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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.