SCHOOL SCIENCE SERIES

EPRODUCTiGN

T. W. Galloway

fBLIC SCHOOL PUBLISHING COMPANY

BLOOM INGTON, iLLlNOiS

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SCHOOL SCIENCE SERIES, NUMBER FOUR*

REPRODUCTION

*For advertisement of other numbers of the series
see page 146

REPRODUCTION .^^l

a\

BY

THOMAS WALTON GALLOWAY

BELOIT COLLEGE

SCHOOL SCIENCE SERIES

JOHN G. COULTER. Publisher
BloominJon, 111.

^

Copyriglit, 1916. by
JOHN G. COULTER

PREFACE

In common with the other books of this series, this
little volume seeks to meet the needs of two classes of
readers. It is intended in the first place as a supplemen-
tary reading book for students in elementary biological
courses; and, secondly, for those members of the reading
public who are interested in a simple, untechnical account
of some of the most wonderful of the processes of life.

One-half of life, whether we are thinking of the life of
man or of the lower animals, is that devoted to the build-
ing up of successful individuals, and to adjusting these
suitably to the demands of their surroundings; the other
half has to do with perpetuating the species. These are
the two great problems of living things. Both are essen-
tial to permanence of life at any level. This book does
not undertake to discuss the first of these problems. It
tries to develop in a continuous way, as the text-book
cannot do, the story of how plants and animals produce
and care for their children. In this way the student can
get a better sense of the progress made from the lower to
the higher organisms, a more adequate idea of the evolu-
tion and perfection of the methods of reproduction.

Furthermore, it is more and more becoming the convic-
tion of thoughtful students of education that our young
people must come to know and appreciate the meanings
of these great functions in human life. Most of them also
agree that this instruction, wherever it is given, in home
or in school, must be related to and imbedded in the larger
body of knowledge of which it is a part. It should not be
isolated or emphasized in such a way as to heighten sex-
consciousness or to produce shock and uneasiness. The
treatment in this book is intended to be such that the
whole organic story becomes a background by means of

which human reproduction and sex may be enveloped.
The human conditions are so interwoven with plant and
animal processes that the essential truths may be assimil-
ated incidentally to the school course in the life-sciences
and with the minimum of special instruction on the sub-
ject, which may easily become hurtful.

The writer is convinced that there is much in the life-
sciences that may be made appealing to the general reader.
There is no field of science from which come more dis-
coveries of vital interest to human life and thought. No
modern progress has brought out more that is wonderful
and important than our advances in biology. Many of
these relate to reproduction and are touched upon in this
essay.

It is a pleasure to acknowledge helpful criticisms and
suggestions from Mr. Maximilian Braam of Hughes High
School, Cincinnati; and from Dr. John G. Coulter, the
editor of the Series. Acknowledgment is also made of
the courtesy of the American Book Company in connec-
tion with use of the illustrations on pages 3, 12, 18, 26, 28,
30, 38, 39, 50, 12, 76, 102, and 103.

T. W. GAI.I.OWAY.

CONTENTS

Chapter Page
1. THE CIRCLE OF LIFE 1

2 WHAT DO WE MEAN BY REPRODUCTION.. 9

3 OFFSPRING OF THE SIMPLEST ORGAN-

ISMS 15

4 REPRODUCTION BY BUDS 20

5 REPRODUCTION BY SPORES 27

6 SCATTERING THE SPORES 33

7 SOME SPECIAL KINDS OF MULTIPLICA-

TION 38

8 RELATIONS OF PARENTS AND OFFSPRING 44

9 CONJUGATION 48

10 EGGS AND SPERMS 53

11 FERTILIZATION 59

12 DIFFERENT KINDS OF PARENTS 66

13 MOSSES AND FERNS 72

13 ALTERNATION OF GENERATIONS 7^

15 SOME EGGS THAT ARE NOT FERTILIZED.. 84

16 THE FAMILY OF THE FROGS 8S

17 THE BIRDS 93

18 MAMMALS AND MAN 97

19 THE YOUNG OF THE HIGHER PLANTS 101

20 RELATIONS OF PARENTS AND OFFSPRING. 107

21 REPRODUCTIVE INSTINCTS Ill

22 HOMES AND HOME-MAKING 116

23 GROWING UP 121

24 THE RATE OF REPRODUCTION 127

25 CROSSING BREEDS 133

26 THE END OF THE CIRCLE 133

REPRODUCTION

CHAPTER ONE.
THE CIRCLE OF LIFE.

1. Why Do We Call It a Circle? If you stop to think
of life on the earth as you have seen it year after year,
you realize that it changes very little. This is true whether
we speak of the life of mankind or of all life of every kind.
There is just about so much grass on the lawn, about so
many weeds in the fence rows, about so many insects in
the air during one year as another. There are just about
as many babies and children and young people and middle-
aged folks and old people and those who are passing away
at one time as at another. Yet we know that all of us are
growing older all the time. Life keeps up a procession in
the same direction, and yet does not get any place, or at
least seems to be continually getting round to the same
place. This sounds like a circle, but the term is rather
misleading. We know very well that it is not the middle-
aged people who themselves come back and start life over
again. It is a new generation that continually follows the
old. On account of this seeming recovery of life in the
face of universal deaths, we call the course of life a circle
or C3^cle. A given individual does not come back to the
starting place, but the race is always being renewed by
new, young individuals.

2. What Events Compose the Circle? If then we
overlook the fact that there is no real circle, let us see
what are the principal points in this seeming round of life.
You knov/ that all plants and animals come into life very

1

2 REPRODUCTION

small and helpless. They go through a time of rapid
growth, which in humans we call childhood and youth.
After a time they become mature. Then, for a while, in
middle-life, they just about hold their own. Gradually
they show signs of old age, and decline, and later die.
This is true of practically all individuals of every kind of
plant and animal. Some of them have very short periods,
lasting a few days or weeks. Many plants go through all
these stages in a year. Still others require centuries or
even thousands of years to pass from the beginning to
the end of life.

3. The Beginnings of Life. No one knows anything of
the actual beginnings of life on the earth, but we all have
seen the 3^oung bean seedling coming out of the seed, the
young tadpole just out of the egg, the young chicken just
hatched, or the young calf or puppy recently born. This
is not really the beginning of life for any one of these,
because if they had not been living before sprouting or
hatching or being born, these things would never have
happened to them. For our present purposes, however,
this may be taken as the beginning of the individual. In
some way there is in this young plant or animal all the
possibilities of the adult. If the conditions are right it
will go on day by day adjusting itself to these conditions
and will come to be pretty much what its parents were.

4. Growth. Growth is increase in size. There may be
other changes in connection with growth, but growth is
just this and nothing more. Living things grow by taking
up water and stretching the old parts, or by taking up
foods of various kinds and building up some new parts.
Growth seems a rather simple thing. It is, however, very
complex, and it is quite different in different living things.

In most higher plants the growth occurs only at certain
definite points. The growth is local. The growing points,
where the cells use the water and foods and thus grow
and form new cells, are usually at the tips of the twigs

THE CIRCLE OF LIFE

and roots and in a thin shell about the plant, beneath the
bark. The inner, older parts of the plant become hard and
rigid, and lose their power of growing. (See Figure 1.)

It is somewhat
different in most
animals. They
grow as the little
pig which "died in
clover," that is to
say they grow "all
over." In them all
the cells, with
some exceptions,
divide and grow.
There are no spe-
c i a 1 regions of
growth.

With all the dif-
ferences in growth,
however, all growth
is alike in that it is
^ -^ due to the fact that

Figure 1. Lengthwise section through a growing some of the cells
root tip of a plant. From Coulter's Plant Life and take in water and

Plant Uses. foods, and expand.

These cells may divide many times and continue to expand
after each division.

5. Immaturity. The period of growth comes early in
life in those organisms that grow all over. Presently it
ceases. In those whose growth is local, it continues
throughout life, but it is always in the youngest parts.
Growth is thus always a sign of immaturity. During
growth the upbuilding processes are more powerful and
rapid than the destructive. The length of the growth
period in plants and animals differs as much as the length
of life itself. These periods correspond in length. If the

4 REPRODUCTION

whole life period of an animal is long, its immaturity is
likely to be long; if the youth is short, the life is likely to
be short.

Organisms frequently pass through striking changes in
appearance during this period of immaturity. The word
larva suggests some of these. The immature (larval)
butterfly is not like a butterfly, but is a worm-like
caterpillar; the immature frog does not look like the adult,
but has a tail and gills, as a fish has. The leaves of the
seedling plant are very different from those of the old
plant. This period is very important in many other
organisms beside man. It is the formative period. The
expression "as the twig is bent the tree inclines," expresses
a general law of life. The growth period is the great time
of adjustment. It is the period in which the individual
gets a chance to make its adjustments to the important
conditions of its life. Later, when the individual is full
grown, changes or adjustments are made with difficulty,
if at all. But in its youth and growth the individual is
plastic; that is, it can be modified without injury better to
fit its environment.

So, in human beings, youth is the time for education, the
time of the formation of habits and of character. What
you may learn without difficulty now may be much more
difficult when you are older. Youth, then, is the great
period of opportunity, as well as the period of growth.
Fortunate indeed is the boy or girl who fully realizes this,
and makes the most of youth's rich opportunities before
it is too late.

6. Maturity. At maturity a plant or animal comes to its
full powers, size, and nature. At this stage the increase
is no longer greater than the outgo. They just about
balance. The length of time that this is true also varies
greatly in different kinds of organisms. Some begin to
decline in a few days or weeks after becoming mature.
This is true of a great many insects. In others there may

THE CIRCLE OF LIFE 5

be a mature period of a great many years, as in the various
trees or in the larger animals. In man full maturity lasts
about fifteen or twenty years; that is, from thirty years of
age to forty-five or fifty. These figures are somewhat
misleading, inasmuch as some of our qualities may not
reach maturity by thirty, and others begin to wane before
we reach thirty.

7. Decline and Old Age. We may think that old age
is just a matter of time. A little thought, however, will
convince you that this is a very small part of the story.
A grasshopper or a mouse "grow old" while a child or
a colt of the same age is still young. It is not primarily
time but something within which makes old age, and the
decline in power that comes with it. In some way the
aging plant or animal cannot continue to adjust itself to
the conditions about it. This adjustability to conditions
we find to be the real essence of life. For a while
the individual meets fully and profits by the surrounding
conditions. It receives stimuli, responds to them, and
becomes better because it does this. It learns, so to speak,
how, through its experiences, to adjust itself the better.
Thus it grows, matures, thrives. After a time, perhaps it
loses some of its plasticity or softness, its tissues harden,
its habits harden, and it no longer meets all its changing
needs so well.

Then, too, it may be that all organisms, and all the cells
in the organisms, make poisons in the very act of living,
which make it harder to live. For example, if a number
of people are shut up in a room, we know that they give
off poisons which check and presently stop life. The same
is true of many germs that multiply in our bodies and
elsewhere. They quite frequently produce substances that
make it harder for themselves to live. If this is true of the
cells in our bodies, we can see how by a slow wearing out or
a slow poisoning each might do its work less and less well,
and thus a decline of the whole organism would follow.

6 REPRODUCTION

Whether this particular explanation is true or not, it is
certain that the loss of power, the decline in the work of
some of the cells of the body, is responsible for what we
call "old age" in the body as a whole.

It is not to be imagined that the external conditions
are without influence in this. Aging comes faster under
some conditions than under others. All the conditions
that help to make life possible have some influence on the
rate of maturing and the rate of decline. We find, for
example, that human beings tend to mature more rapidly
in warm countries. You can "force" plants by increasing
the heat and moisture. In general, the conditions that
hasten maturity also hasten old age. In human beings
many internal conditions and habits also hasten these
things. Worry, dissipation, overwork, lack of worth-while
work, extreme habits of all sorts seem to increase the rate
of living and hasten the moment of decline. It is a paying
thing to respect these ways of nature. She does not
always hurry, but we can never cheat her in the end.

9. Death. As the decline passes on, and the income
becomes less and less able to meet the outgo, the organism
loses more and more its power to adjust itself to the
outside conditions and to meet its own needs thereby.
Death is merely the entire loss of this power to adapt the
inbernal conditions to the external. Dying really begins
when the decline begins. Death is merely like the final
snap of a bar that has been gradually bending toward its
breaking point. When the materials, of which the body
of a plant or animal is made, have lost their power of
adjustment the plant or animal is dead. The very
conditions that stimulated and supported its life before
now cause the decay of the complex materials.

10. The Cycle. If a body is born, grows into and through
youth, matures, grows old and dies, it does not end where
it began; except that the matter of which it was made
came from the outside world and at death goes back to it.

THE CIRCLE OF LIFE 7

How then can we say we have a cycle? Merely because
somewhere along this course, from the early beginnings
to death, the individual has the power to produce other
young individuals. These are as simple and new as it was
at its own beginning. Thus a new start is had, and the
cycle is complete. The dying organism does not become
young itself; but some time before death it produces
others that are young. This is an interesting thing which
we are too much disposed to take for granted; the
offspring of parents however old are not of the age of the
parents, but are young. Why should the product of a
parent forty years old be any less than forty years old?
Here is the fountain of perpetual youth. It is the only one
we are likely to discover; but it is enough. It makes the
eternal circle of new individuals, v/hich supplies the
materials by which the evolution of the race goes on.

IL Application to Ourselves. This chapter teaches that
a fundamental law of life is adjustment to surroundings.
This sounds rather simple, but it is not as simple as it
sounds, especially when applied to human beings. For
the things which make up our "surroundings," or
environment are many and complex, and the question of
right adjustment to them is often a question that puzzles
the wisest of men.

The factors which make up environment we may roughly
classify as natural and artificial, meaning by natural those
fundamental facts as to air, water, food, light, weather,
etc., to which all men in all times have had to adjust
themselves effectively in order to live. By artificial
factors, on the other hand, we mean those facts of life
which have resulted from the activities of man himself;
the things which go to make up what we call civilization.
These are factors which change from generation to
generation, so that what may have been the right adjust-
ment for our grandparents may not be the right adjust-
ment for us. Chief among these artificial factors are what

8 REPRODUCTION

we call the "social and economic conditions," and it is in
connection with these that the great puzzles of life arise.
Often we see conditions in the relations of men to one
another which cause injustice and suffering, and we may,
by studying such situations, find that we ourselves by our
manner of living are partly responsible for such conditions.
Then evidently the thing for us to do is not merely to
"adjust ourselves to environment" as environment
happens to be, but to seek wisely to alter such features
of the man-made environment as cause unjust hardships
to others. So we must not take "adjustment to environ-
ment" as one simple and sufficient rule of human life,
however well it may do for plants and animals. We
alone of living things have the powers of reason that have
created artificial conditions, and we must constantly use
these powers so as to alter these conditions that the best
results for all may prevail. Thus we see that the best
adjustment to environment on our part may often be an
effort to change the environment in some respects, at
least in its human or artificial parts.

CHAPTER TWO.
WHAT DO WE MEAN BY REPRODUCTION?

1. The Individual; Its Upbuilding and Fate. In Chapter
One you saw the course of life in the individual. This course
includes a small start, an increase, a period of maturity,
a decline, and in the end death. This is so universal that
we come to take it for granted; and we forget to inquire
why it is so. We want now to see a little more closely
how the individual behaves in this circle.

In most cases the start is more modest than was
pictured above. Most individuals really start life as a
single cell, which is usually scarcely large enough to be
seen with the naked eye. This is true even of some of
the very largest plants and animals. We think of the oak
as starting in an acorn; but really the acorn is not the
beginning. The acorn already contains a young oak.
The beginning of the new individual was a single cell
back in the tissues of the parent tree. From the fate of
this cell it is clear that the power of growth and
development must be something marvelous. How cr.n a
man or a whale or an oak, with billions of cells and
weighing many pounds, come from such small beginnings?

At the bottom of the whole question is the power of
the living individual to take up water and other substances,
which we call by the general name foods. This power
you are quite familiar with, even if you do not understand
it. The organism so changes foods and combines them as
to make new living matter like that of the living object

10 REPRODUCTION

doing it. Jimmie Jones can take beef and pork, potatoes
and pop corn, molasses, butter, and milk, and they soon
cease to be these particular things, being changed into
Jimmie Jones-stuff, Strangely enough beans will become
Jimmie just as much as pork will. He puts his stamp on
both, and it isn't quite like the stuff in any other living
thing. Indeed, if we were cannibals, as frogs are, and
were to eat the flesh of Jimmie Jones, we would have to
change it just as much as he does pork and beans before
it would be like our own bodies. We could do this. All
living things have this power. We call it assimilation.

2. The Selfishness of This Process. It is quite clear
that this ability to get and use and change other things
into one's own substance is a very selfish power. It looks
purely to upbuilding the individual. It seeks income
rather than outgo. The appetites and longings, which
we know as hunger and thirst, exist in order that the
individual may be driven to do the work necessary to
grow and build up the self. This is the reason that a boy
is always hungry. The instincts for taking food are the
first and most basal that animals have, because the
building up of the self is the very first work they must do.
If they do not do this they will never be able to do
anything else. We may say that individual selfishness
then is the first step in life. While this is true, we have
seen that the individual, in spite of this self-care, finally
declines and dies.

3. The Outcome of Income. The natural result of
assimilation therefore is growth, and then more growth.
But naturally organisms cannot very well go on forever
growing. There must be some sort of an outgo if any
kind of balance is to be kept, such as you actually see in
organisms. If Jimmie Jones eats all the time and never
gives up anything, Jimmie would, become unwieldly; but
this is not all. We know from observation that this
continued self-building would defeat its own ends. Jimmie

MEANING OF REPRODUCTION 11

needs exercise, we say, in order to keep well; but
exercise is outgo. It destroys some of that which has been
built up. You will find, however, that this alternate
building up and tearing down results in a better self than
the pure self-building. Too much income, without
activity, begets softness and stagnant life. Yet in youth
the building up must be more rapid than the tearing down.
This makes growth.

There is still another way in which this excess which is
stored up in youth may be used. Most plants and animals
as they approach maturity cease to use the whole of their
income for their further growth. Instead, they give off
portions of themselves, which finally become entirely
separate and form other individuals of the same kind.
This is called reproduction. It is a kind of growth; but it
is growth beyond the limits of the individual. It starts a
new individual at the expense of the old. Some of the food
which might have gone into the parent goes to build up
the new individual. We have found two ways then
whereby the individual gets rid of some of its income.
These therefore must check its over-growth. They are
activity and reproduction.

