds. The threadlike
character of the thallus can be seen with the naked eye or with a
hand lens, but to study it carefully a microscope magnifying two
hundred diameters or more must be used. The thread is divided into
long cells by cross walls which, according to the species, are either
straight or curiously folded (Fig. 266). The chlorophyll is arranged
in _beautiful spiral bands_ near the wall of each cell. From the
character of these bands the plant takes its name. Each cell is
provided with a _nucleus_ and other _protoplasm_. The nucleus is
suspended near the center of the cell (_a_, Fig. 265) by delicate
strands of protoplasm radiating toward the wall and terminating
at certain points in the chlorophyll band. The remainder of the
protoplasm forms a thin layer lining the wall. The interior of the
cell is filled with cell-sap. The protoplasm and nucleus cannot be
easily seen, but if the plant is stained with a dilute alcoholic
solution of eosin they become clear.
Spirogyra is propagated vegetatively by the breaking off of parts of
the threads, which continue to grow as new plants. Resting-spores,
which may remain dormant for a time, are formed by a process known
as _conjugation_. Two threads lying side by side send out short
projections, usually from all the cells of a long series (Fig. 266).
The projections or processes from opposite cells grow toward each
other, meet, and fuse, forming a connecting tube between the cells.
The protoplasm, nucleus, and chlorophyll band of one cell now pass
through this tube, and unite with the contents of the other cell. The
entire mass then becomes surrounded by a thick cellulose wall, thus
completing the _resting-spore_, or _zygospore_ (_z_, Fig. 266).
[Illustration: FIG. 266.--CONJUGATION OF SPIROGYRA. Ripe zygospores on
the left; _a_, connecting tubes.]
[Illustration: FIG. 267.--STRAND, OR FILAMENT OF ZYGNEMA, freed from
its gelatinous covering.]
_Zygnema_ is an alga closely related to spirogyra and found in
similar places. Its life history is practically the same, but it
differs from spirogyra in having _two star-shaped chlorophyll bodies_
(Fig. 267) in each cell, instead of a chlorophyll-bearing spiral band.
[Illustration: FIG. 268.--THREAD OF VAUCHERIA WITH OÖGONIA AND
ANTHERIDIA.]
_Vaucheria_ is another alga common in shallow water and on damp
soil. The thallus is much branched, but the threads are not divided
by cross walls as in spirogyra. The plants are attached by means of
colorless root-like organs which are much like the root hairs of the
higher plants: these are _rhizoids_. The chlorophyll is in the form
of _grains scattered through the thread_.
Vaucheria has a special mode of asexual reproduction by means of
swimming spores or _swarm-spores_. These are formed singly in a
short enlarged lateral branch known as the _sporangium_. When the
sporangium bursts, the entire contents escape, forming a single large
swarm-spore, which swims about by means of numerous lashes or cilia
on its surface. The swarm spores are so large that they can be seen
with the naked eye. After swimming about for some time they come to
rest and germinate, producing a new plant.
The formation of resting-spores of vaucheria is accomplished by means
of special organs, _oögonia_ (_o_, Fig. 268) and _antheridia_ (_a_,
Fig. 268). Both of these are specially developed branches from the
thallus. The antheridia are nearly cylindrical, and curved toward
the oögonia. The upper part of an antheridium is cut off by a cross
wall, and within it numerous ciliated _sperm-cells_ are formed. These
escape by the ruptured apex of the antheridium. The oögonia are more
enlarged than the antheridia, and have a beak-like projection turned
a little to one side of the apex. They are separated from the thallus
thread by a cross wall, and contain a single large green cell, the
_egg-cell_. The apex of the oögonium is dissolved, and through the
opening the sperm-cells enter. Fertilization is thus accomplished.
After fertilization the egg-cell becomes invested with a thick wall
and is thus converted into a resting-spore, the _oöspore_.
_Fucus._--These are rather large specialized algæ belonging to the
group known as brown seaweeds and found attached by a disk to the
rocks of the seashore just below high tide (Fig. 269). They are firm
and strong to resist wave action and are so attached as to avoid
being washed ashore. They are very abundant algæ. In shape the plants
are long, branched, and multicellular, with either flat or terete
branches. They are olive-brown. Propagation is by the breaking off of
the branches. No zoöspores are produced, as in many other seaweeds;
and reproduction is wholly sexual. The _antheridia_, bearing
_sperm-cells_, and the _oögonia_, each bearing eight _egg-cells_,
are sunken in pits or _conceptacles_. These pits are aggregated in
the swollen lighter colored tips of some of the branches (_s_, _s_,
Fig. 269). The egg-cells and sperm-cells escape from the pits and
fertilization takes place in the water. The matured eggs, or spores,
reproduce the fucus plant directly.
[Illustration: FIG. 269.--FUCUS. Fruiting branches at _s_, _s_. On the
stem are two air-bladders.]
[Illustration: FIG. 270.--NITELLA.]
_Nitella._--This is a large branched and specialized fresh-water alga
found in tufts attached to the bottom in shallow ponds (Fig. 270).
Between the whorls of branches are long _internodes consisting of a
single cylindrical cell_, which is one of the largest cells known in
vegetable tissue. Under the microscope the walls of this cell are
found to be lined with a layer of small stationary chloroplastids,
within which layer the protoplasm, under favorable circumstances,
will be found in motion, moving up one side and down the other (in
rotation). Note the clear streak up the side of the cell and its
relation to the moving current.
FUNGI
Some forms of fungi are familiar to every one. Mushrooms and
toadstools, with their varied forms and colors, are common in fields,
woods, and pastures. In every household the common molds are familiar
intruders, appearing on old bread, vegetables, and even within
tightly sealed fruit jars, where they form a felt-like layer dusted
over with blue, yellow, or black powder. The strange occurrence of
these plants long mystified people, who thought they were productions
of the dead matter upon which they grew, but now we know that a mold,
as any other plant, cannot originate spontaneously; it must start
from something which is analogous to a seed. The “seed” in this case
is a _spore_. A spore may be produced by a _vegetative process_
(growing out from the ordinary plant tissues), or it may be the
result of a _fertilization process_.
_Favorable conditions for the growth of fungi._--Place a piece of
bread under a moist bell jar and another in an uncovered place near
by. Sow mold on each. Note the result from day to day. Moisten a
third piece of bread with weak copper sulfate (blue vitriol) or
mercuric chlorid solution, sow mold, cover with bell jar, note
results, and explain. Expose pieces of different kinds of food in
a damp atmosphere and observe the variety of organisms appearing.
Fungi are saprophytes or parasites, and must be provided with organic
matter on which to grow. They are usually most abundant in moist
places and wet seasons.
[Illustration: FIG. 271.--MUCOR MUCEDO, showing habit.]
[Illustration: FIG. 272.--SPORES OF MUCOR, some germinating.]
_Mold._--One of these molds (_Mucor mucedo_), which is very common on
all decaying fruits and vegetables, is shown in Fig. 271, somewhat
magnified. When fruiting, this mold appears as a _dense mass of long
white hairs_, often over an inch high, standing erect from the fruit
or vegetable on which it is growing.
The life of this mucor begins with a minute rounded spore (_a_,
Fig. 272), which lodges on the decaying material. When the spore
germinates, it sends out a delicate thread that grows rapidly in
length and forms very many branches that soon permeate every part
of the substance on which the plant grows (_b_, Fig. 272). One of
these threads is termed a _hypha_. All the threads together form the
_mycelium_ of the fungus. The mycelium disorganizes the material in
which it grows, and thus the mucor plant (Fig. 271) is nourished. It
corresponds physiologically to the roots and stems of other plants.
When the mycelium is about two days old, it begins to form the
long fruiting stalks which we first noticed. To study them, use a
compound microscope magnifying about two hundred diameters. One of
the stalks, magnified, is shown in _a_, Fig. 274. It consists of a
rounded head, the _sporangium, sp_, supported on a long, delicate
stalk, the _sporangiophore_. The stalk is separated from the
sporangium by a wall which is formed at the base of the sporangium.
This wall, however, does not extend straight across the thread, but
it arches up into the sporangium like an inverted pear. It is known
as the _columella, c_. When the sporangium is placed in water, the
wall immediately dissolves and allows hundreds of spores, which
were formed in the cavity within the sporangium, to escape, _b_.
All that is left of the fruit is the stalk, with the pear-shaped
columella at its summit, _c_. The spores that have been set free by
the breaking of the sporangium wall are now scattered by the wind
and other agents. Those that lodge in favorable places begin to grow
immediately and reproduce the fungus. The others soon perish.
[Illustration: FIG. 273.--MUCOR, showing formation of zygospore on the
right; germinating zygospore on the left.]
[Illustration: FIG. 274.--MUCOR.
_a_, sporangium; _b_, sporangium bursting; _c_, columella.]
The mucor may continue to reproduce itself in this way indefinitely,
but these spores are very delicate and usually die if they do not
fall on favorable ground, so that the fungus is provided with another
means of carrying itself over unfavorable seasons, as winter. This
is accomplished by means of curious _thick-walled resting-spores_
or _zygospores_. The zygospores are formed on the mycelium buried
within the substance on which the plant grows. They originate in the
following way: Two threads that lie near together send out short
branches, which grow toward each other and finally meet (Fig. 273).
The walls at the ends, _a_, then disappear, allowing the contents to
flow together. At the same time, however, two other walls are formed
at points farther back, _b_, _b_, separating the short section, _c_,
from the remainder of the thread. This section now increases in size
and becomes covered with a thick, dark brown wall ornamented with
thickened tubercles. The zygospore is now mature and, after a period
of rest, it germinates, either producing a sporangium directly or
growing out as mycelium.
The zygospores of the mucors form one of the most interesting and
instructive objects among the lower plants. They are, however, very
difficult to obtain. One of the mucors (_Sporodinia grandis_) may be
frequently found in summer growing on toadstools. This plant usually
produces zygospores that are formed on the aërial mycelium. The
zygospores are large enough to be recognized with a hand lens. The
material may be dried and kept for winter study, or the zygospores
may be prepared for permanent microscopic mounts in the ordinary way.
[Illustration: FIG. 275.--YEAST PLANTS.]
_Yeast._--This is a very much reduced and simple fungus, consisting
normally of isolated spherical or elliptical cells (Fig. 275)
containing abundant protoplasm and probably a nucleus, although the
latter is not easily observed. It propagates rapidly by _budding_,
which consists of the gradual extrusion of a wart-like swelling that
is sooner or later cut off at the base by constriction, thus forming
a separate organism. Although simple in structure, the yeast is found
to be closely related to some of the higher groups of fungi as shown
by the method of spore formation. When grown on special substances
like potato or carrot, the contents of the cell may _form spores
inside of the sac-like mother cell_, thus resembling the sac-fungi to
which blue mold and mildews belong. The yeast plant is remarkable on
account of its power to induce alcoholic fermentation in the media in
which it grows.
There are many kinds of yeasts. One of them is found in the common
_yeast cakes_. In the process of manufacture of these cakes, the
yeast cells grow to a certain stage, and the material is then dried
and fashioned into small cakes, each cake containing great numbers of
the yeast cells. When the yeast cake is added to dough, and proper
conditions of warmth and moisture are provided, the yeast grows
rapidly and breaks up the sugar of the dough into carbon dioxid
and alcohol. This is _fermentation_. The gases escape and puff up
the dough, causing the _bread to rise_. In this loosened condition
the dough is baked; if it is not baked quickly enough, _the bread_
“_falls_.” Shake up a bit of yeast cake in slightly sweetened water:
the water soon becomes cloudy from the growing yeasts.
_Parasitic fungi._--Most of the molds are saprophytes. Many other
fungi are parasitic on living plants and animals (Fig. 285). Some
of them have complicated life histories, undergoing many changes
before the original spore is again produced. The _willow mildew_ and
the common _rust of wheat_ will serve to illustrate the habits of
parasitic fungi.
The _willow mildew (Uncinula salicis)_.--This is one of the sac
fungi. It forms white downy patches on the leaves of willows (Fig.
276). These patches consist of numerous interwoven threads that may
be recognized under the microscope as the mycelium of the fungus. The
mycelium in this case lives on the surface of the leaf and nourishes
itself by sending short branches into the cells of the leaf to absorb
food materials from them.
[Illustration: FIG. 276.--COLONIES OF WILLOW MILDEW.]
[Illustration: FIG. 277.--SUMMER-SPORES OF WILLOW MILDEW.]
[Illustration: FIG. 278.--PERITHECIUM OF WILLOW MILDEW.]
[Illustration: FIG. 279.--SECTION THROUGH PERITHECIUM OF WILLOW MILDEW.]
Numerous _summer-spores_ are formed of short, erect branches all over
the white surface. One of these branches is shown in Fig. 277. When
it has grown to a certain length, the upper part begins to segment or
divide into spores which fall and are scattered by the wind. Those
falling on other willows reproduce the fungus there. This process
continues all summer, but in the later part of the season provision
is made to maintain the mildew through the winter. If some of the
white patches are closely examined in July or August, a number of
little black bodies will be seen among the threads. These little
bodies are called _perithecia_, shown in Fig. 278. To the naked eye
they appear as minute specks, but when seen under a magnification of
200 diameters they present a very interesting appearance. They are
hollow spherical bodies decorated around the outside with a fringe
of crook-like hairs. The _resting-spores_ of the willow mildew are
produced in sacs or _asci_ inclosed within the leathery perithecia.
Figure 279 shows a cross-section of a perithecium with the asci
arising from the bottom. The spores remain securely packed in the
perithecia. They do not ripen in the autumn, but fall to the ground
with the leaf, and there remain securely protected among the dead
foliage. The following spring they mature and are liberated by the
decay of the perithecia. They are then ready to attack the unfolding
leaves of the willow and repeat the work of the summer before.
[Illustration: FIG. 280.--SORI CONTAINING TELEUTOSPORES OF WHEAT RUST.]
_The wheat rust._--The development of some of the rusts, as the
common _wheat rust (Puccinia graminis)_, is even more interesting
and complicated than that of the mildews. Wheat rust is also a true
parasite, affecting wheat and a few other grasses. The mycelium
here cannot be seen by the unaided eye, for it consists of threads
which are present within the host plant, mostly in the intercellular
spaces. These threads also send short branches, or _haustoria_ (Fig.
132), into the neighboring cells to absorb nutriment.
[Illustration: FIG. 281.--TELEUTOSPORE OF WHEAT RUST.]
The _resting-spores_ of wheat rust are produced in late summer, when
they may be found in black lines breaking through the epidermis of
the wheat stalk (black-rust stage). They are formed in masses, called
_sori_ (Fig. 280), from the ends of numerous crowded mycelial strands
just beneath the epidermis of the host. The individual spores are
very small and can be well studied only with a microscope of high
power (× about 400). They are brown two-celled bodies with a thick
wall (Fig. 281). Since they are the resting or winter-spores, they
are termed _teleutospores_ (“completed spores”). Usually they do not
fall, but remain in the sori during winter. The following spring each
cell of the teleutospore puts forth a rather stout thread, which
does not grow more than several times the length of the spore and
terminates in a blunt extremity. This germ tube, _promycelium_, now
becomes divided into four cells by cross walls, which are formed from
the top downwards. Each cell gives rise to a short, pointed branch
which, in the course of a few hours, forms at its summit a single
spore called a _sporidium_. This in turn germinates and produces a
mycelium. In Fig. 282 a germinating teleutospore is drawn to show the
promycelium, _p_, divided into four cells, each producing a short
branch with a little _sporidium, s_.
[Illustration: FIG. 282.--GERMINATING TELEUTOSPORE OF WHEAT RUST.]
[Illustration: FIG. 283.--LEAF OF BARBERRY WITH CLUSTER-CUPS.]
[Illustration: FIG. 284.--SECTION THROUGH A CLUSTER-CUP ON BARBERRY
LEAF.]
A most remarkable circumstance in the life history of the wheat rust
is the fact that the mycelium produced by the sporidium _can live
only in barberry leaves_, and it follows that if no barberry bushes
are in the neighborhood the sporidia finally perish. Those which
happen to lodge on a barberry bush germinate immediately, producing a
mycelium that enters the barberry leaf and grows within its tissues.
Very soon the fungus produces a new kind of spores on the barberry
leaves. These are called _æcidiospores_. They are formed in long
chains in little fringed cups, or _æcidia_, which appear in groups on
the lower side of the leaf (Fig. 283). These orange or yellow æcidia
are termed _cluster-cups_. In Fig. 284 is shown a cross-section
of one of the cups, outlining the long chains of spores, and the
mycelium in the tissues.
The æcidiospores are formed in the spring, and after they have been
set free, some of them lodge on wheat or other grasses, where they
germinate immediately. The germ-tube enters the leaf through a
stomate, whence it spreads among the cells of the wheat plant. In
summer one-celled reddish uredospores (“blight spores,” red-rust
stage) are produced in a manner similar to the teleutospores. These
are capable of germinating immediately, and serve to disseminate the
fungus during the summer on other wheat plants or grasses. Late in
the season, teleutospores are again produced, completing the life
cycle of the plant.
[Illustration: FIG. 285.--HOW A PARASITIC FUNGUS WORKS. Anthracnose on
a bean pod entering the bean beneath. (Whetzel.)]
Many rusts besides _Puccinia graminis_ produce different spore forms
on different plants. The phenomenon is called _heterœcism_, and
was first shown to exist in the wheat rust. Curiously enough, the
peasants of Europe had observed and asserted that barberry bushes
cause wheat to blight long before science explained the relation
between the cluster-cups on barberry and the rust on wheat. The true
relation was actually demonstrated, as has since been done for many
other rusts on their respective hosts, by sowing the æcidiospores on
healthy wheat plants and thus producing the rust. The _cedar apple_
is another rust, producing the curious swellings often found on the
branches of red cedar trees. In the spring the teleutospores ooze out
from the “apple” in brownish yellow masses. It has been found that
these attack various fruit trees, producing æcidia on their leaves.
Fig. 285 explains how a parasitic fungus works.
_Puffballs_, _mushrooms_, _toadstools_, _and shelf fungi_.--These
represent what are called the _higher fungi_, because of the size
and complexity of the plant body as well as from the fact that they
seem to stand at the end of one line of evolution. The mycelial
threads grow together in extensive strands in rotten wood or in the
soil, and send out large complex growths of mycelium in connection
with which the spores are borne. These aërial parts are the only
ones we ordinarily see, and which constitute the “mushroom” part
(Fig. 131). Only asexual spores (_basidiospores_) are produced, and
on short stalks (_basidia_) (Fig. 286). In the puffballs the spores
are inclosed and constitute a large part of the “smoke.” In the
mushrooms and toadstools they are borne on _gills_, and in the shelf
fungi (Fig. 134) on the walls of minute pores of the underside. The
mycelium of these shelf fungi frequently lives and grows for a long
time concealed in the substratum before the visible fruit bodies are
sent out. Practically all timber decay is caused by such growth, and
the damage is largely done before the fruiting bodies appear. For
other accounts of mushrooms, see Chap. XIV.
[Illustration: FIG. 286.--PART OF GILL OF THE CULTIVATED MUSHROOM.
_tr_, trama tissue; _sh_, hymenium; _b_, basidium; _st_, sterigma;
_sp_, spore. (Atkinson.)]
LICHENS
Lichens are so common everywhere that the attention of the student
is sure to be drawn to them. They grow on rocks, trunks of trees
(Fig. 287), old fences, and on the earth. They are thin, usually gray
ragged objects, apparently lifeless. Their study is too difficult for
beginners, but a few words of explanation may be useful.
[Illustration: FIG. 287.--LICHEN ON AN OAK TRUNK. (A species of
_Physcia_.)]
Lichens were formerly supposed to be a distinct or separate division
of plants. They are now known to be organisms, each species of which
is a constant association of a fungus and an alga. The thallus is
ordinarily made up of fungous mycelium or tissue within which the
imprisoned alga is definitely distributed. The result is a growth
unlike either component. This association of alga and fungus is
usually spoken of as _symbiosis_, or mutually helpful growth, the
alga furnishing some things, the fungus others, and both together
being able to accomplish work that neither could do independently. By
others this union is considered to be a mild form of parasitism, in
which the fungus profits at the expense of the alga. As favorable to
this view, the facts are cited that each component is able to grow
independently, and that under such conditions the algal cells seem to
thrive better than when imprisoned by the fungus.
Lichens propagate by means of _soredia_, which are tiny parts
separated from the body of the thallus, and consisting of one or more
algal cells overgrown with fungus threads. These are readily observed
in many lichens. They also produce spores, usually ascospores, which
are always the product of the fungus element, and which reproduce the
lichen by germinating in the presence of algal cells, to which the
hyphæ immediately cling.
Lichens are found in the most inhospitable places, and, by means of
acids which they secrete, they attack and slowly disintegrate even
the hardest rocks. By making thin sections of the thallus with a
sharp razor and examining under the compound microscope, it is easy
to distinguish the two components in many lichens.
LIVERWORTS
The liverworts are peculiar flat green plants usually found on wet
cliffs and in other moist, shady places. They frequently occur
in greenhouses where the soil is kept constantly wet. One of the
commonest liverworts is _Marchantia polymorpha_, two plants of which
are shown in Figs. 288, 289. The plant consists of a ribbon-like
thallus that creeps along the ground, becoming repeatedly forked as
it grows. The end of each branch is always conspicuously notched.
There is a prominent midrib extending along the center of each branch
of the thallus. On the under side of the thallus, especially along
the midrib, there are numerous rhizoids which serve the purpose of
roots, absorbing nourishment from the earth and holding the plant in
its place. The upper surface of the thallus is divided into minute
rhombic areas that can be seen with the naked eye. Each of these
areas is perforated by a small breathing pore or stomate that leads
into a cavity just beneath the epidermis. This space is surrounded
by chlorophyll-bearing cells, some of which stand in rows from the
bottom of the cavity (Fig. 290). The delicate assimilating tissue is
thus brought in close communication with the outer air through the
pore in the thick, protecting epidermis.
[Illustration: FIG. 288.
FIG. 289.
PLANTS OF MARCHANTIA.]
[Illustration: FIG. 290.--SECTION OF THALLUS OF MARCHANTIA. Stomate at
_a_.]
At various points on the midrib are little cups containing small
green bodies. These bodies are buds or _gemmæ_ which are outgrowths
from the cells at the bottom of the cup. They become loosened and are
then dispersed by the rain to other places, where they take root and
grow into new plants.
The most striking organs on the thallus of marchantia are the
peculiar stalked bodies shown in Figs. 288, 289. These are termed
archegoniophores and _antheridiophores_ or _receptacles_. Their
structure and function are very interesting, but their parts are so
minute that they can be studied only with the aid of a microscope
magnifying from 100 to 400 times. Enlarged drawings will guide the
pupil.
[Illustration: FIG. 291.--SECTION THROUGH ANTHERIDIOPHORE OF
MARCHANTIA, showing antheridia. One antheridium more magnified.]
The _antheridiophores_ are fleshy, lobed disks borne on short stalks
(Fig. 291). The upper surface of the disk shows openings scarcely
visible to the naked eye. However, a section of the disk, such as is
drawn in Fig. 291, shows that the pores lead into oblong cavities
in the receptacle. From the base of each cavity there arises a
thick, club-shaped body, the _antheridium_. Within the antheridium
are formed many sperm-cells which are capable of swimming about in
water by means of long lashes or cilia attached to them. When the
antheridium is mature, it bursts and allows the ciliated sperm cells
to escape.
The _archegoniophores_ are also elevated on stalks (Fig. 289).
Instead of a simple disk, the receptacle consists of nine or
more finger-like rays. Along the under side of the rays, between
delicately fringed curtains, peculiar flask-like bodies, or
_archegonia_, are situated. The archegonia are not visible to the
naked eye. They can be studied only with the microscope (× about
400). One of them much magnified is represented in Fig. 292. Its
principal parts are the long _neck, a_, and the rounded _venter, b_,
inclosing a large free cell--the egg-cell.
[Illustration: FIG. 292.--ARCHEGONIUM OF MARCHANTIA.]
[Illustration: FIG. 293.--ARCHEGONIOPHORE, WITH SPOROGONIA, OF
MARCHANTIA.]
We have seen that the antheridium at maturity discharges its
sperm-cells. These swim about in the water provided by the dew and
rain. Some of them finally find their way to the archegonia and
egg-cells, the latter being fertilized, as pollen fertilizes the
ovules of higher plants.
After fertilization the egg-cell develops into the spore capsule
or _sporogonium_. The mature spore capsules may be seen in Fig.
293. They consist of an oval spore-case on a short stalk, the base
of which is imbedded in the tissue of the receptacle, from which
it derives the necessary nourishment for the development of the
sporogonium. At maturity the sporogonium is ruptured at the apex,
setting free the spherical spores together with numerous filaments
having spirally thickened walls (Fig. 294). These filaments are
called _elaters_. When drying, they exhibit rapid movements by means
of which the spores are scattered. The spores germinate and again
produce the thallus of marchantia.
[Illustration: FIG. 294.--SPORES AND ELATERS OF MARCHANTIA.]
[Illustration: FIG. 295.--POLYTRICHUM COMMUNE. _f_,_f_, fertile plants,
one on the left in fruit, _m_, antheridial plant.]
[Illustration: FIG. 296.--SECTION OF LEAF OF POLYTRICHUM COMMUNE.]
MOSSES (Bryophyta)
If we have followed carefully the development of marchantia, the
study of one of the mosses will be comparatively easy. The mosses
are more familiar plants than the liverworts. They grow on trees,
stones, and on the soil both in wet and dry places. One of the
common larger mosses, known as _Polytrichum commune_, may serve as
an example, Fig. 295. This plant grows on rather dry knolls, mostly
in the borders of open woods, where it forms large beds. In dry
weather these beds have a reddish brown appearance, but when moist
they form beautiful green cushions. This color is due, in the first
instance, to the color of the old stems and leaves, and, in the
second instance, to the peculiar action of the green living leaves
under the influence of changing moisture-conditions. The inner or
upper surface of the leaf is covered with thin, longitudinal ridges
of delicate cells which contain chlorophyll. These cells are shown in
cross-section in Fig. 296, as dots or granules. All the other tissue
of the leaf consists of thick-walled, corky cells which do not allow
moisture to penetrate. When the air is moist the green leaves spread
out, exposing the chlorophyll cells to the air, but in dry weather
the margins of the leaves roll inward, and the leaves fold closely
against the stem, thus protecting the delicate assimilating tissue.
The _antheridia_ and _archegonia_ of polytrichum are borne in groups
at the ends of the branches on different plants (many mosses bear
both organs on the same branch). They are surrounded by involucres
of characteristic leaves termed _perichætia_ or _perichætal leaves_.
Multicellular hairs known as _paraphyses_ are scattered among the
archegonia and antheridia. The involucres with the organs borne
within them are called _receptacles_, or, less appropriately, “moss
flowers.” As in marchantia, the organs are very minute and must be
highly magnified to be studied.
[Illustration: FIG. 297.--SECTION THROUGH A RECEPTACLE OF POLYTRICHUM
COMMUNE, showing paraphyses and antheridia.]
The antheridia are borne in broad cup-like receptacles on the
antheridial plants (Fig. 297). They are much like the antheridia of
marchantia, but they stand free among the paraphyses and are not
sunk in cavities. At maturity they burst and allow the sperm cells
or _spermatozoids_ to escape. In polytrichum, when the receptacles
have fulfilled their function, the stem continues to grow from the
center of the cup (_m_, Fig. 295). The archegonia are borne in other
receptacles on different plants. They are like the archegonia of
marchantia except that they stand erect on the end of the branch.
The _sporogonium_ which develops from the fertilized egg is shown
in _a_, _b_, Fig. 295. It consists of a long, brown stalk bearing
the spore-case at its summit. The base of the stalk is imbedded in
the end of the moss stem by which it is nourished. The capsule is
entirely inclosed by a hairy cap, the _calyptra, b_. The calyptra is
really the remnant of the archegonium, which, for a time, increases
in size to accommodate and protect the young growing capsule. It is
finally torn loose and carried up on the spore-case. The mouth of
the capsule is closed by a circular lid, the _operculum_, having a
conical projection at the center.
The operculum soon drops, or it may be removed, displaying a fringe
of sixty-four teeth guarding the mouth of the capsule. This ring of
teeth is known as the _peristome_. In most mosses the teeth exhibit
peculiar hygroscopic movements; _i.e._ when moist they bend outwards,
and upon drying curve in toward the mouth of the capsule. This
motion, it will be seen, serves to disperse the spores gradually over
a long period of time.
Not the entire capsule is filled with spores. There are no elaters,
but the center of the capsule is occupied by a columnar strand of
tissue, the _columella_, which expands at the mouth into a thin,
membranous disk, closing the entire mouth of the capsule except the
narrow annular chink guarded by the teeth. In this moss the points of
the teeth are attached to the margin of the membrane, allowing the
spores to sift out through the spaces between them.
When the spores germinate they form a green, branched thread, the
_protonema_. This gives rise directly to moss plants, which appear
as little buds on the thread. When the moss plants have sent their
little rhizoids into the earth, the protonema dies, for it is no
longer necessary for the support of the little plants, and the moss
plants grow independently.
_Funaria_ is a moss very common on damp, open soil. It forms green
patches of small fine leaves from which arise long brown stalks
terminated by curved capsules (Fig. 298). The structure is similar to
that of polytrichum, except the absence of plates on the under side
of the leaves, the continuous growth of the stem, the curved capsule,
double peristome, monœcious rather than diœcious receptacles, and
nearly glabrous unsymmetrical calyptra.
[Illustration: FIG. 298.--FUNARIA HYGROSCOPICA.]
EQUISETUMS, OR HORSETAILS (Pteridophyta)
There are about twenty-five species of equisetum, constituting the
only genus of the unique family _Equisetaceæ_. Among these _E.
arvense_ (Fig. 299) is common on clayey and sandy soils.
In this species the work of nutrition and that of spore production
are performed by separate shoots from an underground rhizome. The
fertile branches appear early in spring. The stem, which is 3
to 6 inches high, consists of a number of cylindrical, furrowed
internodes, each sheathed at the base by a circle of scale leaves.
The shoots are of a pale yellow color. They contain no chlorophyll,
and are nourished by the food stored in the rhizome (Fig. 299).
The spores are formed on specially developed fertile leaves or
_sporophylls_ which are collected into a spike or cone at the end of
the stalk (_a_, Fig. 299). A single sporophyll is shown at _b_. It
consists of a short stalk expanded into a broad, mushroom-like head.
Several large _sporangia_ are borne on its under side. The spores
formed in the sporangia are very interesting and beautiful objects
when examined under the microscope (× about 200). They are spherical,
green bodies, each surrounded by two spiral bands attached to the
spore at their intersection, s. These bands exhibit hygroscopic
movements by means of which the spores become entangled, and are held
together. This is of advantage to the plant, as we shall see. All
the spores are alike, but some of the _prothallia_ grow to a greater
size than the others. The large prothallia produce only archegonia
while the smaller ones produce _antheridia_. Both of these organs are
much like those of the ferns, and fertilization is accomplished in
the same way. Since the prothallia are usually diœcious, the special
advantage of the spiral bands, holding the spores together so that
both kinds of prothallia may be in close proximity, will be easily
understood. As in the fern, the fertilized egg-cell develops into an
equisetum plant.
[Illustration: FIG. 299.--EQUISETUM ARVENSE.
_st_, sterile shoot; _f_, fertile shoot showing the spike at _a_; _b_,
sporophyll, with sporangia; _s_, spore.]
The sterile shoots (_st_, Fig. 299) appear much later in the season.
They give rise to repeated whorls of angular or furrowed branches.
The leaves are very much reduced scales, situated at the internodes.
The stems are provided with chlorophyll and act as assimilating
tissue, nourishing the rhizome and the fertile shoots. Nutriment is
also stored in special tubers developed on the rhizome.
Other species of equisetum have only one kind of shoot--a tall, hard,
leafless, green shoot with the spike at its summit. Equisetum stems
are full of silex, and they are sometimes used for scouring floors
and utensils; hence the common name “scouring rush.”
ISOËTES (Pteridophyta)
_Isoëtes_ or quillwort is usually found in water or damp soil on the
edges of ponds and lakes. The general habit of the plant is seen
in Fig. 300, _a_. It consists of a short, perennial stem bearing
numerous erect, quill-like leaves with broad sheathing bases. The
plants are commonly mistaken for young grasses.
[Illustration: FIG. 300.--ISOËTES, showing habit of plant at _a_; _b_,
base of leaf, showing sporangium, velum, and ligule.]
Isoëtes bears two kinds of spores, large roughened ones, the
_macrospores_, and small ones or _microspores_. Both kinds are formed
in _sporangia_ borne in an excavation in the expanded base of the
leaf. The macrospores are formed on the outer and the microspores on
the inner leaves. A sporangium in the base of a leaf is shown at _b_.
It is partially covered by a thin membrane, the _velum_. The minute
triangular appendage at the upper end of the sporangium is called the
_ligule_.
The spores are liberated by the decay of the sporangia. They form
rudimentary prothallia of two kinds. The microspores produce
prothallia with _antheridia_, while the macrospores produce
prothallia with _archegonia_. Fertilization takes place as in the
mosses or liverworts, and the fertilized egg-cell, by continued
growth, gives rise again to the isoëtes plant.
CLUB-MOSSES (Pteridophyta)
The club-mosses are low trailing plants of moss-like looks and
habit, although more closely allied to ferns than to true mosses.
Except one genus in Florida, all our club mosses belong to the
genus _Lycopodium_. They grow mostly in woods, having 1-nerved
evergreen leaves arranged in four or more ranks. Some of them make
long strands, as the ground pine, and are much used for Christmas
decorations. The spores are all _of one kind_ or form, borne in
_1-celled sporangia_ that open on the margin into two valves. The
sporangia are borne in some species (Fig. 301) as small yellow bodies
in the axils of the ordinary leaves near the tip of the shoot; in
other species (Fig. 302) they are borne in the axils of small scales
that form a catkin-like spike. The spores are very numerous, and
they contain an oil that makes them inflammable. About 100 species
of lycopodium are known. The plants grown by florists under the name
of lycopodium are of the genus _Selaginella_, more closely allied to
isoëtes, bearing two kinds of spores (microspores and macrospores).
[Illustration: FIG. 301.--A LYCOPODIUM WITH SPORANGIA IN THE AXILS OF
THE FOLIAGE LEAVES. (_Lycopodium lucidulum_).]
[Illustration: FIG. 302.--A CLUB-MOSS (_Lycopodium complanatum_).]
ANIMAL BIOLOGY
CHAPTER I
THE PRINCIPLES OF BIOLOGY
Biology (Greek, _bios_, life; _logos_, discourse) means the science of
life. It treats of animals and plants. That branch of biology which
treats of animals is called _zoology_ (Gr. _zoon_, animal; _logos_,
discourse). The biological science of _botany_ (Gr. _botane_, plant or
herb) treats of plants.
Living things are distinguished from the not living by a series of
processes, or changes (feeding, growth, development, multiplication,
etc.), which together constitute what is called life. These processes
are called _functions_. Both plants and animals have certain parts
called _organs_ which have each a definite work, or function; hence
animals and plants are said to be organized. For example, men and most
animals have a certain organ (the mouth) for taking in nourishment;
another (the food tube), for its digestion.
Because of its _organization_, each animal or plant is said to be
an organism. Living things constitute the _organic kingdom_. Things
without life and not formed by life constitute the _inorganic_, or
_mineral, kingdom_. Mark I for inorganic and O for organic after the
proper words in this list: granite, sugar, lumber, gold, shellac, sand,
coal, paper, glass, starch, copper, gelatine, cloth, air, potatoes,
alcohol, oil, clay. Which of these things are used for food by animals?
Conclusion?
=Energy in the Organic World.=--We see animals exerting energy; that
is, we see them moving about and doing work. Plants are never seen
acting that way; yet they need energy in order to form their tissues,
grow, and raise themselves in the air.
=Source of Plant Energy.=--We notice that green plants thrive only in
the light, while animal growth is largely independent of light. In
fact, in the salt mines of Poland there are churches and villages below
the ground, and children are born, become adults, and live all their
lives below ground, without seeing the sun. (That these people are not
very strong is doubtless due more to want of fresh air and other causes
than want of sunlight.)
[Illustration: FIG. 1.--SURFACES OF A LEAF, MAGNIFIED.]
[Illustration: FIG. 2.--A LEAF STORING ENERGY IN SUNLIGHT.]
_The need of plants for sunlight shows that they must obtain something
from the sun._ This has been found to be _energy_. This enables them
to _lift_ their _stems_ in growth, and _form_ the various structures
called _tissues_ which make up their stems and leaves. (See Part I,
Chap. XIII.) It is noticed that they take in food and water from the
soil through their roots. Experiments also show that green plants take
in through pores (Fig. 1), on the under side of their leaves, a gas
composed of carbon and oxygen, and called _carbon dioxid_. The _energy
in the sunlight_ enables the plant _to separate out the carbon of the
carbon dioxid_ and build mineral and water and carbon into organic
substances. The oxygen of the carbon dioxid is set free and returns to
the air (Fig. 2). Starch, sugar, oil, and woody fiber are examples of
substances thus formed. Can you think of any fuel not due to plants?
=How Animals obtain Energy.=--You have noticed that starch, oil, etc.,
will _burn_, or _oxidize_, that is, _unite with the oxygen of the air_;
thus the sun’s energy, stored in these substances, is changed back to
heat and motion. The oxidation of oil or sugar may occur in a furnace;
it may also occur in the living substance of the active animal.
[Illustration: FIG. 3.--Colorless plants, as MUSHROOMS, give off no
oxygen.
A GREEN LEAF, even after it is cut, gives off oxygen (O) if kept in the
sun.]
Fortunately for the animals the plants oxidize very little of the
substances built up by them, since they do not move about nor need
to keep themselves warm. We notice that animals are constantly using
plant substances for food, and constantly drawing the air into their
bodies. If the sunlight had not enabled the green plant to store up
these substances and set free the oxygen (Fig. 3), animals would have
no food to eat nor air to breathe; hence we may say that the sunlight
is indirectly the source of the life and energy of animals. Mushrooms
and other plants without green matter cannot set oxygen free (Fig. 3).
=Experiment to show the Cause of Burning, or Oxidation.=--Obtain a
large glass bottle (a pickle jar), a short candle, and some matches.
Light the candle and put it on a table near the edge, and cover it with
the glass jar. The flame slowly smothers and goes out. Why is this? Is
the air now in the jar different from that which was in it before the
candle was lighted? Some change must have taken place or the candle
would continue to burn. To try whether the candle will burn again
under the jar without changing the air, slide the jar to the edge of
the table and let the candle drop out. Light the candle and slip it up
into the jar again, the jar being held with its mouth a little over
the edge of the table to receive the candle (Fig. 5). The flame goes
out at once. Evidently the air in the jar is not the same as the air
outside. Take up the jar and wave it to and fro a few times, so as to
remove the old air and admit fresh air. The candle now burns in it with
as bright a flame as at first. So we conclude that the candle will not
continue to burn unless there is a constant supply of fresh air. The
gas formed by the burning is carbon dioxid. It is the gas from which
plants extract carbon. (See Plant Biology, Chap. V.) One test for the
presence of this gas is that it forms a white, chalky cloud in lime
water; another is that it smothers a fire.
=Experiment to show that Animals give off Carbon Dioxid.=--Place a
cardboard over the mouth of a bottle containing pure air. Take a long
straw, the hollow stem of a weed, a glass tube, or a sheet of stiff
paper rolled into a tube, and pass the tube into the bottle through a
hole in the cardboard. Without drawing in a deep breath, send one long
breath into the bottle through the tube, emptying the lungs by the
breath as nearly as possible (Fig. 4). Next invert the bottle on the
table as in the former experiment, afterward withdrawing the cardboard.
Move the bottle to the edge of the table and pass the lighted candle
up into it (Fig. 5). Does the flame go out as quickly as in the former
experiment?
If you breathe through a tube into clear lime water, the water turns
milky. The effect of the breath on the candle and on the lime water
shows that carbon dioxid is continually leaving our bodies in the
breath.
[Illustration: FIG. 4.--Breathing into a bottle.[1]]
[Illustration: FIG. 5.--Testing the air in the bottle.[1]]
[1] From Coleman’s “Physiology for Beginners,” Macmillan Co., N.Y.
=Oxidation and Deoxidation.=--The union of oxygen with carbon and
other substances, which occurs in fires and in the bodies of animals,
is called _oxidation_. The separation of the oxygen from carbon such
as occurs in the leaves of plants is called _deoxidation_. _The first
process sets energy free, the other process stores it up._ Animals
give off carbon dioxid from their lungs or gills, and plants give off
oxygen from their leaves. But plants need some energy in growing, so
oxidation also occurs in plants, but to a far less extent than in
animals. At night, because of the absence of sunlight, no deoxidation
is taking place in the plant, but oxidation and growth continue; _so
at night the plant actually breathes out some carbon dioxid_. The
deepest part of the lungs contains the most carbon dioxid. Why was it
necessary to empty the lungs as nearly as possible in the experiment
with the candle? Why would first drawing a deep breath interfere with
the experiment? Why does closing the draught of a stove, thus shutting
off part of the air, lessen the burning? Why does a “firefly” shine
brighter at each breath? Why is the pulse and breathing faster in a
fever? Very slow in a trance?
=The key for understanding any animal= is to find _how it gets food and
oxygen_, and how it uses the energy thus obtained to grow, move, avoid
its enemies, and get more food. Because it moves, it needs senses to
guide it.
=The key for understanding a plant= is to find _how it gets food and
sunlight_ for its growth. It makes little provision against enemies;
its food is in reach, so it needs no senses to guide it. The plant is
built on the plan of having the nutritive activities _near the surface_
(_e.g._ absorption by roots; gas exchange in leaves). The animal is
built on the plan of having its nutritive activities _on the inside_
(_e.g._ digestion; breathing).
=Cell and Protoplasm.=--Both plants and animals are composed of small
parts called _cells_. Cells are usually microscopic in size. They
have various shapes, as spherical, flat, cylindrical, fiber-like,
star-shaped. The living substance of cells is called _protoplasm_. It
is a stiff, gluey fluid, _albuminous_ in its nature. Every cell has a
denser spot or kernel called a _nucleus_, and in the nucleus is a still
smaller speck called a _nucleolus_. Most cells are denser and tougher
on the outside, and are said to have a _cell wall_, but many cells are
naked, or without a wall. Hence the indispensable part of a cell is
not the wall but the nucleus, and a _cell may be defined as a bit of
protoplasm containing a nucleus_. This definition includes naked cells
as well as cells with walls.
=One-celled Animals.=--There are countless millions of animals and
plants the existence of which was not suspected until the invention
of the microscope several centuries ago. They are one-celled, and
hence microscopic in size. It is believed that the large animals and
plants are descended from one-celled animals and plants. In fact, each
individual plant or animal begins life as a single cell, called an egg
cell, and forms its organs by the subdivision of the egg cell into many
cells. An egg cell is shown in Fig. 6, and the first stages in the
development of an egg cell are shown in Fig. 7.
[Illustration: FIG. 6.--Egg cell of mammal with yolk.]
[Illustration: FIG. 7.--Egg cell subdivides into many cells forming a
sphere (morula) containing a liquid. A dimple forms and deepens to form
the next stage (gastrula).]
The animals to be studied in the first chapter are _one-celled
animals_. To understand them we must learn how they eat, breathe, feel,
and move. They are called _Protozoans_ (Greek _protos_, first; _zoon_,
life). All other animals are composed of many cells and are called
_Metazoans_ (Greek _meta_, beyond or after). The cells composing the
mucous membrane in man are shown in Fig. 8. The cellular structure of
the leaf of a many-celled plant is illustrated in Fig. 1. (See also
Chap. I, Human Biology.)
[Illustration: FIG. 8.--MUCOUS MEMBRANE formed of one layer of cells. A
few cells secrete mucus.]
=Method of Classifying Animals.=--The various animals display
differences more or less marked. The question arises, are not some
of them more closely related than others? We conclude that they are,
since the difference between some animals is very slight, while the
difference between others is quite marked.
To show _the different steps in classifying_ an animal, we will take
an example,--the cow. Even little children learn to recognize a cow,
although individual cows differ somewhat in form, size, color, etc.
The varieties of cows, such as short-horn, Jersey, etc., all form one
_species_ of animals, having the scientific name _taurus_. Let us
include in a larger group the animals closest akin to a cow. We see a
cat, a bison, and a dog; rejecting the cat and the dog, we see that
the bison has horns, hoofs, and other similarities. We include it with
the cow in a _genus_ called _Bos_, calling the cow Bos taurus, and the
bison, Bos bison. The sacred cow of India (Bos indicus) is so like the
cow and buffalo as also to belong in the genus Bos. Why is not the
camel, which, like Bos bison, has a hump, placed in the genus Bos?
(Fig. 390.)
The Old World buffaloes,--most abundant in Africa and India,--the
antelopes, sheep, goats, and several other genera are placed with the
genus Bos in a _family_ called the _hollow horns_.
This family, because of its even number of toes and the habit of
chewing the cud, resembles the camel family, the deer family, and
several other families. These are all placed together in the next
higher systematic unit called an _order_, in this case, the order of
_ruminants_.
The ruminants, because they are covered with hair and nourish the young
with milk, are in every essential respect related to the one-toed
horses, the beasts of prey, the apes, etc. Hence they are all placed in
a more inclusive division of animals, the _class_ called _mammals_.
All mammals have the skeleton, or support of the body, on the inside,
the axis of which is called the vertebral column. This feature also
belongs to the classes of reptiles, amphibians, and fishes. It is
therefore consistent to unite these classes by a general idea or
conception into a great _branch_ of animals called the _vertebrates_.
Returning from the general to the particular by successive steps, state
the branch, class, order, family, genus, and species to which the cow
belongs.
=The Eight Branches or Sub-kingdoms.=--The simplest classification
divides the whole animal kingdom into eight branches, named and
characterized as follows, beginning with the lowest: I. PROTOZOANS.
One-celled. II. SPONGES. Many openings. III. POLYPS. Circular;
cup-like; having only one opening which is both mouth and vent. IV.
ECHINODERMS. Circular; rough-skinned; two openings. V. MOLLUSKS. No
skeleton; usually with external shell. VI. VERMES. Elongate body, no
jointed legs. VII. ARTHROPODS. External jointed skeleton; jointed legs.
VIII. VERTEBRATES. Internal jointed skeleton with axis or backbone.
CHAPTER II
PROTOZOA (One-celled Animals)
THE AMEBA
SUGGESTIONS.--Amebas live on the slime found on submerged stems and
leaves in standing water, or in the ooze at the bottom. Water plants
may be crowded into a glass dish and allowed to decay, and after
about two weeks the ameba may be found in the brown slime scraped
from the plants. An ameba culture sometimes lasts only three days.
The most abundant supply ever used by the writer was from a bottle
of water where some oats were germinating. Use ¹⁄₅ or ¹⁄₆ inch
objective, and cover with a thin cover glass. Teachers who object to
the use of the compound microscope in a first course should require a
most careful study of the figures.
[Illustration: FIG. 9.--AMEBA PROTEUS, much enlarged.]
[Illustration: FIG. 10.--AMEBA.
_cv_, contractile vacuole; _ec_, ectoplasm; _en_, endoplasm; _n_,
nucleus; _ps_, pseudopod; _ps′_, pseudopod forming; ectoplasm protrudes
and endoplasm flows into it.]
=Form and Structure.=--The ameba (also spelled amœba) looks so much
like a clear drop of jelly that a beginner cannot be certain that he
has found one until it moves. It is a speck of protoplasm (Fig. 9),
with a clear outer layer, the _ectoplasm_; and a granular, internal
part, the _endoplasm_. Is there a distinct line between them? (Fig. 10.)
Note the central portion and the slender prolongations or _pseudopods_
(Greek, false feet). Does the endoplasm extend into the pseudopods?
(Fig. 10.) Are the pseudopods arranged with any regularity?
Sometimes it is possible to see a denser appearing portion, called the
_nucleus_; also a clear space, the _contractile vacuole_ (Fig. 10).
=Movements.=--Sometimes while the pseudopods are being extended and
contracted, the central portion remains in the same place (this is
_motion_). Usually only one pseudopod is extended, and the body flows
into it; this is _locomotion_ (Fig. 11). There is a new foot made for
each step.
[Illustration: FIG. 11.--The same ameba seen at different times.]
=Feeding.=--If the ameba crawls near a food particle, the _pseudopod is
pressed against it_, or a depression occurs (Fig. 12), and the particle
is soon embedded in the endoplasm. Often a clear space called a _food
vacuole_ is noticed around the food particle. This is the water that is
taken in with the particle (Fig. 12). The water and the particle are
soon absorbed and assimilated by the endoplasm.
[Illustration: FIG. 12.--THE AMEBA taking food.]
=Excretion.=--If a particle of sand or other indigestible matter is
taken in, _it is left behind_ as the ameba moves on. There is a clear
space called the _contractile vacuole_, which slowly contracts and
disappears, then reappears and expands (Figs. 9 and 10). This possibly
aids in excreting oxidized or useless material.
=Circulation= in the ameba consists of the movement of its protoplasmic
particles. It lacks special organs of circulation.
=Feeling.=--_Jarring_ the glass slide seems to be felt, for it causes
the activity of the ameba to vary. It does not take in for food every
particle that it touches. This may be the beginning of _taste, based
upon mere chemical affinity_. The pseudopods aid in feeling.
=Reproduction.=--Sometimes an ameba is seen dividing into two parts. A
_narrowing_ takes place in the middle; the _nucleus also divides_, a
part going to each portion (Fig. 13). The mother ameba finally divides
into two daughter amebas. Sex is wanting.
[Illustration: FIG. 13.--AMEBA, dividing.]
=Source of the Ameba’s Energy.=--We thus see that the ameba moves
without feet, eats without a mouth, digests without a stomach, feels
without nerves, and, it should also be stated, breathes without lungs,
for _oxygen is absorbed_ from the water _by its whole surface_. Its
_movements require energy_; this, as in all animals, is furnished by
the _uniting of oxygen with the food_. Carbon dioxid and other waste
products are formed by the union; these pass off at the surface of the
ameba and taint the water with impurities.
=Questions.=--Why will the ameba die in a very small quantity of
water, even though the water contains enough food? Why will it die
still quicker if air is excluded from contact with the drop of water?
The ameba never dies of old age. Can it be said to be immortal?
According to the definition of a cell (_Chapter I_), is the ameba a
unicellular or multicellular animal?
=Cysts.=--If the water inhabited by a protozoan dries up, it encysts,
that is, it forms a tough skin called a cyst. Upon return of better
conditions it breaks the cyst and comes out. Encysted protozoans may
be blown through the air: this explains their appearance in vessels of
water containing suitable food but previously free from protozoans.
THE SLIPPER ANIMALCULE OR PARAMECIUM
=Suggestions.=--Stagnant water often contains the paramecium as well
as the ameba; or they may be found in a dish of water containing hay
or finely cut clover, after the dish has been allowed to stand in
the sun for several days. A white film forming on the surface is a
sign of their presence. They may even be seen with the unaided eye as
tiny white particles by looking through the side of the dish or jar.
Use at first a ¹⁄₃ or ¹⁄₄ in. objective. Restrict their movements by
placing cotton fibers beneath the cover glass; then examine with ¹⁄₅
or ¹⁄₆ objective. Otherwise, study figures.
=Shape and Structure.=--The paramecium’s whole body, like the
ameba’s, is only one cell. It resembles a slipper in _shape_, but
the pointed end is the hind end, the _front end_ being rounded (Fig.
14). The paramecium is propelled by the rapid beating of numerous
fine, threadlike appendages on its surface, called _cilia_ (Latin,
eyelashes) (Figs.). The cilia, like the pseudopods of the ameba, are
merely prolongations of the cell protoplasm, but they are permanent.
The separation between the outer _ectoplasm_ and the interior granular
_endoplasm_ is more marked than in the ameba (Fig. 14).
[Illustration: FIG. 14.--PARAMECIUM, showing cilia, _c_.
Two contractile vacuoles, _cv_; the macronucleus, _mg_; two
micronuclei, _mi_; the gullet (_Œ_), a food ball forming and ten food
balls in their course from gullet to vent, _a_.]
[Illustration: FIG. 15.]
=Nucleus and Vacuoles.=--There is a large nucleus called the
macronucleus, and beside it a smaller one called the micronucleus. They
are hard to see. About one third of the way from each end is a clear,
pulsating space (bb. Fig. 15) called the pulsating vacuole. These
spaces contract until they disappear, and then reappear, gradually
expanding. Tubes lead from the vacuoles which probably serve to keep
the contents of the cell in circulation.
[Illustration: FIG. 16.--TWO PARAMECIA exchanging parts of their
nuclei.]
=Feeding.=--A depression, or _groove_, is seen on one side, this serves
as a mouth (Figs.). A _tube_ which serves as a gullet leads from the
mouth-groove to the interior of the cell. The mouth-groove is lined
with cilia which sweep food particles inward. The particles accumulate
in a mass at the inner end of the gullet, become separated from it as a
_food ball_ (Fig. 14), and sink into the soft protoplasm of the body.
The food balls follow a circular course through the endoplasm, keeping
near the ectoplasm.
=Reproduction.=--This, as in the ameba, is by division, the
constriction being in the middle, and part of the nucleus going to each
half. Sometimes two individuals come together with their mouth-grooves
touching and exchange parts of their nuclei (Fig. 16). They then
separate and each divides to form two new individuals.
We thus see that the paramecium, though of only one cell, _is a much
more complex and advanced animal than the ameba_. The tiny paddles, or
cilia, the mouth-groove, etc., have their special duties similar to the
specialized organs of the many-celled animals to be studied later.
[Illustration: FIG. 17.--VORTICELLA (or bell animalcule), two extended,
one withdrawn.]
[Illustration: FIG. 18.--Euglena.]
[Illustration: FIG. 19.--SHELL OF A RADIOLARIAN.]
If time and circumstances allow a prolonged study, several additional
facts may be observed by the pupil, _e.g._ Does the paramecium swim
with the same end always foremost, and same side uppermost? Can it move
backwards? Avoid obstacles? Change shape in a narrow passage? Does
refuse matter leave the body at any particular place? Trace movement of
the food particles.
Draw the paramecium.
Which has more permanent parts, the _ameba_ or _paramecium_? Name
two anatomical similarities and three differences; four functional
similarities and three differences.
The ameba belongs in the class of protozoans called _Rhizopoda_ “root
footed.”
=Other classes of Protozoans= are the _Infusorians_, which have many
waving cilia (Fig. 17) or one whip-like flagellum (Fig. 18), and the
_Foraminifers_ which possess a calcareous shell pierced with holes.
Much chalky limestone has been formed of their shells. These and the
radiolarians, which have flinty shells (Fig. 19), are often placed in
the class rhizopoda. To which class does the paramecium belong?
Protozoans furnish a large amount of food to the higher animals.
=To the Teacher.= If plant, animal, and human biology are to be given
in one year as planned, and full time allowed for practical work, the
portions of the text in small type, as Chapter III, may be omitted
or merely read and discussed. Any two of the three parts forming the
course may be used for a year’s course by using all of the text and
spending more time on practical and field work.
CHAPTER III
SPONGES
SUGGESTIONS.--In many parts of the United States, fresh-water
sponges may, by careful searching, be found growing on rocks and
logs in clear water. They are brown, creamy, or greenish in color,
and resemble more a cushion-like plant than an animal. They have
a characteristic gritty feel. They soon die after removal to an
aquarium.
A number of common small bath sponges may be bought and kept for use
in studying the skeleton of an ocean sponge. These sponges should
not have large holes in the bottom; if so, too much of the sponge
has been cut away. A piece of marine sponge preserved in alcohol or
formalin may be used for showing the sponge with its flesh in place.
Microscopic slides may be used for showing the spicules.
[Illustration: FIG. 21.--FRESH-WATER SPONGE.]
[Illustration: FIG. 22.--SECTION of fresh-water sponge (enlarged).]
The small =fresh-water sponge= (Fig. 21) lacks the more or less
vase-like form typical of sponges. It is a rounded mass growing upon a
rock or log. As indicated by the arrows, where does _water enter_ the
sponge? This may be tested by putting coloring matter in the water near
the living sponge. Where does the _water come out_? (Fig. 22.) Does it
pass through _ciliated chambers_ in its course? Is the _surface_ of the
sponge rough or smooth? Do any of the skeletal _spicules_ show on the
surface? (Fig. 21.) Does the sponge thin out near its edge?
[Illustration: FIG. 23.--EGGS and SPICULES of fresh-water sponge
(enlarged).]
The _egg_ of this sponge is shown in Fig. 23. It escapes from the
parent sponge through the _osculum_, or large outlet. As in most
sponges, the first stage after the egg is ciliated and free-swimming.
=Marine Sponges.=--The _grantia_ (Fig. 24) is one of the simplest of
marine sponges. What is the _shape_ of grantia? What is its length and
diameter? How does the free end differ from the fixed end? Are the
_spicules_ projecting from its body few or many?
[Illustration: FIG. 24.--Grantia.]
Where is the _osculum_, or large outlet? With what is this surrounded?
The osculum opens from a central cavity called the _cloaca_. The canals
from the pores lead to the cloaca.
_Buds_ are sometimes seen growing out from the sponge near its base.
These are young sponges formed asexually. Later they become detached
from the parent sponge.
[Illustration: FIG. 25.--Plan of a sponge.]
=Commercial “Sponge.”=--What part of the complete animal remains in the
bath sponge? _Slow growing sponges_ grow more at the top and form tall,
simple, tubular or vase-like animals. _Fast growing sponges_ grow on
all sides at once and form a complicated system of canals, pores, and
oscula. Which of these habits of growth do you think belonged to the
bath sponge? Is there a large hole in the base of your specimen? If so,
this is because the cloaca was reached in trimming the lower part where
it was attached to a rock. Test the _elasticity_ of the sponge when dry
and when wet by squeezing it. Is it softer when wet or dry? Is it more
elastic when wet or dry? How many _oscula_ does your specimen have? How
many _inhalent pores_ to a square inch? Using a probe (a wire with knob
at end, or small hat pin), try to trace the _canals_ from the pores to
the cavities inside.
Do the _fibers_ of the sponge appear to interlace, or join, according
to any system? Do you see any fringe-like growths on the surface which
show that new tubes are beginning to form? Was the sponge growing
faster at the top, on the sides, or near the bottom?
Burn a bit of the sponge; from the odor, what would you judge of its
composition? Is the inner cavity more conspicuous in a simple sponge or
in a compound sponge like the bath sponge? Is the bath sponge branched
or lobed? Compare a number of specimens (Figs. 26, 27, 28) and decide
whether the common sponge has a typical shape. What features do their
forms possess in common?
[Illustration: FIG. 26.--Bath Sponge.]
[Illustration: FIG. 27.--Bath Sponge.]
[Illustration: FIG. 28.--Bath Sponge.]
Sponges are divided into _three classes_, according as their skeletons
are flinty (silicious), limy (calcareous), or horny.
Some of the _silicious sponges_ have skeletons that resemble spun glass
in their delicacy. Flint is chemically nearly the same as glass. The
skeleton shown in Fig. 29 is that of a glass sponge which lives near
the Philippine Islands.
[Illustration: FIG. 29.--Skeleton of a glass sponge.]
The _horny sponges_ do not have spicules in their skeletons, as
the flinty and limy sponges have, but the skeleton is composed of
interweaving fibers of _spongin_, a durable substance of the same
chemical nature as silk (Figs. 30 and 31).
[Illustration: FIG. 30.--A horny sponge.]
[Illustration: FIG. 31.--Section of horny sponge.]
The _limy sponges_ have skeletons made of numerous spicules of lime.
The three-rayed spicule is the commonest form.
The commercial sponge, seen _as it grows in the ocean_, appears as
a roundish mass with a smooth, dark exterior, and having about the
consistency of beef liver. Several large openings (oscula), from which
the water flows, are visible on the upper surface. Smaller holes
(inhalent pores--many of them so small as to be indistinguishable)
are on the sides. If the sponge is disturbed, the smaller holes, and
perhaps the larger ones, will close.
The outer layer of cells serves as a sort of skin. Since so much of
the sponge is in contact with water, most of the cells do their own
breathing, or absorption of oxygen and giving off of carbon dioxid.
_Nutriment_ is passed on from the surface cells to nourish the rest of
the body.
=Reproduction.=--Egg-cells and sperm-cells are produced by certain
cells along the canals. The egg-cell, after it is fertilized by the
sperm-cell, begins to divide and form new cells, some of which possess
cilia. The embryo sponge passes out at an osculum. By the vibration of
the cilia, it swims about for a while. It afterwards settles down with
the one end attached to the ocean floor and remains fixed for the rest
of its life. The other end develops oscula. Some of the cilia continue
to vibrate and create currents which bring food and oxygen.
The _cilia_ in many species are found only in cavities called ciliated
chambers. (Figs. 22, 32.) There are _no distinct organs_ in the sponge
and there is very little _specialization_ of cells. The ciliated cells
and the reproductive cells are the only specialized cells. The sponges
were for a long time considered as colonies of separate one-celled
animals classed as protozoans. They are, without doubt, many-celled
animals. If a living sponge is cut into pieces, each piece will grow
and form a complete sponge.
=That the sponge is not a colony of one-celled animals=, each like
an ameba, but is a many-celled animal, will be realized by examining
Fig. 32, which shows a bit of sponge highly magnified. A sponge
may be conceived as having developed from a one-celled animal as
follows: Several one-celled animals happened to live side by side;
each possessed a thread-like flagellum (E, Fig. 32) or whip-lash for
striking the water. By lashing the water, they caused a stronger
current (Fig. 25) than protozoans living singly could cause. Thus they
obtained more food and multiplied more rapidly than those living alone.
The habit of working together left its impress on the cells and was
transmitted by inheritance.
[Illustration: FIG. 32.--Microscopic plan of ciliated chamber. Each
cell lining the chamber has a nucleus, a whip-lash, and a collar around
base of whip-lash. _Question_: State two uses of whip-lash.]
Cell joined to cell formed a ring; ring joined to ring formed a tube
which was still more effective than a ring in lashing the water into a
current and bringing fresh food (particles of dead plants and animals)
and oxygen.
=No animals eat sponges=; possibly because spicules, or fibers, are
found throughout the flesh, or because the taste and odor is unpleasant
enough to protect them. Small animals sometimes crawl into them to
hide. One species grows upon shells inhabited by hermit crabs. Moving
of the shell from place to place is an advantage to them, while they
conceal the crab and thus protect it.
=Special Report:= _Sponge “Fisheries.”_ (Localities; how sponges are
taken, cleaned, dried, shipped, and sold.)
CHAPTER IV
POLYPS (CUPLIKE ANIMALS)
THE HYDRA, OR FRESH WATER POLYP
[Illustration: FIG. 33.--A HYDRA.]
SUGGESTIONS.--Except in the drier regions of the United States, the
hydra can usually be found by careful search in fresh water ponds
not too stagnant. It is found attached to stones, sticks, or leaves,
and has a slender, cylindrical body from a quarter to half an inch
long, varying in thickness from that of a fine needle to that of a
common pin. The green hydra and the brown hydra, both very small,
are common species, though hydras are often white or colorless. They
should be kept in a large glass dish filled with water. They may be
distinguished by the naked eye but are not studied satisfactorily
without a magnifying glass or microscope. Place a living specimen
attached to a bit of wood in a watch crystal filled with water, or on
a hollowed slip, or on a slip with a bit of weed to support the cover
glass, and examine with hand lens or lowest power of microscope.
Prepared microscopical sections, both transverse and longitudinal,
may be bought of dealers in microscopic supplies. One is shown in
Fig. 39.
Is the hydra’s =body= round or two-sided? (Fig. 35.) What is its
_general shape_? Does one individual keep the same shape? (Fig. 34.)
How does the length of the threadlike _tentacles_ compare with the
length of the hydra’s body? About how many tentacles are on a hydra’s
body? Do all have the same number of tentacles? Are the tentacles
knotty or smooth? (Fig. 35.) The hydra is usually extended and slender;
sometimes it is contracted and rounded. In which of these conditions
is the base (the foot) larger around than the rest of the body? (Fig.
34.) Smaller? How many _openings_ into the body are visible? Is there
a depression or an eminence at the base of the tentacles? For what is
the _opening_ on top of the body probably used? Why are the tentacles
placed at the top of the hydra’s body? Does the _mouth_ have the most
convenient location possible?
[Illustration: FIG. 34.--Forms assumed by Hydra.]
[Illustration: FIG. 35.--HYDRA (much enlarged).]
The conical projection bearing the _mouth_ is called _hypostome_ (Fig.
34). The mouth opens into the _digestive cavity_. Is this the same as
the general body cavity, or does the stomach have a wall distinct from
the _body cavity_? How far down does the body cavity extend? Does it
extend up into the tentacles? (Fig. 39.)
If a _tentacle is touched_, what happens? Is the body ever bent?
Which is more sensitive, the columnar body or the tentacles? In
searching for hydras would you be more likely to find the tentacles
extended or drawn in? Is the hypostome ever extended or drawn in?
(Fig. 34.)
=Locomotion.=--The round surface, or disk, by which the hydra is
attached, is called its foot. Can you move on one foot without hopping?
The hydra moves by alternately elongating and rounding the foot. Can
you discover other ways by which it moves? Does the hydra always stand
upon its foot?
[Illustration: FIG. 36.--NETTLING CELL.
II. discharged, and I. not discharged.]
=Lasso Cells.=--Upon the tentacles (Fig. 35) are numerous cells
provided each with a thread-like process (Fig. 36) which lies coiled
within the cell, but which may be thrown out upon a water flea, or
other minute animal that comes in reach. The touch of the lasso
paralyzes the prey (Fig. 37). These cells are variously called lasso
cells, nettling cells, or thread cells. The thread is hollow and is
pushed out by the pressure of liquid within. When the pressure is
withdrawn the thread goes back as the finger of a glove may be turned
back into the glove by turning the finger outside in. When a minute
animal, or other particle of food comes in contact with a tentacle, how
does the tentacle get the food to the mouth? By bending and bringing
the end to the mouth, or by shortening and changing its form, or in
both ways? (Fig. 34, _C_.) Do the neighboring tentacles seem to bend
over to assist a tentacle in securing prey? (Fig. 34, _C_.)
[Illustration: FIG. 37.--HYDRA capturing a water flea.]
=Digestion.=--The food particles break up before remaining long in the
stomach, and the nutritive part is absorbed by the lining cells, or
endoderm (Fig. 39). The indigestible remnants go out through the mouth.
The hydra is not provided with a special vent. Why could the vent not
be situated at the end opposite the mouth?
=Circulation and Respiration.=--Does water have free access to the body
cavity? Does the hydra have few or nearly all of its cells exposed to
the water in which it lives? From its structure, decide whether it
can breathe like a sponge or whether special respiratory cells are
necessary to supply it with oxygen and give off carbon dioxid. Blood
vessels are unnecessary for transferring oxygen and food from cell to
cell.
[Illustration: FIG. 38.--HYDRAS on pondweed.]
=Reproduction.=--Do you see any swellings upon the side of the
hydra? (Fig. 34, A.) If the swelling is near the tentacles, it is a
_spermary_; if near the base it is an _ovary_. A sperm coalesces with
or fertilizes the ovum after the ovum is exposed by the breaking of the
ovary wall. Sometimes the sperm from one hydra unites with the ovum of
another hydra. This is called _cross-fertilization_. The same term is
applied to the process in plants when the male element, or pollen, of
the flower unites with the ovules, or female element, of the flower
on another plant. The hydra, like most plants and some other animals,
is hermaphrodite, that is to say, both sperms and ova are produced by
one individual. In the autumn, eggs are produced with hard shells to
withstand the cold until spring. Sexual reproduction takes place when
food is scarce. Asexual generation (by budding) is common with the
hydra when food supply is abundant. After the bud grows to a certain
size, the outer layer of cells at the base of the bud constricts and
the young hydra is detached.
=Compare the sponge and the hydra= in the following respects:--many
celled, or one celled; obtaining food; breathing; tubes and cavities;
openings; reproduction; locomotion. Which ranks higher among the
metazoa? The metazoa, or many celled animals, include all animals
except which branch?
[Illustration: FIG. 39.--Longitudinal section of hydra (microscopic and
diagrammatic).]
Figure 39 is a _microscopic view_ of a vertical section of a hydra to
show the =structure of the body wall=. There is an outer layer called
the _ectoderm_, and an inner layer called the _endoderm_. There
is also a thin supporting layer (black in the figure) called the
_mesoglea_. The mesoglea is the thinnest layer. Are the cells larger
in the endoderm or the ectoderm? Do both layers of cells assist in
forming the reproductive bud? The ectoderm cells end on the inside
in contractile tails which form a thin line and have the effect of
muscle fibers. They serve the hydra for its remarkable changes of
shape. When the hydra is cut in pieces, each piece makes a complete
hydra, provided it contains both endoderm and ectoderm.
In what ways does the hydra show “=division of labor=”? Answer this
by explaining the classes of cells specialized to serve a different
purpose. Which cells of the hydra are least specialized? In what
particulars is the plan of the hydra different from that of a simple
sponge? An ingenious naturalist living more than a century ago,
asserted that it made no difference to the hydra whether the ectoderm
or the endoderm layer were outside or inside,--that it could digest
equally well with either layer. He allowed a hydra to swallow a worm
attached to a thread, and then by gently pulling in the thread,
turned the hydra inside out. More recently a Japanese naturalist
showed that the hydra could easily be turned inside out, but he also
found that when left to itself it soon reversed matters and returned
to its natural condition, that =the cells are really specialized= and
each layer can do its own work and no other.
=Habits.=--The hydra’s whole body is a hollow bag, the cavity extending
even into the tentacles. The tentacles may increase in number as the
hydra grows but seldom exceed eight. The hydra has more active motion
than locomotion. It seldom moves from its place, but its tentacles are
constantly bending, straightening, contracting, and expanding. The body
is also usually in motion, bending from one side to another. When the
tentacles approach the mouth with captured prey, the mouth (invisible
without a hand lens) opens widely, showing five lobes or lips, and the
booty is soon tucked within. A hydra can swallow an animal larger in
diameter than itself.
The =endoderm cells= have _ameboid motion_, that is, they extend
pseudopods. They also resemble amebas in the power of _intra-cellular
digestion_; that is, they absorb the harder particles of food and
digest them afterwards, rejecting the indigestible portions. Some of
these cells have _flagella_ (see Fig. 39) which keep the fluid of the
cavity in constant motion.
Sometimes the =hydra moves= after the manner of a small caterpillar
called a “measuring worm,” that is, it takes hold first by the foot,
then by the tentacles, looping its body at each step. Sometimes the
body goes end over end in slow somersaults.
The _length_ of the extended hydra may reach one half inch. When
touched, both tentacles and body contract until it looks to the unaided
eye like a round speck of jelly. This shows _sensibility_, and a few
small star-shaped cells are believed to be _nerve cells_, but the hydra
has not a nervous _system_. Hydras show their liking for light by
moving to the side of the vessel or aquarium whence the light comes.
[Illustration: FIG. 40.--HYDROID COLONY, with nutritive (_P_)
reproductive (_M_) and defensive (_S_) hydranths.]
=The Branch Polyps= (sometimes called _Cœlenterata_).--The hydra is the
_only fresh water representative_ of this great branch of the animal
kingdom. This branch is characterized by its members having only one
opening to the body. The polyps also include the salt water animals
called _hydroids_, _jellyfishes_, and _coral polyps_.
[Illustration: FIG. 41.--“PORTUGUESE MAN-O’-WAR” (compare with Fig.
40). A floating hydroid colony with long, stinging (and sensory)
streamers. Troublesome to bathers in Gulf of Mexico. Notice
balloon-like float.]
=Hydroids.=--Figure 40 shows a _hydroid_, or group of hydra-like
growths, one of which eats and digests for the group, another defends
by nettling cells, another produces eggs. Each hydra-like part of a
hydroid is called a _hydranth_. Sometimes the buds on the hydra remain
attached so long that a bud forms upon the first bud. Thus three
generations are represented in one organism. Such growths show us that
it is not always easy to tell what constitutes an individual animal.
[Illustration: FIG. 42.--The formation of many free swimming
jellyfishes from one fixed hydra-like form. The saucer-like parts (_h_)
turn over after they separate and become like Fig. 43 or 44. Letters
show sequence of diagrams.]
_Hydroids_ may be conceived _to have been developed_ by the failure
of budding hydras to separate from the parent, and by the gradual
formation of the habit of living together and assisting each other.
When each hydranth of the hydroid devoted itself to a special function
of digestion, defense, or reproduction, this group lived longer and
prospered; more eggs were formed, and the habits of the group were
transmitted to a more numerous progeny than were the habits of a group
where members worked more independently of each other.
As the _sponge_ is the first, lowest, and simplest example of the
devotion of _special cells to special purposes_, the hydroid is the
first, lowest, and simplest example of the occurrence of _organs_, that
is of _special parts of the body_ (groups of cells) _set aside for a
special work_.
How many mature hydranths are seen in the hydroid shown in Fig. 40?
Why are the defensive hydranths on the outside of the colony? Which
hydranths have no tentacles? Why not?
=Jellyfish.=--=Alternation of Generations.=--=Medusa.=--With some
species of hydroids, a very curious thing happens.--The _hydranth
that is to produce the eggs falls off_ and becomes independent of the
colony. More surprising still, its appearance changes entirely and
instead of being hydra-like, it becomes the large and complex creature
called _jellyfish_ (Fig. 43). But the _egg of the jellyfish_ produces a
small _hydra-like animal_ which gives rise by budding to a _hydroid_,
and the cycle is complete.
[Illustration: FIG. 43.--A JELLYFISH.]
[Illustration: FIG. 44.--A JELLYFISH (medusa).]
The bud (or reproductive hydranth) of the hydroid does not produce a
hydroid, but a jellyfish; the egg of the jellyfish does not produce a
jellyfish, but a hydroid. This is called by zoologists, _alternation of
generations_. A _complete individual_ is the life from the germination
of one egg to the production of another. So that an “individual”
consists of a hydroid colony fixed in one place together with all the
jellyfish produced from its buds, and which may now be floating miles
away from it in the ocean. Bathers in the surf are sometimes touched
and stung by the long, streamer-like tentacles of the jellyfish. These,
like the tentacles of the hydra, have nettling cells (Fig. 41).
The umbrella-shaped free swimming jellyfish is called a _medusa_ (Fig.
44).
=Coral Polyps.=--Some of the salt water relatives of the hydra
produce buds which remain attached to the parent without, however,
becoming different from the parent in any way. The _coral polyps_ and
_corallines_ are examples of _colonies_ of this kind, possessing a
common stalk which is formed as the process of multiplication goes
on. In the case of coral polyps, the separate animals and the flesh
connecting them secrete within themselves a hard, _limy, supporting
structure known as coral_. In some species, the coral, or stony part,
is so developed that the polyp seems to be inserted in the coral, into
which it withdraws itself for partial protection (Fig. 45).
[Illustration: FIG. 45.--CORAL POLYPS (tentacles, a multiple of _six_).
Notice hypostome.]
The _corallines_ secrete a smooth stalk which affords no protection,
but they also secrete a coating or sheath which incloses both
themselves and the stalk. The coating has apertures through which the
polyps protrude in order to feed when no danger is near (Fig. 46). The
red “corals” used for jewelry are bits of stalks of corallines. The
corallines (Figs. 47, 48) are not so abundant nor so important as the
coral polyps (Figs. 45, 49).
[Illustration: FIG. 46.--RED CORALLINE with crust and polyps (_eight_
tentacles).]
[Illustration: FIG. 47.--SEA FAN (a coralline).]
Colonies of coral polyps grow in countless numbers in the tropical
seas. The coral formed by successive colonies of polyps accumulates
and builds up many islands and important additions to continents. The
Florida “keys,” or islands, and the southern part of the mainland of
Florida were so formed.
[Illustration: FIG. 48.--ORGAN PIPE “Coral” (a coralline).]
The =Sea Anemone=, like the coral polyp, lives in the sea, but like
the fresh water hydra, it _deposits no limy support for its body_.
The anemone is much larger than the hydra and most coral polyps,
many species attaining a height of several inches. It _does not
form colonies._ When its arms are drawn in, it looks like a large
knob of shiny but opaque jelly. Polyps used to be called _zoophytes
(plant-animals)_, because of their flower-like appearance (Figs. 50,
51).
[Illustration: FIG. 49.--UPRIGHT CUT through coral polyp × 4.
_ms_, mouth; _mr_, gullet; _ls, ls_, fleshy partitions (mesenteries)
extending from outer body wall to gullet (to increase absorbing
surface); _s, s_, shorter partitions; _mb, fb_, stony support (of lime,
called coral); _t_, tentacles.]
[Illustration: FIG. 50.--SEA ANEMONE.]
[Illustration: FIG. 51.--SEA ANEMONES.]
CHAPTER V
ECHINODERMS (SPINY ANIMALS)
THE STARFISH
SUGGESTIONS. Since the echinoderms are aberrant though interesting
forms not in the regular line of development of animals, this chapter
may be omitted if it is desired to shorten the course.--The common
starfish occurs along the Atlantic coast. It is captured by wading
along the shore when the tide is out. It is killed by immersion in
warm, fresh water. Specimens are usually preserved in 4 per cent
formalin. Dried starfish and sea urchins are also useful. A living
starfish kept in a pail of salt water will be instructive.
[Illustration: FIG. 52.--Starfish on a rocky shore.]
[Illustration: FIG. 53.--PLAN of starfish; III, madreporite.]
=External Features.=--Starfish are usually brown or yellow. Why? (See
Fig. 52.) Has it a head or tail? Right and left sides? What is the
shape of the _disk_, or part which bears the five arms or _rays_?
(Fig. 53.) Does the body as a whole have symmetry on two sides of a
line (bilateral symmetry), or around a point (radial symmetry)? Do the
separate rays have bilateral symmetry? The _skeleton_ consists of limy
plates embedded in the tough skin (Fig. 54). Is the _skin_ rough or
smooth? Hard or soft? Are the projections (or _spines_) in the skin
long or short? The skin is hardened by the limy plates, except around
the _mouth_, which is at the center of the lower side and surrounded
by a membrane. Which is rougher, the mouth side, (_oral_ side) or the
opposite (_aboral_ side)? Which side is more nearly flat? The _vent_ is
at or near the center of the disk on the aboral surface. It is usually
very small and sometimes absent. Why a vent is not of much use will be
understood after learning how the starfish takes food.