4. What Makes an Organism Reproduce? An organism
through its whole life has been selfishly laying up in its
body the greatest possible amount of material. What
could possibly cause it to change its behavior to the very
unselfish act of giving a portion of its income, and often a
very considerable part of its own body even, to a new
individual, whose future will be wholly distinct from it?
We have not found a full answer to this question; and yet
there are some interesting clues that help us to see how it
might have been caused.

In the simplest kind of organism, a single globular
cell, all of the nourishment must be absorbed through the
outer wall or surface of the sphere. On the other hand,
the amount of nourishment necessary for it is determined

12

REPRODUCTION

Figure 2. Pleurococcus, a common one-
celled plant, as seen under the microscope
— Coulter s Plant Life and Plant Uses.

by the volume of the
same sphere, for the
whole volume must be
fed. Now as this sphere
is nourished and grows,
both the surface and
the volume increase,
but not at the same
rate. The surface in-
creases as the square of
the radius; but the vol-
ume increases as the
cube of the radius. For
example, if by growing
the radius were trebled,
the food-taking sur-
face would increase only nine times; whereas the mass
that is to be fed would be increased twenty-seven timtes.
This shows that the living thing must keep up a right
adjustment between the internal need and the external
supply.

It is important that the student should not fall into an
error here. When we ask why an organism does thus
and so, we may think of either of two things. We are
likely to think of the gain or advantage that will come as
the result of doing it and assign this as a reason. Now
an advantage lies ahead, always; and events to come can't
act as causes, unless the organism is intelligent and can
be thought of as looking ahead. We can see in the case
above that division would be advantageous. It would
increase the surface without changing the volume, and
allow more nutrition and more growth. When we ask
why, we really mean the cause of the thing. The
advantage cannot be the cause. The cause must come
before the event.

Come back to our example. Not all organisms are as
simple as the illustration. Yet it is true of all organisms

MEANING OF REFRODUCTION _ 13

that the food must be absorbed through surfaces, and it is
a volume that is to be nourished. We may say that
organisms must stop growing near the point where
absorption and nutrition are balanced. It may be, when
this condition of balance begins to be felt by a growing
organism, that this very condition stimulates it to
reproduce. This stimulus would be a real cause. In this
way the growing power which is lost in the parent is
renewed in the offspring, v/hich thus takes onward the
torch of life.

5. What is the Meaning of This? Putting together
these two processes, upbuilding and reproduction, we
have an organism first building itself up in a selfish way
through taking in of food and through growth; then,
because of this very growth, unselfishly giving a portion
of itself to start a new individual life. The student must
understand that it is not intended, by the use of the words
selfish and unselfish, that the organisms are conscious of
these tendencies or that they have any moral meaning.
They relate merely to the fact that one tendency and
process builds up the self; the other builds up another
individual and does it at the expense of the self.
Nutrition tends to make the individual continue; but
the individual does not live always by this selfish act.
We have seen that it aKvays dies. Reproduction is at the
expense of this individual, and frequently results in the
immediate destruction of the individual; but it starts a
new life and thus perpetuates the species. It is interesting
that the selfish act has a transient result, while the
unselfish act means permanence and continuance of life.

One of the great truths of life then is this: The best
method thus far found in nature to perpetuate life is an
alternation of self-building and self-sacrifice, of assimila-
tion and reproduction, of emphasis on the individual and
emphasis on the species. This alternation is found in
practically all organisms. It must be a good thing!

14 REPRODUCTION

6. What is Reproduction? The methods whereby
animals and plants reproduce are as widely variable as
are any other of the facts of life. The remainder of this
little book is given to describing some of these methods.
We want here to find what, if any thing, is found in all
the different kinds of reproduction in the plant and
animal kingdoms. We want, in a way, to reduce it to its
very lowest terms. Sometimes it is exceedingly simple.
Again, it is so covered up and complex that one can
scarcely determine the steps. However, reproduction,
whether simple or complex, is always this: the division
of an organism into two or more. This is the fundamental
thing. This is always present in reproduction. This is
reproduction. The other facts that we shall find
associated with this one are not reproduction. Division
of one organism into two or more is the self-sacrificing
act that insures that living things shall not disappear
from the earth. The product of these divisions we call
offspring.

7. Reproduction and the Life-Cycle. The reader will see
at once that it is reproduction which makes the cycle.
Birth, growth, maturity, decline, and death do not join ends
into a cycle. Reproduction is the connection of the passing
individual with a new youth. It is the return part of the
curve that restores the species to its starting point in spite
of the old age and death that overtake the parent.

CHAPTER THREE.

OFFSPRING OF THE SIMPLEST ORGANISMS.

Before we can form any idea of the offspring of the
simplest organisms and of the way they come into
existence, we must become better acquainted with the
organisms themselves.

1. The Simplest Living Things; Their Structures and
Powers. In order to understand the nature of these lowest
forms of life the student must know something about what
the biologist calls a cell. The cell is a small unit of the
living stuff called protoplasm. It commonly has a wall
around it. Our bodies and those of all the higher plants
and animals are made up of millions of cells. Each unit of
living stuff in our bodies has a kind of life of its own,
somewhat as a county has its life within the state. Each
cell lives its own life, takes up its own food, grows, divides,
grows old, and may die. To be sure this is not the whole
story. Beside doing its own private work, it does some
things in relation with the other cells of the body of which
it is a part. It does special work, as secreting or absorbing
or contracting or feeling, for the other cells. It has two
lives, so to speak: its own individual life, and its part of the
life of the whole organism.

Now the simplest animals and plants are something like
one of these single, microscopic cells if it were turned
loose in nature to live an independent life. These
organisms are single cells. They are mostly very minute,
though they vary greatly in size. They must have, and

15

16 REPRODUCTION

do have, all the powers necessary to sustain individual
life, and equally to reproduce and keep the species going.
They get food, and use it both to grow and to supply
energy. They are sensitive to all the important external
conditions of life. They are able to adjust themselves to
these conditions.

2. Where They Are Found. As one might expect,
these minute one-celled plants and animals must live in
moist places. Otherwise they would dry up and lose the
internal water that is absolutely necessary to active life.
Many of them can dry up for days and months and come
again into activity when water returns, but, of course,
they are not active during this period of dryness. We
find them in all waters, both fresh and salt; in the bodies
of larger plants and animals, where they may produce
diseases; in decaying organic matter, where they assist
the decay and live upon the products of it.

They are found in all parts of the world and are among
the most interesting of all living things. They are usually
transparent under the microscope. Many of them are so
small, however, that they can scarcely be seen at all, even
by means of our microscopes of highest-powers.

The great improvement of the compound microscope
has made these simplest organisms one of the most
interesting fields of study in the whole natural realm.
You are able to watch all their activities, and even to
see them passing through the various stages of their life
cycle. Sometimes this cycle is completed in a few hours.

3. Their Importance in Nature. Aside from the mere
fact that they are interesting to look at and to study,
these lowly plants and animals are extremely important
to man, and to the other plants and animals that live on
the earth. Some of the plants, minute as they are, are
green like the leaves of trees. A good example of this is
the plant Pleurococcus which you may see as a green
stain on the north side of fences and trees. Each plant

OFFSPRING OF SIMPLE ORGANISMS 17

is a single cell, but their great numbers make up for their
smallness. The green substance in them enables each
individual cell to manufacture organic food out of the
inorganic materials that come to it.

Other plants, as the bacteria, are not green and have
not the pow^er of making starches and sugars, but they
have other powers equally important. They must get
their food chiefly by attacking other plants and animals,
either after they are dead or v^hile they are still alive.
Those organisms which live at the expense of other living
things we call parasites.

Finally, we have a great many animals that are one-
celled in their structure. These are like the bacteria in not
being able to make their own food. They depend on other
organisms living or dead. They are, however, usually
much larger than the bacteria and have more striking
activities, and rather better development. That is to say,
they are more complex.

These lowly things may be very valuable or very
hurtful to man and his interests. The simpler green plants
may make and store foods, which in turn may be
devoured to support more complex organisms. The bacteria
and one-celled animals attack dead matter, and by
hastening decomposition serve as scavengers. In this
way they destroy dead matter and return the elements
that compose it back to the earth and air where they may
again enter other plants and animals. But for their
action, the bodies of the great mass of animals and plants
that die every year would remain to vex us for a long
time. Within the moist soil itself they are at work
tearing dov/n substances, and thus they prepare the
way for other life. Bacteria also help to ripen butter and
cheese, to make vinegar, to prepare sponges, skins
(leather), flax, and some other fabric plants for their
commercial uses.

The bacteria also do a good deal of damage to man
when they attack foods and other materials that he does

18

REPRODUCTION

not want to have decay or sour, as milk, fruits, meats, etc.

The greatest harm done to man by these simple plants
and animals, however, is in the diseases they produce in
the human body or in the animals and plants that we
depend on. The most of our contagious and infectious
diseases, as tuberculosis, typhoid fever, yellow fever,
sleeping sickness, and scores of others are caused by
these one-celled organisms and the poisons they produce.
Similarly, diseases among hogs, cattle, horses, and
poultry; among garden vegetables, orchard fruits, and
flowers are caused by them.

They do all this
damage in spite of
the minuteness and
small powers of a
single organism,
simply because they
can reproduce so
rapidly and effect-
ively.

4. The Method of
Their Reproduction.
This is often just as
simple as can be.
When a bacterium
grows up to its full
size by taking food,
it may be a simple globe, or rod, or spiral, depending on
the kind. When this has taken place, the cell may at once
divide, by a partition through the middle, into two cells,
each having one-half the material and one-half the size of
the original cell. Each of these daughter cells then grows
up to the adult size, and repeats the process. In some
bacteria this growth and division may take place in less
than an hour. This rapid reproduction is possible because
the plant and the process are both so simple. Because of
the rapid growth and reproduction it comes about that in

Figure 3. Various types of bacteria, much en-
larged. From Coulter s Plant Life attd Plant Uses.

OFFSPRING OF SIMPLE ORGANISMS 19

forty-eight hours the descendants of one bacterium, at
this rate of one division in an hour, would be two raised
to the forty-seventh power.

Most of the one-celled animals and plants have this
method of reproducing by simple division into two,
though few of them multiply so rapidly as the bacteria.

Some of them vary this method sometimes by dividing
the protoplasm of the original cell into several offspring
instead of two. In this case each of the offspring gets a
correspondingly smaller share of the original body.

5. What of the Parent? This method of reproduction
raises an interesting question. The original organism
divides into two equal offspring. There is no visible
difference between these. There is nothing that would
justify us in calling one of them the parent any more
than the other. The substance of the parent has gone
into them equally. We cannot say that the parent has
died in the ordinary sense. There is no corpse; and yet
there is no parent. The parent is destroyed completely,
as parent, in the act of dividing. The old individual, after
being built up, is completely sacrificed in producing two
new individuals. They in their turn do the same thing.

Note. There are some other kinds of reproduction
found in the one-celled plants and animals. Some of
these will be mentioned in other connections, as they will
be better understood there. Simple division is found also
in some of the higher organisms; but we may fairly say
that this simplest of all the methods of reproduction is
particularly representative of the simplest organisms.

CHAPTER FOUR.
REPRODUCTION BY BUDS

1. Reviiew. In the lowly plants and animals which
were studied in the last chapter the offspring are
formed in the simplest possible way, that is, by merely
breaking up the parent into two or more equal parts of
the original organism. In this process the children do
not have to ask, "What shall we do with our parents?"
There are no parents left. Many writers have called
attention to the fact that in plants and animals of this
sort there is no death of the kind we described in an
earlier chapter. The parent sacrifices its individual
existence, to be sure; but the substance of which it is
made seems almost or quite able to renew its youth as it
divides, and thus to preserve itself from old age. Of
course these organisms may be killed by accident and
by unfavorable conditions. Untold millions of them are
destroyed by drouth, by cold, and by attacks of other
organisms, but probably not from mere old age.

This method of reproduction is called division or fission.

2. Budding of the Yeast. There is another group
of single celled plants, called yeasts, that are important in
human industries. They are used in the making of bread,
and in brewing beer, and fermenting wines; all this
because they have a wonderful power of producing
substances that change starches to sugar and break up
sugar into alcohol and gases.

These plants are a little larger than the bacteria, but

20

REPRODUCTION BY BUDS 21

are still very small and simple. The cells are more plump
than the bacteria usually are, varying from elongate to
nearly globular. When condi-
tions are good for their life, and
one of these cells becomes
nearly the mature size, the
growing matter within pushes
out a little pouch in the wall
and some of it flows into this
rounded pocket. This is called
a bud, and it continues to grow,
remaining attached to the old
cell. Intimate internal commun-
ication is kept up between the Figure 4. Cells of yeast in
cells, somewhat like that be- various stages of budding
tween a small room and a larger room in the same house.
The bud is plainly the beginning of a young cell like the
first. As the bud grows larger the connection between it
and the mother cell becomes less. In the meantime the
first cell may start another bud from another point, or the
new cell may itself start a bud. In this way we may get
a considerable group of connected cells, some older and
some younger. Sooner or later, however, the daughter
cells, as they become older, fall apart from the mother
cell and thus become independent. How long they
remain together and how complex the chains become is
determined by the species of yeast and by the food, and
the conditions of moisture and temperature in which
they are growing.

At other times the yeast cell may divide up the
protoplasm on the inside into four small cells, surrounded
by the old mother wall. After rest, these finally break
loose from the mother cell and live an independent life.
Then they grow up to the mature size and begin to
reproduce by budding again. This last is not budding.
It is more like fission. We shall refer to it again later.

3. The Essential Nature of Budding. It will be seen

22 REPRODUCTION

from the above that budding is a form of division or
reproduction, in which an actual portion of the mother
organism forms the beginning. This portion that goes
into the young at the start is small, much less than the
one-half that goes to the young in division. Much of the
nutrition the mother cell takes up after the bud is formed
passes on into the young, because of the close connection
betw^een the bud and the mother cell. The yeast does
not do so much for its bud at the start as is done in
fission; but it keeps up its help longer.

This is the simplest form of budding we find. It is,
however, a very good picture of the essential nature of it
even in the more complex plants and animals in which
we find it. Always in buds some of the very structure of
the parent organism grows directly into a small, young
offshoot or offspring; and a close, nourishing connection
remains by which the young grows at the expense of the
parent, as a kind of temporary parasite on the parent.
Sometimes they separate after a while and live
independent lives. In other cases the young remain
attached permanently to the old organism until the young
themselves are mature and produce other buds. When
the whole series of generations remain together
permanently like this we call it a colony.

4. A More Complex Bud: Hydra. This little fresh-
water polyp is found widely in the ponds and lakes of
North America and is used very commonly in the
laboratory work in zoology. We have in it an animal of
many cells as simple as the student is likely to find. It is
practically a tube open at one end and closed at the other,
the wall of which is two cells thick. Near the open end,
the wall is pushed out in a number of hollow tentacles,
whose cavities are continuous with the cavity of the
animal. When the animal has come about to its mature
size and is getting an abundance of food, and the other
conditions are right, portions of the body wall may
pouch outward with the general cavity of the body

'i/aei/.

Fisure 5. A common form of hydra, much enlarged. The lowermost tentacle
has seized the larva of an insect. The lower figure shows the appearance of a
young hydra cut through from top to bottom and viewed through a microscope, ihe
mature hydra is usually no more than a quarter-inch in length.

24 REPRODUCTION

extending into the pouch. This pouch grows and becomes
elongated, taking the usual shape of the body of hydra.
After a while it produces tentacles at the outer end, a
mouth breaks through, and we soon have a young hydra
attached to the mother. It has been formed purely by
the budding out of the mother. Food may pass into the
mouth either of the mother or the bud and finally get to
any part of the inner cavity. The bud grows both by
the food the mother captures and by that which it
captures for itself. It ultimately becomes free and closes
up the tube at the point where it was connected with
the mother, and depends for a livelihood on its own
exertions. One parent may have several buds of different
sizes attached to it at once. It may continue to produce
buds throughout the season. This condition is not very
different from the yeast, except that this is a many celled
animal; whereas the yeast is a single cell, and a plant.

In many animals of the group to which the hydra
belongs, as in the hydroids and the corals of various
kinds, the buds do not separate from the parent stock.
By clinging together and by having each its own rate of
growth and division, they form most regular, interesting,
and varied colonies, which make them look like branching
plants. This has given them the name of zoophytes, or
plant-animals.

5. Buds in Higher Plants. It is in the common plants
that the student is most familiar v/ith buds. On almost
every plant you have seen buds at the ends of stems, and
arising from the sides of stems in the angles of the
leaves. These side buds are very much like the buds we
have been describing in hydroids, that remain attached to
the parent and form complex colonies. In these plant
buds there are tissues which are continuous with similar
tissues of the parent stem and derived from them. These
buds, when they grow, develop more structures, as stems,
leaves, flowers, and the like, just like those that are to

REPRODUCTION BY BUDS

25

Fis:ure6. Lengthwise sec-
tion through a bud of one of
the higher plants.

be found on the main stem. Fur-
thermore, in a great many plants,
if one of these twigs be cut off and
be given the proper conditions for
life, such a bud or twig is able
to form roots and to develop
a separate plant just as the young
hydra bud does naturally. Such
buds then as we see every day in
plants may be thought of as a kind
of multiplication or reproduction
of the essential plant structures.
The student can see that this is
much more than mere growth as
our arms or fingers grow. It is
more than the lengthening of a
stem after it starts. It is rather
as if we could bud out a new arm
or leg at a new place, which under proper circumstances
would develop all the structures which the body has.

In some of these plants these buds after they are
formed may separate from the tree naturally, fall to the
ground, and finally grow, take root, and form a new
plant. Such are the gemmae of liverworts, the bulblets
of ferns, or lilies, and the "sets" of onions.

6. Practical Use of Budding. In horticulture and
orcharding we use this quality of the bud to propagate a
species. Suppose in some way we find a peculiarly good
individual trees of pecans, oranges, apples, peaches, or
any one of a great many others. Instead of planting its
seeds, we take cuttings consisting of one or more buds
from this tree and graft these into healthy scrub stock.
The stock is a stem with plenty of roots. If the grafting
is properly done, connection will be made with the stock
in such a way that its roots will supply the nourishment
to the choice cutting. This cutting will keep its quality
and not take that of the stock. Ordinarily in grafting

26

REPRODUCTION

much of the scrub stem is
cut away and the graft is
made near the roots. We
may, however, graft a bud
on any new healthy part
of similar kind. Indeed
one can graft the buds of
many varieties of apple
or peach on one stalk, and
get as many different
kinds of fruits from one
tree. Budding and graft-
ing are highly prized
methods of artificial re-
production, and they de-
pend upon this natural process of bud formation in the
plant, which is itself a kind of reproduction.

Figure 7. Diagram of the process of
budding in the cultivation of peaches.
From Coulte7's Plant Life and Plant
Uses.

CHAPTER FIVE.
REPRODUCTION BY SPORES

1. Another Kind of Division. In budding in yeast you
studied a form of division in which the protoplasm of the
mother cell pushed the old wall before it. This wall and
material became a part of the structure of the new
daughters. There is still another way in which the
protoplasm of the mother cell makes daughters. In this
everything takes place inside the old mother wall. It
does not pouch out as in the yeast nor divide into two as
in the bacteria. The method is called internal cell-division.
In such a case we have an ordinary cell, or it may become
very much enlarged. At the outset it may have just one
nucleus and the usual structures found in a cell. As the
cell matures and grows, the nucleus divides into two,
these into four, and so on until there are many small
nuclei lying in this single mass of protoplasm surrounded
by a single cell wall.

Up to this point there may be no trace of any walls in
the interior. The nuclei become scattered through the
protoplasm. The protoplasm nearest each nucleus rounds
off about it. A little later each little ball of protoplasm,
containing one of the daughter nuclei, forms a very
delicate membrane about itself. We have now many
complete though small cells, with walls of their own,
inside the old parent cell wall. These small cells are
spores. As they ripen, the wall of the spore becomes
firmer, the old mother wall breaks down, and the spores
are thus set free.

27

28

REPRODUCTION

Na-

the

A

Figures. Uloihrix, one of the filamentous algae.
The figure at the right shows the production of both
spores and gametes by the same individual. From
Coulter's Plant Life and Plant Uses.

Spores such
as are de-
scribed above
are found in
many of the
algae and
fungi.

2. The
ture of
Spore.

spore differs
from the small
dded daugh-
ter cells of the
yeast, for ex-
ample, in this:
the spore is
merely a re-
productive cell.
It does not
look like the

plant from v^hich it came. Furthermore it takes no
part in getting its own nutrition, as the yeast bud
does. It is nourished by the parent until it is ripe.
The yeast bud looks like its parent plant from the
beginning, only smaller. Whether spores are formed
internally, as described above, or externally, somewhat as
yeast buds are formed, they are always just single cells
with the power to develop into a plant like the mother.
They are not small editions of the plant itself.

3. What of the Original Cell? In the forming of spores
the old parental wall is left behind, and sometimes there
may be fragments of the old protoplasm that did not
enter into any of the spores. These things represent what
is left of the parent cell. There is not enough vitality in
these remnants to enable the mother cell to continue its

REPRODUCTION BY SPORES 29

life and to reproduce again. It is destroyed just about as
effectively as in fission, in which all the mother substance
goes to the daughters. .

The advance that is found in this method over simple
fission is not in preserving the parent cell and reducing
the degree of sacrifice, as was true of budding; but rather
it enables one cell in its destruction to produce many
young instead of two. This means a much more rapid
increase of the species, if only the spores are well enough
endowed to carry on the work.

In addition to the advance mentioned above, it often
happens that there are other cells of the parent plant left
that did not take direct part in making the spores. Such
parts may later give rise to more spore-producmg cells,
and thus the organism may reproduce many times.

4 Many Kinds of Spores. Time would fail us if we
should undertake to describe all the different kinds of
spores we find among plants. We say "among plants
because -animals rarely reproduce by spores. There are
a very few lowly animals that produce spores, and they are
so lowly that we scarcely know whether to call them
plants or animals. On the other hand, practically all
plants form spores.

While most spores are formed as described above,
inside the old mother cell wall, this is by no means always
true In some cases spores may be merely cells formed
by pinching off pieces, so to speak, at the ends of thread-
like branches. In these cases they might be thought of
as a kind of bud. This is the case in the spores of toad-
stools and their close relatives.

The spores of plants are varied in such a way that
they meet the needs of the plants in remarkable fashion.
They may be formed deep inside certain organs and so
need special devices to let them out, such as the active
bursting of a capsule; or they may be formed in the air
at the very tips of delicate branches, so that the least

30

REPRODUCTION

disturbance breaks them off and sets them free. The
spores of the various molds and fungi that live in the air
and on solids are without any power of self motion. On
the other hand, most of the spores of the lower algae,
which live in water, have cilia and can make very definite
and interesting motions through the water.

Figure 9. The formation of spores by wheat-rust. This
parasite is growing inside a leaf of its host, and is discharg-
ing its spores from the under surface of the leaf. Ftvm
Coulter's Plant Life and Plant Uses.

In some plants only one spore may be formed at a
place; in others they may run into the thousands. Spores
even in the same plant may differ much in size, depending
on the way they are formed and the period of
development to which they belong.

5. Kinds of Plants That Bear Spores. For a long time
the plant kingdom was divided into those plants that
reproduce by means of spores, and those that reproduce

REPRODUCTION BY SPORES 31

by means of seeds. Among the so-called spore-bearing
plants we included the algae, the fungi, the liverworts,
the mosses, the ferns and their kindred. We now know
that the higher plants, that is, those with flowers, also
bear spores, and that the flower itself is a spore-producmg
organ, as well as a seed-producing organ. This will be
discussed at more length later.

6. How Spores Behave. They are reproductive bodies
looking wholly to the next generation. As compared with
other cells in the mother plant the spores are usually
highly resistant. Often they float around in the dry air
without hurt. Many of them will stand cold much below
the freezing point of water. In many of the parent plants
these conditions would mean death. On the other hand,
the swimming spores are usually remarkably delicate and
easily destroyed.

While the spore usually does not have the power of
growing in the ordinary way, nor of dividing into two
spores as the bacteria divide, it has a definite manner of
returning to life and activity. Usually the cell wall around
it is a little tough. When conditions are favorable, as for
example, after one of these spores has been floating
around in the atmosphere and comes into a moist place
where its food is abundant, it takes up water and begins
to swell. It then sends out through the softened or
broken wall a delicate tube of its protoplasm, surrounded
by a thin membrane. This tube is the beginning of a
new plant. This process by which the spore starts the
new plant is called germination.

Germination differs very much as to time. In some
kinds of spores germination may begin within a few hours
after the spore escapes. This is true of the ordinary
spores of the bread molds. One may readily see these
spores germinate, and begin to form the fine threads of
the mold, by placing on an ordinary glass slide a decoction
of bread or fruit juice and dusting it with spores. If this
is placed in a moist chamber and watched at frequent

32 REPRODUCTION

intervals during twenty-four or forty-eight hours, the
observer will see stages of germination. If conditions
are not favorable, the spore may withhold germination
for considerable time without hurt. Some other spores
will not germinate even under the most favorable
conditions until after a period of rest.

Among the fresh water algae, many of which flourish
in ponds that are liable to be dried up in late summer and
frozen up in the winter, resting spores often enable the
species to survive these conditions. Drouth would kill
the parent plants or the more delicate kinds of spores.
Freezing would be likely to do the same. The resting
spores, often with thick walls, are unhurt. Furthermore,
even though the moisture and temperature are right, the
food required by the organism may not be present. In
such a case germination would be disastrous, because the
young germinating plant is very tender.

We see then that spores reproduce the plant, but they
do more than this. Because of their variety in form and
in behavior they serve to help adjust the species to some
of the unfavorable features in its surroundings and to
help it take advantage of the favorable ones.

CHAPTER SIX.

SCATTERING THE SPORES

1. The Probkm of Scattering Offspring. Human
parents have a way of wanting to keep their children at
home and to have them settle near by. But if there are
ten children in the family and there are only two hundred
acres of land, it is clear that each child must be content
with twenty acres or must crowd out some neighbor.
Now the problem of these plants that produce so many
spores is even more difficult. If all the spores produced
by one fungus of almost any kind were to fall right
down and germinate on the spot, the crowding would be
such that none could thrive. Furthermore, the food at
one spot suitable for a given species is always limited.
By the time the spores appear the parent plant may have
itself exhausted the food. Evidently the species will have
a much better chance to keep going if these spores are
scattered far and wide. It is sure that most of them will
fall at points where they can never succeed, but out of
the many there is a chance that some will find favorable
places. Wide scattering gives an opportunity to try out
the surroundmgs. Since a single spore cannot try first
one locality and then another, as an animal can, this
scattering of the offspring is the next best way of getting
the members of a species into favorable places.

2. Another Problem. There is another side to this
question of scattering. If, for example, there is an injured
fish in the water of a pond, and a few spores of the fish

33

34 REPRODUCTION

mold should light upon it and germinate and get a footing,
we have two distinct problems. One of them, the
scattering of the young of the species far and wide, was
mentioned in the preceding section. The other grows
out of the fact that this fish, before it has completely
decayed, can- support many plants of the fish mold.
Therefore it is a clear gain to the species if this mold
has a way whereby it can quickly take possession of the
fish. The same problem we find in the molds on a culture
made of a slice of bread in the laboratory. Both of these
classes of organisms have devices for taking full
possession of a limited area quickly, as well as devices
to extend the species to other spots. In the fish mold,
aside from the branching threads of the original parents
which spread rapidly over the fish, there are small, short-
lived swimming spores that germinate quickly and start
new plants near at hand. They are free swimming and
might move to considerable distances in the water, but
they are attracted by the chemical changes in the water
due to the decaying flesh, and so very many of them do
not get away from this attractive spot. Thus a very
luxuriant growth occurs in a very brief time on the fish.
This fact produces the disease and death of many fish,
but it means that the mold is being successful.

3. The Effect of the Medium on the Method of Scattering.
Plants producing spores grow in air, in water, and in
solids, as soil, etc. In the last case, however, it usually
happens that the plant sends the spore-bearing branches
to the surface, so that the spores are set free either in
the air or in water. The problem of scattering the spores
must be solved differently in the air and in the water.
The water is more heavy and supports the spores better.
Furthermore, it keeps them moist, and spores prepared to
live in water need not have such thick walls. They may
indeed lead a very active life, swimming here and there
quite independently of the currents in the water. This is
true of many spores of algae and of a few fungi. If they

REPRODUCTION BY SPORES 35

are not motile and are lighter than water, they may float
at the surface and be carried long distances by the
currents.

The spores of the majority of the fungi, however, are
adapted to the air. They are set free as a dry powdery
mass. You doubtless have seen the dense powder arise
from a broken puff-ball. This is made up of the thousands
of spores which it forms. They have coats which prevent
too great loss of their moisture by evaporation, are not
actively alive while in the atmosphere, have no motion of
their own, and are a little heavier than air, so that in
still air they settle to the earth. When the air is in
motion, however, they are carried far and wide. They
may be dropped temporarily, but unless they fall in a
moist place suitable for their germination so that they
take hold on the solids, they are readily picked up again
and carried on. It is perfectly safe to say that spores
may be carried hundreds of miles in times of high winds.

4. The Special Methods of Scattering Spores. The

following classification of the methods by which spores
are scattered will enable the student to see the variety.
Some of these methods are more effective than others,
but the sum of all is to make plants very widely
distributed.

A. Spores carried by the air.

1. Without any aid from the plant itself, such as
a projection of the spores into the air by some
explosive act.

2. Spores driven to some distance from the parent
plant by the presence of some explosive change
in the plant itself.

B. Spores carried by water.

1. Spores are passively carried by currents of water.

2. In addition to the water currents, some spores
have a power of motion of their own.

30 REPRODUCTION

C. Spores carried by various special moving objects.

1. By adhering to seeds of plants that are carried
by wind, water, etc.

2. Carried by insects, birds, and in less degree by
other animals.

3. Carried by man in his commerce, agricultural
operations, and the other artificial transportation
of materials from one part of the country to
another.

5. Air-Borne Spores. Spores to be best adapted to
being scattered in this way must be freed in a dry,
powdery form. They may be carried singly or in loose
masses. That they are so carried is readily shown by
exposing culture plates to the air, and later placing these
in conditions favorably for germination. This proves
that there are plenty of such spores being carried by the
air. Often a number of species may be discovered on one
plate. Great numbers of spores are necessary to make
this an effective way to spread a species. The chances
are very much against the success of any particular spore.
They are produced in unthinkable numbers. Cobb
estimates that as many as 500,000,000 spores may be
produced from a single head of smutted oats. It is said
that the giant pufT-ball produces as high as 7,000,000,000,000
spores. Of course nobody ever counted these. A certain
small mass is counted under a microscope and the whole
mass estimated from this.

Many plants bearing spores have some elastic tissues
that cause an explosion when the spores are ripe. In this
way they puff the spores into the atmosphere. Here they
are much more sure to be picked up and carried away by
the wind, since most such plants grow within or upon
the surface of the earth or of other solids.

6. Spores Scattered by Water. Reference has already
been made to the free-swimming spores of the water
molds and algae, and to the carrying of spores by running

SCATTERING OF SPORES 37

water. Water is absolutely necessary for the first kind.
Some swimming spores are known to find their way from
plant to plant through the water in the soil itself,
especially soon after rain or heavy dew. This is true of
the fungus causing the "damping-off" of seedlings. Many
parasitic plants that attack seed plants exude their spores
in moist weather, and rains wash them down from the
leaves and bark. Thus they are carried to new parts of
the same plant, or to other plants, by first infecting the
soil about them.

7. Spores Carried by Insects, Birds, etc. A number of
fungi attack fruits, seeds, leaves, and other parts of plants.
Insects and birds may use these for foods. These animals
carry spores of these fungi from an infected to an
uninfected plant, very much as they carry pollen from
flower to flower. The spores adhere to the feet and to the
mouth parts particularly, and these are the parts most
likely to bring them in contact with fresh surfaces.
Furthermore, insects may feed directly on the fungi and
necessarily carry away spores and distribute them widely.

8. Spores Disseminated by Man. Man, in his mastery
of the earth and in his exchange of its products, is sure
to distribute spores. Soil spores are carried far and wide
by plowing and harrowing, by tools and wheels of
vehicles, and by the transportation of soils and manures.
The shipment of infected nursery stock, seeds, and fruits
is responsible for the wide distribution of the spores of
many fungi that attack plants. Similarly, the shipping of
hay, grain, vegetables, and any of the raw food products
tends to spread any spores that are on these plants.
Certain kinds of fungi have thus followed man very
closely in his movements around the earth.

CHAPTER SEVEN.
SOME SPECIAL KINDS OF MULTIPLICATION.

L General. There are some special methods whereby
organisms multiply themselves, which are rather common
but do not exactly fall under any of the heads discussed
above. In some respects they may be thought of as
forms of budding, but they are not exactly so. They
occur in so many different plants and in so many different
ways that it seems desirable to describe them separately.

Figure 10. The reproduction of the strawberry plant by runners. From
Coulter's Plant Life and Plant Uses.

2. Reproduction by Runners. (Stolons). Suppose you
have put out a good healthy strawberry plant. As soon

38

KINDS OF MULTIPLICATION

39

as it gets a good start the next summer, it will begin to
send out some branches from near the point where the
leaves and roots come together. These will run along
the ground instead of growing straight up. At a distance
of several inches from the plant, this runner will put out
small roots from its lower side, and leaves will grow from
the upper side. These soon take the form of a small
strawberry plant connected with the original one. Several
of these young plants may start up in a similar way
around the parent. For a considerable time these young
plants remain connected with the old plant by the runners,
but the runners may gradually die as the new plants get
roots and leaves enough to support full growth. In time
these daughter plants repeat the process.

An exactly similar thing takes place in one of the molds
that we often find on our cultures of bread and similar
substances. The
spores are borne on
branches that grow
up into the air,
but other branches
grow along the
surface of the
bread, and at the
end send root-like
processes down
into the bread and
s p o r e-b earing
branches up into the air
produced.

The runners just described occur at the surface of the
soil or the substance over which it is growing. In many
plants, such as some of the grasses and canes, the runner
passes along beneath the soil, and here and there sends
up a new stalk. These may branch underground and
thus produce a great number of new plants from one.

3. Stolons among Animals. The wonderful animal

Fistire 11. Reproduction of bread mold by spores
and by horizontal branches. From Coulter's Plant
Life and Pi a tit Uses.

In other words, a new plant is

40 REPRODUCTION

group of hydroids, some of whose members illustrate
budding, also contains forms which send out from the
parent special tissues that grow over and attach to the
solid support, often very tightl3^ This serves to hold the
animal fast, but this is not all. From this tissue may
grow up at various distances, depending on the species,
and probably on the nutrition and other conditions of life,
new hydroids like the parent. Several other groups of
animals somewhat less known have very similar habits.
In buds proper there is an actual outgrowing of the body
tissues into the bud; in this case the bud, if it is to be
called so, arises from the attaching tissue rather than from
the body itself.

4. The Value of Stolons. There is more meaning in
this stolon-forming habit than mere multiplication. It is
a special method whereby a plant or an animal that has
once got hold in a locality that furnishes abundant food
for its rapid growth can rapidly take possession of nearby
territory, and can spread out more rapidly than if it
depended on seeds and spores. This method acts
somewhat automatically to adjust the organism to
favorable conditions. If the place is not favorable, the
parent plant will not have energy to form runners, but will
at once produce spores or seeds which may be carried from
the spot to a more favorable one. If it is favorable, there
will be energy enough for both methods of reproduction,
and the organism will take intense possession of the
nearby territory as well as scatter spores. Spores lead to
wide spreading; runners lead to full possession of a
locality.

5. Tubers. Tubers such as we find in Irish potatoes
present a very interesting phase of reproduction. Irish
potatoes have seeds and may be propagated by these;
but in our cultivation of the potato we do not use this
method. From the old plant some stems, not roots, arise
and grow under ground instead of coming out as others

KINDS OF MULTIPLICATION 41

do. These may grow several inches long in loose soil.
At their tips collects food that has been manufactured up
in the leaves. This causes them to enlarge at the tip and
to form the tuber which we imagine belongs to us rather
than to the plant. This potato tuber, as every one knows,
has "eyes." The eye is merely a bud, and from each one
of these eyes a new potato plant may grow. In practise,
we cut the potato in pieces and plant the pieces in
trenches prepared for them in order to get new plants
next year. In nature, the mother plant dies and these
potatoes are left free in the soil, already "planted." They
are not "seed," although we do call them "seed-potatoes."
The next spring, when suitable growing weather comes,
one or more eyes in each of these will send up a new
potato plant.