[Illustration: FIG. 54.--LIMY PLATES in portion of a ray.]
[Illustration: FIG. 55.--Starfish (showing MADREPORITE).]
An organ peculiar to animals of this branch, and called the _madreporic
plate_, or _madreporite_, is found on the aboral surface between the
bases of two rays (Fig. 55). It is wartlike, and usually white or red.
This plate is a _sieve_; the small openings keep out sand but allow
water to filter through.
[Illustration: FIG. 56.--WATER tube System of starfish.
_m_, madreporite; _stc_, stone canal; _ap_, ampulla.]
=Movements: the Water-tube System.=--The water, which is filtered
through the perforated madreporite, is needed to supply a _system of
canals_ (Fig. 56). The madreporite opens into a canal called the _stone
canal_, the wall of which is hardened by the same kind of material
as that found in the skin. The stone canal leads to the ring canal
which surrounds the mouth (Fig. 56). The ring canal sends _radial
canals_ into each ray to supply the double row of _tube feet_ found in
the groove at the lower side of each ray (Fig. 57). Because of their
arrangement in rows, the feet are also called _ambulacral_ feet (Latin
_ambulacra_, “forest walks”). There is a water holder (_ampulla_), or
muscular water bulb at the base of each tube foot (Fig. 58). These
contract and force the water into the tube feet and extend them. The
cuplike ends of the tubes cling to the ground by suction. The feet
contain delicate muscles by which they contract and shorten. Thus the
animal pulls itself slowly along, hundreds of feet acting together.
The tube feet, for their own protection, may contract and retire into
the groove, the water which extended them being sent back into the
ampulla. This system of water vessels (or water-vascular system) of the
echinodermata is characteristic of them; _i.e._ is not found elsewhere
in the animal kingdom. The grooves and the plates on each side of them
occupy the _ambulacral areas_. The rows of spines on each side of the
grooves are freely movable. (What advantage?) The spines on the aboral
surface are not freely movable.
[Illustration: FIG. 57.--Starfish, from below; tube feet extended.]
[Illustration: FIG. 58.--SECTION OF ONE RAY and central portion of
starfish.
_f1_, _f2_, _f3_, tube feet more or less extended; _au_, eye spot;
_k_, gills; _da_, stomach; _m_, madreporite; _st_, stone canal; _p_,
ampulla; _ei_, ovary.]
=Respiration.=--The _system of water vessels serves the additional
purpose_ of bringing water containing oxygen into contact with various
parts of the body, and the starfish was formerly thought to have no
special respiratory organs. However there are holes in the aboral wall
through which the folds of the delicate lining membrane protrude. These
are now supposed to be _gills_ (_k_, Fig. 58).
=The nervous system= is so close to the aboral surface that much of
it is visible without dissection. Its chief parts are a _nerve ring_
around the mouth, which sends off a _branch_ along each ray. These
branches may be seen by separating the rows of tube feet. They end in a
pigmented cell at the end of each ray called the _eye-spot_.
=The food= of starfish consists of such animals as crabs, snails, and
oysters. When the prey is too large to be taken into the mouth, the
starfish _turns its stomach inside out_ over the prey (Fig. 59). After
the shells separate, the stomach is applied to the soft digestible
parts. After the animal is eaten, the stomach is retracted. This odd
way of eating is very economical to its digestive powers, for _only
that part of the food which can be digested and absorbed is taken into
the body_. Only the lower part of the stomach is wide and extensible.
The upper portion (next to the aboral surface) is not so wide. This
portion receives the secretion from five pairs of digestive glands,
a pair of which is situated in each ray. Jaws and teeth are absent.
(Why?) The vent is sometimes wanting. Why?
[Illustration: FIG. 59.--Starfish eating a sea snail.
_b_, stomach everted.]
=Reproduction.=--There is a pair of ovaries at the base of each ray of
the female starfish (Fig. 58). The spermaries of the male have the same
position and form as the ovaries, but they are lighter colored, usually
white.[2]
[2] The sperm cells and egg cells are poured out into the water by
the adults, and the sperm cell, which, like all sperm cells, has a
vibratory, tail-like flagellum to propel it, reaches and fertilizes the
egg cell.
=Regeneration after Mutilation.=--If a starfish loses one or more rays,
they are replaced by growth. Only a very ignorant oyster-man, angry at
the depredations of starfish upon his oyster beds, would chop starfish
to pieces, as this only serves to multiply them. This power simulates
multiplication by division in the simplest animals.
=Steps in Advance of Lower Branches.=--The starfish and other
echinodermata have a more developed nervous system, sensory organs, and
digestion, than forms previously studied; most distinctive of all, they
have a body cavity distinct from the food cavity. The digestive glands,
reproductive glands, and the fluid which serves imperfectly for blood,
are in the body cavity. There is no heart or blood vessels. The motions
of the stomach and the bending of the rays give motion to this fluid in
the body cavity. It cannot be called blood, but it contains white blood
corpuscles.
[Illustration: FIG. 60.--Young starfish crawling upon their mother.
(Challenger Reports.)]
The starfish when first hatched is an actively swimming bilateral
animal, but it soon becomes starlike (Fig. 60). The limy plates of the
starfish belong neither to the outer nor inner layer (endoderm and
ectoderm) of the body wall, but to a third or middle layer (mesoderm);
for echinoderms, like the polyps, belong to the three-layered animals.
In this its skeleton differs from the shell of a crawfish, which is
formed by the hardening of the skin itself.
=Protective Coloration.=--Starfish are brown or yellow. This makes them
inconspicuous on the brown rocks or yellow sands of the seashore. This
is an example of protective coloration.
THE SEA URCHIN
=External Features.=--What is the _shape_ of the body? What kind of
_symmetry_ has it? Do you find the oral (or mouth) surface? The aboral
surface? Where is the body flattened? What is the shape of the spines?
What is their use? How are the tube feet arranged? Where do the rows
begin and end? Would you think a sea urchin placed upside down in
water, could right itself less or more readily than a starfish? What
advantage in turning would each have that the other would not have? The
name sea urchin has no reference to a mischievous boy, but means sea
hedgehog (French _oursin_, hedgehog), the name being suggested by its
spines.
=Comparison of Starfish and Sea Urchin.=--The water system of the sea
urchin, consisting of madreporite, tubes, and water bulbs, or ampullæ,
is similar to that of the starfish. The tube feet and locomotion are
alike. There is no need for well-developed respiratory organs in either
animal, as the whole body, inside and out, is bathed in water. The
method of reproduction is the same.
[Illustration: FIG. 61.--A SEA URCHIN crawling up the glass front wall
of an aquarium (showing mouth spines and tube feet).]
[Illustration: FIG. 62.--A SEA URCHIN with spines removed, the limy
plates showing the knobs on which the spines grew.]
[Illustration: FIG. 63.--SECTION OF SEA URCHIN with soft parts removed,
showing the jaws which bear the teeth protruding in Fig. 62.]
The starfish eats animal food. The food of the sea urchin is almost
exclusively vegetable, hence it needs teeth (Fig. 62, 63); its food
tube is longer than that of a starfish, just as the food tube of a
sheep, whose food digests slowly, is much longer than that of a dog.
[Illustration: FIG. 64.--THE SEA OTTER, an urchin with mouth (_o_) and
vent (_A_) on same side of body.]
The largest species of sea urchins are almost as big as a child’s
head, but this size is unusual. The spines are mounted on knobs, and
the joint resembles a ball-and-socket joint, and allow as wide range
of movement. Some sea urchins live on sandy shores, other species live
upon the rocks. The sand dollars are lighter colored. (Why?) They are
usually flatter and have lighter, thinner walls, for there is danger of
sinking into the sand. The five-holed sand cake or sand dollar has its
weight still further diminished by the holes, which also allow it to
rise more easily through the water. The flattened lower surface of both
starfish and sea urchin causes the body to remain still while the tube
feet are stretching forward for another step.
OTHER ECHINODERMS
The =sea cucumbers=, or =holothurians=, resemble the sea urchin in
many respects, but their bodies are elongated, and the limy plates are
absent or very minute. The mouth is surrounded by tentacles (Fig. 65).
[Illustration: FIG. 65.--SEA CUCUMBERS.]
[Illustration: FIG. 66.--A BRITTLE STAR.]
The =brittle stars= resemble the starfish in form, but their rays are
very slender, more distinct from the disk, and the tube feet are on the
edges of the rays, not under them (Fig. 66).
The =crinoids= are the most ancient of the echinoderms. (Figs. 67,
68.) Their fossils are very abundant in the rocks. They inhabited
the geological seas, and it is believed that the other echinoderms
descended from them. A few now inhabit the deep seas. Some species
are fixed by stems when young, and later break away and become
free-swimming, others remain fixed throughout life.
The four classes of the branch echinoderms are Starfish (_asteroids_),
Sea urchins (_echinoids_), Sea cucumbers (_holothurians_), and Sea
lilies (_crinoids_).
[Illustration: FIG. 67.--CRINOID, arms closed.]
[Illustration: FIG. 68.--DISK OF CRINOID from above, showing mouth in
center and vent near it, at right (arms removed).]
Comparative Review
Make a table like this as large as the page of the notebook will allow,
and fill in without guessing.
===================+=========+========+=========+=========+=========
| AMEBA | SPONGE | HYDRA | CORAL | STARFISH
| | | | POLYP |
-------------------+---------+--------+---------+---------+---------
| | | | |
Is body round, two-| | | | |
sided, or irregular| | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
What organs of | | | | |
sense | | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
Openings into body | | | | |
| | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
Hard or supporting | | | | |
parts of body | | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
How food is taken | | | | |
| | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
How move | | | | |
| | | | |
| | | | |
-------------------+---------+--------+---------+---------+---------
| | | | |
How breathe | | | | |
| | | | |
| | | | |
===================+=========+========+=========+=========+=========
CHAPTER VI
WORMS
SUGGESTIONS:--Earthworms may be found in the daytime after a heavy
rain, or by digging or turning over planks, logs, etc., in damp
places. They may be found on the surface at night by searching with a
lantern. Live specimens may be kept in the laboratory in a box packed
with damp (not wet) loam and dead leaves. They may be fed on bits of
fat meat, cabbage, onion, etc., dropped on the surface. When studying
live worms, they should be allowed to crawl on damp paper or wood. An
earthworm placed in a glass tube with rich, damp soil, may be watched
from day to day.
=External Features.=--Is the body _bilateral_? Is there a _dorsal_ and
_ventral_ surface? Can you show this by a test with a live worm? Do you
know of an animal with dorsal and ventral surface, but not bilateral?
[Illustration: FIG. 69.--An Earthworm.]
Can you make out a head? A head end? A neck? Touch the head and test
whether it can be made to crawl backwards. Which end is more tapering?
Is the mouth at the tip of the head end or on the upper or lower
surface? How is the _vent_ situated? Its shape? As the worm lies on
a horizontal surface, is the body anywhere flattened? Are there any
_very_ distinct divisions in the body? Do you see any _eyes_?
=Experiment= to find whether the worm is sensitive (1) to _touch_,
(2) to _light_, (3) to strong _odors_, (4) to irritating liquids.
Does it show a sense of _taste_? The experiments should show whether
it avoids or seeks a bright light, as a window; also whether any
parts of the body are especially sensitive to touch, or all equally
sensitive. What effect when a bright light is brought suddenly near
it at night?
Is _red blood_ visible through the skin? Can you notice any
_pulsations_ in a vessel along the back? Do all earthworms have the
same number of _divisions_ or rings? Compare the size of the rings or
segments. Can it crawl faster on glass or on paper?
[Illustration: FIG. 70.--MOUTH AND SETÆ.]
[Illustration: FIG. 71.--EARTHWORM, mouth end above.]
A magnifying glass will show on most species tiny bristle-like
projections called _setæ_. How are the setæ arranged? (_d_, Fig. 70.)
How many on one ring of the worm? How do they point? Does the worm feel
smoother when it is pulled forward or backward between the fingers?
Why? Are setæ on the lower surface? Upper surface? The sides? What is
the use of the setæ? Are they useful below ground? Does the worm move
at a uniform rate? What change in form occurs as the front part of the
body is pushed forward? As the hinder part is pulled onward? How far
does it go at each movement? At certain seasons a broad band, or ring,
appears, covering several segments and making them seem enlarged (Fig.
71). This is the _clitellum_, or _reproductive girdle_. Is this girdle
nearer the mouth or the tail?
=Draw= the exterior of an earthworm.
=Dorsal and Ventral Surfaces.=--The earthworm always crawls with the
same surface to the ground; this is called the _ventral_ surface, the
opposite surface is the _dorsal_ surface. This is the first animal
studied to which these terms are applicable. What are the ventral and
dorsal surfaces of a fish, a frog, a bird, a horse, a man?
=The name “worm”= is often carelessly applied to various crawling
things in general. It is properly applied, however, only to
_segmented animals without jointed appendages_. Although a
caterpillar crawls, it is not a worm for several reasons. It has six
jointed legs, and it is not a developed animal, but only an early
stage in the life of a moth or butterfly. A “grubworm” also has
jointed legs (Fig. 167). It does not remain a grub, but in the adult
stage is a beetle. A worm never develops into another animal in the
latter part of its life; its setæ are not jointed.
[Illustration: FIG. 72.--FOOD TUBE of earthworm. (Top view.)]
[Illustration: FIG. 73.--FOOD TUBE AND BLOOD VESSELS of earthworm
showing the ring-like hearts. (Side view.)]
=The Food Tube.=--The earthworm has no teeth, and the food tube, as
might be inferred from the form of the body, is simple and straight. On
account of slight variation in size and structure, its parts are named
the pharynx (muscular), gullet, crop, gizzard (muscular), and the long
intestine extending through the last three fourths of its body (Fig.
72). The functions of the parts of the food tube are indicated by their
names.
[Illustration: FIG. 74.]
=Circulation.=--There is a _large dorsal_ blood vessel above the food
tube (Fig. 73). From the front portion of this tube arise several large
tubular rings or “hearts” which are contractile and serve to keep the
blood circulating. They lead to a _ventral vessel_ below the food
tube (Fig. 74). The blood is red, but the _coloring matter_ is in the
liquid, not in the blood cells.
=Nervous System.=--Between the ventral blood vessels is a _nerve cord_
composed of two strands (see Fig. 75). There is a slight swelling, or
_ganglion_, on each strand, in each segment (Fig. 75). The strands
separate near the front end of the worm, and a branch goes up each side
of the gullet and enters the two pear-shaped _cerebral ganglia_, or
“brain” (Fig. 75).
[Illustration: FIG. 75.--GANGLIA NEAR MOUTH and part of nerve chain of
earthworm.]
=Food.=--The earthworm eats earth containing organic matter, the
inorganic part passing through the vent in the form of circular casts
found in the morning at the top of the earthworm’s hole. What else does
it eat?
The earth worm needs no teeth, as it excretes through the mouth an
_alkaline fluid_ which softens and partly digests the food before it
is eaten. When this fluid is poured out upon a green leaf, the leaf at
once turns brown. The starch in the leaf is also acted upon. The snout
aids in pushing the food into the mouth.
=Kidneys.=--Since oxidation is occurring in its tissues, and impurities
are forming, there must be some way of _removing impurities from the
tissues_. The earthworm does not possess one-pair organs like the
kidneys of higher animals to serve this purpose, but it has numerous
pairs of small tubular organs called _nephridia_ which serve the
purpose. Each one is simply a tube with several coils (Fig. 76). There
is a pair on the floor of each segment (Fig. 76). Each nephridium has
an inner open end within the body cavity, and its outer end opens by a
pore on the surface between the setæ (Fig. 78). The nephridia absorb
waste water from the liquid in the _celom_, or body cavity surrounding
the food tube, and convey it to the outside.
[Illustration: FIG. 76.--TWO PAIRS OF NEPHRIDIA.]
=Respiration.=--The skin of the earthworm is moist, and the blood
capillaries approach so near to the surface of the body that the oxygen
is constantly passing in from the air, and carbon dioxid passing out;
hence it is constantly breathing through all parts of its skin. _It
needs no lungs_ nor special respiratory organs of any kind.
[Illustration: FIG. 77.--Sperm (_sp_) and egg glands (_es_) of
earthworm.]
=Reproduction.=--When one individual animal produces both sperm cells
and egg cells, it is said to be hermaphrodite. This is true of the
earthworm. The egg cell is always fertilized, however, not by the
sperm cells of the same worm, but by sperm cells formed by another
worm. The openings of these ova or _egg glands_ consist of two pairs
of small pores found on the ventral surface of the fourteenth and
fifteenth segments in most species (see Fig. 77). There are also two
pairs of small _receptacles_ for temporarily holding the _foreign
sperm cells_. One pair of the openings from these receptacles is found
(with difficulty) in the wrinkle behind the ninth segment (Fig. 77),
and the other pair behind the tenth segment. The _sperm glands_ are
in front of the ovaries (Fig. 77), but the _sperm ducts_ are longer
than the _oviducts_, and open behind them (Figs. 77, 78). The worms
exchange sperm cells, but not egg cells. The reproductive girdle, or
_clitellum_, already spoken of, forms the case which is to hold the
eggs (see Fig. 71). When the sperm cells have been exchanged, and the
ova are ready for fertilization, the worm draws itself backward from
the collarlike case or clitellum so that it slips over the head. As it
passes the fifteenth and sixteenth segments, it collects the ova, and
as it passes the ninth and tenth segments, it collects the sperm cells
previously received by touching another worm. The elastic, collar-like
clitellum closes at the ends after it has slipped over the worm’s head,
forming a _capsule_. The ova are _fertilized in this capsule_, and some
of them hatch into worms in a few days. These devour the eggs which do
not hatch. The eggs develop into complete but very small worms before
the worms escape from the capsule.
[Illustration: FIG. 78.--Side view showing setæ, nephridia pores, and
reproductive openings.]
=Habits.=--The earthworm is omnivorous. It will eat bits of meat as
well as leaves and other vegetation. It has also the advantage, when
digging its hole, of _eating the earth_ which must be excavated.
Every one has noticed the fresh “casts” piled up at the holes in the
morning. As the holes are partly filled by rains, the casts are most
abundant after rains. The chief _enemies_ of the earthworm are moles
and birds. The worms _work at night_ and retire so early in the morning
that it takes a very early bird to catch a worm. Perhaps the nearest
to an intelligent act the earthworm accomplishes is to _conceal the
mouth of its hole_ by plugging it with a pebble or bit of leaf. They
_hibernate_, going below danger of frost in winter. In dry weather they
burrow several feet deep.
=The muscular coat= beneath, and much thicker than the skin, consists
of two layers: an outer _layer runs around the body_ just beneath the
skin, and an inner, thicker _layer of fibers runs lengthwise_. The worm
crawls by shortening the longitudinal muscles. As the bristles (_setæ_)
point backward, they prevent the front part of the body from slipping
back, so the hinder part is drawn forward. Next, the circular muscles
contract, and the bristles preventing the hind part from slipping back,
the fore portion is pushed forward. Is the worm thicker when the hinder
part is being pulled up or when the fore part is being thrust forward?
Does the earthworm pull or push itself along, or does it do both?
Occasionally it travels backward, _e.g._ it sometimes goes backward
into its hole. Then the bristles are directed forward.
The right and left halves of the body are counterparts of each other,
hence the earthworm is _bilaterally symmetrical_. The lungs and gills
of animals must always be kept moist. The worm _cannot live long in dry
air_, for respiration in the skin ceases when it cannot be kept moist,
and the worm smothers. Long immersion in water is injurious to them,
perhaps because there is far less oxygen in water than in the air.
Darwin wrote a book called “Vegetable Mold and Earthworms.” He
estimated that there were fifty thousand earthworms to the acre on
farm land in England, and that they bring up eighteen tons of soil in
an acre each year. As the acids of the food tube act upon the mineral
grains that pass through it, the earthworm renders _great aid in
forming soil_. By burrowing it makes the soil more _porous_ and brings
up the subsoil.
Although without eyes, the worm is sensitive to light falling upon its
anterior segments. When the light of a lantern suddenly strikes it at
night, it crawls quickly to its burrow. Its sense of touch is so keen
that it can detect a light puff of breath. Which of the foods kept in a
box of damp earth disappeared first? What is indicated as to a sense of
taste?
Why is the bilateral type of structure better adapted for development
and higher organization than the radiate type of the starfish? The
earthworm’s body is a double tube; the hydra’s body is a single tube;
which plan is more advantageous, and why? Would any other color do just
as well for an earthworm? Why, or why not?
The _sandworm_ (Nereis) lives in the sand of the seashore, and swims
in the sea at night (Fig. 79). It is more advanced in structure than
the earthworm, as it has a distinct head (Fig. 80), eyes, two teeth,
two lips, and several pairs of antennæ, and two rows of muscular
projections which serve as feet. It is much used by fishermen for
bait. If more easily obtained, it may be studied instead of the
earthworm.
[Illustration: FIG. 79.--SAND WORM × ²⁄₃ (Nereis).]
=There are four classes in the branch Vermes=: 1) the _earthworms_,
including sandworms and leeches; 2) the _roundworms_, including
trichina, hairworms, and vinegar eels; 3) _flatworms_, including
tapeworm and liver fluke; 4) _rotifers_, which are mere specks in size.
[Illustration: FIG. 80.--HEAD OF SANDWORM (enlarged).]
The =tapeworm= is a flatworm which has lost most of its organs on
account of its parasitic life. Its egg is picked up by an herbivorous
animal when grazing. The embryo undergoes only partial development
in the body of the herbivorous animal, _e.g._ an ox. The next stage
will not develop until the beef is eaten by a carnivorous animal, to
whose food canal it attaches itself and soon develops a long chain of
segments called a “tape.” Each segment absorbs fluid food through its
body wall. As the segments at the older end mature, each becomes full
of germs, and the segments become detached and pass out of the canal,
to be dropped and perhaps picked up by an herbivorous animal and repeat
the life cycle.
The =trichina= is more dangerous to human life than the tapeworm.
It gets into the food canal in uncooked pork (bologna sausage, for
example), multiplies there, migrates into the muscles, causing great
pain, and encysts there, remaining until the death of the host. It is
believed to get into the bodies of hogs again when they eat rats, which
in turn have obtained the cysts from carcasses.
=Summary of the Biological Process.=--An earthworm is _a living machine
which does work_ (digging and crawling; seizing, swallowing, and
digesting food; pumping blood; growing and reproducing). To do the work
it must have a continual _supply of energy_. The energy for its work
is set free by the protoplasm (in its microscopic cells) undergoing
a destructive chemical change (_oxidation_). The waste products from
the breaking down of the protoplasm must be continually removed
(_excretion_). The broken-down protoplasm must be continually replaced
if life is to continue (the income must exceed the outgo if the animal
is still growing). The microscopic cells construct more protoplasm out
of food and oxygen (_assimilation_) supplied them by the processes of
nutrition (eating, digesting, breathing, circulating). This protoplasm
in turn oxidizes and releases more energy to do work, and thus the
cycle of life proceeds.
CHAPTER VII
CRUSTACEANS
CRAWFISH
SUGGESTIONS.--In regions where crawfish are not found, a live crab
may be used. Locomotion and behavior may be studied by providing a
tub of water, or better, a large glass jar such as a broad candy jar.
For suggestions on study of internal structure, see p. 58.
=Habitat.=--Do you often see crawfish, or crayfish, moving about, even
in water where they are known to be abundant? What does your answer
suggest as to the time when they are probably most active?
Why do you never see one building its chimney, even where crawfish
holes are abundant? Is the chimney always of the same color as the
surface soil? Are the crawfish holes only of use for protection? In
what kind of spots are crawfish holes always dug? Why? What becomes of
crawfish when the pond or creek dries up? How deep are the holes? How
large are the lumps of mud of which the chimney is built? How does it
get them out of the hole? Why is the mud built into a chimney instead
of thrown away? (What would happen to a well with its mouth no higher
than the ground?) Why are crawfish scarce in rocky regions, as New
England?
How does the color of the crawfish compare with its surroundings? Is
its color suited to life in clear or muddy water? Define protective
coloration.
=Habits.=--Does the crawfish walk better in water or out of it? Why?
Does it use the legs with the large claws to assist in walking? Do
the swimmerets (under the abdomen) move fast or slow? (Observe it
from below in a large jar of clear water.) What propels it backward?
Forward? Does the crawfish move at a more uniform rate when swimming
backward or forward? Why? In which way can it swim more rapidly? Do
the big legs with claws offer more resistance to the water while it
is swimming backward or forward? How does it hold the tail after the
stroke, while it is darting backward through the water? Hold a crawfish
with its tail submerged and its head up. Can the tail strike the water
with much force? Allow it to grasp a pencil: can it sustain its own
weight by its grip?
=Feeding.=--Offer several kinds of food to a crawfish that has not
been alarmed or teased. Does it prefer bread, meat, or vegetables?
How does it get the food to its mouth? Does it eat rapidly or slowly?
Does it tear the food with the big pincers? Can it gnaw with the small
appendages near the mouth?
=Breathing.=--Does the crawfish breathe with gills or lungs? Place a
few drops of ink near the base of the hind legs of a crawfish resting
quietly in shallow water. Where is the ink drawn in? Where does it come
out? To explain the cause and purpose of this motion, place a crawfish
in a large glass jar containing water, and see the vibratory motion of
the parts under the front portion of the body. There is a gill paddle,
or gill bailer, under the shell on each side of the body that moves at
the same rate.
=Senses.=--Crawfish are best caught with a piece of meat or beef’s
liver tied to a string. Do they always lose hold as soon as they are
lifted above the water? What do you conclude as to the alertness of
their senses? Does the covering of its body suggest the possession of a
delicate or dull sense of touch?
Of what motions are the _eyes_ capable? Touch one of the eyes. The
result? Can a crawfish see in all directions? To test this, place a
crawfish on a table and try whether you can move to a place where you
can see the crawfish without seeing its eyes. What are the advantages
and disadvantages of having the eyes on stalks?
[Illustration: FIG. 81.--CRAWFISH (dorsal surface).]
[Illustration: FIG. 82.]
Touch the body and the several appendages of the crawfish. Where does
it seem most sensitive to _touch_? Which can reach farther, the antennæ
or the big claws? Why are short feelers needed as well as long ones?
Make a loud and sudden noise without jarring the crawfish. Is it
affected by _sound_?
=External Anatomy= (Figs. 81, 82, 83, 84).--Is the body of the crawfish
rounded out (convex) everywhere, or is any part of its surface either
flat or rounded in (concave)? What _color_ has the crawfish? Is this
color of any use to the crawfish?
[Illustration: FIG. 83.--LATERAL VIEW OF CRAWFISH.]
[Illustration: FIG. 84.--FOURTH ABDOMINAL SEGMENT OF CRAWFISH with
swimmeret.]
Make out the two distinct regions or _divisions of the body_ (Fig. 81).
The anterior (front) region is called the head-chest or cephalothorax,
and the posterior (rear) region is called the tail. Which region is
larger? Why? Which is flexible? Why?
Is the _covering_ of the body hard or soft? What is the advantage
of such a covering? What are its disadvantages? How is the covering
modified at the joints to permit motion?
=Tail.=--How many joints, or segments, on the tail? (Figs. 81, 83.)
Does the hard covering of each segment slip under or over the segment
behind it when the abdomen is straight? Does this lessen friction while
swimming forward?
Is there a pair of _swimmerets_ to each segment of the abdomen? (Figs.
82, 86.) Notice that each swimmeret has a main stalk (protopod), an
outer branch (exopod), and an inner branch (endopod) (Fig. 84). Are the
stalk and the branches each in one piece or jointed? The middle part of
the tail fin is called the telson. By finding the position of the vent,
decide whether the food tube goes into the telson (Fig. 82). Should it
be called an abdominal segment? Are the side pieces of the tail fin
attached to the telson or to the sixth segment? Do these side pieces
correspond to swimmerets? Do they likewise have the Y-shaped structure?
(Fig. 86.)
If the swimmerets on the first abdominal segment are large, the
specimen is a male. If they are small, it is a female. Which sex is
shown in Fig. 82? Fig. 86?
=Carapace.=--The covering of the head chest (cephalothorax) is called
the carapace. Has it free edges? The _gills_ are on the sides of the
body and are covered by the carapace (Fig. 87). The projection in front
is called the _rostrum_, meaning beak. Does the rostrum project beyond
the eyes? There is a transverse groove across the carapace which may be
said to divide the head from the abdomen. Where does this groove end at
the sides?
[Illustration: FIG. 85.--1, mandible; 2, 3, maxillæ; 4, 5, 6,
maxillipeds.]
=Legs.=--How many legs has the crawfish? How many are provided with
large claws? Small claws? Is the outer claw hinged in each of the large
grasping pincers? The inner claw?
[Illustration: FIG. 86.--CRAWFISH (ventral surface).]
=Appendages for Taking Food.=--If possible to watch a living crawfish
eating, notice whether it places the food directly into the mouth with
the large claws. Bend the large claws under and see if they will reach
the mouth.
Attached just in front of the legs the crawfish has three pairs of
finger-like appendages, called foot jaws (maxillipeds), with which it
passes the food from the large pincers to its mouth (Figs. 85, 86).
They are in form and use more like fingers than feet. In front of the
foot jaws are two pairs of thin jaws (maxillæ) and in front of the
thin jaws are a pair of stout jaws (mandibles) (Fig. 85). Do the jaws
move sidewise or up and down? Which of the jaws has a jointed finger
(palp) attached to it? Do all of the appendages for taking food have
both exopod and endopod branches on a basal stalk or protopod? Which of
the appendages have a scalloped edge? How would you know from looking
at the crawfish that it is not merely a scavenger? Why are there no
pincers on the hind feet?
[Illustration: FIG. 87.--Gill cover removed and gills exposed. _Mp_,
gill bailer.]
=Sense Organs.=--Find the _antennæ_, or long feelers (Figs. 82, 90).
Are the antennæ attached above or below the eyes? (Fig. 87.)
[Illustration: FIG. 88.--LENGTHWISE SECTION OF MALE CRAWFISH.
_c_, heart; _Ac_, artery to head; _Aa_, artery to abdomen; _Km_,
stomach; _D_, intestine; _L_, liver; _T_, spermary; _Go_, opening of
sperm duct; _G_, brain; _N_, nerve chain.]
Find the pair of _antennules_, or small feelers. Are their divisions
like or unlike each other? Compare the length of the antennules and the
antennæ. Compare the flexibility of the antennæ with that of the other
appendages.
Observe the position of the _eyes_ (Figs. 81, 88). How long are the
eyestalks? Is the stalk flexible or stiff? Touch the eye. Where is the
joint which enables the stalk to move? Is the outer covering of the
eye hard or soft? A mounted preparation of the transparent covering
(cornea) of the eye, seen with lower power of microscope, reveals that
the cornea is made up of many divisions, called facets. Each facet is
the front of a very small eye, hundreds of which make up the whole eye,
which is therefore called a compound eye. The elongated openings to the
_ear sacs_ are located each on the upper side of the base of a small
feeler just below the eye.
=Respiratory System.=--The respiratory organs are gills located on
each side of the thorax in a space between the carapace and body (Fig.
87). The gills are white, curved, and feathery. Is the front gill the
largest or the smallest? The gills overlap each other; which is the
outermost gill? On the second maxilla is a thin, doubly curved plate
called a gill bailer (Fig. 85). The second maxilla is so placed that
the gill bailer comes at the front end of the gill chamber. The bailer
paddles continually, bringing the water forward out of the gill.
The gills are attached below at the base of the legs. Are the gills
thick or thin? How far upward do they go? Does the backward motion in
swimming aid or hinder the passage of the water through the gills? Does
a crawfish, when at rest on the bottom of a stream, have its head up or
down stream? Why?
=Openings.=--The slitlike _vent_ is on the under side of the telson
(Figs. 82, 88). The _mouth_ is on the under side of the thorax behind
the mandibles. At the base of the long antennæ are the openings from
the _green glands_, two glands in the head which serve as kidneys (Fig.
89). The openings of the _reproductive organs_ are on the third pair of
legs in the female, and the fifth pair of legs in the male (Fig. 88).
The eggs are carried on the swimmerets.
[Illustration: FIG. 89.--Level lengthwise section showing
_h_, heart.
_d_, green gland.
_le_, liver.
_kie_, gills.
_kh_, gill cavity.
_ma_, stomach.
(After Huxley.)]
=Internal Structure.=--SUGGESTIONS. If studied by dissection, it will
be necessary to have several crawfish for each pupil, one for gaining
general knowledge, and others for studying the systems in detail.
Specimens should have lain in alcohol for several days.
[Illustration: FIG. 90.--SECTION OF CRAWFISH showing stomach _s_, liver
_li_, and vent _a_.]
=The Food Tube.=--Is the stomach in the head portion of the
cephalothorax or in the thoracic portion? (Figs. 88, 89). Is the
stomach large or small? What is its general shape? Does the gullet
lead upward or backward? Is it long or short? (Fig. 88.) The mid
tube, which is the next portion of the food tube, is smaller than the
stomach. On each side of it are openings from the bile ducts which
bring the secretion from the digestive gland, sometimes called the
liver. Does this gland extend the whole length of the thorax? Is it
near the floor or the top of the cavity? The third and last portion
of the food tube is the intestine. It extends from the thorax to
the vent. Is it large or small? Straight or curved? The powerful
flexor muscles of the tail lie in the abdomen below the intestines.
Compare the size of these muscles with the extensor muscle above the
intestine (Fig. 90). Why this difference? Does the food tube extend
into the telson? Locate the vent (Fig. 90).
=The Circulation.=--The blood is a liquid containing _white
corpuscles_. It lacks red corpuscles and is colorless. The heart is
in the upper part of the thorax. It is surrounded by a large, thin
bag, and thus it is in a chamber (called the _pericardial sinus_).
The blood from the pulmonary veins enters this sinus before it enters
the heart. The origin of this pericardial sinus by the fusing of
veins is shown in Fig. 130. Does one artery, or do several arteries,
leave the heart? There is a larger dorsal artery lying on the
intestine and passing back to the telson; there are three arteries
passing forward close to the dorsal surface (Figs. 89, 91). One large
artery (the sternal) passes directly downward (Figs. 88, 91), and
sends a branch forward and another backward near the ventral surface.
The openings into the heart from the sinus have valvular lips which
prevent a backward flow of blood into the sinus. Hence, when the
heart contracts, the blood is sent out into the several arteries. The
arteries take a supply of fresh blood to the eyes, stomach, muscles,
liver, and the various organs. After it has given oxygen to the
several organs and taken up carbon dioxid, it returns by veins to
pass through the gills on each side, where it gives out the useless
gas and takes up oxygen from the water. It is then led upward by
veins into the pericardial sinus again.
A _double nerve chain_ of ganglia supplies nerve force to the various
nerves (Fig. 92). This main nerve chain lies along the ventral
surface below the food tube (Fig. 90), except one pair of ganglia
which lie above the esophagus or gullet (Fig. 88), and are called the
supra-esophageal ganglia, or brain.
[Illustration: FIG. 91.--Showing heart and main blood vessels.]
[Illustration: FIG. 92.]
=Crustacea.=--Because of the limy crust which covers the crawfish and
its kindred, they are placed in the class called _Crustacea_.
[Illustration: FIG. 93.--CRAB FROM BELOW.]
[Illustration: FIG. 94.--HERMIT CRAB, using shell of sea snail for a
house.]
=Decapods.=--All crustacea which have ten feet belong in the order
called decap′oda (ten-footed). This order includes the crabs, lobsters,
shrimp, etc. The crabs and lobsters are of considerable importance
because of use as food. Small boys sometimes catch crawfish, and in
some instances are known to cook and eat them for amusement, the only
part cooked being the muscular tail. The crab’s tail is small and flat
and held under the body (Fig. 93).
[Illustration: FIG. 95.--DEVELOPMENT OF A CRAB.
_a_, nauplius just after hatching; _b_, _c_, _d_, zoëa; _e_, megalops;
_f_, adult.
=Question:= Which stage is most like a crayfish? Compare with
metamorphoses of insects.]
Since the limy covering to serve the purpose of protection is not soft
enough to be alive and growing, it is evident that the crustacea are
hampered in their growth by their crusty covering. During the first
year the crawfish sheds its covering, or =molts= three times, and once
each year thereafter. It grows very fast for a few days just after
molting, while the covering is soft and extensible. Since it is at
the mercy of birds, fish, and other enemies while in this soft and
defenseless condition, it stays hidden until the covering hardens.
Hence it cannot eat much, but probably by the absorption of water the
tissues grow; that is, enlarge. In the intervening periods, when growth
is impossible, it develops; that is, the tissues and organs change in
structure and become stronger. “Soft-shelled crab” is a popular dish,
but there is no species by that name, this being only a crab just after
molting which has been found by fishermen in spite of its hiding.
=General Questions.=--How do crawfish choose their food? How long
can they live out of water? Why do their gills remain moist out of
water longer than a fish? How do they breathe out of water? Are
they courageous or cowardly animals? When they lose appendages when
fighting or molting, they are readily reproduced, but the part molts
several times in regaining its size. Have you seen crawfish with one
claw smaller than the other? Explain.
Compare the crawfish and crab (Figs. 81, 93, and 95) in the following
particulars: shape, body, eyes, legs, abdomen, habitat, movement.
KEY TO THE FOUR CLASSES IN BRANCH ARTHROPODS
1. INSECTS 3 body divisions, 6 legs
2. ARACHNIDS 2 body divisions, 8 legs
3. MYRIAPODS many body divisions, many legs
4. CRUSTACEANS gill breathers, skeleton (external) limy
By the aid of the key and of figures 96-105, classify the following
Arthropods: tick, thousand-leg centipede, king crab, pill bug,
spider, scorpion, beetle.
[Illustration: FIG. 96.--PILL BUG.]
[Illustration: FIG. 97.--LADY BEETLE.]
[Illustration: FIG. 98.--SCORPION.]
[Illustration: FIG. 99.--TICK before and after feeding.]
[Illustration: FIG. 100.--CENTIPEDE.]
[Illustration: FIG. 101.--ONE SEGMENT OF CENTIPEDE with one pair of
legs.]
[Illustration: FIG. 102.--ONE SEGMENT OF THOUSAND LEGS with two pairs
of legs.]
[Illustration: FIG. 103.--THOUSAND LEGS.]
[Illustration: FIG. 104.--A SPIDER.]
[Illustration: FIG. 105.--KING CRAB.]
=Illustrated Study.= CLASSIFICATION OF ARTHROPODS. Key on p. 61.
CHAPTER VIII
INSECTS
THE GRASSHOPPER
SUGGESTIONS.--Collect grasshoppers, both young and full-grown, and
keep alive in broad bottles or tumblers and feed on fresh grass or
lettuce. When handling a live grasshopper, never hold it by its
legs, as the joints are weak. To keep them for some time and observe
their molts, place sod in the bottom of a box and cover the box with
mosquito netting or wire gauze.
What is the =general shape= of its body? (Fig. 106.) Where is the body
thickest? Is it bilaterally symmetrical, that is, are the two sides of
the body alike? Is the _skeleton_, or hard part of the body, internal
or external? Is the skeleton as stiff and thick as that of a crawfish?
What is the length of your specimen? Its color? Why does it have this
coloration? In what ways does the grasshopper resemble the crawfish?
Differ from it?
[Illustration: FIG. 106.--A GRASSHOPPER.]
=The Three Regions of the Body.=--The body of the grasshopper is
divided into three regions,--the _head_, _thorax_, and _abdomen_.
Which of these three divisions has no distinct subdivisions? The body
of the grasshopper, like that of the earthworm, is made of _ringlike
segments_. Are the segments most distinct in the head, thorax, or
abdomen? Which region is longest? Shortest? Strongest? Why? Which
region bears the chief sense organs? The appendages for taking food?
The locomotory appendages? Which division of the body is most active in
breathing?
=The Abdomen.=--About how many segments or rings in the abdomen? Do
all grasshoppers have the same number of rings? (Answer for different
species and different individuals of the same species.) The first
segment and the last two are incomplete rings. Does the flexibility of
the abdomen reside in the rings, or the joints between the rings? Is
there merely a thin, soft line between the rings, or is there a fold of
the covering? Does one ring slip into the ring before it or behind it
when the abdomen is bent?
As the grasshopper =breathes=, does each ring enlarge and diminish in
size? Each _ring is divided into two parts_ by folds. Does the upper
half-ring overlap the lower half-ring, or the reverse? With magnifying
glass, find a small slit, called a _spiracle_, or breathing hole, on
each side of each ring just above the side groove (Fig. 106). A tube
leads from each spiracle. While the air is being taken in, do the
two portions of the rings move farther apart? When they are brought
together again, what must be the effect? In pumping the air, the
abdomen may be said to work like a bellows. Bellows usually have folds
to allow motion. Is the comparison correct?
How many times in a minute does the grasshopper take in air? If it
is made to hop vigorously around the room and the breathing is again
timed, is there any change?
[Illustration: FIG. 107.--A GRASSHOPPER DISSECTED.]
Find the =ears= on the front wall of the _first abdominal ring_ (Fig.
107). They may be seen by slightly pressing the abdomen so as to widen
the chink between it and the thorax. The ears are merely glistening,
transparent _membranes_, oval in form. A _nerve_ leads from the inner
surface of each membrane. State any advantage or disadvantage in having
the ears located where they are.
=Ovipositor.=--If the specimen is a female, it has an egg-placer or
ovipositor, consisting of _four blunt projections_ at the end of the
abdomen (Fig. 107). If it is a male, there are only two appendages.
These are above the end of the abdomen, and smaller than the parts of
the ovipositor. Females are larger and more abundant than males. In
laying the eggs, the four blunt points are brought tightly together and
then forced into the ground and opened (Fig. 108). By repeating this, a
pit is made almost as deep as the abdomen is long. What sex is shown in
Fig. 106? Fig. 107?
=Draw= a side view of the grasshopper.
[Illustration: FIG. 108.--GRASSHOPPER LAYING EGGS. (Riley.)]
=Thorax.=--This, the middle portion of the body, consists of _three
segments_ or rings (Fig. 107). Is the division between the rings most
apparent above or below? Which two of the three rings are more closely
united?
The front ring (_prothorax_) of the thorax has no rings. Is it larger
above or below? Does it look more like a collar or a cape? (Fig. 106.)
A spiracle is found on the second ring (_mesothorax_, or middle thorax)
just above the second pair of legs. There is another in the soft skin
between the prothorax and mesothorax just under the large cape or
collar. The last ring of the thorax is called the _metathorax_ (rear
thorax).
How many =legs= are attached to each ring of the thorax? Can a
grasshopper walk? Run? Climb? Jump? Fly? Do any of the legs set
forward? (See Fig. 106.) Outward? Backward? Can you give reasons for
the position of each pair? (Suggestion: What is the use of each pair?)
If an organ is modified so that it is suited to serve some particular
purpose or function, it is said to be _specialized_. Are any of the
legs specialized so that they serve for a different purpose than the
other legs?
The leg of a grasshopper (as of all insects) is said to have _five
parts_, all the small parts after the first four parts being counted
as one part and called the foot. Are all the legs similar, that is, do
the short and long joints in all come in the same order? Numbered in
order from the body, which joint of the leg is the largest,--the first,
second, third, or fourth? Which joint is the shortest? The slenderest?
Which joint has a number of sharp points or spines on it? Find by
experiment whether these spines are of use in walking (Fig. 106).
Jumping? Climbing? In what order are the legs used in walking? How many
legs support the body at each step?
[Illustration: FIG. 109.--HOW A GRASSHOPPER WALKS.]
[Illustration: FIG. 110.--HOW A SPIDER WALKS.]
All animals that have ears have ways of communicating by =sounds=. Why
would it be impossible for the grasshopper to have a _voice_, even if
it had vocal cords in its throat? The male grasshoppers of many species
make a =chirping=, or stridulation, by rubbing the wing against the
leg. Look on the inner side (why not outer side?) of the largest joint
of the hind leg for a _row of small spines_ visible with the aid of a
hand lens (Fig. 111). The sound is produced by the outer wings rubbing
against the spines. Have you noticed whether the sound is produced
while the insect is still or in motion? Why? The male grasshoppers of
some species, instead of having spines, rub the under side of the front
wing on the upper side of the hind wing.
[Illustration: FIG. 111.--_A_, ROW OF SPINES, _z_, used in chirping.
_B_, the same more enlarged.]
=Wings.=--To what is the first pair of wings attached? The second pair?
Why are the wings not attached to the prothorax? Why are the wings
attached so near the dorsal line of the body? Why are the second and
third rings of the thorax more solidly joined than the first and second
rings?
Compare the first and second pairs of wings in shape, size, color,
thickness, and use (Fig. 112). How are the second wings folded so as to
go under the first wings? About how many folds in each?
[Illustration: FIG. 112.--GRASSHOPPER IN FLIGHT.]
=Draw= a hind wing opened out.
=Head.=--What is the shape of the head viewed from the front, the side,
and above? _Make sketches._ What can you say of a neck? Is the head
movable in all directions?
What is the position of the large =eyes=? Like the eyes of the
crawfish, they are _compound, with many facets_. But the grasshopper
has also _three simple eyes_, situated one in the middle of the
forehead and one just above each antenna. They are too small to be seen
without a hand lens. How does the grasshopper’s range of vision compare
with that of the crawfish?
Are the =antennæ= flexible? What is their shape? Position? Are they
segmented? Touch an antenna, a wing, a leg, and the abdomen in
succession. Which seems to be the most sensitive to touch? The antennæ
are for feeling; in some species of insects they are also the organs of
hearing.
[Illustration: FIG. 113.]
The =mouth parts= of a grasshopper are highly specialized. They should
be compared with the mouth parts of a beetle shown in Fig. 113, since
the mouth parts of these two insects correspond closely. If the
grasshopper is fed with a blade of fresh grass, the function of each
mouth part may be plainly seen. It is almost impossible to understand
these functions by studying a dead specimen, but a fresh specimen is
much better than a dry one.
[Illustration: FIG. 114.--_a_, FOOD TUBE OF BEETLE.
_b_, gizzard; _d_, intestine; _c_, biliary vessels. See Fig. 127.]
The upper lip, or _labrum_, is seen in front. Is it tapering or
expanded? In what direction is it movable? The dark pointed biting jaws
(_mandibles_) are next. Are they curved or straight? Sharp or blunt
pointed? Notched or smooth? Do they work up and down, or sideways? The
holding jaws (_maxillæ_), each with two jaw fingers (_maxillary palpi_)
are behind the chewing jaws. Why? The lower lip (_labium_) has a pair
of lip fingers (_labial palpi_) upon it. The brown tongue, usually
bathed in saliva, is seen in the lower part of the mouth. Since the
grasshopper has no lips, or any way of producing suction, it must lap
the dew in drinking. Does it merely break off bits of a grass blade, or
does it chew?
The heart, circulation, nervous system, digestive and respiratory
organs of the grasshopper agree mainly with the general description of
the organs of insects given in the next section.
=Microscopic Objects.=--These may be bought ready mounted, or may be
examined fresh. A portion of the covering of the large eye may be cut
off and the dark layer on the inside of the covering scraped off to
make it transparent. What is the shape of the facets? Can you make any
estimate of their number? A portion of the transparent hind wing may be
used, and the “veins” in it studied. A thin bit of an abdominal segment
containing a spiracle will show the structure of these important organs.
[Illustration: FIG. 115.--EGG AND MOLTS OF A GRASSHOPPER.]
=Growth of the Grasshopper.=--Some species hibernate in sheltered
places and lay eggs in the spring, but adult species are scarce at
that season. Most species lay the eggs in the fall; these withstand
the cold and hatch out in the spring. Those hatched from one set of
eggs sometimes stay together for a few days. They eat voraciously, and
as they grow, the soft skin becomes hardened by the deposit of horny
substance called chitin. This prevents further growth until the insect
molts, the skin first splitting above the prothorax. After hatching,
there are five successive periods of growth. At which molt do the very
short wings first appear? (Fig. 115.) After the last molt the animal is
complete, and changes no more in size for the rest of its life. There
has been an attempt among writers to restrict the term grasshopper
to the long-winged, slender species, and to call the shorter winged,
stouter species locusts according to old English usage.
[Illustration: FIG. 116.--COCKROACH.]
[Illustration: FIG. 117.--PRAYING MANTIS, or devil’s horse.]
[Illustration: FIG. 118.--CRICKET.]
[Illustration: FIG. 119.--MOLE CRICKET.]
=Economic Importance of Grasshoppers.=--Great injury is often done to
vegetation by grasshoppers; however, the millions of tiny but ravenous
eaters hatched in early spring are usually soon thinned out by the
birds. The migratory locusts constitute a plague when they appear,
and they have done so since ancient times. The Rocky Mountain locusts
flying eastward have darkened the sky, and where they settled to the
earth ate almost every green thing. In 1874-5 they produced almost
a famine in Kansas, Nebraska, and other Western states. The young
hatched away from the mountains were not healthy, and died prematurely,
and their devastations came to an end. Of course the migrations may
occur again. Packard calculates that the farmers of the West lost
$200,000,000 because of their ravages in 1874-5.
[Illustration: FIG. 120.--FRONT LEG OF MOLE CRICKET. × 3.]
The _cockroaches_ (Fig. 116), =kindred of the grasshoppers=, are
household pests that have migrated almost everywhere that ships go.
The _praying mantis_ (Fig. 117), or _devil’s horse_, also belongs to
this order. It is beneficial, since it destroys other insects. Which of
its legs are specialized? The _walking stick_ (Fig. 121) and _cricket_
(Fig. 118), like most members of the order, are vegetarian.
[Illustration: FIG. 121.--FOUR WALKING STICK INSECTS.]
Are grasshoppers more common in fields and meadows, or in wooded
places? How many different colors have you seen on grasshoppers? Which
colors are most common?
Grasshoppers are very scarce in Europe as they love dry, warm
countries. Why do locusts migrate? Give an instance in ancient times.
How long do most grasshoppers live? Does a grasshopper spread its wings
before it flies? Does it jump and fly together? Can it select the place
for alighting?
NOTE TO TEACHER.--=Field work in Zoology= should be systematic.
Every trip has a definite region and definite line of study in view,
but every animal seen should be noted. The habitat, adaptation by
structure and habits to the environment, relations to other animals,
classification of animals seen, should be some of the ideas guiding
the study. The excursions may be divided somewhat as follows,
according as opportunities offer: Upland woods, lowland woods, upland
pastures, fields, swamps, a fresh-water lake, a pond, lower sea
beach, higher sea beach, sand hills along shore, roadside, garden,
haunts of birds, insect visits to flowers, ground insects, insects in
logs.
An alphabetical letter file may be used for filing individual field
observations. These should be placed before the class orally or in
writing. If accepted as reliable (repeated and revised if necessary),
the observations should be filed away and credit given the student on
a regular scale. Thus will grading and marks be placed to encourage
intelligent study of nature rather than book or laboratory cram. One
per cent to be added to the final grade may be credited for every
species of pupa, every rare insect (with an observed fact as to its
habits) brought in, every bird migration observed, every instance
of protective coloration, mimicry (p. 146), outwitting of enemy,
instance of injurious insects, and how to combat them, etc. Sharp
eyes and clear reasoning will then count as much on school grades as
a memory for words or mechanical following of laboratory directions.
On scale of 100, class work = 50, examination = 25, field work = 25.
=Collecting Insects.=--In cities and towns insects, varying with the
season, are attracted by electric lights. Beetles and bugs will be
found under the lights, moths on posts near the lights, grasshoppers
and crickets and other insects in the grass near by. A lamp placed
by a window brings many specimens. In the woods and in rocky places
insects are found under logs and stones, and under the bark of dead
trees. In open places, prairies, meadows, and old fields with grass
and flowers, it will be easy to find grasshoppers, butterflies, and
some beetles. Ponds and streams are usually rich in animal forms,
such as bugs and beetles, which swim on or under the surface, and
larvæ of dragon flies crawling on the bottom. Dragon flies and other
insects that lay eggs on the water are found flying in the air above.
(In the spring, newly hatched crawfish, tadpoles, and the eggs of
frogs and toads should also be collected, if found.) Moths may be
caught at night by daubing molasses or sirup made from brown sugar
upon the trunks of several trees, and visiting the trees at intervals
with a lantern.
An insect net for catching butterflies and for dredging ponds may
be made by bending a stout wire into a circle one foot in diameter,
leaving enough straight wire to fasten with staples on an old
broomstick. To the frame is fastened a flour sack, or cone made of a
piece of mosquito netting.
Butterflies and moths should be promptly killed, or they will beat
their wings to pieces. The quickest method is by dropping several
drops of gasoline upon the ventral (under) side of the thorax and
abdomen. (Caution: Gasoline should never be used near an open fire,
or lamp, as explosions and deaths result from the flame being led
through the gasoline-saturated air to the vessel containing it.)
A cigar box and a bottle with a notched cork may be used for holding
specimens. Cigar boxes may be used for holding collections of dried
insects. Cork or ribbed packing paper may be fixed in the bottom for
supporting the insect pins. Moth balls or tobacco may be placed in
each box to keep out the insect pests which infest collections.
It is pleasant and profitable to take to the fields a small book
like this one, or even Comstock’s “Manual of Insects,” or Kellogg’s
“American Insects,” and study the insects and their habits where they
are found.
Captured insects which, in either the larval or perfect stage, are
injurious to vegetation, should always be killed after studying their
actions and external features, even if the internal structure is not
to be studied. Beneficial insects, such as ladybugs, ichneumon flies,
bees, mantis (devil’s horse), dragon flies, etc., should be set free
uninjured.
ANATOMY AND GENERAL CHARACTERISTICS OF THE CLASS INSECTA
The =body= of an insect (_e.g._ a wasp, Fig. 122) is divided by means
of two marked narrowings into three parts: the head (_K_), chest (_B_),
and abdomen (_H_).
[Illustration: FIG. 122.--A WASP.]
The =head= is a freely movable capsule bearing four pairs of
appendages. Hence it is regarded as having been formed by the union of
four rings, since the _ancestor of the insects_ is believed to have
consisted of similar rings, each ring bearing a pair of unspecialized
legs. The early grub or caterpillar stage of insects is believed to
resemble somewhat the ancestral form.
The typical =mouth parts= of an insect (Fig. 123), named in order from
above, are (1) an upper lip (labrum, _ol_) (2) a pair of biting jaws
(mandibles, _ok_) (3) a pair of grasping jaws (maxillæ, _A_, _B_), and
(4) a lower lip (labium, _m_, _a_, _b_). The grasping jaws bear two
pairs of jointed jaw fingers (maxillary palpi, _D_, _C_), and the lower
lip bears a pair of similar lip fingers (labial palpi, _d_). The biting
jaws move sideways; they usually have several pointed notches which
serve as teeth. Why should the grasping jaws be beneath the chewing
jaws? Why is it better for the lower lip to have fingers than the upper
lip? Why are the fingers (or palpi) jointed? (Watch a grasshopper or
beetle eating.) Why does an insect need grasping jaws?
[Illustration: FIG. 123.--MOUTH PARTS OF BEETLE.]
[Illustration: FIG. 124.--EXTERNAL PARTS OF A BEETLE.]
The chest, or =thorax=, consists of three rings (Fig. 124) called the
front thorax (prothorax), middle thorax (mesothorax) and hind thorax
(metathorax), or first, second, and third rings. The first ring bears
the first pair of legs, the second ring bears the second pair of legs
and the upper or front wings, and the third ring bears the third pair
of legs and the under or hind wings.
[Illustration: FIG. 125.--LEG OF INSECT.]
The =six feet= of insects are characteristic of them, since no other
animals have that number, the spider having eight, the crawfish and
crabs having ten, the centipedes still more, while the birds and
beasts have less than six. Hence the insects are sometimes called the
Six-Footed class (_Hexapoda_). The insects are the only animals that
have the =body in three divisions=. Man, beasts, and birds have only
two divisions (head and trunk); worms are not divided.
=Define= the class _insecta_ by the two facts characteristic of them
(_i.e._ possessed by them alone), viz.: Insects are animals with ____
and ____. Why would it be ambiguous to include “hard outer skeleton” in
this definition? To include “bilateral symmetry”? “Segmented body”? The
definition of a class must _include_ all the individuals of the class,
and _exclude_ all the animals that do not belong to the class.
The leg of an insect (Fig. 125) has five joints (two short joints,
two long, and the foot). Named in order from above, they are (1) the
hip (coxa), (2) thigh ring (trochanter), (3) thigh (femur), (4) the
shin (tibia), (5) the foot, which has five parts. Which of the five
joints of a wasp’s leg (Fig. 122) is thickest? Slenderest? Shortest?
One joint (which?) of the foot (Fig. 122) is about as long as the
other four joints of the foot combined. Is the relative length of
the joints of the leg the same in grasshoppers, beetles, etc., as
in the wasp (Figs.)? Figure 125 is a diagram of an insect’s leg cut
lengthwise. The leg consists of thick-walled tubes (_o_, _n_) with
their ends held together by thin, easy-wrinkling membranes which
serve as joints. Thus motion is provided for at the expense of
strength. When handling live insects they should never be held by
the legs, as the legs come off very easily. Does the joint motion of
insects most resemble the motion of hinge joints or ball-and-socket
joints? Answer by tests of living insects. There are no muscles in
the foot of an insect. The claw is moved by a muscle (_m_) in the
thigh with which it is connected by the long tendon (_z_, _s_, _t_,
_v_). In which part are the breathing muscles? As the wings are
developed from folds of the dorsal skin, the wing has two layers, an
upper and a lower layer. These inclose the so-called “nerves” or ribs
of the wing, each of which consists of a blood tube inclosed in an
air tube.
[Illustration: FIG. 126.--FOOT OF FLY, with climbing pads.]
The =abdomen= in various species consists of from five to eleven
overlapping rings with their foldlike joints between them. Does each
ring overlap the ring in front or the one behind it?
The =food tube= (Fig. 127) begins at the mouth, which usually contains
salivary glands (4, Fig. 127). What is the color of the grasshopper’s
saliva? The food tube expands first into a _croplike_ enlargement; next
to this is the _stomach_ (6, Fig. 127), which resembles the gizzard in
birds, as its inner wall is furnished with chitinous teeth (_b_, Fig.
114). These reduce the food fragments that were imperfectly broken up
by the biting jaws before swallowing. _Glands_ comparable to the liver
of higher animals open into the food tube where the stomach joins the
small intestine. At the junction of the small and large intestine (9)
are a number of _fine tubes_ (8) which correspond to kidneys and empty
their secretion into the large intestine.
[Illustration: FIG. 127.--VISCERA OF GRASSHOPPER. Key in text. Compare
with Fig. 114.]
[Illustration: FIG. 128.--AIR TUBES OF INSECT.]
The =breathing organs= of the insects are peculiar to them (see Fig.
128). They consist of tubes which are kept open by having in their
walls continuous spirals of horny material called _chitin_. Most
noticeable are the two large membranous tubes filled with air and
situated on each side of the body. Do these tubes extend through the
thorax? (Fig. 128.) The air reaches these two main tubes by a number
of pairs of short windpipes, or _tracheas_, which begin at openings
(_spiracles_). In which division are the spiracles most numerous? (Fig.
128.) Which division is without spiracles? Could an insect be drowned,
_i.e._ smothered, by holding its body under water? Could it be drowned
by immersing all of it but its head? The motion of the air through the
breathing tubes is caused by a bellowslike _motion of the abdomen_.
This is readily observed in grasshoppers, beetles, and wasps. As each
ring slips into the ring in front of it, the abdomen is shortened, and
the impure air, laden with carbon dioxid, is forced out. As the rings
slip out, the abdomen is extended and the fresh air comes in, bringing
oxygen.
[Illustration: FIG. 129.--INSECT’S HEART (plan).]
[Illustration: FIG. 130.--DIAGRAMS OF EVOLUTION OF PERICARDIAL SAC
around insect’s heart from a number of veins (Lankester).]
[Illustration: FIG. 131.--POSITION OF INSECT’S HEART, food tube, and
nerve chain.]
=The Circulation.=--Near the dorsal surface of the abdomen (Fig. 131)
extends the long, slender _heart_ (Fig. 129). The heart has divisions
separated by valvelike partitions. The blood comes into each of the
heart compartments through a pair of openings. The heart contracts
from the rear toward the front, driving the blood forward. The blood
contains bodies corresponding to the _white corpuscles_ of human blood,
but lacks the red corpuscles and the red color. The blood is sent even
to the wings. The _ribs_ on the wings consist of blood tubes inclosed
in air tubes, so that the blood vessels are surrounded by air, and the
purification of the blood is taking place throughout the course of
the circulation. Hence the imperfect circulation is no disadvantage.
The perfect provision for supplying oxygen explains the remarkable
activity of which insects are capable and their great strength, which,
considering their size, is unequaled by any other animals.
[Illustration: FIG. 132.--NERVOUS SYSTEM OF BEE.]
=The Nervous System.=--The heart in backboned animals, e.g. man, is
ventral and the chief nerve trunk is dorsal. As already stated, the
heart of an insect is dorsal; its chief nerve chain, consisting of
a _double row of ganglia_, is near the ventral surface (Fig. 131).
All the ganglia are below the food tube except the first pair in the
head, which are above the gullet. This pair may be said to correspond
somewhat to the brain of backboned animals; the nerves from the eyes
and feelers lead to it. With social insects, as bees and ants, it is
large and complex (Fig. 132). In a typical insect they are the largest
ganglia.
[Illustration: FIG. 133.--FEELER of a beetle.]
=The Senses.=--The sense of _smell_ of most insects is believed to be
located in the feelers. The organ of _hearing_ is variously located
in different insects. Where is it in the grasshopper? The organs of
_sight_ are highly developed, and consist of two compound eyes on the
side of the head and three simple eyes on the top or front of the head
between the compound eyes. The simple eye has nerve cells, pigments,
and a lens resembling the lens in the eyes of vertebrates (Fig. 134).
The compound eye (Fig. 135) has thousands of facets, usually hexagonal,
on its surface, the facets being the outer ends of cones which have
their inner ends directed toward the center of the eye. It is probable
that the large, or compound, eyes of insects only serve to distinguish
bright objects from dark objects. The simple eyes afford distinct
images of objects within a few inches of the eye. In general, the sight
of insects, contrary to what its complex sight organs would lead us
to expect, is not at all keen. Yet an insect can fly through a forest
without striking a twig or branch. Is it better for the eyes that are
immovable in the head to be large or small? Which has comparatively
larger eyes, an insect or a beast?
[Illustration: FIG. 134.--Diagram of simple eye of insect.
_L_, lens; _N_, optic nerve.]
[Illustration: FIG. 135.--COMPOUND EYE OF INSECT.
1, hexagonal facets of crystalline cones. 6, blood vessel in optic
nerve.]
=Inherited Habit, or Instinct.=--Insects and other animals inherit from
their parents their particular form of body and of organs which perform
the different functions. For example, they inherit a nervous system
with a structure similar to that of their parents, and hence with a
tendency to repeat similar impulses and acts. Repeated acts constitute
a habit, and _an inherited habit is called an instinct_. Moths, for
example, are used to finding nectar in the night-blooming flowers, most
of which are white. The habit of going to white flowers is transmitted
in the structure of the nervous system; so we say that moths have
an instinct to go to white objects; it is sometimes more obscurely
expressed by saying they are attracted or drawn thereby.
=Instincts are not Infallible.=--They are trustworthy in only one
narrow set of conditions. Now that man makes many fires and lights at
night, the instinct just mentioned often causes the death of the moth.
The instinct to provide for offspring is necessary to the perpetuation
of all but the simplest animals. The dirt dauber, or mud wasp, because
of inherited habit, or instinct, makes the cell of the right size, lays
the egg, and provides food for offspring that the mother will never
see. It seals stung and semiparalyzed spiders in the cell with the
egg. If you try the experiment of removing the food before the cell is
closed, the insect will bring more spiders; if they are removed again,
a third supply will be brought; but if taken out the third time, the
mud wasp will usually close the cell without food, and when the egg
hatches the grub will starve.
=The Development of Insects.=--The growth and molting of the
grasshopper from egg to adult has been studied. All insects do not
develop exactly by this plan. Some hatch from the egg in a condition
markedly different from the adult. The butterfly’s egg produces a
wormlike caterpillar which has no resemblance to the butterfly. After
it grows it forms an inclosing case in which it spends a quiet period
of development and comes out a butterfly. This change from caterpillar
to butterfly is called the _metamorphosis_. The life of an insect is
divided into four stages: (1) _egg_, (2) _larva_, (3) _pupa_, and (4)
_imago_, or perfect insect (Figs. 136, 137, 138).
[Illustration: FIG. 136.--Measuring worm, the larva of a moth.]
[Illustration: FIG. 137.--Pupa of a mosquito.]
[Illustration: FIG. 138.--THE FOUR STAGES OF A BOTFLY, all enlarged.
_a_, egg on hair of horse (bitten off and swallowed); _b_, larva; _c_,
larva with hooks for holding to lining of stomach; _d_, pupal stage,
passed in the earth; _e_, adult horse fly.]
The egg stage is one of development, no nourishment being absorbed.
The larval stage is one of voracious feeding and rapid growth. In the
pupa stage no food is taken and there is no growth in size, but rapid
development takes place. In the perfect stage food is eaten, but no
growth in size takes place. In this stage the eggs are produced. When
there is very little resemblance between the larva and imago, and
the pupa is quiescent, the metamorphosis, or change, is said to be
_complete_. When, as with the grasshopper, no very marked change takes
place between the larva and imago (that is to say, during the pupa
stage, which is active), the metamorphosis is said to be incomplete.
By studying the illustrations and specimens, and by thinking of your
past observations of insects, determine which of the insects in the
following list have a complete metamorphosis: beetle, house fly,
grasshopper, butterfly, cricket, wasp.
TABLE FOR CLASSIFYING INSECTS (_class Insecta_) INTO ORDERS
ORDER
A₁ =Biting Insects=; mouth parts for grasping and
biting
B₁ Wingless; changes (metamorphosis) NO WINGS
incomplete (_Aptera_)
B₂ Under wings thinner than upper wings, and FAN WINGS
fold like a fan beneath them; changes (_Orthoptera_)
incomplete
B₃ Upper wings hard and thick, protecting SHEATH WINGS
under wings, which fold both lengthwise and (_Coleoptera_)
crosswise beneath them; changes incomplete
B₄ All four wings nearly alike, finely veined,
transparent
C₁ Hind wings smaller than fore, two or NERVE WINGS
three filaments attached to abdomen, (_Neuroptera_)
antennæ long; changes complete
C₂ Hind wings not smaller than fore; no FALSE NERVE WINGS
filaments on abdomen, antennæ (_Pseudoneuroptera_)
inconspicuous; changes incomplete
A₂ =Sucking Insects=; mouth parts for sucking or
licking
B₁ Basal half of upper wing usually leathery, HALF WINGS
other half of wing transparent; lower lips (_Hemiptera_)
transformed into a tube; true bugs
B₂ Four wings covered by scales, holding-jaws SCALY WINGS
(maxillæ) elongated to form a sucking tube (_Lepidoptera_)
coiled under head; changes complete
B₃ Four wings, membranous, hind wings hook to JOINED WINGS
fore wings in flight; mouth parts for both (_Hymenoptera_)
biting and sucking; abdomen with sting;
changes complete
B₄ Two wings, mandibles rudimentary, mouth a TWO WINGS
soft beak (_Diptera_)
B₅ No wings, mandibles rudimentary, mouth a LOST WINGS
horny beak (_Siphonoptera_)
[Illustration: FIG. 139.--MAY FLY. What order (see table)?]
[Illustration: FIG. 140.--SILVER SCALE. (Order?)]
=Exercise in the Use of the Table or Key.=--Write the name of the
order after each of the following names of insects:--
Wasp (Fig. 122)
Weevil (Fig. 163)
Squash bug (Fig. 184)
Ant lion (Fig. 170)
Dragon fly (Fig. 177)
Ichneumon fly (Fig. 159)
House fly (Fig. 172)
Flea (Fig. 173)
Silver scale or earwig (Fig. 140)
Codling moth (Fig. 141)
Botfly (Fig. 138)
=Moths and Butterflies.=--Order ____? Why ____ (p. 82)?
The presence of scales on the wings is a never-failing test of a moth
or butterfly. The wings do not fold at all. They are so large and the
legs so weak and delicate that the butterfly keeps its balance with
difficulty when walking.
The maxillæ are developed to form the long sucking proboscis. How
do they fit together to form a tube? (See Fig. 147.) The proboscis
varies from a fraction of an inch in the “miller” to five inches in
some tropical moths, which use it to extract nectar from long tubular
flowers. When not in use, it is held coiled like a watch spring under
the head (Fig. 148). The upper lip (labrum), under lip (labium), and
lip fingers (labial palpi) are very small, and the mandibles small or
wanting (Fig. 146).
The metamorphosis is complete, the contrast between the caterpillar
or larva of the moth and butterfly and the adult form being very
great. The caterpillar has the three pairs of jointed legs typical
of insects; these are found near the head (Fig. 141). It has also
from three to five pairs of fleshy unjointed proplegs, one pair of
which is always on the last segment. How many pairs of proplegs has
the silkworm caterpillar? (Fig. 143.) The measuring worm, or looper?
(Fig. 136.) The pupa has a thin shell. Can you see external signs of
the antennæ, wings, and legs in this stage? (Fig. 143.) The pupa is
concealed by protective coloration, and is sometimes inclosed in a
silken cocoon which was spun by the caterpillar before the last molt.
Hairy caterpillars usually produce butterflies, and the naked ones
usually produce moths. Hairy ones are uncomfortable for birds to eat.
The naked and brightly marked ones (warning coloration) often contain
an acrid and distasteful fluid. The injuries from lepidoptera are done
in the caterpillar stage. The codling moth (Fig. 141) destroys apples
to the value of $6,000,000 annually. The clothes moth (Fig. 171) is a
household pest. The tent caterpillar denudes trees of their leaves.
The only useful caterpillar is the silkworm (Fig. 143). In Italy and
Japan many of the country dwellings have silk rooms where thousands of
these caterpillars are fed and tended by women and children. Why is
the cabbage butterfly so called? Why can it not eat cabbage? Why does
sealing clothes in a paper bag prevent the ravages of the clothes moth?
=Flight of Lepidoptera.=--Which appears to use more exertion to keep
afloat, a bird or a butterfly? Explain why. Of all flying insects
which would more probably be found highest up mountains? How does the
butterfly suddenly change direction of flight? Does it usually fly in
a straight or zigzag course? Advantage of this? Why is zigzag flight
unnecessary to moths? Bright colors are protective, as lepidoptera are
in greatest danger when at rest on flowers. Are the brightest colors on
upper or under side of wings of butterfly? Why? (Think of the colors in
a flower.) Why is it better for moths to hold their wings flat out when
at rest? Where are moths during the day? How can you test whether the
color of the wings is given by the scales?
State =how moths and butterflies differ= in respect to: body, wings,
feelers, habits; abundance of scales.
=Insects and Flowers.=--We are indebted to insects for the bright
colors and sweet honey of flowers. Flowers need insects to carry their
pollen to other flowers, as cross-fertilization produces the best
seeds. The insects need the nectar of the flowers for food, and the
bright colors and sweet odors are the advertisements of the flowers
to attract insects. There were no flowers in the world before flying
insects were developed. Moths, butterflies, and bees carry most pollen
(see Plant Biology, Chap. VI).
=Comparative Study.=--Make a table like this, occupying entire page
of notebook, leaving no margins, and fill in accurately:--
==========+=========+=========+=========+=========+=========+=========
| | | FLY | DRAGON | BEETLE | BEE
| GRASS- | BUTTER- | pp. 92, | FLY, | pp. 90, | pp. 88,
| HOPPER | FLY | 93 | p. 93 | 91 | 89
----------+---------+---------+---------+---------+---------+---------
| | | | | |
Number and| | | | | |
kind of | | | | | |
wings | | | | | |
| | | | | |
----------+---------+---------+---------+---------+---------+---------
| | | | | |
Descrip- | | | | | |
tion of | | | | | |
legs | | | | | |
| | | | | |
----------+---------+---------+---------+---------+---------+---------
| | | | | |
Antennæ | | | | | |
(length, | | | | | |
shape, | | | | | |
joints) | | | | | |
| | | | | |
----------+---------+---------+---------+---------+---------+---------
| | | | | |
Biting or | | | | | |
sucking | | | | | |
mouth | | | | | |
parts | | | | | |
| | | | | |
----------+---------+---------+---------+---------+---------+---------
| | | | | |
Complete | | | | | |
or | | | | | |
incomplete| | | | | |
metamor- | | | | | |
phosis | | | | | |
| | | | | |
==========+=========+=========+=========+=========+=========+=========
[Illustration: FIG. 141.--CODLING MOTH, from egg to adult. (See
Farmers’ Bulletin, p. 95.)]
[Illustration: FIG. 142.--CABBAGE BUTTERFLY, male and female, larva and
pupa.]
[Illustration: FIG. 143.--LIFE HISTORY OF SILKWORM.]
[Illustration: FIG. 144.--SCALES FROM BUTTERFLIES’ WINGS, as seen under
microscope.]
TO THE TEACHER: _These illustrated studies require slower and more
careful study than the text. One, or at most two, studies will
suffice for a lesson. The questions can be answered by studying the
figures. Weak observers will often fail and they should not be told,
but should try again until they succeed._
[Illustration: FIG. 145.--SCALES ON MOTH’S WING.]
[Illustration: FIG. 146.--HEAD OF BUTTERFLY.]
[Illustration: FIG. 147.--SECTION OF PROBOSCIS of butterfly showing
lapping joint and dovetail joint.]
[Illustration: FIG. 148.--HEAD OF BUTTERFLY (side view).]
FIGS. 141-148. =Illustrated Study of Lepidoptera.=--Study the stages
in the development of _codling moth_, _silkworm moth_, and _cabbage
butterfly_.
Where does each lay its eggs? What does the larva of each feed
upon? Describe the pupa of each. Describe the adult forms. Find the
_spiracles_ and _prolegs_ on the silkworm. Compare _antennæ_ of moth
and butterfly. Which has larger body compared to size of wings?
Describe the _scales_ from a butterfly’s wings as seen under
microscope (144). How are the scales arranged on moth’s wing (145)?
By what part is scale attached to wing? Do the scales overlap?
Study butterfly’s head and _proboscis_ (Figs. 146-148). What shape is
compound eye? Are the antennæ jointed? Is the proboscis jointed? Why
not call it a tongue? (See text.)
Which mouth parts have almost disappeared? What is the shape of cut
ends of halves of proboscis? How are the halves joined to form a tube?
If you saw a butterfly on a flower, for what purpose would you think
it was there? What, if you saw it on a leaf? How many spots on fore
wing of female cabbage butterfly? (Fig. 124, above.)
Does the silkworm chrysalis fill its cocoon? Eggs may be obtained
from U. S. Dept. of Agriculture.
[Illustration: FIG. 149.]
[Illustration: FIG. 150.]
[Illustration: FIG. 151.]
[Illustration: FIG. 152.]
[Illustration: FIG. 153.]
[Illustration: FIG. 154.]
[Illustration: FIG. 155.]
[Illustration: FIG. 156.]
[Illustration: FIG. 157.]
[Illustration: FIG. 158.--Anatomy of bee.]
FIGS. 149-161. =Illustrated Study of Bees and their Kindred.=--Head
of worker (Fig. 149): _o_, upper lip; _ok_, chewing jaws; _uk_,
grasping jaws; _kt_, jaw finger; _lt_, lip finger; _z_, tongue.
How do heads of drone (150) and queen (151) differ as to mouth, size
of the two compound eyes, size and position of the three simple eyes?
Is the head of a worker more like head of drone or head of queen?
Judging by the head, which is the queen, drone, and worker in Figs.
154-156? Which of the three is largest? Smallest? Broadest?
Figure 152 shows hind leg of worker. What surrounds the hollow,
_us_, which serves as pollen basket? The point, _fh_, is a tool for
removing wax which is secreted (_c_, Fig. 157) between rings on
abdomen. In Fig. 158, find relative positions of heart, _v_, food
tube, and nerve chain. Is crop, _J_, in thorax or abdomen? In this
nectar is changed to honey, that it may not spoil. Compare nerve
chain in Fig. 132.
[Illustration: FIG. 159.--Ichneumon fly.]
[Illustration: FIG. 160.]
[Illustration: FIG. 161.--Wasp using pebble.
From Peckham’s “Solitary Wasps,” Houghton, Mifflin & Co.]
Compare the cells of _bumble bee_ (Fig. 153) with those of hive bee.
They differ not only in shape but in material, being made of web
instead of wax, and they usually contain larvæ instead of honey. Only
a few of the queens among bumble bees and wasps survive the winter.
How do ants and honey bees provide for the workers also to survive
the winter? Name all the social insects that you can think of. Do
they all belong to the same order?
The ichneumon fly shown enlarged in Fig. 159 lays its eggs under
a caterpillar’s skin. What becomes of the eggs? The true size of
the insect is shown by the cross lines at _a_. The eggs are almost
microscopic in size. The pupæ shown (true size) on caterpillar are
sometimes mistaken for eggs. The same mistake is made about the pupa
cases of ants. Ichneumon flies also use tree-borers as “hosts” for
their eggs and larva. Is this insect a friend of man?
The _digging wasp_ (Figs. 160 and 161) supplies its larva with
caterpillars and closes the hole, sometimes using a stone as pounding
tool. Among the few other uses of tools among lower animals are the
elephant’s use of a branch for a fly brush, and the ape’s use of a
walking stick. This wasp digs with fore feet like a dog and kicks the
dirt out of the way with its hind feet.
Are the wings of bees and wasps more closely or less closely veined
than the wings of dragon flies? (Fig. 177.) For an interesting
account of the order “Joined-wings” (bees and their kindred) see
Comstock’s “Ways of the Six-footed,” Ginn & Co.
=Illustrated Study of Beetles.=
[Illustration: FIG. 162.--Diving beetle (_Dysticus_), with larva, _a_.]
[Illustration: FIG. 163.--Weevil.]
[Illustration: FIG. 164.]
[Illustration: FIG. 165.]
[Illustration: FIG. 166.--Click beetle.]
[Illustration: FIG. 167.--MAY BEETLE.]
[Illustration: FIG. 168.]
[Illustration: FIG. 169.--Colorado beetle (potato bug).]