There are many plants, especially early spring plants,
that store up food in one or several underground bodies,
and then die down. This allows multiplication, but in
addition it puts the plant's substance beneath the soil
where it may better endure the drouth of late summer and
the cold of v/inter. Also, a new mature plant can spring
from these underground stores of food much more
quickly than from a small seed. Thus, like the stolon, it
is a way of getting quick action. The tulip affords a
familiar example of this habit. Among wild flowers,
spring beauty, dutchman's breeches, and jack-in-the-pulpit
also have this habit.

6. Reproduction by Leaves. Leaves, with their delicate
tender structure, would not seem adapted to reproduction.
Yet there are certain fleshy leaves which fall to the
ground, and, if moisture is sufficient, they will begin to
grow roots from the under side and to send up a little
stem from the upper side. In a few plants, as some
begonias, one can get a new plant by using a leaf instead
of a twig as a cutting. A very attractive little fern is
known as the "walking fern" from a surprising habit it

42 REPRODUCTION

has. It has a simple leaf which runs on into a very-
tapering, drooping point at its free end. Where this
touches the moist ground the tip takes root and a new
fern starts. This serves the same purpose as was
described for runners.

6. Division in Many-Celled Organisms. In an earlier
chapter we saw how simple plants, such as bacteria, and
simple animals, as protozoa, divide into two. It is more
difficult to see how a complex animal with special organs,
such as mouth, digestive tract, heart, brain, kidneys, and
so forth, could possibly divide. Yet this very thing
happens quite commonly in animals of the grade of
earthworms. It is not true of the earthworm itself, but
it is true of other members of the same division of the
animal kingdom.

In worms the division is across the body. Since the
mouth, brain, eyes, and other special organs are at the
anterior end, these structures must be repeated about half-
way back for what is to be the posterior worm. The
same is true of the structures that occur at the posterior
end. The anterior worm must have a set of these made
for him. Of course these new tail structures must lie in
front of the new head structures of the rear worm. All
these organs usually develop before the two worms
separate. We sometimes see four or more such worms in
a row, not yet separated, all developed from one worm
and soon to break apart.

In some other types of organisms, as in some of the
hydroids, the division is said to be lengthwise. In this
case the mouth would be split in two, as would all other
such organs. In this way each daughter animal gets one-
half of each of the original general organs.

7. Regeneration of Lost Parts. If a boy cuts a small
piece out of his finger, we fully expect the wound to heal.
A scar may be formed, but the space is largely filled up
and the skin grows over all. This happens so regularly

KINDS OF MULTIPLICATION 43

that we do not stop to realize its meaning. It means that
lost parts can be regrown. Now we humans could not
grow a new arm or even a new finger. We do not have
much power of regenerating lost structures, but we have
enough to heal wounds.

If a lizard loses its tail, it is said that it does in some
degree grow again. In crayfishes, if antennae or other
appendages be lost, new ones may grovvr out. This
suggests that this power is seen to better advantage in
the lower than in the higher animals. It is even more
true in animals still lower. In the earthworm it has been
shown that the head, brain, mouth and all necessary
anterior organs may be cut away. If this is done some
six or eight segments back of the head, all these lost
organs will be formed again in front of the cut. Similarly,
new posterior organs will be regenerated if posterior
segments are removed.

In hydra, which is one of the very simplest of the many-
celled animals, it is said that any length of the body
.anywhere may be able to regenerate all the lost parts.

CHAPTER EIGHT.
RELATIONS OF PARENTS AND OFFSPRING

1. Parental Sacrifice. In all these kinds of reproduction
you have studied you see that to form the offspring is a
drain on the parent. A part of the parent's body goes
directly to form each of the young, or some special
growth takes place from the parent which forms the
young, and in doing so uses up food materials that might
have gone to strengthen the parent instead. This
sacrifice is the one unvarying fact in all the varying
methods of reproduction.

2. The Species and the Individual. In such plants and
animals as we have been studying, all that an individual
can do for the species is to reproduce offspring. This is
the very simplest and easiest form in which to introduce
individual sacrifice for the race. The species flourishes in
proportion as individuals first build themselves up, and
then reverse matters and exhaust themselves in putting
offspring on the way to success.

3. The Degrees of the Sacrifice. While all plants and
animals seem driven by their nature to make this sacrifice,
there seems to be a distinct tendency, as we go up the
scale, to make the sacrifice as light as possible and still
do the work. At least we find it very much lighter in
some organisms than in others. For example, we saw in
the bacteria and some other simple forms that the parent
was at once completely destroyed in forming the two
offspring. In the yeast, on the contrary, the new cells

44

PARENTS AND OFFSPRING 45

bud off from the old and the parent continues its own
life alongside the new ofTspring. Two offspring cost
much less of the body of the yeast parent than of bacteria.
In the case of spores, the sacrifice is still less. Only a
small part of the parent enters into them.

4. The Size and Number of Offspring. In the bacteria
the two offspring are each just one-half the size of the
parent. The same is true of all other forms that
reproduce by simple division, as some worms. This is an
expensive method. Only two offspring are formed "in
these cases and the parent is entirely destroyed. In the
case of the yeast, the parent produces much smaller
offspring to start with and then allows it to grow up to
standard size. This is even more true in the forms th:it
produce spores. Many of these may produce thousands
of spores which are only a minute fraction of the size of
the parent plant. The parent may be completely used up
in this process or may use a part of its energies, leaving
some of its strength for reproduction some other time.

5 How the Problem is Solved. It may help you to under-
stand what happens in different organisms if you see what
possible solutions there are. In reproducing, parents

1. May be completely destroyed:

(a) By producing two offspring, each one-half the
size of the parent, as in the bacteria and other
forms that simply divide.

(b) By producing several or many minute offspring,
as in some cases of reproduction by spores.

2. May not use up all their substance in reproduction:
(a) Producing a few young, but much smaller

than one-half the parent when first produced.
Such are the budded cells in yeast or the
young strawberry plants formed by runners.
Here the offspring is of new substance made
by the parent rather than the old substance
of the plant itself.

46 REPRODUCTION

(b) Producing a large number of minute young in

particular portions of the body. Not all the

parent is used up. This is the case in many

plants.

It should be remembered that many organisms which

are not actually destroyed outright by the formation of

their young are still so exhausted by producing and

maturing them that they die, and do not reproduce again.

All our annual herbs would fall in this class. The same

is true of some animals, as the salmon, which is often so

exhausted by reproducing that death follows.

6. The Problems Related to the Size and Number of
the Offspring. We know that in the long run an animal
or plant needs to bring only one of its offspring to
complete maturity during its own life in order to leave
the species as well represented as before. But there are
many disasters between the young and their maturity.
Therefore very many more must be produced than will
ever come to maturity. This is true of all organisms. If
all the offspring that any species can produce were to
live and mature and produce indefinitely, that species,
in a few years, would become a pest. Many must be
produced in order to insure one.

Now the advantage in having offspring like the bacteria,
one-half grown at birth, is very clear. It only takes a
little time for it to become adult, and the dangers that it
will not do so are less than if it were one-thousandth part
of the adult. On the other hand, the parent is completely
destroyed and we have only two of the half-grown
offspring instead of the one adult. The advantage of a
form that produces thousands of small offspring is that
there is more chance of one in a thousand surviving than
of one in two, and beside they can be scattered over a
wider territory and this increases their chances. On the
other hand, these small young have much further
to go in developing and the chances of disaster

PARENTS AND OFFSPRING , 47

are correspondingly increased. It is more expensive to
produce large offspring, but they are nearer their goal.
With a given outlay many more of the small offspring can
be produced, but they are not so sure. Each method has
its advantages.

7. The Tendency to Diminish the Size of Offspring. As
we come up in the plant and animal kingdoms, we find that
the size of that part of the parent which enters into each
of the offspring is decreased. We find further that less
and less of the substance of the parent is given up to
making offspring, and that more of the parental body is
left to live and reproduce again and again through a
considerable period. Thus, instead of parents dying in
producing the offspring, the parents may live along side
by side with them for a considerable period. By this
means the parent may produce even more offspring than
if it gave all its substance to offspring at the outset; and it
may distribute them through a better period of time.

8. Combination of Methods in One Parent. There are
some organisms that use several methods of reproduction.
As we have seen, one of the molds produces many small
spores, and at the same time, or a little later, it sends out
a stolon or two and thus starts a new plant as vigorous
as the first. By the first method it gets the advantage of
numbers and distribution; by the second it gets more
quickly matured offspring, but not so many of them. This
combination is a most successful one to insure the
adjustment of the plant to its conditions of living. It is
found in many plants and animals.

CHAPTER NINE.
CONJUGATION.

1. Review. Let us bring together the kinds of
reproduction we have studied thus far. In some forms we
have seen the whole parent divide into two offspring, each
one-half as large as the original parent. In others we
have seen the whole parent divide into many, small
spore-like offspring. Yet others put forth smaller bodies
which grow into new individuals without exhausting the
mother organism. Still others have special organs in
which many minute, single-celled spores are produced
and from which the spores escape without the destruction
of the parent.

In many of these cases the offspring begin at once to
grow into the adult. Some of them, however, may rest
days or months before they begin to develop. All of
them have the power to develop directly without any
special stimulation other than from heat, moisture, food,
and so forth.

2. Offspring That May Unite. We have purposely
omitted description of an interesting thing that sometimes
takes place even in many of the plants and animals
mentioned above, side by side with what we have already
described. In some of the fresh water algae (as Ulothrix,
a simple filamentous plant) the contents of the cells under
certain conditions divide into many motile spore-like
bodies. Some of these may swim around for a while and
then settle down and germinate into the filamentous form

48

CONJUGATION 49

which becomes adult. Some of them, smaller ones,
behave with a surprising difference. Instead of
germinating, these latter swim a while and then unite in
pairs, completely fusing the two small offspring into one,
which is twice as large as either. After uniting, this
resulting cell germinates and produces a new plant very-
much as the swimming spores do. Here we find two
methods in one plant, somewhat similar and yet with a
most important difference. (See the figure on page 28.)

This difference is so important and plays such a part in
the reproduction of all higher forms that we must examine
it more carefully. The new point is that offspring, instead of
developing, unite by twos. This union is not reproduction,
although it starts the development of a new plant. Instead
it is just the opposite of reproduction. The plant
reproduced when the divisions occurred that formed the
swimming spores. When these unite in pairs there are
only half as many individuals as before the unions. There
has been decrease instead of increase.

The individuals resulting from the union of the two
cells are more vigorous and more capable of development
than either of the cells was before the union. The union
has a value in connection with reproduction; but it is not
reproduction.

3. Gametes. Single-celled offspring thus may have
either of tvv^o fates: (1) they may develop without union
of any sort, in which case we call them spores; or (2)
they may unite by twos to form a body that develops with
especial vigor. In this case we call them gametes, which
means mates or uniting bodies. You will see that this
new united body is formed very differently from the way
in which spores are formed. The union probably means
something in strength and vitality for the next generation.

In the illustration above, all the gametes are of the
same size and form. No one could in any way tell them
apart. Such union of similar cells we call conjugation.

50

REPRODUCTION

4. Spirogyra. Of the thread-like green algae that we
find in our ponds this is one of the most beautiful. The
pupil should see it under the microscope, if possible. It
is a chain of elongated cells joined end to end. The green
matter (chlorophyll) is arranged in one or more strikingly
regular spiral bands. This is a perfect cell with nucleus,
protoplasm, and all the cell organs. As in cells generally,

these have been
formed by the di-
vision of mother
cells. The whole
filament of cells
came by division
from one cell.
When the right
time comes, two fil-
aments that are ly-
ing side by side
send out from their
various cells short
branches. Each of
these branches
grows and unites
with a branch from
the nearest cell in
the other filament.
When they meet,
the partition dis-
solves at the point
of union, and the
cavities of the two
cells are thus put
into communica-
tion. A little later
Figure 12. Spirogyra as viewed under the the protoplasm of
microscope. The figures at the right show the pro- qj^^ Qf these cells

cess of conjugation. F7-o7n Coulter's Plant Life ayid
Plant Uses.

flows through this

CONJUGATION

51

little tunnel into the other cell. In this cell the two masses
fuse as completely as the gametes of Ulothrix did. The
new body, made up of the protoplasm and nuclei of the
cells, forms a wall about itself inside the w^U of the
mother cell.

In the meantime the other cells of the two filaments
have been doing the same thing. Thus a row of bodies
may be found in one of the mating filaments, while the
other filament will be just a row of empty cells. This is
conjugation also. Later each of these united bodies
germinates and begins a new filament, which again
increases by division.

5. Paramecium. This extremely active little animal is so
abundant and so transparent that it is very satisfactory
for students to study with the microscope. It reproduces
by fission, much as the bacteria do. But it frequently
varies this by another performance no less interesting.
Ordinarily paramecia swim about without paying much

attention to each

^^^mm^wmimi/m

other. At certain
times, however, ow-
ing to causes we
know very little
about, they begin to

unite in pairs. They

Figure 13. Para;«^r?'«;«, one of the protozoa, , , f.^co I'nf/-. r^-na

magnified. This is a common, one-celled ani- ^^ "OI IliSe mio one,

mal, abundant in stagnant water. It reproduces ^g other cells we

rapidly by division of the who'e body into two

offspring. Occasionally fusion of two individuals have Studied in this
occurs. Paramecium moves actively by means , rpi i •

of the lashing movements of its cilia, indicated in chapter, i hey brmg
the drawing by the fringe of lines. their mouths to-

gether, and for a considerable time swim round side by
side as one animal. While they are together thus the
nucleus in each divides, and a part of the nucleus of each
Paramecium passes into the other by way of the mouth.
This incoming nucleus in each case unites with the part
of the nucleus of the other which it finds remaining. Each

52 REPRODUCTION

animal now has part of its own nucleus and part of that
of another animal. After this the animals separate. This
differs in several respects from the other conjugations
described above. The union of the animals is temporary.
Each, however, contributes a portion of its nucleus
permanently to the other. The number of individuals is
not diminished as in other cases we have described. There
has just been a change in the inner substance of each
animal. After a union of this sort the Paramecium has a
period of reproduction by fission.

6. Must These Unions Occur? In some cases it appears
clear that the unions, while common, are not absolutely
necessary. Often, even in forms that normally unite, the
gametes may develop at once without union. Taking the
animal and plant kingdom as a whole, however, the
gametes do not find it easy to develop freely into the adult
organism without conjugating. In some types the union
seems to be absolutely necessary.

7. What is the Value of the Union? What possible
reason or value these unions have is one of the most
interesting questions in biology. We know that they must
have some meaning in life because they are so nearly
universal. We are not perfectly sure just what the
advantage is, but in some way it is prophetic; it looks to
the quality of the future generations. It is pretty well
established that the stock formed by uniting two cells
from different strains is better, generally speaking, than
that formed from a single strain. It seems to have more
continuous vigor and more variety of development. It
appears that the plant or animal, which results from the
union of two cells, is less liable to be just like either
parent than one resulting from a single parent only. The
uniting cells seem to stimulate one another, and, perhaps,
to produce a kind of renewal of youth.

CHAPTER TEN
EGGS AND SPERMS.

1. Conjugation the Starting Point. There have been
no differences in the gametes or mating bodies in those
species we have studied. The ciliated gametes of Ulothrix
are of the same size and structure. The mating cells of
Spirogyra are apparently alike. The paramecia that unite
are as nearly alike as it is possible for organisms to be.
Indeed, we call the process conjugation only when the
gametes are alike, so far as we can perceive. This
condition must be looked upon as the simplest kind of
union of offspring. It seems to be the beginning of a
process which is very common in both plants and c.nimals.
This we must now study.

2. Beginning of Differences in Gametes. Pandorina
is a simple green plant made up, when mature, of sixteen
cells held together by a jelly which they have secreted.
It is not a plant you are likely to see, but it is
described in both botanies and zoologies, because it is
hard to say whether it is more like plants or animals. It
starts as a single cell. By a series of divisions the mature
colony of sixteen cells is finally formed. Any one of these
sixteen cells may start a new colony by dividing again.
Or, instead of this, any one or all of these cells may
divide into a number of gametes, which are small and
ciliated. These escape from the jelly into the water and
unite in pairs. The gametes are almost alike, but differ
more or less in size. A smaller and a larger unite.

53

54 REi PRODUCTION

In Eudorina, which is very much like Pandorina, there
is much more difference in the size of the two kinds of
gametes. Some of the gametes are quite large and plump.
Others are small and spindle-shaped. The differences are
at once recognized under the microscope. One of the thin
cells unites with one of the plump ones. A small one
never unites with a small one, or a large one with another
large one. The result is the same as in conjugation. But
we call the process fertilization when one gamete is much
larger than the other. The small gamete is said to
fertilize the large one. This name expresses an early
guess as to the value which this union has. It suggests
that the small cell stimulates or nourishes the large one
for a better development. But we now have good reason
to think that the relation is a somewhat deeper one. Each
gamete makes a definite contribution to the individual
which results from the combination.

3. Ovum and Sperm. What has just been described is
the beginning of the differences which we find in the
offspring (gametes) of all the higher plants and animals.
The larger of the gametes is an egg, the smaller is a
sperm, and it may be very small indeed as compared with
the egg. The difficulty now is not to tell them apart, but
to find anything in which they are alike. In appearance
they differ about as much as cells can. Both, however,
are single cells. In the egg there is a large amount of
nourishment stored by the parent. On the other hand,
the sperm is a cell with little more to it than a nucleus.
It carries no nourishment, but is usually exceedingly
active. All the higher plants and animals produce these
two kinds of cells.

4. Eggs and Their Characteristics. An egg, as we have
seen, is a cell. It may have some very peculiar structures
and powers, but it must always be remembered as a cell.
The shell and the white of a hen's egg are not parts of the
egg in this sense. Scientifically speaking, the yolk is the

EGGS AND SPERMS -55

egg proper, while the shell and the white are merely
protecting and nourishing structures about it. The yolk
is a single very large cell.

Eggs usually have large nuclei, and a good supply of
protoplasm. They are without power of motion. They
vary in size from that of the ostrich down until they
are too small to be seen with the naked eye. There is
little connection between the size of the animal or plant
and the size of the egg it produces. The eggs of humming
birds are many hundred times as large as those of trees
or of human beings. Eggs are plump, well-nourished,
and sluggish cells. They need to be stimulated to make
them active.

5. The Development of Eggs. It was said a moment
ago that the egg is a cell. So it is, but there is another
fact that must be mentioned about it. It is not just like
the cells of the body from which it comes. In order to
make this clear we must recall a few facts about the
structure of cells. In each cell, aside from the more fluid
protoplasm, (cytoplasm) there is a definite protoplasmic
body called the nucleus. In this nucleus there is a very
important substance called chromatin. As the time
approaches for a cell to divide, this chromatin tends to
collect into a number of rod-like bodies known as
chromosomes. The number of these in the body cells of
a given species of plants or animals is practically constant.
These chromosomes behave in a very interesting way in
the development of an egg.

Let us suppose that the nucleus of the ordinary cells
of an animal body that produces an egg has sixteen of
these chromosomes. By a process which we will not
study in detail here, the nucleus of the egg cell loses just
one-half its chromosomes as it prepares for fertilization.
In the supposed case the nucleus of the ripe egg cell
would contain eight chromosomes instead of the sixteen
which is characteristic of the other cells.

56

REPRODUCTION

l'^»^-:i

KIM

im.

Fisnre 14. Diagram of the process of division of the cell nucleus. In the
first picture the spherical nucleus is seen in the cytoplasm that surrounds it;
the net-like arrangement of the chromatin is indicated. In the second the chro-
matin is in a continuous band, this being the first stage m the division pro-
cess In the middle picture the chromatin has resolved itself into dehnite chro
mosomes which are dividing at the middle of the spindle. In the fourth picture
the newly formed chromosomes are migrating toward the poles of the spindle.
The last picture shows the formation of the daughter nuclei and the beginning
of the new cell wall. The spindle fibers soon disappear.

EGGS AND SPERMS ^ 57

This point you must keep in mind. We shall need it
to make clear what happens later. The cells of animal
bodies have twice as many chromosomes as their ripe
eggs have.

6. Sperms and Their Characteristics. In many ways,
as we have seen, the sperms are opposite in their nature
from the eggs. The sperms are always minute, even
more minute than the smallest eggs. Animal sperms are
almost all quite active,

with an active tail or

flagellum that drives them

through the fluid in which

they occur. Sperms are Figure is. Two examples of animal

real cells, however. They sperms, very much enlarged.

have a perfect nucleus, and a delicate supply of protoplasm,

most of which is in the tail mentioned above. Sperm cells

vary in shape rather more than eggs. Usually a species

produces many more of the small sperms than of the

large ova or eggs.

7. The Development of Sperms. In development the
nuclei of sperms of animals behave just as those of the
eggs. If the body cells have sixteen chromosomes in
their nuclei, these divide, as sperms are being formed,
in such a way that each sperm nucleus gets just eight.
As the biologist says, there is a reduction division in
the forming of eggs and sperms by which they get only
X chromosomes when there are 2 X chromosomes in the
cells of the body of the parent organism. The mother
cells of the sperms are not large cells to start with. The
divisions that produce the sperms take place rapidly and
the protoplasm does not grow much in the meantime.
Hence the sperms cannot fall heir to much protoplasm,
and so are small.

8. The Reduction Division in Plants. What has just
been said about the reduction division in animals does not
apply to plants in their formation of eggs and sperms. It

58 REPRODUCTION

IS true, however, that plants, like animals, do have in their
life history a reduction in the number of chromosomes
which compensates for the doubling of this number that
occurs when sperm and egg fuse.

Plants differ from animals in having what is called
alternation of generations, a phenomenon described in a
later chapter. One of these generations (gametophyte)
bears gametes, the other (sporophyte) bears spores, and
the two together complete the life cycle of the plant.
The reduction division occurs in connection with the
formation of the spores.

9. Sex in the Offspring. The differences between the
eggs and sperms are not just occasional, exceptional
facts. They are very constant differences in the plant and
animal kingdoms. Animals and plants regularly produce
two kinds of offspring, eggs and sperms; usually neither of
these can develop alone; they unite into one individual,
and this individual has all the powers of the species. These
differences in the gametes are differences of sex. They
are the most fundamental differences in sex. The qggs
and sperms are the "sex-cells." The egg is a female cell,
or offspring; the sperm is a male offspring. Fertilization
produces a new individual made up of the two kinds of cells.

CHAPTER ELEVEN.
FERTILIZATION.

1. Review of Conjugation. In an earlier chapter a
study was made of the union of gametes that are wholly-
similar. This sort of union is called conjugation, and is
quite common among the lower plants and animals. In
these gametes there is no outward sign of the differences
which we think of as belonging to males and females.
We now wish to study the union of eggs and sperms,
such as were described in the preceding chapter, where
there is a very striking difference in the gametes. These
differences are sex differences and we call the offspring
sex-cells. Their union we call fertilization.

2. The Effects of the Special Development of Eggs and
Sperms. In Chapter Ten it was shown that, with all their
differences, eggs and sperms agree in one important
particular. In both cases, when ripe, they have in their
nuclei only one-half the number of chromosomes usual in
the cells of the species. There are some interesting results
that seem to come from this reduction in the chromosomes.
Under ordinary circumstances neither of these cells has
the power of dividing again, or of developing any further
in any way. There are exceptions to this, but it is true as
a general thing. In some of the gametes which are alike
we saw that they might resume development separately if
they did not happen to unite. In the case of eggs and
sperms, unless they unite, both will die. Union, then, has
become almost imperative in these special cells. The sperm

59

60 REPRODUCTION

is too used up to divide; and the egg has too much
protoplasm to be stimulated into division by the small
amount of nuclear material in it. They do not behave as
young cells. They are like two run-down batteries.

In the second place, these cells are very different in
their structure and development. The egg with its large
size and rich nutrition is passive and sluggish, while the
sperm is reduced to the very lowest living terms. Both
these cells are essential to the on-going of the species.
Their very differences, therefore, will make it absolutely
sure that the powers they have and the work they do
must be very different.

Eggs develop much more slowly, sometimes requiring
years; are usually produced in much smaller numbers;
have no ability to take an active part in the mating, but
secrete substances that attract the male cells. The
sperms, on the contrary, are actively sensitive to the
substances secreted by the egg or its surrounding tissues,
are produced rapidly and in enormous numbers, swim
actively about and find the female cells. It is thus seen that
their powers and behavior are strongly complemientary
and that they are wonderfully adapted to each other:
passive and motile, secretion and sensitiveness, attraction
and responsiveness, large amount of food substances in
protoplasm and almost no protoplasm at all. This
adjustment between male and female gametes is the most
fundamental fact of sex and mating, and helps determine
all the other facts to which we shall give attention later.

3. Miethod of Fertilization. In the union of the sperm
with the egg there are two distinct problems. One is the
actual task of uniting these two cells into one when they
have come into the same region. The other is that of
bringing the sperms and eggs into such close range that
they can have any chance of uniting. This latter problem
must be solved by the parents that produce the cells, and
is solved in very different ways in different plants and
animals. It will be considered in the next chapter.

FERTILIZATION

61

As has been suggested above, the eggs have much
attraction for the sperms vi^hen they come near to one
another. The sperms move toward the egg, attach
themselves to the surface, and one of them (usually only
one) succeeds in penetrating the egg membrane. The
sperm enters the protoplasm of the egg. When it is in

%

A ■••;• ^ •/'•r.vH'v'-/

Figure 16. Diagram of the process of fertilization in one of the lower animals.
A, sperms entering the outer region of the egg. B, one sperm only has entered the
inner part of the egg and has altered as indicated at the right. C, the nuclei of
sperm and egg are now similar in appearance. D, a stage of the process in which
the chromosomes become distinct. E, splitting of the chromosomes. F, first divis-
ion of the fertilized egg, with maternal and paternal chromosomes equally repre-
sented in the daughter cells.

62 REPRODUCTION

the protoplasm of the egg it looks like a new nucleus. The
egg also has its own nucleus; hence the egg is now a cell
with two nuclei in it. These two nuclei exert an attraction
for each other; they gradually move together through
the protoplasm, and finally fuse.

5. The Union of Egg and Sperm: Its Results. The
process described above is called fertilization and is
found in practically all the higher animals and plants.
In nature it is much like the conjugation described for
the lower plants and animals, and may have been
developed from it. When the full union of the sperm
with the egg has been finished, we have a well nourished
cell with a nucleus made up of two parts, coming equally
from a male and a female cell. The protoplasm and food
of this cell, on which further growth is supported, come
almost entirely from the female cell.

The make-up of this new nucleus is peculiarly
interesting and important. The student will recall that
the nucleus of the egg, as it ripened, lost one-half of its
chromosomes. That is to say, if 2X is the number of
chromosomes found in the cells of the body in a given
species, these are reduced to X in the egg. The same is
true of the sperm nucleus. Therefore, when these two
bodies unite, they bring to the union two nuclei of just
one-half value so far as chromosomes are concerned.
When they unite the nucleus is completely restored to
the proper number of chromosomes. Whatever was lost
has been restored; and, instead of being from one source
only, the new cell has material in it usually coming from
two individual and distinct parents. It is now known as
a fertilized egg.

Recall that the forming of the fertilized egg is not
reproduction. Reproduction gave the egg and the sperm
cell. They were the offspring of their respective parents —
two quite different kinds of offspring. The eggs and
sperms were male and female individuals. They were so
feeble that both of them would have died but for their

FERTILIZATION 63

union. When they unite there is only one individual where
there were two before. This is just the opposite of
reproduction, which gives two individuals where there
was only one before. But this new individual has powers
of development which neither of the cells that entered
into it had. Instead of being feeble, as these two cells
were, it is completely renewed. It has youth and the
power to grow into an adult of the species to which it
belongs.

A fertilized egg, then, is the result of a union of two
individuals from different sources. Each adult is not one
offspring merely. It is a composite made up of two
offspring, a male and a female.

6. Fertilization and "Blood." We have a saying that
"blood will tell," and we mean by it that good or bad
qualities in the parents are sure in the long run to crop
out in their descendants. The reasons for this always
interest us. This wonderful process of fertilization throws
some light on the fact of inheritance. We know that
everything that is actually inherited, in the biological
sense, comes by way of these sex cells. To be sure,
parents can influence and change their offspring in other
ways than this, but such influence is not inheritance.

Now if this is true, we can make some valuable
conclusions from what we have. All the protoplasm
outside the nucleus came from the mother; the matter
in the nucleus, and only that, came equally from both
parents. But so far as we can see, in the long run,
offspring are no more liable to be like the mother than
like the father. These facts show pretty conclusively
that those qualities in which the parents are unlike are
carried somehow by the nuclei, because only the nuclei
come equally from both parents. It is clear that likeness
to one parent or the other is not determined by bulk of
protoplasm; otherwise the female characteristics would
be much more likely to be transmitted than those of the

64 REPRODUCTION

male. It is believed by many students of the subject
that they are carried by the chromosomes which are so
equally shared by the male and female in fertilization.

7. The Narrow Bridge. Genetics is the name of a divi-
sion of biological science; it is the experimental study of
evolution and heredity; its aim is to ascertain the knowl-
edge that is necessary for the improvement of inherited
characters; it is a division of science which has already led
to great improvements in the races of domesticated
animals and cultivated plants and it holds the promise of
great results in the improvement of the human race. In
his very interesting book on that subject*, Professor
Walter has a paragraph which reads about as follows:

"Whatever may ultimately prove to be the determiners
of the hereditary characters which appear in successive
generations, it is evident that they are located in the
fertilized egg. This single cell is the actual bridge of
continuity between the generations. Moreover, it is the
only bridge.

"For the majority of animals the Qgg develops entirely
outside of and independent of the mother, thus limiting to
the egg-cell itself all possible maternal contributions to
the offspring. Although there is abundant evidence that
half of the filial characteristics come from the male parent,
the only actual fragment of the paternal organism given
over to the new individual is the single sperm-cell. Thus
the entire factor of heritage is packed into the two germ-
cells derived from the respective parents and, in all prob-
ability, into the nuclei of these germ-cells, since the nuclei
are apparently the only portions of these cells that
invariably take part in fertilization.

"When it is remembered that the human egg-cell is
only about 1-125 of an inch in diameter, and that this is a
gigantic size as compared with that of the human sperm
cell, and, furthermore, when one passes in rapid review

"Genetics, H. E. Walter, The Macmillan Company.

FERTILIZATION 65

the marvelous array of characteristics that make up the
sum total of what is obviously inherited in man, the
wonder grows that so small a bridge can stand such an
enormous trafnc. A sharp-eyed patrol of this bridge that
is the strategic focus of heredity is proving to be one of
the most effective points of attack in the entire campaign
of genetics."

8. Artificial Fertilization. The process described in
this chapter varies considerably in different species of
animals and plants, but what has been said will serve to
give you an idea of what occurs in the great majority of
eggs and sperms that develop into adult plants or animals.
Usually an egg dies and disintegrates if it is not fertilized
by a sperm nucleus. However, a most wonderful discovery
was made only a few years ago. Some eggs of sea-
urchins were experimented with. Now the eggs of sea-
urchins, so far as we know, never develop without being
fertilized. But a scientist took such eggs directly from
the ovary, where they could not have been exposed to
sperms, and by putting them in water of a different density
from that of ordinary sea water and then returning them
to the sea water, he succeeded in haA ing them begin to
develop, instead of die and decompose as they would
naturally do without fertilization. In other words, by
outside chemical stimulation, eggs were "artificially
fertilized," so that they began to develop without uniting
with sperms. This work has been repeated many times
since, and we find that the same thing is possible with
many different kinds of eggs; of worms, mollusks, and
even of vertebrates. It is also found that numbers of
other chemical substances and even other kinds of stimuli
may so arouse these eggs as to start development. All
of this suggests that the work of the sperm is to act as
a stimulant to the sluggish egg, and cause it to become
active in development, when it could not do so unaided.

CHAPTER TWELVE.
DIFFERENT KINDS OF PARENTS.

1. Review of Beginning of Sex in Offspring. We have

seen that the striking differences between eggs and sperms
are rather constant for all higher organisms. These
differences are the first signs of sex; indeed they are the
most important elements in sex. We call the egg a
female gamete and the sperm a male gamete. It is
important to remember that the gametes are the offspring
in reproduction. They do not merely unite and develop
into offspring. When they are produced the parent has
"reproduced." Reproduction consists in the formation
and the separation of these male and female cells from
the parent. All the other facts of sex with which we are
familiar come from this starting point.

2. Simplest Cases in Which Eggs and Sperms are
Found. You remember that there are no eggs and sperms
in the simplest form of reproduction. There we see
merely fission or budding from one parent, with no union
of any kind. The simplest unions we have discovered
are those of conjugation, in which two similar cells, often
from the same parent, unite. From this we pass gradually
to different kinds of gametes which regularly unite. In
some cases eggs and sperms are produced by the same
mdividual. They may be produced at the same time or
at different times. A parent which produces both male
cells and female cells cannot rightly be called either male
or female. It is called an hermaphrodite. The word is

66

KINDS OF PARENTS 67

derived from Hermes and Aphrodite, Greek male and
female gods.

Many of the lower plants, and some of the simpler
animals produce both kinds of gametes in the same
individual. In such a plant as Vaucheria, or Oedogonium,
or some of the moss plants, both kinds of gametes are
produced near together on the same plant.

In the fresh-water hydra, described in Chapter Four as
reproducing by buds, reproduction by gametes also occurs.
In this little animal eggs and sperms are formed at
somewhat different parts of the body, and each hydra is,
so to speak, one sex at one point and the other sex at
another point.

This state of having both sexes in one organism is
known as hermaphroditism. In addition to the instances
mentioned above, it occurs regularly in many of the
worms, in snails, oysters, etc. Hermaphroditism may
occur in occasional individuals of higher species, even
among the vertebrates.

3. The Organs That Produce Eggs and Sperms.

Although a plant or an animal may produce both male
and female offspring at the same time, it is usually true
that such a parent has special and different organs for
each. Often they are definitely located at different parts
of the body.

The organs that produce the gametes are quite differently
named in different organisms. Generally among animals
the male organ, which produces sperms, is known as a
spermary or testis, and female organ is called an ovary.
Among plants the organ that produces sperms is called
an antheridium. The female organ in which the egg is
produced is called, in different groups, oogonium or
archegonium.

Where gametes are alike, there is only one kind of
organ to produce them. There is no reason why there
should be more. When the gametes become different,

68 REPRODUCTION

the sex of the cells seems to be stamped on the organs
that produce them. An experienced biologist can usually
tell which sex an organ represents, even though he has
never seen the organism before. The sex quality of the
organ becomes as marked as that of the gametes
themselves. The gametes are specialized. The organ
that produces them becomes equally so.

4. Specialization of the Parents. Where the gametes
are alike, there is no difference in the organs that produce
them, and the parents are all alike. But a step higher up
we also find different kinds of gametes, produced in
different types of organs, but all in one kind of parent.
One of the very best illustrations of this in the animal
kingdom is the common earthworm. In certain segments
of its body-cavity it produces sperms; in other segments
it is producing eggs. Each earthworm must perform all
the duties of father and mother.

But in the very same group of worms, in some of the
marine forms, we find a surprising difference. In these
one animal produces one or the other kind of gametes;
not both. If one segment of these worms produces
sperms, all the segments produce sperms, and the whole
animal is a male. Other worms produce eggs only. These
eggs and sperms from different animals must unite. Here
we have sex in the gametes; sex in the organs that produce
the gametes; and sex in the individual that bears the
organs. Beginning with the differentiation of eggs and
sperms, differentiation of sex has worked back into the
parents which produce them. This is the first time that
we have found organisms permanently and wholly male
(father) and female (mother) in a strict sense. In some
animals in which sex is distinct the differences between
males and females cannot be detected externally, though
there are internal differences.

5. Further Differentiations of Parents. This difference
in the sex organs is the most fundamental difference in

KINDS OF PARENTS 69

the parent. All other differences are secondary to these
and grow out of them. The task of forming and caring
for eggs is so different from the task of forming and caring
for sperms that the parents, at first differing only in the
internal organs that produce gametes, come to differ in
many external particulars. This is known as sex-
dimorphism. This is the state we are most familiar with
in the higher animals and in man. The males and fe-
males of most higher animals are more or less
conspicuously different from one another. It very often
happens that the males of a species of birds, we will say,
differ more in general appearance from the females of that
species than they differ from males of an entirely different
species. Put in another way, if we were to find the male
and female of the rose-breasted grosbeak apart in nature
without any chance to find out the facts about them
except by external appearance, we should undoubtedly
think they belonged to different species. These external
differences between males and females of a species are
found in birds, in many mammals including man, in some
fishes and amphibians, and in many insects.