=Illustrated Study of Beetles= (Figs. 162-169).--Write the life
history of the _Colorado beetle_, or potato bug (Fig. 169), stating
where the eggs are laid and describing the form and activities of
each stage (the pupal stage, _b_, is passed in the ground).
Do the same for the MAY BEETLE (Figs. 167-168). (It is a larva--the
white grub--for three years; hogs root them up.) Beetles, like moths,
may be trapped with a lantern set above a tub of water.
Where does a _Scarab_ or sacred beetle of the Egyptians, also called
tumble bug (Fig. 164), lay its eggs (Fig. 165)? Why?
How does the _click beetle_, or jack snapper (Fig. 166), throw itself
into the air? For what purpose?
The large proboscis of the _weevil_ (Fig. 163) is used for piercing a
hole in which an egg is laid in grain of corn, boll of cotton, acorn,
chestnut, plum, etc.
How are the legs and body of the _diving beetle_ suited for swimming
(Fig. 162)? Describe its larva.
What is the shape of the lady bug (Fig. 97)? It feeds upon plant lice
(Fig. 185). Is any beetle of benefit to man?
[Illustration: FIG. 170.--Life history of ant lion.]
=Illustrated Study of Ant Lion, or Doodle Bug= (Fig. 170).--Find the
pitfall (what shape?); the larva (describe it); the pupa case (ball
covered with web and sand); the imago. Compare imago with dragon fly
(Fig. 177).
How does ant lion prevent ant from climbing out of pitfall (see Fig.
170)? What is on edge of nearest pitfall? Explain.
Ant lions may be kept in a box half filled with sand and fed on ants.
How is the pitfall dug? What part of ant is eaten? How is unused food
removed?
How long is it in the larval state? Pupal state? Keep net over box to
prevent adult from flying away when it emerges.
[Illustration: FIG. 171.]
[Illustration: FIG. 172.--Metamorphosis of house fly (enlarged).]
[Illustration: FIG. 173.--Metamorphosis of flea.]
[Illustration: FIG. 174.--Louse.]
[Illustration: FIG. 175.--Bed bug. × 5.]
[Illustration: FIG. 176.--Life history of mosquito.]
=Illustrated Study of Insect Pests= (Figs. 171-176).--Why does the
_clothes moth_ (171) lay its eggs upon woolen clothing? How does the
larva conceal itself? The larva can cut through paper and cotton, yet
sealing clothes in bags of paper or cotton protects them. Explain.
The _house fly_ eats liquid sweets. It lays its eggs in horse dung.
Describe its larval and pupal forms. Banishing horses from city would
have what beneficial effect?
Describe the _louse_ and its eggs, which are shown attached to a
hair, natural size and enlarged.
Describe the _bed bug_. Benzine poured in cracks kills bed bugs. Do
bed bugs bite or suck? Why are they wingless?
Describe the larva, _f_, pupa, _g_, and the adult _flea_, all shown
enlarged. Its mandibles, _b_, _b_, are used for piercing. To kill
fleas lather dog or cat completely and let lather remain on five
minutes before washing. Eggs are laid and first stages passed in the
ground.
How does the _mosquito_ lay its eggs in the water without drowning
(176)? Why are the eggs always laid in still water? Which part of the
larva (wiggletail) is held to the surface in breathing? What part of
the pupa (called tumbler, or bull head) is held to the surface in
breathing? Give differences in larva and pupa. Where does pupa change
to perfect insect? Describe mouth parts of male mosquito (at left)
and female (at right). Only female mosquitoes suck blood. Males suck
juice of plants. Malarial mosquito alights with hind end of body
raised at an angle. For figure see Human Biology, Chap. X. Why does
killing fish and frogs increase mosquitoes? 1 oz. of kerosene for 15
ft. of surface of water, renewed monthly, prevents mosquitoes.
What is the use to the squash bug (Fig. 184) of having so bad an odor?
[Illustration: FIG. 177.]
FIG. 177. =Illustrated Study of Dragon Fly.=--3 shows dragon fly
laying its eggs in water while poised on wing. Describe the larval
form (water tiger). The extensible tongs are the maxillæ enlarged.
The pupa (1) is active and lives in water. Where does transformation
to adult take place (5)? Why are eyes of adult large? its legs small?
Compare front and hind wings.
Do the eyes touch each other? Why is a long abdomen useful in flight?
Why would long feelers be useless? What is the time of greatest
danger in the development of the dragon fly? What other appropriate
name has this insect? Why should we never kill a dragon fly?
[Illustration: FIG. 178.--The tarantula.]
[Illustration: FIG. 179.--Trap-door spider.]
[Illustration: FIG. 180.]
[Illustration: FIG. 181.--Anatomy of spider.]
[Illustration: FIG. 182.--Laying egg.]
[Illustration: FIG. 183.--Foot of spider.]
=Illustrated Study of Spiders= (Figs. 178-183).--The tarantula, like
most spiders, has eight simple eyes (none compound). Find them (Fig.
178). How do spiders and insects differ in body? Number of legs?
Which have more joints to legs? Does trap-door spider hold the door
closed (Fig. 179)? How many pairs of spinnerets for spinning web has
a spider (_Spw_, 180)? Foot of spider has how many claws? How many
combs on claws for holding web? Spiders spin a cocoon for holding
eggs. From what part of abdomen are eggs laid (_E_, 182; 2, 181)?
Find spider’s air sacs, _lu_, Fig. 181; spinning organs, _sp_; fang,
_kf_; poison gland, _g_; palpi, _kt_; eyes, _au_; nerve ganglia,
_og_, _ug_; sucking tube, _sr_; stomach, _d_; intestine, _ma_; liver,
_le_; heart, _h_, (black); vent, _a_. Give two reasons why a spider
is not an insect. How does it place its feet at each step (Fig.
110)? Does the size of its nerve ganglia indicate great or little
intelligence? Why do you think first part of body corresponds to both
head and thorax of insects?
[Illustration: FIG. 184.--Squash bug, or stink bug.]
The following Farmer’s Bulletins are available for free distribution to
those interested, by the U. S. Department of Agriculture, Washington,
D.C.:--
Farmer’s Bulletin No. 47, Insects affecting the Cotton Plant; No.
59, Bee Keeping; No. 70, The Principal Insect Enemies of the Grape;
No. 80, The Peach Twig Borer; No. 99, Three Insect Enemies of
Shade Trees; No. 120, The Principal Insects affecting the Tobacco
Plant; No. 127, Important Insecticides; No. 132, The Principal
Insect Enemies of Growing Wheat; No. 145, Carbon Bisulphid as an
Insecticide; No. 146, Insecticides and Fungicides; No. 152, revised,
Mange in Cattle; No. 153, Orchard Enemies in the Pacific Northwest;
No. 155, How Insects affect Health in Rural Districts; No. 159, Scab
in Sheep; No. 165, Silkworm Culture; No. 171, The Control of the
Codling Moth; No. 172, Scale Insects and Mites on Citrus Trees; No.
196, Usefulness of the Toad; No. 209, Controlling the Boll Weevil
in Cotton Seed and at Ginneries; No. 211, The Use of Paris Green in
controlling the Cotton Boll Weevil; No. 212, The Cotton Bollworm; No.
216, The Control of the Boll Weevil; No. 223, Miscellaneous Cotton
Insects in Texas; No. 247, The Control of the Codling Moth and Apple
Scab.
[Illustration: FIG. 185.--Female plant louse, with and without wings
(enlarged).]
The following bulletins of the Bureau of Entomology may be obtained
from the same source at the prices affixed: Bulletin No. 25 (old
series), Destructive Locusts, 15c.; No. 1 (new series), The Honey
Bee, 15c.; No. 3, The San José Scale, 10c.; No. 4, The Principal
Household Insects of the U. S., 10c.; No. 11, The Gypsy Moth in
America, 5c.; No. 14, The Periodical Cicada, 15c.; No. 15, The
Chinch Bug, 10c.; No. 16, The Hessian Fly, 10c.; Nos. 19, 23, and
33, Insects Injurious to Vegetables, 10c. each; No. 25, Notes on
Mosquitoes of the U. S., 10c.; No. 42, Some Insects attacking the
Stems of Growing Wheat, Rye, Barley, and Oats, 5c.; No. 50, The
Cotton Bollworm, 25c.; No. 51, The Mexican Boll Weevil, 25c.
Bureau of Plant Industry--Bulletin No. 88, Weevil-resisting
Adaptations of the Cotton Plant, 10c. This gives an instructive
account of the struggle of a plant for existence against an insect
enemy.
[Illustration: FIG. 186.--Gall fly (enlarged) and oak gall with larva,
and one from which a developed insect has escaped.]
[Illustration: FIG. 187.--PLAN OF MOUTH PARTS OF THE INSECT ORDERS.
_A_, straight wings, nerve wings, false nerve wings; _B_, joined wings;
_C_, scaly wings; _D_, half wings; _E_, two wings.
_ol_, upper lip; _ok_, biting jaws; _uk_, holding jaws; _ul_, under
lip; _kt_, jaw fingers; _lt_, lip fingers.]
[Illustration]
[Illustration: Pearl divers.]
CHAPTER IX
MOLLUSKS
THE FRESH-WATER MUSSEL
SUGGESTIONS.--The mussel is usually easy to procure from streams and
lakes by raking or dredging. In cities the hard-shelled clam, or
quahog, is for sale at the markets, and the following descriptions
apply to the anodon, unio, or quahog, with slight changes in regard
to the siphons. Mussels can be kept alive for a long time in a tub
with sand in the bottom. Pairs of shells should be at hand for study.
=External Features.=--The shell is an elongated oval, broader and
blunter at one end (Fig. 188). Why does the animal close its shell?
Does it open the shell? Why? Does it thrust the foot forward and pull
up to it, or thrust the foot back and push? (Mussels and clams have no
bones.) Does it go with the blunt or the more tapering end of the shell
forward? (Fig. 188.) Can a mussel swim? Why, or why not?
Lay the shells, fitted together, in your hand with _the hinge side away
from you and the blunt end to the left_ (Fig. 188). Is the right or the
left shell uppermost? Which is the top, or dorsal, side? Which is the
front, or anterior, end? Is the straight edge at the top or the bottom?
Our word “valve” is derived from a word meaning shell, because the
Romans used shells for valves in pumps. Is the mussel a univalve or a
bivalve? Which kind is the oyster? The snail?
Does the mussel have _bilateral symmetry_? Can you find a _horny
covering_, or epidermis, over the limy shell of a fresh specimen? Why
is it necessary? Does water dissolve lime? Horn? Find a bare spot. Does
any of the shell appear to be missing there?
The bare projection on each shell is called the _umbo_. Is the umbo
near the ventral or the dorsal line? The posterior or anterior end? Is
the surface of the umbones worn? Do the umbones rub against the sand as
the mussel plows its way along? How are the shells held together? Where
is the _ligament_ attached? (Fig. 189.) Is it opposite the umbones or
more to the front or rear? (Fig. 189.) Is the ligament of the same
material as the shell? Is the ligament in a compressed condition when
the shell is open or when it is closed? (Fig. 189.) When is the muscle
relaxed?
[Illustration: FIG. 188.--ANODON, or fresh-water mussel.]
[Illustration: FIG. 189.--DIAGRAM OF SHELL open and closed, showing
muscle, _m_, and ligament, _b_.]
[Illustration: FIG. 190.--MUSSEL crawling in sand.]
Notice the _lines_ on the outside of the shell (Figs. 188 and 190).
What point do they surround? They are _lines of growth_. Was each line
once the margin of the shell? If the shell should increase in size,
what would the present margin become? (Fig. 191.) Does growth take
place on the margin only? Did the shell grow thicker as it grew larger?
Where is it thinnest?
=Draw= the outside of the shell from the side. Draw a dorsal view. By
the drawings write the names of the margins of the shell (p. 98) and of
other parts learned, using lines to indicate the location of the parts.
Study the surface of the shell inside and out. The inside is called
_mother-of-pearl_. Is it of lime? Is the deeper layer of the shell of
lime? (When weak hydrochloric acid or strong vinegar is dropped on limy
substances, a gas, carbon dioxid, bubbles up.) Compare the thickness
of the _epidermal layer_, the middle _chalky layer_, and the inner,
_pearly layer_.
[Illustration: FIG. 191.--DIAGRAM. Change of points of attachment of
muscles as mussel enlarges. (Morgan.)]
=Anatomy of the Mussel.=--What parts protrude at any time beyond the
edge of the shell? (Fig. 190.) The shell is secreted by two folds of
the outer layer of the soft body of the mussel. These large, flaplike
folds hang down on each side, and are called the _mantle_. The two
great flaps of the mantle hang down lower than the rest of the body
and line the shell which it secretes (Fig. 192). The epidermis of
the mantle secretes the shell just as the epidermis of the crawfish
secretes its crust. Can you find the pallial line, or the line to which
the mantle extended on each shell when the animal was alive? A free
portion of the mantle extended like a fringe below the pallial line.
[Illustration: FIG. 192.--CROSS SECTION OF MUSSEL. (Diagram, after
Parker.)]
The shells were held together by two large _adductor muscles_. The
anterior adductor (Fig. 193) is near the front end, above the foot.
The posterior adductor is toward the rear end, but not so near the end
as the anterior. Can you find both _muscle scars_ in the shells? Are
they nearer the ventral or dorsal surface? The points of attachment
traveled downward and farther apart as the animal grew (see Fig. 191).
Higher than the larger scars are small scars, or impressions, where the
protractor and retractor muscles that extend and draw in the foot were
attached.
[Illustration: FIG. 193.--ANATOMY OF MUSSEL. (Beddard.)]
The muscular _foot_ extends downward in the middle, halfway between
the shells (Fig. 193). On each side of the foot and behind it hang
down the two pairs of =gills=, the outer pair and the inner pair (Fig.
192). They may be compared to four V-shaped troughs with their sides
full of holes. The water enters the troughs through the holes and
overflows above. Is there a marked difference in the size of the two
pairs of gills? A kind of chamber for the gills is made by the joining
of the mantle flaps below, along the ventral line. The mantle edges
are separated at two places, leaving openings called _exhalent_ and
_inhalent siphons_.
Fresh water with its oxygen, propelled by _cilia_ at the opening and on
the gills, enters through the lower or inhalent siphon, passes between
the gills, and goes to an upper passage, leaving the gill chamber by
a slit which separates the gills from the foot. For this passage, see
arrow (Fig. 194). The movement of the water is opposite to the way the
arrow points. After going upward and backward, the water emerges by the
exhalent siphon. The gills originally consisted of a great number of
filaments. These are now united, but not completely so, and the gills
still have a perforated or lattice structure. Thus they present a large
surface for absorbing oxygen from the water.
[Illustration: FIG. 194.--MUSSEL.
_A_, left shell and mantle flap removed.
_B_, section through body.
=Question:= Guided by other figures, identify the parts to which lines
are drawn.]
The =mouth= is in front of the foot, between it and the anterior
adductor muscle (Fig. 194). On each side of the mouth are the _labial
palps_, which are lateral lips (Fig. 195). They have cilia which convey
the food to the mouth after the inhalent siphon has sent food beyond
the gill chamber and near to the mouth. Thus both food and oxygen enter
at the inhalent siphon. The foot is in the position of a lower lip, and
if regarded as a greatly extended lower lip, the animal may be said to
have what is to us the absurd habit of using its lower lip as a foot.
The foot is sometimes said to be hatchet-shaped (Fig. 195). Do you see
any resemblance? Does the foot penetrate deep or shallow into the sand?
(Fig. 190.) Why, or why not?
[Illustration: FIG. 195.--MUSSEL. From below. Level cut across both
shells.
_Se_, palp; _P_, foot; _O_, mouth; _G_, liver; _Gg_, _Vg_, _Pg_,
ganglia.]
[Illustration: FIG. 196.--HEART OF MUSSEL, with intestine passing
through it.]
[Illustration: FIG. 197.]
The =food tube= of the mussel is comparatively simple. Behind the
mouth it enlarges into a swelling called the _stomach_ (Fig. 193).
The bile ducts of the neighboring liver empty into the stomach. The
_intestine_ makes several turns in the substance of the upper part
of the foot, and then passing upward, it runs approximately straight
to the vent (or anus), which is in the wall of the exhalent siphon.
The intestine not only runs through the _pericardial cavity_ (celome)
surrounding the heart, but through the ventricle of the heart itself
(Fig. 196).
The =kidneys= consist of tubes which open into the pericardial
chamber above and into the gill chamber below (_Neph._, Fig. 193).
The tubes are surrounded by numerous blood vessels (Fig. 198) and
carry off the waste matter from the blood.
The =nervous system= consists of _three pairs of ganglia_ and nerves
(Fig. 197). The ganglia are distinguishable because of their orange
color. The pedal ganglia on the front of the foot are easily seen
also; the visceral ganglia on the posterior adductor muscle may be
seen without removing the mussel from the shell (Fig. 193). The
reproductive organs open into the rear portion of the gill cavity
(Fig. 193). The sperms, having been set free in the water, are drawn
into the ova by the same current that brings the food. The eggs are
hatched in the gills. After a while the young mussels go out through
the siphon.
=Summary.=--In the gills (Fig. 198) the blood gains what? Loses what?
From the digestive tube the blood absorbs nourishment. In the kidneys
the blood is partly purified by the loss of nitrogenous waste.
[Illustration: FIG. 198.--DIAGRAM OF MUSSEL CUT ACROSS, showing mantle,
_ma_; gills, _kie_; foot, _f_; heart, _h_; intestine, _ed_.]
The cilia of the fringes on the inhalent, or lower, siphon, vibrate
continually and drive water and food particles into the mouth cavity.
Food particles that are brought near the labial palps are conveyed by
them to the mouth. As the water passes along the perforated gills, its
oxygen is absorbed; the mantle also absorbs oxygen from the water as
it passes. The water, as stated before, goes next through a passage
between the foot and palp into the cavity above the gills and on out
through the exhalent siphon. By stirring the water, or placing a drop
of ink near the siphons of a mussel kept in a tub, the direction of its
flow may be seen. The pulsations of the heart are plainly visible in a
living mollusk.
=Habits of the Mussel.=--Is it abundant in clear or muddy water; swift,
still, or slightly moving water? Describe its track or furrow. What
is its rate of travel? Can you distinguish the spots where the foot
was attached to the ground? How long is one “step” compared to the
length of the shell? The animal usually has the valves opened that it
may breathe and eat. The hinge ligament acts like the case spring of a
watch, and holds the valves open unless the adductor muscles draw them
together (Fig. 189).
When the mussel first hatches from the egg, it has a triangular shell.
It soon attaches itself to some fish and thus travels about; after two
months it drops to the bottom again.
=Other Mollusca.=--The _oyster’s_ shells are not an exact pair, the
shell which lies upon the bottom being hollowed out to contain the
body, and the upper shell being flat. Can you tell by examining an
oyster shell which was the lower valve? Does it show signs of having
been attached to the bottom? The young oyster, like the young mussel,
is free-swimming. Like the arthropoda, most mollusks undergo a
metamorphosis to reach the adult stage (Fig. 199).
[Illustration: FIG. 199.--OYSTER.
_C_, mouth; _a_, vent; _g_, _g′_, ganglia; _mt_, mantle; _b_, gill.]
[Illustration: FIG. 200.--TROCHUS.]
[Illustration: FIG. 201.--CYPRÆA. (Univalve, with a long opening to
shell.)]
Examine the shells of clams, snails, scallops, and cockles. Make
drawings of their shells. The slug is very similar to the snail except
that it has no shell. If the shell of the snail shown in Fig. 202 were
removed, there would be left a very good representation of a slug.
=Economic Importance of Mollusca.=--Several species of clams are eaten.
One of them is the _hard-shell clam_ (quahog) found on the Atlantic
coast from Cape Cod to Texas. Its shell is white. It often burrows
slightly beneath the surface. The _soft-shell clam_ is better liked
as food. It lives along the shores of all northern seas. It burrows a
foot beneath the surface and extends its siphons through the burrow to
the surface when the tide is in, and draws into its shell the water
containing animalcules and oxygen.
_Oysters_ to the value of many millions of dollars are gathered and
sold every year. The most valuable oyster fisheries of the United
States are in Chesapeake Bay. The young oysters, or “spat,” after they
attach themselves to the bottom in shallow water, are transplanted.
New oyster beds are formed in this way. The beds are sometimes strewn
with pieces of rock, broken pottery, etc., to encourage the oysters
to attach themselves. The dark spot in the fleshy body of the oyster
is the digestive gland, or liver. The cut ends of the tough adductor
muscles are noticeable in raw oysters. The starfish is very destructive
in oyster beds.
_Pearls_ are deposited by bivalves around some irritating particle
that gets between the shell and the mantle. The pearl oyster furnishes
most of the pearls; sometimes pearls of great value are obtained from
fresh-water mussels in the United States. Name articles that are made
partly or wholly of mother-of-pearl.
[Illustration: FIG. 202.--A SNAIL.
_l_, mouth; _vf_, _hf_, feelers; _e_, opening of egg duct; _fu_, foot;
_ma_, mantle; _lu_, opening to lung; _a_, vent.]
=Study of a Live Snail or Slug.=--Is its body dry or moist? Do
land snails and slugs have lungs or gills? Why? How many pairs of
tentacles has it? What is their relative length and position? The
eyes are dark spots at bases of tentacles of snail and at the tips
of the rear tentacles of slug. Touch the tentacles. What happens? Do
the tentacles simply stretch, or do they turn inside out as they are
extended? Is the respiratory opening on the right or left side of the
body? On the mantle fold or on the body? (Figs. 202-3-4.) How often
does the aperture open and close?
[Illustration: FIG. 203.--A SLUG.]
[Illustration: FIG. 204.--CIRCULATION AND RESPIRATION IN SNAIL.
_a_, mouth; _b_, _b_, foot; _c_, vent; _d_, _d_, lung; _h_, heart.
Blood vessels are black. (Perrier.)]
Place the snail in a moist tumbler. Does the whole under surface seem
to be used in creeping? Does the creeping surface change shape as the
snail creeps? Do any folds or wrinkles seem to move either toward
the front or rear of its body? Is enough mucus left to mark the path
traveled? The fold moves to the front, adheres, and smooths out as
the slug or snail is pulled forward.
=Cephalopods.=--The highest and best developed mollusks are the
=cephalopods=, or “head-footed” mollusks. Surrounding the mouth
are eight or ten appendages which serve both as feet and as arms.
These appendages have two rows of sucking disks by which the animal
attaches itself to the sea bottom, or seizes fish or other prey with
a firm grip. The commonest examples are the _squid_, with a long body
and ten arms, and the _octopus_, or devilfish, with a short body and
eight arms. Cephalopods have strong biting mouth parts and complex
eyes somewhat resembling the eyes of backboned, or vertebrate,
animals. The large and staring eyes add to the uncanny, terrifying
appearance.
[Illustration: FIG. 205.--A SQUID.]
The sepia or “ink” discharged through the siphon of the squid makes
a dark cloud in the water and favors its escape from enemies almost
as much as its swiftness (Fig. 205). The squid sometimes approaches
a fish with motion so slow as to be imperceptible, and then suddenly
seizes it, and quickly kills it by biting it on the back behind the
head.
The octopus is more sluggish than the squid. Large species called
devilfish sometimes have a spread of arms of twenty-five feet. The
_pearly nautilus_ (Fig. 206) and the _female of the paper argonaut_
(Fig. 207) are examples of cephalopods that have shells. The
_cuttlefish_ is closely related to the squid.
[Illustration: FIG. 206.--PEARLY NAUTILUS. (Shell sawed through to show
chambers used when it was smaller, and siphuncle, _S_, connecting them.
Tentacles, _T_.)]
[Illustration: FIG. 207.--PAPER ARGONAUT (female).
× ¹⁄₃ (_i.e._ the animal is three times as long and broad as figure).]
[Illustration: FIG. 208.--PAPER ARGONAUT (male). × ¹⁄₂.]
=General Questions.=--The living parts of the mussel are very soft, the
name mollusca having been derived from the Latin word _mollis_, soft.
Why is it that the softest animals, the mollusks, have the hardest
coverings?
To which class of mollusks is the name acephala (headless) appropriate?
Lamellibranchiata (platelike gills)?
Why is a smooth shell suited to a clam and a rough shell suited to an
oyster? Why are the turns of a snail’s shell so small near the center?
Why does the mussel have no use for head, eyes, or projecting feelers?
In what position of the valves of a mussel is the hinge ligament in a
stretched condition? How does the shape of the mussel’s gills insure
that the water current and blood current are brought in close contact?
The three classes of mollusks are: the pelecypoda (hatchet-footed);
gastropoda (stomach-footed); and cephalopoda (head-footed). Give an
example of each class.
Comparison of Mollusks.
=====+==========+==========+==========
| MUSSEL | SNAIL | SQUID
-----+----------+----------+----------
| | |
Shell| | |
| | |
-----+----------+----------+----------
| | |
Head | | |
| | |
-----+----------+----------+----------
| | |
Body | | |
| | |
-----+----------+----------+----------
| | |
Foot | | |
| | |
-----+----------+----------+----------
| | |
Gills| | |
| | |
-----+----------+----------+----------
| | |
Eyes | | |
| | |
=====+==========+==========+==========
=Comparative Review.=--(To occupy an entire page in notebook.)
============+==========+==========+==========+==========+==========
| GRASS- | | | |
| HOPPER | SPIDER | CRAYFISH | CENTIPEDE| MUSSEL
------------+----------+----------+----------+----------+----------
| | | | |
Bilateral | | | | |
or radiate | | | | |
------------+----------+----------+----------+----------+---------
Appendages | | | | |
for | | | | |
locomotion | | | | |
------------+----------+----------+----------+----------+---------
Names of | | | | |
divisions | | | | |
of body | | | | |
------------+----------+----------+----------+----------+---------
Organs and | | | | |
method of | | | | |
breathing | | | | |
------------+----------+----------+----------+----------+---------
| | | | |
Locomotion | | | | |
| | | | |
============+==========+==========+==========+==========+=========
CHAPTER X
FISHES
[Illustration]
SUGGESTIONS.--The behavior of a live fish in clear water, preferably
in a glass vessel or an aquarium, should be studied. A skeleton may
be prepared by placing a fish in the reach of ants. Skeletons of
animals placed on ant beds are cleaned very thoroughly. The study of
the perch, that follows, will apply to almost any common fish.
=Movements and External Features.=--What is the _general shape of the
body_ of a fish? How does the dorsal, or upper, region differ in form
from the ventral? Is there a narrow part or neck where the head joins
the trunk? Where is the body thickest? What is the ratio between the
length and height? (Fig. 209.) Are the right and left sides alike? Is
the symmetry of the fish bilateral or radial?
The _body of the fish may be divided_ into three regions,--the head,
trunk, and tail. The trunk begins with the foremost scales; the tail is
said to begin at the vent, or anus. Which regions bear appendages? Is
the head movable independently of the trunk, or do they move together?
State the advantage or disadvantage in this. Is the body depressed
(flattened vertically) or compressed (flattened laterally)? Do both
forms occur among fishes? (See figures on pages 123, 124.)
How is the _shape of the body advantageous for movement_? Can a fish
turn more readily from side to side, or up and down? Why? Is the
head wedge-shaped or conical? Are the jaws flattened laterally or
vertically? The fish swims in the water, the bird swims in the air.
Account for the differences in the shape of their bodies.
[Illustration: FIG. 209.--WHITE PERCH (_Morone Americana_).]
Is the _covering of the body_ like the covering of any animal yet
studied? The scales are attached in little pockets, or folds, in the
skin. Observe the shape and size of scales on different parts of the
body. What parts of the fish are without scales? Examine a single
scale; what is its shape? Do you see concentric lines of growth on a
scale? Sketch a few of the scales to show their arrangement. What is
the use of scales? Why are no scales needed on the head? How much of
each scale is hidden? Is there a film over the scale? Are the colors in
the scale or on it?
=The Fins.=--Are the movements of the fish active or sluggish? Can it
remain stationary without using its fins?
Can it move backward? How are the fins set in motion? What is the color
of the flesh, or muscles, of a fish? Count the fins. How many are in
pairs? (Fig. 209.) How many are vertical? How many are on the side?
How many are on the middle line? Are the paired or unpaired fins more
effective in balancing the fish? In turning it from side to side? In
raising and lowering the fish? In propelling it forward? How are some
of the fins useful to the fish besides for balancing and swimming?
The hard _spines_ supporting the fins are called the fin rays. The fin
on the dorsal line of the fish is called the _dorsal_ fin. Are its
rays larger or smaller than the rays of the other fins? The perch is
sometimes said to have two dorsal fins, since it is divided into two
parts. The fin forming the tail is called the tail fin, or _caudal_
fin. Are its upper and lower corners alike in all fishes? (Fig. 228.)
On the ventral side, just behind the vent, is the ventral fin, also
called the anal fin. The three fins mentioned are unpaired fins. Of the
four-paired fins, the pair higher on the sides (and usually nearer the
front) are the _pectoral_ fins. The pair nearer the ventral line are
the _pelvic_ fins. They are close together, and in many fish are joined
across the ventral line. The ventral fins are compared to the legs,
and the pectoral fins to the arms, of higher vertebrates. (Fig. 244.)
Compare fins of fish, pages 123, 124.
Make a =drawing= of the fish seen from the side, omitting the scales
unless your drawing is very large.
Are the =eyes= on the top or sides of the head, or both? Can a fish
shut its eyes? Why, or why not? Is the eyeball bare, or covered by
a membrane? Is the covering of the eyeball continuous with the skin
of the head? Is there a fold or wrinkle in this membrane or the
surrounding skin? Has the eye a pupil? An iris? Is the eye of the
fish immovable, slightly movable, or freely movable? Can it look with
both eyes at the same object? Is the _range of vision_ more upward or
downward? To the front or side? In what direction is vision impossible?
Can a fish close its eyes in sleep? Does the eyeball appear spherical
or flattened in front? The ball is really spherical, the lens is very
convex, and fish are nearsighted. Far sight would be useless in a dense
medium like water.
[Illustration: FIG. 210.--BLACKBOARD OUTLINE OF FISH.]
In what direction are the =nostrils= from the eyes? (Fig. 211.) There
are two pairs of nostrils, but only one pair of nasal cavities, with
two nostrils opening into each. There are no nasal passages to the
mouth, as the test with a probe shows that the cavities do not open
into the mouth. What two functions has the nose in man? What function
has it in the fish?
[Illustration: FIG. 211.--HEAD OF CARP.]
There are _no external_ =ears=. The ear sacs are embedded in the bones
of the skull. Is hearing acute or dull? When fishing, is it more
necessary not to talk or to step lightly, so as not to jar the boat or
bank?
What is the use of the large openings found at the back of the head on
each side? (Fig. 211.) Under the skin at the sides of the head are thin
membrane bones formed from the skin; they aid the skin in protection.
Just under these membrane bones are the gill covers, of true bone.
Which consists of more parts, the membranous layer, or the true bony
layer in the gill cover? (Figs. 211 and 212.)
[Illustration: FIG. 212.--SKELETON OF PERCH.]
Is the =mouth= large or small? Are the _teeth_ blunt or pointed? Near
the outer edge, or far in the mouth? (Fig. 212.) Does the fish have
lips? Are the teeth in one continuous row in either jaw? In the upper
jaw there are also teeth on the premaxillary bones. These bones are in
front of the maxillary bones, which are without teeth. Teeth are also
found in the roof of the mouth, and the tongue bears horny appendages
similar to teeth. Are the teeth of the fish better suited for chewing
or for grasping? Why are teeth on the tongue useful? Watch a fish
eating: does it chew its food? Can a fish taste? Test by placing bits
of brown paper and food in a vessel or jar containing a live fish. Is
the throat, or gullet, of the fish large or small?
The =skeleton= of a fish is simpler than the skeleton of other
backboned animals. Study Fig. 212 or a prepared skeleton. At first
glance, the skeleton appears to have two vertebral columns. Why?
What bones does the fish have that correspond to bones in the human
skeleton? Are the projections (processes) from the vertebræ long or
short? The _ribs_ are attached to the vertebræ of the trunk, the last
rib being above the vent. The tail begins at the vent. Are there more
tail vertebræ or trunk vertebræ? Are there any neck (cervical) vertebræ
(_i.e._ in front of those that bear ribs)? The first few ribs (how
many?) are attached to the central body of the vertebræ. The remaining
ribs are loosely attached to processes on the vertebræ. The ribs of
bony fishes are not homologous with the ribs of the higher vertebrates.
In most fishes there are bones called intermuscular bones attached to
the first ribs (how many in the perch?) which are possibly homologous
to true ribs; that is, true ribs in the higher vertebrates may have
been developed from such beginnings.
[Illustration: FIG. 213.]
Which, if any, of the _fin skeletons_ (Fig. 214) are not attached
to the general skeleton? Which fin is composed chiefly of tapering,
pointed rays? Which fins consist of rays which subdivide and widen
toward the end? Which kind are stiff, and which are flexible? Which
of the fin rays are segmented, or in two portions? The outer segment
is called the radial, the inner the basal segment. Which segments are
longer? There is one basal segment that lacks a radial segment; find it
(Fig. 212).
[Illustration: FIG. 214.--SOFT-RAYED AND SPINY-RAYED FINS.]
What is the advantage of the backbone plan of structure over the
armor-plate plan? You have seen the spool-like body of the vertebra in
canned salmon. Is it concave, flat, or convex at the ends?
[Illustration: FIG. 215.--CARP, with right gill cover removed to show
gills.]
[Illustration: FIG. 216.--SKELETON AROUND THROAT OF FISH.]
The =gills= are at the sides of the head (Fig. 215) under the opercula,
or gill covers. What is the color of the gills? Do the blood vessels
appear to be very near the surface of the gills, or away from the
surface? What advantage in this? Are the gills smooth or wrinkled?
(Fig. 215.) What advantage? The bony supports of the gills, called the
gill arches, are shown in Fig. 216 (_k_₁ to _k_₄). How many arches
on each side? The gill arches have projections on their front sides,
called gill rakers, to prevent food from being washed through the
clefts between the arches. The fringes on the rear of the gill arches
are called the gill filaments (_a_, Fig. 216). These filaments support
the thin and much-wrinkled borders of the gills, for the gills are
constructed on the plan of exposing the greatest possible surface to
the water. Compare the plan of the gills and the human lungs. The gill
opening on each side is guarded by seven rays (_kh_, Fig. 216) along
the hinder border of the gill cover. These rays grow from the tongue
bone. (_Zu_, Fig. 216. This is a rear view.)
[Illustration: FIG. 217.--CIRCULATION IN GILLS.]
[Illustration: FIG. 218.--NOSTRILS, MOUTH, AND GILL OPENINGS OF
STING-RAY.]
Watch a live fish and determine how the water is forced between the
gills. Is the mouth opened and closed in the act of breathing? Are the
openings behind the gill covers opened and closed? How many times per
minute does fresh water reach the gills? Do the mouth and gill covers
open at the same time? Why must the water in contact with the gills
be changed constantly? Why does a fish usually rest with its head up
stream? How may a fish be kept alive for a time after it is removed
from the water? Why does drying of the gills prevent breathing? If the
mouth of a fish were propped open, and the fish returned to the water,
would it suffocate? Why, or why not?
[Illustration: FIG. 219.--GILL OPENINGS OF EEL.]
=Food Tube.=--The gullet is short and wide. The stomach is elongated
(Fig. 220). There is a slight constriction, or narrowing, where it
joins the intestine. Is the intestine straight, or does it lie in
few or in many loops? (Fig. 220.) The liver has a gall bladder and
empties into the intestine through a bile duct. Is the liver large or
small? Simple or lobed? The spleen (_mi_, Fig. 220) lies in a loop
of the intestine. The last part of the intestine is straight and
is called the rectum. Is it of the same size as the other portions
of the intestine? The fish does not possess a pancreas, the most
important digestive gland of higher vertebrates.
[Illustration: FIG. 220.--ANATOMY OF CARP. (See also colored figure 4.)
_bf_, barbels on head (for feeling); _h_, ventricle of heart; _as_,
aortic bulb for regulating flow to gills; _vk_, venous sinus; _ao_,
dorsal aorta; _ma_, stomach; _l_, liver; _gb_, gall cyst; _mi_, spleen;
_d_, small intestine; _md_, large intestine; _a_, vent; _s_, _s_, swim
bladder; _ni_, _ni_, kidney; _hl_, ureter; _hb_, bladder; _ro_, eggs
(roe); _mhe_, opening of ducts from kidney and ovary.
=Questions:= Are the kidneys dorsal or ventral? The swim bladder? Why?
Why is the swim bladder double? Does blood enter gills above or below?]
The _ovary_ lies between the intestine and the air bladder. In Fig.
220 it is shown enlarged and filled with egg masses called roe. It
opens by a pore behind the vent. The silver lining of the body cavity
is called the peritoneum. (See Chap. VII, Human Biology.)
Is the _air bladder_ simple or partly divided in the perch? In the
carp? (Fig. 220.) Is it above or below the center of the body? Why?
The air bladder makes the body of the fish about as light as water
that it may rise and sink with little effort. When a fish dies, the
gases of decomposition distend the bladder and the abdomen, and the
fish turns over. Why?
Where are the _kidneys_? (Fig. 220.) Their ends unite close under the
spinal column. The ureters, or tubes, leading from them, unite, and
after passing a small urinary bladder, lead to a tiny urinary pore
just behind the opening from the ovary. (Colored figure 4.)
=The Circulation.=--The fish, unlike other vertebrates, has its
breathing organs and its heart in its head. The gills have already
been described. The heart of an air-breathing vertebrate is near its
lungs. Why? The _heart_ of a fish is near its gills for the same
reason. The heart has one auricle and one ventricle. (Colored figure
1.)
[Illustration: FIG. 221.--PLAN OF CIRCULATION.
_Ab_, arteries to gills; _Ba_, aortic bulb; _V_, ventricle.]
Blood returning to the heart comes through several veins into a
_sinus_, or antechamber, whence it passes down through a valve into
the _auricle_; from the auricle it goes forward into the _ventricle_.
The ventricle sends it into an _artery_, not directly, but through
a _bulb_ (as, Fig. 220), which serves to maintain a steady flow,
without pulse beats, into the large artery (_aorta_) leading to the
gills. The arteries leading from the gills join to form a _dorsal
aorta_ (_Ao_, Fig. 221), which passes backward, inclosed by the lower
processes of the spinal column. After going through the _capillaries_
of the various organs, the blood returns to the heart through veins.
The _color of the blood_ is given by red corpuscles. These are
nucleated, oval, and larger than the blood corpuscles of other
vertebrates. The blood of the fish is slightly above the temperature
of the water it inhabits.
[Illustration: FIG. 222.--BRAIN OF PERCH, from above.
_n_, end of nerve of smell; _au_, eye; _v_, _z_, _m_, fore, mid, and
hind brain; _h_, spinal bulb; _r_, spinal cord.]
Notice the general shape of the =brain= (Fig. 222). Are its
subdivisions distinct or indistinct? Are the lobes in pairs? The
middle portion of the brain is the widest, and consists of the two
_optic lobes_. From these lobes the optic nerves pass beneath the
brain to the eyes (_Sn_, Fig. 223). In front of the optic lobes lie
the two cerebral lobes, or the _cerebrum_. The small _olfactory
lobes_ are seen (Fig. 224) in front of the cerebrum. The olfactory
nerves may be traced to the nostrils. Back of the optic lobes (mid
brain) is the cerebellum (hind brain), and back of it is the _medulla
oblongata_, or beginning of the spinal cord.
[Illustration: FIG. 223.--BRAIN OF PERCH, side view.]
[Illustration: FIG. 224.--BRAIN OF PERCH, from below.]
Taking the eyeball for comparison, is the whole brain as large as one
eyeball? (Fig. 222.) Judging from the size of the parts of the brain,
which is more important with the fish, thinking or perception? Which
is the most important sense?
The scales along a certain line on each side of the fish, called the
lateral line, are perforated over a series of lateral line sense
organs, supposed to be the chief organs of _touch_ (see Fig. 209).
[Illustration: FIG. 225.--THE STICKLEBACK. Instead of depositing the
eggs on the bottom, it makes a nest of water plants--the only fish that
does so--and bravely defends it.]
=Questions.=--Which of the fins of the fish have a use which
corresponds to the keel of a boat? The rudder? A paddle for sculling?
An oar? State several reasons why the head of the fish must be very
large, although the brain is very small. Does all the blood go to the
gills just after leaving the heart?
Make a list of the different species of fish found in the waters of
your neighborhood; in the markets of your town.
[Illustration: FIG. 226.--ARTIFICIAL FECUNDATION. The egg-cells and
sperm-cells are pressed out into a pan of water.]
[Illustration: FIG. 227.--NEWLY HATCHED TROUT, with yolk-sac adhering,
eyes large, and fins mere folds of the skin. (Enlarged.)]
=Reproduction.=--The female fish deposits the unfertilized eggs,
or ova, in a secluded spot on the bottom. Afterward the male fish
deposits the sperms in the same place (see Fig. 225). The eggs, thus
unprotected, and newly hatched fish as well, are used for food by
fish of the same and other species. To compensate for this great
destruction, most fish lay (spawn) many thousands of eggs, very few
of which reach maturity. Higher vertebrates (_e.g._ birds) have, by
their superior intelligence, risen above this wasteful method of
reproduction. Some kinds of marine fish, notably cod, herring, and
salmon, go many miles up fresh rivers to spawn. It is possible that
this is because they were originally fresh-water species; yet they die
if placed in fresh water except during the spawning season. They go
because of _instinct_, which is simply an inherited habit. Rivers may
be safer than the ocean for their young. They are worn and exhausted by
the journey, and never survive to lay eggs the second time.
[Illustration: FIG. 228.--A SHARK (_Acanthias vulgaris_).]
The _air bladder is developed from the food tube_ in the embryo fish,
and is homologous with lungs in the higher vertebrates. Are their
functions the same?
Fish that _feed on flesh have a short intestine_. Those that eat plants
have a long intestine. Which kind of food is more quickly digested?
There are _mucous glands in the skin_ of a fish which supply a
secretion to facilitate movement through the water; hence a freshly
caught fish, before the secretion has dried, feels very slippery.
The air bladder, although homologous to lungs, is not a breathing organ
in common fishes. It is filled by the formation of gases from the
blood, and can be made smaller by the contraction of muscles along the
sides of the body; this causes the fish to sink. In the gar and other
ganoids, the air bladder contains blood vessels, is connected with the
gullet, and is used in breathing. Organs _serving the same purpose_ in
different animals are said to be _analogous_. To what in man are the
gills of the fish analogous? Organs having _a like position and origin_
are said to be _homologous_. The air bladders of a fish are homologous
with the lungs of man; but since they have not the same use they are
not analogous.
How does the tail of a shark or a gar differ from the tail of common
fishes? (Fig. 228.) Do you know of fish destitute of scales? Do you
know of fish with whiplike feelers on the head? (Figs.) Why are most
fishes white on the under side?
=Comparative Review.=--(Copy table on one page or two facing pages of
notebook.)
=========+===========+===========+===========+===========+===========
| IS THERE | | DIGESTIVE | |
| A HEAD? | METHOD OF |ORGANS AND | RE- |
| A NECK? | FEEDING | DIGESTION |PRODUCTION | SENSES
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Ameba | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Sponge | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Hydra | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Starfish | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Earthworm| | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Wasp | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Mussel | | | | |
| | | | |
---------+-----------+-----------+-----------+-----------+-----------
| | | | |
Fish | | | | |
| | | | |
=========+===========+===========+===========+===========+===========
[Illustration: FIG. 229.--DRAWING THE SEINE.]
[Illustration: FIG. 230.--SUNFISH.
FIG. 231.--TUNNY.
FIG. 232.--SWORDFISH.
FIG. 233.--SWELLFISH.
FIG. 234.--TURBOT.
FIG. 235.--CARP.
FIG. 236.--HERRING.
FIG. 237.--SPECKLED TROUT.
FIG. 238.--PERCH.
FIG. 239.--SALMON.
=Seven Food Fish. Three Curious Fish.=
SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)]
[Illustration: FIG. 240.--SEA HORSE (_hippocampus_), with incubating
pouch, _Brt._
FIG. 241.--BAND FISH.
FIG. 242.--TORPEDO. Electrical organs at right and left of brain.
FIG. 243.--LANTERN FISH (_Linophryne lucifer_). (After Collett.)
FIG. 244.--LUNG FISH of Australia (_Ceratodus miolepis_).
FIG. 245.--TRUNK FISH.
FIG. 246.--SEAWEED FISH. × ¹⁄₅ (_Phyllopteryx eques_).
=Remarkable Fish.= SPECIAL REPORTS. (Encyclopedia, texts, dictionary.)]
KEY TO THE BRANCHES, OR SUB-KINGDOMS
A₁ =One-celled Animals= (_Protozoans_) I. PROTOZOANS
A₂ =Many-celled Animals= (_Metazoans_)
B₁ RADIATE (around a center). Without head;
all aquatic, resembling plants, and often
fixed to bottom
C₁ Walls of body serving as digestive
organs
D₁ Many openings, no tentacles II. SPONGES
(_Porifera_)
D₂ One opening, which is both mouth and III. POLYPS
vent; tentacles for seizing prey (_Cœlenterata_)
C₂ Digestive tube distinct from body wall, IV. ECHINODERMS
spiny skin
B₂ BILATERAL. With anterior and posterior
end; dorsal and ventral surface
C₁ Body of successive segments; legs V. VERMES
without joints
C₂ External skeleton of successive rings; VI. ARTHROPODS
jointed legs
C₃ Body soft; no skeleton; usually bearing VII. MOLLUSKS
a limy shell
C₄ Internal jointed skeleton, attached to VIII. VERTEBRATES
an axis or vertebral column
=Examples.=--Tell the branch to which each of the following
animals belongs: crayfish, earthworm, thousand leg, white grub,
sea anemone, ameba, tapeworm, caterpillar, beetle, sparrow, snake,
oyster, starfish, fish. Be prepared to state the reason for each
classification.
The =classes= in the branch =vertebrata= are: 1. Fishes (_pisces_). 2.
Frogs and Salamanders (_batrachia_). 3. Reptiles (_reptilia_). 4. Birds
(_aves_). 5. Mammals (_mammalia_).
[Illustration: FIG. 247.--A SNAIL. (Which branch? Why?)]
CHAPTER XI
BATRACHIA
The theory of evolution teaches that animal life began in a very simple
form in the sea, and that afterward the higher sea animals lost their
gills and developed lungs and legs and came out to live upon the land;
truly a marvelous procedure, and incredible to many, although the
process is repeated every spring in countless instances in pond and
brook.
In popular language, every cold-blooded vertebrate breathing with
lungs is called a reptile. The name reptile is properly applied only
to lizards, snakes, turtles, and alligators. The common mistake of
speaking of frogs and salamanders as reptiles arises from considering
them only in their adult condition. Reptiles hatch from the egg as tiny
reptiles resembling the adult forms; frogs and salamanders, as every
one knows, leave the egg in the form of tadpoles (Fig. 248). The fact
that frogs and salamanders begin active life as fishes, breathing by
gills, serves to distinguish them from other cold-blooded animals, and
causes naturalists to place them in a separate class, called batrachia
(twice breather) or amphibia (double life).
TADPOLES
SUGGESTIONS.--Tadpoles may be studied by placing a number of frog’s
eggs in a jar of water, care being taken not to place a large number
of eggs in a small amount of water. When they hatch, water plants
(_e.g._ green algæ) should be added for food. The behavior of frogs
may be best studied in a tub of water. A toad in captivity should be
given a cool, moist place, and fed well. A piece of meat placed near
a toad may attract flies, and the toad may be observed while catching
them, but the motion is so swift as to be almost imperceptible. Live
flies may be put into a glass jar with a toad. Toads do not move about
until twilight, except in cloudy, wet weather. They return to ponds and
brooks in spring at the time for laying eggs. This time for both frogs
and toads is shown by trilling. All frogs, except tree frogs, remain in
or near the water all the year.
[Illustration: FIG. 248.--METAMORPHOSES OF THE FROG, numbered in order.]
Do =eggs hatch= and tadpoles grow more rapidly in a jar of water kept
in a warm place or in a cold place? In pond water or drinking water?
Can the tadpoles be seen to move in the eggs before hatching? When do
the external gills show? (Fig. 248.)
What =parts= may be described in a tadpole? What is the shape of the
tail? _Compare the tadpole with the fish_ as to (1) general shape, (2)
covering, (3) fins, (4) tail, (5) gills.
Do the external =gills= disappear before or after any rudiments of
limbs appear? (6, 7, Fig. 248.) Can you locate the gills after they
become internal? (Fig. 249.)
[Illustration: FIG. 249.--TADPOLE, from below, showing intestine and
internal gills. (Enlarged.)]
In what state of growth are the _legs_ when the tadpole first goes to
the surface to breathe? Which legs appear first? What advantage is
this? What becomes of the tail? Is the tail entirely gone before the
frog first leaves the water? Are tadpoles habitually in motion or at
rest?
Is the =intestine= visible through the skin? (Fig. 249.) Is it straight
or coiled? Remembering why some fish have larger intestines than
others, and that a cow has a long intestine and a cat a short one,
state why a tadpole has a relatively longer intestine than a frog.
=Compare= the mouth, jaws, eyes, skin, body, and habits of _tadpole and
frog_.
FROGS
Prove that frogs and toads are _beneficial to man_. Did you ever know
of a frog or toad destroying anything useful, or harming any one,
or causing warts? How many pupils in class ever had warts? Had they
handled frogs before the warts came? Frogs are interesting, gentle,
timid animals. Why are they repulsive to some people?
=Environment.=--_Where are frogs found_ in greatest numbers? What
occurs when danger threatens them? What _enemies_ do they have? What
color, or tint, is most prominent on a frog? Does the color “mimic”
or _imitate_ its surroundings? What is the color of the under side of
the body? (Fig. 250.) Why is there greater safety in that color? What
enemies would see water frogs from below? Do tree frogs mimic the bark?
The leaves?
Can a _frog stay under water_ for an indefinite time? Why, or why not?
What part of a frog is above the surface when it floats or swims in a
tub of water? Why? Do frogs croak in the water or on the bank? Why do
they croak after a rain? Do toads croak?
Are the _eggs_ laid in still or flowing water? In a clear place or
among sticks and stems? Singly, or in strings or in masses? (Fig.
248.) Describe an egg. Why do frogs dig into the mud in autumn in cold
climates? Why do they not dig in mud at the bottom of a pond? Why is
digging unnecessary in the Gulf states?
Describe the =position= of the frog when still (Fig. 250). What
advantage in this position? Does the frog use its fore legs in swimming
or jumping? Its hind legs? How is the frog fitted for jumping? Compare
it in this respect with a jumping insect; a jumping mammal. How is it
fitted for swimming? Is the general build of its body better fitted for
swimming or jumping? How far can a frog jump?
[Illustration: FIG. 250.--PAINTED FROG (_Chorophilus ornatus_), of
Mexico.]
=External Features.=--The frog may be said to have two _regions in
its body_, the head and trunk. A neck hardly exists, as there is only
one vertebra in front of the shoulders (Fig. 252), although most
vertebrates have seven neck (cervical) vertebræ. There are no tail
(caudal) vertebræ, even in the tadpole state of frogs and toads.
The _head_ appears triangular in shape when viewed from what direction?
The head of a frog is more pointed than the head of a toad. Is the
skull a closed case of broad bones or an open structure of narrow
bones? (Fig. 252.)
Describe the _mouth_. Observe the extent of the mouth opening (Fig.
251). Are _teeth_ present in the upper jaw? The lower jaw? Are the
teeth sharp, or dull? Does the frog chew its food? Is the _tongue_
slender or thick? (Fig. 251.) Is it attached to the front or the back
of the mouth? In what direction does the free end extend when the
tongue lies flat? Is the end pointed or lobed? How far out will the
tongue stretch? For what is it used? Why is it better for the teeth to
be in the upper jaw rather than in the lower jaw? That the teeth are of
little service is shown by the fact that the toad with similar habits
of eating has no teeth. Will a toad catch and swallow a bullet or
pebble rolled before it? The toad is accustomed to living food, hence
prefers a moving insect to a still one.
[Illustration: FIG. 251.--HEAD OF FROG.]
=The Senses.=--Compare the _eyes_ with the eyes of a fish in respect to
position and parts. Are the eyes protruding or deep-set? Touch the eye
of a live frog. Can it be retracted? What is the shape of the pupil?
The color of the iris? Is the eye bright or dull? What probably gave
rise to the superstition that a toad had a jewel in its head? Is there
a third eyelid? Are the upper and lower eyelids of the same thickness?
With which lid does it wink? Close its eye?
Observe the large oval _ear_ drum or tympanum. What is its direction
from the eye? (Fig. 251.) The mouth? Is there a projecting ear? Does
the frog hear well? What reason for your answer? As in the human ear,
a tube (the Eustachian tube) leads from the mouth to the inner side of
the tympanum.
How many _nostrils_? (Fig. 251.) Are they near together or separated?
Large or small? A bristle passed into the nostril comes into the mouth
not far back in the roof. Why must it differ from a fish in this?
How do the _fore and hind legs_ differ? How many toes on the fore
foot or hand? On the hind foot? On which foot is one of the toes
rudimentary? Why is the fore limb of no assistance in propelling the
body in jumping? Do the toes turn in or out? (Fig. 250.) How does
the frog give direction to the jump? What would be the disadvantage
of always jumping straight forward when fleeing? Which legs are more
useful in alighting?
[Illustration: FIG. 252.--SKELETON OF FROG.]
=Divisions of the Limbs.=--Distinguish the upper arm, forearm, and hand
in the fore limb (Figs. 252 and 253). _Compare with skeleton of man_
(Fig. 399). Do the arms of a man and a frog both have one bone in the
_upper arm_ and two in the _forearm_? Both have several closely joined
bones in the _wrist_ and five separate bones in the _palm_. Do any of
the frog’s fingers have three joints? _Compare also the leg of man_and
the hind leg of the frog (Figs. 253 and 399). Does the _thigh_ have one
bone in each? The shank of man has two bones, shin and splint bone. Do
you see a groove near the end in the shank bone of a frog (Fig. 252),
indicating that it was formed by the union of a shin and splint bone?
The first two of the five bones of the ankle are elongated, giving the
hind leg the appearance of having an extra joint (Fig. 253). The foot
consists of six digits, one of which, like the thumb on the fore limb,
is rudimentary. The five developed toes give the five digits of the
typical vertebrate foot. Besides the five bones corresponding to the
instep, the toes have two, three, or four bones each. How is the hind
foot specialized for swimming? Which joint of the leg contains most
muscle? (Fig. 254.) Find other bones of the frog analogous in position
and similar in form to bones in the human skeleton.
[Illustration: FIG. 253.--SKELETON OF FROG.]
[Illustration: FIG. 254.--LEG MUSCLES OF FROG.]
Is the =skin= of a frog tight or loose? Does it have any appendages
corresponding to scales, feathers, or hair of other vertebrates? Is the
skin rough or smooth? The toad is furnished with glands in the skin
which are sometimes swollen; they form a bitter secretion, and may be,
to some extent, a protection. Yet birds and snakes do not hesitate to
swallow toads whole. Show how both upper and under surfaces of frog
illustrate protective coloration.
All batrachians have large and _numerous blood vessels in the skin_ by
which gases are exchanged with the air, the skin being almost equal to
_a third lung_. That the skin may function in this way, it must not
become dry. Using this fact, account for certain habits of toads as
well as frogs.
If a frog is kept in the dark or on a dark surface, _its skin will
become darker_ than if kept in the light or on a white dish. Try
this experiment, comparing two frogs. This power of changing color
is believed to be due to the diminution in size of certain pigment
cells by contraction, and enlargement from relaxation. This power is
possessed to a certain degree not only by batrachians but also by many
fishes and reptiles. The chameleon, or green lizard of the Gulf states,
surpasses all other animals in this respect (Fig. 280). What advantage
from this power?
[Illustration: FIG. 255.--DIGESTIVE CANAL OF FROG.
_Mh_, mouth; _Z_, tongue pulled outward; _S_, opening to larynx; _Oe_,
gullet; _M_, stomach; _D_, intestine; _P_, pancreas; _L_, liver; _G_,
gall bladder; _R_, rectum; _Hb_, bladder; _Cl_, cloaca; _A_, vent.]
=Digestive System.=--The large mouth cavity is connected by a short
throat with the gullet, or esophagus (Fig. 255). A slit called the
glottis opens from the throat into the lungs (Fig. 255). Is the gullet
long or short? Broad or narrow? Is the stomach short or elongated? Is
the division distinct between the stomach and gullet, and stomach and
intestine? Is the liver large or small? Is it simple or lobed? The
pancreas lies between the stomach and the first bend of the intestines
(Fig. 255). What is its shape? A bile duct connects the liver with
the small intestine (_Dc_, Fig. 255). It passes through the pancreas,
from which it receives several pancreatic ducts. After many turns, the
small intestine joins the large intestine. The last part of the large
intestine is called the rectum (Latin, straight). The last part of the
rectum is called the cloaca (Latin, a drain), and into it the ducts
from the kidneys and reproductive glands also open. The kidneys are
large, elongated, and flat. They lie under the dorsal wall. The urinary
bladder is also large. Does the salamander have a similar digestive
system? (Fig. 256.) Why are the liver and lungs (Fig. 256) longer in a
salamander than in a frog?
[Illustration: FIG. 256.--ANATOMY OF SALAMANDER.
_1a_, heart; _2_, lungs; _3a_, stomach; _3b_, intestine; _3c_, large
intestine; _4_, liver; _8_, egg masses; _10_, bladder; _11_, vent.]
=Respiration.=--How many _lungs_? Are they simple or lobed? (Fig.
256.) A lung cut open is seen to be baglike, with numerous ridges on
its inner surface. This increases the surface with which the air may
come in contact. In the walls of the lungs are numerous capillaries.
Does the frog _breathe with mouth open or closed_? Does the frog have
any ribs for expanding the chest? What part of the head expands and
contracts? Is this motion repeated at a slow or rapid rate? Regularly
or irregularly? There are valves in the nostrils for opening and
closing them. Is there any indication of opening and closing as the
throat expands and contracts? The mouth and throat (pharynx) are filled
with air each time the throat swells, and the exchange of gases (which
gases?) takes place continually through their walls and the walls of
the lungs. At intervals the air is forced through the glottis into the
lungs. After a short time it is expelled from the lungs by the muscular
abdominal walls, which press upon the abdominal organs, and so upon the
lungs. Immediately the air is forced back into the lungs, so that they
are kept filled. In some species the lungs regularly expand at every
second contraction of the throat. This is shown by a slight outward
motion at the sides. Does the motion of the throat cease when the frog
is under water? Why would the frog be unable to breathe (except through
the skin) if its mouth were propped open? Why does the fact that the
breathing is so slow as to almost cease when hibernating, aid the frog
in going through the winter without starving? (Chap. I.) Why must frogs
and toads keep their skins moist? Which looks more like a clod? Why?
=The Heart and Circulation.=--What is the shape of the heart? (Fig.
257.) Observe the two auricles in front and the conical ventricle
behind them. The great arterial trunk from the ventricle passes
forward beyond the auricles; it divides into two branches which turn
to the right and left (Fig. 257). Each branch immediately subdivides
into three arteries (Fig. 257), one going to the head, one to the
lungs and skin, and a third, the largest, passes backward in the
trunk, where it is united again to its fellow. (Colored Fig. 2.)
Both of the pulmonary veins, returning to the heart with pure
blood from the lungs, empty into the left auricle. Veins with the
impure blood from the body empty into the right auricle. Both the
auricles empty into the ventricles, but the pure and impure blood
are prevented from thoroughly mixing by ridges on the inside of the
ventricle. Only in an animal with a four-chambered heart does pure
blood from the lungs pass unmixed and pure to all parts of the body,
and only such animals are warm-blooded. The purer (_i.e._ the more
oxygenated) the blood, the greater the oxidation and warmth.
The red corpuscles in a frog’s _blood_ are oval and larger than those
of man. Are all of them nucleated? (Fig. 258.) The flow of _blood_ in
the web of a frog’s foot is a striking and interesting sight. It may
be easily shown by wrapping a small frog in a wet cloth and laying it
with one foot extended upon a glass slip on the stage of a microscope.
[Illustration: FIG. 257.--PLAN OF FROG’S CIRCULATION.
Venous system is black; the arterial, white. _AU_, auricles; _V_,
ventricle; _L_, lung; _LIV_, liver. Aorta has one branch to right,
another to left, which reunite below. Right branch only persists in
birds, left branch in beasts and man.]
[Illustration: FIG. 258.--FROG’S BLOOD (magnified 2500 areas). Red
cells oval, nucleated, and larger than human blood cells. Nuclei of two
white cells visible near center. (Peabody.)]
[Illustration: FIG. 259.--BRAIN OF FROG.]
[Illustration: FIG. 260.--NERVOUS SYSTEM OF FROG.]
The =brain= of the frog (Fig. 259) is much like that of a fish (Fig.
224). The _olfactory_, _cerebral_, and _optic lobes_, _cerebellum_
and _medulla_ are in the same relative position, although their
relative sizes are not the same. Compared with the other parts,
are the olfactory lobes more or less developed than in a fish? The
cerebral hemispheres? The optic lobes? The cerebellum? There is a
cavity in the brain. It is readily exposed on the under surface of
the medulla by cutting the membrane, which is there its only covering
(Fig. 259).
[Illustration: FIG. 261.--Position of legs in tailless (_A_) and tailed
(_B_) amphibian.]
=Frogs and toads are beneficial= (why?) and do not the slightest injury
to any interest of man. If =toads= are encouraged to take up their
abode in a garden, they will aid in ridding it of insects. A house may
be made in a shady corner with four bricks, or better still, a hole a
foot deep may be dug to furnish them protection from the heat of the
day. A toad’s muzzle is not so tapering as a frog’s (why?), its feet
are not so fully webbed (why?), and its skin is not so smooth (why?).
In case of doubt open the mouth and rub the finger along the upper jaw;
a frog has sharp teeth, a toad none at all. The tadpoles of frogs,
toads, and salamanders are much alike. In toad’s spawn the eggs lie in
strings inclosed in jelly; frogs spawn is in masses (Fig. 248).
Any batrachian may easily be passed around the class after placing it
in a tumbler with gauze or net tied over top. It should be kept in a
box with two inches of moist earth on the bottom. If no live insects
are obtainable for feeding a toad, bits of moist meat may be dangled
from the end of a string. If tadpoles are placed in a pool or tub in
a garden, the toads hatched will soon make destructive garden insects
become a rarity.
Does a frog or a =salamander= have the more primitive form of body?
Why do you think so? Salamanders are sometimes called mud puppies. The
absurd belief that salamanders are poisonous is to be classed with
the belief that toads cause warts. The belief among the ancients that
salamanders ate fire arose perhaps from seeing them coming away from
fires that had been built over their holes on river banks by travelers.
Their moist skin protected them until the fire became very hot.
Describe the “mud puppy” shown in Fig. 262. In the West the pouched
gopher, or rat (Fig. 371), is sometimes absurdly called a salamander.
[Illustration: FIG. 262.--BLIND SALAMANDER (_Proteus anguinus_). × ¹⁄₂.
Found in caves and underground streams in Balkans. Gills external, tail
finlike, legs small.]
CHAPTER XII
REPTILIA (REPTILES)
This =class= is divided into _four orders_ which have such marked
differences of external form that there is no difficulty in
distinguishing them. These orders are represented by _Lizards_,
_Snakes_, _Turtles_, and _Alligators_. Of these, only the forms of
lizards and alligators have similar proportions, but there is a marked
difference in their size, lizards being, in general, the smallest, and
alligators the largest of the reptiles.
[Illustration: FIG. 263.--A SALAMANDER.]
[Illustration: FIG. 264.--A LIZARD.]
=Comparison of Lizards and Salamanders.=--To make clear the difference
between reptiles and batrachians, it will be well to compare the orders
in the two classes which resemble each other in size and shape; namely,
lizards and salamanders (Figs. 263 and 264). State in a tabular form
their differences in _skin, toe, manner of breathing, development from
egg, shape of tail, habitat, habits_. Each has an elongated body, two
pairs of limbs, and a long tail, yet they are easily distinguished. Are
the differences suggested above valid for the other batrachians (frogs)
and other reptiles (_e.g._ turtles)? Trace the same differences between
the toad or frog (Fig. 250) and the “horned toad,” which is a lizard
(Fig. 265).
[Illustration: FIG. 265.--“HORNED TOAD” LIZARD, of the Southwest
(_Phrynosoma cornita_). × ²⁄₃.]
STUDY OF A TURTLE OR TORTOISE
SUGGESTIONS.--Because of the ease with which a tortoise or turtle may
be caught and their movements and habits studied, it is suggested
that one of these be studied as an example of reptiles. Besides a
live specimen, a skeleton of one species and the shells of several
species should be available.
[Illustration: FIG. 266.--EUROPEAN POND TURTLE (_Emys lutaria_). (After
Brehms.)]
The =body (of a turtle or tortoise) is divided= distinctly into
_regions_ (Fig. 266). Is there a head? Neck? Trunk? Tail? The trunk is
inclosed by the _so-called shell_, which consists of an upper portion,
the _carapace_, and a lower portion, the _plastron_. How are the other
regions covered? What is the shape of the head? Is the mouth at the
front, or on the under side? Where are the _nostrils_? Are the motions
of breathing visible? Is there a beak or snout? Do the jaws contain
teeth?
Do the =eyes= project? Which is thinner and more movable, the upper or
lower lid? Identify the third eyelid (_nictitating membrane_). It is
translucent and comes from, and is drawn into, the inner corner of the
eye. It cleanses the eyeball. Frogs and birds have a similar membrane.
The circular =ear= drum is in a depression back of the angle of the
mouth. What other animal studied has an external ear drum?
The tortoise has a longer, more flexible =neck= than any other reptile.
Why does it have the greatest need for such a neck? Is the skin over
the neck tight or loose? Why?
Do the =legs= have the three joints or parts found on the limbs of most
vertebrates? How is the skin of the legs covered? Do the toes have
_claws_? Compare the front and hind feet. Does the tortoise slide its
body or lift it when walking on hard ground? Lay the animal on its back
on a chair or table at one side of the room in view of the class. Watch
its attempts to right itself. Are the motions suited to accomplish the
object? Does the tortoise succeed?
What are the prevailing =colors= of turtles? How does their coloration
correspond to their surroundings?
What parts of the tortoise extend at times beyond the shell? Are any of
these parts visible when the _shell is closed_? What movements of the
shell take place as it is closed? Is the carapace rigid throughout? Is
the plastron?
=The Skeleton= (Fig. 267).--The _carapace_ is covered with thin
_epidermal plates_ which belong to the skin. The bony nature of the
carapace is seen when the plates are removed, or if its inner surface
is viewed (Fig. 267). It is seen to consist largely of wide _ribs_ (how
many?) much flattened and grown together at their edges. The ribs are
seen to be rigidly attached to the vertebræ. The rear projections of
the vertebræ are flattened into a series of bony plates which take the
place of the sharp ridge found along the backs of most vertebrates.
Show that the shell of a turtle is not homologous with the shells of
mollusks. Does the turtle have shoulder blades and collar bones? Hip
bones? Thigh bones? Shin bone (fibia) and splint bone (fibula)? (Fig.
267.)
[Illustration: FIG. 267.--SKELETON OF EUROPEAN TORTOISE.
_C_, rib plates; _M_, marginal plates; _B_, plastron; _H_, humerus
bone; _R_, radius; _U_, ulna; _Fe_, femur.]
[Illustration: FIG. 268.--THREE-CHAMBERED HEART OF A REPTILE (tortoise).
_a_, veins; _b_, _f_, right and left auricles; _cg_, ventricle; _d_,
arteries to lungs; e, veins from lungs; _i_, _n_, two branches of
aorta. Compare with Fig. 269 and colored Fig. 2.]
Do the plates formed by the ribs extend to the edge of the carapace?
See Fig. 267. About how many bony plates form the carapace? The
plastron? Do the horny plates outside correspond to the bony plates of
the shell? How many axial plates? How many costal (rib) plates? How
many border plates? Which plates are largest? Smallest? Do the horny
plates overlap like shingles, or meet edge to edge? Is there any mark
where they meet on the bony shell? Basing it upon foregoing facts,
give a connected and complete description of the structure of the
carapace. Compare the skeleton of the turtle with that of the snake,
and correlate the differences in structure with differences in habits.
[Illustration: FIG. 269.--PLAN OF REPTILIAN CIRCULATION. See arrows.]
=Draw= the tortoise seen from the side or above, with its shell closed,
showing the arrangement of the plates.
Place soft or tender vegetable =food=, lettuce, mushroom, roots,
berries, and water, also meat, in reach of the turtle. What does it
prefer? How does it eat? It has no lips; how does it drink?
Study the =movements= of its eyeballs and eyelids, and the respiratory
and other movements already mentioned. State a reason for thinking
that no species of land animals exists that lacks the simple power of
righting itself when turned on its back.
[Illustration: FIG. 270.--REPTILIAN VISCERA (lizard).
_lr_, windpipe; _h_, heart; _lu_, lungs; _le_, liver; _ma_, stomach;
_dd_, _md_, intestines; _hb_, bladder.]
=Tortoise, Turtle, Terrapin.=--The turtles belong to the order of
reptiles called _chelonians_. No one can have any difficulty in knowing
a member of this order. The subdivision of the order into families is
not so easy, however, and the popular attempts to classify chelonians
as turtles, tortoises, and terrapins have not been entirely successful.
Species with a vaulted shell and imperfectly webbed toes and _strictly
terrestrial_ habits are called _tortoises_. Species with flattened
shells and _strictly aquatic_ habits should be called _terrapins_
(_e.g._ mud terrapin). They have three instead of two joints in the
middle toe of each foot. The term _turtle_ may be applied to species
which are _partly terrestrial and partly aquatic_ (_e.g._ snapping
turtle (Fig. 271)). Usage, however, is by no means uniform.
[Illustration: FIG. 271.--SNAPPING TURTLE (_Chelydra serpentina_).]
Most reptiles eat animal food; green terrapins and some land tortoises
eat vegetable food. Would you judge that carnivorous chelonians catch
very active prey?
The fierce _snapping turtle_, found in ponds and streams, sometimes has
a body three feet long. Its head and tail are very large and cannot be
withdrawn into the shell. It is carnivorous and has great strength of
jaw. It has been known to snap a large stick in two. The _box tortoise_
is yellowish brown with blotches of yellow, and like its close kinsman,
the pond turtle of Europe (Fig. 266), withdraws itself and closes its
shell completely. Both lids of the plastron are movable, a peculiarity
belonging to these two species. The _giant tortoise_ of the Galapagos
Islands, according to Lyddeker, can trot cheerfully along with three
full-grown men on its back. “Tortoise shell” used for combs and other
articles is obtained from the overlapping scales of the _hawkbill
turtle_, common in the West Indies. The _diamond-back terrapin_, found
along the Atlantic Coast from Massachusetts to Texas, is prized for
making soup.
[Illustration: FIG. 272.--A RATTLESNAKE.]
[Illustration: FIG. 273 _a_.--HEAD OF VIPER, showing typical triangular
shape of head of venomous snake.]
[Illustration: FIG. 273 _b_.--SIDE VIEW, showing poison fangs; also
tongue (forked, harmless).]
[Illustration: FIG. 274.--VIPER’S HEAD, showing poison sac at base of
fangs.]
[Illustration: FIG. 275.--SKULL, showing teeth, fangs, and quadrate
bone to which lower jaw is joined. See Fig. 284].
=Poisonous snakes of United States= named in order of virulence: 1.
Coral snakes, _Elaps_, about seventeen red bands bordered with yellow
and black (colored figure 6) (fatal). 2. Rattlesnakes (seldom fatal).
3. Copperhead (may kill a small animal size of dog). 4. Water moccasin
(never fatal). 5. Ground rattler.--_Effects_: Pulse fast, breathing
slow, blood tubes dilated, blood becomes stored in abdominal blood
tubes, stupefaction and death from blood being withdrawn from brain.
Always two punctures, the closer together the smaller the snake.
_Remedies_: Ligature between wound and heart, lance wound and suck;
inject into wound three drops of 1 per cent solution of chromic acid
or potassium permanganate. Give strychnine, hypodermically, until
strychnine symptoms (twitchings) appear. If symptoms of collapse recur,
repeat dose. Digitalin or caffein acts like strychnine; alcohol has
opposite effect.
[Illustration: FIG. 276.--“GLASS SNAKE,” a lizard without legs.]
[Illustration: FIG. 277.--SKULL OF ELAPS. See colored Fig. 5.]
[Illustration: FIG. 278.--SKULL OF LAMPROPELTIS.]
=Protective Coloration and Mimicry.=--When an animal imitates the color
or form of its _inanimate surroundings_ it is said to be _protectively
colored_ or formed. Give an instance of _protective coloration_or
_form_ among lizards; butterflies; grasshoppers; amphibians;
echinoderms. When an animal imitates the color or form of _another
animal_ it is said to _mimic_ the animal. Mimicry usually enables an
animal to deceive enemies into mistaking it for an animal which for
some reason they avoid. The milkweed butterfly has a taste that is
repulsive to birds. The viceroy butterfly is palatable to birds, but
it is left untouched because of its close resemblance to the repulsive
milkweed butterfly. The harlequin snake (_Elaps_) of the Gulf states
is the only deadly snake of North America (Figs. 277, 278). It is very
strikingly colored with rings of scarlet, yellow, and black. This is an
example of warning_ coloration_. The coral snake (_Lampropeltis_) has
bands of scarlet, yellow, and black (colored Fig. 6) of the same tints,
and it is hardly distinguishable from the harlequin. The coral snake
is said to _mimic_ the harlequin snake. It also imitates the quiet
inoffensive habits of the harlequin snake, which fortunately does not
strike except under the greatest provocation. The rattles of the less
poisonous and seldom fatal rattlesnake (Fig. 272) may be classed as an
example of _warning sound_ which most animals are quick to heed and
thus avoid encounters which might be destructive to either the snake or
its enemy.
[Illustration: FIG. 1
FIG. 2
FIG 3.
COLORED FIGURES 1, 2, 3.--CIRCULATION IN FISH, REPTILE, MAMMAL.
In which is blood from heart all impure? Mixed? Both pure and impure?]
[Illustration: FIG. 4.--ANATOMY OF CARP. For description see Fig. 220,
page 117.]
[Illustration: THE HARMLESS CORAL SNAKE MIMICS THE DEADLY HARLEQUIN
SNAKE.
FIG. 5.--HARLEQUIN SNAKE (_Elaps_).
FIG. 6.--CORAL SNAKE (_Lampropeltis_).]
[Illustration: FIG. 279.--GILA MONSTER (_Heloderma suspectum_), of
Arizona. If poisonous, it is the only instance among lizards. It is
heavy-built, orange and black mottled, and about 16 inches long.
Compare it with the green lizard (Fig. 280).]
[Illustration: FIG. 280.--CHAMELEON (_Anolis_), or green lizard of
southern U.S. Far excels European chameleon (Fig. 281) and all known
animals in power of changing color (green, gray, yellow, bronze, and
black).]
=Survival of the Fittest=.--The two facts of most far-reaching
importance in the history of animals and plants are: (1)
_Heredity_; animals inherit the characteristics of their parents.
(2) _Variation_; animals are not exactly like their parents. The
first fact gives stability, the second makes progress or evolution
possible. The climate of the world is slowly changing, and animals
must change to adapt themselves to it. A more sudden change of
environment (surroundings) of animals occurs because of migration or
isolation; these in turn are caused by the crowding of other animals
or by the formation or disappearance of geographical barriers, such
as deserts, water, mountain chains.
[Illustration: FIG. 281.--CHAMELEON OF SOUTHERN EUROPE.]
The young vary in many ways from their parents. Some have a more
protective color or form, sharper claws, swifter movements, etc.
The individuals possessing such beneficial variations live longer
and leave more offspring, and because of heredity transmit the
desirable qualities to some of their young. Variations which are
disadvantageous for getting food, defense, etc., cause shorter life
and fewer offspring. Thus the _fittest survive_, the unfit perish; an
automatic _natural selection_ occurs.
Darwin taught that variations are infinitesimal and gradual. Recent
experiments and observations seem to show that many variations are
by sudden jumps, somewhat resembling so-called “freaks of nature.”
As to whether these “sports,” or individuals with new peculiarities,
survive, depends upon their fitness for their environment. “Survival
of the fittest” results from this natural selection, but the
selection occurs between animals of marked, not infinitesimal,
differences, as Darwin taught. Darwin’s theory is probably true for
species in the usual state of nature; the new theory (of De Vries) is
probably true for animals and plants under domestication and during
rapid geographical changes.
[Illustration: FIG. 282.--EMBRYO OF A TURTLE, showing four gill slits.
(Challenger Report.)]
=Table for Review= (for notebooks or blackboards).
========================+========+========+========+========+========
| FISH | TADPOLE| FROG | TURTLE | LIZARD
------------------------+--------+--------+--------+--------+--------
| | | | |
Limbs, kind and number | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Are claws present? How | | | | |
many? | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Covering of body | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Teeth, kind of, if | | | | |
present | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Which bones found in man| | | | |
are lacking? | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Chambers of heart | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Respiration | | | | |
| | | | |
------------------------+--------+--------+--------+--------+--------
| | | | |
Movements | | | | |
| | | | |
========================+========+========+========+========+========
[Illustration: FIG. 283.--BIG-HEADED TURTLE (_Platysternum
megalocephalum_). × ¹⁄₂. China. This and Fig. 282 suggest descent of
turtles from a lizardlike form. Figure 282 shows earlier ancestors to
have been gill breathers.]
CHAPTER XIII
BIRDS
[Illustration]
SUGGESTIONS.--The domestic pigeon, the =fowl=, and the English
sparrow are most commonly within the reach of students. The last
bird has become a pest and is almost the only bird whose destruction
is desirable. The female is somewhat uniformly mottled with gray
and brown in fine markings. The male has a black throat with the
other markings of black, brown, and white, in stronger contrast
than the marking of the female. As the different species of birds
are essentially alike in structural features, the directions and
questions may be used with any bird at hand. When studying feathers,
one or more should be provided for each pupil in the class. The feet
and bills of birds should be kept for study.
Does the =body of the bird=, like the toad and turtle, have a head,
trunk, tail, and two pairs of limbs? Do the fore and hind limbs differ
from each other more or less than the limbs of other backboned animals?