6. Nature of External DifTerence between Male and
Female Parents. It is not possible here to call your
attention to all the ways in which the bodies of male and
female parents differ. The differences are greater in the
higher and more active animals. In general the males
are more highly colored, stronger, fiercer, and more
active. They often have special organs of combat, and
instincts to use these. The female is usually more retiring
and less endowed with instinct to seek out her mate or to
fight other members of the species. Her structures and
instincts relate more to care of the young. You can find
many illustrations of these statements, as well as some
exceptions to them, by field observation of birds,
mammals, frogs, insects, and spiders.

7. The Causes of the Differences. We are reasonably

70 REPRODUCTION

certain that the development of the sex organs and of the
cells within these is the chief cause of the differences we
see between male and female animals. For example, in
the very early development of an individual it is usually
impossible to tell which sex an animal is going to be. It
is only as the testes and the ovaries develop that the
external signs of sex are shown. If we take a male
chicken in early life and remove its testes, it will fail to
develop spurs and some other externa^l signs of its
maleness. Much the same thing is true if the ovaries of
a young female chicken are removed. It is much more
difficult to see any difference between a male and a
female thus deprived of the internal sex organs than
between the normal, natural sexes. This shows that it is
the sex cells that determine the nature of the parent body
rather than that the nature of the parent body determines
the sex cells.

8. The Advantage of these Differences. We know
that the developing testes and sperms put into the blood
materials that stimulate the growth of the male characters

even in such remote parts as the vocal organs, muscles,
and so forth. It is the presence of these substances that
stimulates the growth of muscles and nervous system.
If these substances are absent because of removal, or
because of abuse of the developing sex organs, the
physical and mental qualities do not develop normally.

You may wonder what value these differences between
males and females have. Or you may take for granted
that the sexes should be different and ask no questions
about it. Why should the males differ in so many ways
from the females? Is there any advantage to the species
in having them different?

We have seen that sperms and eggs stimulate the
individuals producing them very differently. There is,
however, another side to the matter. The task of the
male, the work done by him, and the service rendered

KINDS OF PARENTS 71

the race by the sperm cell and the male parent, are so
different from that rendered by the egg and the female,
that the very doing of the necessary work of the two
sexes results in differences, just as the farmer becomes
different from the banker or teacher by giving his time
and thought to different things.

We have seen that the egg cell is large, passive, and
highly nourished, while the male cell is minute, poorly
nourished, and exceedingly active. When these gametes
unite, it is the egg that attracts, while it remains passive,
and it is the male cell that is aroused by the presence of
the egg and actively seeks out the female cell and unites
with it. The role or function of the two cells is different.
It is inevitable that the parent that produces eggs, if it is
to do its proper motherly work, will become modified in
nature and instincts and in structure by producing the
eggs and bringing them to the proper condition for
fertilization. Similarly, the structures and the instincts
demanded of the parent that is to produce sperms will
be very different from those of the mother.

We can thus see that certain internal forces are at work
making male parents and female parents different, and
that there are duties and tasks suitable to each, so different
from the other, that the internal differences will be used
and increased by use.

CHAPTER THIRTEEN.

MOSSES AND FERNS

1. General Grade of Development. Just above the
green water plants, called algae, and the colorless fungi,
including molds, mushrooms, toadstools, and the like, we
find some green plants that begin
to look more like the higher plants
with which we are familiar.
Among these are the mosses and
ferns. In them we find for the
first time a clear differentiation
between roots that take up water,
leaves that manufacture food, and
stems that connect the leaves and
the roots. The lower plants have
no such clear differentiation of
their bodies.

The mosses and ferns are not so
well developed as the higher seed-
bearing plants, but they have so
many of the characteristics of the
higher plants that no one can get a
real understanding of the seed-
plants without a study of these
lower forms. Furthermore, the
method of reproduction in mosses
and ferns will help us understand
what happens in the higher plants.

hignre 17. An individual
mature moss plant, show-
ing general similarity of its
body to that of higher plants.
From Coulter's Plant Life
and Plant Uses.

n

MOSSES AND FERNS

7Z

2. The Life Cycle in a Moss. This Hfe history is more
complex than anything we have yet described, but it will
well repay careful study.

a. The Germination of
the Spore. If we start
with a spore, we find
that after a longer or
shorter period of rest
it germinates. This
means that the soft,
inner living part
swells, bursts the old
spore w^all, and sends
out a tube. This tube
becomes green, like a
filamentous alga, man-
ufactures food, grows,
and branches abund-
antly. The whole
thing at this stage is
called a protonema,
the word referring to
its thread-like appear-
ance. This stage is
not usually noticed.

b. Budding. Bud-like out-
growths next appear at
various points on these
threads. These buds do not grow into new threads
like the old ones from which they spring, but di-
vide in such a way as to form upright stalks or
stems. Each of these stalks develops root-like
structures and leaves, lengthens considerably, and
becomes one of the leafy moss plants with which
we are all acquainted.

c. Formation of Gametes and Fertilization. At the

Fisiire 18. A young moss plant
(magnified I arising from the proton-
ema. From Coulters Plant Life
a>td Plant Uses.

74

REPRODUCTION

^•^^

top of this leafy stalk there is sometimes a thick
cluster of leaves. At the tip of the stem, in the
tissues surrounded by these leaves, the moss plant
develops two kinds of structures not found
elsewhere on the plant. One of
these is like a minute flask with
a very long narrow neck. I'his
is really a kind of ovary or fe-
male organ, and it is called an
archegonium. In the bottom of
the flask is a large, plump cell,
which is the egg. The other
kind of organ that develops at
the top of the stem is club-
shaped, being attached to the
end of the stem by its stalk.
This is a male organ and is
called an antheridium. When the
antheridium is mature it bursts,
and from it escapes a great num-
ber of minute, ciliated, free-mov-
ing cells. These are sperms.
The bursting of the antheridium
occurs when the end of the stem
is moist, as when a drop of dew
or rain is among the leaves.
Through this moisture the
sperms swim about until they
come near a fluid secretion pro-
duced by the archegonium.
They are attracted by this secre-
tion. Some of them swim down the neck of the
flask, and one of them unites with the eggs at the
bottom, thus fertilizing it.

Fisure 19. Antheridium
of moss discharging sperms;
much magnified. From
Coulter's Plant Life and
Plant Uses.

In the moss we have one kind of parent plant
with two kinds of sex organs which produce two

MOSSES AND FERNS

75

entirely different kinds of gametes. In other words,
the moss described is hermaphroditic.

d. The Sporophyte and the Formation of Spores.

Evidently we now have a ferti-
lized egg. Judging from what we
have learned of animals, we might
expect this fertilized egg to es-
cape and to develop directly into
a new moss plant. But it does
not do this. It begins to divide
right where it is in the bottom
of the flask at the top of the up-
right stem. It develops a mass of
cells, known as a foot, that con-
nects it with the tissues of the
mother plant. Just above this is
a delicate stalk that may become
an inch or more long, called the
seta. At the top of this is a swol-
len portion, the capsule, in which
spores develop. All this develops
from the fertilized egg. The
whole structure is known as the
sporophyte, because its work is to
produce spores. It has no leaves
and gets the nourishment neces-
sary to grow and mature its
spores from the leafy moss plant
which is the gametophyte. (See
page 58.) Within the capsule
certain cells by their division pro-
duce numerous -spores; these final-
ly escape from the capsule and
the cycle is completed. We are
back to the point at which we
started, the spore that germinates.

^m

WcK^

Figure 20. Young
archegonium of
moss; much magni-
fied. From Coul-
ter s Plant Life and
Plant Uses.

76

REPRODUCTION

3. Summary of Reproduction in the Moss. In this life
cycle we have found that the moss has three methods of
forming more plants, i. e., of reproducing: (1) The
formation of spores in the capsule; (2) the budding of the
protonema by which erect moss plants are formed; and
(3) the formation of the gametes, by the union of which
the sporophyte arises. (Any generation of plants which
produces spores is a sporophyte, but that particular kind
of sporophyte we find in mosses is called a sporogonium.
The visible parts of all flowering plants are parts of the
sporophyte generation.)

4. The Life Cycle of the Fern. In middle and late
summer we find on the under surface of the leaves of
oidinary ferns numerous spots. These contain many
spores which escape in due time. As in the moss, we will
begin with the spore.

a. Germination of Spore and For-
mation of the Gametophyte. The
spore germinates by sending out
a tube as in the moss, but instead
of forming a long-branched fila-
ment, it divides in all planes and
makes a small, flat, heart-shaped
green body known as a prothal-
lium. This is not likely to be
seen by the student unless his at-
tention is called to it. It will
grow only in moist places. It
lies flat, has delicate root-like
structures (rhj^oids) on the un-
der side, and a notch at the

prothallium is the gametophyte

Fissure 21. Prothallia of
fern. The figure at the left
shows a young sporophyte
into which the fertilized egg
has developed. Frum Conl-
ter's Plant Life and Plant
Uses.

growing end.
generation.

This

b. The Formation of Gametes and Fertilization. The

green upper side of the gametophyte receives the

MOSSES AND FERNS , 11

light, and its cells manufacture foods as do the
leaves of the higher plants. At certain points on
the under surface two kinds of bodies are formed,
with exactly the same names and the same
functions as those that grow at the top of the leafy
moss plant. The archegonium is much the same
shape as in the moss, but the antheridium is more
flat and rounded. The sperms, as in the moss, must
have moisture in which to swim to the archegonium.
The t^^ at the bottom is fertilized just as in the
moss.

c. Development of Sporophyte and Formation of
Spores. The fertilized ^^^ divides, and the four
cells formed by the first divisions develop into the
parts of the new plant. Unlike the moss embryo,
the fern embryo does not depend long for
nourishment on the small gametophyte. As soon as
its growth causes it to break out of the small cavity
of the archegonium, it begins to develop roots that
take hold of the soil and leaves that manufacture
food for further growth. Furthermore, instead of
stopping with a small seta and capsule, growth
continues in the fern sporophyte until we frequently
have a rather large plant with roots and numerous
handsome leaves. Later in the season these leaves
produce on their under surfaces the spores with
which we started.

5. Comparison of Moss and Fern. It will be seen from
the above that the moss and fern follow very much the
same course of development in their life cycle: spore
germination; development of the plant that bears gametes;
formation of gametes; fertilization; development of the
embryo into another generation of the plant wholly
different in appearance from the gametophyte; the
development of spores by this new generation
(sporophyte); the escape and germination of the spores.

78

REPRODUCTION

It will be noticed in both kinds of plants that when the
spores germinate they produce a plant that forms gametes
and not spores; and when the gametes unite they start a
plant that develops spores and not gametes. We have in
both a regular alternation of two different kinds of
individuals in one life cycle.

There are also some interesting differences:

Moss

1. The gametophyte is a
leafy plant; the most
conspicuous part of the
cycle; the part called the
"moss-plant."

Fern

1, The gametophyte is a
poorly developed part;
the poorest part of the
cycle; the part called the
prothallium.

2. T h e sporophyte is
wholly parasitic on the
gametophyte, and develops
only slightly, being com-
posed of foot, seta, and
capsule. It is called a
sporogonium.

2. The sporophyte soon
becomes independent of
the gametophyte, fixes
itself to the soil, develops
leaves and roots and is
the real "fern plant."

CHAPTER FOURTEEN.
ALTERNATION OF GENERATIONS.

1. Summary of Reproductive Methods. We may class
the methods of reproduction that have been studied as
follows:

1. Those that occur without union of gametes, as in
fission, budding, spore formation, etc. (non-sexual).

2. Those that involve union of gametes, whether
similar or unlike (sexual).

We have studied many forms of plants and animals in
which both non-sexual and sexual reproduction are found.
For example, hydra buds and also produces eggs and
sperms; many of the algae reproduce both by swimming
spores and by gametes. In the forms referred to, however,
we must note one important fact: the final organisms
produced by the tv/o methods were alike. We could not
tell by looking at an individual hydra whether it had been
formed as a bud or had come from a fertilized egg.

2. Alternation of Generations. There is another step in
the story which we must now master. It often happens
that this reproduction by union (sexual) and reproduction
without union (non-sexual) occur in the same species, in
regular alternation, as we have seen in mosses and ferns.
Furthermore, the individual that results from non-sexual
reproduction is different from the individual formed by
the union of gametes, usually so different that no one
would take them as belonging to the same species. This
is called alternation of generations. If we illustrate by

79

BO REPRODUCTION

letters, we may describe such an alternation in this way:
An individual A reproduces non-sexually, and when the
offspring become mature they are not As, but Bs. B, when
mature, develops gametes which unite, and the fertilized
eggs develop into organisms that are not like their parent
B, but like the grandparent A. A by budding or spore-
formation produces B; B, in turn, by sexual union,
produces A.

3. The Moss and Fern Illustrate this Alternation.

What has been described in the preceding section is
exactly the thing that happens in the mosses and ferns.
The small prothallium in the fern, which has been called
the gametophyte, has the two kinds of gametes. These
unite, start a new plant, which is the large fern plant that
grows to be very different from the little microscopic
prothallium. This large plant is the sporophyte generation.
It has a period of growth, and when it becomes mature it
cannot in any way produce eggs and sperms, but produces
great numbers of spores without any sexual union
whatever. We have seen that these spores germinate into
the gametophyte. The sporophyte is one generation and
the gametophyte is another. These generations regularly
alternate.

In the moss we have exactly the same facts and in the
same order. In the fern both generations live independent
lives and the sporophyte is the better developed generation.
In the moss the gametophyte is the more important
generation and the sporophyte is parasitic on it. One
question about the moss may very properly be raised by
the student at this point. How do we know that the
structure that bears the spores in the moss is really a new
generation and not merely a part of the regular moss
plant, as it looks to be? That it is a new generation is
shown by the fact that it is produced by the development
of a fertilized egg. We know always that a new generation
begins when we start with a fertilized egg.

ALTERNATION OF GENERATIONS 81

In mosses and ferns, then, we have a good example of
alternating generations, in which the spore is the beginning
of the gametophyte generation of the plant, and the
fertilized egg is the beginning of the sporophyte
generation.

4, The Behavior of the Chromosomes in the Life Cycle
of Mosses and Ferns. In Chapter Eleven it was shown that
mature eggs and sperms have only X chromosomes in
their nuclei before they unite, 2 X being the number found
regularly in the body cells. When the gametes have
united, the number of chromosomes is thereby doubled.
The alternation of generations in the moss and fern shows
this in a very interesting way. If we start with the
fertilized egg, after the union of the gametes has brought
the chromosomes up to 2 X, we find that the following cell
divisions give to all the daughter cells of the developing
sporophyte 2 X chromosomes. This continues to be true
until just before the spores are to be formed. At this
time a reduction division occurs, similar to that described
in Chapter Ten, and the spore has only X chromosomes.
When the spore germinates, and divides to form the
gametophyte, its descendant cells continue to have X
chromosomes all through the life of the gametophyte.
The gametes formed in this gametophyte also possess the
X number of chromosomes, and are consequently ready to
unite. At their union the nucleus becomes 2 X once more.

5. Alternation of Generations in Animals. Alternation
of generations is much more common in plants than in
animals, but we have some very interesting examples
of it among animals. Indeed, we first knew of it among
animals. In the group of animals to which the
fresh water hydra belongs, there are many species similar
to hydra. Most of them differ from hydra in that
when they form new individuals by budding, the new
individuals do not escape and become independent, but
remain attached. The result of this is finally a colony of

82 REPRODUCTION

many attached individuals that have arisen by budding
from a single parent. After a period of this kind of
budding, the colony forms other buds of a different shape
and structure. When these mature they detach themselves
and become free sw^imming jelly-fish. No naturalist,
discovering them sw^imming in the water, unless he knew
the facts just stated, would ever suppose for a moment
that these jelly-fish were in any way related to the colony
from which they actually came. The free jelly-fish
produces gametes, which unite sexually and form embryos.
When the embryos develop they are not like their parents
the jelly-fish, but are like their grandparents, the tubular
hydroids. They settle down and reproduce by budding.

Many such instances are found in the coelenterates (that
branch of the animal kingdom to which the hydra belongs)
and among the parasitic worms, such as liver flukes, tape
worms, and the like.

6. Some Advantages in Alternation of Generations in
Animals. We do not know what forces have brought
about alternation of generations, but we can see that it
may be of some advantage to the organisms having it. It
gives a kind of double chance for organisms to scatter and
to become adapted to life conditions. For example, in
attached forms such as hydroids, the budding enables a
single individual that manages to become attached in a
favorable place gradually to take complete possession of
that spot by budding. Being attached has advantages, but
it also has handicaps. If conditions change, the colony
may be destroyed. Besides, there is no chance in budding
for wide distribution. Now the formation of another kind
of individual which is free-swimming, and able to produce
eggs and sperms, gives the fixed colony a chance to spread
its offspring widely and to seek out many favorable
localities for growth. In this way the advantages of both
methods are combined in one species.

In the parasitic form, the alternation is often an aid in

ALTERNATION OF GENERATIONS 83

getting back and fort', from one species of host to another,
as is so often necessary. For example, the liver fluke is
in the snail for a while, in the liver of the sheep a while,
and in the water of the pond between times. It is during
these alternations of generations, with their differences of
structure and habits and instincts, that these perilous
changes are made.

CHAPTER FIFTEEN.
SOME EGGS THAT ARE NOT FERTILIZED.

1. The Fate of Eggs. As we have seen, some of the
eggs formed by plants and animals are fertilized by the
sperms and then may develop into mature plants or
animals. But a great many fail to be fertilized, and such
eggs, no matter how perfect they are, cannot preserve
their life under ordinary circumstances. Such finally die
and decompose. Investigators have found that they can
take the eggs of many of the lower animals while they
are in good condition, even though they have not been
fertilized, and, by changing the external conditions about
them in certain ways, stimulate them to begin development
as though they had been fertilized. (See page 65.)

2. Parthenogenesis. There is one other exception which
is so remarkable as to demand attention. Quite a number
of organisms regularly produce eggs that develop into
the adult without fertilization by the male cell. We do
not know whether they are stimulated in some special
way while in the body of the parents, or have the power
within themselves to develop without any stimulus. This
development without fertilization is parthenogenesis. The
circumstances under which it takes place are different in
different organisms. In some cases, as in the queen bee,
the mother can, apparently, determine at any time
whether the eggs shall be fertilized or not. In other cases,
as in some of the rotifers (microscopic animals), the non-
fertilized eggs ("summer eggs") are laid at certain seasons

84

EGGS NOT FERTILIZED , 85

of the year and the eggs requiring fertilization ("winter
eggs") are produced at other seasons. In some cases the
mothers may differ, some forming both summer and winter
eggs and others parthenogenetic eggs only.

Furthermore, there is occasional parthenogenesis even
among forms where fertilization is the rule. For example,
it is known that the sj)orophyte of ferns may sometimes
develop from cells of the gametophyte without fertilization.

3. The Case of the Honey Bee. Perhaps the best known
case of parthenogenesis is that of our common bees. The
queen, who is the one perfect female of the hive, receives
a large supply of sperms at mating. This is stored in a
sac opening into the duct along which eggs come from the
ovaries on their way outwards. It is believed that the
queen can control the sperm supply in such a way that
eggs may pass to the surface either with sperm or without.
In doing this, the queen is doubtless controlled by
temperature, food, the conditions in the hive, the size of
the cells provided for the eggs, etc. When she forces out
sperms on the passing eggs and they are fertilized, they
develop into the workers (females). If the eggs are not
fertilized, they develop into the males (drones). While
the workers are females, they are not perfectly developed
females as the queen is. Apparently any fertilized egg
may develop a queen if the larva is specially nourished to
that end. Observers claim that the workers may lay
unfertilized eggs that may develop. There are many cases
of parthenogenesis found among the kindred of the bees,
the other social insects, such as bumble bees, wasps, ants,
etc. Some of these are as interesting as the case of the
honey bee, but they are not so well known to the general
student.

4. Hydatina, the Rotifer. This little "wheel animalcule,"
of about the grade of development shown by worms, is
found in stagnant water. Its life history has been very
well studied. There are three kinds of eggs produced,

86 REPRODUCTION

"summer eggs" of two sizes, and "winter eggs." The
summer eggs are thin-shelled and are not fertilized. The
larger ones develop at once and produce females. These
females may in rapid succession produce several
generations of parthenogenetic females. Later in the
season, these females lay the thick-shelled winter eggs,
which must be fertilized in order to develop. About this
time the males appear, hatched, seemingly, from the
smaller summer eggs. After fertilization, the winter eggs
lie dormant through the winter and develop, with the
return of warmth, into the females with which we began.
It has been found that external conditions, such as
temperature, state of the water, food, etc., have a part in
determining the kinds of eggs produced and the length
of the parthenogenetic generations.

5. The Aphids, or Plant Lice. A condition similar in
many respects to the last is found in the aphids, a group
of small sucking insects that are parasitic on the tender
twigs, roots, and leaves of many plants. In the autumn
there are females and males, and the eggs are fertilized.
These eggs are attached to the twigs of the host plants
in crevices where they may be partly protected. In the
spring they hatch out into females, which in their turn lay
eggs that hatch without fertilization. All the offspring at
this time are females with this power of laying
parthenogenetic eggs. This may continue for ten or
twelve generations, giving rise to an unthinkable number
of offspring which may be a great tax on the host plant.
Finally, in the autumn, a generation is formed that
includes both males and females. These mate and the
fertilized eggs go over the winter, as described at the
beginning, until the following spring. In some aphid
mothers, the parthenogenetic eggs develop before they
leave the body and the young are thus brought forth alive
(vivipary).

6. Parthenogenesis and Non-Sexual Reproduction. At

EGGS NOT FERTILIZED 87

first thought it might seem that parthenogenesis is just
one of the non-sexual methods of reproduction, like
budding or spore formation. A spore is a reproductive
cell that can develop without fertilization. Then why is
not parthenogenesis a form of spore reproduction? Two
or three facts, however, make us realize that
parthenogenesis is more related to sexual reproduction.
In the first place, the parthenogenetic cells are produced
in ovaries, where eggs arise; and in the second place, in
such forms as the bees, it seems that any egg may become
either a fertilized egg or a parthenogenetic one. It would
seem, therefore, that parthenogenesis is a case where the
process has gone backward; where a cell that might be
expected to unite has given up union and has come to
develop without it.

CHAPTER SIXTEEN.
THE FAMILY OF THE FROGS

1. The Family Tree. A great many of our examples in
the earlier part of this book have been taken from the
plants and the lower animals, the invertebrates. The
frogs, along with the fishes, birds, and men, are vertebrates.
The class of vertebrates to which frogs belong is not a
very large or important one, but it is one of the very most
interesting because of its method of reproduction and
development. In the family are frogs and toads, tailless
forms, including many kinds of tree toads; and a number
of slimy animals with tails, somewhat like lizards, that
live in water or moist places. These latter are newts,
salamanders, sirens, "mud-dogs," and the like.

The frogs and toads breathe in the air, and may live on
land, but they (the frogs, particularly) spend much of
their time in or near the water. Most of the family would
die if long out of water.

2. Reproductive Habits of the Frog. The frogs have
two sexes. The mother lays large masses of eggs in the
water. The egg proper, which is about the size of medium
shot, is dark in color and is surrounded by a layer of clear
transparent gelatin which helps to hold the eggs together
in globular masses or in strings, depending on the species.
Frogs do not lay eggs in nests, or specially prepared
places; but the frogs and even the land toads go regularly
in early spring to the shallow margins of pools and
streams. The eggs are frequently attached by the gelatin

THE FAMILY OF FROGS 89

to sticks or leaves of grasses or to other stationary objects
in the water.

3. Mating and Fertilization. While the mother is laying
the eggs in the .water, the male frog pours out great
numbers of sperm cells over them, also in the water.
These sperms can swim, and under the attraction of the
eggs one sperm cell unites with each of the eggs. The
gelatin is not a living part of the egg, and therefore the
sperm must pass through this until it reaches the dark
cell within. The head of the sperm containing the nucleus
passes into the egg proper and unites completely with the
nucleus of the egg. This forms a fertilized egg or embryo
with all the powers of developing into a mature frog.

4. The Early Development. If we were watching one of
these eggs with a microscope, we should see, about two
hours after fertilization, a little groove passing round the
egg and marking it off into two hemispheres. This shows
that the one-celled embryo has now become two-celled.
A little later it divides again, at right angles to the first
division, into four cells. These four cells are equal. Soon
other walls appear at right angles to both of those
previously formed. These new walls divide each of the
four cells into two, one of which (the upper) is consider-
ably smaller than the other. Divisions of all the cells
continue to take place rapidly. By the end of twenty-four
hours there are too many cells to count.

During this time the embryo, while changing its shape a
little, is not larger than it was at the start, yet there are
hundreds of cells where there was one at first. It follows
then that the cells in dividing have become much smaller.
Yet each has a little mass of protoplasm, a nucleus, and
all the other parts that a cell is entitled to have.
Furthermore, each one of the 2X chromosomes in the
nucleus made up of the union of male and female nuclei
splits with every division, and thus every nucleus has still
2X chromosomes.

90 REPRODUCTION

The first difference in these young cells showed at the
eight-celled stage when we had four small and four large
cells. At this time we know that the small cells are to
make the outer part of the skin, the nervous system, and
the sensitive parts of the animal generally. The larger
cells will give rise to the digestive tract and its glands.
These cells then are different, although they are all
descended from the same cell at the beginning. This is
called differentiation. The cells, from this time on,
differentiate more and more. Some of them become nerve
cells, some become bone, others become gland cells,
muscle cells, connective tissue, blood cells, pigment cells,
and so forth.

In three or four days changes enough have occurred to
enable us to see at a glance which end is to be head and
which tail; which side is to be back and which belly;
which right and which left. In a few days more, the
young tadpole breaks out of the envelop of gelatin and we
say it is hatched. From this point on it leads a different
life, because its environment is greatly changed.

5. The Life of the Tadpole. As the young frog, which
is called a tadpole, develops, it has organs suiting it to life
in the water. It has a soft skin that would dry up in a
few minutes in the air, it has gills by which it takes its
oxygen from the water, it has a fin-like tail by which it
swims freely, it has no legs that would enable it to walk.
In a word, it is a water-living, fish-like creature with no
adaptations whatever for an air and land life. During a
period varying from three or four months to two years,
depending on the species and the conditions of life, this
tadpole may continue. During this time it eats vegetable
matter. The tadpoles of the large species like the bull-
frog may become three or four inches in length.

6. The Great Change. If the tadpole stopped here, his
history, perhaps, would be as interesting as most others.
He might be considered a strange kind of fish. But he

THE FAMILY OF FROGS

91

does not stop here. His later behavior is one of the
surprises of nature. Usually during the same summer in
which he hatched, he begins to undergo some changes that
almost make him over into a new animal. These are both
inside and outside changes. On the outside he begins to

Figure 22. Stages in the life cycle of the frog,
grow legs, first the hind pair where the tail joins the body,
and later a front pair close to the head. During this time
the tail is gradually being absorbed by the blood corpuscles
that circulate through it. By means of the blood this
material is turned over to the growing animal very much

92 REPRODUCTION

as though he had eaten his own tail and digested it. The
tail finally disappears entirely.

The inside changes are even more wonderful. The
intestine, coiled like a watch spring, in which he digested
vegetable food, becomes more straight, and becomes suited
to animal food. The gills by which he got oxygen from
the water gradually disappear, while deeper in his body
is developing a pair of lungs into which he takes air
through the nostrils. The blood vessels from the heart
change so they can take proper care of this new kind of
supply of oxygen. The frog doesn't take a vacation during
this time. He has to capture food, and must keep his wits
about him every minute so that some otner animal will not
capture him. It is really a remarkable performance. It is
as though a gasoline launch were gradually changed into
an electric automobile, which could run either on land
or in water, and during the whole of the transformation
was a perfectly usable vehicle!

CHAPTER SEVENTEEN.
THE BIRDS.

1. When the Chicken Leaves the Egg. When a young
chicken, or other bird, comes out of the egg, we are
disposed to take him as he is and ask no questions about
his past. At this time the young bird is enough like its
parents for us to recognize it as a bird. To be sure, it
makes some changes after it hatches, but it has all the
organs of the adult, and it lives in the same general way
that it does when it grows up. It is not very hard to
imagine that a young chick plus proper food should in due
time become a laying hen or a fighting cock. After
hatching it passes through no such changes as we saw in
the passage of the tadpole into the frog.

But the events back of this appearance of the bird from
the tgg make a most remarkable chapter in its history.
Indeed many of the things that happen within the shell
are not unlike the passage of the tadpole into the frog.

2. The Character of the Egg. The egg of the bird has
a limy shell about it, and inside that is a tough membrane.
Just within this membrane is the sticky "white" of the egg.
Not one of these things is a part of the real egg. All of
them were added after the egg was formed. The real egg
is the part we call the yellow, or yolk.

Most of us have seen in the body of an old hen, behig
prepared for the table, the ovary with a number of yolks
of different sizes, like little potatoes around a potato
plant. These are of different ages, and one or two may be

93

94

REPRODUCTION

about as large as the yolk in an ordinary egg. The larger
ones are about ready to escape from the ovary and start
to the outside world. When the egg (or yolk) is ready
it passes from the ovary into the body cavity and enters
the large opening of the oviduct, or egg tube, which
carries it to the outside world. As it goes down the
oviduct the wall of this tube secretes the albumen (white)
all round the yolk. It goes gradually twisting down the

Figure 23. Diagram of internal anatomy of pigeon. From CoUoti's Des
criptive Zoology.

oviduct and finally comes to rest at a point where the
shells are formed around it. Soon afterward the hen lays
the egg.

3. Fertilization and Development. It must be clear
that fertilization of an egg like this could not take place
as it does in the frog. A sperm could not possibly work
its way through the shell or through the sticky albumen.
If the egg is to be fertilized, it is necessary for the sperm
to unite with it early in its course through the oviduct,
and before any of these materials are added. This means
that the sperm cells must be inserted in the outer opening

THE BIRDS . 95

of the tube and then ascend to the upper and inner part
of it where the egg enters. This is just what happens.
When the male and female bird mate, or copulate, the
sperms are discharged in large numbers into the cloaca,
or opening of the digestive tract, from which they make
their way upward into the oviduct. Only one is necessary
to fertilize each egg. The others die.

After fertilization it requires the fertilized egg, or
embryo, several hours to pass down the oviduct, get its
shells, and escape. During this time the nucleus, or
protoplasm, of the young embryo divides a number of
times, so that when it is laid it is not really an egg. It is
a young chicken of, perhaps, several hundred cells. It
does not at this time look the least like a chicken. It is
just a little round spot which one sees on top of the yolk
if an egg is broken and put in a saucer.

4. Development and Hatching. Such an egg as this,
which is really a young chicken, will keep its life for a
while if the egg is put aside, but not for very long. If it is
left long the young chick dies, and the egg begins to
decompose. If, however, the egg when first laid is put in
a constant, warm temperature, the cell division continues,
and the young chick which was at first just a little spot of
cells on one side of the yolk, grows all round the yolk. It
develops a heart, and blood vessels that run out over the
yolk and collect food from it and bring this back to the
growing parts. Thus when the egg is warmed by the
hen's body in the nest, or by an incubator, the same sort of
development takes place that we studied in the frog. Only
in this case there is so much food in the egg that all the
steps similar to those which occur in the frog after it
hatches take place in the chick within the egg. In other
words, the frog has further to go after it hatches than the
bird has The bird goes further in its development on the
strength of the food which the mother stores in the egg.

5. The Changes at Hatching. There are some important

96 REPRODUCTION

changes for the chick at the moment of hatching. Up to
this time the oxygen, which is necessary for all life, passes
through the shell and finds its way into the blood directly
by means of some special embryonic membranes. When
the chick breaks the shell these membranes dry up and all
the oxygen goes into the lungs in the ordinary way.
Before hatching all the food has been taken by the blood
from the substances in the egg. Almost immediately after
hatching the chick begins to practice its instincts for
pecking at food, and soon gets to using its digestive tract.
Other vital activities follow and the young chick soon
performs all the important functions in just the same way
the adult does.

6. The Sexes in Birds. The males and females are
always distinct in birds. That is to say, one individual
produces sperms and another eggs. Furthermore, the two
parents, when adult, are usually quite unlike in appearance,
instincts, and behavior. The chicken is a good illustration
here, though not better than many other birds. The
rooster is larger, more brilliantly colored, more
aggressive, more noisy, and has certain structures which
the hen either does not have, or not in such degree, as
spurs for fighting, comb, wattles, etc. In many birds the
male has better developed powers of song. It is thought
that many of these qualities in which male and female
birds differ are adaptations that enable each the better to
meet the work which it must do. For example, the spurs
of the cock, his greater size, and his aggressiveness seem
to fit in with the fact that in some measure he takes the
lead and protects the flock that surrounds him.

Birds have power to reproduce only by the union of
sperms and eggs.

CHAPTER EIGHTEEN.
MAMMALS AND MAN.

1. The Special Development of Mammals. The

specialization of mammals, as compared with other
vertebrates, is chiefly in connection with reproduction and
care of young. There is no group in which these functions
are more successfully cared for than in mammals. No
group has developed higher, finer, more successful instincts
and practises. The name mammals comes from the
mammary or milk glands by which the young are
nourished after birth. The developing embryo is carried
for a considerable period of its early development in an
internal organ of the mother. Here it is nourished and
protected from the unfavorable conditions outside. It is
largely because of these facts, and the instincts and habits
that grow up about them, whereby the bonds between the
young and the parents are strengthened, that the mam-
mals are so successful and seem to be at the head of the
animal kingdom.

2. Man's Place with the Mammals. As an animal, man
is not different from the higher mammals in any very
important particulars. He has all the characters of the
mammals and some particular ones beside. His
reproduction is identical with theirs in all important
respects. He cares for his young somewhat better than
the others, and educates them longer, gives them a better
home, and more sympathy, but the beginnings of
everything man does for his children are found in what
other mammals do for theirs.

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98 REPRODUCTION

3. The Gametes in Mammals. As in birds, there is no
reproduction in mammals except by the formation of eggs
and sperms. The sexes are always separate. The female
reproduces by small eggs, much smaller even than those
of the frog. Sperm cells are produced by the males in
testes just as in frogs and birds.

The mammals are like the birds in that the eggs are
fertilized within the body of the mother. This is not
because of a shell about the egg as in the case of birds.
It is rather because the embryo when fertilized is going to
remain in the body of the female and there develop. It
is incubated within the mother instead of in a nest. For
this reason the sperms must be inserted into the special
female organ, the vagina, by a special act of mating
called copulation. From the vagina the sperms ascend
and meet the eggs as they come down from the ovaries.
The meeting place of sperm and egg is usually the organ
in which the young are retained during early development.
This organ is the uterus, or womb. It is a special organ
formed by a great enlargement of the oviducts or tubes
that lead from the ovaries to the outside.

Fertilization itself differs in no way from that studied in
the lower plants and animals.

4. Early Dievelopment of the Embryo. After fertilization
the fertilized egg (embryo) divides into two cells, then
into four, eight, sixteen, etc., just as in other animals. By
steps similar to those studied, the embryos become
differentiated into nerve, and muscle, and cartilage and the
other tissues. These steps need not be followed again.
The point which makes the mammal embryo so peculiar
and interesting is this: there is little food in the egg,
hence it cannot live as long as the frog's egg or the hen's,
on the strength of its own food. So, very soon after
fertilization the embryo attaches itself by root-like out-
growths to the tender walls of the uterus. Through these
connections it takes up nourishment from the blood of the

MAMMALS AND MAN . 99

mother. Thus it grows, literally a parasite on the mother
just as the sporophyte of the moss is a parasite on the
gametophyte.

As the heart and blood vessels of the young mammal
develop, the latter run out to these connections with the
mother just as those of the chick did over the foodstuff in
the Ggg. Oxygen as well as food is thus received from the
blood of the mother, and the carbon dioxide and other
wastes are returned to it.

This internal development continues for very different
lengths of time in different animals. In one of the groups
of mammals, the marsupials, which includes the opossum
and kangaroo, the young are carried only for a short time.
They are born in a very immature condition. They are
then placed in an outside pouch which contains the milk
glands. Here the young remain until they are mature
enough to take some care of themselves. In the higher
mammals, the period within the uterus varies from a few
days to a year or more. For the large mammals it is
usually a little less than a year. In these the development
at birth is greater than it is in the marsupials.