Does any other vertebrate use them for purposes as widely different?
=Eye.=--Does the _eyeball_ have parts corresponding to the eyeball of
a fish or frog; viz., cornea, iris, pupil? Which is more movable, the
upper or lower _eyelid_? Are there any lashes? The bird (like what
other animal?) has a third eyelid, or nictitating membrane. Compare its
thickness with that of the other lids. Is it drawn over the eyeball
from the inner or outer corner of the eye? Can you see in the human eye
any wrinkle or growth which might be regarded as remains, or vestige,
of such a membrane?
How many =nostrils=? In which mandible are they located? Are they
nearer the tip or the base of the mandible? (Fig. 284.) What is their
shape? Do the nasal passages go directly down through the mandible or
do they go backward? Is the inner nasal opening into the mouth or into
the throat?
The beak or =bill= consists of the upper and lower mandibles. The
outside of the beak seems to be of what kind of material? Examine the
decapitated head of a fowl or of a dissected bird, and find if there is
a covering on the bill which can be cut or scraped off. Is the mass of
the bill of bony or horny material? With what part of the human head
are the mandibles homologous? (Fig. 284.)
[Illustration: FIG. 284.--SKULL OF DOMESTIC FOWL.
_q_, quadrate (“four-sided”) bone by which lower jaw is attached to
skull (wanting in beasts, present in reptiles; see Fig. 277).]
=Ears.=--Do birds have external ears? Is there an _external opening_
leading to the ear? In searching for it, blow or push forward the
feathers. If found, notice its location, size, shape, and what
surrounds the opening. There is an owl spoken of as the long-eared owl.
Are its ears long?
The =leg= has three divisions: the uppermost is the _thigh_ (called
the “second joint” in a fowl); the middle division is the _shank_
(or “drumstick”); and the lowest, which is the slender bone covered
with scales, is formed by the union of the _ankle_ and _instep_. (The
bones of the three divisions are named the femur, tibiotarsus, and
tarsometatarsus). The _foot_ consists entirely of toes, the bones of
which are called phalanges. Is there a bone in each claw? (See Fig.
285.) Supply the numerals in this sentence: The pigeon has ____ toes,
the hind toe having ____ joints; of the three front toes, the inner has
____ joints (count the claw as one joint), the middle has ____ joints,
and the outer toe has ____ joints (Fig. 285). Is the thigh of a bird
bare or feathered? The shin? The ankle? Where is the ankle joint of
a bird? Do you see the remains of another bone (the splint bone, or
fibula) on the shin bone of the shank? (Fig. 285 or 286.) Why would
several joints in the ankle be a disadvantage to a bird?
[Illustration: FIG. 285.--LEG BONES OF BIRD.]
[Illustration: FIG. 286.--SKELETON OF BIRD.
_Rh_, vertebræ; _Cl_, clavicle; _Co_, coracoid; _Sc_, scapula; _St_,
sternum; _H_, humerus; _R_, radius; _U_, ulna; _P_, thumb; _Fe_, femur;
_T_, tibia. See Fig. 394.
=Questions:= Which is the stiffest portion of the vertebral column? How
are the ribs braced against each other? Which is longer, thigh bone or
shin? Compare shoulder blade with man’s (Fig. 399). Which is the extra
shoulder bone? Compare tail vertebræ with those of extinct bird, Fig.
290.]
The _thigh_ hardly projects beyond the skin of the trunk, as may be
noticed in a plucked fowl. The thigh extends forward from the hip joint
(Figs. 286, 299) in order to bring the point of support forward under
the center of weight. Why are long front toes more necessary than long
hind toes? As the bird must often bring its head to the ground, the hip
joints are near the dorsal surface and the body swings between the two
points of support somewhat like a silver ice pitcher on its two pivots.
Hence stooping, which makes a man so unsteady, does not cause a bird to
lose steadiness.
The =wing= has three divisions which correspond to the upper arm,
forearm, and hand of man (Fig. 286). When the wing is folded, the three
divisions lie close alongside each other. Fold your arm in the same
manner. The similarity of the bones of the first and second divisions
to the bones of our upper _arm_ and _forearm_ is very obvious (Fig.
286). Explain. The _hand_ of a bird is furnished with only three digits
(Fig. 287). The three palm bones (metacarpals) are firmly united (Fig.
287). This gives firmness to the stroke in flying.
[Illustration: FIG. 287.--HAND AND WRIST OF FOWL (after Parker).
_DG. 1-3_, digits; _MC. 1-3_, metacarpals; _CC. 3_, wrist.]
[Illustration: FIG. 288.--HAND, WRIST (_c_), FOREARM, AND ELBOW OF
YOUNG CHICK (after Parker).]
That the bird is _descended from animals_ which had the fingers and
palm bones less firmly united is shown by comparing the hands of
a _chick_ and of an _adult_ fowl (Figs. 287, 288). The wrist also
solidifies with age, the five carpals of the chick being reduced to two
in the fowl (Figs. 287, 288). The thumb or first digit has a separate
covering of skin from the other digits, as may be seen in a plucked
bird. The degenerate hand of the fowl is of course useless as a hand
(what serves in its place?) but is well fitted for firm support of
the feathers in flying. The two bones of the forearm are also firmly
joined. There are eighteen movable joints in our arm and hand; the bird
has only the three joints which enable it to fold its wing. The wrist
joint is the joint in the forward angle of the wing.
[Illustration: FIG. 289.--BREASTBONE AND SHOULDER BONES OF CASSOWARY.]
[Illustration: FIG. 290.--A FOSSIL BIRD (_archæopteryx_) found in the
rocks of a former geological epoch.
=Question:= Find two resemblances to reptiles in this extinct bird
absent from skeletons of extant birds.]
Since the fore limbs are taken up with locomotion, the =grasping
function= has been assumed by the _jaws_. How does their shape adapt
them to this use? For the same reason the _neck_ of a bird surpasses
the necks of all other animals in what respect? Is the trunk of a bird
flexible or inflexible? There is thus a _correlation_ between structure
of neck and trunk. Explain. The same correlation is found in which of
the reptiles? (Why does rigidity of trunk require flexibility of neck?)
Why does the length of neck in birds correlate with the length of legs?
Examples? (See Figs. 314, 315, 332.) Exceptions? (Fig. 324.) Why does a
swan or a goose have a long neck, though its legs are short?
To make a firm support for the wings the vertebræ of the back are
immovably joined, also there are three bones in each shoulder, the
collar bone, the shoulder blade, and the coracoid bone (Fig. 286). The
collar bones are united (why?) and form the “wishbone” or “pulling
bone.” To furnish surface for the attachment of the large flying
muscles there is a prominent ridge or keel on the breastbone (Fig.
286). It is lacking in most birds which do not fly (Fig. 289).
[Illustration: FIG. 291.--QUILL FEATHER.
_D_, downy portion.]
The =feathers= are perhaps the most characteristic feature of birds.
The large feathers of the wings and tail are called _quill feathers_. A
quill feather (Fig. 291) is seen to consist of two parts, the _shaft_,
or supporting axis, and the broad _vane_ or web. What part of the shaft
is round? Hollow? Solid? Is the shaft straight? Are the sides of the
vane usually equal in width? Can you tell by looking at a quill whether
it belongs to the wing or tail, and which wing or which side of the
tail it comes from? Do the quills overlap with the wide side of the
vane above or beneath the next feather? Can you cause two parts of the
vane to unite again by pressing together the two sides of a split in
the vane? Does the web separate at the same place when pulled until it
splits again?
[Illustration: FIG. 292.--I, CONTOUR FEATHER. II, III, PARTS OF QUILL
FEATHER, enlarged.]
The hollow part of the shaft of a quill feather is called the _quill_.
The part of the shaft bearing the vane is called the _rachis_ (rā-kis).
The vane consists of slender _barbs_ which are branches of the shaft
(II, Fig. 292). As the name indicates (see dictionary), a barb
resembles a hair. The barbs in turn bear secondary branches called
_barbules_, and these again have shorter branches called _barbicels_
(III, Fig. 292). These are sometimes bent in the form of hooklets (Fig.
292, III), and the hooklets of neighboring barbules interlock, giving
firmness to the vane. When two barbules are split apart, and then
reunited by stroking the vane between the thumb and finger, the union
may be so strong that a pull upon the vane will cause it to split in a
new place next time.
[Illustration: FIG. 293.--A DOWN FEATHER, enlarged.]
There are =four kinds= of feathers, (1) the _quill_ feathers, just
studied; (2) the _contour_ feathers (I, Fig. 292), which form the
general surface of the body and give it its outlines; (3) the _downy_
feathers (Fig. 293), abundant on nestlings and found among the contour
feathers of the adult but not showing on the surface; (4) the _pin_
feathers, which are hair-like, and which are removed from a plucked
bird by singeing. The contour feathers are similar in structure to the
quill feathers. They protect the body from blows, overlap so as to shed
the rain, and, with the aid of the downy feathers retain the heat, thus
accounting for the high temperature of the bird. The downy feathers are
soft and fluffy, as they possess few or no barbicels; sometimes they
lack the rachis (Fig. 293). The pin feathers are delicate horny shafts,
greatly resembling hairs, but they may have a tuft of barbs at the ends.
A =feather grows= from a small projection (or papilla) found at the
bottom of a depression of the skin. The quill is formed by being molded
around the papilla. Do you see any opening at the tip of the quill for
blood vessels to enter and nourish the feather? What is in the quill?
(Fig. 291.) The rachis? A young contour or quill feather is inclosed in
a delicate sheath which is cast off when the feather has been formed.
Have you seen the sheath incasing a young feather in a molting bird?
There are considerable =areas= or tracts on a bird’s skin =without
contour feathers=. Such bare tracts are found along the ridge of the
breast and on the sides of the neck. However, the contour feathers lie
so as to overlap and cover the whole body perfectly (Fig. 294).
[Illustration: FIG. 294.--DORSAL AND VENTRAL VIEW OF PLUCKED BIRD,
showing regions where feathers grow.]
The shedding of the feathers is called =molting=. Feathers, like the
leaves of trees, are delicate structures and lose perfect condition
with age. Hence the annual renewal of the feathers is an advantage.
Most birds shed twice a year, and with many the summer plumage is
brighter colored than the winter plumage. When a feather is shed on
one side, the corresponding feather on the other side is always shed
with it. (What need for this?) A large _oil gland_ is easily found on
the dorsal side of the tail. How does the bird apply the oil to the
feathers?
[Illustration: FIG. 295.--WING OF BIRD.
_1_, false quills (on thumb); _2_, primaries; _3_, secondaries;
tertiaries (dark) are one above another at right; _a_, _b_, coverts.]
[Illustration: FIG. 296.
_A_, point dividing primaries from secondaries; _B_, coverts.]
[Illustration: FIG. 297.--CEDAR WAXWING, with regions of body marked.
_S_, forehead; _Sc_, crown (with crest); _Hh_, nape; _K_, throat; _Br_,
breast; _Ba_, lower parts; _R_, back; _Rt_, tail; _B_, tail coverts;
_P_, shoulder feathers (scapulars); _T_, wing coverts; _HS_, primaries;
_AS_, secondaries; _Al_, thumb feathers.]
In describing and classifying birds, it is necessary to know the names
of the various external =regions= of the body and plumage. These may
be learned by studying Figs. 295, 296, 297, 298. The quills on the
hand are called primaries, those on the forearm are the secondaries,
those on the upper arm are the tertiaries. Those on the tail are called
the _tail quills_. The feathers at the base of the quills are called
the _coverts_. The thumb bears one or more quills called the spurious
quills. Is the wing concave on the lower or upper side? What advantage
is this when the bird is at rest? When it is flying?
[Illustration: FIG. 298.--PLAN OF BIRD. _s_, center of gravity.]
[Illustration: FIG. 299.--POSITION OF LIMBS OF PIGEON.]
=Control of Flight.=--Did you ever see a bird sitting on a swinging
limb? What was its chief means of balancing itself? When flying, what
does a bird do to direct its course upward? Downward? Is the body level
when it turns to either side? Birds with long, pointed wings excel in
what respect? Examples? Birds with great wing surface excel in what
kind of flight? Examples. Name a common bird with short wings which has
a labored, whirring flight. Is its tail large or small? Does it avoid
obstacles and direct its flight well? Why or why not? When a boat is to
be turned to the right, must the rudder be pulled to the right or the
left? (The rudder drags in the water and thus pulls the boat around.)
When the bird wishes to go upward, must its tail be turned up or down?
How when it wishes to go down? When a buzzard soars for an hour without
flapping its wings, does it move at a uniform rate? For what does it
use the momentum gained when going with the wind?
[Illustration: FIG. 300.
_a_, clambering foot of chimney sweep; _b_, climbing foot of
woodpecker; _c_, perching foot of thrush; _d_, seizing foot of hawk;
_e_, scratching foot of pheasant; _f_, stalking foot of kingfisher;
_g_, running foot of ostrich; _h_, wading foot of heron; _i_, paddling
foot of gull; _k_, swimming foot of duck; _l_, steering foot of
cormorant; _m_, diving foot of grebe; _n_, skimming foot of coot.
=Question:= Does any bird use its foot as a hand? (Fig. 320.)]
=Flying.=--When studying the quill feathers of the wing, you saw that
the wider side of the vane is beneath the feather next behind it.
During the downward stroke of the wing this side of the vane is pressed
by the air against the feather above it and the air cannot pass through
the wing. As the wing is raised the vanes separate and the air passes
through. The convex upper surface of the wing also prevents the wing
from catching air as it is raised. Spread a wing and blow strongly
against its lower surface; its upper surface. What effects are noticed?
Study the =scales= on the leg of a bird (Fig. 300). Why is the leg
scaly rather than feathered from the ankle downward? Which scales are
largest? (Fig. 300.) How do the scales on the front and back differ?
What can you say of the scales at the bottom of the foot; at the joints
of the toes? Explain. How does the covering of the nails and bill
compare in color, texture, hardness and firmness of attachment with the
scales of the leg?
[Illustration: FIG. 301.--AN ALTRICAL BIRD, _i.e._ poorly developed at
hatching. Young pigeon, naked, beak too weak for eating.]
[Illustration: FIG. 302.--A PRECOCIAL BIRD (well developed at
hatching). Feathered, able to run and to pick up food. Precocity is a
sign of instinctive life and low intelligence. A baby is not precocious.
=Question:= Is pigeon or fowl exposed to more dangers in infancy?]
=Draw= an outline of the bird seen from the side. Make drawings of the
head and feet more detailed and on a larger scale.
Why does a goose have more feathers suitable for making pillows than a
fowl? In what country did the domestic fowl originate? (Encyclopedia.)
Why does a cock crow for day? (Consider animal life in jungle.)
=Activities of a Bird.=--Observe a bird _eating_. Does it seem to chew
or break its food before swallowing? Does it have to lift its head in
order to swallow food? To swallow drink? Why is there a difference?
After feeding the bird, can you feel the food in the crop, or
enlargement of the gullet at the base of the neck? (Fig. 304.)
Feel and look for any movements in _breathing_. Can you find how often
it breathes per minute? Place hand under the bird’s wing. What do you
think of its _temperature_; or better, what temperature is shown by
a thermometer held under its wing? Do you see any connection between
the breathing rate and the temperature? Test (as with the crayfish)
whether a bird can _see_ behind its head? Notice the movements of the
nictitating membrane. Does it appear to be transparent?
Watch a bird _fly_ around a closed room and review the questions on
Control of Flight.
_Bend_ a bird’s leg and see if it has any effect upon its toes. Notice
a bird (especially a large fowl) walk to see if it bends its toes as
the foot is lifted. Pull the rear tendon in a foot cut from a fowl for
the kitchen. Does the bird have to use muscular exertion to _grasp_ a
stick upon which it sits? Why, or why not? When is this bending of the
toes by bending the legs of special advantage to a hawk? To a duck? A
wading bird? Why is a fowl safe from a hawk if it stands close to a
tree?
[Illustration: FIG. 303.--HEAD OF WOODPECKER.
_c_, tongue; _a_, _b_, _d_, hyoid bone; _e_, _q_, windpipe; _f_,
salivary gland.]
Do you see any signs of teeth in the bird’s jaws? Why are duck’s
“teeth” (so called by children) not teeth? Can the tongue of a bird be
pulled forward? (Fig. 303.) What is its shape? If there is opportunity,
dissect and study the slender, bony (hyoid) apparatus to which the base
of the tongue is attached (Fig. 303), the opening of the windpipe, or
trachea, the slit-like opening of windpipe which is so narrow as to
prevent food falling into the windpipe.
[Illustration: FIG. 304.--ANATOMY OF DOVE × ¹⁄₂.
_bk_, keel of breastbone; _G_, _g_, brain; _lr_, windpipe; _lu_, lung;
_h_, heart; _sr_, gullet; _k_, crop; _dr_, glandular stomach; _mm_,
gizzard; _d_, intestine; _n_, kidney; _hl_, ureter; _eil_, openings of
ureter and egg duct into cloaca, _kl_.]
[Illustration: FIG. 305.--FOOD TUBE OF BIRD.
_P_, pancreas; _C_, cæca.
=Question:= Identify each part by means of Fig. 304.]
=The Internal Organs, or Viscera= (Figs. 304 and 305).--The viscera
(vis′se-ra), as in most vertebrates, _include_ the food tube and its
glands; the lungs, the heart, and larger blood vessels; the kidneys
and bladder and the reproductive organs. The lower part, or gullet,
is enlarged into a _crop_. It is largest in grain-eating birds. It
is found in the V-shaped depression at the angle of the wishbone,
just before the food tube enters the thorax. The food is stored and
softened in the crop. From the crop the food passes at intervals into
the glandular stomach. Close to this is the muscular stomach, or
gizzard. Are the places of entrance and exit on opposite sides of the
gizzard, or near together? (Fig. 304.) Is the lining of the gizzard
rough or smooth? Why? Is the gizzard tough or weak? Why are small
stones in the gizzard? Why do not hawks and other birds of prey need a
muscular gizzard? The liver and pancreas empty their secretions into
the intestines by several ducts a little way beyond the gizzard. Beyond
the mouths of two cæca (Fig. 305) the many-coiled intestine empties
into the straight rectum, which terminates in a widened part called
the cloaca. Not only the intestine, but the two ureters of the urinary
system and the two genital ducts of the reproductive system all empty
into the cloaca (Figs. 304, 305).
[Illustration: FIG. 306.--POSITION OF LUNGS AND AIR SACS (Pigeon).
_Tr_, windpipe; _P_, lungs; _Lm_, sac under clavicle with prolongation
(_Lh_) into humerus; _La_, sacs in abdomen.]
The =lungs= have their rear surfaces attached to the spinal column and
ribs (_lu_, Fig. 304). They are connected with thin-walled, transparent
_air sacs_ which aid in purifying the blood. When inflated with warm
air, they probably make the body of the bird more buoyant. For the
names, location, and shape of several pairs of air sacs, see Fig. 306.
The connection of the air sacs with hollows in the humerus bones is
also shown in the figure. Many of the _bones are hollow_; this adds to
the buoyancy of the bird. The pulmonary artery, as in man, takes dark
blood to the lungs to exchange its carbon dioxide for oxygen. Of two
animals of the same weight, which expends more energy, the one that
flies, or the one that runs the same distance? Does a bird require more
oxygen or less, in proportion to its weight, than an animal that lives
on the ground? Are the vocal cords of a bird higher or lower in the
windpipe than those of a man? (Fig. 307.)
The heart of a bird, like a man’s heart, has four chambers; hence it
keeps the purified blood separate from the impure blood. Since pure
blood reaches the organs of a bird, oxidation is more perfect than in
the body of any animals yet studied. Birds have higher temperature than
any other class of animals whatsoever. Tell how the jaws, tail, and
wings of the fossil bird Archæopteryx differed from living birds (Fig.
290).
[Illustration: FIG. 307.--POSITION OF VOCAL CORDS (_str_) OF MAMMAL AND
BIRD.
=Question:= Does a fowl ever croak after its head and part of its neck
are cut off? Explain.]
SUGGESTIONS.--In the field work, besides seeking the answers to
definite questions, pupils may be required to hand in a record of the
places and times of seeing a certain number of birds (20 to 40), with
the actions and features which made each distinguishable. Also, and
more important, each pupil should hand in a record of a careful and
thorough outdoor study of one common species (see below) as regards
habits, nesting, relation to environment, etc.
=Field Study of a Common Species.=--(_For written report._) Name of
species. _Haunts._ Method of locomotion when not flying. _Flying_
(rate, sailing, accompanying sound if any, soaring).
What is the _food_? How obtained? _Association_ with birds of its own
species. _Relation_ to birds of other species.
Where does it build its _nest_? Why is such a situation selected? Of
what is the nest built? How is the material carried, and how built
into the nest? Does the bird’s body fill the nest?
Describe the _eggs_. Does the male bird ever sit or otherwise assist
female before hatching? Does it assist after hatching?
How long is taken to lay a sitting of eggs? How long before the birds
are hatched? _When hatched_ are they helpless? Blind? Feathered? (Figs.
301, 302.) Do the nestlings require much food? How many times is food
brought in an hour? How distributed? Even if the old birds sometimes
eat fruit do they take fruit to the young? What do they feed to the
young? How long before they leave the nest? Do the parents try to teach
them to fly? Do the parents care for them after the nest is left? What
songs or calls has the bird?
[Illustration: FIG. 308.--EUROPEAN TOMTIT’S NEST. What are the
advantages of its shape?]
[Illustration: FIG. 309.--TAILOR BIRD’S NEST (India).
Instinct for nest building highly perfected.]
=General Field Study.=--(_For written report._) Name the best and
poorest flyers you know; birds that fly most of the time; birds that
seldom fly. Observe birds that pair; live in flocks. Does their
sociability vary with the season? Do you ever see birds quarreling?
Fighting? What birds do you observe whipping or driving birds larger
than themselves? Which parent do young birds most resemble? Name the
purposes for which birds sing. Which senses are very acute? Why?
Dull? Why? Can you test your statements by experiment? A partridge
usually sits with 18 to 24 eggs in nest. About how long after laying
first egg before sitting begins? Do several partridge hens lay in the
same nest?
[Illustration: FIG. 310.--HOUSE WREN.]
_Haunts._--Name some birds that are found most often in the following
localities: about our homes, in gardens and orchards, fields and
meadows, in bushes, in the woods, in secluded woods, around streams
of water, in thickets, in pine woods.
_Size._--Name birds as large as a robin or larger, nearly as large,
half as large, much smaller.
_Colors._--Which sex is more brilliant? What advantage are bright
colors to one sex? What advantage are dull colors to the other sex?
Which have yellow breasts, red patch on heads, red or chestnut
breasts, blue backs, black all over?
_Habits._--Name the birds that walk, jump, swim, live in flocks, sing
while flying, fly in undulations, in circles, have labored flight.
Such books as Wright’s “Birdcraft” (Macmillan, N. Y.), Clark’s “Birds
of Lakeside and Prairie” (Mumford, Chicago), and Pearson’s “Stories
of Bird Life” (B. F. Johnson, Richmond), will be of great help. The
last book is delightfully written, and is one of the few treating of
bird life in the South.
=Economic Importance of Birds.=--Farmers find their most valuable
allies in the class _aves_, as birds are the deadliest enemies of
insects and gnawing animals. To the innumerable robbers which devastate
our fields and gardens, nature opposes the army of birds. They are
less numerous than insects and other robbers, it is true, but they
are skillful and zealous in pursuit, keen of eye, quick, active, and
remarkably voracious. The purely insectivorous birds are the most
useful, but the omnivorous and graminivorous birds do not disdain
insects. _The perchers and the woodpeckers should be protected most
carefully._ The night birds of prey (and those of the day to a less
degree) are very destructive to field mice, rabbits, and other gnawing
animals. Some ignorant farmers complain continually about the harm done
by birds. To destroy them is as unwise as it would be to destroy the
skin which protects the human body because it has a spot upon it! It
cannot be repeated too plainly that to hunt useful birds is a wrong and
mischievous act, and it is stupid and barbarous to destroy their nests.
[Illustration: FIG. 311.--SCREECH OWL (_Megascops asio_).
=Question:= Compare posture of body, position of eyes, and size of
eyes, with other birds.]
[Illustration: FIG. 312.--GOSHAWK, or chicken hawk.]
Injurious birds are few. Of course birds which are the enemies of other
birds are enemies of mankind, but examples are scarce (some owls and
hawks). Many birds of prey are classed thus by mistake. Sparrow hawks,
for instance, do not eat birds except in rare instances; they feed
chiefly upon insects. A sparrow hawk often keeps watch over a field
where grasshoppers are plentiful and destroys great numbers of them.
When a bird is killed because it is supposed to be injurious, the
crop should always be examined, and its contents will often surprise
those who are sure it is a harmful bird. The writer once found two
frogs, three grasshoppers, and five beetles that had been swallowed
by a “chicken hawk” killed by an irate farmer, but no sign of birds
having been used for food. Fowls should not be raised in open places,
but among trees and bushes, where hawks cannot swoop. Birds which live
exclusively upon fish are, of course, opposed to human interests.
Pigeons are destructive to grain; eagles feed chiefly upon other birds.
[Illustration: FIG. 313.--ROAD RUNNER, or chaparral bird (Tex. to
Cal.). What order? (Key, p. 177.)]
If the birds eat the grapes, do not kill the birds, but plant more
grapes. People with two or three fruit trees or a small garden are
the only ones that lose a noticeable amount of food. We cut down the
forests from which the birds obtain part of their food. We destroy
insect pests at great cost of spraying, etc. The commission the birds
charge for such work is very small indeed. (See pages 177-183.)
[Illustration: FIG. 314.--WOOD DUCK, male (_Aix sponsa_). Nests in
hollow trees throughout North America. Also called summer duck in
South. Why?]
The =English sparrow= is one bird of which no good word may be said.
Among birds, it holds the place held by rats among beasts. It is
crafty, quarrelsome, thieving, and a nuisance. It was imported in 1852
to eat moths. The results show how ignorant we are of animal life, and
how slow we should be to tamper with the arrangements of nature. In
Southern cities it produces five or six broods each year with four to
six young in each brood. (Notice what it feeds its young.) It fights,
competes with and drives away our native useful birds. It also eats
grain and preys upon gardens. They have multiplied more in Australia
and the United States than in Europe, because they left behind them
their native enemies and their new enemies (crows, jays, shrikes,
etc.) have not yet developed, to a sufficient extent, the habit of
preying upon them. Nature will, perhaps, after a long time, restore the
equilibrium destroyed by presumptuous man.
=Protection of Birds.=--1. Leave as many trees and bushes standing as
possible. Plant trees, encourage bushes.
2. Do not keep a cat. A mouse trap is more useful than a cat. A tax
should be imposed upon owners of cats.
3. Make a bird house and place on a pole; remove bark from pole that
cats may not climb it, or put a broad band of tin around the pole.
4. Scatter food in winter. In dry regions and in hot weather keep a
shallow tin vessel containing water on the roof of an outhouse, or
out-of-the-way place for shy birds.
5. Do not wear feathers obtained by the killing of birds. What feathers
are not so obtained?
6. Report all violators of laws for protection of birds.
7. Destroy English sparrows.
[Illustration: FIG. 315.--GREAT BLUE HERON. In flight, balancing with
legs.]
=Migration.=--Many birds, in fact most birds, migrate to warmer
climates to spend the winter. Naturalists were once content to speak
of the migration of birds as a wonderful instinct, and made no attempt
to explain it. As birds have the warmest covering of all animals,
the winter migration is not for the purpose of escaping the cold; it
is probably to escape starvation, because in cold countries food is
largely hidden by snow in winter. On the other hand, if the birds
remained in the warm countries in summer, the food found in northern
countries in summer would be unused, while they would have to compete
with the numerous tropical birds for food, and they and their eggs
would be in danger from snakes, wild cats, and other beasts of prey so
numerous in warm climates. These are the best reasons so far given for
migration.
[Illustration: FIG. 316.--EUROPEAN SWALLOWS (_Hirundo urbica_),
assembling for autumn flight to South.]
The =manner= and =methods of migration= have been studied more
carefully in Europe than in America. Migration is not a blind,
infallible instinct, but the route is learned and taught by the old
birds to the young ones; they go in flocks to keep from losing the
way (Fig. 316); the oldest and strongest birds guide the flocks (Fig.
317). The birds which lose their way are young ones of the last brood,
or mothers that turn aside to look for their strayed young. The adult
males seldom lose their way unless scattered by a storm. Birds are
sometimes caught in storms or join flocks of another species and arrive
in countries unsuited for them, and perish. For example, a sea or marsh
bird would die of hunger on arriving in a very dry country.
[Illustration: FIG. 317.--CRANES MIGRATING, with leader at point of
V-shaped line.]
The =landmarks of the route= are mountains, rivers, valleys, and coast
lines. This knowledge is handed down from one generation to another.
It includes the location of certain places on the route where food is
plentiful and the birds can rest in security. Siebohm and others have
studied the routes of migration in the Old World. The route from the
nesting places in northern Europe to Africa follows the Rhine, the Lake
of Geneva, the Rhone, whence some species follow the Italian and others
the Spanish coast line to Africa. Birds choose the lowest mountain
passes. The Old World martin travels every year from the North Cape to
the Cape of Good Hope and back again! Another route has been traced
from Egypt along the coast of Asia Minor, the Black Sea and Ural Mts.
to Siberia.
=Field Study of Migration.=--Three columns may be filled on the
blackboard in an unused corner, taking several months in spring or fall
for the work. _First_ column, birds that stay all the year. _Second_
column, birds that come from the south and are seen in the summer
only. _Third_ column, birds that come from the north and are seen in
winter only. Exact dates of arrival and departure and flight overhead
should be recorded in notebooks. Many such records will enable American
zoologists to trace the migration routes of our birds. Reports may be
sent to the chief of the Biological Survey, Washington, D.C.
[Illustration: FIG. 318.--APTERYX, of New Zealand. Size of a hen, wings
and tail rudimentary, feathers hair-like.]
=Molting.=--How do birds arrange their feathers after they have been
ruffled? Do they ever bathe in water? In dust? Dust helps to remove old
oil. At what season are birds brightest feathered? Why? Have you ever
seen evidence of the molting of birds? Describe the molting process
(page 120).
[Illustration: FIG. 319.--GOLDEN, SILVER, AND NOBLE PHEASANTS, males.
Order? (Key, p. 177.) Ornaments of males, brightest in season of
courtship, are due to sexual selection (Figs. 321-7-9, 333).]
[Illustration: FIG. 320.--COCKATOO.]
[Illustration: FIG. 321.--BIRD OF PARADISE (Asia).]
=Adaptations for Flying.=--Flight is the most difficult and
energy-consuming method of moving found among animals, and careful
adjustment is necessary. For balancing, the heaviest muscles are
placed at the lower and central portion of the body. These are the
flying muscles, and in some birds (humming birds) they make half of
the entire weight. Teeth are the densest of animal structures; teeth
and the strong chewing muscles required would make the head heavy
and balancing difficult; hence the chewing apparatus is transferred
to the heavy gizzard near the center of gravity of the body. The
bird’s neck is long and excels all other necks in flexibility, but
it is very slender (although apparently heavy), being inclosed in a
loose, feathered skin. A cone is the best shape to enable the body to
penetrate the air, and a small neck would destroy the conical form. The
internal organs are compactly arranged and rest in the cavity of the
breast bone. The bellows-like air sacs filled with warm air lighten
the bird’s weight. The bones are hollow and very thin. The large tail
quills are used by the bird only in guiding its flight up and down,
or balancing on a limb. The feet also aid a flying bird in balancing.
The wing is so constructed as to present to the air a remarkably large
surface compared with the small bony support in the wing skeleton. Are
tubes ever resorted to by human architects when lightness combined with
strength is desired? Which quills in the wing serve to lengthen it?
(Fig. 296.) To broaden it? Is flight more difficult for a bird or a
butterfly? Which of them do the flying machines more closely resemble?
Can any bird fly for a long time without flapping its wings?
[Illustration: FIG. 322.--HERRING GULL. (Order?)]
=Exercise in the Use of the Key.=--Copy this list and write the name
of the order to which each of the birds belongs. (Key, page 177.)
Cockatoo (Fig. 320)
Sacred Ibis (Fig. 328)
Screech Owl (Fig. 311)
Nightingale (Fig. 325)
Top-knot Quail (Fig. 329)
Wren (Fig. 310)
Apteryx (Fig. 318)
Lyre bird (Fig. 327)
Road Runner (Fig. 313)
Ostrich (Fig. 332)
Penguin (Fig. 330)
Pheasant (Fig. 319)
Wood Duck (Fig. 314)
Jacana (Fig. 324)
Sea Gull (Fig. 322)
Heron (Fig. 315)
Hawk (Fig. 312)
KEY, OR TABLE, FOR CLASSIFYING BIRDS (_Class Aves_) INTO ORDERS
ORDERS
A₁ =Wings not suited for flight=, 2 or 3 toes RUNNERS
A₂ =Wings suited for flight= (except the penguin)
B₁ _Toes united by a web for swimming, legs short_
C₁ Feet placed far back; wings short, tip not DIVERS
reaching to base of tail (Fig. 300)
C₂ Bill flattened, horny plates under margin of BILL-STRAINERS
upper bill (Fig. 323)
C₃ Wings long and pointed, bill slender SEA-FLIERS
C₄ All four toes webbed, bare sac under throat GORGERS
B₂ _Toes not united by web for swimming_
C₁ Three front toes, neck and legs long, tibia WADERS
(shin, or “drumstick”) partly bare
C₂ Three front toes, neck and legs not long
D₁ Claws short and blunt (_e_, Fig. 300)
E₁ Feet and beak stout, young feathered, SCRATCHERS
base of hind toe elevated
E₂ Feet and beak weak, young naked MESSENGERS
D₂ Claws long, curved and sharp, bill hooked ROBBERS
and sharp
D₃ Claws long, slightly curved, bill nearly PERCHERS
straight
C₃ Two front and two hind toes (Fig. 300)
D₁ Bill straight, feet used for climbing FOOT-CLIMBERS
D₂ Bill hooked, both bill and feet used for BILL-CLIMBERS
climbing
=The Food of Birds.=--Extracts from Bulletin No. 54 (United States
Dept. of Agriculture), by F. E. L. Beal.
The practical value of birds in controlling insect pests should be
more generally recognized. It may be an easy matter to exterminate
the birds in an orchard or grain field, but it is an extremely
difficult one to control the insect pests. It is certain, too,
that the value of our native sparrows as weed destroyers is not
appreciated. Weed seed forms an important item of the winter food of
many of these birds, and it is impossible to estimate the immense
numbers of noxious weeds which are thus annually destroyed. If crows
or blackbirds are seen in numbers about cornfields, or if woodpeckers
are noticed at work in an orchard, it is perhaps not surprising that
they are accused of doing harm. Careful investigation, however, often
shows that they are actually destroying noxious insects; and also
that even those which do harm at one season may compensate for it by
eating insect pests at another. Insects are eaten at all times by the
majority of land birds. During the breeding season most kinds subsist
largely on this food, and rear their young exclusively upon it.
[Illustration: FIG. 323.--HEAD OF DUCK.]
[Illustration: FIG. 324.--JACANA. (Mexico, Southwest Texas, and
Florida.)
=Questions:= What appears to be the use of such long toes? What
peculiarity of wing? head?]
=Partridges.=--Speaking of 13 birds which he shot, Dr. Judd says:
These 13 had taken weed seed to the extent of 63 per cent of
their food. Thirty-eight per cent was ragweed, 2 per cent tick
trefoil, partridge pea, and locust seeds, and 23 per cent seeds of
miscellaneous weeds. About 14 per cent of the quail’s food for the
year consists of animal matter (insects and their allies). Prominent
among these are the Colorado potato beetle, the striped squash
beetle, the cottonboll-weevil, grasshoppers. As a weed destroyer the
quail has few, if any, superiors. Moreover, its habits are such that
it is almost constantly on the ground, where it is brought in close
contact with both weed seeds and ground-living insects. It is a good
ranger, and, if undisturbed, will patrol every day all the fields in
its vicinity as it searches for food.
[Illustration: FIG. 325.--NIGHTINGALE, × ¹⁄₃.
FIG. 326.--SKYLARK, × ¹⁄₃.
Two celebrated European songsters.]
=Doves.=--The food of the dove consists of seeds of weeds, together
with some grain. The examination of the contents of 237 stomachs
shows that over 99 per cent of the food consists wholly of vegetable
matter.
=Cuckoos.=--An examination of the stomachs of 46 black-billed
cuckoos, taken during the summer months, showed the remains of 906
caterpillars, 44 beetles, 96 grasshoppers, 100 sawflies, 30 stink
bugs, and 15 spiders. Of the yellow-billed cuckoos, or “rain-crow,”
109 stomachs collected from May to October, inclusive, were examined.
The contents consisted of 1,865 caterpillars, 93 beetles, 242
grasshoppers, 37 sawflies, 69 bugs, 6 flies, and 86 spiders.
[Illustration: FIG. 327.--LYRE BIRD, male.]
=Woodpeckers.=--Careful observers have noticed that, excepting a
single species, these birds rarely leave any conspicuous mark on a
healthy tree, except when it is affected by wood-boring larvæ, which
are accurately located, dislodged, and devoured by the woodpecker.
Of the flickers’ or yellow-hammers’ stomachs examined, three were
completely filled with ants. Two of the birds each contained more
than 3,000 ants, while the third bird contained fully 5,000. These
ants belong to species which live in the ground. It is these insects
for which the flicker is reaching when it runs about in the grass.
The yellow-bellied woodpecker or sapsucker (_Sphyrapicus varius_) was
shown to be guilty of pecking holes in the bark of various forest
trees, and sometimes in that of apple trees, and of drinking the
sap when the pits became filled. It has been proved, however, that
besides taking the sap the bird captures large numbers of insects
which are attracted by the sweet fluid, and that these form a very
considerable portion of its diet. The woodpeckers seem the only
agents which can successfully cope with certain insect enemies of
the forests, and, to some extent, with those of fruit trees also.
For this reason, if for no other, they should be protected in every
possible way.
[Illustration: FIG. 328.--SACRED IBIS. (Order?)]
=The night hawk, or “bull bat,”= may be seen most often soaring high
in air in the afternoon or early evening. It nests upon rocks or bare
knolls and flat city roofs. Its food consists of insects taken on the
wing; and so greedy is the bird that when food is plentiful, it fills
its stomach almost to bursting. Ants (except workers) have wings and
fly as they are preparing to propagate. In destroying ants night
hawks rank next to, or even with, the woodpeckers, the acknowledged
ant-eaters among birds.
[Illustration: FIG. 329.--TOP-KNOT QUAIL, or California Partridge.
(West Texas to California.)]
=The kingbird, or martin=, is largely insectivorous. In an
examination of 62 stomachs of this bird, great care was taken to
identify every insect or fragment that had any resemblance to a
honeybee; as a result, 30 honeybees were identified, of which 29 were
males or drones and 1 was a worker.
=Blue Jay.=--In an investigation of the food of the blue jay 300
stomachs were examined, which showed that animal matter comprised 24
per cent and vegetable matter 76 per cent of the bird’s diet. The
jay’s favorite food is mast (_i.e._ acorns, chestnuts, chinquapins,
etc.), which was found in 200 of the 300 stomachs, and amounted to
more than 42 per cent of the whole food.
[Illustration: FIG. 330.--PENGUIN OF PATAGONIA. Wings used as flippers
for swimming.]
=Crow.=--That he does pull up sprouting corn, destroy chickens, and
rob the nests of small birds has been repeatedly proved. Nor are
these all of his sins. He is known to eat frogs, toads, salamanders,
and some small snakes, all harmless creatures that do some good by
eating insects. Experience has shown that they may be prevented from
pulling up young corn by tarring the seed, which not only saves the
corn but forces them to turn their attention to insects. May beetles,
“dorbugs,” or June bugs, and others of the same family constitute the
principal food during spring and early summer, and are fed to the
young in immense quantities.
=Ricebird.=--The annual loss to rice growers on account of bobolinks
has been estimated at $2,000,000.
=Meadow Lark.=--Next to grasshoppers, beetles make up the most
important item of the meadow lark’s food, amounting to nearly 21 per
cent. May is the month when the dreaded cut-worm begins its deadly
career, and then the lark does some of its best work. Most of these
caterpillars are ground feeders, and are overlooked by birds which
habitually frequent trees, but the meadow lark finds and devours them
by thousands.
[Illustration: FIG. 331.--Umbrella holding the nests of social weaver
bird of Africa; polygamous.]
=Sparrows.=--Examination of many stomachs shows that in winter the
tree sparrow feeds entirely upon seeds of weeds. Probably each bird
consumes about one fourth of an ounce a day. Farther south the tree
sparrow is replaced in winter by the white-throated sparrow, the
white-crowned sparrow, the fox sparrow, the song sparrow, the field
sparrow, and several others; so that all over the land a vast number
of these seed eaters are at work during the colder months reducing
next year’s crop of worse than useless plants.
=Robin.=--An examination of 500 stomachs shows that over 42 per
cent of its food is animal matter, principally insects, while the
remainder is made up largely of small fruits or berries. Vegetable
food forms nearly 58 per cent of the stomach contents, over 47 per
cent being wild fruits, and only a little more than 4 per cent being
possibly cultivated varieties. Cultivated fruit amounting to about
25 per cent was found in the stomachs in June and July, but only a
trifle in August. Wild fruit, on the contrary, is eaten in every
month, and constitutes during half the year a staple food.
=Questions.=--Which of these birds are common in your neighborhood?
Which of them according to the foregoing report are plainly
injurious? Clearly beneficial? Doubtful? Which are great destroyers
of weed seeds? Wood-borers? Ants? Grain? Why is the destruction of
an ant by a night hawk of greater benefit than the destruction of an
ant by a woodpecker? Name the only woodpecker that injures trees.
If a bird eats two ounces of grain and one ounce of insects, has it
probably done more good or more evil?
[Illustration: FIG. 332.--AFRICAN OSTRICH, × ¹⁄₂₀. (Order?)]
CHAPTER XIV
MAMMALS (BEASTS AND MAN)
SUGGESTIONS.--A tame rabbit, a house cat, or a pet squirrel may be
taken to the school and observed by the class. Domestic animals may
be observed at home and on the street. A study of the teeth will
give a key to the life of the animal, and the teacher should collect
a few mammalian skulls as opportunities offer. The pupils should be
required to identify them by means of the chart of skulls (p. 194).
If some enthusiastic students fond of anatomy should dissect small
mammals, the specimens should be killed with chloroform, and the
directions for dissection usual in laboratory works on this subject
may be followed. There is a brief guide on page 223. The following
outline for the study of a live mammal will apply almost as well to
the rabbit or squirrel as to the cat.
=The Cat.=--The house cat (_Felis domestica_) is probably descended
from the Nubian cat (_Felis maniculata_, Fig. 333) found in Africa. The
wild species is about half again as large as the domestic cat, grayish
brown with darker stripes; the tail has dark rings. The lynx, or wild
cat of America (_Lynx rufus_), is quite different. Compare the figures
(333, 335) and state three obvious differences. To which American
species is the house cat closer akin, the lynx (Fig. 335) or the ocelot
(Fig. 334)? The domestic cat is found among all nations of the world.
What is concluded, as to its nearest relatives, from the fact that the
Indians had no cats when America was discovered? It was considered
sacred by the ancient Egyptians, and after death its body was embalmed.
The =body of the cat= is very flexible. It may be divided into five
regions, the head, neck, trunk, tail, and limbs. Its eyes have the
same parts as the eyes of other mammals. Which part of its eye is most
peculiar? (Fig. 333.) What part is lacking that is present in birds?
How are the eyes especially adapted for seeing at night? Does the pupil
in the light extend up or down or across the iris? Does it ever become
round?
[Illustration: FIG. 333.--WILD CAT OF AFRICA (_Felis maniculata_), ×
¹⁄₈.]
What is the shape and position of the _ears_? Are they large or small
compared with those of most mammals? They are fitted best for catching
sound from what direction? What is thus indicated in regard to the
cat’s habits? (Compare with ears of rabbit.) Touch the _whiskers_ of
the cat. What result? Was it voluntary or involuntary motion? Are the
_nostrils_ relatively large or small compared with those of a cow? Of
man?
Is the _neck_ long or short? Animals that have long fore legs usually
have what kind of a neck? Those with short legs? Why? How many _toes_
on a fore foot? Hind foot? Why is this arrangement better than the
reverse? Some mammals are sole walkers (_plantigrade_), some are toe
walkers (_digitigrade_). To which kind does the cat belong? Does it
walk on the ends of the toes? Does it walk with all the joints of the
toes on the ground? Where is the _heel_ of the cat? (Fig. 334.) The
_wrist_? To make sure of the location of the wrist, begin above: find
the shoulder blade, the upper arm (one or two bones?), the lower arm
(one or two bones?), the wrist, the palm, and the fingers (Fig. 337).
Is the heel bone prominent or small?
[Illustration: FIG. 334.--OCELOT (_Felis pardalis_), of Texas and
Mexico, × ¹⁄₉.]
In what direction does the _knee_ of the cat point? The heel? The
elbow? The wrist? Compare the front and hind _leg_ in length;
straightness; heaviness; number and position of toes; sharpness of
the _claws_. What makes the _dog’s claws_ duller than a cat’s? What
differences in habit go with this? Judging from the toe that has become
useless on the fore foot of the cat, which toe is lacking in the hind
foot? Is it the cat’s thumb or little finger that does not touch the
ground? (Fig. 337.) Locate on your own hand the parts corresponding to
the pads on the forefoot of a cat. Of what use are soft pads on a cat’s
foot?
Some animals have short, soft =fur= and long, coarse over hair. Does
the cat have both? Is the cat’s fur soft or coarse? Does the fur have a
color near the skin different from that at the tip? Why is hair better
suited as a covering for the cat than feathers would be? Scales? Where
are long, stiff bristles found on the cat? Their length suggests that
they would be of what use to a cat in going through narrow places? Why
is it necessary for a cat to be noiseless in its movements?
[Illustration: FIG. 335.--LYNX (_Lynx rufus_). The “Bob-tailed cat”
(North America).]
Observe the =movements of the cat=.--Why cannot a cat come down a tall
tree head foremost? Did you ever see a cat catch a bird? How does a
cat approach its prey? Name a jumping insect that has long hind legs;
an amphibian; several mammals (Figs. 362, 374). Does a cat ever trot?
Gallop? Does a cat chase its prey? When does the cat move with its heel
on the ground? The claws of a cat are withdrawn by means of a tendon
(see Fig. 338). Does a cat seize its prey with its mouth or its feet?
How does a cat make the purring sound? (Do the lips move? The sides?)
How does a cat drink? Do a cat and dog drink exactly the same way? Is
the cat’s tongue rough or smooth? How is the tongue used in getting the
flesh off close to the bone? Can a cat clean a bone entirely of meat?
[Illustration: FIG. 336.--JAGUAR, of tropical America.]
In what state of development is a newly born kitten? With what does the
cat _nourish its young_? Name ten animals of various kinds whose young
are similarly nourished. What is this class of animals called? Why does
a cat bend its back when it is frightened or angry? Does _a cat or a
dog_ eat a greater variety of food? Which refuses to eat an animal
found dead? Will either bury food for future use? Which is sometimes
troublesome by digging holes in the garden? Explain this instinct.
Which lived a solitary life when wild? Which had a definite haunt, or
home? Why are dogs more sociable than cats? A dog is more devoted to
his master. Why? A cat is more devoted to its home, and will return
if carried away. Why? Why does a dog turn around before lying down?
(Consider its original environment.)
[Illustration: FIG. 337.--SKELETON OF CAT.]
=The Skeleton= (Fig. 337).--Compare the _spinal column_ of a cat in
form and flexibility with the spinal column of a fish, a snake, and a
bird.
The _skull_ is joined to the spinal column by two knobs (or _condyls_),
which fit into sockets in the first vertebra. Compare the jaws with
those of a bird and a reptile. There is a prominent ridge in the temple
to which the powerful chewing muscles are attached. There is also a
ridge at the back of the head where the muscles which support the head
are attached (Fig. 348).
[Illustration: FIG. 338.--CLAW OF CAT (1) retracted by ligament, and
(2) drawn down by muscle attached to lower tendon.]
Count the _ribs_. Are there more or fewer than in man? The breastbone
is in a number of parts, joined, like the vertebræ, by cartilages.
Compare it with a bird’s sternum; why the difference? The shoulder
girdle, by which the front legs are attached to the trunk, is hardly to
be called a girdle, as the collar bones (clavicles) are rudimentary.
(They often escape notice during dissection, being hidden by muscles.)
The shoulder blades, the other bones of this girdle, are large, but
relatively not so broad toward the dorsal edge as human shoulder
blades. The clavicles are tiny because they are useless. Why does the
cat not need as movable a shoulder as a man? The pelvic, or hip girdle,
to which the hind legs are attached, is a rigid girdle, completed
above by the spinal column, to which it is immovably joined. Thus the
powerful hind legs are joined to the most rigid portion of the trunk.
=Mammals.=--The cat belongs to the _class Mammalia_ or mammals. The
characteristics of the class are that the young are not hatched from
eggs, but _are born alive, and nourished with milk_ (hence have lips),
and the _skin is covered with hair_. The milk glands are situated
ventrally. The position of the class in the animal kingdom was shown
when the cow was classified (p. 9). Their care for the young, their
intelligence, and their ability to survive when in competition with
other animals, causes the mammals to be considered the highest class in
the animal kingdom.
According to these tests, what class of vertebrates should _rank next
to mammals_? Compare the heart, lungs, blood, and parental devotion of
these two highest classes of animals.
[Illustration: FIG. 339.--SKELETON OF LION (cat family).]
=The first mammals=, which were somewhat like small opossums, appeared
millions of years ago, when the world was inhabited by giant reptiles.
These reptiles occupied the water, the land, and the air, and their
great strength and ferocity would have prevented the mammals from
multiplying (for at first they were small and weak), but the mammals
carried their young in a pouch until able to care for themselves, while
the reptiles laid eggs and left them uncared for. The first mammals
used reptilian eggs for food, though they could not contend with the
great reptiles. Because birds and mammals are better parents than
reptiles, they have conquered the earth, and the reptiles have been
forced into subordination, and have become smaller and timid.
[Illustration: FIG. 340.--WALRUS (_Trichechus rosmarus_).]
=Classification of Mammals.=--Which two have the closest _resemblances_
in the following lists: Horse, cow, deer. Why? Cat, cow, bear. Why?
Monkey, man, sheep. Why? Rat, monkey, squirrel. Why? Giraffe, leopard,
camel. Why? Walrus, cat, cow. Why? Check the five mammals in the
following lists that form a group _resembling each other most closely_:
Lion, bear, pig, dog, squirrel, cat, camel, tiger, man. State your
reasons. Giraffe, leopard, deer, cow, rat, camel, hyena, horse, monkey.
State reasons.
[Illustration: FIG. 341.--WEASEL, in summer; in Canada in winter it is
all white but tip of tail.]
=Teeth and toes= are the basis for subdividing the class mammalia
into orders. Although the breathing, circulation, and internal organs
and processes are similar in all mammals, the external organs vary
greatly because of the varying environments of different species. The
internal structure enables us to place animals together which are
essentially alike; _e.g._ the whale and man are both mammals, since
they resemble in breathing, circulation, and multiplication of young.
The external organs guide us in separating the class into orders. The
teeth vary according to the food eaten. The feet vary according to
use in obtaining food or escaping from enemies. This will explain the
difference in the length of legs of lion and horse, and of the forms of
the teeth in cat and cow. Make a careful study of the teeth and limbs
as shown in the figures and in all specimens accessible. Write out the
dental formulas as indicated at the top of page 194. The numerals above
the line show the number of upper teeth; those below the line show the
number of lower teeth in one half of the jaw. They are designated as
follows: _I_, incisors; _C_, canine; _M_, molars. Multiplying by two
gives the total number. Which skulls in the chart have the largest
canines? Why? The smallest, or none at all? Why? Compare the molars
of the cow, the hog, and the dog. Explain their differences. In which
skulls are some of the molars lacking? Rudimentary? Why are the teeth
that do not touch usually much smaller than those that do?
[Illustration: FIG. 342.--FOOT OF BEAR (_Plantigrade_).]
[Illustration: FIG. 343.--POLAR BEAR (_Ursus maritimus_).]
KEY, OR TABLE, FOR CLASSIFYING MAMMALS (_class Mammalia_) INTO ORDERS
Orders
A₁ =Imperfect Mammals=, young hatched or
prematurely born
B₁ Jaws a birdlike beak, egg-laying _Mon′otremes_
B₂ Jaws not beaklike, young carried in
pouch _Marsu′pials_
A₂ =Perfect Mammals=, young not hatched, nor
prematurely born
{C₁ Front part of both jaws lack
{ teeth _Eden′tates_
{
B₁ {C₂ Teeth with sharp points for
_Digits { piercing shells of insects _Insect′ivors_
with {
claws_ {C₃ Canines very long, molars suited
{ for tearing _Car′nivors_
{
{C₄ Canines lacking, incisors very
{ large _Rodents_
B₂ {C₁ Head large; carnivorous _Ceta′ceans_
_Digits {
not {C₂ Head small; herbivorous _Sire′neans_
distinct_{
{C₁ Five toes, nose prolonged into a
{ snout _Proboscid′eans_
{
{C₂ Toes odd number, less than five _E′quines_ }
B₃ { }
_Digits {C₃ Toes even number, upper front }_Un-
with { teeth lacking, chew the cud _Ru′minants_ } gu-
nails or{ }lates_
hoofs_ {C₄ Toes even number, upper front }
{ teeth present, not cud-chewers _Swine_ }
{
{C₅ All limbs having hands _Quad′rumans_
{
{C₆ Two limbs having hands _Bi′mans_
=Exercise in Classification.=--Copy the following list, and by
reference to figures write the name of its order after each mammal:--
Ape (Figs. 405, 406)
Rabbit (Fig. 345)
Dog (Figs. 356, 408)
Hog (Figs. 357, 393)
Bat (Figs. 347, 370)
Cat (Figs. 337, 348)
Armadillo (Figs. 349, 365)
Cow (Figs. 344, 386)
Walrus (Fig. 340)
Monkey (Figs. 352, 401)
Horse (Figs. 355, 395)
Ant-eater (Figs. 354, 364)
Antelope (Fig. 391)
Mole (Figs. 367, 368)
Beaver (Figs. 372, 373)
Duckbill (Fig. 359)
Tapir (Fig. 384)
Dolphin (Figs. 379, 397)
Use chart of skulls and Figs. 381, 382, 395-400 in working out this
exercise.
=Chart of Mammalian Skulls (Illustrated Study)=
5 1 2
Man’s dental formula is (_M_ -, _C_ -, _I_ -)² = 32.
5 1 2
In like manner fill out formulas below:--
Cow (_M_ - _C_ - _I_ -)² = 32
Rabbit (_M_ - _C_ - _I_ -)² = 28
Walrus (_M_ - _C_ - _I_ -)² = 34
Bat (_M_ - _C_ - _I_ -)² = 34
Cat (_M_ - _C_ - _I_ -)² = 30
Armadillo (_M_ - _C_ - _I_ -)² = 28
Horse (_M_ - _C_ - _I_ -)² = 40
Whale (_M_ - _C_ - _I_ -)² = 0
Am. Monkey (_M_ - _C_ - _I_ -)² = 36
Sloth (_M_ - _C_ - _I_ -)² = 18
Ant-eater (_M_ - _C_ - _I_ -)² = 0
Dog (_M_ - _C_ - _I_ -)² = 42
Hog (_M_ - _C_ - _I_ -)² = 44
Sheep (_M_ - _C_ - _I_ -)² = 32
[Illustration: FIG. 344.--Skull and front of lower jaw of COW.]
[Illustration: FIG. 345.--RABBIT.
_A_, _B_, incisors; _C_, molars.]
[Illustration: FIG. 346.--WALRUS (see Fig. 341).]
[Illustration: FIG. 347.--BAT.]
[Illustration: FIG. 348.--CAT.]
=Chart of Mammalian Skulls=
[Illustration: FIG. 349.--ARMADILLO.]
[Illustration: FIG. 350.--HORSE (front of jaw).]
[Illustration: FIG. 351.--GREENLAND WHALE.]
[Illustration: FIG. 352.--AMERICAN MONKEY.]
[Illustration: FIG. 353.--SLOTH (Fig. 363).]
[Illustration: FIG. 354.--ANT-EATER (Fig. 364).]
[Illustration: FIG. 355.--HORSE.]
[Illustration: FIG. 356.--DOG. Upper (_A_) and lower (_B_) jaw.]
[Illustration: FIG. 357.--HOG.]
[Illustration: FIG. 358.--SHEEP.]
The =lowest order of mammals= contains only two species, the duckbill
and the porcupine ant-eater, both living in the Australian region. Do
you judge that the _duckbill_ of Tasmania (Fig. 359) lives chiefly in
water or on land? Why? Is it probably active or slow in movement? It
dabbles in mud and slime for worms and mussels, etc. How is it fitted
for doing this? Which feet are markedly webbed? How far does the web
extend? The web can be folded back when not in use. It lays two eggs
in a nest of grass at the end of a burrow. Trace resemblances and
differences between this animal and birds.
[Illustration: FIG. 359.--DUCKBILL (_Ornithorhynchus paradoxus_).]
[Illustration: FIG. 360.--SPINY ANT-EATER (_Echidna aculeata_). View of
under surface to show pouch. (After Haacke.)]
The _porcupine ant-eater_ has numerous quill-like spines (Fig. 360)
interspersed with its hairs. (Use?) Describe its claws. It has a long
prehensile tongue. It rolls into a ball when attacked. Compare its jaws
with a bird’s bill. It lays one egg, which is carried in a fold of
the skin until hatched. Since it is pouched it could be classed with
the pouched mammals (next order), but it is egg-laying. Suppose the
two animals in this order did not nourish their young with milk after
hatching, would they most resemble mammals, birds, or reptiles?
Write the name of this _order_. ____ (See Table, p. 193.) _Why_ do you
place them in this order (____)? (See p. 193.) The name of the order
comes from two Greek words meaning “one opening,” because the ducts
from the bladder and egg glands unite with the large intestine and form
a cloaca. What other classes of vertebrates are similar in this?
[Illustration: FIG. 361.--OPOSSUM (_Didelphys Virginianus_).]
=Pouched Mammals.=--These animals, like the last, are numerous in the
Australian region, but are also found in South America, thus indicating
that a bridge of land once connected the two regions. The _opossum_ is
the only species which has penetrated to North America (Fig. 361). Are
its jaws slender or short? What kinship is thus suggested? As shown by
its grinning, its lips are not well developed. Does this mean a low or
a well-developed mammal? Where does it have a thumb? (Fig. 361.) Does
the thumb have a nail? Is the tail hairy or bare? Why? Do you think it
prefers the ground or the trees? State two reasons for your answer.
It hides in a cave or bank or hollow tree all day, and seeks food at
night. Can it run fast on the ground? It feigns death when captured,
and watches for a chance for stealthy escape.
The _kangaroo_ (Fig. 362), like the opossum, gives birth to imperfectly
developed young. (Kinship with what classes is thus indicated?) After
birth, the young (about three fourths of an inch long) are carried in
a ventral pouch and suckled for seven or eight months. They begin to
reach down and nibble grass before leaving the pouch. Compare fore legs
with hind legs, front half of body with last half. Describe tail. What
is it used for when kangaroo is at rest? In jumping, would it be useful
for propelling and also for balancing the body? Describe hind and fore
feet. _Order_ ____. _Why?_ ____. See key, page 193.
[Illustration: FIG. 362.--GIANT KANGAROO.]
=Imperfectly Toothed Mammals.=--These animals live chiefly in South
America (sloth, armadillo, giant ant-eater) and Africa (pangolin). The
sloth (Fig. 363) eats leaves. Its movements are remarkably slow, and a
vegetable growth resembling moss often gives its hair a green color.
(What advantage?) How many toes has it? How are its nails suited to its
manner of living? Does it save exertion by hanging from the branches of
trees instead of walking upon them?
[Illustration: FIG. 363.--SLOTH of South America.]
[Illustration: FIG. 364.--GIANT ANT-EATER of South America. (See
Fig. 354.) Find evidences that the edentates are a degenerate order.
Describe another ant-eater (Fig. 360).]
Judging from the figures (363, 364, 365), are the members of this order
better suited for attack, active resistance, passive resistance, or
concealment when contending with other animals? The ant-eater’s claws
(Fig. 364) on the fore feet seem to be a hindrance in walking; for what
are they useful? Why are its jaws so slender? What is probably the
use of the enormous bushy tail? The nine-banded armadillo (Fig. 365)
lives in Mexico and Texas. It is omnivorous. To escape its enemies, it
burrows into the ground with surprising rapidity. If unable to escape
when pursued, its hard, stout tail and head are turned under to protect
the lower side of the body where there are no scales. The three-banded
species (Fig. 366) lives in Argentina. Compare the ears and tail of the
two species; give reasons for differences. Why are the eyes so small?
The claws so large? _Order_ ____. _Why?_ ____.
[Illustration: FIG. 365.--NINE-BANDED ARMADILLO of Texas and Mexico.
(_Dasypus novemcinctus._) It is increasing in numbers; it is very
useful, as it digs up and destroys insects. (See Fig. 349.)]
[Illustration: FIG. 366.--THREE-BANDED ARMADILLO (_Tolypeutes
tricinctus_).]
=Insect Eaters.=--The soft interior and crusty covering of insects
makes it unnecessary for animals that prey upon them to have
flat-topped teeth for grinding them to powder, or long cusps for
tearing them to pieces. The teeth of insect eaters, even the molars
(Fig. 368), have many sharp tubercles, or points, for holding insects
and piercing the crusty outer skeleton and reducing it to bits. As most
insects dig in the ground or fly in the air, we are not surprised to
learn that some insect-eating mammals (the bats) fly and others (the
moles) burrow. Are the members of this order friends or competitors of
man?
[Illustration: FIG. 367.--THE MOLE.]
[Illustration: FIG. 368.--SKELETON OF MOLE. (Shoulder blade is turned
upward.)]
Why does _the mole_ have very small eyes? Small ears? Compare the shape
of the body of a mole and a rat. What difference? Why? Compare the
front and the hind legs of a mole. Why are the hind legs so small and
weak? Bearing in mind that the body must be arranged for digging and
using narrow tunnels, study the skeleton (Fig. 368) in respect to the
following: Bones of arm (length and shape), fingers, claws, shoulder
bones, breastbone (why with ridge like a bird?), vertebræ (why are the
first two so large?), skull (shape). There are no eye sockets, but
there is a snout gristle; for the long, sensitive snout must serve in
place of the small and almost useless eyes hidden deep in the fur. Is
the fur sleek or rough? Why? Close or thin? It serves to keep the mole
clean. The muscles of neck, breast, and shoulders are very strong.
Why? The mole eats earthworms as well as insects. It injures plants by
breaking and drying out their roots. Experiments show that the Western
mole will eat moist grain, though it prefers insects. If a mole is
caught, repeat the experiment, making a careful record of the food
placed within its reach.
[Illustration: FIG. 369.--SKELETON OF BAT.]
As with the mole, the skeletal adaptations of _the bat_ are most
remarkable in the hand. How many fingers? (Fig. 369.) How many nails on
the hand? Use of nail when at rest? When creeping? (Fig. 369.) Instead
of feathers, the flying organs are made of a pair of extended folds
of the skin supported by elongated bones, which form a framework like
the ribs of an umbrella or a fan. How many digits are prolonged? Does
the fold of the skin extend to the hind legs? The tail? Are the finger
bones or the palm bones more prolonged to form the wing skeleton?
[Illustration: FIG. 370.--VAMPIRE (_Phyllostoma spectrum_) of South
America. × ¹⁄₆.]
The skin of the wing is rich in blood vessels and nerves, and serves,
by its sensitiveness to the slightest current of air, to guide the bat
in the thickest darkness. Would you judge that the bat has sharp sight?
Acute hearing?
The moles do not _hibernate_; the bats do. Give the reason for the
difference. If bats are aroused out of a trance-like condition in
winter, they may die of starvation. Why? The mother bat carries the
young about with her, since, unlike birds, she has no nest. How are the
young nourished? _Order_ ____. _Why?_ ____. (Key, p. 193.)
[Illustration: FIG. 371.--POUCHED GOPHER (_Geomys bursarius_) × ¹⁄₄, a
large, burrowing field rat, with cheek pouches for carrying grain.]
[Illustration: FIG. 372.--Hind foot _a_, fore foot _b_, tail _c_, of
BEAVER.]
[Illustration: FIG. 373.--BEAVER.]
[Illustration: FIG. 374.--POSITION OF LIMBS IN RABBIT.]
=The Gnawing Mammals.=--These animals form the most numerous order of
mammals. They _lack canine_ teeth. Inference? The incisors are four
in number in all species except the rabbits, which have six (see Fig.
345). They are readily recognized by their _large incisors_. These
teeth grow throughout life, and if they are not constantly worn away
by gnawing upon hard food, they become inconveniently long, and may
prevent closing of the mouth and cause starvation. The hard enamel
is all on the front surface, the dentine in the rear being softer;
hence the incisors sharpen themselves by use to a chisel-like edge.
The molars are set close together and have their upper surfaces level
with each other. The ridges on them run crosswise so as to form a
continuous filelike surface for reducing the food still finer after
it has been gnawed off (Fig. 345). The lower jaw fits into grooves in
place of sockets. This allows the jaw to work back and forth instead of
sidewise. The rabbits and some squirrels have a hare lip; _i.e._ the
upper lip is split. What advantage is this in eating? In England the
species that burrow are called rabbits; those that do not are called
hares.
Name six enemies of rabbits. Why does a rabbit usually sit motionless
unless approached very close? Do you usually see one before it dashes
off? A rabbit has from three to five litters of from three to six young
each year. Squirrels have fewer and smaller litters. Why must the
rabbit multiply more rapidly than the squirrel in order to survive?
English rabbits have increased in Australia until they are a plague.
Sheep raising is interfered with by the loss of grass. The Australians
now ship them to England in cold storage for food. Rabbits and most
rodents lead a watchful, timid, and alert life. An exception is the
porcupine, which, because of the defense of its barbed quills, is dull
and sluggish.
The common rodents are:--
squirrels
rabbits
rats
mice
beavers
muskrats
porcupines
guinea pig
pouched gopher
prairie dog
prairie squirrel
chipmunk
ground hog
field mouse
Which of the above rodents are commercially important? Which are
injurious to an important degree? Which have long tails? Why? Short
tails? Why? Long ears? Why? Short ears? Why? Which are aquatic? Which
dig or burrow? Which are largely nocturnal in habits? Which are
arboreal? Which are protected by coloration? Which escape by running?
By seeking holes?
=Economic Importance.=--Rabbits and squirrels destroy the eggs and
young of birds. Are rabbits useful? Do they destroy useful food? The
use of beaver and muskrat skins as furs will probably soon lead to
their extinction. Millions of rabbits’ skins are used annually, the
hair being made into felt hats. There are also millions of squirrel
skins used in the fur trade. The hairs of the tail are made into fine
paint brushes. The skins of common rats are used for the thumbs of kid
gloves. _Order_ ____. _Why?_ ____.
[Illustration: FIG. 375.--FLYING SQUIRREL (_Pteromys volucella_). ×
¹⁄₄.]
=Elephants.=--Elephants, strange to say, have several noteworthy
resemblances to rodents. Like them, elephants have no canine teeth;
their molar teeth are few, and marked by transverse ridges and the
incisors present are prominently developed (Figs. 376, 377). Instead
of four incisors, however, they have only two, the enormous tusks, for
there are no incisors in the lower jaw. Elephants and rodents both
subsist upon plant food. Both have peaceful dispositions, but one order
has found safety and ability to survive by attaining enormous size and
strength; the other (_e.g._ rats, squirrels) has found safety in small
size. Explain.
Suppose you were to observe an elephant for the first time, without
knowing any of its habits. How would you know that it does not eat
meat? That it does eat plant food? That it can defend itself? Why would
you make the mistake of thinking that it is very clumsy and stupid?
Why is its skin naked? Thick? Why must its legs be so straight? Why
must it have either a very long neck or a substitute for one? (Fig.
376.) Are the eyes large or small? The ears? The brain cavity? What
anatomical feature correlates with the long proboscis? Is the proboscis
a new organ not found in other animals, or is it a specialization of
one or more old ones? Reasons? What senses are especially active in the
proboscis? How is it used in drinking? In grasping? What evidence that
it is a development of the nose? The upper lip?
[Illustration: FIG. 376.--HEAD OF AFRICAN ELEPHANT.]
[Illustration: FIG. 377.--MOLAR TOOTH OF AFRICAN ELEPHANT.]
The tusks are of use in uprooting trees for their foliage and in
digging soft roots for food. Can the elephant graze? Why, or why
not? There is a finger-like projection on the end of the snout which
is useful in delicate manipulations. The feet have pads to prevent
jarring; the nails are short and hardly touch the ground. _Order_ ____.
_Why?_ ____. Key, page 193.
=Whales, Porpoises, Dolphins.=--As the absurd mistake is sometimes made
of confusing _whales_ with fish, the pupil may compare them in the
following respects: eggs, nourishment of young, fins, skin, eyes, size,
breathing, temperature, skeleton (Figs. 209, 379, and 397).
[Illustration: FIG. 378.--HARPOONING GREENLAND WHALE (see Fig. 351).]
_Porpoises and dolphins_, which are smaller species of whales, live
near the shore and eat fish. Explain the expression “blow like a
porpoise.” They do not exceed five or eight feet in length, while the
deep-sea whales are from thirty to seventy-five feet in length, being
by far the largest animals in the world. The size of the elephant is
limited by the weight that the bones and muscles support and move. The
whale’s size is not so limited.
The _whale_ bears one young (rarely twins) at a time. The mother
carefully attends the young for a long time. The _blubber_, or thick
layer of fat beneath the skin, serves to retain heat and keep the body
up to the usual temperature of mammals in spite of the cold water.
It also serves, along with the _immense lungs_, to give lightness to
the body. Why does a whale need large lungs? The _tail of a whale_ is
horizontal instead of vertical, that it may steer upward rapidly from
the depths when needing to breathe. The _teeth_ of some whales do not
cut the gum, but are reabsorbed and are replaced by horny plates of
“whalebone,” which act as strainers. Give evidence, from the flippers,
lungs, and other organs, that the whale is descended from a land
mammal (Fig. 397). Compare the whale with a typical land mammal, as
the dog, and enumerate the specializations of the whale for living in
water. What change took place in the general form of the body? It is
believed that on account of scarcity of food the land ancestors of the
whale, hundreds of thousands of years ago, took to living upon fish,
etc., and, gradually becoming swimmers and divers, lost the power of
locomotion on land. _Order_ ____. _Why?_ ____.
[Illustration: FIG. 379.--DOLPHIN.]
Elephants are rapidly becoming extinct because of the value of their
ivory tusks. Whales also furnish valuable products, but they will
probably exist much longer. Why?
The =manatees and dugongs= (sea cows) are a closely related order
living upon water plants, and hence living close to shore and in the
mouths of rivers. _Order_ ____. _Why?_ ____.
[Illustration: FIG. 380.--MANATEE, or sea cow; it lives near the shore
and eats seaweed. (Florida to Brazil.)]
=Hoofed Mammals.=--All the animals in this order walk on the tips of
their toes, which have been adapted to this use by the claws having
developed into _hoofs_. The order is subdivided into the _odd-toed_
(such as the horse with one toe and the rhinoceros with three) and the
_even-toed_ (as the ox with two toes and the pig with four). All the
even-toed forms except the pig and hippopotamus chew the cud and are
given the name of _ruminants_.
=Horse and Man Compared= (Figs. 381, 399).--To which finger and toe
on man’s hand and foot does the toe of a horse’s foot correspond? Has
the horse kneecaps? Is its heel bone large or small? Is the fetlock on
toe, instep, or ankle? Does the part of a horse’s hind leg that is most
elongated correspond to the thigh, calf, or foot in man? On the fore
leg, is the elongated part the upper arm, forearm, or hand? Does the
most elongated part of the fore foot correspond to the finger, palm, or
wrist? On the hind foot is it toe, instep, or ankle? Is the fetlock at
the toe, instep, or heel? (Fig. 385.) Is the hock at the toe, instep,
heel, or knee? _Order_ ____. _Why?_ ____.
[Illustration: FIG. 381.--Left leg of man, left hind leg of dog and
horse; homologous parts lettered alike.]
=Specializations of the Mammals.=--The early mammals, of which the
present marsupials are believed to be typical, had five toes provided
with claws. They were not very rapid in motion nor dangerous in fight,
and probably ate both animal and vegetable food.
[Illustration: FIG. 382.--SKELETONS OF FEET OF MAMMALS.
_P_, horse; _D_, dolphin; _E_, elephant; _A_, monkey; _T_, tiger; _O_,
aurochs; _F_, sloth; _M_, mole.
=Question:= Explain how each is adapted to its specialized function.]
According to the usual rule, they tended to increase faster than the
food supply, and there were continual contests for food. Those whose
claws and teeth were sharper drove the others from the food, or preyed
upon them. Thus the specialization into the bold flesh eating beasts
of prey and the timid vegetable feeders began. Which of the flesh
eaters has already been studied at length? The insectivora escaped
their enemies and found food by learning to burrow or fly. The rodents
accomplished the same result either by acquiring great agility in
climbing, or by living in holes, or by running. The proboscidians
acquired enormous size and strength. The hoofed animals found safety in
flight.
[Illustration: _Equus_
_Protohippus_
_Pliohippus_
_Miohippus_
_Mesohippus_
_Orohippus_
FIG. 383.--Feet of the ancestors of the horse.]
[Illustration: FIG. 384.--TAPIR OF SOUTH AMERICA (_Tapirus
americanus_). × ¹⁄₂₅.
=Questions:= How does it resemble an elephant? (Fig. 376.) A horse? (p.
210.)]
[Illustration: FIG. 385.--HORSE, descended from a small wild species
still found in Western Asia.]
=Ungulates=, as the horse, need no other protection than their great
speed, which is due to lengthening the bones of the legs and rising
upon the very tip of the largest toe, which, to support the weight,
developed an enormous toe-nail called a hoof. The cattle, not having
developed such speed as the horse, usually have horns for defense. If a
calf or cow bellows with distress, all the cattle in the neighborhood
rush to the rescue. This unselfish instinct to help others was an aid
to the survival of wild cattle living in regions infested with beasts
of prey. Which of Æsop’s fables is based upon this instinct? The habit
of rapid grazing and the correlated habit of chewing the cud were also
of great value, as it enabled cattle to obtain grass hurriedly and
retire to a safe place to chew it. Rudiments of the upper incisors
are present in the jaw of the calf, showing the descent from animals
which had a complete set of teeth. The rudiments are absorbed and the
upper jaw of the cow lacks incisors entirely, as they would be useless
because of the cow’s habit of seizing the grass with her rough tongue
and cutting it with the lower incisors as the head is jerked forward.
This is a more rapid way of eating than by biting. Which leaves the
grass shorter after grazing, a cow or a horse? Why? Grass is very slow
of digestion, and the ungulates have an alimentary canal twenty to
thirty times the length of the body. Thorough chewing is necessary for
such coarse food, and the ungulates which chew the cud (ruminants) are
able, by leisurely and thorough chewing, to make the best use of the
woody fiber (cellulose) which is the chief substance in their food.
[Illustration: FIG. 386.--SKELETON OF COW. Compare with horse (Fig.
395) as to legs, toes, tail, mane, dewlap, ears, body.]
=Ruminants= have four divisions to the stomach. Their food is first
swallowed into the roomy _paunch_ in which, as in the crop of a bird,
the bulky food is temporarily stored. It is not digested at all in the
paunch, but after being moistened, portions of it pass successively
into the _honeycomb_, which forms it into balls to be belched up and
ground by the large molars as the animal lies with eyes half closed
under the shade of a tree. It is then swallowed a second time and
is acted upon in the third division (or _manyplies_) and the fourth
division (or _reed_). Next it passes into the intestine. Why is the
paunch the largest compartment? In the figure do you recognize the
paunch by its size? The honeycomb by its lining? Why is it round? The
last two of the four divisions may be known by their direct connection
with the intestine.
[Illustration: FIG. 387.--Food traced through stomachs of cow. (Follow
arrows.)]
[Illustration: FIG. 388.--Section of cow’s stomachs. Identify each.
(See text.)]
[Illustration: FIG. 389.--OKAPI. This will probably prove to be the
last large mammal to be discovered by civilized man. It was found in
the forests of the Kongo in 1900.
=Questions:= It shows affinities (find them) with giraffe, deer, and
zebra. It is a ruminant ungulate (explain meaning--see text).]
The true _gastric juice_ is secreted only in the fourth stomach.
Since the cud or unchewed food is belched up in balls from the round
“honeycomb,” and since a ball of hair is sometimes found in the stomach
of ruminants, some ignorant people make the absurd mistake of calling
the ball of hair the cud. This ball accumulates in the paunch because
of the friendly custom cows have of combing each other’s hair with
their rough tongues, the hair sometimes being swallowed. Explain the
saying that if a cow stops chewing the cud she will die.
[Illustration: FIG. 390.--AFRICAN CAMEL (_Camelus dromedarius_).]
Does a cow’s lower jaw move sidewise or back and forth? Do the ridges
on the molars run sidewise or lengthwise? Is a cow’s horn hollow? Does
it have a bony core? (Fig. 344.)
[Illustration: FIG. 391.--PRONG-HORNED ANTELOPE (_Antelocarpa
Americana_). Western states.]
The permanent hollow horns of the cow and the solid deciduous horns of
the deer are typical of the two kinds of horns possessed by ruminants.
The prong-horned antelope (Fig. 391) of the United States, however, is
an intermediate form, as its horns are hollow, but are shed each year.
The hollow horns are a modification of hair. Do solid or hollow bones
branch? Which are possessed by both sexes? Which are pointed? Which
are better suited for fighting? Why would the deer have less need to
fight than the cattle? Deer are polygamous, and the males use their
horns mostly for fighting each other. The sharp hoofs of deer are also
dangerous weapons. The white-tail deer (probably the same species as
the Virginian red deer) is the most widely distributed of the American
deer. It keeps to the lowlands, while the black-tailed deer prefers a
hilly country. The moose, like the deer, browses on twigs and leaves.
The elk, like cattle, eats grass.
[Illustration: FIG. 392.--ROCKY MOUNTAIN SHEEP (_Ovis montana_). ×
¹⁄₂₄.]
The native sheep of America is the big horn, or Rocky Mountain sheep
(Fig. 392). The belief is false that they alight upon their horns
when jumping down precipices. They post sentinels and are very wary.
There is also a native goat, a white species, living high on the Rocky
Mountains near the snow. They are rather stupid animals. The bison once
roamed in herds of countless thousands, but, with the exception of a
few protected in parks, it is now extinct. Its shaggy hide was useful
to man in winter, so it has been well-nigh destroyed. For gain man
is led to exterminate elephants, seals, rodents, armadillos, whales,
birds, deer, mussels, lobsters, forests, etc.
[Illustration: FIG. 393.--PECCARY (_Dicotyles torquatus_) of Texas and
Mexico. × ¹⁄₁₂.]
Our only native hog is the peccary, found in Texas (Fig. 393). In
contrast with the heavy domestic hog, it is slender and active. It is
fearless, and its great tusks are dangerous weapons. The swine are the
only ungulates that are not strictly vegetable feeders. The habit of
fattening in summer was useful to wild hogs, since snow hid most of
their food in winter. The habit has been preserved under domestication.
Are the small toes of the hog useless? Are the “dew claws” of cattle
useless? Will they probably become larger or smaller? _Order?_
[Illustration: =Illustrated Study=
FIG. 394.--BIRD.
FIG. 395.--HORSE.
FIG. 396.--OX.
FIG. 397.--DOLPHIN.
FIG. 398.--FISH.]
[Illustration: =Illustrated Study=
FIG. 399.--MAN.
FIG. 400.--CHIMPANZEE. (See Fig. 406.)]
=Illustrated Study of Vertebrate Skeletons=: Taking man’s skeleton as
complete, which of these seven skeletons is most incomplete?
Regarding the fish skeleton as the original vertebrate skeleton, how
has it been modified for (1) walking, (2) walking on two legs, (3)
flying?
Which skeleton is probably a degenerate reversion to original type?
(p. 209.)
How is the horse specialized for speed?
Do all have tail vertebræ, or vertebræ beyond the hip bones? Does
each have shoulder blades?
Compare (1) fore limbs, (2) hind limbs, (3) jaws of the seven
skeletons. Which has relatively the shortest jaws? Why? What seems to
be the typical number of ribs? limbs? digits?
Does flipper of a dolphin have same bones as arm of a man?
How many thumbs has chimpanzee? Which is more specialized, the foot
of a man or a chimpanzee? Is the foot of a man or a chimpanzee better
suited for supporting weight? How does its construction fit it for
this?
Which has a better hand, a man or a chimpanzee? What is the
difference in their arms? Does difference in structure correspond to
difference in use?
Which of the seven skeletons bears the most complex breastbone?
Which skeleton bears no neck (or cervical) vertebræ? Which bears only
one?
Are all the classes of vertebrates represented in this chart? (p.
125.)
[Illustration: FIG. 401.--SACRED MONKEY OF INDIA (_Semnopithecus
entellus_). × ¹⁄₁₂.]
=Monkeys, Apes, and Man.=--Study the figures (399, 400); compare apes
and man and explain each of the differences in the following list: (1)
feet, three differences; (2) arms; (3) brain case; (4) jaws; (5) canine
teeth; (6) backbone; (7) distance between the eyes.
[Illustration: FIG. 402.--LEMUR (_Lemur Mongoz_). × ¹⁄₁₀. Which digit
bears a claw?]
_A hand_, unlike a foot, has one of the digits, called a thumb, placed
opposite the other four digits that it may be used in grasping.
Two-handed man and four-handed apes and monkeys are usually placed in
one order, the _Primates_, or in two orders (see table, page 193). The
lowest members of this order are the _lemurs_ of the old world. Because
of their hands and feet being true grasping organs, they are placed
among the primates, notwithstanding the long muzzle and expressionless,
foxlike face. (Fig. 402.) Next in order are the _tailed monkeys_, while
the _tailless apes_ are the highest next to man.
[Illustration: FIG. 403.--BROAD-NOSED MONKEY. × ¹⁄₁₀. America.]
[Illustration: FIG. 404.--NARROW-NOSED MONKEY. × ¹⁄₁₂. Old World.]
[Illustration: FIG. 405.--GORILLA. (Size of a man.)]
The _primates of the New World_ are all monkeys with long tails and
broad noses. They are found from Paraguay to Mexico. The _monkeys and
apes of the Old World_ have a _thin partition_ between the nostrils,
and are thus distinguished from the monkeys of the New World, which
have a _thicker partition_ and have a broader nose. (Figs. 403, 404.)
The monkeys of America all have _six molar teeth_ in each half jaw
(Fig. 352); the monkeys and apes of the Old World have thirty-two teeth
which agree both in number and arrangement with those of man.
Which of the primates figured in this book appear to have the arm
longer than the leg? Which have the eyes directed forward instead of
sideways, as with cats or dogs?
Nearly all the primates are _forest dwellers_, and inhabit warm
countries, where the boughs of trees are never covered with ice or
snow. Their _ability in climbing_ serves greatly to protect them from
beasts of prey. Many apes and monkeys are able to assume the upright
position in walking, but they touch the ground with their knuckles
every few steps to aid in preserving the balance.
[Illustration: FIG. 406.--CHIMPANZEE.]
The _Simians_ are the highest family of primates below man, and include
the gorilla, chimpanzee, orang, and gibbon. Some of the simians weave
together branches in the treetops to form a rude nest, and all are very
affectionate and devoted to their young. How are apes most readily
distinguished from monkeys? (Figs. 401, 406.)
The study of man as related to his environment will be taken up in
detail in the part called Human Biology. We will there examine the
effect upon man’s body of the rapid changes since emerging from
savagery that he has made in food eaten, air breathed, clothing, and
habits of life.
[Illustration: FIG. 407.--ANATOMY OF RABBIT.
_a_, incisor teeth;
_b_, _b′_, _b″_, salivary glands;
_k_, larynx;
_l_, windpipe;
_c_, gullet;
_d_, diaphragm (possessed only by mammals);
_e_, stomach;
_g_, small intestine;
_h_, _h′_, large intestine;
_f_, junction of small and large intestine;
_g_, _g′_, cæcum, or blind sac from _f_ (corresponds to the shrunken
rudimentary vermiform appendix in man);
_m_, carotid arteries;
_n_, heart;
_o_, aorta;
_p_, lungs;
_q_, end of sternum;
_r_, spleen;
_s_, kidney;
_t_, ureters (from kidney to bladder _v_).
2 brain of rabbit:
_a_, olfactory nerves;
_b_, cerebrum;
_c_, midbrain;
_d_, cerebellum.]
=Table for Review=
==============+=======+=======+=======+=======+=======+=======+=======
| FISH | FROG | TURTLE| BIRD | CAT | HORSE | MAN
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Names of limbs| | | | | | |
| | | | | | |
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Acutest sense | | | | | | |
| | | | | | |
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Digits on fore| | | | | | |
and hind limb | | | | | | |
| | | | | | |
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Locomotion | | | | | | |
| | | | | | |
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Kind of food | | | | | | |
| | | | | | |
--------------+-------+-------+-------+-------+-------+-------+-------
| | | | | | |
Care of young | | | | | | |
| | | | | | |
==============+=======+=======+=======+=======+=======+=======+=======
[Illustration:
St. Bernard
Eskimo
Poodle
Dachshund
German mastiff
English bloodhound
Pointer
Bulldog
Greyhound
Newfoundland
Shepherd
Spitz
FIG. 408.--ARTIFICIAL SELECTION. Its effects in causing varieties
in one species. Which of the dogs is specialized for speed? Driving
cattle? Stopping cattle? Trailing by scent? Finding game? Drawing
vehicles? Going into holes? House pet? Cold weather? In Mexico there
is a hairless dog specialized for hot climates. The widely differing
environments under various forms of domestication cause “sports” which
breeders are quick to take advantage of when wishing to develop new
varieties. Professor De Vries by cultivating American evening primroses
in Europe has shown that a sudden change of environment may cause not
only varieties but new species to arise.]
HUMAN BIOLOGY
CHAPTER I
INTRODUCTION
To which _branch_ of animals does man belong? To which _class_ and
_order_ in that branch? (Animal Biology, pages 125, 193.) There is no
other animal _species in the same genus or order_ with man. This shows
a wide _physical_ difference between man and other animals, but man’s
_mind_ isolates him among the other animals still more.
[Illustration: FIG. 1.--FACIAL ANGLES of Caucasian (nearly 90°) and
Ethiopian (about 70°). The angle between lines crossing at front of
upper jaw near base of nose, one line drawn from most prominent part of
forehead, the other through hole of ear.]
The human species is divided into =five varieties= or races: 1.
_Caucasian_ (Fig. 1). Skin fair, hair wavy, eyes oval. (Europe except
Finns and Lapps, Western Asia, America.) 2. _Mongolian._ Skin yellow,
hair straight and black, face flat, nose blunt, almond eyes. (Central
Asia, China, Japan, Lapps and Finns of Europe, Eskimos of North
America.) 3. _Americans._ Skin copper red, hair straight, nose straight
or arched. (North and South America.) 4. _Malay._ Skin brown, face
flat, hair black. (Australia and Islands of Pacific.) 5. _Ethiopian_
(Fig. 1). Skin dark, hair woolly, nose broad, lips thick, jaws and
teeth prominent, forehead retreating, great toe shorter than next toe
and separate. (Africa, America.)
There is a _struggle between the races_ for the possession of
different lands. The Caucasian is gaining in Australia, Africa, and
America. With difficulty the Mongolians are kept from the western
shores of America. The Ethiopian in America shows a lessened rate
of increase every decade; this may be due to the tendency of the
race to crowd into cities and the strain of suddenly changing from
jungle life in less than two centuries. _Civilization is a strain_
upon any race. It is destroying the American Indian. The Mongolian
and Caucasian survive civilization best, but insanity is increasing
rapidly among the latter.
[Illustration: FIG. 2.--INDIAN WEAPONS: LANCE AND ARROW HEADS. From a
bank of mussel shells (remains of savage feast) at Keyport, N.J.]
=Man’s Original Environment.=--Primitive man lived without the use
of fire or weapons other than sticks or stones. His _first home
was in the tropics_, where his needs were readily supplied, and
probably in Asia. Many nations have a tradition of a home in a
garden (Greek, _paradisos_). His food was chiefly _tree fruits and
nuts_. When because of crowding he left nature’s garden, he acquired
skill in _hunting and fishing_ and the use of fire that flesh might
supplement the meager fruits of colder climates. His weapons were
of rough (chipped) stone at first--_in the old stone age_. In this
age the mammoth lived. He learned to polish implements in the _new
stone age_. The Indians were in that stage when Columbus came to
America (Figs. 2, 3). The cultivation of grain and the domestication
of animals probably began in this age. The _bronze_ and _iron ages_
followed the stone age.
[Illustration: FIG. 3.--INDIAN TOMAHAWK. Polished Stone. Keyport, N.J.]
=The Reaction between Man and his Environment.=--The estimates by
various geologists of the time man has existed as a species vary from
20,000 to 200,000 years. The _active life out of doors_ which man led
for _ages_ (Fig. 4) _has thoroughly adapted_ his body _only for such
a life_. Now steam and other forces work for him, and his _muscles_
dwindle; his _lungs_ are seldom fully expanded, and the unused
portions become unsound; he lives in tight houses, and the impure
air makes his _blood_ impure and his _skin_ delicate; he eats _soft
concentrated_ food, and his _teeth_ decay and his too roomy _food
tube_ becomes sluggish. His _nerves and brain_ are fully active and
they become unsound from overwork and impure blood.[3]
[3] It has been prophesied that the future man will be a brownie-like
creature with near-sighted eyes, shrunken body, slim little legs
and arms, large hairless head, toothless gums, a stomach using only
predigested food, muscles suited only to push an electric button
or pull a lever, and mind very active. But this disregards the
indispensable need of a sound mind for a sound body. There cannot even
be a play of emotion without a change in the circulation.
[Illustration: FIG. 4.--PRIMITIVE MAN, showing clothing and weapons of
chase and war.]
=Degeneration of Unused Parts.=--Several facts just stated illustrate
the biological law that _disuse causes degeneration_.
=Man’s Modification of his Environment.=--The energy of the world,
whether of coal, waterfall, oil, forest, or rich soil, has the sun
as its source. _All of these are being destroyed by man_, often
with recklessness and wantonness. The promised land which “flowed
with milk and honey” is now almost a desert. Other examples are
Italy, Carthage, Spain. The destruction of forests causes floods
which wash away the soil. _It is estimated that there are only one
fourth as many song birds in the United States as there were fifteen
years ago._ Insects and weeds or deserts replace rich soil, noble
quadrupeds, singing birds, and stately trees. Many farmers, however,
preserve the fertility of the soil.
=To the erect posture= is due man’s free use of his hands and
the _coöperation of hands and senses_. This has given man his
intellectual development. The erect position has given greater
freedom to the chest. _Man uses fewer organs of locomotion than
any other animal._ The opossum has two hands, but they are on
the hind limbs. The ape has four hands, but must use them all in
locomotion. (What is a hand?) The erect position, however, makes
_spinal deformity_ easier to acquire, and the _whole weight being
upon one hip_ at each step man is liable to hip-joint diseases.
In the horizontal trunk the organs lie one behind another; in man
they _lie one upon another_, and are more liable to _crowding_ and
_displacement_. The prone position in sickness helps to restore
them. Large blood vessels at neck, armpits, and groins, which occupy
protected positions in quadrupeds, are _held to the front and
exposed_ to danger. The _open end_ of the vermiform appendix and
of the windpipe are _upward_ in the erect trunk of man. Valves are
lacking in some vertical veins and present where little needed in
horizontal veins. But the _freedom of the hands_ more than makes up
for all the disadvantages of erectness.
=The Survival of the Fittest.=--_Those who do not work degenerate._
Those who overwork, or work with only a few organs, as the brain and
nerves, degenerate. The workers survive and _increase in numbers_,
the idle perish and _leave few descendants_.
=What rate of adjustment to new environment= is possible for man? This
has not been ascertained; _it is probably much slower than has been
generally imagined_. The natives of Tasmania, New Zealand, and many
of the Pacific Islands became _extinct in less than a century_ after
adopting clothing and copying other habits from Europeans. Life in
the country in civilized lands differs less from the environment of
primitive man than does life in cities. Cities have been likened to
the lion’s cave in the fable, to which many tracks led, but from which
none led. _The care of health in cities_ is now making rapid strides
along the biological basis of purer air, more open space, less noise,
simple food, and pure water. Biology, by supplying as a standard
the conditions which molded man’s body for ages, furnishes a simple
and sure basis for hygiene. To mention one instance among many, man
blundered for centuries in attempting the cure of consumption, and
well-nigh gave up in despair. Yet it has recently been shown that if
the sufferer returns only in a measure to the open-air habits of his
remote ancestors, tuberculosis is one of the most curable of diseases.
The biological guide to health is surer and simpler than tinkering with
drugs, fussing with dietetics, and avoiding exposure. _Man is of all
animals least thoroughly adjusted to his environment_, because of his
continual and rapid progress. _Disease_ may be defined as the _process
by which the body adapts_, or attempts to adapt, _itself to_ so sudden
a _change of environment_ that some organ has failed to work in harmony
with the others. By disease the body comes into adjustment with the new
condition, or attempts to do so.
=Protoplasm.=--The life and growth of man’s body, as the life and
growth of all animals and plants, depend upon the activity of the
living substance called _protoplasm_, as manifested in minute bodies
called _cells_. In fact, protoplasm cannot exist outside of cells. The
cells of the human body and their relation to the body as a whole will
next be considered.
[Illustration: FIG. 5.--AN AMEBA, highly magnified. _nu_, nucleus;
_psd_, false foot.]
=The Ameba.=--Of all the animal kingdom, the _minute creatures that
can be seen only with a microscope_ are most different from man. One
of the most interesting of these is the _a-me′ba_ (Fig. 5; spelled
also _amœba_, see Animal Biology, Chap. II). _A thousand of them
placed in a row would hardly reach an inch._ Some may doubt whether
the ameba is a complete animal. Study the figures of it, and no head,
or arms, or legs, or mouth can be found. It appears, when still, to
be merely a _lump of jelly_. But the ameba can _push out any part
of its body as a foot_, and move slowly by rolling its body into
the foot. _It can put out any part of its body as an arm_, and take
in a speck of food; or, if the food happens to be near, the ameba
can _make a mouth in any part of its body_, and swallow the food by
closing around it (Animal Biology, Fig. 12). The ameba has no lungs,
but _breathes with all the surface of its body_. Any part of its body
can do anything that another part can do. When the ameba grows to a
certain size, it multiplies by squeezing together near the middle
(Animal Biology, Fig. 13) _and dividing into two parts_. Amebas have
not been observed to die of old age; starvation and accident aside,
they are immortal.
[Illustration: FIG. 6.--A WHITE BLOOD CELL, magnified; forms noticed at
intervals of one minute.]
=The Ameba and Man Compared.=--The microscope shows us that the skin,
the muscles, the blood,--in fact, _all parts of the body_,--_contain
numberless small parts called cells_. These cells are continually
changing with the activities of the body. One of the most interesting
kinds of cells we shall find to be the _white blood cells_, or
corpuscles. One is shown in Fig. 6, with the changes that it had
undergone at intervals of one minute. The thought readily occurs that
_these cells, although part of man’s body, resemble the ameba_ that
lives an independent life. A man or a horse or a fish--in fact any
animal not a protozoan--has something of the nature of a colony, or
collection, of one-celled animals. We are now prepared to understand
a little as to how the body grows, and how a cut in the skin is
repaired. _The cells take the nourishment brought by the blood, use
it, and grow and multiply like the ameba._ Thus new tissue is formed.
All animals and vegetables--that is to say, all living things--are
made of cells.
[Illustration: FIG. 7.--DIAGRAM OF A CELL.
_p_, protoplasm; _n_, nucleus; _n′_, nucleolus.]
=A living cell= _always contains a still smaller body called a_
=nucleus= (Fig. 7). There is sometimes a small dot in the nucleus,
called the _nucleolus_. _The main body of the cell consists of the
living substance called_ =protoplasm=, _containing nitrogen_. Usually,
but not always, there is a wall surrounding the cell, called the _cell
wall_. Workers with the microscope found long ago that animals and
plants are constructed of little chambers which they called cells.
It was found later that the soft contents in the little chambers is
of more importance than the walls which the protoplasm builds around
itself. A living cell is not like a cell in a honeycomb or a prison. In
biology we define a cell as _a bit of protoplasm containing a nucleus_.
No smaller part of living matter can live alone. The protoplasm of the
nucleus is called nucleoplasm; the rest of the protoplasm is called
cytoplasm.
[Illustration: FIG. 8.--A CELL (from involuntary muscle), so slender
that it is called a _fiber_.]
A _fiber_ is threadlike, and is either a slender cell (Fig. 8), a
slender row of cells (Fig. 10), or a branch of a cell. A =tissue= is
defined as _a network of fibers or a mass of similar cells serving the
same purpose_, or doing the same work. A _membrane_ is a thin sheetlike
tissue.
=The Nature of the Human Body.=--The human body is _a community of
cells_, and may be compared to a community of people. It is a crowded
community, for all the citizens live side by side as they work. They
are so small that it takes several hundred of them to make a line an
inch long. We should never have suspected the existence of cells had it
not been for the microscope; but now we know that they eat and breathe
and work and divide into young cells which take the place of the old
ones.
A child that is born in a =community of people= may become a railroad
man and carry food and other freight from place to place; so, in
the great =community of cells= (see Fig. 9) making up the human
body, _the red blood cells, like the railroad man_, are employed
in carrying material from place to place. But the community is
old-fashioned, for the citizens build canals instead of railroads
for their commerce (see Fig. 84). Just as a child may grow up to
be a _farmer_ and aid in the conversion of crude soil into things
suitable for the use of man, so _the digestive cells_ take the food
we eat and change it into material with which the cells can build
tissue. Some of the citizens of a community must, at times, take _the
part of soldiers_ and policemen, and protect the community against
the attacks of enemies. _The white blood cells_, already referred
to, may be called the soldiers; for they go to any part attacked by
injurious germs, a particle of poison, or other enemy, and try to
destroy the enemies by devouring or digesting them. At other times
they help to repair a break in the skin. If a splinter gets into the
skin, the white blood cells form a white pus around the splinter
and remove it. In fact, the white blood cell has been referred to
as a kind of _Jack-at-all-trades_. In the human community there are
certain persons who reach the positions of _teachers, lawmakers,
and governors_; they instruct and direct the other members of the
community. Just so, in the community of cells, there are certain
cells called _nerve cells_ (see Fig. 11) that have the duty of
governing and directing the other cells. The nerve cells are most
abundant in the brain. Large cities must have _scavengers_. Likewise
in the human body, a community composed of millions of cells, there
are certain _cells in the skin and the kidneys_ which have this duty.
They are continually removing impurities from the body.[4]
[4] From Coleman’s “Hygienic Physiology,” The Macmillan Co., N.Y.
[Illustration: FIG. 9.--VARIOUS CELLS of the body. (Jegi.) Tiny
citizens of the bodily community.]
=Division of Labor.=--There is a great advantage in each cell of
the human body _having its special work_, instead of having to do
_everything for itself_, as each ameba cell must do. _Under this system
each cell can do its own work better than a cell of any other kind
can do it._ Among wild tribes there is very little division of labor.
Each man makes his own weapons, each knows how to weave coarse cloth,
how to cook, how to farm, etc. Savages do not have as good weapons
as do people who leave the making of weapons to certain men whose
special business it is. What kind of pocketknives or pencils do you
think the boys of this country would have if each boy had to make his
own pocketknife or pencil? What kind of scissors and thread would the
girls have if each girl had to make them herself? Our muscle cells
can contract better than the ameba; the cells in the lungs can absorb
oxygen better than the ameba. We have just as great an advantage in
digestion, feeling, and other processes; for the ameba eats without
a mouth, digests without a stomach, feels without nerves, breathes
without lungs, and moves without muscles. Division of labor between the
sexes also occurs among the higher animals. Those who desire that man
and woman should have the same education and work would violate the
biological law of “progress by specialization,” which could only cause
race degeneration.
A part of the body which is somewhat distinct from surrounding parts,
and has special work to do, is called an =organ=; the special work
which the organ does is called its =function=. The eye is the organ of
sight. The skin is an organ; its function is to protect the body. This
book will treat of (1) the structure, appearance, and position of each
organ, or =anatomy=; (2) the function of each organ, or =physiology=;
(3) the conditions of health for each organ, or =hygiene=; (4) the
conditions under which each organ worked in the primitive life of the
race; (5) the effects of change of environment; (6) the anatomy of
man compared with the lower animals. (5) belongs to the science of
=Ecology=. These sciences are parts of the science of =Biology=.
[Illustration: FIG. 10.--THREE MUSCLE FIBERS from the heart (showing
the nuclei of six cells).]
[Illustration: FIG. 11.--NERVE CELLS, showing their branches
interlacing.]
=The Tissues.=--_As the organs have different functions, they must have
different structures that they may be adapted to their work._ Just as a
house must have brick for the chimney, shingles for the roof, and nails
to hold the timbers and other parts together, so the body has various
tissues to serve different purposes. The bones must not be constructed
like the muscles, and the muscles cannot be like the skin. The chief
work of the cells is to construct the tissues and repair them. During
life changes are constantly going on. Careful little workmen are
keeping watch over every part of the body; thrifty little builders are
busy in repairing and restoring. No sooner is one particle removed
than another takes its place. In one direction the cells, acting as
undertakers, are hurrying away matter which is dead; in the other
direction the unseen builders are filling the vacant places with matter
that is living.
=The Seven Tissues.=--There are seven kinds of tissues. Two of them,
the muscular and nervous tissues, are called the _master tissues_,
since they control and expend the energies of the body. The other
five tissues are called the _supporting tissues_, since they supply
the energy to the master tissues, support them in place, nourish and
protect them.
=The Master Tissues.=--The =muscular tissue= consists chiefly of rows
of cells placed end to end (Fig. 10). These cells have the remarkable
property of becoming broader and shorter when stimulated by impulses
from nerve cells.
[Illustration: FIG. 12.--CONNECTIVE TISSUE CELLS, removed from among
the fibers of Fig. 13.
_n_, _c_, nucleus; _p_, branches.]
The =nerve tissue= consists of cells with long, spiderlike branches
(Fig. 11). Some nerve cells have branches several feet long, so long
that they go from the backbone to the foot. The branches are called
_nerve fibers_ (Fig. 142). Nerve fibers which carry impulses _to_ the
nerve cells are called _sensory fibers_. The nerve fibers which carry
impulses _from_ the nerve cells are called _motor fibers_. The organs
are set to work by impulses through the motor fibers. Besides these two
master tissues there are five =supporting tissues=.
[Illustration: FIG. 13.--CONNECTIVE TISSUE FIBERS.
_a_, _b_, bundles of white fibers; _c_, a yellow fiber.]
=Connective tissue=, like all other tissues, _contains cells_ (see
Fig. 12), but it consists chiefly of fine fibers. These fibers are of
two kinds,--very fine _white fibers which are inelastic_, and larger
_yellow fibers which are very elastic_ (see Fig. 13). Connective tissue
is found in every organ, binding together the other tissues and cells.
It is interwoven among the muscle cells, and the tendons at the ends
of the muscles are composed almost wholly of it. If every other tissue
were removed, the connective tissue would still give a perfect model of
all the organs. How abundant this tissue is in the skin may be known
from the fact that leather consists entirely of it.
=Fatty (Adipose) Tissue.=--Fatty tissue is formed by _the deposit of
oil in connective tissue cells_ (see Fig. 14). Fat is held in meshes
of connective tissue fibers. That fatty tissue consists not alone
of fat, but of fibers also, is shown when hog fat is rendered into
lard, certain tough parts called “cracklings” being left. What is the
difference between beef fat and tallow?
[Illustration: FIG. 14.--FATTY TISSUE. Five fat cells, held in bundles
of connective tissue fibers.
_a_ is a large oil drop; _m_, cell wall; nucleus (_n_) and protoplasm
(_p_) have been pushed aside by oil drop (_a_).]
=Epithelial tissue= consists of one or more _layers of distinct cells
packed close together_ (see Fig. 15). It contains no connective tissue
or other fibers, and is the simplest of the tissues. Epithelial
tissue forms the outer layer of the skin, called the _epidermis_, and
the mucous membrane lining the interior of the body. It contains no
blood vessels, the _epithelial cells obtaining their nourishment from
the watery portion_ of the blood which soaks through the underlying
tissues. Epithelial cells are usually transparent; for instance, the
blood is visible beneath the mucous membrane of the lips. The finger
nails are made of epithelial cells, and they are nearly transparent.
[Illustration: FIG. 15.--EPITHELIAL TISSUE (epidermis of skin,
magnified).]
[Illustration: FIG. 16.--EPITHELIAL TISSUE; cells forming two glands in
wall of stomach.]
[Illustration: FIG. 17.--SIX GLAND CELLS: at left, shrunken after
activity; at right, rested, full of granules.]
There are _two classes_ of epithelial cells; one class forms
_protective coverings_ (Fig. 15); the _other class_ forms the lining
of =glands= (Fig. 16). Glands are cavities whose lining of epithelial
cells (Fig. 17) form either useful fluids called _secretions_ to aid
the body in its work, or harmful fluids called _excretions_ to be cast
out, or excreted. Most glands empty their fluids through tubes called
_ducts_.
=Cartilag′inous tissue= is tough, yet elastic. Cartilage or gristle
may be readily felt in the ears, the windpipe, and the lower half of
the nose. This tissue consists of _cartilage cells embedded in an
intercellular substance through which run connective tissue fibers_
(see Fig. 18). If yellow fibers predominate, the cartilage is yellow
and very elastic, as in the ear; if white fibers predominate, it is
white and less elastic, as in the pads of gristle between the bones
of the spinal column. Cartilage is to prevent jars, and, in movable
joints, to lessen friction.
=Bony (Osseous) Tissue.=--Solid bone is seen under the microscope to
contain many minute cavities (Fig. 19). _In these cavities the bone
cells lie_ self-imprisoned in walls of stone; for these cells have
formed the bone by depositing limestone and phosphate of lime around
themselves. There are _minute canals_ (3, Fig. 19), however, through
which nourishment comes to the cells. The watery portion of the blood
passes through these small canals from the blood vessels that flow
through _the larger canals_ (1, Fig. 19). Bone cells may live for
years, although some of the other cells of the body live only a few
hours.
[Illustration: FIG. 18.--CARTILAGINOUS TISSUE. A thin slice highly
magnified.
_a_, _b_, _c_, groups of cells; _m_, intercellular substance.]
New cells to repair the tissues are formed by subdivision of the
cells, as with the ameba. Unlike protozoans, many-celled animals
are mortal because the outer cells prevent the deeper cells from
purifying themselves perfectly and obtaining pure food and oxygen.
Even the arteries of an old man become hardened by the deposit of
mineral matter which the body has been unable to excrete.
[Illustration: FIG. 19.--BONY TISSUE. Thin slice across bone, as viewed
through microscope.
Larger blood tubes pass through the large holes (1); the cavities
containing bone cells lie in circles, and are connected by fine tubes
(3) with the larger tubes.]
=The body is kept alive and warm= by burning, or oxidation. One fifth
of the air is oxygen gas. We breathe it during every minute of our
existence. It is carried by the blood to all the tissues. Not one of
the cells could work without oxygen. Without it the body would soon be
cold and dead, for oxygen keeps the body alive and warm by uniting in
the cells with sugar, fat, and all other substances in the body except
water and salt. Oxygen burns or consumes the substances with which it
unites, and the process is called _oxidation_. Hence the cells have to
be continually growing and multiplying to repair the tissue and replace
the material used up by oxidation. Sugar and flour and fat oxidize,
or burn, outside of the body, as well as in it, as can be proved by
throwing them into a fire. Water and salt are two foods that do not
burn. Hence they can furnish no heat or energy to the body. Water puts
out a fire instead of helping it, and so does salt. Throw salt into a
fire or on a stove; it will pop like sand, but will not burn.
The cells need the oxygen of fresh air; they need food for the oxygen
to unite with, but _they are injured by many substances called
poisons_. Arsenic destroys the red blood cells. Strychnine attacks the
nerve cells in the spinal cord. Alcohol attacks the epithelial cells
lining the stomach and, when it is absorbed, attacks the nerve cells
and other cells. Morphine attacks the nerve cells.
WRITTEN EXERCISES.--Draw a series of seven pictures to show the seven
tissues (Figs. 10, 14, 15, 18, 19). Write the “Autobiography” of a
White Blood Cell (see also pages 59 and 68). The Rewards of Caring
for the Health. Health and the Disposition. Which is more important,
a Thorough Knowledge of Geography or of Physiology? Five Things which
people Value above Health (and lose health to obtain). The Blessings
that follow Good Health. The Tissues Compared (function, proportion
of cells, intercellular material and fibers, activity, rate of
change).
See also pages 50, 116. Pupils should choose their own subjects.
CHAPTER II
THE SKIN
NOTE TO TEACHER.--The experiments should be assigned in turn to the
pupils as each chapter is reached: _e.g._ this set of 13 will leave
3 pupils in a class of 39 to stand responsible for each experiment.
Each pupil should do the work separately and credit may be given for
the best results. Encourage (or require) each pupil to try every
experiment and record them in a note book.
_Experiment 1._ (At home or in class.) =Albinism.=--Study a white
rabbit as an example of albinism. Does albinism affect only the skin?
What evidence that its blood is of normal color?
_Experiment 2._ =Use of Hairs on the Skin.=--Let one pupil rest his
hand upon the desk behind him while another touches a hair on his
hand with a pencil. He should speak at the moment, if it is felt.
Do the hairs increase the sensitiveness of the skin? What was their
use with primitive man? Are the hands of all your acquaintances
equally hairy? Are the hairs to be classed as rudimentary? Will they
disappear? Will the race become baldheaded?
_Experiment 3._ (Home or school.) =Invisible Perspiration.=--Hold
a piece of cold glass near the hand or place the cheek near a cold
window pane and notice for evidence of moisture. Its source?
_Experiment 4._--=Effect of Evaporation on Temperature.=--Read a
thermometer and cover its bulb with a moist cloth. Read again after
twenty minutes. Repeat experiment in breeze.
_Experiment 5._ Moisten one hand and allow it to dry. Touch the other
hand with it. Explain result.
_Experiment 6._ =Absorbing Power of Fabrics.=--Wet the hands and dry
them upon a piece of cotton cloth. Repeat with woolen, linen, and
silk. Arrange in list according to readiness in absorbing water.
_Experiment 7._ =Rates of Drying.=--Immerse the cloths in water and
hang them up to dry. Test their rates of drying with dry powder or by
touch.
_Experiment 8._ =Test Looseness of Weave= of above cloths by
measuring the distance pieces of equal length will stretch.
[Illustration: COLORED FIGURE 1.--SECTION OF SKIN (diagram, enlarged 25
times). On the left the connective tissue fibers of the true skin are
shown.
In cutis (_c_), or dermis, find capillaries, nerve fibers, fat cells,
_two_ sweat glands and ducts, _four_ oil glands (two in section), _two_
hairs, _three_ nerve papillæ, _five_ papillae containing capillaries,
_two_ muscles for erecting hairs. In epidermis find flat cells, round
cells, and pigment cells.
FIG. 2.--WHERE THE FOOD IS ABSORBED (villus of intestine).
FIG. 3.--WHERE THE FOOD IS USED (cells with lymph spaces).
FIG. 4.--IDEAL SECTION OF MAMMAL.
Compare with organs of man (colored Fig. 6).
_j_, _j_, jaws; _ol_, nerve of smell; _op_, nerve of sight; _b_, brain;
_t_, tongue; _ep_, epiglottis; _oe_, gullet; _th_, thymus gland; _lg_,
lung; _h_, heart; _l_, liver; _g_, stomach; _s_, spleen; _p_, pancreas;
_k_, kidney; _d_, diaphragm; _m_, muscle; _u_, bladder; _ch_, spinal
cord; _v_, vertebræ.]
_Experiment 9._ =Does Cotton or Wool protect better from Radiant
Heat?=--Lay a thermometer in the sun for ten minutes, first covering
it with a woolen cloth. Note change in reading. After it regains
first reading, repeat, covering it with a cotton cloth of same weight
and texture. Conclusion? Expose wrists or arms to sun for five
minutes, one protected by the cotton, the other by the wool. Result?
Conclusion?
_Experiment 10._ =Rates of Heat Absorption and Radiation by Different
Colors.=--Expose thermometer to sunlight, covered successively by
pieces of cloth of same thickness, material, and texture. Use black,
blue, red, yellow, and white cloth. Note rise of temperature for
equal times in each case; also the fall of temperature for equal
times after removal to shade.
_Experiment 11._ =Effects of Dry Powders.=--Prepare two squares from
the same piece of leather (_e.g._ an old shoe). Moisten them both,
and apply face powder to one. Which dries more quickly? Repeat after
oiling them. Powder a portion of the face or arm daily for a week and
compare with the clean portion.
_Experiment 12._ =Dissect the kidney= of an ox or sheep, making out
the parts mentioned in the text, p. 26.
_Experiment 13._ (In class.) =Emergency Drill.=--Have one pupil wet
an imaginary burn on the arm of another, treat it with flour or soda,
and bandage. (See text.)
=The Skin has Two Layers.=--The outer layer is called the _epidermis_;
it is _thinner, more transparent, and less elastic_ than the inner
layer, or _dermis_. The epidermis is composed of epithelial cells
packed close together (see colored Fig. 1).
=The dermis=, or inner layer, is a closely woven sheet of _connective
tissue_ (colored Fig. 1) containing a great number of _sweat_ and
_oil glands_, _roots of hairs_, _blood vessels_, _absorbent vessels_
(lymphatics), and _nerves_ (colored Fig. 1). The dermis is sometimes
called the true skin because it is of greater importance than the
epidermis. It is united loosely to the underlying organs by a layer
of connective tissue. It is in this layer that fat is stored. The
upper surface of the dermis rises into a multitude of projections (see
colored Fig. 1) called _papil′læ_ (singular, papilla). The epidermis
fits closely over them and completely levels up the spaces between them
except on the palms and the soles. Here the papillæ are in rows, and
there is a fine ridge in the skin above each row of papillæ (Fig. 24).
In the papillæ are small loops of blood vessels and sometimes a nerve
fiber (colored Fig. 1).
[Illustration: FIG. 20.--EPIDERMIS OF ETHIOPIAN.]
[Illustration: FIG. 21.--EPIDERMIS OF CAUCASIAN.]
=The epidermis= _is composed of a mass of cells_ held together by a
cement resembling the white of an egg. The cells near the surface are
hard and flattened; those deeper down near the dermis are round and
soft (see Fig. 21). These cells are living cells. They are kept alive
by the nourishment in the watery portion of the blood which soaks
through from the blood tubes in the neighboring papillæ. Hence these
cells are growing cells; they subdivide when they reach a certain
size, and replace those wearing away at the surface, thus constantly
repairing the epidermis. The dry outer cells wear away rapidly. They
have no nuclei and are dead cells. The new cells forming beneath push
them so far away from the dermis that nourishment no longer reaches
them, and they die.
=Pigment.=--The cells in the lower layers of the epidermis contain
grains of coloring matter, or pigment. All other cells of the
epidermis are transparent; the pigment has the function of absorbing
and arresting light. Albinos or animals entirely without pigment have
pallid skins and pink eyes (Exp. 1).
=Immigrants from a Cloudy to a Sunny Climate. Adaptation.=--The cells
of the deeper tissues can readily be exhausted by the stimulation
of too much light. The sunnier the climate, the greater the need of
pigment; hence the dark skin of the negro and the blonde skin and
hair of the Norwegian. European immigrants to sunny America will
grow darker. The Indian’s skin is better suited to our climate than
is a fair skin. Brunettes have a better chance for adaptation than
blondes. The American type when developed will doubtless be brunette.
=The hair= grows from a pit or follicle (Fig. 22). _Blood vessels and a
nerve fiber go to the root_ or bulb from which a hair grows. The hair
will grow until this papilla, or bulb, is destroyed (Exp. 2).
[Illustration: FIG. 22.--DEVELOPMENT OF A HAIR AND TWO OIL GLANDS.]
=Adaptation of the scalp to a tight warm covering= is accomplished
through the shedding of the hair rendered useless by the covering.
It is impossible to stop the growth of superfluous hair unless the
hair papillæ are destroyed with an electric needle, such is the
vitality of hair; yet many men, by overheating the head and cutting
off the circulation with tight hats, destroy much of the hair before
reaching middle age. The health of the hair can be restored and its
loss be stopped by going bareheaded except in the hot sun or in
extremely cold weather. This frees the circulation; cold air and
light stimulate the cells of the scalp. Some men wear hats, even at
night in summer. The brain needs the protection of the hair. Beard
protects the larynx or voice box, which is large and exposed in man.
It was also a protection in hunting wild beasts and in war. Compare
mane of lion, not possessed by lioness. “Goose-flesh” after a cold
bath is caused by the contraction of small muscles (colored Fig. 1),
raising the now tiny hairs in an absurdly useless effort to keep the
body warm.
=The nails= are dense, thick plates of epidermis growing from a number
of papillæ situated in a groove, or fold, of the skin; there are many
fine papillæ along the bed from which the nail grows. Since it grows
from its under side as well as from the little fold of skin at its
root, the nail is thicker at the end than near the root.
[Illustration: FIG. 23.--_A_, DEVELOPMENT OF SWEAT GLAND; _B_, SWEAT
TUBE DEVELOPED.]
The =oil glands= empty into the hair follicles (colored Fig. 1). They
form an oil from the blood that _keeps the hair glossy and the surface
of the skin soft and flexible_ by preventing excessive drying. Hair oil
should never be used upon the hair, as the oil soon becomes rancid, and
besides causes dust and dirt to stick to the hair.
=The sweat glands= (Fig. 23), like the hair bulbs, are deep in the
lowest part of the dermis. _A sweat gland has the form, of a tube
coiled into a ball_ (colored Fig. 1). This tube continues as a duct
through the two layers of skin, and its opening at the surface is
called a _pore_ (Fig. 24). The perspiration evaporates as fast as it
flows out through the pores, if the secretion is slow; but if poured
out rapidly, it gathers into drops (Exp. 3). The perspiration is
chiefly water, containing in solution several salts, including common
salt and a trace of a white, crystalline substance called _urea_. The
material for the perspiration is furnished by the blood flowing around
the gland in a network of fine tubes. The amount of the perspiration is
controlled in two ways: by _nerves that regulate the activity of the
epithelial_ cells lining the gland, and by nerves that _regulate the
size of the blood vessels_ supplying the gland (Fig. 25).
[Illustration: FIG. 24.--PORES on ridges in palm of hand.]
THOUGHT QUESTIONS.--=Freckles, Warts, Moles, Scars, Proud Flesh,
Pimples, Blackheads.= Use these names in the proper places below:--
A rough prominence formed by several papillæ growing through the
epidermis at a weak spot and enlarging is called a ____. Small
patches of pigment developing on the hands and face from much
exposure to the sun are called ____. The growth of exposed dermis
sprouting through an opening in the epidermis due to accident is
called ____. (This should be scraped off and cauterized to aid the
epidermis to grow over it again.) Sometimes a cut heals in such a way
that no epidermis and therefore no pigment cells cover the place of
injury, which is occupied only by white fibrous tissue (cicatricial
tissue) of the true skin. In this case the mark left is called a
cicatrice or ____. If pores or the openings of oil glands become
clogged, but not enlarged, little swellings called ____ may result.
An enlarged pore filled with oil and dirt is called a ____. A spot
present since birth, dark with pigment, and often containing hairs
and blood vessels, is called a ____.
=Regulation of Temperature.=--As is well known, rapid running or
violent exercise of any kind causes profuse perspiration. The sweat
glands are connected with the brain by means of nerves, and when the
body has too much heat, a _nerve impulse from the lowest part of the
brain causes the sweat glands to form sweat more rapidly_. Heat and
exercise may cause the activity of the sweat glands to increase to
forty times the usual rate. The evaporation of the sweat cools the
body, for a large amount of heat is required to evaporate a small
amount of water (Exp. 4 and 5). This is shown by the cooling effect of
sprinkling water on the floor on a warm day. By fanning we hasten the
cooling of the body (Exp. 4).
Exercise tends to heat the body, but it also _causes us to breathe
faster and causes much blood to flow through the skin_. Both of these
effects aid in cooling the body, for the cool air is drawn into the
lungs, becomes warm, and takes away heat when it leaves; and the warm
blood flowing in the skin loses some of its heat to the cool air in
contact with the skin.
=Effects of Alcohol upon the Skin.=--The more blood goes to the skin,
the more blood is cooled. The body as a whole may be cooler, but _we
feel warmer when there is more blood in the skin because of the effect
of the warm blood upon the nerves_ of temperature. There are no nerves
for perceiving temperature except in the skin and mucous membrane,
and the body has practically no sensation of heat or cold except from
the skin or mucous membrane. That alcoholic drinks make the skin
red is commonly noticed. Often _the skin is flushed_ by one drink;
the bloodshot eyes and purple nose of the toper are the results of
habitual use. Can you explain why alcohol brings a _deceptive feeling_
of warmth? Why does alcohol increase the danger of freezing during
exposure in very cold weather? During the chill which precedes a fever,
the body (except the skin) is really warmer than usual.
Exercise will relieve internal congestion and send the blood to the
skin better than alcohol. This is the effect sought by sedentary people
who use it to replace exercise. The long and sad experience of the
race with alcohol proves that the attempt to adapt the body to its use
should be given up.
THOUGHT QUESTIONS. =The Functions of the Skin.=--=1.= State a fact
which shows that the skin is a protection; gives off offensive
substances; regulates the temperature. =2.= What is lacking in the
skin when it cracks or chaps? Why does this occur more often in cold
weather? When the hands are bathed with great frequency?
=Effects of Indoor and Outdoor Life.=--_Those who live much out
of doors, exposed to sunlight and pure, cold air, are robust and
hardy_; while those whose occupations keep them constantly indoors,
especially if no physical labor is necessary, show by their pale
skins, their fat and flabby, or their thin and emaciated bodies, the
weakening effect of such a life. We are descended from ancestors who
lived in the open air, and it is impossible for a human being to live
much indoors without degeneration of the body and shortening of life.
=A Well-trained Skin.=--We hear a great deal about training the
muscles, the brain, the eye, the hand; yet we may fail to realize
that the skin also can be trained and its powers developed, or it
can be allowed to become weak and powerless. Soundness of the skin
is as essential to health as soundness of any other organ. A rosy
color indicates good health because of a well-balanced circulation.
Paleness often means internal congestion and great liability to
indigestion, colds, etc. Hence we think a rosy skin beautiful and a
pale skin ugly. With the skin in a healthy condition, the danger of
taking most diseases is removed.
=Characteristics of a Vigorous Skin.=--A person who readily takes
cold, who is fearful of drafts of air at all times, has a weak skin.
To one who has a healthy skin drafts are dangerous only when the
skin is moist with perspiration, and the body is inactive; cold
drafts may then do harm. Cold air and cold water are the best means
of toughening a tender skin. _A bath is to the skin what gymnastic
exercises are to the muscles._ The muscle fibers in the walls of the
blood vessels and the nerves controlling them need exercise as well
as the rest of the body (Fig. 25).
[Illustration: FIG. 25.--BLOOD VESSELS, with the VASO-MOTOR NERVES
which accompany and control them.]
=Importance of Bathing.=--_If we followed the outdoor life and wore
the scanty clothing of savage races, the rains, the cool air, and the
sunlight would keep our skins vigorous and sound._ But want of exercise
to induce perspiration allows the sweat glands to become stopped up.
The wearing of _clothes_ is a very uncleanly custom. Clothes make the
skin inactive, yet confine the impurities which the weakened skin may
still be able to excrete. Thick and heavy clothing and overheated rooms
prevent the nerves from being stimulated by cold air and sunlight. _The
best way to counteract these weakening conditions is by frequent cool
or cold baths._ An _air bath_, which consists of exposing the bare skin
to the air for half an hour or more before dressing in the morning, may
take the place of a cold bath. Even the lower animals bathe: birds,
dogs, and many lower animals bathe in the rivers. An elephant sometimes
takes a bath by showering water over his back with his trunk.
=Treatment of Burns.=--_Wet_ the burn with a little water and sprinkle
common _baking soda_ or flour thickly on it. Bind with a narrow
_bandage_. For deeper burns soak a small square of cloth in a strong
solution of baking soda, bandage it on wound, and keep it wet with the
solution. Olive, cotton seed, and linseed _oils_ are excellent for
burns (Exp. 13).
=Hygiene of Bathing.=--A bath should not be taken within an hour after
a meal. _Cold baths_ (1) should never be taken in a cold room nor
when the skin is cold; (2) are more beneficial in summer and in warm
climates, but are necessary in winter for those who live in overheated
houses or dress very warmly; (3) should be followed in winter by
vigorous rubbing and a glowing reaction; (4) should usually not last
longer than one minute in winter. _Warm baths_ (1) are more cleansing
than cold baths; (2) should not be used alone but should always be
followed by a dash of cold water; (3) are better than cold baths if the
body is greatly fatigued; (4) are more beneficial when going to bed
than upon rising.
Cold baths and very hot baths are both _stimulants_ to the nervous
system and cause an expenditure of nervous energy. For one whose
nervous energy is at a very low ebb cold baths may be weakening if
prolonged beyond a few seconds. For one with skin relaxed and body
sluggish from indoor life, cool baths arouse activity, tone up the
body, and may be as beneficial as outdoor exercise in restoring
vigorous health. As with every hygienic measure, each person must find
out by experience what suits him best.
=Clothing= was first employed for ornament. In cold climates it
aids in maintaining the uniform temperature of the body; to it man
owes his distinction of being the most widely distributed of animal
species. Clothing prevents rapid escape of bodily heat by confining
air, a non-conductor of heat, in its meshes. Hence, the effect of
clothing varies with the _weave_; likewise with the tendency of its
fibers _to keep dry_, for if water replaces air in the meshes, the
body loses heat rapidly. For cool clothing the weave should be hard
and tight, for warm clothing it should be soft and loose. The warmth
of clothing is affected more by its weave than by its weight. The
weave may be tested by stretching; the fabric with softest weave
will stretch the most (Exp. 8). _Linen_ makes the coolest of all
clothing because it weaves hard with small meshes; _silk_ ranks next
in coolness. When warmth is desired, linen or _cotton_ garments
should be made of fabrics woven like stockings. Linen and cotton both
absorb water rapidly and dry rapidly (Exp. 6); if _woolen_ did also,
it would make the warmest of all clothing, but it dries so slowly
(Exp. 7) that it cools the body after the activity is over instead
of drying rapidly and, as with linen and cotton, keeping the body
cool during the exertion (Exp. 5). Woolen weaves with the largest air
meshes of all materials; hence its warmth increases perspiration, but
woolen removes perspiration most slowly and tends to relax the skin
if the wearer has an active skin or makes active exertion. Woolen
is best for underclothing during extreme cold only or for persons
who never make such vigorous muscular exertion as to perspire. In
general, cotton or linen is best for underwear. They possess the
added advantages of less cost and of not shrinking out of size and
shape when washed. A mixture of cotton and silk or of cotton and wool
is more durable than either alone. Cotton and linen, unlike woolen,
are not attacked by insect pests.
It is better to depend more upon outer clothing than underclothing
for warmth. In the Gulf states the wearing of woolen outer clothing
indoors during warm weather (which lasts eight months) is unhealthful
and uncleanly because of the perspiration absorbed; this is as absurd
as to wear cotton outer clothing in Northern states during the eight
cold months.
Black clothing absorbs twice, blue almost twice, red and yellow
almost one and a half times, as much heat as white clothing (Exp.
10). Which material protects best from radiant heat? (Exp. 9.)
Because large blood vessels are near the surface at the _neck,
wrists, and ankles_ very thin or no covering at those points aids
greatly in keeping the body cool. High collars, long sleeves, and
high shoes are unhealthful in warm climates and in summer. What
objection to black shoes in summer? Patent leather? Show how women
dress more sensibly in hot weather than men.
The =kidneys= are located on each side of the spinal column in the
“small of the back” and extend slightly above the level of the waist.
They are _bean-shaped organs about four inches long_ (Fig. 26). The
kidneys of a sheep or ox closely resemble those of man. They are
outside of the peritoneum (Fig. 99) and attached to the rear wall of
the abdomen. A large artery (12, colored Fig. 5) goes to each kidney
and divides into many capillaries which surround _tubules_ in the
kidneys (Fig. 27). The secretion, containing nitrogenous impurities of
the blood, is continually being deposited in the tubules, which take
it to a _funnel-shaped cavity_ at the inner edge of the kidney (Fig.
26). From this cavity a white tube called the _ureter_ leads down to a
storage organ in the pelvis called the bladder.
[Illustration: FIG. 26.--SECTION OF KIDNEY.
_RA_, renal artery; _Py_, pyramids surrounding hollow space from which
the ureter (_U_) leads the secretion to the bladder.]
=Changes in Blood in the Kidneys.=--The water holding the nitrogenous
waste varies in amount with the amount of water drunk and with the
activity of the skin, being less in summer when the perspiration is
great. The lungs aid the skin and kidneys in disposing of superfluous
moisture. The kidneys have almost the entire responsibility of
relieving the body of certain _mineral salts_ and a white crystalline
solid called _urea_. This is very injurious if retained, causing
headaches, rheumatism, and other troubles.
[Illustration: FIG. 27.--PLAN OF A URINARY TUBULE, _Tb_, with artery
_A_, and _V_ in _pV_.]
THOUGHT QUESTIONS. =Hygiene of the Skin.=--=1.= What kind of a scar
is not affected by freckles or tan? =2.= Can a scar on a negro
be white? =3.= Does a scar on a child grow in size? =4.= Why is
heat most oppressive in moist weather? =5.= How do you account for
the shape and location of the usual bald spot? =6.= How does the
wearing away of the outer cells of the epidermis contribute to the
cleanliness of the body? =7.= Why does the palm of the hand absorb
water more rapidly than the back of the hand? =8.= Is it more
necessary for mental workers to bathe often or change their clothes
often? For physical workers? =9.= Is cotton or woolen clothing more
liable to stretch or shrink out of shape or size? To catch fire? To
make the skin clammy with moisture? To cost more? To be eaten by
moths?
[Illustration: FIG. 28.--THE SKELETON.]
CHAPTER III
THE SKELETON
_Experiment 1._ (At home.) =Is the Arch of the Foot Elastic?=--Wet
the foot in a basin of water and, while sitting, place the foot flat
upon a piece of paper. Draw the outline of the track. Repeat, but
stand with your whole weight upon the foot. Draw track. Conclusion?
(Take sketches to school. Which sketch shows the flattest foot?)
Devise a method for measuring the length of the foot with and without
the weight of the body upon it. What difference? Conclusion?
_Experiment 2._ =Composition of Bone.=--Place a bone in a hot fire
and let it remain for three or four hours. It will keep its shape
however long you burn it; but unless you handle it carefully when you
take it out, it will crumble to pieces. If not thoroughly burned, the
bone will be black from the carbon of the animal matter still left in
it. _Experiment 3._ Obtain a slender bone like the rib of a hog or
the leg bone of a fowl, and put the raw bone into a vessel containing
strong vinegar or two ounces of muriatic acid and a pint of water.
Leave it there for four days. When the bone is taken out, it can be
tied into a knot. The acid may be washed off, and the bone preserved
in a bottle of alcohol or glycerine.
_Experiment 4._ =The Forms of Joints.=--Obtain the disjointed bones
of a fowl or small mammal and place them one at a time in their
sockets and study the fit and motion of the joints.
_Experiment 5._ =Pivot Joints.=--Through what fraction of a circle do
the pivot joints in the forearm and neck allow the hand and head to
rotate?
=Review Questions.=--Where are the bone cells? How does nourishment
reach them? How has the mineral part of the bones been deposited? How
long may bone cells live? Name animals with outside skeletons. Inside
skeletons. No skeleton.
=Forms and Uses of Bones.=--The three chief _uses of bones are
protection, motion, and support_. In order to fulfill these purposes,
the bones must have different sizes, shapes, and positions. The bones
are classed by _shape_, as _long, flat, and irregular_. Those whose
chief use is _to protect are broad and flat_. The bones which _furnish
support are thick and solid_; those designed to _aid in motion are long
and straight_. Including six small bones in the ear, there are two
hundred and six bones in the adult skeleton.
=Gross Structure of Bones.=--The structure of a long bone is shown
in Fig. 29. It has a long, _hollow shaft_ of hard, compact bone, and
_enlarged ends_ composed of spongy bone. The hollow in the shaft is
_filled with yellow marrow_, which is composed of blood vessels and
fat, and aids in nourishing the bone. The long bones are found in the
limbs (Fig. 28). The ribs and other flat bones and the irregular bones
contain no yellow marrow; they are spongy inside, and hard and compact
near the surface. There is a _red marrow_ in the cavities in the spongy
parts of bones (Fig. 29). _New red blood cells are formed in this
marrow._ The bones have a close-clinging, fibrous covering composed of
connective tissue and blood vessels. It is called _periosteum_.
[Illustration: FIG. 29.--FEMUR, sawed lengthwise. The red blood cells
are formed in the red marrow of the spongy part.]
[Illustration: FIG. 30.--FRONT VIEW OF RIGHT FEMUR.]
=Chemical Composition of Bone.=--Experiments (2 and 3) show that the
bones contain a _mineral or earthy substance_, which makes them hard
and stiff, and a certain amount of _animal matter, called gelatine_,
which binds the mineral matter together and makes the bones tough and
somewhat elastic. The fire burned out the animal matter of the first
bone, and the acid dissolved out the mineral matter of the second bone.
_The mineral matter is chiefly lime, and makes up about two thirds
of the weight of the bone._ (Why is more mineral than animal matter
needed?) The animal gelatine is a gristly substance. As the body grows
old, the animal matter of the bones decreases, and they become lighter.
They are more easily broken and do not heal so readily as the bones of
young persons.
=The skeleton is subdivided= into the bones of the _head, trunk, and
limbs_. The bones of the trunk are those of the spine, the chest, the
shoulder blades, collar bone, and hip bones.
[Illustration: FIG. 31.--VERTEBRAL COLUMN. Side view.]
=The spinal or vertebral column= is made up of twenty-six bones (Fig.
31). It is the axis of the human skeleton, to which all other bones are
directly or indirectly attached. Animals with inside skeletons have
this column, and are called vertebrates. Fish, reptiles, birds, beasts,
apes, and man are vertebrates. The spine, as this column is sometimes
called, is not only the main connecting structure and support of the
body, but it forms a channel through which passes the spinal cord.
Fig. 32 shows a =vertebra=, or one of the bones that compose the
column. The three _projecting points or processes_ are for the
attachment of ligaments and muscles. The _main body_ of each vertebra
is for supporting the weight transmitted by the column above. Just
behind this thick body is a _half ring_ (Fig. 32), which with the
half rings on the other vertebrae form the channel for the spinal
cord. Between the vertebrae are thick pads of gristle, or cartilage,
which act as cushions to prevent jars, and by compression allow
bending of the spinal column in all directions.
[Illustration: FIG. 32.--SIDE AND UNDER VIEW OF A VERTEBRA.]
=The Chest= (see Fig. 75).--The twelve pairs of ribs are attached to
the spinal column behind, and extend around toward the front of the
body, somewhat like hoops. The first seven pairs, called _true ribs_,
are attached directly to the flat breastbone, or _sternum_. Each of the
next three pairs, called _false ribs_, is attached to the pair above
it. The last two pairs, called _floating ribs_, are free in front.
=The Shoulder Girdle.=--_The collar bones_ (Fig. 28) can be traced from
the shoulders until they nearly meet on the breastbone at the top of
the chest. The collar bone is shaped like the italic letter _f_; it
helps to form the shoulder joint and holds the shoulder blade out from
the chest that the motions of the arm may be free.
The flat, triangular _shoulder blade_ (Fig. 75) can be felt by reaching
with the right hand over the left shoulder. It spreads over the ribs
like a fan. Its edges can be made out, especially if the shoulder is
moved while it is being felt. The high ridge which runs across the bone
can be felt extending to the top of the shoulder.
=The Pelvic Girdle.=--The edges of the _hip bones_ can be felt at the
sides of the hips (Fig. 28). The hip bones, with the base of the spine,
form a kind of basin called the _pelvis_.
The =skull= (Fig. 33) rocks, or nods, on the top vertebra. It consists
of the cranium, or brain case, and the bones of the face. The shapes
and names of the bones of the skull are shown in Fig. 33.
[Illustration: FIG. 33.--HUMAN SKULL, disjointed.]
=Adaptations of the Skull for Protection.=--Its arched form is best
for resisting pressure and turning aside blows. Like all flat bones,
the skull has a spongy layer of bone between the layers of compact
bone forming the outer and inner surfaces; hence it is elastic and not
easily cracked. The nose, brow, and cheek bones project around the eye
for its protection. The delicate portions of the ear are embedded in
the strongest portion of the skull. The branches of the nerves of smell
end in the lining of the bony nasal chambers. The spinal cord rests
securely in the spinal canal.
The =arms and legs= have bones that closely correspond to each other.
The Latin names of these bones, as well as of all the other bones, are
given in Fig. 28. There are 30 bones in each arm and 30 in each leg
(Fig. 34). Here is a list of the bones of the arm, followed by the
names in brackets of the corresponding leg bones: upper arm bone [thigh
bone], 2 forearm bones [shin bone and splint bone], 8 wrist bones [7
ankle bones], 5 palm bones [5 bones of instep], 14 finger bones [14 toe
bones]. The shin bone is the larger bone between knee and ankle. The
long, slender splint bone and the shin bone are bound side by side.
[Illustration: FIG. 34.--BONES OF ARM AND LEG.]
[Illustration: FIG. 35.--SUTURES OF SKULL.]
=Differences between Arm and Leg.=--There is a saucer-like bone, called
the _kneecap_, embedded in the large ligament which passes over each
knee. There is no such bone in the elbow. There is one less bone in the
ankle than in the wrist, hence there are the same number of bones in
the arm and leg. The shoulder joint is more freely movable than the hip
joint. The fingers are longer and more movable than the toes; the thumb
moves far more freely than the big toe. The instep is much stronger
than the palm; for each instep must support, unaided, the weight of the
whole body at each step, with any other weight that the person may be
carrying. The palm is nearly flat, but the instep is arched to prevent
jars. When the weight of the body is thrown on the foot at each step,
the top of the arch is pressed downward, making the foot longer than
before. The arch springs up when the weight is removed (Exp. 1).
ILLUSTRATED STUDY. =The Shapes of Bones.=--Write _L_, _F_, or _I_
after these names (see Fig. 28, etc.), according as the bones
are long, flat, or irregular: face, cranium, vertebra, hip, rib,
breastbone, collar bone, shoulder blade, upper arm bone, lower arm
bones, wrist, palm, fingers, thigh bone, shin bone, splint bone,
ankle, instep, toes, kneecap.
=Structure of Joints.=--The meeting of two bones forms a joint
(Exp. 4). Some of the joints are immovable. The skull bones join in
zigzag lines called _sutures_, formed by the interlocking of sawlike
projections (Fig. 35). These _immovable_ joints are necessary for the
protection of the brain, which is the most delicate of the organs.
The brain attains almost its full size by the seventh year of life;
its bony case needs to grow very little after that. The joints of the
pelvis are also immovable. All _movable joints have two cartilages_,
and as the bones turn, one cartilage slips over the other. There is an
intermediate class of joints found between the vertebræ and where the
ribs join the breastbone. These joints depend for their motion upon the
flexibility and compressibility of their cartilages. They are called
mixed, or _elastic_, joints, and allow slight motion. _Such a joint has
only one cartilage._
=Kinds of Movable Joints.=--The movable joints are found chiefly
in the limbs. When one end of the bone is rounded and fits into a
cuplike hollow, the joint allows motion in all directions, and is
known as a _ball-and-socket_ joint. The hip joints and shoulder joints
are examples. A _hinge joint_ allows motion in only two (opposite)
directions; for example, the to-and-fro motion of the elbow. A _pivot_
joint allows a rotary motion; examples, the first vertebra on the
second, one bone of forearm upon the other. A gliding joint consists of
several bones that slide upon one another, as at the wrists and ankles.
=The Four Features presented by a Movable Joint= (Fig. 36).--If not
held in place, the bones would slip out of their sockets, hence there
are _ligaments_, or tough bands, to bind the bones together. Sudden
jolts would jar the bones and injure them; shocks are prevented by a
layer of elastic _cartilage_ over the end of each bone. The moving
of one bone over another in bending a joint would wear the bone
with friction unless the cartilages were very smooth and lubricated
with a fluid called the _synovial fluid_. The synovial fluid would
be constantly escaping into the surrounding tissues except for the
collarlike ligament called the _capsule_, which surrounds the joint and
is attached to each bone entirely around the joint (Fig. 36).
[Illustration: FIG. 36.--DIAGRAM OF A JOINT.]
THOUGHT QUESTIONS. =The Kinds of Joints.=--Write _B_, _H_, _G_,
_E_, _P_, or _I_ after these names according to the kind of joint
(ball-and-socket, hinge, gliding, elastic, pivot, immovable): between
bones of skull, head nodding, head turning, vertebræ, lower jaw, ribs
to breastbone (Fig. 75), shoulder, elbow, wrist, fingers, hip, knee,
ankle, toes.
=Growth of Bones.=--The blood vessels pass into the bones from the
periosteum. _If the periosteum is removed, the larger blood vessels
are taken away and the bone beneath it perishes._ If the underlying
bone is removed and the periosteum left, the bone will be replaced.
A curious proof of the active circulation in the bone is furnished
when madder is mixed with the food of pigs. In a few hours the bones
become a darker pink than usual; and if the madder is fed to the
pigs for a few days, their bones become red. A child grows in height
chiefly during three or four months in spring and summer; but its
body broadens and becomes heavier during autumn.
=Health of the Bones.=--It is plain that _a strong and free
circulation of pure blood contributes to the health and strength of
the bones_; good food and pure air make pure blood. Cases of “delayed
union,” or slow mending of broken bones, occur more often with
intemperate than with sober people. This is because the vitality of
the bone cells has been weakened by the use of alcohol. Many surgeons
dislike to operate on an old drunkard.
=Posterior Curvature of the Spine.=--The spine (see Figs. 28, 31)
has two backward curves (opposite chest and hips) and two forward
curves (at loins and neck). The deformity called posterior curvature
is chiefly an exaggeration of the upper posterior curve. Round
shoulders is the slightest, and hunchback the most marked, degree
of this deformity. Causes: 1, _bending over the work_ while either
standing or sitting; 2, _slipping down in the seat_, as in Figure 51;
3, working habitually with the _work low in front_, as reading and
writing at too low a desk (Fig. 49), or bending over while hoeing,
sitting on the floor (Japanese and Chinese); 4, _weak muscles_
in the back; 5, wearing shoes with _high heels_; 6, binding the
ribs down with _tight clothing_; 7, walking with the _head drooped
forward_ or the chest flat; 8, wearing suspenders without a pulley,
or lever, at the back; 9, carrying the hands in the pockets. (Swing
the arms to keep the hands out of the pockets and break the habit);
10, wearing a coat or vest that is tight at the back of the neck.
This deformity is brought about by _stretching the ligaments_ at the
back side of the spine, and by _compressing the cartilages until
they become wedge-shaped_, with the thin part of the wedge in front.
The flexibility of the spine is a great advantage, but it increases
the risk of deformity. One of the most serious evils of posterior
curvature is a flat chest and restricted breathing.
[Illustration: FIG. 37.--INCORRECT POSTURE.]
[Illustration: FIG. 38.--CORRECT POSTURE, but strained and stiff.]
=Lateral Curvature of the Spine.=--A perfect spine curves to neither
side (Fig. 47), but is perfectly erect. The least habitual lateral
curvature is deformity. Causes: 1, writing at a _desk that is too
high_; 2, habitually carrying a book, satchel, or other _weight in
the same hand_; 3, carrying the _head on one side_ (Fig. 46); 4,
habitually standing with the weight on the same foot; 5, a certain
defect of vision (astigmatism, Chap. IX).
=To overcome Spinal Deformities.=--The work, or the manner of doing
the work, should be so changed as _to give extra labor to the
neglected muscles_. Avoid the habits mentioned above as causing
deformity. Sit and stand in the manner described in the next
paragraph. Sleeping on the back upon a hard mattress without a pillow
tends to cure posterior curvature and flat chest.
=The correct position= in standing is: _chest forward, chin in, hips
back_ (Figs. 38, 39). To sit correctly, _sit far back in the chair_
(Figs. 49, 50, 51) with the body erect and balanced. In youth the
bones are soft and growing; they will readily grow into perfect
shape, and will almost as readily grow deformed.
=Sprains.=--_Immerse the part in hot water_ for half an hour, then
_bandage_ to keep the part at rest. _Use the limb as little as
possible._ It may be necessary for a physician to apply a plaster
dressing to a very bad sprain where the ligament is torn from the
bone.
=Broken Bones.=--To prevent bone from cutting flesh and skin, do not
move the person until a temporary splint has been provided by tying
sticks or umbrellas around the limb with handkerchiefs.
PRACTICAL QUESTIONS. =The Skeleton.=--=1.= What kind of a chair back
causes one to slide forward in the seat? =2.= What fault in sitting
is made necessary by using a chair with so large a seat that the
front edge strikes the occupant behind the knee? =3.= Why is the
shoulder more often dislocated than the hip? =4.= High pillows may
cause what deformity? =5.= Find three bones in the body not attached
to other bones. Find twenty-five bones attached to other bones by
one end only (Figs. 28 and 39). =6.= What deformities may result
from urging a young child to stand or walk? =7.= Which bone is most
often broken by falling upon the shoulder? =8.= Where in bones is
fat stored for future use? =9.= Ligaments grow very slowly. Why is
recovery from a sprain often tedious?
[Illustration: FIG. 39.--THE HUMAN SKELETON IN ACTION.]
CHAPTER IV
THE MUSCLES
It has already been stated that there are at least two muscles attached
to a bone to move it in opposite directions. Since there are two
hundred and six bones, you are not surprised to learn that to move the
bones and accomplish the various purposes just stated, there are five
hundred and twenty-six (526) skeletal muscles.
=Two Kinds of Muscles.=--All muscles are controlled by means of the
nervous system. Some of them are directed by parts of the brain that
work consciously; others are controlled by the spinal cord and the
parts of the brain that work unconsciously. Those of the first kind are
_usually controlled by the will_, but they sometimes act involuntarily.
_They are called voluntary muscles._ They move the bones and are
located in the limbs and near the surface of the trunk (Fig. 44). The
other kind of muscles are _never controlled by the will, and are called
involuntary muscles_. We cannot cause them to act, nor can we prevent
them from acting. They contract more slowly than the voluntary muscles.
Most of them are tubular and found in the cavity of the trunk. The
involuntary muscles _belong to the internal organs_, and relieve the
will of the responsibility and trouble of the activity of these organs;
otherwise, the mind would have no time for voluntary actions.
=Gross Structure of Voluntary Muscles.=--A beefsteak is seen to be
chiefly red, although parts of it are white or yellowish. The white or
yellowish flesh is fat; the red, lean flesh is voluntary muscle. If a
piece of beef is thoroughly boiled, it may be easily separated into
_bundles the size of large cords_. These bundles may, by the use of
needles, be picked apart and separated into _threadlike fibers_ (Fig.
40).
[Illustration: FIG. 40.--MUSCLE BUNDLES bound together by connective
tissue sheaths.]
=Microscopic Structure of Muscles.=--These threadlike fibers may, under
a magnifying glass, be separated into _fine strands called fibrils.
These last are the true muscle cells_; they are shown by the microscope
to be crossed by many dark lines (Fig. 48). Hence _voluntary muscles
are called striated or striped muscles_. Prolonged boiling and patient
picking with a needle are needed to dissect muscle, because the bundles
are held together by thin, glistening sheets of connective tissue by
which they are surrounded. This connective tissue surrounds and holds
in place the separate fibers of each bundle (Fig. 40).
[Illustration: FIG. 41.--TWO MUSCLE FIBERS OF HEART.]
[Illustration: FIG. 42.--INVOLUNTARY MUSCLE CELLS (or fibers).]
The fibrils of involuntary muscles are _spindle-shaped_ (see Fig. 42).
There are no cross lines on the fibrils; hence involuntary muscles are
called _smooth or unstriped muscles_. The heart fibers are exceptional;
they are the only involuntary muscle fibers that are striped (Fig. 41).
THOUGHT QUESTIONS. =Classification of Some of the Muscles.=--Copy the
following list and mark _I_ for involuntary and _V_ for voluntary
after the appropriate muscles.
Muscles for chewing. Muscles of gullet. Muscles of the heart. Muscles
that move arms. Muscles for breathing. Muscles in the skin that cause
the hair to stand on end. Muscles that move eyelids. Muscles that
contract pupil of eye. Muscles for talking. Muscles that contract and
expand the arteries (in blushing and turning pale). Muscles that move
eyeball. Muscles that give expression to the face.
=Tendons.=--_The connective tissue which binds the fibers of muscles
into bundles, and forms sheaths for the bundles, extends beyond the
ends of the muscles and unites to form tough, inelastic white cords
called tendons._ Some muscles are without tendons, and are attached
directly to bones. Study the figures and find examples of this (see
Figs. 44, 75). To realize the toughness of tendons, feel the tendons
under the bent knee or elbow, where they feel almost as hard as wires.
_The tendons save space_ in places where there is not room enough for
the muscles, and permit the bulky muscles to be located where they are
out of the way. Wherever the tendons would rise out of position when
a joint is bent, as at the wrist and ankle, they are bound down by a
ligament.
[Illustration: FIG. 43.--(For blackboard.) BICEPS relaxed and
contracted.]
=Arrangement of Voluntary Muscles.=--_Circular_ muscles, called
_sphincter muscles_, are found around the mouth and eyes. Muscles that
extend straight along the limb either bend it and are called _flexors_,
or straighten it and are called _extensors_. Most of the voluntary
muscles are arranged in pairs and cause motion in opposite directions;
they are said to be _antagonists_. The biceps (Fig. 43) bends the arm.
Its antagonist is the triceps on the back of the arm. By feeling them
swell and harden as they shorten, locate on your own body the muscles
mentioned in Fig. 44.
=How a Muscle grows Stronger; its Blood Supply.=--Nature has provided
that any part of the body shall receive more blood when it is working
than when it is resting. _When it works the hardest, the blood tubes
expand the most and its blood supply is greatest._ So whenever a muscle
is used a great deal, an unusual amount of material is carried to it
by the blood, the cells enlarge and multiply, and the muscle grows.
The walls of the capillaries are so thin that the food which is in the
blood readily passes from them to the muscle. Because of the oxidation
taking place, a working muscle is warmer than one at rest. _By use a
muscle grows large, firm, and of a darker red_; by disuse, it becomes
small, flabby, and pale. But if muscles are worked too constantly,
especially in youth, their cells do not have time to assimilate food
and oxygen, and their growth is stunted.
Unless the meal has been a very light one, vigorous exercise should
not be taken after eating, as the blood will be drawn from the food
tube to the muscles and the secretion of the digestive fluids will be
hindered. Persons whose entire circulation is weak may find that light
exercise after a meal, such as walking slowly, may help circulation and
digestion.
=Why the Muscles work in Harmony.=--_When a boy throws a stone, almost
every part of the body is concerned in the action._ His arms, his legs,
his eyes, the breathing, the beating of the heart, are all modified
to assist in the effort. As the boy wills to throw the stone, nerve
impulses are sent to all the organs that can assist, and they are
excited to just the amount of action needed.
[Illustration: Illustrated Study of Muscular Function
Draw a dotted line from each function mentioned on margin to the muscle
or muscles having that function.
Bows the head?
Straightens the elbow?
Straightens the fingers?
Swings leg outward?
Bends the knee?
Straightens the knee?
Crosses the leg?
Straightens toes?
Draws shoulder back?
Lifts the whole arm outward and upward?
Draws whole arm downward and forward?
Bends the elbow?
Bends the fingers?
Raises the body on the toes?
Raises toes?
FIG. 44.--SUPERFICIAL MUSCLES AFTER THE STATUE OF “THE DIGGER” (Lami).]
=The Nerve Impulse and the Contraction.=--Each nerve that goes to a
muscle is composed of many fibers; the fibers soon separate and go to
all parts of the muscle, _and each muscle fiber receives its nerve
fiber_ (see Fig. 45). In the brain each fiber is stimulated at once,
and all the fibers shorten and thicken together. This change is spoken
of as contraction; but since the muscle does not become smaller, the
word may be misleading. When the muscle shortens, it thickens in
proportion and occupies as much space as it did when relaxed.
=Where does Muscular Energy come from?=--_The nerve does not furnish
the energy which the muscle uses when contracting. The muscle cells
have already stored up energy from the food and oxygen brought to them
by the blood_, and the process called oxidation sets free the energy.
Activity of muscle may increase the carbon dioxid output fivefold.
Mental work has practically no effect upon it.
[Illustration: FIG. 45.--MOTOR NERVE FIBERS, ending among fibrils of
voluntary muscle. Compare with Fig. 48.]
=How a Muscle stays Contracted.=--The muscle relaxes at once after
contraction; and in order to keep it contracted, nerve impulses must be
sent in quick succession, causing in fact many contractions; the effect
of this is sometimes visible, as the trembling of the muscle. Figure 47
shows an easy standing posture.
=What causes Fatigue.=--Fatigue or exhaustion is due to the using up of
the living material in the nerve cells and muscle cells by oxidation.
Rest is necessary to give cells opportunity to repair themselves. Why
is it less fatiguing to walk for an hour than to stand perfectly still
for ten minutes?
[Illustration: FIG. 46.--IMPROPER POSITION; causes spine to curve to
side; raises one hip and shoulder above the other.]
[Illustration: FIG. 47.--BEST POSITION; chest is free to expand, and
weight is easily shifted from one foot to other.]
=Degeneration of Muscles= begins with habitual disuse. We dare not
furnish a substitute for the work of a muscle, if we wish the muscle to
remain sound. A belt or a stay at the waist will cause the muscles of
the trunk to become flabby and the abdomen to relax and protrude.
=How Muscular Activity helps the Health.=--Life is change, stagnation
is death. _Muscular activity uses up the food, gives a good appetite,
and sets the digestive organs to work; it uses up the oxygen and sets
the lungs to work; but most of all, every contraction of a muscle helps
the blood to flow._ As a muscle contracts, it presses upon the veins
and lymphatics, and, by this pressure, forces the blood and lymph along
(Fig. 48). In any ordinary activity, dozens of muscles are being used.
That the effect upon the circulation is very powerful, is shown by the
rosy skin, deep breathing, and rapid heart beat. The many benefits of
an active circulation of the blood and lymph will be discussed in the
next chapter. See page 67.
[Illustration: FIG. 48.--CAPILLARIES among fibers of voluntary (cross
striped) muscle. (Peabody.)]
A grave danger from athletics is that of developing the muscles,
including the heart, to an enormous extent by training; then _when
training ceases the muscles undergo fatty degeneration from disuse_.
Heart disease and other diseases may follow. Many athletes die young,
killed by trying to turn their bodies into mere machines for running,
boxing, or rowing, instead of living complete lives. _The athletic
ideal is not the highest ideal of health_; general activity, resembling
the occupations of hunting and farming by which the early race
supported itself, is best for health. Many kinds of factory work use
only one set of muscles. The savage did not lead a monotonous life, and
monotony is bad for both muscles and nerves.
=Advantages of Work and Play over Gymnastic Exercises.=--The interest
that comes from doing something useful, makes muscular exertion
doubly beneficial to the health. The lifting of dumbbells, Indian
clubs, and pulley weights, and letting them down again, tends to
become very irksome, even though done with the knowledge that the
exercise will benefit the health. _Useful labor and games place
definite objects in view and do not require so great an effort of the
will nor exhaust the nerves so much as mere exercise._ The interest
in the work or the game serves to arouse all the nerves and muscles
to work in harmony.
[Illustration: FIG. 49.--DESK TOO LOW. (Jegi.)]
[Illustration: FIG. 50.--CORRECT POSITION.]
[Illustration: FIG. 51.--SLIPPING DOWN IN SEAT.]
=An Advantage of Gymnastics over Work and Play.=--Gymnastics can
furnish any required variety of exercises and _can develop exactly
the muscles that need development and leave those idle that have
become overdeveloped_ by doing constantly one kind of work or playing
continually the same game. The _deformity of a flat chest_ (and round
shoulders which always accompany it) does not so often indicate a
weak chest or small lungs as it indicates weak or relaxed muscles
of the back and the habit of sitting in a relaxed position at work
(Figs. 49, 50, 51). _Gymnastic exercise is not wholly an artificial
custom._ Cats stretch themselves, stretching each leg in succession;
many animals gambol and play. A gymnastic drill, taken to music and
with large numbers of pupils in the drill, is interesting as work or
play, and should not be neglected for any study, however important.
=Environment of Early Man and Modern Man.=--A well-developed man
of one hundred and fifty pounds weight should have sixty pounds of
muscles. The proportion is often different in the puny bodies of the
average civilized men, such as clerks, merchants, lawyers, and other
men with sedentary occupations; their bodies are as likely to be
lean and scrawny or fat and flabby as to be correctly proportioned.
Why does a normal man have sixty pounds of muscles instead of twenty
pounds of puny strings such as would have sufficed for a clerk,
student, or a writer? This is because, in his native condition, he
had to seek his food by roaming through the forest, contending with
wild beasts or with other savage men, often traveling many miles a
day, climbing trees, etc.
=Too Rapid Change of Environment; Destructive Tendencies of
Civilization.=--_It is impossible for the human body to change
greatly in a few hundred years._ The body of man served him for many
ages for the manner of life outlined above. It was suited for these
conditions, and the muscles and the organs that support them cannot
accommodate themselves to changed conditions in a few generations. It
has only been a few hundred years since the ancestors of the Britons
and Germans, for instance, were running wild in the German forests,
clad in the skins of wild beasts. Yet _civilized man lets his muscles
fall into disuse_, he takes a trolley car or horse vehicle to go
half a mile, an elevator to climb to the height of thirty feet. He
neglects all his muscles except those that move the tongue and the
fingers of the right hand. He never makes enough exertion to cause
him to draw a deep breath, and his lungs contract and shrivel. He
seldom looks at anything farther than a few inches from his nose, and
his eyes become weak. At the same time that he neglects his muscles
and his lungs, he overworks his brain and his stomach; yet he expects
his body to undergo the rapid changes to suit the demands of his
life. Such rapid changes in the human race are impossible. A man that
does not see that _sound health is the most valuable thing in the
world, except a clear conscience_, is in danger both of wrecking his
own happiness _and of failing in his duty to others_.
THOUGHT QUESTIONS. =Shoes.=--=1.= What the faults of shoes may be
in size; shape; sole; heel; toe; instep. =2.= Name deformities
resulting to skin of foot; nails; joints; arch; ankle; spine. =3.=
State effects of uncomfortable shoes on muscular activity; mind and
disposition. =4.= State effect of aversion to walking on muscles;
circulation. =5.= If a shoe is too loose, it slips up and down at
the heel and chafes the skin there; if too tight, there is pressure
on the toes, which causes a corn or ingrowing nail. Have your shoes
been correct, or have they been too loose or too tight? According to
this test, what proportion of people wear shoes that are too tight?
=6.= How many sprained ankles have you known among boys; girls? =7.=
Why is it that people who grow up in warm climates have high, arched
insteps, and short, broad, elastic feet, but people of the same race
who pass their childhood in cold climates often have long narrow feet
with low arches and sometimes have the deformity called “flat foot”?
[Illustration: FIG. 52.--ARCH OF FOOT. It forms an elastic spring.]
=Instinct as a Guide for using the Muscles.=--The instinctive feeling
called _fatigue tells us when to rest_. There is also a _restless,
uneasy feeling that comes over a normal human being when confinement
and restraint of the muscles have reached an unhealthy limit. This
feeling should not be repressed_ for long at a time. Many, ruled by
avarice, ambition, interest in sedentary work, a silly notion of
respectability, or a false conception of duty, have repressed this
feeling and have lost it. There is then a feeling of languor, and a
disinclination to the very activity which health demands. An unheeded
instinct is as useless as an alarm clock that has been habitually
disregarded.
=Exercise and Climate.=--In our warmest states and in the tropics,
one hour’s vigorous physical labor a day, combined with the ordinary
activities of life, will keep a person in good condition. In the
colder states, muscular exertion for several hours is needed daily.
=Complete Living.=--Numberless people have devoted themselves to
an intellectual occupation, and planned to keep their bodies sound
by gymnastics and special exercises. Because of the monotony of
exercises, they are soon given up in nearly every instance. _The
safest way is never to allow all the energies to be devoted to a
one-sided occupation, but so to plan one’s life and work that a
part of the time is devoted to some physical work_, whether it be
in a garden, workshop, or orchard; in walking a long distance to
the office; at bookbinding, cooking, wood carving, or any one of
various other useful occupations. The result of manual training shows
_that not only strength of body, but strength of mind, is promoted
by physical labor_. Problems of war and of the chase kept active
both the body and mind of the savage. Hence he led a more nearly
complete life than his civilized descendants, and his body was strong
accordingly. We should admit the hopelessness of having permanent
good health without muscular activity and should determine that
muscular exertion shall be as much a habit and pleasure as eating and
sleeping.
=Alcohol and Muscular Strength.=--Benjamin Franklin, one of the
wisest and greatest of Americans, was a printer when he was a young
man. In his autobiography he gives an account of his experience as a
printer in London. He says: “I drank only water; the other workmen,
fifteen in number, were great drinkers of beer. On occasion I carried
up and down stairs a large form of types in each hand, when others
carried but one in both hands. They wondered to see, from this and
several instances, that the Water-American, as they called me, was
stronger than themselves, who drank strong beer. My companion at the
press drank every day a pint before breakfast, a pint at breakfast
with his bread and cheese, a pint between breakfast and dinner, a
pint at dinner, a pint in the afternoon about 6 o’clock, and another
when he had done his day’s work. I thought it a detestable custom,
but it was necessary, he supposed, to drink strong beer that he might
be strong to labor.”
EXERCISES IN WRITING.--The Right and the Wrong Way to ride a Bicycle.
Pay Day at a Factory. A Graceful Form: how Acquired; how Lost. A
Drinking Engineer and a Railway Wreck.
PRACTICAL QUESTIONS.--=1.= Can we always control the voluntary
muscles? Do we shiver with the voluntary or involuntary muscles?
=2.= If a man had absolute control over his muscles of respiration,
what might he do that he cannot now do? =3.= Why is one who uses
alcoholic drinks not likely to be a good marksman? =4.= Why should a
youth who wishes to excel in athletic contests abstain from the use
of tobacco? =5.= Is there any relation between the amount of bodily
exertion necessary for a person’s health and the amount of wealth
or the amount of intelligence he possesses? =6.= Can you relax the
chewing muscles so that the lower jaw will swing loosely when the
head is shaken? Can you relax your arm so that it falls like a rope
if another person raises it and lets it fall? =7.= The average man
has sixty pounds of muscle and two pounds of brain; one half of the
blood goes through the muscles and less than one fifth goes through
the brain. What inference may you draw as to the kind of life we
should lead? =8.= Why is a slow walk of little value as exercise?
=9.= How can we best prove that we have admiration and respect for
our wonderful bodies? =10.= Why is the ability to relax the muscles
thoroughly of great benefit to the health? How is this ability
tested? (Question 6.) =11.= Why is it as correct to say that the
muscles support the skeleton as the reverse?
[Illustration: COLORED FIGURE 5. DIAGRAM OF CIRCULATION.
1. Head arteries (carotid).
2. Nameless arteries (innominate).
3. Collar bone (subclavian) artery.
4. Great bend of the aorta.
5. Pulmonary arteries.
6. Thoracic aorta.
7, 10. Abdominal aorta.
8. Artery to liver (hepatic).
9. Artery to spleen (splenic).
11. Artery to intestine (mesenteric).
12. Artery to kidney (renal).
13. Descending vena cava.
14. Nameless vein (innominate, 15 and 16 before branching).
15. Collar bone vein (subclavian).
16. Jugular vein.
17. Pulmonary vein.
18. Ascending vena cava.
19. Vein from liver (hepatic).
20. Vein from stomach (gastric).
21. Vein from spleen.
22. Vein from intestine.
23. Vein to liver (portal).
24. Vein from kidney.
25. Right auricle.
26. Left auricle.
27. Right ventricle.
28. Left ventricle.
29. Thoracic duct.
30. Stomach.
31. Spleen.
32. Liver.
33. Kidneys.
34. Duodenum.
35. Ascending colon.
36. Descending colon.
37. Lymphatic glands of mesentery.]
CHAPTER V
THE CIRCULATION
_Experiment 1._ =Anatomy of Mammalian Heart.=--Get a sheep’s or
beef’s heart from the butcher. Get the whole heart, not simply the
ventricles (as usually sold). Note the blood vessels, four chambers,
thickness of different walls, valves, cords, openings.
_Experiment 2._ =Does Gravity affect the Blood Flow?=--Hold the right
hand above the head for a few minutes. At the same time let the left
hand hang straight down. Then bring the hands together and see which
is of a darker red because of containing more blood. Now reverse the
position of the hands for a few minutes, and find whether the effect
is reversed. (Entire class.)
_Experiment 3._ =Study of Human Blood.=--Examine a drop of blood
under the microscope, first diluting it with a little saliva. See
Fig. 60.
_Experiment 4._ =The Circulation in a Frog.=--Wrap a small frog in a
moist cloth, lay on a slip of glass, place under the microscope, and
study the circulation in the web of its foot.
_Experiment 5._ (Entire class.) =Effect of Exercise upon the
Pulse.=--Tap a bell as the second hand of a watch begins a minute
and let the pupils count the pulse at the radial artery on the wrist
above base of thumb. Repeat standing, or after gymnastics or recess.
Result?
_Experiment 6._ =The Action of the Valves in the Veins.=--Place the
tip of the middle finger on one of the large veins of the wrist;
with the forefinger then stroke the vein toward the elbow so as to
push the blood from a portion of it, keeping both fingers in place.
The vein remains empty between the fingers. _Lift the finger nearer
the heart and no blood enters the vein; there is a valve above which
holds it back. Lift the other finger and the vein fills instantly._
Stroke a vein toward the hand, and notice that the veins swell
up into little knots where the valves are. Stroke in the reverse
direction. Result?
_Experiment 7._ =Finding the Capillary Pressure.= This is found by
pressing a glass plate or tumbler upon a red part of the skin. When
the skin becomes pale the capillary pressure is counterbalanced.
_Experiment 8._ =Emergency Drill.=--Let one pupil come forward, mark
with blue chalk or pencil the position on his arm of a supposedly cut
vein. Let another pupil use means to stop the imagined blood flow.
_Experiment 9._ Let another pupil stop the flow from an imaginary
cut artery marked red. See text. _Experiment 10._ In a case of nose
bleed do not let pupil lean over a bowl. (Why?) Cause him to stand
rather than lie. (Why? See Exp. 2.) Apply cold water to contract
arteries to nose, also have pupil hold a small roll of paper or a
coin under upper lip (to make muscular pressure on arteries to nose).
_Experiment 11._ Let one pupil treat another for a bruise (see p.
62). _Experiment 12._ Emergency drill, restoration from fainting (see
p. 57).
=The Cells have a Liquid Home.=--The cells in the body of man, like
the ameba, live in a watery liquid. This liquid is called _lymph_.
The cells cannot move about as the ameba does to obtain food, so the
_blood_ brings the food near them and it soaks through the blood
tubes into the lymph spaces next to the cells (see colored Fig. 3).
The ameba gives off waste material into the water; the cells of the
body give it off into the lymph to be carried off by the circulation.
The blood, then, has _two functions_: (1) to take nourishment to the
tissues; (2) to take away waste material from them.
=The Organs of Circulation.=--These are the _heart_, which propels
the blood; the _arteries_, which take blood away from the heart; the
_veins_, which take the blood back to the heart; and the _capillaries_
(Fig. 53), which take the blood from the arteries to the veins.
[Illustration: FIG. 53.--CAPILLARIES, connecting artery (_b_) with vein
(_a_).]
=The heart= is a cone-shaped organ about the size of its owner’s fist.
It lies in a diagonal position behind the breastbone, with the small
end of the cone extending toward the left. The smaller end (Exp. 1)
taps or beats against the chest wall at a point between the fifth and
sixth ribs on the left side. The breastbone and ribs protect it from
blows. An inclosing membrane called the _pericardium_ secretes a serous
fluid and lessens the friction from its beating.
=Why the Heart is Double.=--_There must be a pump to move the impure
blood from the body to the lungs_ to get oxygen from the air, and there
must be _another pump to send the pure blood from the lungs back to the
body_. Hence there are two pumps bound together into one heart, beating
at the same time like two men keeping step, or like two carpenters
keeping time with their hammers. There are valves in the heart, as in
other pumps. These valves are so arranged that when any part of the
heart contracts and forces the blood onward, the blood cannot return
after that part of the heart relaxes. Are the pumps placed one behind
the other? Or is one above the other? Neither; they are side by side,
with a fleshy partition between them (Fig. 54). The pump on the right
moves the impure blood from the body to the lungs, and the one on the
left moves the pure blood from the lungs to the body. There is no
direct connection between the right and left sides of the heart.
[Illustration: FIG. 54.--DIAGRAM OF HEART.
Notice the two dark spots in the right auricle, and four dark spots in
left auricle, where the veins enter. Does the aorta pass in front of,
or behind, the pulmonary artery?]
=To trace one complete circuit of the blood= (Fig. 54), let us begin
with the blood in the _capillaries_ of the outer tissues, such as the
skin or muscles. The blood goes through small veins which unite into
_two large veins_, through which it enters the receiving chamber, or
_right auricle_, goes through the _tricuspid valve_ into the expelling
chamber, or _right ventricle_, then through a _semilunar valve_ into
the _pulmonary artery_ leading to the _lungs_. Becoming purified while
passing through the _capillaries of the lungs_, the blood goes _through
the pulmonary veins_ to the _left auricle_ (Fig. 54), then through
the _bicuspid_ or mitral valve, to the _left ventricle_, whence it is
forced through a _semilunar valve_ into the largest artery of the body,
called the _great aorta_ (Fig. 54). Thence it goes to the _smaller
arteries_, and then to the _capillaries_ of the tissues in general,
thus completing the circuit.
[Illustration: FIG. 55.--THE LEFT SIDE OF HEART (plan), showing the
left ventricle at the moment when relaxing and receiving the blood from
the auricle; and the same at the beginning of contraction to send blood
into aorta. Notice action of the valve.]
=Structure of Veins and Arteries.=--Seen under the microscope the
arteries and veins show that they are made of _three kinds of tissues_
arranged in _three coats_ (Fig. 56): a tissue resembling epithelial
tissue (Chap. 1), as a lining to lessen friction; an outer connective
tissue (Chap. 1), to give elasticity; and a middle coat of muscular
tissue to enable the vessels to change in size. Let us see why blood
vessels must have these three properties.
=Why the Blood Vessels must be Elastic.=--The aorta and its branches
are always full of blood. When the left ventricle with its strong,
muscular walls contracts, the blood in the aorta and small blood
tubes _cannot move forward fast enough to make room for the new
supply so suddenly sent out of the ventricle_. Where can this blood
go? If a cup is full, it cannot become more full; not so with an
artery. The elastic connective tissue allows it to expand as a rubber
hose does under pressure. The first part of the aorta having expanded
to receive the incoming blood, _the stretched walls contract_ because
of the elasticity of the outer connective tissue coat _and force
blood into the portion of the aorta just ahead_, forcing it to expand
in turn. Thus _a wave of expansion_ travels along the arteries. This
wave is called the _pulse_.
=The Pulse= may be most easily felt in the wrists and neck. As the
artery stretches and springs back, one beat of the pulse is felt. In
men there are about _seventy heart beats or pulse beats a minute_.
In women the rate is about eighty a minute. It is slowest when one
is lying down, faster while sitting, still faster when standing,
and fastest of all during running or violent exercise. (Exp. 5.) It
should not be thought that the muscular or middle layer of the artery
actively contracts and helps to send along the pulse wave; for this
wave is simply the passive stretching and contracting of the outer
connective coat, and travels like a wave crossing a pond when a stone
is dropped into the water. The force of the pulse is furnished, not
by the muscle fibers in the artery, but by the beat of the heart; the
outer, or connective tissue, coat enables the pulse to travel. Why
must there be a middle, or muscular, coat for variation in size?
[Illustration: FIG. 56.--SECTION OF ARTERY, _A_, AND VEIN, _V_, showing
inner coat, _e_ (endothelial); middle coat, _m_ (muscular); and third
coat, _a_ (connective tissue).]
=Use of the Middle Coat; Quantity of Blood and its
Distribution.=--The body of an adult contains about five quarts of
blood. The blood furnishes the nourishment needed for the activity of
each organ. The more vigorous the work of any organ, the greater is
the amount of blood needed. _The whole amount of blood in the body
cannot be suddenly increased, but the muscular coat of the arteries
going to the working organ relaxes, and allows the arteries to become
enlarged by the pressure from the heart._ Consequently, more blood
goes to the active organ, and the other organs get along with less
blood for the time. When we are studying, our brains get more blood;
when running, the leg muscles get more; after a hearty dinner, the
stomach and intestines get more than any other part of the body. Why
is it difficult to do the best studying and digest a meal at the same
time? We see that the muscular coat of the arteries is a very useful
coat, for _it enables the supply of blood to be increased in any
organ which is in temporary need of it_.
=Why the Blood Vessels must be Smooth.=--The inner coat of the heart
and other blood vessels is made of tissue like the epithelial tissue
which forms the epidermis and the smooth lining of the mouth and
other organs. _The purpose of this lining is to lessen friction_,
and thus save the work of the heart. The friction is greatest in the
capillaries because of their small size. The inner coat of smooth
cells is the only coat that is prolonged to form the capillaries (see
Fig. 57).
[Illustration: FIG. 57.--CAPILLARIES MAGNIFIED, SHOWING CELLS forming
their walls. Notice that each cell has a nucleus and three branches.]
=The capillaries= are small, thin, short, and very numerous. _They are
very small_ so that they may go in between the cells of the tissues.
_The capillaries are very thin_ so that the nourishment from the blood
may pass readily into the tissues, and the waste material pass readily
into the blood. _They are very short_ so that the friction may be less;
and _they are very numerous_ so that all parts of the tissues may be
supplied with blood, and that the blood may flow very slowly through
them. Because of the number of the capillaries, their total volume is
several hundred times larger than the volume of the arteries that empty
into them, or of the veins that flow from them. Hence the blood flows
slowly through the capillaries, as water flows slowly through a lake
along the course of a river. All the changes between the blood and
the lungs, and between the blood and the tissues, take place in the
capillaries, and the object of the other parts of the circulation is
merely to move the blood continually through the capillaries.
=The effect of gravity= is to retard the flow in certain parts of the
body and aid the flow in other parts, according to the position of
the body (Exp. 2).
=Fainting= is usually due to _lack of blood in the brain_, which
in turn results from a weakening of the heart beat. Since the
brain cannot work without fresh blood, fainting is accompanied by
unconsciousness. Recovery from fainting is aided by loosening the
clothing at the neck and by placing the head of the patient a little
lower than the body so that the weight of the blood may aid the flow
to the brain. Dashing a little cold water in the face shocks the
nerves and arouses the heart to stronger beats.
=The veins have valves= placed frequently along their course (Fig.
58). These valves are pockets made by a fold in the inner coat of the
wall of the vein. When a boy places his hand in his pocket, the pocket
swells out; but if he rubs his hand on the outside of the pocket from
the bottom toward the top, it flattens down. So with the action of the
blood upon the valves in the veins. (Repeat Exp. 6 in class.)
[Illustration: FIG. 58.--VALVES IN VEINS. (Jegi.)]
=How Muscular Exercise aids the Heart.=--_When a muscle contracts_,
it hardens and presses upon a vein which goes through the muscle,
and _the blood is pressed out of the vein_ (see Fig. 58). The blood
cannot go toward the capillaries, for the valves fill and close when
it starts that way; so it must all go out toward the heart. _When
the muscle relaxes_, the blood that has been pressed forward cannot
go back because of the valves, but the valves nearer the capillaries
open, and _the veins are filled from the capillaries_ (Fig. 53). When
the muscle contracts again, the same effect on the blood movement is
repeated. We see, therefore, that every contracting muscle converts
into a pump the vein running through it, and when a person works or
exercises, many little pumps are working all over the body, aiding
the heart in its function. This aid makes the blood flow faster and
relieves the heart of part of its work, so that it beats faster, just
as a horse might trot faster if another horse helped to draw the load
(Exp. 3). The pressure of a contracting muscle upon an artery does
not aid the blood flow in the artery because the latter is destitute
of valves.
=How Breathing aids the Heart.=--Breathing is a blood-pumping process
as well as an air-renewing process. When the chest expands, blood is
drawn into it. When the chest contracts, the flow of blood away from
it is aided. As the chest expands, the downward pressure of a great,
broad muscle, the diaphragm (Fig. 74) compresses the liver, stomach,
and other abdominal organs, and forces the venous blood upward into
the expanding chest, thus helping it on its way to the heart. But if
the abdominal wall is weakened by tight lacing or by the pressure of
belts and bands which support the clothing, the weak abdominal wall
yields to the downward pressure of the diaphragm, and no compression
of the liver or aid to the circulation will result.
[Illustration: FIG. 59.--THE VENTRICLES OF A DOG’S HEART relaxed
(above), and contracted (below).]
=How the Blood Vessels are Controlled.=--Evidently the blood vessels
are not regulated by the will. We cannot voluntarily increase the
beating of the heart, or cause it to slacken its action. Even an
actor cannot cause his face to turn pale or to blush at will. This
is because the tiny muscles in the walls of the blood vessels are
involuntary muscles. They are controlled by nerves of the sympathetic
system called vaso-motors. They are not subject to the will (see Fig.
25). The nerve center which controls the blood vessels is located
in the top of the spinal cord at the base of the brain. When cold
air strikes the skin the nerves near the arteries are stimulated,
the arteries in the skin contract, and the skin turns white. When
the heat from a hot fire strikes the skin, the nerves are soothed,
the arteries relax, and the face becomes red. When the stomach is
filled with food, the heart beats faster and sends more blood to aid
in digestion. When we run fast, the heart beats fast to supply more
blood to the muscles, but it slows down as sleep comes on, that the
body and brain may rest.
=Parts of the Blood.=--The blood which flows from a cut finger seems
to be a bright red throughout. When a drop of it is looked at through
a microscope, however, the liquid itself is seen to be almost as clear
as water. This liquid is called the _plasma_. Floating in it are
millions of biconcave disks containing a pigment (hemoglobin) which
gives the red color to the blood. The disks are called _red corpuscles_
(Fig. 60). A few irregularly shaped bodies, nucleated and almost
transparent, and called _white corpuscles_, are also found in the
blood. The red corpuscles go only where the plasma carries them (Exps.
3, 4). The white corpuscles sometimes leave the blood vessels entirely.
At times one may be seen shaped like a dumb-bell, half of it through
the wall of the blood vessel and half still in the blood vessel.
After the corpuscle is out, no hole can be found to account for its
mysterious passage. _The white corpuscles consist of protoplasm. The
red corpuscles contain no protoplasm. Hence the latter are not really
alive._
[Illustration: FIG. 60.--HUMAN BLOOD CELLS (magnified 40,000 areas),
showing many red cells and a single white blood cell on left, larger
than red cells. (Peabody.)]
[Illustration: FIG. 61.--SIDE AND FRONT VIEWS OF FROG’S AND MAN’S RED
CORPUSCLES, drawn to same scale. Compare outline, concavity, diameters.]
=The Use of Each Part of the Blood.=--The _plasma_ keeps the blood in a
liquid state, so that it may flow readily; the plasma also transports
the food that has been eaten and digested, and carries carbon dioxid to
the lungs and other waste material to the kidneys. The _red corpuscles_
transport the oxygen from the lungs to the tissues. The _white
corpuscles_ devour and destroy irritating particles, such as drugs,
poisons, and germs. They are of great importance in purifying the blood
and as a protection against disease. One is shown in Fig. 60.
=The sounds of the heart beat= may be heard by applying the ear to the
chest. They are two, a _long, dull_ sound and a _short, clear_ one. The
first comes from the vibration of the bicuspid valve together with an
unexplained tone arising from large contracting muscles, in this case
the walls of the ventricles. The second, or short, clear sound, is
produced by the sudden closing and vibration of the semilunar valves.
=Changes in the Composition of the Blood as it passes through the
Various Organs.=--When the blood is forced out by the heart, part of
it goes to the stomach and intestines through arteries which divide
into capillaries. These capillaries _absorb all kinds of food_ from
the alimentary canal except the fats (see p. 64), and unite to form
the portal vein, which takes the absorbed food to the liver. In the
liver some of the _impurities of the blood are burned up_ and changed
into bile. The blood, purified and laden with food, is carried from
the liver to the heart, where it reënters the general blood stream.
The blood flow from the food tube through portal vein and liver to the
heart, as just described, is called the _Portal circulation_.
_Renal circulation._ Two branches from the aorta carry blood to the
_kidneys_. There the _urea_ and _a large amount of water_ are taken
out, and the purified blood is emptied into the large vein that leads
up to the heart.
_Pulmonary circulation_ (Fig. 67). This is the circulation through the
lungs. During this circulation _carbon dioxid gas is removed_ from the
blood and _oxygen is added_ to it.
[Illustration: FIG. 62.--BLOOD CLOT separated from serum.]
Some impurities and a large amount of water escape from the blood as it
passes through the skin.
=Coagulation.=--So long as blood is in an uninjured blood vessel it
remains a liquid. In a few minutes after it flows from a blood vessel,
it forms into a stiff, _jellylike mass called a clot_ (Fig. 62). The
process of forming the clot is called coagulation, and it is brought
about by the albuminous substance called fibrin, which is always in
the plasma of healthy blood. On exposure to air the _fibrin forms
into a network of fine threads throughout the mass_ (Fig. 63) and the
corpuscles become entangled in the meshes. The clot consists of the
fibrin of the plasma and corpuscles; the watery portion of the plasma,
called the _serum_, separates from the clot (Fig. 62). The property of
coagulating is a great safeguard, as a clot often plugs up a cut blood
vessel. What is the difference between serum and plasma?
[Illustration: FIG. 63.--NETWORK OF FIBRIN IN HUMAN BLOOD (enlarged).]
=Veins and Arteries compared.=--The veins have _thin, soft walls_ and
the arteries have _thick, tough, elastic walls_. When a vein is cut,
it may usually be closed by pinching the walls of the end together.
If an artery is cut, the _walls will not readily stick together_, but
often stand open until the end of the artery is tied. For this reason,
and because an artery is subject to the direct pressure of the heart,
a cut artery is more dangerous to life than a cut vein. Because of the
toughness of the arteries, and because they are _located close to the
bones_, they are less likely to be cut than the veins, which are softer
and nearer the surface. The veins begin in capillaries and _empty into
the auricles_; the arteries begin at _the ventricles_ and empty into
capillaries; and there is a semi-lunar valve at the origin of each
artery.
=Cuts and Bruises.=--1. _Wash_ a cut under _running_ water. 2. _Stop
the bleeding._ The washing in cold water may do this. Elevating an
injured arm or leg will aid the blood greatly in forming a clot at
the opening. 3. _Bandage_ firmly with a strip of cloth and sew the
end. Keep wet the part of the bandage where the cut is; this lowers
the temperature of the wound. It may be necessary to hold a gaping
wound closed with strips of surgeon’s plaster placed across the cut.
A handkerchief folded first into a triangle and then into a narrow
bandage is often useful. A cut artery may be known from a cut vein by
the brighter _color of the blood_, and by the flow being _stronger at
each heart beat_, while the flow from a vein is uniform. Pressure to
stop the flow of blood from an artery should be applied _between the
cut and the heart_; but when the blood comes from a vein, the pressure
should be applied _to the side of the cut farthest from the heart._
Apply hot water immediately for several minutes to a =bruise=. Either a
bruise or a cut may be washed with a weak solution of some antiseptic
such as carbolic acid. After washing a bruise it may be bound with a
cloth soaked in witch hazel or arnica.
THE LYMPHATIC SYSTEM
This system contains and conveys a liquid called the lymph. It consists
of lymph spaces, lymph tubes, (lymphatics), and lymphatic glands.
_Lymph corresponds nearly to the blood without the red corpuscles._ It
is the familiar liquid seen in a blister, or oozing out where the skin
has been grazed without breaking a blood vessel.
=Necessity for Lymph and Lymph Spaces.=--The body cannot be nourished
with the albumin, sugar, oxygen, and other digested food in the blood,
until this food passes out of the blood vessels. The food leaves the
blood through the thin walls of the capillaries. Many of the cells do
not touch the capillaries, and the _lymph penetrates the spaces between
the cells to reach them_ (see colored Fig. 3). If there were no lymph
spaces, these cells could not get any food. The lymph bathes the cells,
and the cells absorb what they want from the nourishing fluid. The red
corpuscles bearing the oxygen cannot pass through the capillary walls.
Oxygen, being a gas, readily passes through the walls and reaches the
cells through the lymph in the lymph spaces. The waste materials must
go back into the blood; carbon dioxid passes back through the capillary
walls and is taken to the lungs; how the other waste materials formed
in the cells pass back will soon be explained.
=Need of Lymphatics.=--_The plasma continually passes into the tissues,
but it cannot return directly into the blood._ The lymph contains waste
material which must be removed, and also much unused food which nature,
like an economical housekeeper, will offer to the tissues again. _There
are vessels called lymphatics that take the lymph back into the blood_
(see Fig. 64).
=The Lymphatic Circulation= (Fig. 64).--The blood flow does not begin
nor end, but makes a never ending circle. The countless _lymphatics
begin, with open ends, in the lymph spaces_ between the cells
(colored Fig. 3). The smaller lymphatics unite into larger ones until
finally they all unite into two large ones that empty into the large
veins under the collar bones, near the neck. The one that empties
under the left collar bone (3, Fig. 66) is called the _thoracic duct_
because it goes up through the thorax just in front of the spinal
column (1, Fig. 66). The other at the right side of the neck is
called the _right lymphatic duct_ (see Figs. 64, 65).
[Illustration: FIG. 64.--SURFACE LYMPHATICS OF HAND.]
In persons with the _dropsy_, the lymph accumulates in the lymph
spaces and is not drained away by the lymph flow. Dropsy usually
shows itself first by swelling of the feet and the leg below the
knee. (Why? See Exp. 2.)
There is a set of lymphatics called _lacteals_, situated in the
abdomen, which have the function of absorbing digested fats from the
intestine (Figs. 66, 100, and colored figure 2).
[Illustration: FIG. 65.--DIAGRAM TO SHOW THE TWO PARTS OF THE BODY
DRAINED BY THE TWO LYMPH DUCTS.]
=What makes the Lymph Flow?=--The heart does not, for its pressure
is not transmitted beyond the blood tubes. _The successive pressures
of a working muscle_ move the lymph forward in the lymphatics in
the same way that the blood is moved forward in the veins, and the
valves keep it from moving back. When riding a trotting horse, or
in a jolting vehicle, the lymph is moved beyond the valves at every
jolt (Fig. 64). Without exercise the lymph stagnates, and the body
becomes poisoned by its own wastes. At every expansion of the lungs
lymph is drawn into the chest; and it is forced out of the chest at
every contraction. Deep breathing is as great a benefit to the body
in moving stagnant lymph as it is in purifying the blood.
[Illustration: FIG. 66.--CHIEF LYMPHATIC VESSELS AND GLANDS of trunk.
1, 3, Thoracic duct (emptying at 3); 2, receptacle for chyle (lacteals
below it).]
=The lymphatic glands= are kernel-like enlargements along the
lymphatics, and they contain a great many lymph cells which _purify the
lymph as it passes through them_. The lymphatic glands are numerous in
the armpits and the groins. The cells in the lymph glands multiply, and
some of them are carried by the lymph into the blood _to become those
remarkable little bodies, the white corpuscles_.
HYGIENE OF THE CIRCULATION
=Effects of Work, Fresh Air, and Rest on Corpuscles and Plasma.=--_Work_
uses up the nutritious elements in the blood. A few hours after food is
eaten the nutritious materials in the blood are found to be increased.
By the breathing of _fresh air_ the carbon dioxid in the plasma is
diminished and the oxygen in the colored corpuscles is increased,
changing the blood to a brighter red. _Sleep_ gives time for the
exhausted cells and depleted blood to be replenished. _Loss of sleep_
means longer hours of activity and greater consumption of nutriment
with shorter hours for replacing the nutriment. The pale skin of one
who has lost sleep tells of the exhausted condition of the blood.
=How the Muscles help the Circulation.=--The imperative need of
muscular exercise to keep the body sound exists because of the lack of
other means to cause movement in the veins and lymphatics. Good food,
pure air, and plenty of exercise are necessary for healthy blood. Many
so-called “blood purifiers” are advertised to entrap the ignorant.
It is impossible to imagine how “blood purifiers” can aid the blood.
_The blood is purified, not by putting anything into the blood, but
by something going out of it as it passes through the skin, kidneys,
liver, and lungs._ These organs all send out impurities brought to them
by the blood.
=The one great hygienic effect of muscular exercise= is an _active
circulation_, and from an active circulation _nine chief effects_ may
be traced. The effects upon the body will be given in order, beginning
with the surface--skin, fat, muscles, bones; and the effects upon the
internal organs are given in order of position, beginning with the
highest--brain, lungs, heart, digestive organs.
=Effects of Exercise and Improved Circulation.=--1. _The skin_ is
made fresh, pink, and smooth from the flushing of the capillaries; it
is purified by the perspiration and the renewal of cells. 2. If _the
fat_ is too great in amount, it is burned up; if it is too small in
amount, the better nourishment brought by the blood increases it. 3.
_The muscles_ are better fed (see Fig. 48) and grow firm, strong, and
large. 4. _The skeleton_ is held in proper position by the stronger
muscles, and deformity is prevented. 5. _The brain._ The pure, fresh
blood, loaded with oxygen from expanded lungs, flushes every capillary
of the brain, clears the mind, and doubles or trebles its power to
work. 6. _The lungs_ are expanded by deep breathing if the exercise be
rapid and vigorous. A slow stroll or saunter is not of value. 7. _The
circulation._ Every contracting muscle aids the heart in its work. The
deep breathing moves stagnant lymph. 8. _The stomach._ Exercise burns
up the food and increases the appetite. 9. _General effects._ Exercise
promotes good humor, decreases loafing, cigarette smoking, gossiping,
and other vices.
=The effect of tobacco on the heart=, if cigarettes or cigars are used,
is sometimes to cause attacks of irregular beating; the heart flutters
faintly for a while, then palpitates strongly, then flutters again.
This condition is called _tobacco heart_, or _trotting heart_.
=Effect of Alcohol upon the Circulation.=--After a person has taken
an alcoholic drink his face and skin are likely to become flushed,
and perhaps his heart beats faster. Most investigators have found
that the _alcohol itself does not directly increase or strengthen the
action of the heart_. Hence it is probably wrong to call alcohol a
heart stimulant. The flushing of the skin is believed to be due to the
relaxing effect of alcohol. It relaxes, it paralyzes, the vasomotor
nerves which control the little muscle fibers in the walls of the blood
vessels. The relaxing and enlarging of the blood vessels decreases the
resistance to the blood flow, and the heart beats faster under its
lighter load. The narcotic effect of alcohol is much more powerful than
its irritating or stimulating effect. The effect of alcohol in causing
fatty degeneration of the muscles often weakens the heart and other
blood vessels.
=Climate and Brain Work.=--_In going to sleep_ the vessels in the
skin dilate and _blood is drawn from the brain to the skin_. It is
difficult to go to sleep when cold, for cold sends the blood to
the brain and keeps the mind active. On the same principle, mental
work is difficult in very warm weather _because of the enlarged
capillaries in the skin_ and the withdrawal of blood from the
brain to the skin. This increases the perspiration and keeps the
temperature of the body down to normal, but it deprives the brain of
blood needed for good mental work. Mental workers in warm weather and
in warm climates _should seek every condition favoring coolness_.
Benjamin Franklin was accustomed to strip himself almost entirely
of clothing when he was writing and wanted his brain to work at its
best. The wearing of _barefoot sandals_ and the _thinnest cotton
clothing, light in color_, helps to prevent mental inertia in hot
weather. In the Gulf states in summer and in our tropical islands the
best mental work can be done by _rising at dawn and working before
the hot part of the day begins_. Some of the greatest thinkers in the
world have lived in warm climates (Greece and India), but they _wore
very few clothes_ and _ate moderately_ of the simplest food (see p.
44).
=Congestion= is a swelling of the blood vessels of some part, with
the accumulation of blood therein. Congestion is _active_ when a
_rapid_ flow of blood distends the capillaries. Example, flushing of
face when running. Congestion is _passive_ when there is a narrowing
of the outlet of the capillaries, the blood moves slowly and partly
stagnates in the swollen vessels. Example, when the nose feels
stopped up during a cold. If a syringe is worked so fast that the
rubber tube swells, this is like active congestion; if the end of the
tube is pinched together so that moderate pumping causes it to swell,
this is like passive congestion.
=Inflammation= is congestion where the vessels of any part are
strained and injured. _White corpuscles collect_ there to repair
the vessels and devour the blood that escapes and stagnates there.
They also _destroy germs_ that have usually found lodgment and begun
to multiply. The serum of the blood also destroys the germs by the
antitoxins in it. Inflammatory troubles are: colds, rheumatism,
diarrhœa, and all diseases with name ending “_itis_.” An inflamed
part is red, swollen, hot, and painful.
=Prevention and Care of Colds.=--_A cold is an inflammation of a
mucous membrane._ Colds are prevented by so living as to encourage
a _free, vigorous circulation_, and especially by not coddling the
body so tenderly that the circulation becomes deranged by the least
exposure. The circulation may be _deranged by overheating_ as well
as by chilling the body; usually it would be more appropriate to say
that the person caught “a hot” than “a cold.” At the _first sign of
a cold_ vigorous exercise, a cold bath, or going outdoors into cold
air may aid in sending fresh blood to remove the stagnation and stop
the inflammation. A warm foot bath and hot drinks may relieve by
drawing blood from the congested mucous membrane. _After the cold
has become fixed_ such measures will not help, but the cure is aided
by helping the skin to keep its full share of blood. The cold must
run its course. The cells will be given every chance to repair the
injury and destroy the germs (if any) by avoiding hard work, eating
moderately of digestible food, avoiding drugs, especially infallible
drugs advertised in newspapers, even if recommended by otherwise
intelligent people. Repeated colds tend to become a disgusting
disease called _chronic catarrh_. Constricting the blood vessels of
the skin causes congestion of the (internal) mucous membranes. _A
skin tenderly protected_ constricts more readily than one accustomed
to cold. _Cold is the best preventive of cold._ Cold baths, pure air,
light clothing, free breathing, moderate eating, ward off colds.
Fussing with sprays, gargles, and drugs will not; for the main factor
in bringing on a cold is not germs, nor temperature, but _the state
of the system itself_. Persons who have suffered much with colds have
found that after substituting _cotton underwear_ for woolen, colds
became very rare. Linen will have a similar effect, but it is not as
durable, soft, or heat-retaining as cotton (see p. 16).
PRACTICAL QUESTIONS.--=1.= Through what kind of skin do the
blue veins in the wrist show most plainly? =2.= Which is more
compressible, a vein or an artery? =3.= Why are those who take little
exercise likely to have cold feet? (p. 57.) =4.= Where does the
so-called venous blood flow through an artery? =5.= What vein begins
and ends in capillaries? (The portal vein, colored Fig. 5.) =6.= To
what purifying organ, after leaving the lungs, does the heart send
part of the blood for further purification? (Colored Fig. 5.) =7.=
What keeps the blood moving between the beats of the heart?
CHAPTER VI
THE RESPIRATION
_Experiment 1._ (Home.) =Study of the Throat.=--Sit with the back to
the light. Study the open mouth and throat with a mirror and make out
the uvula, tonsils, and other parts shown in Fig. 68.
_Experiment 2._ =Anatomy of Lungs.=--Study fresh lungs of sheep, hog,
fowl, or frog. Will they float? Will they contract when expanded by
air blown in through a quill or other tube? What is the structure of
the windpipe? Can you distinguish the arteries from the veins by the
stiffness of their walls? Which contain pure blood? Study branching
of air tubes. Make a sketch.
_Experiment 3._ =Tests of Expired Air.=--Breathe upon a mirror,
bright knife blade, or cold window pane. Result? State your
conclusion. _Experiment 4._--Carbon dioxid added to limewater will
cause a white cloud consisting of particles of limestone. Breathe
through a tube or straw or the hollow stem of a reed into clear
limewater. Result? Conclusion? (Limewater may be had at druggist’s
or made by pouring water upon a lump of unslackened lime and
draining it off when lime has settled.) _Experiment 5._ Breathe for
several minutes upon the bulb of a thermometer. Result? Conclusion?
_Experiment 6._ Breathe a few times into a large, carefully cleaned
pickle jar, or a bottle. Cork it tightly, and set it in a warm place
for several days. Then uncork and smell the air in it. Result?
Conclusion? _Experiment 7._ Pierce a small hole in a card, place card
over a wide-mouthed bottle, and breathe into bottle through a tube,
lemonade straw, or hollow reed. Pull out straw. Place bottle, mouth
downward, on table, and slip out card. Slide bottle to edge of table
and lift lighted candle into bottle. Result? _Experiment 8._ Place
bottle of fresh air over lighted candle. Result? Conclusion? (See
Animal Biology, p. 4.)
_Experiment 9._ (School.) =Testing the Air of a Room.=--Fill a fruit
jar or large bottle with water, and take it into a room containing
many people. Pour out the water. (This insures that all the air now
in the jar is air obtained in the room to be tested.) Seal the jar if
test is not to be made at once. Test by pouring in two tablespoonfuls
of clear limewater and shake. If the limewater turns milky, the
ventilation is bad.
_Experiment 10._ (Home and school.) =Homemade Current
Detector.=--Dangle a bit of paper by means of a spider web or thread
from the end of a walking stick or ruler. (Or test with the flame of
a candle.) Hold it near cracks of window, above and below doors, and
especially before openings intended for entry and exit of air, and
test if air moves as desired.
_Experiment 11._ =Ventilation of the Schoolroom.=--Let the whole
class rise, and with the fingers test cracks around doors and
windows. Wherever the air feels cold to the hand the air is entering.
_Experiment 12._ =Dust.=--With a mirror cause a sunbeam to play like
a search light into a closed room several hours after it has been
swept. Result? Do the same in a room where every window and door were
open during sweeping and left open afterwards. Result? Conclusion?
Note also the amount of dust on the furniture of each room.
_Experiment 13._ =Study of Habitual Quiet Breathing.=--Without any
more disturbance of the breathing than can be helped, direct your
attention to your breathing while sitting quietly. Record motions of
any parts of chest and abdominal walls that may be noticeable. If
necessary, lay the hands successively against different parts of the
wall to test for motion. Think of another subject, and later repeat
observations.
_Experiment 14._ =Study of Deep Breathing.=--Place your hands
successively upon the front and sides of your chest, waist, and
abdomen, while drawing in and sending out deep breaths. What motions
of the several parts are observed at each stage?
_Experiment 15._ =Study of Elasticity as a Factor in Breathing.=--(1)
Notice whether in quiet breathing there is an elastic rebound as the
breath goes either in or out. If so, it is due to the elasticity
of the cartilages or air cells of lungs, or both. (2) Breathe by
inflating the lungs strongly at each breath. Is the air then forced
out without effort? (3) Breathe by flattening the chest and abdomen
as much as possible at each breath. Does the air then rush in without
effort?
_Experiment 16._ =Chest Breathing.=--Try to breathe wholly by deep
expansions and contractions of chest wall. What motions, if any, are
noticed in abdominal wall as breath goes in? As it goes out? (Test
motions with hand.)
_Experiment 17._ =Abdominal Breathing.=--Try to hold the chest walls
still and breathe by strong contraction and expansion of abdomen. Do
the chest walls move at all? Neither “chest breathing” nor “abdominal
breathing” is the normal way. See text.
_Experiment 18._ =Full Breathing.=--Try breathing by outward and
inward movement of walls of chest, _waist_, and abdomen. Do you
succeed? This is normal breathing. Is the motion greater at the front
or the sides of the waist? Put a belt around the waist tight enough
to stay in place and repeat. Is the waist motion interfered with?
_Experiment 19._ =How the Ribs are Lifted.=--Make a model-like sketch
to represent backbone, breastbone, and two ribs, using pins to make
joints loose at corners. Use cords for diagonals. What happens when
cord _ac_ is pulled? When cord _bd_ is pulled? The cords correspond
to the two sets of muscles between the ribs.
[Illustration]
_Experiment 20._ =Study of Laughing.=--Place the hands upon the waist
and abdomen when laughing. What motion occurs at each sound of laugh?
Draw in the abdominal wall with a jerk. What is the effect upon the
breath?
_Experiment 21._ =Modifications of the Breath.=--Write I, E, or IE
after each word in this list, according as inspiration, expiration,
or both, are involved in the action. (Test with sham acts if
possible.) Sighing, sobbing, crying (of a child), coughing, laughing,
yawning, sneezing, hiccoughing, snoring.
_Experiment 22._ =Effects of Exercise.=--Count and record the rates
of breathing before and after vigorous exercise.
_Experiment 23._ =Comparative Study.=--Observe and record the rate
and manner of breathing of cow, horse, dog, cat, etc. Is the air
drawn in or sent out more quickly? Is there a pause? If so, after
which stage of breathing?
_Experiment 24._ =Emergency Drill.=--Resuscitation from drowning,
etc. See Coleman’s “Elements of Physiology,” page 356.
=Necessity for Breathing and for Specialized Organs of Breathing.=--The
body is a self-regulating machine which possesses energy. This
energy, like that of steam engines, arises from oxidation which takes
place continually, but at a varying rate. Food for fuel is taken at
intervals, but oxygen must be taken in continually. Man breathes about
eighteen times per minute. The blood in the tissues soon becomes
dark because of loss of oxygen and absorption of carbon dioxid. It
is then pumped through the heart to the organ which has the function
of absorbing oxygen and giving off carbon dioxid (Fig. 67). In some
animals, as the ameba and the earthworm, the surface of the body
suffices for breathing. This cell breathing is the true essential
respiration; it is universal among living things, both plants and
animals. _To supply the deeper cells large animals require a breathing
surface greater than the area of the skin. This is supplied by having
the oxygen-absorbing surface folded inward to form folds, tubes, and
cavities_ of great complexity. If the lungs of a man were unfolded and
all their tubes and cavities spread upon one surface, an area of more
than one hundred square feet (or ten feet square) would be covered.
Each =respiration=, or breath, consists of the passing in of the air,
or _inspiration_, sending it out, or _expiration_, and a _pause_ after
one but not after both of the other stages.
[Illustration: FIG. 67.--CIRCULATION THROUGH LUNGS (schematic):
“venous” blood (in pulmonary artery) black; “arterial” blood (in
pulmonary veins) white.]
[Illustration: FIG. 68.--OPEN MOUTH, showing palate and tonsils.]
[Illustration: FIG. 69.--LUNGS, _P_; with trachea, _TA_; thyroid gland,
_th_; larynx, _L_; and hyoid bone, _H_.]
=The Air Passages.=--The air usually passes in at the nose and
returns by the same way, except during talking or singing. Observe
your mouth with a mirror (Fig. 68); at the back part, an arch is seen
which is the rear boundary line of the mouth (Exp. 1). Just above
the arch is likewise the rear boundary line of the nasal passages.
The funnel-shaped cavity beyond, into which both the mouth and nasal
passages open, is called the _pharynx_ (far′inks), or throat (see Fig.
68, also Fig. 83). Below, two tubes open from the pharynx. One is
the _trachea_ (trā′kea) or windpipe, the other is the _esophagus_ or
_gullet_. At the top of the trachea is the cartilaginous _larynx_, or
voice box. If the finger is placed upon the larynx or Adam’s apple,
it is plainly felt to move up and down when swallowing. The opening
into the larynx is provided with a lid of cartilage, the epiglottis.
Inside the larynx, the vocal cords are stretched from front to back.
Just below the larynx comes the _trachea_ proper, which is a tube about
three fourths of an inch in diameter and about four inches long (Fig.
69). It consists of hoops of cartilage (Fig. 69) which are not complete
circles, but are shaped somewhat like the letter C, being completed at
the rear by involuntary muscular tissue, whose function is to draw the
ends together at times (for instance, during coughing) and reduce the
size of the tube. The function of the hoops of cartilage is to keep the
windpipe open at all times. If it should be closed by pressure, life
might be lost. These rings of cartilage may be felt in the neck.
[Illustration: FIG. 70.--LOBULE OF LUNG.]
The lower end of the trachea is just behind the upper end of the
breastbone; there it divides into two large tubes. These subdivide
into a great number of smaller branches called _bronchial tubes_.
Cartilage is found in the walls of all but the smallest of the tubes.
The subdivision continues, somewhat like the branching of a tree, until
the whole lung is penetrated by bronchial tubes. Each tiny tube finally
ends in a wider funnel-shaped chamber called a _lobule_ (Fig. 70), into
which so many dilated sacs, called _air cells_, open, that the walls of
the terminal chamber or lobule may be said to consist of tiny cups, or
air cells, placed side by side. The lobules, or clusters of air cells,
are chiefly near the surface of the lung. (The word “cell” is here used
in its original sense to denote a cavity or chamber, and not in the
sense of a protoplasmic cell.)
[Illustration: FIG. 71.--CAPILLARIES AROUND AIR SACS OF LUNGS (enlarged
30 diameters). Air sacs in white spaces. Dark lines are capillaries.
(Peabody.)]
The _air cells are elastic_ and enlarge by stretching as the chest
expands; hence, the cells must have many of the _yellow_ elastic fibers
of connective tissue in their walls. They are lined with an exceedingly
thin membrane of epithelial cells through which _oxygen and carbon
dioxid are exchanged_. In the walls of the air cells there is _a
network of capillaries_ (Fig. 71). The dark red blood comes into these
capillaries from the pulmonary arteries, and is changed to a bright red
by the time it leaves them to enter the pulmonary veins. The air leaves
the lungs warmer, moister, and containing more carbon dioxid than when
it entered.
Most of the =mucous membrane lining the air passages= has a surface
layer of ciliated cells. _Cilia are tiny thread-like projections_ (Fig.
72) which continually wave to and fro, the quicker stroke always being
outward; for their function is to remove particles of dust and germs
that may find entrance to the air passages. When the mucus containing
the dust is raised nearly to the larynx, it may be thrown out by
coughing. _Near the opening of the nostrils are placed many hairs_,
hundreds of times larger than cilia, through which the air is strained
as it enters the nose. Hairs are multicellular; cilia are parts of
cells. See Animal Biology, Fig. 14.
[Illustration: FIG. 72.--CILIATED CELLS, lining the air passages.]
=The Lungs.=--The entire _chest cavity_ is occupied by the lungs except
the space occupied by the heart, the larger blood vessels, and the
gullet. The right lung has three lobes, or divisions, and the left
lung has two lobes. The lungs are light pink in early life, but become
grayish and darker as age advances. This change is more marked in those
who dwell in cities, or wherever the atmosphere is smoky and dusty.
The lungs are covered and inclosed by a smooth membrane called the
_pleura_. This membrane turns back and lines the chest wall, so that
when the chest expands, the two sleek membranes glide over each other
with far less friction than would be the case if the lungs and chest
wall were touching (Exp. 2).
[Illustration: FIG. 73.--VERTICAL SECTION OF TRUNK, showing diaphragm,
cavities of thorax and abdomen.]
=The Respiratory Muscles.=--(Repeat Exps. 13, 14, 15.) The chief
breathing muscles are the _diaphragm_ (see Figs. 73 and 74), the
muscles _forming the abdominal walls_ (see Fig. 44), and _two sets of
short muscles_ (an internal and an external set), _between the ribs_.
They are called _intercostals_. (They are the flesh eaten when eating
pork ribs.) The _diaphragm_, which is shaped like a bowl turned upside
down, rounds up under the base of the lungs somewhat like a dome and
separates the chest from the abdomen. Its hollow side is toward the
abdomen and its edges are attached to the lowest ribs and the vertebra
of the loins. Inspiration is brought about by the rising of the ribs
and the descent of the diaphragm. Expiration takes place when the ribs
descend, the abdominal walls draw in, and the transmitted pressure
lifts the relaxed diaphragm.
[Illustration: FIG. 74.--DIAPHRAGM (or midriff), seen from below.
(Cunningham.)
The central portion (light) is tendinous. As the diaphragm descends, it
acts like the piston of a great pump and the blood is forced up through
the vena cava, and the lymph through the thoracic duct (Fig. 66).]
=Inspiration.=--To cause inspiration the diaphragm contracts, it
flattens and descends, since its edges are attached lower than its
middle (Fig. 73); the lungs descend with it, thus lengthening the
chest from top to bottom; at the same time the ribs are raised upward
and outward (Fig. 76) by the contraction of the outer set of muscles
between the ribs. Thus the _chest is made longer, broader, and deeper
from front to back_. The lungs expand when the chest expands, and the
air rushes in. Why is this? The lungs contain no muscles and cannot
expand themselves; the air cannot be pulled in, for its parts do
not stick together. The true reason is that the air has weight. The
atmosphere has a height of many miles, and the air above is pressing
on that below. When the chest walls are raised there would be an empty
space or vacuum between these walls and the lungs, did not the pressure
of _the outside air push air through the windpipe into the lungs and
expand them_ (Exp. 19).
[Illustration: FIG. 75.--FRAMEWORK OF CHEST.]
=Expiration.=--In very active breathing the abdominal walls actively
contract so that they press strongly upon the digestive organs, which
in turn _press the diaphragm up. The ribs are also drawn down and in_.
Thus the chest becomes smaller and forces the air to flow out through
the windpipe (Exps. 20 and 21).
[Illustration: FIG. 76.--BLACKBOARD SKETCH, to show how the chest is
expanded when the ribs move upward and outward.]
THOUGHT QUESTIONS.--_Why breathing with the waist is easier than
breathing with the upper chest. Effects of confining the waist_.
1. There are two pairs of ____ ribs below, while there are none
above. 2. There are three pairs of ____ ribs below, while there
are none above, but all ribs of the upper chest are ____ ribs. 3.
The lower of the joints between the seven pairs of true ribs and
the sternum are more flexible than the upper joints because ____.
(Observe the joints in Fig. 75.) 4. The walls of the waist swing ____
and ____, while the walls of the upper chest must move ____ and ____.
5. The bones of the ____ rest upon the upper chest. In upper chest
breathing their weight, and the weight of both of the ____ must,
therefore, be lifted. (Fig. 28.) Test by trying it.
[Illustration: FIG. 77.
FIG. 78.
FIG. 79.
FIG. 77.--FEMALE FIGURE ENCASED IN CORSET. Expansion at the waist is
here impossible and the breathing is called “collar-bone breathing.”
FIG. 78.--MALE FIGURE. Here, owing to pressure of clothing and faulty
position, expansion of chest is hindered and breath is taken by the
“abdominal method.”
FIG. 79.--FIGURE PROPERLY POISED AND FREE. Here the entire thorax can
move freely, and natural breathing is the result. (For blackboard.)
From Latson.]
=Hygienic Habits of Breathing.=--Chest breathing uses chest chiefly,
abdominal breathing uses abdomen chiefly, full breathing uses both.
These three forms depend upon whether the breathing is carried on
by using the muscles of (1) the chest, (2) the abdomen, or (3) both
(see Figs. 77, 78, 79). There has been much debate among physicians,
surgeons, and singers as to which of these methods is best. Probably
this question would not have been raised but for the confining and
deforming effect of clothing upon the waist. _Full breathing is used by
children of all races, by both men and women of wild tribes, and by men
of civilized countries._ It is undoubtedly the natural way, as well as
the easiest and most effective way (Exps. 16, 17, 18).
Breathing with the upper chest is exhausting because of the stiffness
of the upper part of the bony cage (see Fig. 75); for it is inclosed
by true ribs fixed to the breastbone by short cartilages. The ribs
in the waist (Fig. 75) are either floating in front or fixed by
long cartilages to the ribs above. In pure abdominal breathing
the diaphragm must contract more than in full breathing in order
to descend, because its edges have been drawn together and fixed
by binding the ribs at the waist. In full breathing the floating
and false ribs at the waist (five pairs in all) float in and out
as nature provided. As they move out, this broadens and deepens
the chest, and aids the flattening of the diaphragm by moving its
edges farther apart. Those persons, perhaps one in a thousand, who
voluntarily deform the body with tight clothing are beneath contempt.
But so uniform is the pressure of tight clothes and shoes that the
wearer soon becomes unconscious of them, and so powerful are the
effects that not one person in a thousand escapes deformity and
injury. Children’s clothing should be supported by the shoulders, and
adults’ clothing by both shoulders and hips, but by the waist, never.
=Cellular Respiration.=--The chemical activities within the cells and
their need of oxygen, not the amount of oxygen in the lungs or blood,
determine how much oxygen the cells absorb from the blood. Oxygen
cannot be forced even into the blood beyond the required amount. Deep
breathing movements, however, help the flow of the blood and lymph.
Carried to excess, they tire the will and exhaust the nerves.
=Changes in Blood while in the Lungs.=--The coloring matter
(or hemoglobin) of the corpuscles absorbs oxygen (and becomes
oxy-hemoglobin). Carbon dioxid is given off from the plasma. The blood
becomes a brighter red.
=Changes in Air in the Lungs.=--The air entering the lungs consists of
about one fifth oxygen and four fifths nitrogen. This nitrogen is of
no use to the body, and is exhaled unchanged. _A part of the oxygen
inspired is taken up by the blood, and carbon dioxid is sent out in its
place._ About half a pint of water is given off through the lungs in a
day. Minute quantities of injurious animal matter are also given off
in the breath from even the soundest person. The air leaves the lungs
warmer, damper, and with more carbon dioxid than when it entered (Exps.
3 to 9).
[Illustration: FIG. 80.--VENTILATION OF STOVE-HEATED ROOM.[5]
How are the inlet and outlet situated with reference to the stove?]
[5] From Coleman’s Elements of Physiology (400 pp.). The Macmillan
Co., N.Y.
Persons with decayed teeth, catarrh, indigestion, diseased lungs,
or other unsoundness give off still more of this material. When
many people are assembled in a badly ventilated room, the amount of
injurious animal matter in the air is much increased, and is called
“_crowd poison_.” Its odor is strong and repulsive to one who just
enters the room, but the sense of smell becomes dull to it in a few
minutes. It would seem that nature gives a fair warning against harm;
but if we disregard the warning it soon ceases.
=People who are really Unclean.=--Nature’s plan seems to be for us
to live out of doors. Air once breathed is impure. It is just as
unfit to enter our bodies as muddy water or decayed food. Yet many
who call themselves cleanly and refined, and _will not allow a speck
of dirt to remain on their clothes, nor use a spoon just used by
another, do not object to breathing into their lungs, over and over
again, the cast-off air from the lungs of others_. If a window is
opened for ventilation, they are horror-stricken for fear of drafts.
Drafts are injurious only to persons perspiring, or to those who have
coddled the skin by continually overheating it. There are thousands
of schools, churches, and theaters all over the land which reek daily
with the malodorous particles from the lungs of their occupants.
Although the air in them is odorless to those who occupy them, it is
disgusting to any one who enters from the fresh air. Figure 80 shows
the correct ventilation of a stove-heated schoolroom.
=Dust= causes catarrh of the bronchial tubes and chronic inflammation
of the lungs; it prepares for consumption, by gradually weakening
the lungs of those who breathe it. Intelligence and common sense are
necessary to prevent it from accumulating in the house. The chief
purpose of the house cleaning should be not only to remove bits of
paper from the floor, which do no harm even to the shoes, but _to
remove impurities from the air_. _It does no good to stir up the dust
and allow it to settle down again_ (Exp. 12). In many houses dust is
thus allowed to accumulate for months. Experiments show that dust and
germs floating in the air are not diminished to a great extent by a
gentle draft through the room. The windows must be open and sweeping
done in the direction of the air currents; the windows should be _left
open for a long while after the sweeping_. A windy day is best for
sweeping.
The habit some housekeepers have of buying furnishings and
bric-à-brac for the home until it looks like a retail store or
junk shop, makes it almost impossible to clean their houses. A few
articles, carefully selected, adorn a home more than many bought
at random, and they do not litter the house and serve as traps for
dust. With all precautions some dust may settle down. This should not
simply be stirred up again with a feather duster, but _the dusting
should be done with a damp cloth_. Ashes should be sprinkled before
they are moved. Carpet sweepers, but never brooms, should be used
upon carpets. Carpets and lace curtains are truly dust traps, in
which dust will accumulate without limit. Those who value the health
will not use such uncleanly abominations, at least in bedrooms.
Though linoleum, bare floors with movable rugs, oiled and painted
floors, may not look so comfortable as a fixed carpet, they bring
far more comfort in the end. _The weakening effect of ordinary dust
is one of the chief causes of lung diseases_, and prepares a fertile
soil for the consumptive germ. The sputum coughed up by consumptives
falls upon the floor or street, soon dries, and the germs are driven
about by the wind. In many cities there is a law against spitting in
public places, and the streets are flushed with water before they are
swept.
[Illustration: FIG. 81.--The air enters through a special inlet and is
warmed as it passes through hood surrounding the stove.]
[Illustration: FIG. 82.--Chimney with a passage behind fireplace, or
grate, in which the air is warmed as it enters.]
=Ventilation= presents no difficulties in the summer time or in warm
climates. The reason that it is a difficult question in cold weather
is because the air furnished must be not only pure, but warm. To keep
cold air out often means to keep foul air in. _Heating with hot air_,
by which system pure air is passed over a furnace, and fresh air
constantly admitted, may be a good method (Figs. 80, 81), but is often
a dismal failure because it dries out the air, which in turn dries out
the skin. To prevent this, wide vessels of water should be set at the
inlets. Dry air is cooling. Why? Dr. Barnes proved that moist air at
65° is as comfortable as dry air at 71°. Air saturated with vapor at
60° will _only be 50 per cent saturated at 80°_. Such air dries out
the mucous membrane of eyes, nose, and throat. Heating by _hot water_
circulating in pipes, or _by steam_, gives no means of introducing
fresh air, and is likely to cause worse ventilation than any other
method. The radiators should stand close to windows or other fresh-air
inlet, that the air may be heated as it enters, and the outlet for air
should be farthest from the radiators. The same rules apply to heating
by _stoves_. An oil stove for heating is an inconceivable iniquity to
any but a person densely ignorant of hygiene. Heating by _fireplaces_
(Fig. 82) is the most healthful of all methods, for there is a constant
removal of air through the chimney, and this air will be replaced;
even if all doors and windows are closed, it will come in through tiny
cracks. _Radiant heat_ travels in straight lines from a fireplace
and _warms solid objects_, but not the air passed through. Hence an
open fire will keep the body warm with the room at a low temperature.
Fireplaces, however, do not afford sufficient heat in severe climates.
_Stoves_ are not as healthful as fireplaces, for there is not so
much air removed through the pipe as through the chimney. _Carbon
monoxid_, unlike carbon dioxid, is an _active_ poison causing the blood
corpuscles to shrivel. It passes through red-hot iron or a cracked
stove or furnace.
[Illustration: FIG. 83.--BLACKBOARD SKETCH.]
[Illustration: FIG. 84.--Facial expression in mouth breathing, and
breathing through the nose.]
=Reasons for Breathing through the Nose= (Fig. 83).--(1) The many
blood vessels in the mucous membrane lining the nasal passages so
_heat the air_ that it does not irritate the bronchial tubes. (2)
_The hairs in the nostrils strain the air_ and catch dust; the cilia
of the nasal passages also do this. (3) A mouth-breather often
_swallows food before chewing it sufficiently_, because he cannot
hold his breath longer. (4) The nasal mucous membrane of an habitual
mouth-breather _dries and shrinks_ and obstructs the circulation,
bringing on _catarrh of the nose_. (5) Mouth breathing causes an
_unpleasant expression of countenance_ (see Fig. 84). (6) The breath
does not come through the nose as quickly as through the mouth; the
_lungs are kept more expanded_, and one does not get “out of breath”
so quickly. (7) _The voice of the mouth breather has a hard twang_,
not a full, resonant tone as when the nostrils are open. (8) _Flavors
and odors_ are better appreciated. Sometimes the sense of smell
is almost lost by mouth breathers. If one cannot breathe through
the nose, even for a short time, there is probably an adenoid, or
tonsil-like, growth in nose or pharynx, and a physician should be
consulted. “Adenoids” are glandular or grapelike in form.
=Diseases of the Respiratory Organs.=--_A cold or catarrh is an
inflammation of a mucous membrane._ If the inflammation is in the
nasal passages, it is called a _cold_ in the head; if it is in the
pharynx, it is called a _sore throat_; if it is in the larynx or
voice box, there is _hoarseness_; if it is in the bronchial tubes,
it is _bronchitis_; finally, if it is in the air cells, it is
_pneumonia_. If the air is cut off from access to the air cells,
there is an attack of the painful disease called _asthma_, which is
accompanied by a feeling of suffocation. Some believe that asthma
is caused by the mucous membrane lining the finest bronchial tubes
becoming inflamed and swollen, and closing the tubes; others think
that the muscles in the large bronchial tubes contract and close the
tubes. _Pleurisy_ is inflammation of the pleura and makes breathing
painful. If much fluid forms between the pleuras, the inner pleura
may press upon the lungs and interfere with breathing.
=Alcohol= not only weakens the blood vessels near the surface, but the
blood vessels in general. Weakened and congested blood vessels in the
lungs make them more liable to pneumonia and other congestive diseases.
Continual congestion causes an abnormal growth of connective tissue
fiber in the walls of the cells. This diminishes the capacity of the
lungs and interferes with the exchange of carbon dioxid and oxygen.
=Tobacco.=--It is often asked why cigarettes are so much more injurious
to the health than pipes and cigars. The nature of the paper of
cigarettes and various other absurd reasons have been assigned. The
true reason is that the cigarette smoker usually _inhales_ the tobacco
smoke. Cigar smoke, if drawn into the lungs, would usually be coughed
up at once. Cigarette smoke is weaker--it is so weak that the smoker is
not content simply to absorb the nicotine through the mucous membrane
of the mouth; he draws it into the lungs. The very mildness of the
smoke leads to inhalation. Hence, as the _surface_ of the lungs is a
_hundred times greater_ than the surface of the mouth, and _its lining
much thinner_, cigarette smoking is far more injurious than cigar
smoking.
The poison accumulates in the bowl of a pipe; hence an old pipe is
very injurious. The irritation of tobacco smoke often sets up a
chronic dry catarrh of the air passages; rarely it causes cancer of
lips or tongue. Sir Henry Thompson says: “The only persons who enjoy
smoking and find it tranquillizing at times are those who smoke in
great moderation. Men who are rarely seen without a cigar between
the lips, have long ceased to enjoy smoking. They are confirmed in a
habit, and are merely miserable when the cigar is absent.” They do
not smoke for pleasure, but to escape misery which wiser men escape
by avoiding tobacco altogether.
[Illustration: FIG. 85.
FIG. 86.
FIG. 85.--FLATTENED CHEST and waist organs sunken from wearing tight
clothing since the age of fourteen. Such women often walk with bodies
bent forward to hide the prominent abdomen.
FIG. 86.--A NATURAL WOMAN.]
PRACTICAL QUESTIONS.--=1.= State how in the case of a person with
round shoulders a gradual remolding of cartilages (which ones?),
the strengthening of the muscles (which ones?), and the practice of
deep breathing may each contribute toward acquiring an erect and
perfect figure. =2.= Should a hat be well ventilated? (A punch for
making the holes costs a dime.) Should a hat be stiff or soft? =3.=
Name habits that impair the power of the lungs. =4.= How could you
convince a person that a bedroom should be open while and after it
is swept? That it should be ventilated at night? =5.= Which is the
more injurious to others, tobacco chewing which causes the ground
to be unclean, or smoking which renders the air impure? =6=. Why do
those who stand straight up to hoe not get tired half so quickly as
those who bend or “hump” over? (Chap. VI.) =7.= Why do students who
sit in rocking chairs, or from other causes lean the head forward
when they study, often find that they recover from drowsiness if they
sit erect, or sit in a straight chair? =8.= How are high collars a
fruitful source of bad colds? =9.= If the draft up the chimney of
the fireplace, when the fire is burning, takes up a volume of air
sufficient for many people, why is it unnecessary to open a window?
=10.= Why does cold impure air make a person colder than cold pure
air? (p. 14.) =11.= Do the modern customs of uniformity in dress for
all classes and climates, shipping foods from great distances, one
section or nation imitating the ways of another section or nation,
lead toward health or disease? Do such customs violate or conform
to the great biological law that life is a process of adaptation to
environment?
[Illustration: FIG. 87.--SUSPENDERS should have a pulley or lever at
the back, that the strap on one side may loosen when one shoulder is
raised.]
[Illustration: COLORED FIGURE 6.--ORGANS OF THE TRUNK.
_cb_, collar bone; _r_, ribs; _z_, tongue bone (hyoid); _k_, _k_,
cartilages of larynx; _l_, windpipe; _s_, thyroid gland; _rv_, right
ventricle; _lv_, left ventricle; _ru_, right auricle; _lu_, left
auricle; _a_, aorta; _ka_, artery to head (carotid); _sa_, subclavian
artery; _la_, pulmonary artery; _oh_, superior vena cava; _hv_, jugular
vein; _lu_, lungs; _f_, diaphragm; _lb_, liver; _g_, gall bladder;
_s_, stomach; _x_, spleen; _n_, mesentery with vessels; _d_, small
intestine; _gd_, large intestine; _b_, cæcum; _w_, vermiform appendix;
_h_, bladder.]
CHAPTER VII
FOOD AND DIGESTION
_Experiment 1._ =Tests for Acid, Alkaline, and Neutral
Substances.=--Repeat tests described in General Introduction.[6]
[6] See also Peabody’s “Laboratory Exercises in Physiology,” Holt, N.Y.
_Experiment 2._ =Test for Starch.=--See General Introduction.
_Experiment 3._ =Test for Grape Sugar.=--See General Introduction.
_Experiment 4._ =Test for Proteid.=--See General Introduction.
_Experiment 5._ =Test for Fats.=--See General Introduction.
_Experiment 6._ =Human Teeth.=--Study the form of teeth from every
part of the mouth. Get a handful from a dentist. Break some of the
teeth to make out their structure. Classify them. Draw section,
enlarged.
_Experiment 7._ =Study of the Teeth.= (At home.)--Sit with the back
to the light and look into a mirror, with the mouth wide open. Do
you see the four kinds of teeth named in text? Which are fitted for
cutting? Which for grinding? Are any suited for tearing? Are any
of the teeth pointed? What is the difference in the bicuspids and
molars? Are there any decayed places? Are the teeth clean? Are the
so-called canine teeth so long that they project beyond the line of
the other teeth, as they do in a dog? Do the edges of the upper and
lower incisors meet when the mouth is closed, or do they miss each
other like the blades of scissors? How many roots has each lower
tooth? (See Fig. 92.). Which tooth has the longest root?
_Experiment 8._ =Structure of Mammalian Stomach.=--Get a piece of
tripe from the market. Study its several coats. The velvety inner
coat is covered with mucous membrane. (Photomicrograph, Fig. 95.)
_Experiment 9._ =Model of Human Food Tube.=--Make a model of the food
tube out of yellow cambric, giving to each organ its correct size.
Follow the dimensions given in text.
=Necessity for Foods.=--Growing plants and growing animals need new
material to enable them to _increase in size or grow_. Plants never
cease to grow while they live; most mammals attain their full size in
one fifth of the time occupied by their whole lives. (By this rule how
long ought man to live?) Animals, moreover, _move from place to place_,
and _work_ with their muscles. The energy for this comes from the food
they eat. Plants do not use food for this purpose. Another need for
food comes from the _necessity for heat_ in all living things. The
activities of animals cause the tissues to wear out, or break down, and
food furnishes material with which new living matter is built up by
the cells and the _tissues repaired_. We have already stated the rôle
of oxygen in setting free energy in the living substance of the cell
by oxidizing it. There is no furnace in the body as in an engine, but
the oxidation occurs in the cells themselves and the fuel is built up
into living matter by the cells before it is oxidized. Plants must lift
mineral from the inorganic to the organic world before it can be food
for animals. Plants can assimilate minerals; animals cannot. The body
cannot make bone out of limewater. The iron in iron tonics cannot be
used. Iron makes the grain brown, and the peach red. There is ten times
as much iron in our food as the body needs.
State four reasons why animals need food. Which of these reasons is
very powerful with plants? Least powerful? Absent altogether? Why is
constant breathing necessary for life? When is breathing more rapid?
Why? People who lead what kind of lives usually have poor appetites?
Good appetites? Why? What was the first distinct organ evolved by
animals? (Animal Biology, Chap. IV.)
=The Body is a Machine for transferring Energy.=--Energy cannot be
destroyed, but it can be transferred and changed in form. When a coin
is rubbed on the table, muscular energy, supplied by oxidation in the
muscle, produces the motion. Friction may change motion into heat, and
the coin will become very hot. The uniting of food and oxygen in the
cells of the body gives the heat and motion (energy) of the body. Only
substances which will oxidize, or burn, are true foods. Water, salt,
and carbon dioxid will not burn; hence, they cannot give rise to energy
in the body. But the sun energy, acting in the green leaf, tears apart
the carbon from the oxygen (Plant Biology, Chap. XIII), sets free the
oxygen, and the carbon is stored in starch for future burning. Sunshine
is energy (light and heat). The sun sustains the life of plants and
through them the life of animals. The oxidation in the body is so slow
that it can hardly be called a burning, but it is faster than the
oxidation of iron in rusting or of wood in rotting, and is about equal
to the continual burning of two candles.
=The Four Kinds of Nutrients, or Food Stuffs.=--The _kinds of food
which we eat seem to be numberless, but they contain only four kinds
of food stuffs_,--starches, fats, proteids, and minerals. Many foods
contain all four classes of food stuffs. Milk contains sugar (a
changed form of starch), cream (a fat), curd (a proteid), and water (a
mineral). Oatmeal contains starch, oil, gluten, and water.
USES OF THE NUTRIENTS, OR FOOD STUFFS
1. Proteids. The tissue-building foods (also of value
as fuel).
2. Starches (and sugars) }
} Energy and heat (fuel) and fat producing
} foods.
3. Fats (and oils) }
4. Minerals (water, salt). Important aids in using other foods.
=Relative Fuel Value.=--A pound of fat produces as much heat in the
body as 2.3 lb. of proteid or 2.3 lb. of starch, the last two having
equal fuel value in the body.
=Starch and the sugars= are closely related; starch readily changes
into sugar. They contain much carbon and are called =carbohydrates=.
Starch is especially abundant in grains, seeds, and fleshy roots (Fig.
88). The sugar in ripe fruit and in honey is called _fruit sugar_.
_Milk sugar_ is found in sweet milk. _Grape sugar_ is found in grapes
and honey; the small grains seen in raisins consist of grape sugar; it
can also be prepared artificially from starch. _Cane sugar_ is found in
cane, in sap of the maple, and in the sugar beet (Exps. 2, 3).
[Illustration: FIG. 88.--A TINY BIT OF POTATO, highly magnified,
showing cells filled with grains of starch. Cooking bursts these cells.]
=Fats= include the fats and oils found in milk, flesh, and plants. A
fat, such as tallow, is solid at the ordinary temperature; while an
oil, such as olive oil, is liquid at the same temperature. Tallow was
oil while it was in the warm body of the ox. Sugar is transformed into
fatty tissue as readily as is fatty food itself.
=Proteids= are the only foods that contain the tissue-building
nitrogen. Protoplasm cannot be formed without nitrogen. We do not
often see a pure proteid food, for this food stuff is not so readily
separated from foods containing it as are starch, sugar, and fat.
Albu_men_, or white-of-egg, is proteid united with four times its
weight of water. Pure proteid is also called albu_min_. Coagulation
by heat is one test for proteid (Exp. 4). These are the names of
proteids, or albumins, found in several common foods: _casein_, the
curd or cheesy part of milk; _myosin_ of lean meat; _fibrin_ in blood;
_legumin_ in beans and peas; _gluten_, or the sticky part of wet
flour; _gelatin_ in bones. Proteid is valuable to the body as fuel as
well as a tissue builder. We could burn beans and peas as well as the
strictly fuel foods, starch and fat, in an engine, and get heat to
move the engine. If one takes up athletics or hard physical labor, he
should increase the amount of fats and carbohydrates eaten, but not
of proteid. Muscular activity increases the carbon waste but not the
nitrogen waste of the body.
=Minerals.=--The iron of the blood and the mineral salts in bone
(carbonate and phosphate of lime) must enter the body in organic form
in order to be used. Water and salt are mineral foods. The body is
about two thirds water. The cells must do their work under water.
They cannot live when dried. Water enables the blood to flow; and the
blood is not only the feeder, but also the washer and cleanser of the
tissues. Some persons get out of the habit of drinking plenty of water,
and their health suffers thereby. In such a case drinking plenty of
water will be safer and more effective than taking poisonous drugs to
restore health.
=Adulteration of Food.=--Sometimes _cheaper materials_, of little or
no value as food but of no great injury to health, are added to foods.
_Examples:_ water added to milk, sawdust to ground spices, chicory
to coffee, glucose to maple syrup. Other forms of adulteration not
only cheat the purse but _tend to destroy health_, or actually do so.
_Examples:_ Boracic acid or formalin added to milk to prevent souring,
copper to canned peas, etc., to give a bright green color; salicylic
acid or borax used in minute quantities as a preservative with canned
corn, tomatoes, etc.; acids added to “apple” vinegar; dried fruit
treated with sulphur to prevent a dull color. Pure food laws tend to
repress these evils. It is best to buy foods in their original form.
For instance, lemons are more reliable than vinegar. A bit of lemon
at each plate, in households that can afford it, is far preferable to
vinegar. We should always buy from neighbors when possible. Farmers and
gardeners should do their own drying and canning. For purity of water,
see Chap. X.
=The Daily Ration.=--_A quarter of a pound_ (4 oz.) _of proteid foods
and one pound_ (16 oz.) _of fuel foods_ (total 20 oz. of water-free
foods) are needed to replace the daily =waste= of the body. Hence a
_balanced ration_ has proteid and fuel food in the ratio of 4 to 16, or
1 to 4. But recent experiments at Yale University indicate that 2 oz.
of proteid daily are more strengthening than four.
_Appetite is a perfect guide for those who lead an active life and
eat slowly of simple food._ Highly seasoned food and complex mixtures
deprave the appetite; it then leads astray, instead of guiding safely.
Of course the appetite cannot guide one to eat the right kind and
quantity of food at a table where the food lacks any of the four
necessary food stuffs, or where innutritious or indigestible food is
provided. It is well to select one food for a meal because it is rich
in proteids, another because it is rich in fat, and the third because
it is rich in starch or sugar. (See table, p. 95.) Intelligence in
regard to diet enables a housekeeper to provide nourishing food for
less money than an ignorant housekeeper often pays for food deficient
in nourishing qualities.
=A Balanced Ration.=--A deficiency of starch may be supplied by an
excess of fat or sugar. It is most essential to provide proteid as it
cannot be replaced by any other food stuff. An excess of proteid is
most harmful. An excess of starch or fat is oxidized into water and
carbon dioxid, which are harmless waste products; an excess of proteid
is changed into urea which may become harmful by overworking the liver
and kidneys which excrete it.
COMPOSITION OF ONE OUNCE OF VARIOUS FOODS IN FRACTIONS OF AN OUNCE
========================+=======+=======+========+=======+=====+=====
| | | CARBO- | | MIN-|
| PRO- | | HY- | | ERAL|WOODY
| TEIDS | FATS | DRATES | WATER |SALTS|FIBER
------------------------+-------+-------+--------+-------+-----+-----
=Daily Ration= |=4 oz.=|=2 oz.=|=14 oz.=|=2 qt.=| | =0=
| | | | | |
I. NUTS. | | | | | |
Pecan | .103 | .708 | .143 | .03 | .017|
Walnut | .158 | .574 | .16 | .03 | .014|
Almonds | .235 | .53 | .12 | .078 | |
Cocoanut | .056 | .51 | | .35 | | .04
Chestnut | .037 | .02 | .38 | .54 | .009| .02
| | | | | |
II. FRUITS. | | | Sugar | | |
Peach | .007 | | .045 | .85 | .007| .04
Apple | .004 | | .072 | .84 | .005| .05
Blackberry | .005 | | .040 | .86 | .004| .01
Cherry | .005 | | .10 | .84 | .007| .02
Grape | .125 | | .15 | .70 | .005|
Fig (dried) | .040 | .014 | .50 | | |
Banana | .050 | | .20 | .75 | |
| | | | | |
III. ANIMAL FOOD. | | | | | |
Lean beef | .20 | .035 | .009 | .75 | .016|
Fat pork | .098 | .489 | | .390 | .023|
Smoked ham | .25 | .365 | | .278 | .101|
Whitefish | .181 | .029 | | .780 | .010|
Poultry | .210 | .038 | | .740 | .012|
Oysters | .175 | .005 | | .800 | .015|
Cow’s milk | .035 | .040 | .040 | .870 | .007|
Eggs | .125 | .120 | | .735 | .010|
Cheese | .335 | .243 | | .368 | .054|
Butter | .003 | .910 | | .060 | .021|
| | | | | |
IV. PODS OR LEGUMES. | | | Starch | | |
Beans | .25 | .020 | .52 | .125 | .035| .060
Peas | .217 | .019 | .577 | .12 | .028| .032
Peanuts | .2947 | .465 | .162 | .02 | .028| .043
| | | | | |
V. GRAINS. | | | | | |
Wheat flour (white)| .110 | .020 | .703 | .150 | .017| .003
Wheat bread | .080 | .015 | .490 | .400 | .012| .003
Oatmeal | .126 | .056 | .630 | .150 | .030| .016
Maize (corn) | .100 | .067 | .706 | .135 | .014| .015
Rice | .050 | .008 | .832 | .100 | .005| .040
| | | | | |
VI. VEGETABLES. | | | | | |
Potatoes | .012 | .001 | .205 | .767 | .009| .006
Cabbage | .02 | .030 | .058 | .910 | .007| .015
========================+=======+=======+========+=======+=====+=====
=Studies based on Table.=--What nuts are rich in proteids? What
fruits? What animal foods? What legumes? What grains? What foods are
rich in fats? What are rich in carbohydrates? Which grains have much
starch? Which nut? Which fruits have much sugar? A family was living
chiefly on corn bread, potatoes, syrup, cakes, and sweetmeats: what
two of the four food stuffs were deficient in their diet? Another
family lived chiefly on fat pork, bread, rice, vegetables, and
fruit: which food stuff was deficient? A dozen eggs weigh 1¹⁄₂ lb.
Which give cheaper nourishment, eggs at 15 cents a dozen or beef at
15 cents a pound? Which is cheapest among the foods abounding in
proteid? Fat? Carbohydrates? Which is cheaper food, a pound of beef
at 20 cents or a pound of pecans at the same price? (Fig. 101.) What
food contains most water? Least water? Which of the foods abounding
in proteid is costliest? Cheapest? Notice that nearly all foods
containing much proteid are costly. Water and woody fiber are not
counted as nutriment. What weight of nutriment in 1 oz. of cow’s
milk? If a quart of whole milk costs 12 cts., what is a quart of
skimmed milk worth?
=How the Right Proportions of Fuel Foods and Proteid are reached by
Different Nations.=--Milk has an excess of nitrogen, and oatmeal
an excess of carbon; oatmeal and milk form a popular food with the
Scotch. Potatoes are mostly starch and water, and an Irishman who
tried to live on potatoes alone would have to eat seven pounds a day
to get enough proteid. The Irish peasant keeps a cow and chickens;
by eating milk and eggs he gets along on half the amount of potatoes
named above. The Mexicans eat bread made of corn meal, and supply the
proteid by using beans as a constant article of diet. Hundreds of
millions of people in Asia (the Hindus, Chinese, and others) subsist
mainly on rice, which contains only five per cent of proteid and no
fat; the chief addition they make is butter, or other fat, and beans,
which contain vegetable proteid.
=Outline of Digestion.=--The food is made soluble in the alimentary
canal and is absorbed by the blood vessels and lymphatics in its walls.
This canal is about thirty feet long (Figs. 89, 90) and consists of--
(1) The =mouth=, where the food remains about a minute, while it is
chewed and mixed with the _saliva_; the saliva changes a portion of the
_starch_ to malt sugar.
(2) The =gullet=, a tube nine inches long, running from mouth to
stomach and lying in front of the spinal column.
[Illustration: =Illustrated Study of Food Tract.=
FIG. 89.--ORGANS OF TRUNK from the side.
_L_, larynx; _th_, thyroid gland; _T_, trachea; _St_, breastbone; _C_,
heart; _D_, diaphragm; _F_, liver; _E_, stomach; _I_, intestine; _Co_,
colon; _R_, rectum; _V_, bladder.
=Question:= Parts of which organs are farther back than spinal column?
Compare this figure with colored Fig. 6.
FIG. 90.--DIGESTIVE ORGANS, from the front (liver turned up).
1, gullet; 2, stomach; 3, spleen; 4, pancreas; 5, liver (turned
upward); 6, gall bladder; 7, 8, 9, small intestine; 9′, junction of
small with large intestine; 10, caecum (blind sac); 11, vermiform
appendix; 12, 12′, 12″, ascending, transverse, and descending colon;
13, rectum (straight) just below S-shaped flexure of colon.
=Question:= Compare with Fig. 89, and colored Fig. 6.]
(3) The =stomach=, a large pouch where the food is stored, and
from which it passes in the course of several hours, having become
semi-liquid, and the _proteids_ having been partly digested by the
_gastric juice_, an acid secretion from the small glands in the stomach
walls.
(4) The =small intestine=, a narrow tube more than twenty feet long,
where the _fats_ are acted upon for the first time, and where the
_starches_ and _proteids_ are also acted upon, and where, after about
ten hours, the digestion of the three classes of foods is completed by
_pancreatic juice_ from the _pancreas_, and _bile_ from the _liver_.
(5) The =large intestine=, about five feet long, where the last remnant
of nutriment is _absorbed_, and the _indigestible materials_ in the
food are gathered together (Exp. 9).
=The Teeth.=--The main body of the tooth consists of bone-like
_dentine_, or ivory. Hard, shining _enamel_ protects the crown, or
visible portion. The part of the tooth beneath the gum is called the
_neck_, and the part in the bony socket, is called the _root_. The
enamel ends just beneath the gum, where it is overlapped by _cement_ of
the root. There is a pulp cavity in every tooth (Fig. 91); it contains
_pulp_ made up of connective tissue, with nerves and blood vessels
which enter at the tip of the root (Exp. 6).
[Illustration: FIG. 91.--CANINE TOOTH CUT LENGTHWISE.]
The _temporary_ set of teeth is completed at about two years of age
and consists of twenty teeth. The teeth cannot grow as the jaw grows,
and soon a larger and _permanent_ set starts to growing deeper in the
jaw. At the age of twelve or thirteen years all the permanent set have
appeared except the four wisdom teeth, which appear between the ages
of seventeen and twenty-five. The second set not only replaces the
twenty of the first set, but to fill the larger jaws twelve molars are
added, three at the back in each half jaw, making thirty-two teeth
in the second set (Exp. 7). The teeth in each quarter of the mouth,
named in order from the front, are: two _incisors_, one _canine_, two
_premolars_, three _molars_.
[Illustration: FIG. 92.--THE PERMANENT TEETH in right half of lower
jaw.]
[Illustration: FIG. 93.--UPPER JAW WITH TEETH.]
=Care of the Teeth.=--The best way to care for the teeth is _to keep
the digestion perfect_. Perfect digestion tends to preserve the teeth,
and sound teeth tend to keep the digestion perfect. The teeth should be
_washed regularly_. Prepared chalk is the best dentifrice. Do not rub
across, but from gums to teeth, to prevent rubbing the gums loose from
the teeth. An unclean brush may harbor germs. _Toothpicks_ and dental
floss are useful. If one eats only soft food, in which the mill and the
cooking stove have left no work for the teeth, the teeth will decay;
for it seems to be a law of nature that useless organs are removed. The
pressure from _chewing hard food is an aid_ to the teeth by helping the
circulation and nerves in the pulp. To take a _very hot or very cold_
drink into the mouth may cause the _enamel to crack_. If a tooth aches,
or a small decayed place is found in it, a dentist should be consulted
at once. A tooth is so valuable to the health that no tooth should be
extracted when it can be saved.
=The process of digestion= consists in liquefying the food that it may
pass through the walls of the food tube into the blood, and through
the walls of the blood vessels into the tissues. It is accomplished:
(1) by _mechanical_ means, including the chewing muscles, the teeth,
and three layers of muscles in the walls of the food tube; (2) by
_chemical_ means, or the action of alkalies and acids upon the food;
(3) by _organic_ agency, or the action of ferments. A _ferment_ (or
_enzyme_) is a vegetable substance which has the power of producing a
chemical change in large quantities of substance brought in contact
with it, without being itself changed. There is one ferment secreted in
the mouth, two in the stomach, and three in the small intestine.
=Digestion in the Mouth.=--_Saliva_ is formed by six glands: one in the
cheek in front of each ear, one at the angle of each lower jaw, and one
pair is beneath the tongue. Each gland opens into the mouth by a duct.
Saliva is ropy because it is mixed with mucus formed by the mucous
membrane lining the mouth; it usually contains air bubbles. There is a
ferment in the saliva called _ptyalin_, which has the power of changing
starch to malt sugar. If a bit of bread is chewed for a long time,
it becomes sweet, because some of the _starch is changed to sugar_.
The flow of saliva is caused by chewing, or by the sight, or even the
thought, of agreeable food. Dryness of food is by far more powerful
than anything else in causing the saliva to flow. Saliva is secreted
only one fourth as fast when eating oatmeal and milk as when eating dry
toast (Fig. 94).
[Illustration: FIG. 94.--CELLS OF A SALIVARY GLAND
_A_, after rest, full of granules; _B_, after short activity; _C_,
after prolonged activity, cells shriveled and granules lost.]
Starchy grains and fruits were eaten by early man without cooking,
and required more chewing than sweet, ripe fruits or oils or
proteids. Hence the saliva was given the power of acting upon the
starch, for it must remain in the mouth longer. The saliva is
alkaline; and if the food is not thoroughly mixed with it, the
stomach digestion will also be imperfect, for the _alkaline saliva is
necessary to excite an abundant flow of gastric juice in the stomach_
(Exp. 1).
=Eating slowly= is difficult because of the grinding and cooking of
food; hence the common practice of overeating. To eat slowly (1) do
not take large mouthfuls; (2) do not take a second morsel until the
first has been swallowed; (3) sit erect or lean back after putting
food into the mouth; (4) the hands should lie idle most of the time.
To lean forward and keep food traveling to the mouth like coal into a
chute means overeating with all its bad effects.
_Chewing gum_ is a coarse and impolite habit, and wastes the saliva,
besides weakening the glands and irritating the stomach by the saliva
that is continually swallowed. _Chewing tobacco_ has several of these
disadvantages, besides allowing the poison in the tobacco to be
absorbed by the mucous lining of the mouth.
=The pharynx= (far′inks), =or throat=, is a muscular bag suspended
behind the nose and mouth. (See Fig. 89, also Fig. 83.) There are
_seven openings_ into the pharynx: two from the nostrils, two from
the ears, one each from the mouth, larynx, and gullet. Which of these
openings are downward? Forward? Lateral?
=The gullet= (or esophagus) is a muscular tube about nine inches long.
(See Fig. 89.) Like the rest of the food tube, it is lined with mucous
membrane. It has two layers of muscles in its walls, the fibers of
one layer running lengthwise, and the fibers of the other layer being
circular. In _swallowing_, the food does not fall down the gullet of
its own weight, but _the circular bands of muscle in front of the food
relax_, and _those behind it contract and push it on into the stomach_.
This wavelike motion is called _peristalsis_.
=The stomach=, the greatest enlargement of the food tube, is like _a
large bag lying sideways_. It lies to the left side of the abdomen.
The walls of the stomach consist chiefly of _muscular fibers which run
lengthwise, crosswise, and slantwise_, making three coats (Exp. 7,
also Fig. 95). As soon as the food reaches the stomach, the layers of
muscles begin to contract, changing the size of the stomach, first in
length, then in breadth, thus churning the food to and fro, and mixing
it with the gastric juice, a fluid more active than the saliva. For
as the food enters the stomach, the mucous membrane lining it turns
a bright red, and many little gastric glands in the lining begin to
secrete gastric juice.
[Illustration: FIG. 95.--MUSCULAR AND OTHER LAYERS IN WALL OF STOMACH.
1, mucous lining; 2, layer of blood vessels and connective tissue; 3,
muscular layers (involuntary muscles); 4, connective-tissue fibers.
(Peabody.)]
=Digestion in the Stomach.=--The stomach churns the food from two to
four hours after the meal, according to the kind of food eaten, the way
it has been cooked, and the thoroughness with which it has been chewed.
The _gastric juice_ is chiefly water, and contains two ferments called
_pepsin_ and _rennin_, and a small quantity of _hydrochloric acid_.
Rennin acts upon the curd of milk, and is abundant only during infancy.
Hydrochloric acid kills germs that may enter the stomach, and changes
the food which has been made alkaline by the saliva into an acid
condition (Exp. 1). This enables the _pepsin to act upon the proteid
part of the food_, for pepsin will not act while the food is alkaline.
Gastric juice _digests lean meat_, which is a proteid food, by first
dissolving the connective tissue that holds the fibers in place, and
they fall apart; it then acts upon the fibers separately and makes
them soluble. Like human fatty tissue (Fig. 14), _fat meat_ consists
of cells filled with fat and held together by threads of connective
tissue. The cell walls and the threads, both being proteid, are soon
dissolved by the gastric juice, and the free fat is melted into oil,
but still undigested. The food is reduced in the stomach to a creamy,
half-fluid mass called _chyme_. Where the stomach opens into the small
intestine, there is a folding in or narrowing of the tube so as to form
a kind of valve called the _pylorus_. After the food has been changed
to chyme, this fold relaxes every minute or two, and allows some of the
chyme to escape into the intestine.
[Illustration: FIG. 96.--A PORTION OF SMALL INTESTINE cut open to show
the folds in its lining.]
=The small intestine= is about one inch in diameter and twenty feet
long, with many coils and turns in its course (Fig. 90). Its mucous
lining is wrinkled into numerous _folds_ in order to increase the
secreting and absorbing surface (Fig. 96). On and between the folds are
thousands of little threadlike projections called _villi_ (Fig. 97).
In each villus are found fine capillaries and a small lymphatic called
a _lacteal_ (colored Fig. 2). The villi are so thick that they make
the lining of the intestine like velvet, and enormously increase the
absorbing surface.
[Illustration: FIG. 97.--LINING OF SMALL INTESTINE, magnified, showing
villi and mouths of intestinal glands.]
=Digestion in the Small Intestine.=--This is by far the most active and
important of the digestive organs. The mouth digests a small part of
the starch, and the stomach digests a small part of the proteid; _the
small intestine digests most of the starch, most of the proteid, and
all of the fats_. The food is in the mouth a few minutes, and in the
stomach two or three hours; it is in the small intestine ten or twelve
hours. There are thousands of small glands called _intestinal glands_
that open between the villi (Fig. 97) and secrete the intestinal juice,
which _digests cane sugar_. Besides these, there are two very large and
active glands, the pancreas and liver, which empty into the intestine
by ducts.
=The Pancreas.=--The small intestine is the most important of the
digestive organs, chiefly because it receives the secretion from the
pancreas, the most important of digestive glands. The pancreas is a
_long_, _flat_, _pinkish gland situated behind the stomach_ (see Fig.
90). The pancreatic juice contains _three powerful ferments_, one of
which (amylopsin) digests the starches, another (trypsin) digests
proteids, and the third (steapsin), with the aid of the bile, breaks
up the fats into tiny globules. Fat in small globules floating in a
liquid is called an _emulsion_; fresh milk is an emulsion of cream
(Fig. 98). Fat is not changed to another substance by digestion, but
it is emulsified, and in this condition it readily passes through
the walls of the intestines and is absorbed by the lymphatics called
_lacteals_ (colored Fig. 5) found in the villi. It then ascends through
the _thoracic duct_ to a large vein at the left side of the neck
(Fig. 100). _The digested proteid, starch, and sugar pass into the
capillaries of the portal vein, and go to the liver_ on their way to
the general circulation (Fig. 100). The portal circulation empties into
the large ascending vein leading to the right auricle (Fig. 100).
[Illustration: FIG. 98.--JUNCTION OF LARGE AND SMALL INTESTINE.]
=The Liver.=--This large, chocolate-colored gland is located just
beneath the diaphragm on the right side (Fig. 90, colored Fig. 6). It
is on a level with the stomach, which it partly overlaps in front.
The liver has three important functions: (1) _It is a storeroom_;
digested sugar and starch are stored in it as a substance called
_liver starch_ (or glȳ′cogen). (2) _It is a guardian_, and destroys
poisonous substances which may be swallowed, and which would
otherwise enter the blood. Twice as much morphine or other poison
is necessary to kill a man when it is taken by the mouth and passes
through the liver as when it is injected through the skin. Alcohol,
morphine, coffee, and drugs are partly burned up in the liver. (3)
_It is a gland_, and secretes bile. The bile is made chiefly from
waste products and impurities in the blood; it is an excretion.
Although an excretion, it is of use on its way out of the body. It is
alkaline and helps to neutralize the acid in the chyme; it excites
the peristalsis, or wavelike motion, of the intestines, and it aids
the pancreatic juice to emulsify the fats.
[Illustration: FIG. 99.--DIAGRAM OF TRUNK to show the many folds of the
PERITONEUM supporting the liver, stomach, and intestines.]
=The large intestine, or colon=, is about two and one half inches in
diameter and five feet long. _The small intestine joins it in the lower
right side of the abdomen_ (Fig. 90). There is a fold, or valve, at
the juncture, and just below the juncture there is a tube attached to
the large intestine, called the _appendix_, which sometimes becomes
inflamed, causing a disease called _appendicitis_ (Figs. 90, 98). The
appendix is a vestigial (_vestigium_, trace) or rudimentary organ, long
since useless. _Absorption_ of the watery part of the food continues in
the colon, but the colon secretes no digestive fluid. The undigested
and innutritious parts of the food are regularly cast out of the
colon.[7] The _peritone′um_ is a membrane with many folds that supports
the food tube (Fig. 99).
[7] No truly refined person will allow business, pleasure, haste, or
neglect to interfere with regular attention to emptying the colon.
This is more necessary for real cleanliness than regular baths.
=Absorption.=--The way in which the various digested foods are
absorbed has been stated in several preceding topics. What is the
name of the organs of absorption in the small intestine? Which of the
following pass into the lacteals, and which into the capillaries of
the portal vein: sugar, digested proteid, emulsified fats? Water and
salt need no digestion, and are absorbed all along the food tube, the
absorption beginning even in the mouth. What reasons can you give for
the absorption of food being many times greater in the small intestine
than in the stomach? Through what large tube is the fat carried in
passing from the lacteals to the veins? Into what large vein do all
the capillaries that take part in absorption empty? (Colored Fig.
5.) What is the provision for storing the sugar so that it will
not pass suddenly into the blood after a meal, but may be given to
the blood gradually? Food is assimilated, or changed into living
matter (protoplasm), in the cells. Blood and lymph (except the white
corpuscles) are not living matter. (Fig. 100.)
[Illustration: FIG. 100.--THE TWO PATHS OF FOOD ABSORPTION. Thoracic
duct (for fats); through the portal vein and liver (for all other
foods).]
THOUGHT QUESTIONS. =The Digestive Organs.=--=1.= In which of the
digestive organs is only one kind of secretion furnished by glands?
=2.= In which organ are three kinds of secretions furnished by
glands? =3.= Which class of food goes through the lymphatics? =4.=
Which classes of foods go through the liver? =5.= Which classes of
foods are digested in only one organ? =6.= Which classes of foods
are digested in two organs? =7.= Which division of the food tube is
longest? Broadest? Least active? Most active? =8.= Soup is absorbed
quickly; why does eating it at the beginning of a meal tend to
prevent overeating?
=Hygienic Habits of Eating.=--In hot weather much blood goes to the
skin and little to the food tube, and digestion is less vigorous.
Hearty eaters suffer from heat in summer because of much fuel, and
because the blood is kept away from the skin where it would become
cool and then cool the whole body. Some persons believe that the
stomach should be humored and given nothing that it digests with
difficulty; others believe that it should be gradually trained to
digest any nutritious food. Some believe that no animal food should
be eaten; others believe that animal food is as valuable as any. Some
believe that all food should be eaten raw, but this would irritate a
delicate stomach. It is doubtless best to use no stimulant, either
tea or coffee, pepper or alcohol. Some eat fast and drink freely at
meals; it is better to eat slowly and drink very little or none at
all while eating, nor soon afterwards. Some eat five meals a day, and
between meals if anything that tastes good is offered them; others eat
only two or three meals a day, and never between meals, thus allowing
the digestive organs time to rest. Some omit breakfast and some omit
supper. Some prepare most of the food with grease; this is a tax upon
digestion. Physical workers often believe in eating the peelings and
seeds of fruits, and partaking freely of weedy vegetables, such as
cabbage, turnip tops, string beans. Mental workers usually try to
reject all woody fiber and indigestible pulp from the food before
swallowing it. Some eat large quantities of food and digest a small
portion; others eat little but digest nearly all.
=The Power of Adaptation of the Digestive Organs.=--Of course some
habits of eating are better for the health than others, yet the
undesirable ways often bring so little injury that they are not
discontinued. This shows that the food tube has great powers of
adaptation to different conditions. But there are limits to this
adaptation; there is an old saying that what is one man’s meat is
another man’s poison. A brain worker cannot follow the same diet as
a field hand without working at a disadvantage. An irritable stomach
may be injured by coarse food that would furnish only a healthful
stimulus to a less sensitive one. A business man who has little
leisure at noon should take the heaviest meal after business hours.
In general, it may be said that it does not make so much difference
_what_ is eaten as _how_ it is eaten, and _how much_ is eaten. There
is a common tendency to exaggerate the importance of dietetics.
THOUGHT QUESTIONS. =Indigestion.=--I. _A Fetid Breath._ =1.=
Name three causes of bad breath. =2.= Let us investigate whether
indigestion could cause a bad breath. In what kind (two qualities) of
weather does meat spoil the quickest? =3.= Suppose that meat or other
food is put into a stomach with its gastric glands exhausted and its
muscular walls tired out, what will be the rate of digestion, and
what might happen to the food? =4.= Odorous contents of the stomach
(_e.g._ onion) can be taken by the blood to the lungs where it will
taint the breath.
After answering the above questions, write in a few words how
indigestion may cause a bad breath.
II. _A Coated or Foul Tongue._ =1.= When the doctor visits you, at
what does he first look? =2.= What sometimes forms on old bread? (p.
158.) =3.= Do you think such a growth possible on undigested bread in
the stomach? =4.= The microscope shows the coating on the bread to
be a growth of mold. If it forms on the walls of the stomach, it may
extend to what?
III. _Stomach Ache._ =1.= How can you tell whether fruit preserved
in a sealed glass jar is fermenting? =2.= What connection is there
between belching after eating too freely of sweet or starchy food,
and the observation above? =3.= A muscle gives pain when it is
stretched. Why does belching sometimes give relief to an uneasy
stomach? =4.= Can you, by using these facts, explain a cause of
stomach ache?
=For what Kind of Man were the Human Digestive Organs created?=--That
food is best to which the food tube has been longest accustomed. It
would be of the greatest value as a guide to diet if we knew the food
eaten by early man during the many ages _when he led a wild life
in the open air_. The organs of early man were doubtless perfectly
adapted to the life he led. The food tube is adapted to the needs of
those long ages, for a few centuries of civilization cannot change
the nature of the digestive organs; yet some people disregard natural
appetites and try to force the digestive organs to undergo greater
changes in a few months than centuries could bring about.
=To test whether an Article of Food belonged to Man’s Original
Diet.=--Scientists agree that the human race began in a warm country;
that _early man was without gristmills, stoves, or fire, and ate his
food raw_. If an article of food is pleasant to the taste in its raw,
pure state, there is little doubt that it, or a similar food, was
eaten by primitive man before he knew the use of fire in preparing
his food. Apply this test to the following foods, underlining those
foods that pass the test: apples, bananas, lettuce, turnip greens,
turnips, fruits, nuts, beef, fowls, eggs, oysters, green corn,
cabbage, pork, watermelons, grains, crabs, fish, white or Irish
potatoes, yams, tomatoes.
[Illustration: FIG. 101.--BLACKBOARD DIAGRAM. Amount of nourishment
(black) and waste (white) in several foods. (After Latson.)]
=The Order in which Man increased his Bill of Fare.=--Flesh-eating
animals have a short food tube, as their food is digested quickly;
they have long, pointed teeth for tearing, sharp claws for holding,
and a rough tongue for rasping meat from the bones. Man’s even teeth,
long food tube, soft and smooth tongue, and flattened nails, indicate
that he is suited for a diet largely vegetable (see Table, p. 111).
_The race at first probably ate tree fruits_,[8] both nuts and fleshy
fruits (Fig. 101). Because of famine, or after migration to colder
climates, and after learning the use of fire, the race probably began
to use flesh for food. Afterward the hunters became farmers and
learned to cultivate grain, which formed a most important addition to
the food supply, and made possible a dense population. Coarse, woody
foods, like the leaves and stems of herbs, were probably added last
of all. Woody fiber (cellulose) can be digested by cattle, but it
cannot be digested by man.
[8] See Genesis i. 29. Some raw food should be eaten daily. Pecans are
the most digestible of all nuts. A half dozen or more eaten
regularly for breakfast will prevent constipation or cure it in ten
days or less.
=The Natural Guide in Eating is Taste.= Man should preserve his taste
uncorrupted as, next to his conscience, his wisest counselor and
friend. It has been developed and transmitted through countless ages
as a precious heritage. Simple food is more delicious to people with
natural tastes than the most artificial concoctions are to those with
perverted taste.
=Animal Food.=--The _flesh_ of animals furnishes proteid and fat (Fig.
102). As cooking coagulates and hardens albumin, raw or half-cooked
meat is said to be more digestible than cooked meat; but meat that is
not thoroughly cooked is dangerous because it may contain trichinæ
(“Animal Biology,” p. 50) and other parasites. Lean meats contain much
proteid. Some persons who cannot easily digest starch and sugar because
of fermentation eat fat for a fuel food. _Beef tea_ and beef extracts
contain but a small part of the proteid in meat and all of the waste
matter, including urea.
[Illustration: FIG. 102.--DIAGRAM SHOWING CUTS OF BEEF.
1. sirloin
2. loin
3. rump
4. round
5. top sirloin
6. prime ribs
7. blade
8. chuck
9. neck
10. brisket
11. cross-rib
12. plate
13. navel
14. flank
15. shoulder
16. leg]
=============+=============+=============+=============+==============
MAMMALS |CARNIVORA, OR|HERBIVORA, OR|OMNIVORA, OR | FRUGIVORA, OR
COMPARED |FLESH-EATERS | HERB-EATERS | ALL-EATERS | FRUIT-EATERS
-------------+-------------+-------------+-------------+--------------
Examples. |Cat, dog, |Cow, horse. |Hog, peccary.|Man, monkey.
|lion. | | |
-------------+-------------+-------------+-------------+--------------
Length of |3 times |30 times |10 times |12 times
food tube. |length of |length of |length of |length of
|body. |body. |body. |head-trunk.
-------------+-------------+-------------+-------------+--------------
Teeth. |Pointed for |Layers of |Cutting teeth|Teeth even,
|tearing |enamel and |project. |close
|flesh. Canine|dentine |Canines form |together.
|teeth long. |forming |tusks. |Canines not
| |ridges. | |projecting.
-------------+-------------+-------------+-------------+--------------
Digits. |Sharp claws. |Hoofs. |Hoofs. |Flattened
| | | |nails.
-------------+-------------+-------------+-------------+--------------
Colon. |Smooth. |Sacculated. |Smooth. |Sacculated.
=============+=============+=============+=============+==============
_Milk_ of cows is improperly called a perfect food by some writers.
Although it contains the four classes of food stuffs, the proteid
is in excess, the fuel food being deficient. Buttermilk is more
digestible than sweet milk. Buttermilk and sugar form a valuable
food for infants. Skimmed milk still contains the proteid, the most
nutritious part of the milk. Sour milk, or “clabber,” and curds
pressed into “cottage cheese” are more digestible than sweet milk.
_Cream_ is more easily digested than _butter_, which is a solid fat.
_Cheese_ is a very concentrated proteid food, and should be eaten
sparingly. _Eggs_ are a valuable food. Is there more proteid or
fat in eggs? (See Table.) Pork and veal are the most indigestible
of meats. _Fish_ is nearly as nutritious as meat. There used to be
a supposition that fish nourished the brain because it contains
phosphates; but there are more phosphates in meat than in fish, and
more in grains than in meat.
_Grains_ contain considerable proteid (gluten), but they especially
abound in starch. Wheat flour contains more gluten than corn meal,
hence it is more sticky, and retains the bubbles of gas so that the
dough rises well in bread making. Eggs are sometimes added to corn
meal to make it sticky and cause it to rise well. Which grain has
the largest percentage of oil? (See Table.) Of starch? Of gluten?
Which is poorest in gluten? _Grains may be made to resemble fruit_ by
long cooking at a high temperature (300° Fahr.), for their starch is
thus changed to _dextrin_, a substance resembling sugar. You learned
that the starch of fruit is turned into sugar as the sun ripens it.
Dextrin is yellow and gives the dark color to toasted bread. It
is changed to sugar almost instantly when brought in contact with
saliva. It is used as a paste on postage stamps.
_Vegetables contain much water and woody fiber._ _White potatoes_
are underground stems and are _one fifth starch_. Yams, or sweet
potatoes, resemble roots, and contain both starch and sugar. _Beans
and peas are very nutritious._ They have been called “the lean meat
of the vegetable kingdom.” They require boiling for several hours. If
the skins are removed by pressing them through a colander, they are
very easy of digestion. This _purée_ of beans makes delicious soup.
“Hull-less beans” and “split peas” are also sold by grocers.
PRACTICAL QUESTIONS.--=1.= Clothing and shelter for man or beast
economize what kind of food? =2.= Why should bread remain longer in
the mouth than meat? =3.= In snowballing, what is the appearance
of the hands when they itch from cold? Extreme cold irritates and
congests the stomach more quickly than it does the hands. Why is it
that ice water does not satisfy the thirst, but often produces a
craving to drink more water? =4.= Should biscuits having a yellow
tint or dark spots due to soda be eaten or thrown away? =5.= Why,
during an epidemic, are those who have used alcohol as a beverage
usually the first to be attacked? =6.= Do you buy more wood
(cellulose) when you buy beans or when you buy nuts? (p. 95.) =7.=
Do you buy more water when you buy bread or when you buy meat? =8.=
Why do people who live in overheated rooms often have poor appetites?
(p. 90.) =9.= Explain how the stomach may be weakened by the eating
of predigested foods. =10.= Why are deep breathing and exercises that
strengthen weak abdominal walls better for the liver than are drugs?
(See p. 58.) =11.= Sixty students at the University of Missouri found
by doing without supper that their power to work was greater, their
health better, and many of them gained in weight. So they ate only
two meals thereafter. If sixty plowboys tried the experiment, would
the result probably have been the same? =12.= If a person began to
eat less at each meal, or only ate one meal a day, yet gained in
weight, should he agree with a friend who told him he was starving
himself? Should he agree if, instead of gaining, he lost weight?
=13.= Why is half-raw or soggy bread harder to digest than the raw
grain itself? Which would be thoroughly chewed and cause a great
flow of saliva? =14.= Ask a fat person whether he drinks much water.
A lean person. =15.= Why is one whose waist measures more than his
chest a bad life insurance risk? =16.= What changes in habits tend to
make a rheumatic middle-aged person more youthful? =17.= How is the
ingenious “fireless cooker” constructed?
=Atwater’s Experiments with Alcohol.=--A few years ago Professor
Atwater proved that if alcohol is taken in small quantities, it is so
completely burned in the body that not over two per cent is excreted.
He inferred that it is a food, since it gives heat to the body and
possibly gives energy also. His experiments did not show whether any
organ was weakened or injured by its use. As alcohol is chiefly burned
in the liver, it probably cannot supply energy as is the case with food
burned in nerve cell and muscle cell. The heat supplied by its burning
is largely lost by the rush of blood to the skin usually caused by
drinking the alcohol. Dr. Beebe, unlike Professor Atwater, experimented
upon persons who had never taken alcohol, and whose bodies had not had
time to become trained to resist its evil effects. He found that it
caused an increased excretion of nitrogen. When the body became used to
it, this decreased, but the proteid excreted by the kidneys contained
an abnormal amount of a harmful material called _uric acid_. Uric
acid, a substance which is present in rheumatism and other diseases,
is usually destroyed by the liver. As the burden of destroying the
alcohol falls chiefly upon the liver, it is not surprising to find that
it is so weakened and injured by alcoholic drink that it cannot fully
perform its important functions. Bright’s disease and other diseases
accompanied by uric acid are more frequent among persons who use
alcoholic drinks.
=Definition of Food.=--_A food is anything which, after being
absorbed by the body, nourishes the body without injuring it._ Does
alcohol or tobacco come within this definition?
=Advantages of Good Cooking.=--Taste and flavor may be developed;
parasites are killed; taste may be improved by combining foods;
starch grains are burst and the food softened. Thus digestion is
aided.
=Disadvantages of Bad Cooking.=--Proteid foods are hardened; flavors
may be driven off; too many kinds of food may be mixed; cooked
vegetables are more likely to ferment than raw vegetables; palatable
food may be made tasteless or soggy or greasy; soda and other
indigestible ingredients may be added; food may be so highly seasoned
as to cause catarrh of the stomach; it may so stimulate the appetite
that so much is eaten as to overload the stomach. Food may be made so
soft that it cannot be chewed and is eaten too rapidly; for instance,
bread shortened with much grease.
=The Five Modes of Cooking.=--Food may be cooked (1) by _heat
radiating from glowing coals_ or a flame, as in broiling; (2) by
_hot air_, as baking in a hot oven; (3) by _boiling in hot water or
grease_, as frying; (4) by _hot water_, not boiling, as in stewing;
(5) by _steaming_.
=Radiant Heat.=--_Toasting_ bread and _broiling_ meat are examples.
The meat should be turned over every ten seconds to send its juices
back and forth, thus preventing their escape, and broiling the meat
in the heat of its own juices. _Roasting_ is an example of this
method combined with the second method. The fire should be hot at
first in order to sear the outside of the meat and prevent the escape
of its juices. If the piece roasted is small, the hot fire may be
kept up; but if it is large, a longer time is required, and the fire
should be decreased, otherwise the outside will be scorched before
the central part becomes heated. White, or Irish, potatoes roasted
with their skins on best retain their flavor as well as valuable
mineral salts (potash, etc.).
=Cooking by hot air= can only be used with moist foods. Baking
is an example. Foods only slightly moist are made hard, dry, and
unpalatable if cooked by this method.
=Cooking by Boiling.=--To boil _potatoes_ so as to make them mealy
instead of soggy, the water should be boiling when they are put in,
and after they are cooked the water should be poured off and the
pot set on the back of the stove for the potatoes to dry. Boiling
_onions_ drives off the acrid, irritating oil. Rapid boiling of
vegetables gives less time for the water to dissolve out the
nutrients. (See Steaming.) Raw _cabbage_ is treated by the stomach
as a foreign substance, and sent promptly to the intestine; cabbage
boiled with fat may remain in the stomach for five hours. Instead,
it should be boiled in clear water for twenty minutes. _Beans_ and
_peas_ require several hours’ boiling.
=Cooking in hot liquid below the boiling point= is better than
boiling. In _frying_ meat, it should be put in hot grease that a
crust may be formed to prevent the grease from soaking in. Grease
much above boiling point becomes decomposed into fatty acids and
other indigestible products. Hence butter is more digestible than
cooked fats. In whatever way meat is cooked, it should never be
salted until the cooking is finished or the salt will draw out the
juices which flavor it. _Eggs_ may be cooked by placing them in
boiling water and setting the kettle off the stove at once to cool. A
finely minced hard-boiled egg is as digestible as a soft-boiled egg.
Since boiling for more than a very few minutes coagulates and hardens
albumin, there is no such thing as boiling meat without making it
tough and leathery throughout. It may be stewed, a process which
belongs to the next method.
In _stewing meat_, it may be plunged into boiling water for a few
minutes; this coagulates the albumin on the surface. The fire should
then be reduced, or the vessel set on the cooler part of the stove,
or a metal plate should be placed beneath it, that the water may
barely simmer. The water should show a temperature of 185° or 190°
if tested with a thermometer. A piece of meat cooked in this way is
tender and juicy.
=Cooking by steam= requires a double vessel or a vessel with a
perforated second bottom above the water, through which the steam may
rise to the food that is to be steamed. _Steamed vegetables_ have a
better flavor and are more nutritious than those cooked in any other
way. A steamer is different from a double boiler. _Oatmeal_ should
be cooked for at least forty minutes, and it is more digestible if
steamed for several hours until it is a jelly. To do this, it may
be cooked during the preparation of two meals. Cooking that leaves
it lumpy and sticky is a disadvantage, and makes it more likely to
ferment than if eaten raw.
THOUGHT QUESTIONS. =Cooking.=--_Meat._ =1.= In making soup, why
should the meat be put in while the water is cold? =2.= In roasting
meat, why should the oven be hot at first, and more moderate
afterward? How should you regulate the temperature in boiling or
stewing meat? =3.= What happens to salt or anything salty on a
cloudy, damp day? This is because the salt attracts ____. This shows
that meat should not be salted until after it has been cooked,
because if salted before ____. =4.= Very tough meat should be b__ed
or st__ed. =5.= Meat may be prevented from becoming grease-soaked
when frying by having the grease very ____, use very ____, simply
greasing the ____.
=6.= _Bread._ Bread crust causes the ____ to be used more and cleans
them. It will not ____ together in the stomach like the crumb. It
increases the quantity of the ____, and is more digestible than the
crumb, since the ____ has been changed by slow heat to ____ (p.
112). Therefore loaves or biscuit should be (large or small?) and
they should (touch or be separated?) in a pan. =7.= How can you tell
whether the oven has been too hot while the bread was baking? =8.=
Why can you tell best about the digestibility of bread when you are
slicing it? =9.= Regulating the heat is the greatest art of the
cook. How may the temperature of the oven be lowered by means of the
damper? The draft? The fuel?
EXERCISES IN WRITING.--Story of a Savage who went to dwell in a City
(his trouble with artificial ways). Is it easier to learn Physiology
or to practice it? How to make Bread. Describe People seen in an
Audience (tell what their appearance suggests). A Scene at a Dinner
Table. Thoughts of a Physician on his Round of Visits. A Good Cook.
A Bad Cook. Is Cooking a Greater Accomplishment than Piano Playing?
Common Causes of Illness. The Influence of Imperfect Digestion
upon the Other Organs. Effect of Lack of Muscular Activity. The
Way of the Transgressor is Hard. What Fools we Mortals be! Health
Fads. Temperance in all Things. The Right Way the Easiest. Looking
Back. Looking Forward. Hygiene of the Schoolroom. Patent Medicines.
Microbes. Mind Cure. Nervous Women. Dissipated Men. How a Friend
of mine lost his Health. Why a Friend of mine is Sound and Strong.
Tobacco. It never pays to neglect the Health. Which does more Harm,
an Ignorant Cook or an Ignorant Janitor? A Visit to a Sick Room.
Alcohol and Crime. Natural Instincts and Appetites; how preserved,
how lost. A Lesson about Alcohol based upon the Morning News. Effects
of Alcohol upon the Greatness of our Country (workmen, voters,
soldiers, children). Adam’s Apothecary Shop. Adam’s Ale (water).
CHAPTER VIII
THE NERVOUS SYSTEM
=Review Questions introducing this Subject.=--What is a cell? What
are the five supporting tissues? What are the two master tissues? Why
are they so called? What kind of cells have many branches? Does the
food ever come in contact with the salivary glands? When you look
at a basket of apples, the sight “makes your mouth water.” Is there
a connection between the eye and the mouth? What two tissues enable
the skin to blanch and to blush? Do the different organs share the
blood in the same proportions at all times? How can this proportion
be changed? How is the brain protected from injury? How is the spinal
cord protected? Is the hole for the spinal cord through the main body
of the vertebra, or behind the main body?
=Harmonious Activity.=--Strike suddenly at the eye of another, and the
lids fall to protect it, and the hands rise to ward off the blow. If
a grain of dust gets into the eye, the tear glands form tears to wash
it out. If you touch the hand unexpectedly to a hot iron, the muscles
of the arm jerk the hand away. If the foot of a sleeping person is
tickled, the muscles of the leg pull it away. Many muscles coöperate
in the act of running. If the human being were merely an assemblage of
working organs, the organs might act independently, and there would be
such confusion that the body would be powerless, and life could not be
maintained. The nervous system enables the organs to work together for
the common good. Why does an ameba not need a nervous system?
=The Need of Nerve Centers as well as Nerves.=--If there were no
central office in a telephone system of one thousand subscribers, then
every subscriber, in order to communicate with every other subscriber,
would need one thousand wires running into his house; all together,
there would have to be several hundred thousand (to be exact, 499,500)
wires. With a central office only one thousand are needed. As a
telephone system has central offices, so the nervous system has nerve
centers. Nerve centers contain nerve cells. Although there are some
subordinate nerve centers in the spinal cord, the greatest collection
of nerve centers in our bodies is in the skull, and is called the
_brain_. Fishes were the lowest animals studied in animal biology found
to possess a true brain.
The nervous system, unlike a telephone system, has other duties
besides allowing _communication_. It enables us to _think_, and, after
reflection, to _will_ and to _act_ by controlling the various organs.
[Illustration: FIG. 103.--Showing a NEURON, _A_, or nerve cell with all
its parts--dendrites, cell body, and axon; _B_, a portion of a white
fiber highly magnified. (Jegi.)]
=The Units of which the Nervous System is Constructed.=--A nerve cell
with all its branches, or fibers, is called a _neuron_ (see Fig. 103);
some neuron branches are several feet long. Neurons are the units
that compose the nervous system. The living substance in cells is
called _protoplasm_. The protoplasm in nerve cells possesses the most
marvelous and varied powers of any known substance, for the nerve cells
are the seat of the mind.
[Illustration: FIG. 104.--LARGE NERVE TRUNK, such as supplies the
muscles. Cross-section (magnified 6 diameters), showing bundles of
nerve fibers. (Peabody.)]
=Nerve Cells and Fibers.=--The many branches of nerve cells make them
the most remarkable of all cells for irregularity in shape. Since
_the protoplasm of the cell continues into the fibers_, it is plainly
wrong to consider the nerve cell as something apart from its fibers.
It is not a complete cell without them. A cell usually has many
short branches called _dendrons_ or _dendrites_ (see Fig. 103) for
communicating with near-by cells, and one long branch called an _axōn_
(Fig. 103) for communicating with distant parts. The axons form the
fibers that go to the skin, muscles, and other organs.
=A Nerve.=--These long branches, or axons, of nerve cells go all
over the body and are often bound together into visible cords called
_nerves_, or nerve trunks (Fig. 104).
[Illustration: FIG. 105.--_c_, a white fiber with its fatty sheath
(dark); _d_, two gray fibers (without sheath).]
=White and Gray Fibers= (Fig. 105).--Some fibers have a _fatty
covering_ surrounding the _thread of protoplasm_; they are white and
glistening, and are called _white fibers_. Others are without this
fatty covering, and are called _gray fibers_. Both kinds of fibers have
_connective tissue_ on the outside to strengthen them. If we let a lead
pencil represent a white fiber, the lead corresponds to the axis of
protoplasm; the wood corresponds to the white, shiny fat that surrounds
it; and the varnish corresponds to connective tissue on the surface of
the fiber. A number of white fibers together makes a white mass that
is called _white matter_. The axis of a white fiber, of course, is not
white. A mass of cells or of gray fibers is called _gray matter_. The
oxidation of the gray matter, or protoplasm, in neurons gives rise to
nerve energy.
=Feeling Cells and Working Cells.=--Nerve cells are divided into two
classes: _sensory cells_, which feel or receive impressions; and _motor
cells_, which send out impressions to the working organs. Those fibers
which carry impressions to the receiving cells are called _sensory
fibers_; those which carry impulses from the cells to the working
organs are called _motor fibers_.
=Ganglia and Nerve Centers.=--Nerve cells are not scattered uniformly
in nervous tissue, but are gathered into groups. A group of nerve
cells is called a _ganglion_ (Fig. 106). One or more ganglia having a
single function, such as to control the muscles of breathing, form what
is called a _nerve center_. The brain consists of a number of nerve
centers with their connecting fibers.
[Illustration: FIG. 106.--A GANGLION.]
[Illustration: FIG. 107.--CROSS-SECTION OF SPINAL CORD, showing area of
gray matter (dark).]
=Gross Structure of the Spinal Cord.=--The nerve fibers from nearly
all over the body lead to cells situated in a large cord in the spinal
column called the _spinal cord_. The spinal cord is _separated by a
deep fissure almost into halves_ (Fig. 107). The cells are situated in
the central portion of each half, and the _two masses of gray matter_
thus formed are connected by a narrow isthmus of gray matter. The outer
part of the cord consists chiefly of white fibers. The _white matter
is thus on the outside of the cord_ (Fig. 107). The brain, unlike the
cord, has the gray matter on the outside and the white matter on the
inside. For microscopic study of the spinal cord, see Fig. 108.
=The Work of the Spinal Cord.=--There are two functions of the cord:
reflex action and transmission of impulses from the body to the brain.
Reflex action is action that takes place without the aid of the will.
[Illustration: FIG. 108.--SECTION OF SPINAL CORD, showing nerve cells
(large black spots) with their branches (black dots and lines). Five
bundles of nerve fibers are shown near upper margin. (Peabody.)]
=Reflex action= never begins in the cord, but at the outer end of a
sensory fiber, usually located in the _skin_. The impression goes to
the cord along a _sensory fiber_. It is received in a _sensory cell_
and transferred by dendrons to a _motor cell_ which sends back an
impulse along a _motor fiber_ to a _muscle_; the muscle contracts and
the action is complete. At least two nerve cells are necessary for
reflex action. The actions of the lowest animals are almost entirely
reflex.
=Reflex Action, Consciousness, and Will.=--Usually not all of the
force of the impulse is transferred to the motor cell. The sensory
cell by means of another of its many branches may _transfer part of
the impulse to a cell which sends it to the brain_. Hence a reflex act
is not necessarily an unconscious one. If you unintentionally touch
the hand to a hot stove pipe, you may be conscious of the pain and the
involuntary jerking away of the hand at the same time.
=Reflex Action and the Will.=--The will may _inhibit_, or prevent, an
expected reflex act. Yet many reflex acts occur in spite of the effort
of the will to prevent them. One cannot always keep from closing the
eyes before a threatened blow even if from the other side of a plate
glass window, and it is known there is no danger. Sneezing is a reflex
act and cannot always be prevented. The forming of saliva and other
secretions are reflex acts. _Reflex acts are quicker than voluntary
acts._ An eighth of a second is about the time required for a person to
press an electric button after seeing a signal; a reflex act may occur
in a shorter time.
[Illustration: FIG. 109.--BRAIN AND SPINAL CORD.]
=The Brain consists of Three Chief Parts.=--(1) There is an enlargement
at the top of the spinal cord called the _medulla_, or the medulla
oblongata. It may be regarded as the part of the spinal cord within
the skull (see Figs. 109, 110, 114). (2) Above the medulla is the
_cerebellum_, or little brain. (3) The _cerebrum_, or large brain,
fills all the skull except the small part occupied by the medulla and
cerebellum. The cerebrum covers the cerebellum. (Fig. 110.) Is this
true of the monkey’s brain? (See Fig. 113.)
=The work of the medulla= is chiefly to control the vital functions
(see Figs. 110, 114). Here are located the centers for regulating the
_breathing_, the _heart beat_, the _size of the blood vessels_ (thus
regulating nutrition), and also the less important centers that control
_swallowing_, _secretion of saliva_, and _vomiting_. The center for
breathing is sometimes called the _vital knot_, because although the
cerebrum and cerebellum may be removed from an animal without causing
immediate death, the slightest injury to the vital knot kills the
animal at once. In cases of hanging, death is caused by injury to this
center.
[Illustration: FIG. 110.--THE BRAIN (cerebrum, cerebellum, medulla).]
[Illustration: FIG. 111.--ASSOCIATION FIBERS, connecting cells within
the cerebrum. (Jegi.)]
=Automatic Action.=--The center called the vital knot is said to
regulate the breathing automatically, not reflexly. Reflex acts start
in the skin; _automatic acts start in the interior of the body_. _The
condition of the blood regulates the breathing_ automatically during
sleep, and partly regulates it during waking. If too much carbon dioxid
accumulates in the blood this excites the vital knot, which sends out
stronger impulses to the respiratory muscles. Deeper breathing follows,
which purifies the blood, and the breathing is then shallow or slow
until carbon dioxid accumulates again.
=The Four Kinds of Nerve Action and the Centers that control
them.=--The _cord_ controls chiefly _reflex_ action; the _medulla_
controls chiefly _automatic_ action; the _cerebellum_ controls chiefly
_coördinate_, or harmonizing, action; the _cerebrum_ controls the
purely _voluntary_ acts, for it is the seat of _consciousness_ and
_thought_. The medulla, like the cord, has the gray matter on the
inside (Fig. 109).
[Illustration: FIG. 112.--SENSORY AND MOTOR FIBERS. (Jegi.)]
=Structure of the Cerebellum.=--The cerebellum, like the cerebrum, has
the gray matter or cells on the outside. The gray matter is folded into
furrows that are not nearly so winding as the folds in the cerebrum
(see Fig. 115). The fibers going to the surface cells have a branched
arrangement called the _arbor vitæ_, or tree of life, which is shown
where the cerebellum is cut. The cerebellum, like the cerebrum, is
deeply cleft and thus divided into halves, called _hemispheres_,
connected by a band of white matter.
[Illustration: FIG. 113.--BRAIN OF A MONKEY. Numerals show location of
motor centers. (See Fig. 115.)]
[Illustration: FIG. 114.--THE LOBES OF THE RIGHT SIDE OF BRAIN and
their functions. (Jegi.)
The speech center is true only for left-handed persons. Medulla is
marked “Bulb.”]
=The work of the cerebellum= is to aid the cerebrum in controlling the
muscles. _It coördinates the muscular movements_; that is, it makes the
muscles act at the right time and with due force in complex acts, such
as standing, walking, talking. A man could strike just as hard without
the action of the cerebellum, but he would not be likely to hit what he
aimed at. A drunken man staggers and fails to control the muscles in
walking because the alcohol has caused the blood to collect and congest
around the cerebellum and press upon it. One whose cerebellum has been
injured by accident staggers like a drunken man.
[Illustration: FIG. 115.--MOTOR AND SENSORY AREAS OF LEFT HEMISPHERE.
Speech center marked “Lips.”
In what region are the motor centers? The sensory centers?]
=Coverings of the Brain.=--Lining the skull and covering the cerebrum
are found _two membranes_ which inclose a lymph-like fluid. Thus a kind
of _water bed_ is made which surrounds the soft and delicate cerebrum
and protects it from jars. A membraneous net, or meshwork, of blood
vessels covers the cerebrum and plentifully supplies it with blood.
=Structure of the Cerebrum.=--The gray matter, or cell mass of the
cerebrum, forms a surface layer, called the _cortex_ (“bark”), about
one eighth of an inch thick. This _gray layer is deeply folded_, the
folds, or _convolutions_, being separated by deep furrows, some of
them an inch deep (see Fig. 110). Thus the area of the surface layer
is increased to several times what it would be if smooth. Intelligence
increases with increase in the number and depth of the convolutions.
The greater part of the cerebrum is white matter. This consists largely
of associational _fibers_ (Fig. 111) _which connect the cells in the
gray matter with each other_ and with important interior ganglia at the
base of the cerebrum (Fig. 112). These basal ganglia are the largest
parts of the brains of the lower vertebrates (Animal Biology, Figs.
222, 259). Why do these animals not need large cerebrums? The human
cerebrum comprises nearly seven eighths of the weight of the brain. A
deep fissure divides it into the right and left cerebral hemispheres. A
band of white matter connects the hemispheres.
=Functions of the Cerebrum.=--The cerebrum is the seat of
_consciousness_ and thought, and of all activity controlled by the
_will_. It also _directs the work of the lower nerve centers_ in the
spinal cord, medulla, and cerebellum.
It receives sensory messages from all parts of the skin and through
the special senses. It sends out motor messages to all the voluntary
muscles, and more indirectly to the involuntary muscles. The cerebral
fibers are of three kinds: _sensory_, _associational_ (connecting cells
in cerebrum), and _motor_ (Figs. 111, 112). It is estimated that the
cerebrum alone contains 9,200,000,000 cells.
=Spinal and Cranial Nerves.=--The nerves from the spinal cord go out
through notches between the vertebræ. Since there are _thirty-one
pairs_ of _spinal nerves_ (Fig. 109) and only twenty-four vertebræ,
some of the nerves go out through holes in the sacrum. The _cranial
nerves_ (to eyes, ears, tongue, nose, face, etc.) leave the brain
through holes in the cranium, or skull. There are _twelve pairs_ of
them.
=Relation of the Cerebrum to the Lower Centers.=--As already stated,
nerve activities are of four kinds,--reflex, automatic, coördinate,
and voluntary. A manufactory has more complex work than a shop. A
man with a shop may enlarge it into a factory and leave trained
assistants in charge of the different shops, keeping only the general
management for himself. If he should cease to control his assistants
entirely, the work of the factory would soon be in disorder. If the
manager should try to direct everything, he would become exhausted.
So the cerebrum, the seat of the will and the reason, leaves the
reflex centers in the spinal cord, medulla, and cerebellum to do most
of the work. If the mind wishes the hand to move and grasp the hand
of a friend, the motor center in the cerebrum sends a message to the
cerebellum; and if the cerebellum has been well trained, the act is
accurately performed.
=A less imperfect wisdom than that of the mind= is in the lower nerve
centers. The reason and will control the lower centers through the
cerebrum, but the control is very limited. It is well that this is
so, not only for the relief of the cerebrum, but for the safety of
the body. Can you change the rate of the heart beat by the exercise
of the will? Can you blush at will, or prevent the flushing of the
capillaries when you are embarrassed, or when you go close to a hot
fire? It is impossible for a person to commit suicide by holding the
breath. What change in the blood would soon force a breath to be
taken? Repeat the two examples of reflex action triumphing over the
will which have already been given. We shall next take up a system of
nerves almost independent of the will.
=The ganglionic or sympathetic= portion of the nervous system controls
the viscera (_vis′sē-ra_), or internal organs, _e.g._ peristalsis of
food tube, tone of arteries. The nerves that go to the viscera branch
off from the spinal nerves not far from the spinal column, and enter a
row of ganglia on each side of the spine (see Fig. 115). Each ganglion
is connected by nerves with the one above and below it, so that they
appear like two knotted cords suspended one on each side of the spinal
column and tied together below; for both chains of ganglia end in the
same ganglion in the pelvis. Some of the fibers from the spinal cord
pass through these ganglia on their way to the viscera, losing their
white sheaths in the ganglia and emerging as gray fibers. The spinal
cord and brain with the fibers which do not pass through the double
chain of ganglia are called the _cerebro-spinal system_. The double
chain of ganglia and the fibers which go through them are called the
_ganglionic_ or _sympathetic_ system.
[Illustration: FIG. 116.--DIAGRAM OF SYMPATHETIC SYSTEM showing double
chain of ganglia; also plexus at heart and solar plexus.]
=Why these Nerves are called the Sympathetic System.=--These nerves,
after leaving the double chain of ganglia, form many intricate networks
of ganglia and fibers. Each network is called a _plexus_ (Fig. 116).
The largest of the plexuses is just back of the stomach, and is called
the _solar plexus_. A blow upon the stomach may paralyze this plexus
and cause sudden death. _The plexuses and fibers connect the viscera
so perfectly that one organ cannot suffer without the others changing
their activity, or sympathizing with it._ An overloaded stomach causes
the heart to beat faster and send it more blood; a loss of appetite
usually accompanies illness and allows the stomach to rest. This
sympathy is necessary, for if one organ is diseased, the others do not
continue to work and tax the strength of the ailing organ.
=How the Sympathetic and Cerebro-spinal Nerves Differ.=--The ganglionic
nerves (1) contain mostly _gray fibers_; (2) pass _through ganglia_
after leaving the spinal cord; (3) control the _unconscious_ activities
of the body; (4) pass to organs which contain slow-acting _involuntary
muscles_, not to sense organs and quick-acting voluntary muscles;
(5) transmit impulses _slowly_ (about 20 ft. instead of 100 ft. per
second). Crawfish and insects have hardly more than the ganglionic
system of nerves (Animal Biology, Figs. 92, 132, 197).
=Examples of the Supervisory Functions of the Sympathetic
System.=--Regulation of the heart beat and of the size of the blood
vessels; secretion of sweat glands; contraction of pupils of eyes in a
bright light; peristalsis.
=Examples of Sympathetic Nerve Impulses reaching Consciousness.=--Pain
in colic and cramps; “heartburn” (pain in stomach from indigestion);
backache (from nerves in organs prolapsed by tight clothing pulling
upon their attachments at spine); hunger; thirst.
=The Mind and Health.=--A contented or peaceful mind is indispensable
to soundest health. Worry causes difficult breathing with bated
breath. Happiness brings full, easy breathing. Biological study of
physiology shows the futility of making health a care or anxiety,
and teaches “no meddling” with the body, whether by stimulating
it, drugging it, deforming it, overheating it, half smothering it
in close rooms, cultivating artificial instincts, etc. If the body
degenerates through wrong living, and disease ensues, a new way of
living is needed, not some quick and wonderful remedy. The new life
will renew the body and nothing else can.
HYGIENE OF THE NERVOUS SYSTEM
=Necessity of Food, Fresh Air, and Rest for Sound Nerves.=--The
health of the nerves depends upon a free supply of pure, nutritious
blood. Nearly one fifth of the blood goes to the brain. It is clear
that the brain cannot give out energy until it has first received it;
the blood supplies energy to the brain. The blood in turn receives
the nourishment from food and pure air. A rested cell is full of
nourishment; a tired cell is shriveled (see Fig. 117).
[Illustration: FIG. 117.--EFFECTS OF FATIGUE ON NERVE CELLS.
_A_, resting cell, _B_, fatigued cell, with its body and nucleus
shrunken.]
=Sleep.=--During waking hours energy is used up faster than it is
stored in the cells, and protoplasm is oxidized faster than the cells
can replace it. During sleep the opposite is true; repair is more rapid
than waste. During sleep the muscles are strengthened, the breathing is
less, the heart beats more slowly, less heat is produced, digestion is
slower, less blood goes to the brain. Why is it necessary to be more
warmly protected by clothing or bed covering when asleep than when
awake? Above all, the nervous system has an opportunity to recuperate
from the constant activity of waking hours. The eye and the ear are
rested by darkness and silence. Sleep caused by morphine or other drug
is not normal sleep and brings little refreshment.
=Practical Suggestions.=--Sleep is deepest during the second hour
after going to sleep, and a greater shock is given to the nervous
system by waking a sleeper during that hour than at another time. An
alarm clock is a very unhealthful device. One who cannot trust to
nature even to awaken has great presumption. If one does not rise
promptly upon waking naturally, the instinct to awake when enough
sleep has been taken will be lost, and the habit of sleeping too much
will be formed, and the brain, like the muscles, will become weak
from inactivity. Infants sleep most of the time, and it is injurious
to them to be waked. Adults usually require about eight hours of
sleep. There is a risk in going to sleep in a warm room, for the
bed covering which is comfortable then may not be enough to prevent
taking cold when the fire goes out. Sleep usually comes more promptly
to one who goes to bed at the same hour each night. The muscles are
relaxed in sleep, and relaxing them perfectly upon lying down and
breathing slowly, tends to bring sleep. One who is sleepless usually
finds that he is breathing fast and is holding the head stiff on
the shoulders, the teeth clenched, and the muscles contracted, even
though he is lying down. Excitement and worry during the day, but
especially just before retiring, tend to produce sleeplessness. One
who overworks his mind by too great attention to business is inviting
ruin. A student who loses sleep while preparing for an examination
will probably fail. Rested brain cells and pure blood are needed for
good work.
=Rules for Preventing Sleepiness.=--(1) Do not sit close to stove or
especially a fireplace or in very warm room, and do not wear very
warm clothing in the house. (2) Let in fresh air freely. (3) Do not
sit in rocking chair nor with chest flattened. (4) Make the last meal
a very light one.
=Habits.=--Our habits of doing and thinking and feeling really
constitute our characters. This shows the importance of right habits.
By gradually changing our habits we can strengthen our characters and
form them somewhat as we wish. When a muscle contracts in a certain
way, this act makes it easier for the muscle to contract in that way
the next time; thus great muscular strength may be developed. _When
a nerve cell acts, the circulation around the cell is increased, the
fibers develop by use, and the act is easier the next time._ We cannot
entirely get rid of our habits, because we cannot get rid of our brains.
=Healthy fatigue= is caused by the accumulation of waste products
resulting from the oxidation of substances in nerve, muscle, and gland
cells. The presence of waste in the tissues affects the nerves. We
are rested and strong when these wastes are removed and the tissues
are supplied with fresh food and oxygen. Work causes the accumulation
of _carbon dioxid, which is nature’s narcotic_.[9] The drowsy feeling
that ensues is more pleasant than the drowsy feeling from alcohol or
opium. Those who do not employ nature’s narcotic but free themselves of
it by hurried, anxious breathing become restless and crave artificial
narcotics.
[9] It has been found that it is injurious to rebreathe expired air
containing one per cent of carbon dioxid, but a far greater
percentage is harmless if introduced into fresh air, thus indicating
that the injury from poor ventilation comes chiefly from the “crowd
poison,” or organic particles thrown off.
=Fatigue without work= occurs with people who are idle. The
oxidation in their cells is not complete, and poisonous products
of the incomplete burning result. This is known as self-poisoning
(auto-toxemia). The poisons are taken by the blood to the nerves and
brain, and give a tired feeling as effectually as does hard work; or
the food may ferment in the food tube and form poisons which increase
the tired feeling. Such persons are usually irritable, while persons
who are fatigued by useful labor are likely to be dull and drowsy.
[Illustration: FIG. 118.--THE SITUATION OF HEADACHES with reference to
their causes.]
=Headaches= are caused by poisons in the blood or by pressure of
blood congested in the head. Like all other pains they should be a
source of benefit in that they show us ways of living to be shunned
in the future. Many persons, however, not only derive no profit from
a headache, but by unwise efforts to cure the pain, bring permanent
injury to themselves in addition to the suffering of the headache.
_Bromides_, _opium_, and other _poisons_ deaden and weaken the nervous
system while preventing the headache from being felt. _Headache
powders_, phenacetin, acetanelid, antikamnia, and other vile poisons
made from coal tar, shock and weaken the heart and reduce the vital
activities so that the headache is no longer felt. In consequence of
shocks from repeated doses of such drugs, the heart will not work so
well, and may give way some time in the future when an effort or strain
makes unusual demands upon it. Their use has made heart disease more
prevalent. The liver and kidney cells and the white corpuscles have to
destroy and remove the drugs. Many people are foolish enough to injure
their bodies and risk death rather than suffer pain or avoid pain by
prudent living.
_Sick headaches are foretold_ by a dull feeling, sleepiness after
eating, a coated tongue, and constipation. It would be better to remove
the undigested, spoiled food from the stomach (four glasses of water
will cause vomiting) than to take a drug. At the first indication of
trouble, abstain from eating, or use a fruit diet for twenty-four
hours, and drink water freely. This will enable the body to dispose of
the excess of waste matter.
=The Highest Living Medical Authority on Drugs.=--Dr. Osler, formerly
of Johns Hopkins University and now of Oxford University, says:
“But the new school does not feel itself under obligation to give
any medicines whatever, while a generation ago not only could few
physicians have held their practice unless they did, but few would
have thought it safe or scientific. Of course there are still many
cases where the patient or the patient’s friends must be humored
by administering medicine, or alleged medicine, where it is not
really needed, and indeed often where the buoyancy of mind, which
is the real curative agent, can only be created by making him wait
hopefully for the expected action of medicine; and some physicians
still cannot unlearn their old training. But the change is great.
The modern treatment of disease relies very greatly on the old
so-called natural methods, diet and exercise, bathing and massage,
in other words giving the natural forces the fullest scope by easy
and thorough nutrition, increased flow of blood, and removal of
obstructions to the excretory systems or the circulation in the
tissues. One notable example is typhoid fever. At the outset of the
nineteenth century it was treated with “remedies” of the extremest
violence,--bleeding and blistering, vomiting and purging, antimony
and calomel, and other heroic remedies. Now the patient is bathed
and nursed and carefully tended, but rarely given medicine. This
is the result partly of the remarkable experiments of the Paris
and Vienna schools into the action of drugs which have shaken the
stoutest faiths; and partly of the constant and reproachful object
lesson of homeopathy. No regular physician would ever admit that the
homeopathic “infinitesimals” could do any good as direct curative
agents; and yet it was perfectly certain that homeopaths lost no more
of their patients than others. There was but one conclusion to draw,
that most drugs had no effect whatever on the diseases for which they
were administered.”--“Encyclopædia Americana,” Vol. X. (Munn & Co.,
New York.)
=Applying Hygienic Tests Systematically.=--The cause of ill health
(_e.g._ a headache) should be sought with system and thoroughness,
applying the tests in rotation to every function of the body:
_Lungs._ Is the air habitually breathed fresh and free from dust?
Is the body held up, and is the chest or waist cramped by clothing?
_Muscles._ Is enough physical exertion made to cause deep breaths
to be drawn? _Food._ Is it simple, digestible, and eaten properly?
_Drink._ Is the water pure? _Cleanliness_, _Work and Rest_,
_Clothing_, _Ventilation_, and _Mental State_ may be inquired into
until the source of trouble is found and the cause of ill health
removed. To give drugs and leave the cause of ill health untouched,
is to fail. There are signs of coming weakness or illness which, if
heeded and the ways of living improved, will usually prevent illness.
Among these signs are headaches, paleness, sensitiveness to cold,
heavy feeling or pain after meals, constipation. Huxley says that
young people should so learn physiology and so understand their
bodies that they will _heed the first sign of nature’s displeasure,
and not wait for a box on the ear_.
=Nervous Children.=--A report on the health of the school children
in one of our large cities shows that one third of the children in
those schools have some disorder of the nerves. Nervousness (weakened
control of the nerves) may show itself by sluggishness of mind,
great _irritability of temper_, frequent _spells of the_ “_blues_,”
or by _involuntary movements_ of a _jerky_ or fidgety kind. Sound
development of city children’s nerves is hindered because of the
constant noise in cities both day and night; by _shortening of the
hours of sleep_; by _excessive use of sugar_ for food; by living much
among people with _no chance to be alone and let the nerves rest_,
and among boys by the _use of cigarettes_.
=How to Prevent the School from injuring Children.=--(1) _Ventilation_
is of first importance. Breathing the breath of fifty other children
does far more harm than overstudy. (2) _The time devoted to work_
should not be long, especially in the lower grades (no study out
of school). (3) The _work should be diversified_; not only printed
words, but pictures, natural objects, and the outdoor world should
be studied. (4) The teacher and parent should see that _the habitual
poise_ of the child is favorable to health. (5) The children should
be _encouraged to play_. Running games at recess are of the greatest
value, and are as indispensable to the health of a boy or girl as of
a colt. (6) _Physical exercise_ should be provided at short intervals
between lessons, especially _stretching exercises_ and _movements that
straighten the spine and hips and elevate the chest_.
=The Effect of Alcohol upon Nerve Function.=--In attacking the nerve
centers, alcohol begins with the cerebrum, the highest, and proceeds
toward the lowest. Hence as a man becomes drunk he first talks
foolishly (cerebrum affected), then he staggers (cerebellum affected),
and he finally goes to sleep and breathes very hard (medulla affected)
in a drunken stupor. It rarely happens that the breathing center is
completely disabled and the man dies from the strong poison. The
greatest evil of alcohol is seen in the case of steady drinking. This
gradually destroys the soundness of the nervous system and weakens
self-control. The tendency with nearly all drinkers is to increase the
amount taken.
=Not Total Abstainers, but the Advocates of Universal Moderation are
the Visionaries.=--The evil results from alcohol are so great as to
be almost incredible. The plainest statements of its effects are
sometimes denounced as unscientific by persons prejudiced in its favor.
A part of the two billion dollars annually paid for liquors is used in
influencing public opinion through the press.
PRACTICAL QUESTIONS.--=1.= Why does travel often cure a sick person
when all else fails? =2.= Why is working more healthful than “taking
exercise”? (p. 47.) =3.= Is it better for children to play or to
take exercise? =4.= Why can one walk and carry on a conversation at
the same time? (p. 127.) =5.= How does indigestion cause a headache?
(p. 133.) =6.= Does perfectly comfortable clothing from head to foot
help to make one at ease in company? Does uncomfortable clothing tend
to make one awkward? =7.= Why is it as important to have the shoes
and clothes perfectly comfortable when going out as when staying
at home? =8.= When one’s finger is cut, where is the pain? =9.= In
what two ways may opening a window when a student is becoming dull
and drowsy at his books enable him to wake up and study with ease?
=10.= What kinds of cells shrivel like a baked apple when they become
fatigued? (Fig. 117.) =11.= A nerve or nerve fiber can hardly become
tired or fatigued, for the nerve cell supplies the energy. What
do we mean when we say the nerves are worn out? (Fig. 117.) =12.=
Why do you throw cold water upon a fainting person? =13.= Why does
constant, moderate drinking undermine the health more than occasional
intoxication? =14.= Why does stoppage of the circulation cause one
to faint? (See Chap. VI.) =15.= Why is grazing the skin often more
painful than cutting it? (Colored Fig. 1.) =16.= Why do the lower
animals always act upon sudden impulse? What part of the brain
enables man to retain sensations and not act upon them until later?
=17.= Does “nervousness” more probably indicate a bright mind or a
high temper? =18.= What is the effect of a cold bath upon the nerves?
(Chap. II.) =19.= Did you ever know a cigarette smoker whose hand
trembled? =20.= Need there be any fear of a sobbing child holding
its breath until it dies? =21.= Why is muscle tone greater in cold
weather?
=The True Function of Stimulants.=--One whose heart has nearly given
out because of exposure to severe weather may be temporarily revived
by alcohol. _It will not be wise to do so unless it is certain that a
warm fire and protection will be reached before the reaction comes._
Much less would be necessary to revive an abstainer than a drunkard.
_Habitually_ disturbing the body with stimulants makes them ineffective
in a time of emergency. A cup of coffee will not keep a watcher awake
if he is used to coffee.
=Definitions: Stimulant, Narcotic, Poison.=--_A stimulant is
anything that excites the body to activity, but is of no help or of
insignificant help, in replacing the strength used up._
_A narcotic is anything that deadens or dulls the nervous system._ It
comes from a word meaning “to benumb.”
_Poisons_ are active substances, which, taken in quantities, as man
takes food, destroy life; in smaller quantities they injure the body
and may destroy life. Alcohol is a poison. Wine, beer, whisky, contain
varying quantities of it.
=The Narcotic and Stimulant Effects of Poisons.=--Examples of poisons
are alcohol, nicotin, opium, arsenic, strychnin. Poisons excite the
body when taken in small doses, while in large doses they produce
paralysis and death. _The irritating or stimulating effect is due to_
derangement of the functions or to the efforts of the cells to free the
body of the destructive substance. _The narcotic effect is due to_ the
poison having so benumbed the nerves and injured the cells that their
activities cease, or become less for a time. You readily see how the
same poison can be both a stimulant and a narcotic: _the stimulating
effect always comes first, followed by the stupefying effect_. If the
dose is very small, the stimulating effect will last longer; if it is
large, the narcotic effect is greater and felt more quickly. A habit
of using stimulants is an invariable sign of weakness. The first dose
of morphine or cocaine may be the first step in a lifelong blight
of strength and happiness. If physicians whose treatment of a case
results in leaving a patient with a drug or alcohol habit were sued for
malpractice, they would be less reckless. The annual consumption of
morphine is estimated at twenty-seven grains per capita in China, and
fifty grains in the United States.
=Reaction.=--_This is the depressed and exhausted condition that comes
on after a period of unnatural activity._ It follows the exciting
effects of a stimulant.
=Natural Stimulants.=--If there were nothing to arouse activity, life
would be impossible. A cold wind is a natural stimulant. _The activity
aroused by a cold wind is just enough to help the body withstand the
cold; artificial stimulants cause an expenditure having no relation
to the needs of the body._ Hence there is a great waste of energy.
Feelings may stimulate, as love for his family may stimulate a man to
labor. The desire for knowledge may stimulate a boy to study. Hunger
may stimulate a man to eat. Hunger is a natural stimulant, and is not
likely to make him eat to excess; tea, coffee, pepper, etc., arouse
a false appetite. These things are used chiefly for their stimulant
effect, for they contain little or no nourishment. We will now
study about artificial stimulants. _Such stimulants always cause an
unregulated and unhealthy action, and are always followed by reaction._
=How much Strength is stored in the Body?=--Dr. Tanner of Minnesota
believed that most people eat too much. _Another physician said that
no human being could go forty days without food._ Dr. Tanner made the
experiment. He lost thirty-six pounds in weight, but he weighed 121¹⁄₂
pounds and had considerable strength at the end of the forty days. The
first thing he ate at the close of his fast was the juice of a ripe
watermelon.
Once some miners were shut in by the caving of a part of a mine. But,
unlike the case just described, _they were without water as well as
food_. When, by digging, the rescuers reached them seven days after,
several were still found alive, although most of them had died. The
miners, no doubt, had nourishment in their bodies for some weeks more
of life, but the body lacked water to dissolve it and bring it within
the reach of the cells most needing it.
=A Stupendous Fact.=--These incidents show how wisely the body is made,
and prove that the cells store up nourishment for weeks ahead. _The
large amount of nourishment stored in the human body_ is one of the
most striking and important facts with which the science of physiology
has to deal, and it should be borne in mind, or we may make great
mistakes about some very simple matters and especially in regard to the
effects of stimulants.
=Foolish Rashness.=--Did you ever get so tired that you had to give
up and stop, however much you would have liked to continue at work or
play? _To rest was the wise thing to do._ Because you know there is
much energy stored in the body, this need not tempt you to go on until
you almost break down. Probably you know _people who are conceited
about their bodies_ and say they are “made of cast iron”; that nothing
can hurt them. Such conceit will be almost sure to get its possessor
into trouble.
=How a Safeguard may be broken down.=--It is a very wise arrangement
that, _under ordinary conditions, we cannot get at the surplus energy
we have_. Carbon dioxid and other wastes accumulate in the tissues
and paralyze the nerves. Fatigue and other feelings compel us to be
provident, as it were; yet stimulants and narcotics, by irritating the
nerve cells, arouse them and cause us to expend some of this reserve
energy. Thus man is enabled to get at this precious store which he
should save for emergencies, when he is sick and cannot digest food,
or when he is making some mighty effort. A weak, ill man who has eaten
very little for weeks, when delirious is sometimes so powerful that it
takes several strong men to hold him in bed. But the delirious mania
often uses up the little energy left, and costs the man his life.
=The only source of energy for man’s body= is the union of food and
oxygen; he must get his energy from the same source that the engine
does; and this is from his food, which serves as fuel, and the
oxygen which burns it. If one has been working hard preparing for
examinations, or gathering hay, or in attending to some important
business, or has been under the excitement of some pleasure trip, and
_feels “blue” and worn out, then let him bear the result like a man_,
or like a true boy or girl, as the case may be. Giving up for a while,
or “toughing it out” with the blues, or losing a little time from
business, will not hurt, but will restore strength, while a stimulant
will leave him less of a man than before.
=Nervousness.=--The attempt to divide the race into brain workers,
muscle workers, and loafers, whether men or women, is a powerful
factor in race degeneration. Leonard Hill says: “Hysteria and nervous
exhaustion are the fruits not of overwork, but of lack of varied and
interesting employment. The absurd opinion that hard work is menial
and low, leads to most pernicious consequences. The girl who, turning
from brain work to manual labor, can cook, scrub, wash, and garden,
invites the bloom of health to her cheeks; while the fine do-nothing
lady loses her good looks, suffers from the blues, and is a nuisance
to her friends and a misery to herself.” A Japanese lady holds views
similar to those of Dr. Hill. Read footnote.[10]
[10] =Statement by Madame Toyi Niku= of Yeddo, Japan, after a six
months’ visit to the United States.--“Worry and inactivity, it seems
to me, sharply mark the women of your middle classes. I did not
attempt to study your leaders of society, for they are much alike
the world over--the same fuss, the same display of jewels and
finery, the same scandals, the same uselessness. Your women do not
diversify enough. If they are good cooks, they stop there; perhaps
another is a good housekeeper, another can sew finely; but doing one
thing makes narrow-mindedness. In Japan we strive to do many things.
The worry troubles of your women, it seems to me, come largely from
improper eating and overeating. I have sat at many of your tables
and there is too much food on them and too much variety. First,
women overeat, then they doctor, then they starve, and then they
become nervous. A woman’s diet, especially a mother’s, should always
be simple. Cut down eating and increase variety of labor and
exercise. My own people live that way with a result that we have
better feminine bodies, better skins, and better tempers than your
women. I like the brightness of your young women. Perhaps you will
take the hideous hats off them some day, find a substitute for the
bad corset, and let them wear clothes that are loose, yet are soft
and clinging. They are bound up in their clothes too much now and
their judgment of colors and combinations is not good. Their
clothing is either garish or very dull in hue. The simplest girl in
Japan knows how to harmonize color with herself.”--_Mother’s
Magazine_, November, 1907.
SUBJECTS FOR DEBATE.--(1) Does the Chinese woman deform her body less
than the Caucasian woman and suffer less from it? (2) Does as much
disease originate in the dining room as the barroom? (3) Are drugs a
necessary evil? (4) Does pride cause as much illness as ignorance?
(5) Is it ever right to neglect the health? (6) Does the mind or the
way of living have more effect upon the health?
=Disuse and Degeneration.=--Many persons in civilized countries
cherish a vain hope of having sound muscles without habitual use
of them, pure blood without deep breathing, a strong circulation
in an inactive body, a fresh skin without keeping the body sound,
a hearty appetite without enough physical labor to use the food
already eaten, steady nerves with a part of the body overworked
and a part stagnating from disuse. Their flabby muscles, pale
skins, highly seasoned food to arouse appetite, narcotics to deaden
irritable nerves, and the wide use of drugs as a fancied substitute
for right living all show the attempt to be a miserable failure.
If the parents leading such a life escape with fairly good health
and average length of life, they leave a few unhealthy children in
whom physical degeneration is plain. Complete, balanced living only
prevents degeneration. Although there are cases of illness which are
not necessarily a disgrace, disease usually originates in weakness of
character or lack of common sense. The snob who thinks himself above
physical labor, the dupes who at the bidding of avaricious fashion
mongers think more of clothes than of a free body, the narrow,
unbalanced man, who concentrates all his energies on one ambition,
the short-sighted one who worries, all grow into a diseased state.
CHAPTER IX
THE SENSES
_Experiment 1._ =Where are the Nerves of Touch most Abundant?=--Open
a pair of scissors so that the points are one eighth of an inch
apart, and touch both points to the tip of the finger. Are they felt
as one or as two points? Find how far they must be separated to be
felt as two points when applied to the back of the neck. Record
results. Caution: The person should be blindfolded, or should look
away while the tests are being made. Two pins stuck in a cork will be
more convenient to use than scissors.
_Experiment 2._ =Nerves of Temperature, or Thermic Nerves.=--Draw the
end of a cold wire along the skin. Does the wire feel cold all the
time? Repeat with a hot wire. Do you conclude that temperature is
felt only in spots?
[Illustration: FIG. 119.--“COLD” SPOTS (light shading). “HOT” SPOTS
(dark), skin of thigh.]
=Muscular Sense.=--_Experiment 3._ Make tests of the ability to
distinguish the weight of objects weighing nearly the same, when
laid by another in outstretched hand; also by laying them in the
hand while it rests upon a table. Which test showed more delicate
distinctions? In which were muscles brought into use? _Experiment 4._
Close the eyes and let some one move your left arm to a new position;
then see if you can with the forefinger of the right hand touch the
forefinger of the left hand in its new position at the first attempt.
_Experiment 5._ =Functions of the Several Parts of the Tongue.=--Test
the tip, edges, and back of the tongue with sugar, vinegar, quinine,
and salt. Where is the taste of each most acute? Record results.
=Flavors.=--_Experiment 6._ Blindfold a member of the class, and
while he holds his nostrils firmly closed by pinching them, have him
place successively upon his tongue a bit of potato and of onion.
Can he distinguish them? _Experiment 7._ Mark _F_ after each of the
following foods that have a flavor (see text): vanilla, apple, lemon,
beef, peaches, grapes, coffee, onion, potato, cinnamon.
_Experiment 8._ =A Smelling Contest.=--Place the following and other
things having taste in vials around which paper has been pasted to
conceal their contents: pepper sauce, vinegar, kerosene, flavoring
extracts (diluted), several perfumes, iodine, bits of banana, lemon,
apple, etc. Number the vials and have pupils test and write results
in a list. Correct the lists and announce pupil having keenest sense
of smell.
_Experiment 9._ =A tasting contest= may be arranged in a similar way.
Smelling and tasting tests should be made quickly as these senses are
soon dulled by repeating a sensation.
_Experiment 10._ =Advantage of Two Eyes over One.=--Try to touch
forefinger to something held by another at arm’s length from you,
bringing the finger in from the side: (1) with one eye closed; (2)
with both eyes open. Result? Conclusion? We tell the distance of an
object by the amount of convergence of the eyeballs needed to look at
it.
_Experiment 11._ =Duration of Impression.=--Whirl a stick with a
glowing coal on one end (see Fig. 123).
_Experiment 12._ =Color Blindness.=--Provide a number of yarns of
different tints, and the same tints. Test color blindness by having
each pupil match tints and assort the yarns.
_Experiment 13._ =Fatigue of Optic Nerve.=--Gaze long and steadily at
a moderately bright object, then close the eyes. Result? Conclusion?
_Experiment 14._ =Dissection of Eye.=--The eye of an ox is an
interesting subject for dissection. The lens is like a clear crystal.
Make out all parts named in the text (see Fig. 122).
_Experiment 15._ =Image formed by a Convex Lens.=--For a few cents
obtain from a jeweler a convex lens, or use a strong pair of
spectacles worn by an old person. Hold the lens a few feet from a
window (darken any other windows near). A little beyond the lens hold
a white card or book open at a blank page to catch the image. Have
some one walk before the window.
_Experiment 16._ =Work of Iris.=--Notice the size of the pupils.
Cover one eye with the hand for a few minutes. Uncover and look
in a mirror. Gaze at bright window and look again in the mirror.
Conclusion? Do the two pupils still keep the same size when one eye
is shaded?
_Experiment 17._ =Accommodation.=--By holding your finger or a pencil
in line with writing on the blackboard, you find that you cannot see
both finger and blackboard distinctly at the same time--first one and
then the other is distinct. Explain (see text).
_Experiment 18._ =Astigmatism= (effect of unequal curvature of cornea
or lens along certain lines). With end of crayon draw about twelve
straight, even lines crossing at one point on the blackboard. Have
the lines of equal distinctness. How many pupils report that the
lines in certain directions are blurred? Inquire whether these pupils
have frequent headaches from eye strain.
_Experiment 19._ =Can Sound reach the Ear through the Bones?=--Hold a
watch between the lips and notice its ticking. Close the teeth down
upon it and notice any change in the sound. Cover one, then both
ears, and note the result.
_Experiment 20._ =Test keenness of hearing= by having pupils walk
away from a ticking watch until it becomes inaudible. Test each ear.
A “stop” watch is preferable.
_Experiment 21._ =Advantage of Two Ears over One.=--Have the class
stand in a circle. Blindfold some one and place him in the middle of
the circle. Let various pupils clap the hands as the teacher points
to each. Can the blindfolded one point in the direction whence the
sound comes? Stop one ear with a handkerchief and repeat. Result?
Conclusion? From what two points in the circle does the sound fall
upon both ears alike?
_Experiment 22._ =The Cause of Nasal Tones.=--Let a pupil go to the
back of the room and read a paragraph, and hold his nose until partly
through the reading. Or the teacher may read with his face and hand
hidden by a large book. Let the other pupils raise their hands when
they notice a change in the quality of the reader’s voice. Does the
experiment show that a “nasal” tone comes partly through the nose
or through the mouth only? Does stoppage of the nostrils by catarrh
cause a nasal tone?
=Five Differences between Special and General Sensation.=--First, the
nerves of special sense all end in special organs at the surface; for
instance, the touch corpuscles are for touch, the eye is for sight,
etc. There are many nerves in the body that do _not end in special
organs_; these nerves give what is called general sensation. A second
difference is that general sensation _tells of the condition of
the interior of the body_, while special sensations tell us of the
condition of the surface of the body and of the outside world. Third,
_general sensations are not so exact_ as the reports of the special
senses. One can locate a point on the skin that has been touched
much more accurately than he can locate an internal pain. A fourth
difference is that the meaning of each special sensation must be
learned (usually in infancy); but the _meaning of general sensations
is inherited_. This inherited knowledge of what general sensations
mean is also called instinct. Fifth, the _sympathetic nerves usually
bring general sensations_; the spinal and cranial nerves usually
bring special sensations.
=Examples of general sensations= are hunger, thirst, satiety,
nausea, faintness, giddiness, fatigue, weight, aching, shuddering,
restlessness, blues, creepy feeling, tingling, sleepiness, pain,
illness. Any nerve can convey the general sensation of pain, if
injured along its course. If a nerve of touch is cut, there is no
sensation of touch, but of pain. Touch sensations come only from the
ends of the nerves. General sensations are of many kinds. We are
only half conscious of some of them; many of them are hard even to
describe.
=Hygiene of the General Sensations.=--General sensation is an
invaluable aid to the health. Without it as a guide, the body could
not remain alive a single day. _Pain_ should be heeded as our best
friend, and not killed with poisonous drugs as if it were our worst
enemy. We should not deaden the stomach ache with an after-dinner
cigar. If we do not go to bed when sleepy, the _desire for sleep_ may
leave us, and we will undergo untold suffering from sleeplessness.
_Thirst_ should be satisfied with cool water, which quenches it the
best; he who makes his teeth ache with ice water will inflame his
stomach and be continually thirsty. He who does not stop eating when
his _hunger_ is satisfied, will distend his stomach with food, and
the stretched organ will be harder to satisfy thereafter; in fact,
eating after a feeling of satiety may cause indigestion so that the
cells will not get the food. A dyspeptic is always hungry, for the
cells are starving. _Fatigue_ of body or mind gives us wise counsel;
but this feeling may be deadened by alcohol or tobacco, and work
continued until the body is injured. We should heed the warning of
pain or fatigue or restlessness as promptly as an engineer heeds
a red flag on the railway track. One who uses narcotics acts like
a reckless engineer who removes the danger signal and goes ahead,
hoping by good luck to escape an accident.
Most of the =nerves of touch= end in papillæ of the dermis as
_microscopic, egg-shaped bodies_ (Fig. 120). There are also many in
the interior of the mouth, especially on the tongue. On the palms they
are arranged in curved lines, and on the tips of the fingers they are
in circular lines, with one papilla in the center. The delicacy of the
sense of touch varies very much in different parts of the skin. _This
delicacy refers to two things_: the ability to feel the slightest
pressure and the ability to tell the exact point of the skin that is
touched. A lighter pressure can be felt on the forehead and temples
than with any part of the body. (Why is it best for this to be the
case?) The greatest delicacy in locating the point of the skin touched
is found to be located in the tip of the tongue, the lips, and the
ends of the fingers (Exp. 1). (Why is it best that this is so?) This
delicacy is least in the middle of the back. The delicacy varies with
the number of touch corpuscles in different parts of the skin. The
sense of touch is capable of great cultivation, as in the case of the
blind.
[Illustration: FIG. 120.--DIFFERENT KINDS OF TOUCH BODIES AT ENDS OF
NERVES.
_A_, from cornea of the eye; _B_, from the tongue of a duck; _C_, _D_,
_E_, from the skin of the fingers. (Jegi.)]
=The temperature sense= is given by special nerves called the thermic
nerves (Exp. 2). That the _thermic nerves are easily fatigued_ is
noticed soon after entering a bath of hot water; it is also shown
by the fact that in cold countries the nose or ears of a person may
freeze without his feeling it.
=The Muscular Sense.=--_The special sense of touch gives some sense
of weight._ A weight upon the skin must be increased by one third
before it feels heavier, but by lifting an object so as to _bring
into action the muscular sense residing in nerves ending in the
muscles_ an increase of only one seventeenth of the original weight
can be noticed (Exp. 3). This sense gives us a continual _account of
the position of the limbs_ (Exp. 4).
=The end organs of taste= are located in the papillæ of the tongue. The
tongue has a fuzzy look because of the numerous papillæ.
=The principal tastes= are only four; namely, sweet (tasted chiefly by
tip of tongue), sour and saline (sides of tongue), bitter (tasted on
the back of tongue) (Exp. 5).
=The nerves of smell= end in the mucous membrane of the upper half
of the two nasal chambers; the _fibers are spread over the upper
proportion of the walls_. The direct current of air does not pass as
high as these nerve endings; hence sniffing aids the perception of
odors. This sense is able to bring up the associations of early life
more powerfully than any of the senses. The odor of a flower like one
that grew in an old garden can almost restore the consciousness of the
past. _We smell gases only_; solids and liquids cannot affect this pair
of nerves (Exp. 8).
=Flavors.=--The tastes that we call flavors are really smells. We
confuse them with taste, because they accompany food that is in the
mouth. Name some foods that seem “tasteless” when one has a severe
cold in the head. Why is this? Some of the most repulsive drugs can be
easily swallowed if the nose is held (Exp. 6 and 7).
=Hygiene of the Senses of Taste and Smell.=--A savage or a beast
uses the senses of taste and smell to find out whether things are
good to eat or not. If a civilized man’s senses are not perverted,
and he eats only simple foods that have a pleasant taste, they will
not injure him or cause him sickness. Things that are poisonous
usually have unpleasant tastes and often have unpleasant odors. These
senses are naturally of wonderful delicacy. They can be cultivated
to a still more remarkable degree, or they can be blunted and almost
destroyed. Chronic catarrh dulls or destroys the sense of smell. The
loss or even the weakening of the perception of flavors is an injury
to the working of the closely related sense of taste. When a person
loses the enjoyment of delicate flavors, he wants food to have strong
seasoning and more decided taste to prevent it from being insipid.
Everything must be either very greasy or very sweet or very salty or
very sour, to please his degenerate senses. Wheat, corn, and other
grains have each its own pleasant taste, yet such persons must have
lard in their bread because they are not capable of appreciating
anything with a delicate taste. In England, butter is not salted and
its delicate taste is enjoyed; in America, salt is added to preserve
it, and most people have come to prefer the strong taste of salty
butter to the delicate taste of pure butter, and do not like it
unless its true taste is partly hidden by the taste of salt (Exp. 9).
=Deceiving the Sense of Taste.=--The habit of using narcotics like
_tea_ and _coffee_ is usually begun by concealing the repulsive
bitter taste of the substance by mixing sugar, cream, and other
agreeable things with it. Licorice is sometimes mixed with _tobacco_
to weaken its biting taste. _Pure alcohol_ would never be drunk by
any one who had the least respect for the sense of taste, but the
agreeable flavor of grapes, apples, and other fruit which still
remains in wine, cider, and brandy, conceals the repulsive taste
of the alcohol. _Beer_ has the insipid taste of grain which has
undergone decomposition or partial rotting, and hops are added
because the strong bitter taste of hops is needed to hide the
stale, rancid taste of the rotted grain. _Eggnog_ is made of eggs,
a nourishing food; sugar, which has an agreeable taste; water, a
refreshing drink, and alcohol, a fiery poison. A very good eggnog is
often made without alcohol, but a good one could hardly be made with
any of the pleasant ingredients left out. The best eggnog is made by
using the fresh juice of lemon, orange, or grape, instead of alcohol.
=Effect of Narcotics.=--Tobacco, alcohol, opium, and other narcotics
dull the senses of taste and smell and prevent the enjoyment of
delicate flavors. They accomplish this as much by their effect upon
the brain as upon the nerves themselves.
=It is Wrong to eat Food that is not Relished.=--Unpalatable food is
not likely to be well digested. It is a law of the body that _the
food which is enjoyed the most is digested the best_. This applies
to a hungry person eating food with its own honest taste, not to
food disguised by the taste of something else. The rule does not
apply to a taste perverted by having been forced to become accustomed
to poisonous things. People who munch their food slowly enjoy the
pleasures of taste the most, and digest their food the best. The
nerves of taste and smell easily become fatigued. The first whiff
from a cologne bottle is the strongest. Highly flavored foods should
be eaten moderately, if we would obtain the greatest enjoyment from
them.
THOUGHT QUESTIONS.--=1. Interfering with the Body.= What is the
natural direction of growth of the big toe? =2.= Think of six evil
results, direct or indirect, which will follow from displacing it by
tight shoes (p. 48). =3.= Which part of the spinal column, designed
in infinite wisdom to be most flexible, do some people try to make
the most inflexible? =4.= The mobility of the false and floating ribs
was intended as a blessing. Some people interpret the blessing as an
opportunity to do what? =5.= Name six articles which warn us to avoid
them by their bitter, burning, or nauseating tastes, yet which are
used by man. =6.= Name six feelings which are intended as warnings
for our guidance, but which are commonly disregarded.
=The eyes= on the rays of the starfish are mere spots of pigment.
Insects have lenses in their eyes. The eyes of vertebrates are all
formed on the same general plan as the human eye.
=The eyeballs= are globes about an inch in diameter. They are placed in
deep, bony sockets, called _orbits_, in the front part of the skull.
The optic nerve, other nerves, and several large blood vessels pass to
the eye through a hole in the back of the orbit. A soft cushion of fat
is in the orbit behind the eyeball. A pressure upon the eyeball causes
the eye to sink into the socket, for the fat yields to the pressure.
This is a protection to the eye.
=The eyelids= protect the eyes from dust, and at times from the light.
They are aided in this by the eyelashes.
[Illustration: FIG. 121.--TEAR GLANDS AND DUCTS of right eye. (Jegi.)]
=The tears= are formed by _tear glands_ situated above the eyeball in
the portion of the orbit farthest from the nose, just beneath the bony
brow where it feels the sharpest (Fig. 121). They are about the size of
almonds. A saltish liquid is continually oozing from the tear glands
and passing over the eyeball; it is carried into the nose through the
_nasal duct_ (Fig. 121). The tears reach this duct through _two small
canals_, which open into the eye in the little fleshy elevation at
the inner corners of the eye (Fig. 121). The opening of one of the
canals may be seen by looking into a mirror. Sometimes these canals are
stopped up, and what is called a “weeping eye” results. A temporary
stoppage may occur during a cold in the head.
Tears prevent friction between eye and lid. Winking applies the tears
to the ball. Small glands along the edges of the lids form a kind
of oil which usually prevents the tears from flowing over the lids.
Sometimes this oily secretion is so abundant, especially during sleep,
as to cause the lids to stick together. The mucous membrane of the
eyelids continues as a transparent membrane (the conjunctiva) which
passes over the front of the ball.
[Illustration: FIG. 122.--THE ANATOMY OF THE EYE.]
=The globe of the eye= consists of its outer wall and the soft contents
(Fig. 122). The wall has three layers or coats. The outer coat is
the tough _sclerotic_ (Greek, _skleros_, hard), composed of dense
connective tissue (Exp. 14). It gives strength and firmness to the
eyeball. It shows between the lids as the “white of the eye.” It is
white and opaque except in front; there it bulges out to form the
transparent _cornea_. This clear portion of the wall may be seen by
looking at the eye of another from the side.
The second coat, called the _choroid_, consists of blood vessels and
a loose connective tissue containing many dark brown or black pigment
granules. The choroid absorbs superfluous light. Cats’ eyes shine at
night because this coat in their eyes reflects some light. The choroid
separates from the sclerotic toward the front of the eye and forms the
colored _iris_. The iris makes the eyes beautiful, and it also serves
the useful purpose of regulating the amount of light. The hole in the
iris is called the _pupil_ (Exp. 15).
The third and innermost coat, the sensitive pinkish layer called the
_ret′in-a_, is the most important and characteristic tissue in the eye.
It receives the light rays, and retains the image for a fraction of a
second (Exp. 11). Hence the pictures in a kinetoscope (Fig. 123) appear
as one moving picture. The retina is made chiefly of the fibers of the
optic nerve. This nerve contains about five hundred thousand fibers,
and enters at the back of the ball. The spot where it enters contains
no nerve endings and is not sensitive to light. It is called the _blind
spot_. The spot where the light most often falls is most sensitive to
light. It is the _yellow spot_ (Fig. 122).
[Illustration: FIG. 123.--STROBOSCOPE, the original of the kinetoscope.
The observer looks through the slits of a rapidly revolving disk and a
new image falls on the retina before the last image has faded. Compare
the pictures in the figure.]
=Test for the Blind Spot.=--In this experiment shut the right eye and
be careful not to let the left eye waver.
* Read this line slowly. Can you see the star all the time? (If so,
hold the book farther or closer and repeat.)
=Within the coats of the ball=, like the pulp within the rind of an
orange, are the soft contents, divided into three parts. The first is
a watery liquid in front, which serves to keep the cornea bulged out
(Fig. 122). It is called the _a′que-ous humor_. The main cavity of the
ball is occupied by a clear, jellylike substance called the _vit′re-ous
humor_, which serves to keep the ball distended. Back of the iris, and
separating the two humors just named, is the _crys′tal-line lens_, a
beautiful clear lens, convex or rounded out on both sides (Exp. 14).
It serves to bring the light to a focus on the retina, thereby forming
images of outside objects.
=The eye, like a camera=, has a dark lining, the choroid; the retina
corresponds to the sensitive plate, and the lens brings the rays to a
focus on it and forms the image.
[Illustration: FIG. 124.--CROSSING OF OPTIC NERVES showing that one
nerve reaches same half of both eyes.]
=The Path of Light in the Eye.=--The light enters through the
transparent cornea and passes through the aqueous humor. As it goes
through the pupil, the iris shuts off all the light that is not needed.
The crystalline lens receives the light that has been allowed to pass,
and so bends the rays that by the time they have passed through the
vitreous humor they fall upon the retina in just the right way to form
a tiny image of anything outside (Exp. 11). The choroid absorbs any
light that passes the retina. The iris and choroid of albinos have no
pigment; hence albinos squint their eyes to shut out some of the light.
=Accommodation.=--In order to focus the light upon the retina, the
_lens must change shape for every change in the distance of the object
looked at_ (see Fig. 125). The shape of the lens can be readily
changed, for it is elastic and has muscular fibers around its edges
(Exp. 17).
[Illustration: FIG. 125.--Change of lens in accommodation. (Jegi.)]
=Defects in the Eye.=--Some eyeballs are too long, and the lens
brings the rays to a focus before they reach the retina. Such eyes
are _nearsighted_ (Fig. 126) and require glasses that round inward
(concave). Some eyeballs are too flat, and the rays are not brought to
a focus soon enough. Such eyes are _farsighted_ and require glasses
that round outward (convex). See Fig. 127. (Repeat Exp. 15.)
[Illustration: FIG. 126.--(1) NEARSIGHTED EYE (ball too long), which
only focuses rays for near objects (2) when concave glasses are used
(3).]
[Illustration: FIG. 127.--FARSIGHTED EYE (ball too short) which needs
convex lens to focus rays upon retina.]
=Care of the Eyes.=--Because the eyes can do a large amount of work
without giving pain, they are often abused. When reading or doing
intricate work, turn the eyes from the work occasionally and look at
some distant object; stop work before the eyes are tired. Twilight of
early evening has ruined many good eyes. You should always stop work
before the twilight begins, for the light fades so gradually that you
will surely be straining the eyes before you know it. Do not work with
the light in front; the glare of the light makes objects appear dim.
The light should come from above, and (for right-handed people) from
the left. Do not read papers or books printed in fine type. We should
not read when convalescing from illness; with the head bent down; when
the eyes are sore; in jolting cars. Heating the eyes by a burner,
or drying the eyeballs in a dry, stove-heated atmosphere, using a
light without a shade, cause trouble with students’ eyes. Of what are
blood-shot eyes often a sign? Our eyes are best suited for seeing at
a distance because primitive man had no houses, books, sewed clothes.
Effort is required to shape the lens for seeing near objects. Most
cases of nearsightedness begin when children are taught to read under
eight years old. The eyes are sometimes injured by the use of tobacco.
THOUGHT QUESTIONS. =The Eye.=--=1.= The eye is shielded from blows
by bony projections of ____, ____, and ____. =2.= The hairs of the
eyebrows lie inclined toward ____, in order to turn ____ from the
____. =3.= I find by trying it that I (can or cannot?) see the
position of a window with my eyes closed. =4.= The pupil appears to
be black, because no ____ is ____ from the interior wall of the eye.
I know that the iris is partly muscle, because it ____ the size of
the ____.
=Sound.=--Anything that is sending off sound does so by vibrating, or
shaking to and fro, very rapidly. For instance, a vibrating violin
string sets every particle of air near it swinging to and fro. The
nearest particles of air strike the next ones and bounce back, these
in turn strike against others, and thus vibrations called sound waves
are sent through space in all directions from the sounding body. We
feel these waves with the ear.
=The ear= consists of three portions: the _external_ ear, the _middle_
ear (or drum), and the _internal_ ear (or labyrinth, see Fig. 128).
The cranial nerve connecting the ear with the brain is called the
_auditory_ nerve. The outer and middle ear pass on the vibrations of
air to the ends of the fibers of the auditory nerve in the internal ear.
[Illustration: FIG. 128.--MIDDLE AND INTERNAL EAR (greatly enlarged).]
=The external ear= consists of a large wrinkled _cartilage_ on the
exterior of the head and a _canal_ leading from it, called the
_meatus_. This passage is closed at its inner end by the drum membrane
or _drum skin_. It is often called the drum, but this name is properly
applied to the whole middle ear. A trial will show that the drum skin
cannot be seen even with the aid of a bright light, for the passage
is slightly curved (see Fig. 128). Hence a missile or a flying insect
cannot go straight against the ear drum. The skin lining this passage
contains _wax glands_, which secrete a bitter sticky wax, which helps
to keep the passage flexible. This wax catches dust and usually stops
insects that may enter. If an insect enters the ear, it may often be
coaxed out by a bright light held close to the ear. The ear wax in
a healthy ear dries with dust and scales of epidermis and falls out
in flakes, thus cleansing the ear. It is unwise to probe into the
ear with a hard object or even with the corner of a towel. It is not
necessary to insert the finger in the meatus to cleanse it; it is
one inch long, but only about one fourth inch across. (How large is
the little finger?) The cartilaginous ears on the sides of the head
should be carefully washed because of their many crevices. If ear wax
is deposited too fast, it will cause temporary deafness and earache.
It may be syringed out with warm water. Earache is usually caused by
a small boil which requires time to relieve itself by bursting. Warm
water poured into the upturned ear, or hot flannels or compresses
applied to the side of the head will lessen the suffering. Each ear has
three muscles for moving it. Once they were doubtless useful to all,
but like the scalp muscle they have become so weakened by disuse as to
be useless to most people. They are vestigial organs.
=The middle ear=, or drum chamber, contains air (Fig. 128). It is
separated from the outer ear by the drum membrane. It contains three
bones which stretch across it and conduct the sound waves from the drum
membrane to the inner ear. State the order in which they are placed
(see Fig. 128). The middle ear is connected with the pharynx by a tube
(the _Eustachian tube_; pronounced yoo-stake´e-an, see Fig. 128). This
tube is opened every time we swallow. It allows the air from the throat
to enter the middle ear and keep the air pressure equal on each side
of the drum skin. This tube and the middle ear are lined with mucous
membrane.
A _cold in the head_ or a sore throat may extend through this tube to
the middle ear and affect the hearing. This occurs because the tube is
closed by congestion of its lining; the air of the middle ear may be
partly absorbed, and the pressure of the outside air may cause the drum
membrane to bulge inward, and to be stretched so tight that it cannot
vibrate freely.
=The inner ear= is called the _labyrinth_, because of its winding
passages. There is a spiral passage called the _snail shell_ and three
simpler passages called the _loops_ (Fig. 128). The inner ear is filled
with a limpid liquid which conveys the vibrations to the _ends of the
auditory nerve_ found in the snail shell. If the auditory nerve or
labyrinth becomes diseased, the deafness is probably incurable. Quinine
and other drugs may cause deafness.
=Sense of Equilibrium.=--Some fibers of the auditory nerve end in the
loops and are not believed to be used in hearing. It is believed that
each loop acts like a carpenter’s level, and the varying pressure of
the fluid upon the nerves in the loops tells us the position of the
body and constitutes the sense of equilibrium. There are how many of
these loops in each ear? (Fig. 128.)
CHAPTER X
BACTERIA AND SANITATION
_Experiment 1._ =Yeast Plants.=--With a microscope examine a drop
from a glass of water in which you have washed grapes or apples (Fig.
129).
_Experiment 2._ =Fermentation.=--Put a tablespoonful of sugar into
this water and set the glass in a warm place for a day or two. Do
you see any bubbles of gas? Have the odor and taste changed? Does
the microscope show that the yeast plants are now more abundant? By
fermentation, or the growth of yeast in sugar, sugar is changed into
carbon dioxid, a gas, and alcohol, a liquid.
_Experiment 3._ =A Sanitary Map.=--Construct a sanitary map of the
community. Indicate houses where consumption, typhoid fever, or other
transmissible diseases have occurred, with number of cases. Mark
location of stagnant waters where mosquitoes breed, mark garbage
dumps, unclean streets. Suggest where improvements may be made in
drainage, dust, noises, sunshine, shade, etc.
[Illustration: FIG. 129.--YEAST CELLS magnified 200 diameters, or
40,000 areas. Yeast plants multiply by budding. Notice small cells
growing on larger and older ones.]
=Bacteria=, or microbes, the smallest living things, are visible only
under a microscope of high power. (See “Plant Biology,” p. 182.) They
obtain food either from dead tissue or from degenerate tissue of living
plants and animals. The green plants and the animals now upon the earth
have proved their _fitness to survive_ by successfully resisting these
one-celled vegetable germs, or bacteria. Microbe diseases attack only
the weaker individuals of the human species, or those who have gone
to regions where there are microbes which their bodies have not yet
acquired the power of resisting.
=Usefulness of Bacteria.=--Their chief work is to destroy dead tissue
and return it to the soil and air for the use of green plants again,
otherwise the earth would be filled with carcasses, etc. They are
indispensable in soil formation. They give the agreeable flavors to
butter and cheese, and cause milk to sour. A rod-shaped bacterium is
called a _bacillus_ (Fig. 130); a spherical one is a _coccus_.
=Multiplication of Bacteria.=--This is by division or _fission_.
Sometimes, instead of dividing, a little rounded mass known as a
_spore_ appears. The spore breaks out and the bacterium itself
perishes. Species which do not produce spores are readily destroyed,
but spores have a hard, tough shell, and they may be dried or heated
even to boiling without being killed. Spores float through the air
and start new colonies. _Most common bacteria grow best between 70°
and 95° F._ They render it difficult to preserve foods, _especially
proteid foods_ (cheese, lean meat, eggs, etc.). Food decays slowly if
at all below 70° and above 125°. Direct sunlight, or the temperature
of boiling water (212° F.) kills bacteria but not spores. Pantries,
kitchen, and sickrooms should have bright walls and all the light
possible. Boiling water should be poured into the sink, and dish cloths
should be thoroughly washed in boiling water.
=Diseases due to Bacteria.=--A germ disease is usually due partly
or wholly to substances called toxins produced by the bacteria.
Most disease germs attack a single organ of the body. _Diphtheria_
is caused by a species (Fig. 130) that grows on the mucous membrane
of the throat; this germ produces a powerful toxin. The germs of
_typhoid fever_ (Fig. 131) and _Asiatic cholera_ multiply in the
small intestine. In both these diseases the source of infection is
the diarrhœal discharges from the alimentary canal. Flies may carry
the germs on their feet from the discharge to food. Sometimes typhoid
fever cases occur throughout a town because the water supply has
become contaminated by sewage. Cases may occur only in families that
buy milk from a certain dairy, because the milk cans have been washed
in contaminated water. In caring for a typhoid patient all suspicious
material should be disinfected or burned. Germs of _tuberculosis_
(called _consumption_ if the disease is in the lungs) may float through
the air. Recent investigations indicate, however, that infection
usually occurs through the alimentary canal, the germs being swallowed,
then absorbed and taken to the lungs in the blood or lymph. To prevent
a patient from reinfecting himself in new parts of the lungs or
elsewhere, he should carefully cleanse his teeth, mouth, and throat (by
gargling with formal or lysol) before eating.
[Illustration: FIG. 130.--BACILLUS OF DIPHTHERIA.]
[Illustration: FIG. 131.--BACILLUS OF TYPHOID FEVER.]
[Illustration: FIG. 132.--CULEX OR COMMON MOSQUITO, above (possibly
carries dengue fever). ANOPHELES OR MALARIAL MOSQUITO, below (not
always infected). Body of malarial mosquito is never held parallel to
the supporting surface (unless a leg is missing); it has five long
appendages to the head, the culex (above) has only three. (Draw.)]
[Illustration: FIG. 133.--PROTECTIVE WHITE CORPUSCLE (phagocyte)
digesting a microbe.]
=Mosquito Fevers.=--_Malaria_, _yellow fever_, and probably _dengue_
are transmitted each by a different genus of mosquito (Fig. 132). A
mosquito of the malarial genus may bite a patient and suck into its
body blood-corpuscles containing spores of the malarial parasite (a
protozoan animal, see “Animal Biology,” p. 7). Afterwards a spore
(in another stage) may be transmitted by this mosquito when it bites
another person. The germ enters a red corpuscle, grows, and finally
divides into many little spores. At this moment the corpuscle itself
breaks up, setting free in the blood the spores and toxin formed. This
causes the chill and fever. This development usually takes forty-eight
hours, hence the fever occurs every other day. These mosquitoes _begin
to fly at dusk_. How are they recognized? (Fig. 132.) They should be
kept out of houses by screens or from the beds by netting. Kerosene
should be poured on breeding places at the rate of one ounce for
fifteen square feet of standing water. This should be repeated twice
a month. Cactus macerated in water may be used, and forms a permanent
film on the water. Stagnant pools may be filled or drained (Exp.
4). _Malarial patients should themselves be screened, as the chief
source of danger to others_; for only mosquitoes who suck the blood
of malarial patients will transmit the disease. Even then it is only
transmitted to those whose white blood corpuscles are unable to protect
them (Fig. 133).
=Further Means of Protection against Disease Germs.=--The best
protection is physical vigor. There are certain substances called
_opsonins_ which exist in the plasma of the blood of disease-resisting
persons; these opsonins give the white corpuscles the power to devour
disease germs. The serum of the blood also develops antitoxins which
neutralize the toxins formed in disease. Not only can the white
corpuscles and serum kill bacteria, but most of the secretions
of the healthy body (gastric juice, nasal secretions, etc.) are
bacteria-killing as well. Persons in a low state of health most readily
succumb to disease. Excess in eating may lessen the germicidal power of
gastric juice and inactivity that of the lymph. The same germ disease
does not usually attack the same person twice, as the body becomes
immune; that is, an opsonin, or an antitoxin, is developed which cures
the first attack and remains to protect the body in future.
The periods of quarantine or isolation for several common germ diseases
are given in the following table:--
==============+=============+=======================================
|FROM EXPOSURE|
NAME OF | TILL FIRST | PATIENT IS INFECTIOUS
DISEASE | SYMPTOMS | TO OTHERS
--------------+-------------+---------------------------------------
Diphtheria |2 days |14 days after membrane disappears.
Mumps |10-22 days |14 days from commencement.
Scarlet fever |4 days |Until all scaling has ceased.
Smallpox |12-17 days |Until all scabs have fallen.
Measles |14 days |3 days before eruption till scaling and
| |cough cease.
Typhoid fever |11 days |Until diarrhœa ceases.
Whooping cough|14 days |3 weeks before until 3 weeks after
| |beginning to whoop.
==============+=============+=======================================
=Water Supply.=--Bacteria are more abundant in flowing streams than in
water standing in lakes or reservoirs (contrary to the usual belief).
They are most abundant in rivers that flow through populous regions.
They are comparatively scarce in dry, sandy soils, and very numerous
in moist, loamy soils. The water of cities should never be taken from
a stream or lake into which sewerage flows unless it is thoroughly
filtered. Filters are constructed thus: first a layer of small stones,
next a layer of coarse sand, lastly a layer of very fine sand on top,
the total thickness being four or five feet. Beneficial microbes
live upon the grains of sand and destroy all, or nearly all, of the
dangerous microbes as the water slowly soaks through. The construction
of such waterworks is left to sanitary engineers, of course, and the
average citizen does not need to know the details.
=The department of street cleaning= should receive the willing
coöperation of all citizens. Banana peelings, paper, etc., should
not be thrown upon the street or school grounds. Garbage, ashes, and
rubbish should be placed in separate cans, as the rules provide.
Garbage cans, if not thoroughly cleaned, acquire unpleasant odors and
breed flies and bacteria. They should be thoroughly washed with very
hot water and sal soda and scalded with boiling water and scrubbed with
an old broom.[11]
[11] The chief =Disinfectants= are: _fresh air_, _sunshine_, _heat_,
_formaldehyde_, etc. Airing and sunning will destroy some germs in
bedding and clothing as effectually as chemicals. Boiling and
steaming are the best ways of applying heat. _Formaldehyde_ is a
volatile liquid. After room is sealed and strips of paper pasted all
over cracks, a specially constructed generator is applied to
keyhole, and room kept closed for 12 hours. _Mercuric chloride_
(corrosive sublimate) is used 1 part to 1000 parts of water for
disinfecting soiled clothing, towels, utensils, surgeon’s
instruments, and wounds. In place of this, _carbolic acid_, 5 per
cent solution, may be used, but it is not so good a germicide.
=The chief duties of the Health Department= are: quarantine isolation
and disinfection, with the purpose of preventing or controlling
contagious and infectious diseases; inspection of dairies,
slaughterhouses, and other sanitary work; inspection of milk[12] and
other food stuffs; the department gathers vital statistics; it enforces
the rules for disinfection of public buildings.
[12] =Milk= may be sterilized by boiling, but boiled milk is not
digestible nor nutritious. Milk may be Pasteurized by immersing
bottles of milk in water which is kept nearly (but not quite) at
boiling point (160° F.) for five minutes. But this makes the milk
less valuable than fresh milk, and destroys beneficent microbes.
Buttermilk has many such microbes, which kill injurious microbes and
purify the stomach. Cleanliness, or an _aseptic_ condition, is far
preferable to _antiseptics_.
=Importance of Coöperation with the Health Department.=--Only an
ignorant and short-sighted person would fail to coöperate promptly and
cheerfully with local or state health officers. It is for the benefit
and protection of every one that the truth concerning contagious
diseases be reported promptly. Only in this way may outbreaks of
disease be prevented and many lives saved. He is a bad citizen and
a public enemy who will conceal a case of disease dangerous to the
community. Outbreaks of fatal diseases may be easily prevented or
stamped out if the health officer is sustained and his directions
carried out.
INDEX
I, V, X, etc. = Introduction: P = Plant Biology: A = Animal Biology: H
= Human Biology.
Aboral surface, A 35.
Aborted seeds, P 166.
Absorption, H 106.
Abutilon, P 156.
Accessory fruit, P 164, 169.
Accommodation in eye, H 143, 153.
Acephala, A 107.
Acid, ix.
Adaptation to environment, P 6, A 148, 185, 201, 205, 207, H 19, 108,
109, 110.
Adenoid growths, H 86.
Adipose tissue, H 12.
Adulteration of food, H 93.
Adventitious roots, P 36; buds, P 114.
Aerial roots, P 34.
Aggregate fruit, P 168.
Air cells, H 75.
Air plants, P 35.
Akenes, P 165.
Albinism, H 16, 18.
Albumen, H 92.
Albumin, H 92.
Alcohol and circulation, H 67; and fermentation, H 158; and food, H
113; and muscles, H 50; and nerves, H 135; and skin, H 20.
Algar, P 179, 183, 195.
Alkaline, ix.
Alternation of generation, P 179, A 30, 31.
Ambulacral, A 36.
Ameba, A 10.
Americans, H 1.
Anadon, A 98.
Anatomy, H 9.
Anemophilous, P 149.
Animal food, H 95, 110.
Annual plant, P 17.
Antelope, A 215.
Antennæ, A 68, 87.
Anther, P 135, 144, 180.
Antheridium, P 178, 186, 198, 200, 202, 203.
Ant-eater, giant, A 199; spiny, A 196.
Ant-lion, A 91.
Ape, A 220.
Apical dehiscence, P 166.
Appendicitis, H 106.
Appendix, vermiform, H 106.
Appetite, H 94, 110.
Aptera, A 82.
Apteryx, A 174.
Aquarium, A 17.
Archegonium, P 178, 198, 200, 202, 203.
Argonaut, paper, A 107.
Arm, H 33.
Armadillo, A 200.
Arrowhead, H 2.
Arteries, H 51, 53, 54, 61.
Arthropoda, A 9, 125.
Arum family, P 140.
Ash, P 92.
Asiatic cholera, H 160.
Assimilation, P 97, H 90.
Association fibers, H 123, 126.
Asthma, H 86.
Astigmatism, H 144.
Athletics, H 46, 47.
Atwater’s experiments, H 113.
Auricle, H 53.
Automatic action, H 123.
Axil, P 112.
Axis, plant, P 15.
Axon, H 119.
Bacillus, H 158, 159.
Bacteria, P 39, 109, 182, H 158, 159, 160, 161.
Bandage, H 62.
Barberry, P 157, 193.
Bark, P 54, 66, 67.
Bark-bound trees, P 54.
Bast, P 61, 66.
Bat, A 202.
Baths, H 23, 24.
Batrachia, A 126.
Bean, P 20, 28, 39, 194, H 95, 96, 112.
Beaver, A 204.
Bedbug, A 92, 93.
Bee, bumble, A 89; honey, A 88.
Beebe’s experiments, Dr., H 113.
Beef, H 111; tea, H 111.
Beetle, A 90, 91.
Berry, P 167.
Biennial plant, P 17.
Big-headed turtle, A 149.
Bilateral, A 34, 49, 98.
Bile, H 105.
Bill of bird, A 151.
Biology defined, A 1, H 9.
Birds, A 150.
Blind spot, H 151.
Blood, H 58; quantity of, H 55; of insects, A 78.
Blood vessels, H 52; control of, H 58.
Board of Health, H 163.
Boll weevil, A 95, 96.
Boll worm, A 95, 96.
Bones, H 29; composition of, H 31; growth of, H 14, 36; forms of, H
28, 29, 34; structure of, H 30.
Bony tissue, H 13.
Borax, H 93.
Brace cells, P 67.
Bracts, P 134.
Brain, H 122; coverings of, H 125; of fish, A 118.
Branch, P 111, A 9.
Breathing, forms of, H 80; of bird, A 161; of insect, A 76; through
mouth, H 85.
Breeding, plant, P 7, 8.
Bronchial tubes, H 75.
Bruises, H 62.
Bryophytes, P 181.
Bud propagation, P 121.
Budding, P 127, 128.
Buds, P 72, 82, 87, 111; flower, P 115; fruit, P 115.
Bureau of entomology, A 95.
Burns, H 24.
Burs, P 172, 174.
Bushes, P 191, A 171.
Butterfly, A 83.
Cabbage, P 113, H 95.
Cabbage butterfly, A 84, 86, 87.
Callus, P 56.
Calyx, P 133.
Cambium, P 63, 65.
Camel, A 214.
Candle, xv, A 5.
Cane sugar, H 92, 104.
Capillaries, H 52, 53, 56.
Capsule, P 165.
Carbohydrate, P 95, H 91, 95.
Carbon, vii, xviii, P 92.
Carbon, dioxid, A 24, P 22, 93, 106, H 60, 76, 81, 132; monoxid, H 85.
Carnivorous, P 99, H 111.
Carp, A 112, 117, 123.
Carpel, P 136.
Cartilage, H 13, 35.
Castor bean, P 24.
Cat, A 184.
Caterpillar, tent, A 84.
Catkin, P 158.
Caucasian, H 1, 2.
Caulicle, P 20, 22, 25.
Cedar apple, P 194.
Cell, P 42, 63, 145, 176, A 6, 7, H 5, 6.
Celom, A 46.
Cephalopod, A 106.
Cerebellum, H 122, 124.
Cerebro-spinal system, H 128, 129.
Cerebrum, H 122, 125, 126.
Chelonia, A 143.
Chemistry, xv.
Chemical symbols, xv.
Chest, H 32.
Chewing, H 90, 101.
Chimpanzee, A 219, 221.
Chirping, A 66.
Chitin, A 77.
Chlorophyll, P 86, 94, 101, 183, 186.
Cholera, H 160.
Choroid, H 150, 152.
Chyme, H 103.
Cigarettes, H 67, 86.
Cilia, A 14, 20, 101, 103, H 76.
Ciliated chamber, A 17.
Cion, P 125.
Circulation, H 51; and breathing, H 58; and exercise, H 67; hygiene
of, H 68; in ameba, A 12; in insect, A 77; in fish, A 117; portal, H
60, 105; pulmonary, H 60; renal, H 60.
City, H 4.
Cladophylla, P 100.
Clam, hardshell, A 104; softshell, A 104.
Class, A 9.
Classification, of animals, A 8, 125; of birds, A 177; insects, A 82;
mammals, A 193.
Cleft graft, P 126.
Cleft leaf, P 75.
Cleistogamous, P 151.
Click-beetle, A 91.
Climate, and clothing, H 25; and brain work, H 68; and early man, H 2.
Climbing plants, P 129.
Clitellum, A 43, 47.
Cloaca, A 18.
Clot, H 61.
Clothes moth, A 84, 92, 93.
Clothing, H 16, 25.
Clover, P 39.
Club mosses, P 203.
Cluster, flower, P 155, 159; centrifugal, P 156, 159; centripetal, P
156; indeterminate, P 156.
Coagulation, H 61.
Cockroach, A 71.
Cocoon, A 84.
Codling moth, A 84, 86, 87, 95.
Cœlenterata, A 28.
Colds, care of, H 69, 86.
Coleoptera, A 82.
Collecting insects, A 72.
Colon, H 106, 111.
Colonies, plant, P 11.
Colorado beetle, A 90, 91.
Coloration, warning, A 84, 146; protective, A 34, 37, 49.
Colors of flowers, A 85.
Comparative study, A 85, 108, 122, 223; moth and butterfly, A 85.
Composite flowers, P 140.
Compositions, subjects for, H 15, 50, 116, 141.
Compound substance, vii.
Congestion, H 68.
Conjugation, P 185.
Conjunctiva, H 150.
Connective tissue, H 11, 54, 120.
Consumption, H 159.
Convolution, H 126.
Cooking, H 114.
Coördination, H 124.
Copper head, A 145.
Coral, A 31.
Coralline, A 31.
Coral snake, A 145, 146.
Cork, P 66, 67.
Corn, P 3, 25, 26.
Cornea, H 150.
Corolla, P 133; funnel form, P 138; labiate, P 138; personate, P 139;
rotate, P 138; salver form, P 138.
Corpuscles, origin of, H 30; red, H 59; white, H 59, 60, 65, 68.
Corset, H 58, 80, 87.
Cortex, P 44.
Corymb, P 159.
Cotton plant, P 7, A 95.
Cotyledon, P 20.
Cricket, A 71.
Cross-fertilization, A 25.
Crowd poison, H 82.
Cryptogam, P 176, 180, 183-204.
Cuckoo, A 179.
Currant, P 157.
Cuttings, P 121, 123, 124.
Cuttlefish, A 107.
Cyme, P 159, 160.
Cypræa, A 104.
Cysts, A 13.
Cytoplasm, H 6.
Darwin, A 48, 148.
Debates, subjects for, H 141.
Deciduous, P 82.
Decumbent, P 50.
Degeneration, H 3, 4, 141.
Dehiscence, P 144, 164.
Deliquescent, P 51.
Dendron, H 119.
Dependent plants, P 106.
Dermis, H 17.
Devil’s horse, A 71.
De Vries, A 148, 224.
Dextrin, H 112.
Diaphragm, H 77, 78.
Dichogamy, P 144.
Dicotyledon, P 20.
Dicotyledonous stems, P 61.
Digestion, P 95, H 89, 96, 100.
Digitate, P 74.
Digits, A 222, H 111.
Dimorphous, P 144.
Diœcious, P 138, 170.
Diphtheria, H 160.
Diptera, A 82.
Disease, defined, H 5.
Disinfection, H 163.
Dispersal of seeds, P 172.
Dissection, P 30.
Division of labor, A 27, 29, H 8.
Dodder, P 35, 106.
Dog, A 224.
Dolphin, A 209.
Doodle bug, A 91.
Dorsal, A 43.
Dove, A 179.
Dragon fly, A 93.
Drainage, H 158, 161.
Dropsy, H 64.
Drugs, H 60, 130, 133.
Drupe, P 168.
Drupelet, P 168.
Duckbill, A 196.
Dust, H 82, 158.
Ear, of bird, A 151; of frog, A 131; of fish, A 112; of man, H 154.
Earthworm, A 42.
Echinoderms, A 9, 34, 125.
Ecology, P 14, H 9.
Economic importance of birds, A 167; insects, A 93; mollusks, A 105;
rodents, A 206.
Ectoderm, A 26, 87.
Ectoplasm, A 11, 14.
Egg, of insect, A 81; of hen, H 95, 96, 112.
Elaters, P 198.
Element, viii.
Embryo, P 26, 180.
Embryo sac, P 180.
Enamel, H 98.
Endoderm, A 26, 27, 37.
Endodermis, P 44.
Endoplasm, A 11, 14.
Endosperm, P 21, 24.
Energy, H 96, 140; in ameba, A 12; organic, A 2, 3; plant, A 2, 3, 5.
Entomophilous, P 148.
Environment, P 6, A 148, H 2, 3, 4, 48.
Enzyme, H 100.
Epicotyl, P 23, 25.
Epidermis, of leaf, P 86, 87; of man, H 17; of mussel, A 98.
Epigeal, P 23.
Epiphyte, P 35, 110.
Epithelial, H 12, 54.
Equisetums, P 201.
Erect posture, H 3.
Esophagus, H 74, 101.
Essays, subjects for, H 15, 25, 50, 116.
Essential organs, P 135.
Ethiopian, H 12, 18.
Evaporation, viii.
Excretion, A 12.
Excurrent, P 51.
Exercise, H 45, 48, 49, 57, 67.
Expiration, H 79.
Explosive seeds, P 172.
Eye, H 149; of bird, A 150; of frog, A 30; of grasshopper, A 67, 79;
of fish, A 111.
Fainting, H 57.
Family, A 8.
Fangs, venomous, A 145.
Farmers’ bulletins, A 95.
Fatigue, of muscles, H 45; of nerves, H 130, 131, 136.
Fats, test for, xi.
Fatty tissue, H 12, 103.
Feather, A 155.
Fehling’s solution, xi.
Ferment, H 100, 103, 104, 158.
Fermentation, P 190, H 158.
Fern, P 176.
Fertilization, P 144; cross, P 144, 146, A 85; self, P 145, 147, 188.
Fiber, H 2.
Fibrin, H 61.
Fibro-vascular bundles, P 61, 90.
Field study, P 3, 6, 8, 14, 19, 27, 46, 57, 71, 84, 91, 101, 110,
118, 128, 132, 143, 152, 162, 170, 174, 181, A 10, 22, 42, 71, 72,
97, 127, 165, 166, 167, 184.
Filament, P 135.
Filter, H 163.
Fins, A 110, 113.
Flagellum, A 21, 27.
Flatworm, A 49.
Flavors, H 142, 147.
Flea, A 92, 93.
Flight, of bird, A 157, 175; of moth, A 84.
Floral envelopes, P 133.
Florets, P 140.
Flower, P 133, 180, A 85; apetalous, P 136; clusters, P 155;
complete, P 136; diclinous, P 137; double, P 142; imperfect, P 137;
incomplete, P 136; lateral, P 136; naked, P 136; perfect, P 137;
pistillate, P 137; regular, P 138; staminate, P 137; sterile, P 137;
solitary, P 156; terminal, P 156.
Fly, horse, A 81; house, A 92, 93.
Foliage, P 16.
Follicle, P 165.
Food, H 88; defined, H 114; of birds, A 177.
Food stuffs, H 91.
Food tube, of bird, A 163; of fish, A 116; of insect, A 76; of man, H
97; of mussel, A 102.
Foot, H 29.
Foraminifera, A 15, 18.
Forestry, P 68.
Formaldehyde, H 163.
Formalin, H 93.
Framework of plant, P 15.
Frog, A 128.
Frond, P 176, 178, 181.
Fruit, P 163, H 95.
Fucus, P 186.
Funaria, P 201.
Function, A 1, H 9.
Fungi, P 187.
Fungus, P 107, 108, 184, 187, 195.
Gametophyte, P 179.
Gamopetalous, P 134.
Gamosepalous, P 134.
Ganglion, A 45, H 120.
Ganglionic system, H 127.
Garbage, H 163.
Gasteropod, A 108.
Gastric juice, H 103.
Gastrula, A 7.
General sensation, H 144, 145.
Generation of plants, P 16.
Genus, A 8.
Geographical barriers, A 148.
Geotropism, P 44, 47.
Germination, P 22, 23, 27.
Gila monster, A 147.
Gills, of mussel, A 100; of fish, A 115.
Glands, lymphatic, H 65.
Gland tissue, H 13.
Glomerule, P 160.
Gnawing mammals, A 203.
Gopher, pouched, A 204.
Gorilla, A 221.
Grafting, P 125.
Grain, H 95, 112.
Grantia, A 18.
Grape sugar, x, H 88, 92.
Grasshopper, A 70.
Grit cells, P 67.
Guard cells, P 88.
Gullet, H 74, 94, 101.
Gymnastics, H 47.
Gymnosperm, P 26, 170.
Gypsy moth, A 95.
Habit, H 131.
Hairs, P 87, H 19.
Hands, H 4; defined, A 220.
Headaches, H 132, 133.
Heart, human, H 51, 52; insect, A 77; sound of, H 60.
Heating, H 84.
Hemiptera, A 82.
Hemoglobin, H 59, 81.
Herb, P 17.
Heredity, A 147, 153, H 4.
Hessian fly, A 95.
Hill, Dr. L. H., quoted, H 140.
Hilum, P 21, 26.
Hip, H 4, P 168.
Hollyhock, P 147.
Homology, P 135.
Horned toad, A 140.
Host, P 107.
House fly, A 92, 93.
Houstonia, P 107.
Human species, H 1, A 220.
Hydra, A 22.
Hydranth, A 29.
Hydrochloric acid, H 103.
Hydroid, A 28, 29, 30.
Hygiene, H 49, 66, 80, 107, 129, 141.
Hymenoptera, A 82.
Hyphæ, P 107, 188.
Hypocotyl, P 22.
Hypogeal, P 23.
Hypostome, A 23.
Ichneumon fly, A 89.
Imago, A 81.
Immunity, H 158, 160.
Indehiscent, P 164.
Indian, H 2.
Indusium, P 177.
Inflammation, H 68, 86.
Inflorescence, P 155, 160.
Infusoria, A 16.
Inhibit, H 68.
Inorganic, A 1.
Insecticides, A 95.
Insects, A 73, 75; biting, A 82; classified, A 82; sucking, A 82.
Inspiration, H 77.
Instinct, A 80, 121, H 49.
Intercostal, H 77.
Internode, P 52.
Intestinal gland, H 104.
Intestine, H 98, 103, 106.
Involucre, P 34, 141, 163, 164.
Iodine test for starch, x.
Iris, H 143, 151.
Iron, vii, P 39.
Iron tonics, H 90.
Isoëtes, P 203.
Ivory, H 98.
Jacana, Mexican, A 178.
Jay, blue, A 181.
Jelly fish, A 29, 30.
Joints, H 29, 35, 36.
Kangaroo, A 198.
Key fruit, P 164.
Kidneys, of fish, A 117; of insects, A 76; of man, H 26, 27; of
mussel, A 102; of worm, A 45.
Kinetoscope, H 151.
Labial palpi, A 68, 74, 101.
Labium, A 68, 74.
Laboratory, P 3.
Labrum, A 68, 74.
Labyrinth, H 157.
Lacteal, H 64, 65, 104, 105.
Lady bug, A 91.
Lamellibranch, A 107.
Landscape, P 13.
Lark, meadow; A 182; sky, A 179.
Larkspur, P 148, 149.
Larva, A 81.
Larynx, H 72.
Lasso cell, A 34.
Lateral spinal curvature, H 37.
Latex tubes, P 67.
Leaf, apex of, P 80; base of, P 80; function of, P 92; margin of, P
80; structure, P 86.
Leaf scar, P 90.
Leaves, arrangement of, P 82; shapes of, P 78, 85.
Leg, of bird, A 152; of horse, A 210; of insect, A 74; of man, H 33.
Legume, P 165, H 95.
Legume family, P 35, 169.
Lemur, A 220.
Lenticel, P 89.
Lepidoptera, A 82, 87.
Lichens, P 195.
Ligneous, P 17.
Lime water, xx, H 70.
Liver, H 105.
Liverworts, P 196.
Lobes of leaf, P 75.
Lobule of lung, H 75.
Locule, P 136, 163, 166.
Loculicidal dehiscence, P 166.
Louse, A 92, 93.
Lumber, P 68.
Lungs, of bird, A 165; of man, H 76.
Lycopodium, P 204.
Lymph, H 52, 62, 63.
Lymphatics, H 62, 63.
Lymph spaces, H 63.
Macrospore, P 203, 204.
Madreporite, A 35.
Malaria, H 160.
Malay, H 1.
Mammal, A 184, H 111; classified, A 193; defined, A 189.
Manatee, A 209.
Mandibles, A 68, 74.
Mantis, praying, A 3.
Mantle, A 99.
Marchantia, P 196.
Maxillæ, A 68, 74.
Maxillary palpi, A 68, 74.
May beetle, A 90, 91.
May fly, A 83.
Measuring worm, A 81, 84.
Medulla, H 122, 123.
Medullary ray, P 64.
Medusa, A 31.
Mesoglea, A 26.
Mesophyll, P 86.
Metamorphosis of insect, A 80, 81, 82.
Metazoan, A 1.
Micropyle, P 21, 26.
Microscope, P 21, 26.
Microspore, P 203.
Midrib, P 77.
Migration of birds, A 171, 173.
Milk, H 91, 95, 96, 112.
Mimicry, A 146.
Mind and health, H 129.
Minerals, xiv, H 90, 91, 93, 95.
Mint family, P 139.
Mistletoe, P 109.
Moccasin, A 145.
Mold, P 188.
Mole, A 201.
Mollusk, A 9, 97, 125.
Molting, A 69, 174.
Mongolian, H 1.
Monkey, A 220.
Monocotyledons, P 20, 25, 63.
Monœcious, P 138, 150, 170.
Morphine, H 105.
Morula, A 7.
Mosquito, A 92, 93, 96, H 160, 161.
Mosses, P 199.
Moss, Spanish, P 110.
Moth, A 83.
Mother-of-pearl, A 99.
Motor, cell, H 120; fiber, H 120.
Mullein, P 87.
Municipal sanitation, H 162, 163.
Muscadine, P 36.
Muscles, H 39; arrangement of, H 41; control of, H 39, 44; function
of, H 39, 43; growth, H 42; kinds of, H 39; structure of, H 39.
Muscles and health, H 45.
Muscular sense, H 142, 146.
Muscular tissue, H 11.
Mushroom, P 107, 194.
Mussel, A 96, 103.
Mycelium, P 107, 108, 188.
Mychorrhiza, P 108.
Nails, H 19.
Narcotic, H 137, 148.
Nasal tone, H 144.
Natural selection, P 8, A 148.
Nautilus, chambered, A 107.
Nectar, A 8, P 148.
Nephridium, A 45.
Nerve, H 119; spinal, H 127; cranial, H 127.
Nerve cell, H 119; fatigue of, H 130.
Nerve center, H 117, 120.
Nerve fiber, H 119.
Nerve tissue, H 11.
Nerves, vaso-motor, H 23.
Nervous children, H 135.
Nervous system, of bee, A 78; of man, H 117; of mussel, A 102.
Nest building, A 166, 182.
Neuron, H 118.
Neuroptera, A 82.
Neutral substances, ix.
Nitella, P 187.
Nitric acid test for proteid, xi.
Nitrogen, viii, P 39, 40, H 81.
Nitrogenous compounds, xi.
Nodes, P 20, 52.
Nodules, P 39, 40.
Nose bleed, H 52.
Nostoc, P 184.
Nostril, of bird, A 151; of fish, A 112.
Notebooks, P 3.
Nucleolus, A 6, H 6.
Nucleoplasm, H 7.
Nucleus, P 144, 185, A 6, 11, 14, H 6, 18.
Nutrients, H 91.
Nuts, P 164, H 95.
Octopus, A 106.
Oil gland, H 20.
Oils, test for, xi.
Okapi, A 214.
Oleander, P 86.
Omnivorous, A 47, H 111.
One-celled animals, A 7.
Oögonia, P 186.
Opossum, A 197; H 4.
Opsonin, H 162.
Optic nerve, H 151, 152.
Oral surface, A 35.
Orang, A 222.
Orbit, H 149.
Orchid, P 35, 110.
Order, A 9.
Organ, A 1, H 9.
Organic, xiv, A 1.
Organism, A 1.
Orthoptera, A 82.
Oscillatoria, P 184.
Osculum, A 18.
Osier, Dr. William, quoted, H 133.
Osmosis, P 42, 48.
Outdoor life, H 5, 22.
Ovary, P 135, 144, 163, 170, A 25, 37, 117.
Overgrowth, P 12.
Oviduct, A 46.
Ovule, P 144, 186.
Oxidation, xii, A 3, 4, 5, H 14, 90, 91, 120.
Oxygen, viii, A 4, 5, H 4, 76, 81, 140.
Oyster, A 104.
Palisade cells, P 86.
Palmate, P 74.
Pancreas, H 104.
Panicle, P 158.
Papilla, H 17.
Pappus, P 141.
Paramecium, A 13.
Parasites, P 107, A 49, 93.
Parenchyma, P 60, 86.
Partridge, A 178.
Pearls, A 105.
Peccary, A 217.
Pedicel, P 162.
Peduncle, P 62.
Peltate, P 77.
Pelvis, H 33.
Pepsin, H 103.
Perch, A 109, 110, 123.
Perennial, P 17.
Pericarp, P 164, 165, 169.
Peristalsis, H 102, 106, 127.
Peritoneum, H 106.
Pests, insect, A 93.
Petals, P 134.
Petiole, P 76.
Phagocyte, H 161.
Pharynx, H 73, 85, 101.
Pheasant, A 174.
Phenogam, P 177, 180.
Phosphorus, vi.
Photo-synthesis, P 94, 101.
Phyllotaxy, P 84.
Physics, xiv.
Physiology, H 9.
Pigment, H 18.
Pine cone, P 27, 170.
Pinna, P 181.
Pinnate, P 74.
Pinnatifid, P 76.
Pistil, P 135.
Plantain, P 157.
Plant societies, P 9.
Plants, unlikeness of, P 9.
Plastron, A 141.
Pleura, H 76.
Plexus, H 128.
Plumule, P 20, 23, 25.
Plur-annual, P 18.
Pod, P 164.
Poison, H 137.
Pollen, P 135, 144, 180, A 85.
Pollen basket, A 88.
Pollination, P 144, 145; artificial, P 153.
Polyp, A 9, 22, 125.
Polypetalous, P 134.
Polysepalous, P 134.
Polytrichum, P 199.
Pome, P 169.
Portal vein, H 105.
Portuguese man-o’-war, A 28.
Posterior curvature of spine, H 37.
Potato, H 92, 95, 112; bug, A 90.
Practical questions, H 50, 69, 87, 112, 136.
Primates, A 220.
Primitive man, H 3.
Primrose, P 149.
Proboscis, of butterfly, A 83, 87; elephant, A 207.
Prolegs, A 84, 87.
Propagation by buds, P 121.
Prop-roots, P 36.
Protection of birds, A 171.
Protective resemblance, A 34, 146.
Proteid, xi, H 88, 91, 92, 94, 95, 96, 104.
Proterandrous, P 146.
Proterogynous, P 146.
Prothallus, P 178, 202.
Protoplasm, xiv, P 42, 94, 97, 185, A 6, 11, H 5, 6, 59, 106, 118.
Protozoa, A 7, 9, 11, 125.
Pruning, P 105.
Pseud-annual, P 17.
Pseudoneuroptera, A 82.
Pseudopod, A 11.
Pteridophytes, P 181, 201, 203.
Ptyalin, H 100.
Puffball, P 194.
Pulse, H 55.
Pure food law, H 93.
Pylorus, H 103.
Pyxis, P 166.
Quarantine, H 163.
Quarter-sawed, P 70.
Quill, A 156.
Rabbit, A 205, 223.
Radial symmetry, A 34, 125.
Ration, daily, H 94, 96.
Rattlesnake, A 145.
Reaction, H 151, 152.
Receptacle, P 134, 163.
Rectum, A 134, H 97.
Reflex action, H 121.
Regeneration of lost parts, A 37.
Rennin, H 103.
Reproduction, A 12, 15, 20, 25, 37, 46, 120.
Reptiles, A 139.
Respiration, cellular, H 81; human, H 70; hygiene of, H 80; in
plants, P 97, 103.
Resting spore, P 184, 185, 189, 191, 192.
Retina, H 151, 152.
Rhizome, P 52, 202.
Rhizopoda, A 16.
Road runner, A 169.
Robin, A 183.
Root cap, P 44.
Root climber, P 129.
Root hairs, P 41, 42, 46.
Rootlet, P 41.
Root pressure, P 99, 104.
Roots, and air, P 41; forms of, P 32; function, P 38; structure, P
38, 43; systems, P 32.
Rotifer, A 49.
Round worm, A 49.
Ruminant, A 213.
Rust, P 192.
Salamander, A 134, 138, 139.
Saliva, H 96, 100, 112.
Salt, x, H 93.
Samara, P 164.
Sand, xiii.
Sandworm, A 49.
Sanitary map, H 158.
San José scale, A 95.
Sap, P 67.
Saprophyte, P 107, 108.
Scab in sheep, A 95.
Scales, of bird, A 161; fish, A 110; moth, A 89.
Scallops, A 104.
Scape, P 161.
Scarab, A 90, 91.
School and health, H 135.
Sclerotic, H 150.
Scouring rush, P 203.
Scramblers, P 129.
Sea anemone, A 33.
Sea fan, A 32.
Sea horse, A 124.
Sea urchin, A 38.
Seed, P 20, 163, 180; coat, P 21.
Selaginella, P 204.
Selection, natural, P 8; artificial, P 8.
Sense, muscular, H 143; thermic, H 142.
Senses of insects, A 76.
Sensory, cell, H 120; fiber, H 120, 121.
Sepal, P 133, 169.
Septicidal capsule, P 166.
Serum, H 61.
Sessile, P 77.
Setæ, A 43, 48.
Sexual selection, A 174.
Shark, A 121.
Shelf fungus, P 194.
Shoes, H 48.
Shoulder, H 32.
Shrub, P 19.
Sick headache, H 133.
Sieve tubes, P 66.
Silicle, P 167.
Silique, P 167.
Silkworm, A 84, 86, 95.
Silver scale, A 83.
Siphon, A 101.
Siphonoptera, A 82.
Skeleton, of bird, A 152; cat, A 188; frog, A 131; of fish, A 113;
man, H 28; chart of, A 218.
Skin, H 16.
Skull, H 63; mammalian, A 194.
Sleep, H 130.
Slipper animalcule, A 13.
Sloth, A 199.
Slug, A 105.
Smell, H 147.
Snail, A 105.
Societies, P 9.
Soil, P 40, 47, A 48.
Soredia, P 196.
Sori, P 177, 192.
Souring of milk, H 158.
Spadix, P 140.
Sparrow, A 182; English, A 170.
Spathe, P 138, 140.
Specialization, A 20, 27, 66, 210, H 8.
Species, A 8.
Spermary, A 25, 27.
Spermatophytes, P 180.
Spicule, A 18.
Spider, A 94.
Spike, P 157.
Spinal cord, H 120, 121.
Spinal deformities, H 37.
Spine, H 31.
Spiracle, A 77, 87.
Spirogyra, P 184.
Sponges, A 17, 125; glass, A 19; horny, A 19; limy, A 19.
Spontaneous combustion, xiii.
Sporangium, P 177, 186, 188, 201, 203, 204.
Spore, P 176, 178, 181, 184, H 159.
Sporophyll, P 180, 201.
Sporophyte, P 177.
Sports, A 148, 224.
Sprain, H 38.
Squash bug, A 93, 95.
Squid, A 106.
Stamen, P 135.
Starch, x, P 95, 101, H 88, 91.
Starvation, H 138.
Stem, P 49; endogenous, P 59; exogenous, P 61; kinds of, P 49.
Sterilizing wounds, H 163.
Stickleback, A 119.
Stigma, P 135, 144, 145.
Stimulant defined, H 137.
Stipule, P 76, 84.
Stock, P 125.
Stomate, P 87.
Stone age, H 2.
Stone fruit, P 168.
Storage of food, P 99.
Street cleaning, H 163.
Struggle to live, P 4, 6, A 147, H 4.
Study, comparative, A 82, 149, 223.
Style, P 135, 163.
Sugar, H 91, 100.
Sulphur, vii.
Summer-spore, P 191.
Sun energy, P 95, A 2, H 91.
Sunlight, A 2, H18.
Survival of fittest, P 7, A 147, H 4, 141.
Sutures, H 35.
Swarm-spores, P 186.
Sweat gland, H 20.
Symbiosis, P 196.
Sympathetic system, H 127, 129.
Syngenesious, P 141.
Synovial fluid, H 36.
Tadpole, A 126, 134.
Tanner, Dr., H 138.
Tapeworm, A 49.
Tarantula, A 94.
Taste, H 110, 143, 146.
Tear gland, H 149.
Teeth, H 88, 98, 99, 111; of frog, A 130.
Teleutospores, P 192.
Temperature, H 21; nerves of, H 142, 146.
Tendon, H 41.
Tendril, P 101.
Terrapin, A 143, 144.
Thallophyte, P 181, 184.
Thallus, P 184, 197.
Thompson, Sir Henry, on smoking, H 87.
Thoracic duct, H 64, 65, 105.
Thorns, P 101.
Thought questions, H 20, 27, 79, 107, 109, 116.
Thyrse, P 160.
Thyroid gland, H 97.
Tillandsia, P 110.
Timber, decay of, P 195.
Tissue, H 7, 10, P 60, 62.
Toad, A 137.
Toadstool, P 194.
Tobacco, and heart, H 67; and lungs, H 86; and taste, H 148; when
enjoyable, H 87.
Tortoise, A 140, 143, 144.
Torus, P 134, 169.
Touch, H 145, A 119.
Toxin, H 160, 161.
Toyi Niku, Madame, quoted, H 141.
Trachea, H 74.
Tracheid, P 65.
Transpiration, P 98, 103.
Trap-door spider, A 94.
Tube feet, A 35.
Tuberculosis, H 5, 160.
Tumble bug, A 90, 91.
Turtle, A 140, 143, 144.
Twiners, P 129, 131.
Typhoid fever, H 159.
Umbel, P 159.
Umbo, A 98.
Undergrowth, P 12.
Ungulate, A 212.
Urea, H 94.
Uric acid, H 114.
Urinary tubule, H 27.
Vacuole, A 11, 12, 14.
Valve, P 164, H 51, 53, 57.
Vampire, A 203.
Variation, A 147, P 2.
Variety, A 8.
Vaso-motor nerves, H 23, 68.
Vaucheria, P 186.
Vegetables, H 95, 112.
Venomous snakes, A 143.
Vent, A 42.
Ventilation, H 71, 82, 83.
Ventral, A 43.
Ventricle, H 53.
Vermes, A 9, 125.
Vermiform appendix, H 4, 106.
Vertebra, H 71, 82, 83.
Vertebrates, A 9, 125.
Vertebrate skeletons, A 218.
Verticellate, P 84.
Vestigial organs, H 106.
Villi, H 104.
Vinegar, H 94.
Viscera, H 127; of bird, A 163.
Vitreous humor, H 152.
Voluntary act, H 122, 124.
Warning sound, A 147.
Wasps, digging, A 89.
Water-pore, P 88.
Waterworks, H 163.
Weevil, A 90, 91, 96.
Whale, A 208.
Wheat rust, P 192.
White corpuscles, H 59; origin of, H 61; work of, H 60, 161, 162.
White weed, or ox-eye daisy, P 155.
Whorled, P 84.
Willow mildew, P 190.
Wind travelers, P 173.
Wings, of grasshopper, A 67; of bird, A 153, 158.
Woodpecker, A 180.
Woody fiber, P 17.
Worms, A 42.
Wounds of plants, P 56.
Written exercises, H 15, 50, 116.
Yeast plants, P 190, H 158.
Yellow fever, H 160.
Yellow spot, H 151.
Zoology defined, A 1.
Zoophytes, A 33.
Zygnema, P 185.
Zygospore, P 185, 189, 190.
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Transcriber’s Notes
Inconsistent and obsolete spelling, hyphenation, etc. have been
retained, except as listed below.
Depending on the hard- and software used to read this text and their
settings, not all elements may display as intended. Scales and
factors of enlargement or reduction as given in illustration captions
are not necessarily correct.
Page P 65, legend with Fig. 78: reference letter f does not appear in
the illustration.
Page P 107, (b, Fig 132): reference letter b does not appear in the
illustration.
Page P 111: the text refers to an apple bud in Fig. 137, the
illustration caption refers to an apricot bud.
Page A 16-A 17: there is no Fig. 20 in the source document.
Page A 96: there is no caption or other explanation with the third
illustration (hazelnut leaf, fruit and insect).
Page H 8, ... canals instead of railroads for their commerce (see
Fig. 84): it is not clear which illustration is referred to; Fig. 84
does not show this distinction.
Page H 11, ... called nerve fibers (Fig. 142): there is no Fig. 142,
nor is it clear to which figure showing nerve fibers this phrase
refers.
Page H 88, Practical Question 6: the reference to Chapter VI is
included in Chapter VI.
Page H 105, ... fresh milk is an emulsion of cream (Fig. 98): Fig. 98
shows something unrelated.
Page H 161, Page H 161: Stagnant pools may be filled or drained (Exp.
4): there are only three experiments with this chapter; Experiment 3
mentions stagnant water.
Changes made:
Footnotes, tables and illustrations have been moved out if text
paragraphs.
Some minor typographical errors and missing or extraneous punctuation
have been corrected silently; where relevant, illustration
captions have been standardised. Blanks to be filled out have been
standardised to a series of underscores.
The parts of the book have been included in the page numbering:
lower case Roman numerals for the index, prefixes I, P, A and H
for the Introduction and the parts on plants, animals, and humans
respectively.
Page I ix: page number P 1 inserted in Table of Contents for Part I
Chapter 1.
Page I xi: page number H 29 (section The Skeleton) changed to H 28.
Page I xvii: [See also experiments with candle and breath, in
Introduction to Human Biology.] and related hyperlinks changed to
[See also experiments with candle and breath, in The Principles of
Biology.] and relevant hyperlinks.
Page P31: Fig. B has been rotated 90°.
Page P 89: ... at their middles on either side the opening, ...
changed to ... at their middles on either side of the opening, ....
Page P 91: ... the table on page =88= ... changed to ... the table on
page 88 ....
Page A8: (Fig. 389.) changed to (Fig. 390.)
Page A 42: ... a test with live worm ... changed to ... a test with a
live worm ....
Page A 91: Parenthesis deleted from ... Where does a Scarab (or
sacred beetle ....
Page A93: Illustration caption Fig. 177 added.
Page A 94: parenthesis deleted from (Does the size of its nerve
ganglia ....
Page A 143, caption with Fig. 270: ... lr, liver ... changed to ...
le, liver ....
Page A 174: Describe the molting process (page 120) changed to
Describe the molting process (page 157).
Page A 177: D¹ Bill hooked, ... changed to D₂ Bill hooked, ....
Page A 193: C¹ Head large; ... changed to C₁ Head large; ...; C¹ Five
toes, ... changed to C₁ Five toes, ...; Dolphin (379, 397) changed to
Dolphin (Figs. 379, 397).
Page A 200: (See Fig. 347.) changed to (See Fig. 349.)
Page H 17: question mark deleted from ... a cotton cloth of same
weight and texture?
Page H 25: ... keeping the body cool during the exertion (Exp. o)
changed to ... keeping the body cool during the exertion (Exp. 5).
Pahe H 38: ... sit far back in the chair (Figs. 60, 61, 62) ...
changed to ... sit far back in the chair (Figs. 49, 50, 51) ....
Page H 54: ... blood vessels must have these three properties?
changed to ... blood vessels must have these three properties.
Page H 56: Fig. 57 rotated 180°.
Page H 70: (See Animal Biology, p. 14.) changed to (See Animal
Biology, p. 4.)
Page H 72: Make a model like sketch ... changed to Make a model-like
sketch ....
Page H 110, Fig. 101: individual elements rotated 90° clockwise.
Page H 140 (footnote): closing quote mark inserted after ... how to
harmonize color with herself.
Page H 158: parenthesis deleted after ... 200 diameters, or 40,000
areas).
Index: some page numbers corrected and book (I, P, A or H, see above)
letters added.
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