5. Birth and its Changes. Birth in mammals may be
said to correspond to hatching in the birds. The young
mammal passes through all its embryonic stages in the
uterus and has all its principal organs ready for use when
born. While it is living one kind of life (that within the
mother) it is being made ready for a very different one.
The change in birth is like that in hatching, a very sudden
one. The change of life in the tadpole on the other hand
comes very gradually.

Before birth the young are surrounded by the body of
the mother and have a constant temperature- At birth
they are brought into a very much colder and more
changeable temperature. Before birth all the food and
oxygen are taken up by the blood from the mother's blood.
At birth this supply ceases, and the lungs for the first

100 REPRODUCTION

time are used and oxygen taken through them. Similarly
the digestive tract has been developed merely for the use
it was going to serve, not for any value it had before birth.
One can readily see that birth is not in any sense the
beginning of life. It is merely a change from one kind of
life on the part of the embryo to another kind. It is
similar to that which the toad makes when it passes from
living and breathing in water to living in the air.

6. Care after Birth. It must not be thought that the
mammal young are, or ought to be, completely independent
at birth. Just as in birds, there is a period in which the
young demand a great deal of care from the parent. This
is accomplished in many ways, but the particular form of
care in which we are interested is that peculiar to mammals
and which gives them their name. This is by means of
the secretion known as milk. It is produced by skin
glands which have become highly modified and often
greatly enlarged. It consists of water, of salts from the
blood, of a form of sugar, of considerable oil which in fine
particles gives the milk its whiteness, and of certain
proteins. It is thus a complete food for the young animal.
From the point of view of successful reproduction, milk
makes it possible for more of the young to live than could
possibly come to maturity without it. Carrying the young
in the body and furnishing them with a complete food
when first born are two most wonderful inventions, so to
speak. They go far toward insuring success to the group
of animals that use them.

All that has been said about the reproduction and
development of mammals applies to man.

CHAPTER NINETEEN.
THE YOUNG OF THE HIGHER PLANTS.

1. Vegetative Reproduction among Plants. Already
we have referred to the fact that many plants produce new
plants by buds, or tubers, or roots, or runners, and even
by leaves. The higher plants differ very much in respect
to this rough and ready kind of multiplication. Some
plants have none of these methods, others may use two
or three of them.

2. The Older Idea of Reproduction in Plants. Until
recent years the reproduction of plants by seeds would
have been described as follows:

"The seed contains an embryo. When the seed
germinates, the embryo breaks through and develops
roots and leaves that enable it to get its own nourishment.
It now grows until it becomes mature. The mature plant
forms flowers which are its reproductive organs. Each
complete flower, in addition to the protective and colored
parts (sepals and petals), contains both male and female
organs. The stamens are male organs and the pistils are
female organs. The pollen, arising from the stamen, is the
male cell and corresponds to the sperm, but has in itself
no power of motion. The ovary develops an egg cell deep
in each ovule. When the P9llen is carried to the stigma
and the pollen tube grows down into the ovule and unites
with the egg, the male cell is fertilizing the female cell.''

This is not the correct interpretation of sex reproduction
in plants, although it is the way in which many people

101

102

REPRODUCTION

understand it. There is enough of fact and enough of
fiction in this interpretation to make it necessary to give
the process in a little more detail.

3. The Modern View of Reproduction in Flowering
Plants. Botanists now describe this process as follows:

The plant develops from the embryo in the seed and
presently produces flowers. Flowers are really clusters
of special leaves; sepals, petals, stamens, and pistils being
each a set of these spe-
cial leaves about the end
of a stem. The stamens
and pistils are like the
leaves of the fern plant
in that they bear spores.
The other leaves do not.
The stamen is not a male
organ; it is a spore-
bearing leaf. The whole
plant is therefore a spor-
ophyte. The pollen is
not a male cell; it is, at
first, just a spore. The
pistil is not a female or-
gan; it is also a spore-
bearing leaf, and deep in
each ovule at least one
large spore is borne. The
spores (pollen) borne by
the stamens are smaller

spores than those borne Figure 24. Diagram of lengthwise see-
by the pistil. The spores tion through a complete flower. From
in the stamen escape; Coulter's Plant Life and Plant Uses.

those in the pistil are deep in the tissues and can not
escape. When the pollen spore is carried to the pistil
it germinates by producing a tube which grows into the
ovary. The nucleus of the pollen cell divides once

YOUNG OF HIGHER PLANTS

103

or twice, and two or more of
these nuclei pass down the
tube and reach the tissues in
the ovary. In the meantime
the nucleus of the large spore
in the ovary has divided
into eight or more nuclei,
and one of these becomes the
nucleus of an egg. The
nuclei in the pollen tube es-
cape and one of them unites
with the egg nucleus. In this
way fertilization takes place.
Thus we see that pollen
grains are not sperms, but
nuclei in the pollen tube after
the pollen has germinated are
really the sperms. The egg
is not formed directly by the
growth of the ovary tissues,
but by the division of the
nuclei in the large spore
which the ovary produced.

4. What is the Real Differ-
ence Between the Old and
New Views? In the old view
we have just a straight, di-
rect union of a male cell pro-
duced by a plant (such as an
apple tree) with a female cell
produced by the same apple
blossom. In the new view
we have the flower producing
spores as in the fern, only in
the flower we have two kinds
of spores: a small spore pro-

Fisnre 25. Diagrammatic view
of a pistil, showing entering pollen
tubes. One of them has reached
the tissue which contains the egg,
and fertilization is about to occur.
From Coulter's Plant Life and
Plant Uses.

104 REPRODUCTION

duced in the stamen and escaping, and a large spore pro-
duced in the ovule, and not escaping. The small spore
(pollen) grows into a small male plant (male gameto-
phyte) : the large spore in the ovule grows in its place
inside the ovary in the pistil into a small female gameto-
phyte. The small male gametophyte produces two
sperms, one of which unites with the egg that is formed
in the female gametophyte.

In other words, the old view thought of plants as
reproducing by the sexual method merely, as in the
higher animals. The new view states that seed-plants
have an alternation of generations just as the fern has.
It states that the seed plant has a generation that produces
spores, and these in turn produce another generation that
forms gametes. According to the old view the embryo in
the acorn is the child of the oak tree. According to the
new view it is the grandchild.

5. What are the Proofs that there is an Alternation
of Generations in Seed Plants? It is not possible here
to give all the facts that convince the botanist that the
modern view is the right one, but there are two or three
things that may make it seem reasonable even to a
beginner. Everybody agrees that a new generation starts
when gametes unite. So when the nucleus from the pollen
tube unites with the nucleus of the egg cell, and this
fertilized cell begins to grow, we are sure we have a new
plant started. We can trace the growth of this plant at all
stages into the seed, and through germination, and on to
maturity. Furthermore, when these cells unite we have
the 2X chromosomes that we found in the sporophyte of
the moss and the fern; and this 2X condition of the nucleus
continues all through the life of the flowering plant.

In the second place, when the pollen is formed, it is
formed very much like the spores in the fern. The
chromosomes are reduced to the X stage as they are in
the spore-formation of ferns. The pollen furthermore

YOUNG OF HIGHER PLANTS - 105

germinates as a spore does and its nucleus divides to form
the nucleus that fertilizes the egg. A real male cell never
germinates or divides so far as we know. The pollen does
not unite with the egg; one of the cells descended from
the pollen unites with the egg. In a similar way the large
cell first formed in the ovule, which has been called the
large spore (megaspore), is not itself fertilized. It is not
an egg. It divides several times, and one of its descend-
ants becomes an egg.

Finally, while there are many differences between the
alternation of generations in the fern and the alternation
in the higher plants, we can find conditions in plants lying
between (connecting links) that prove to us that the
higher seed plants have a clear alternation between
sporophyte and gametophyte, and show that this
alternation in the seed plants is evolved from the
alternation in the lower plants.

6. Changes from Fern to Flowering Plant. The following
are the chief changes that would have to come to the fern
to make a flowering plant out of it:

1. Some of the leaves only would bear spores while the
others would give up this work altogether. We find this
condition among some ferns.

2. There would need to be produced two kinds of
spores, small and large; the small producing a male
gametophyte and the large a female gametophyte. This
also is found among some of the allies of the ferns.

3. The size of the gametophyte must be very much
smaller than we find in the common fern. Indeed the
gametophyte in the seed plant is little larger than the
spore. This is true also of some of the fern plants.

4. The large spores would not escape from the leaf that
produces them, but would germinate and the resulting
plants would live parasitically on the tissues of the
sporophyte.

5. Because the seed plants are mostly aerial and the

106 REPRODUCTION

female cell is formed deep in the tissues of the sporophyte,
a delicate motile sperm cell could not reach the egg.
Hence the small spore in germinating produces a tube
that penetrates the tissues and allows the sperms to pass
down through it. Sperms of ferns and mosses have cilia,
and are active in motion. The sperms of seed plants
evidently have no need for activity of motion, yet we find
that the sperms of some of the lower seed plants have
cilia, which strongly suggests that their ancestors had
need for ciliated and actively moving sperms.

CHAPTER TWENTY.
RELATIONS OF PARENTS AND OFFSPRING.

1. Review. In Chapter Eight we studied these relations
in some of the lower plants and animals. We found that
reproduction is always a sacrifice on the part of the
parent; that this sacrifice is necessary to keep the species
going; that the parent is completely destroyed in the
lowest forms of reproduction, as fission; and that the
parent can economize by giving a smaller part of itself
to each offspring. Thus we saw a reduction in the amount
of substance which went into each offspring.

2. What Parents Must Do. Just the same problems
confront the parent in the higher forms as were discovered
in the lower. Two parents must, on the average, bring to
maturity two offspring during their own life time in order
to keep the race where it now is. The problem of parents
is to hit upon the best way to do this. It is for the good
of the race that the parent shall not be used up in this
sacrifice until enough offspring have been produced to
allow two to survive the disasters that confront them.
On the other hand, the parent must sacrifice enough
matter and energy in reproduction to insure the species.

3. Condition in Higher Organisms. In the higher plants
and animals we have found two methods of reproduction
that are peculiarly prevalent: reproduction by spores, and
reproduction by gametes. In both of these methods the
offspring consists of a single cell, whereas the adult may
include millions of cells. Thus the ratio of the offspring to

107

108 REPRODUCTION

the parent is in volume very small. This, as we have seen,
is much more economical to the parent, but it puts a long
period of immaturity and dangers before the offspring.

In this situation the organism has two possible ways of
increasing the chances of enough offspring coming to
maturity. In the first place, it may produce a much larger
number of the single-celled offspring in order to overcome
the great fatality. Or, it may give especial care and
protection to the offspring and thus diminish the fatalities.
Indeed it may do both. It is in this care of offspring after
they are produced that the higher plants and animals excel.

4. Parental Care of Offspring. You must not jump to
the conclusion that the care of young by parents is
necessarily conscious and deliberate. In man it is partly
so, but for the most part it is instinctive and unconscious.
It is none the less valuable on that account. The care of
offspring in some way or other is one of the most common
things in nature. That it is a good arrangement is
shown both by the wide-spread occurrence and by the
kind of success that comes to those species in which it
is best developed. Remember also that parental care
means sacrifice just as reproduction does. It is another
kind of sacrifice.

5. Different Forms of Parental Care. The ways in
which parents may help their immature young are almost
as varied as are the plants and animals themselves. There
are, however, certain classes of caretaking that are
conspicuous because they are found so often. Thus we
note the storing up of extra food in the eggs, as in
reptiles and birds. Eggs may be laid where an abundance
of food will be found as soon as they are hatched,
as in flies, beetles, and many other insects. Parents
may give aid in hatching, by carrying the eggs
around attached to the body, as in lobsters, or by
incubation, as in birds, or by carrying the eggs and young
in the body during early development, as in the higher

PARENTS AND OFFSPRING 109

plants, some sharks, some snakes, and all the mammals
with a few exceptions. Special protection may be
furnished the young after hatching, as by the coats of
seeds, and by active efforts, as in many of the higher
animals. Birds capture food for their young, and the
mammals secrete it in the form of milk. Special education
of the young through imitation and other faculties is seen
in birds and many mammals.

It is not our purpose to dwell at length on the different
forms which the care of parents for offspring may take.
But it is our purpose to make clear that this kind of care
after reproduction makes it possible to diminish the
original cost to the parent in substance. When bacteria
divide into two half-sized individuals, the daughter cells
have as much substance of the parent as is possible, but
there is no parent left to give them any care. This is
successful. No group is more successful on its plane of
living than the bacteria. At the other extreme we have
man, in whom the embryo has very little endowment in
the egg itself, but has the maximum of parental care, in
that it is carried in the body, is supplied with food, and
receives definite protection and education for a long period
after birth. Men can keep the species up, that is, each
fr.mily can bring two to maturity on the average, with a
birth rate of three or four during the generation.

6. Effects of Parental Care in Higher Forms. There
are several things, especially important in human life,
that grow out of this increasing care of parents for the
young after hatching or birth. These things have great
influence on the species and on the relations of individuals.

In the first place, the period of infancy and helplessness
grows longer and longer as we ascend the scale of life.
The higher the parent physically and mentally, the more
difference there is between the offspring and the mature
parent; the further the offspring have to go in their
development. Thus there is the more need for parental

110 REPRODUCTION

care, and the more opportunity for education. This makes
it possible for the young to progress faster and more
safely than if they had to learn every thing through their
own experiences.

Secondly, the care of j'oung tends to hold the parents
together. This is true during the breeding season at least,
and thus something of a home or social life is developed.
We see this among ants, bees, birds, and the higher
mammals. There is no doubt that this adds to the
efficiency of a species.

In the third place, the long period of dependence of the
young on the parents tends to develop in the parents
themselves the qualities that make better parents of them.
Anything that increases their sympathy and disposition
to make sacrifices for the offspring w^ill react on the
welfare of the offspring and for the good of the species.
It is possible that the good points of parents themselves
have thus been increased from generation to generation.

The highest human sentiments cluster about marriage,
parenthood, and care of young, and these play a most
important part in the progress of mankind socially and
morally. Indeed all social progress is closely related to
these fundamental capacities and tendencies in connection
with reproduction and care of young.

CHAPTER TWENTY-ONE.
REPRODUCTIVE INSTINCTS.

1. Introduction. Thus far we have been discussing
reproduction chiefly as a process whereby individuals
increase the number of species. Reproduction thus viewed
seems to be a result that can be had by a number of
different kinds of machinery, much as we may cultivate
corn with a crooked stick, or with a hoe, a single plow, or
an up-to-date cultivator. The methods differ in efficiency,
but all lead to the same result. The real meaning of the
process is very much the same whatever method is used.

2. Tendencies in Life. It does not explain the fact of
reproduction, however, merely to say that the species
would die out if the individuals do not reproduce. What
difference does it make to the individual if the species
does die out? We cannot imagine that the individual
plant or animal is conscious of this fact, or that
it is directly influenced in its behavior by this fact. Deep
within the living thing is the tendency to grow, and equally
the tendency to divide. We have no real explanation of
how it comes to be, but we do know that as we ascend the
scale of life the process of reproduction becomes more and
more complex. There come also to be various tendencies
in plants and animals, associated with reproduction, that
we describe as habits or instincts. Some of these are
peculiarly important and interesting, and help make
reproduction more efficient.

3. The Meaning of Instincts. If an individual learns to

111

112 REPRODUCTION

do a certain thing and does it so often as to come to do it
readily and without conscious attention we say it has
become a habit. If an individual inherits a tendency to
do a thing a certain way, and this tendency thus belongs
to the whole species we say it is an instinct. Instincts are
thus more deeply ingrained into life than habits are. They
are not "learned."

The great vital acts, like feeding, adapting one's self to
climatic conditions, and mating and reproducing are
surrounded by instincts such as have been described. If
an infant is hungry, it instinctively cries and seeks for its
food. If a particle of food is placed on the back of its
tongue it automatically and instinctively swallows. It is
very certain that food-getting, adjustment to cold, mating,
and reproduction could not possibly take place in plants
and animals with any such precision as we have seen, if
it were not for these deep instincts.

4. Somie of the Instincts Connected with Reproduction.

The instincts that tend to make reproduction certain and
efficient are of three classes:

(1) The instinct of reproduction itself, which in a
purely unconscious way prompts the animal, when it
begins to approach maturity, to form the reproductive
cells. These are the deepest of all these instincts, indeed
they are so deep that we know very little about just how
they work.

(2) The instincts connected with mating, which bring
the sex cells together so that they may unite.

(3) The instincts of caring for the offspring until it is
able to care for itself.

5. The Sex Instincts and Impulses. When minute
gametes are produced it is easy to see that it is something
of a problem to bring them together and cause them to
unite. The simplest instinct connected with mating is the
attraction exerted by one gamete on the other. When the
female gamete secretes substance in the water, the male

REPRODUCTIVE INSTINCTS 113

gamete is so sensitive to it that it at once responds, very-
much as a young animal swallows when food is in its
mouth. There is here something inherited in the nature
of the sperm that impels it toward the egg.

When one gamete comes to be formed by one parent
and the other gamete by a wholly different one, it is not
enough that the gametes attract one another. They are
so separated that neither can influence the other until
they are brought together. In order to bring the gametes
together, the parents must attract one another. Out of
this condition of different parents, carrying different kinds
of cells that must be brought together, we have arising
the selfish sex desires that lead to the attraction and
mating of the parents. These impulses are evidently felt
by many of the lower animals as well as by the higher.
They are usually stronger in the males than in the females,
and cause the males to seek out the females. They are
among the most powerful instincts known among animals,
and insure that the gametes will be brought together.

In connection with this purely mating instinct, we find
a number of others that are only indirectly connected
with mating. Such are the singing and acting instincts of
the male birds at the mating season; the actions of spiders
at the same period; the fierce fighting instincts of some of
the larger male mammals and of some birds; the instinct
of flight in the mating of the queen bee. Many other
similar phenomena might be mentioned.

6. Relation of the Sex Instincts to the Reproductive
Instincts. It has been repeated frequently that the whole
of reproduction is a process of sacrifice. It looks toward
the species. The instincts that lead to it may be fairly
described as unselfish, without implying that the organism
is conscious of it or deserves any credit for it. On the
other hand, the instincts of sex point solely to satisfying
selfish desires and appetites. They are like hunger and
thirst in that they involve satisfaction rather than
sacrifice. They are just as selfish as eating.

114 REPRODUCTION

7. The Tendency in Man. In lower animals and plants
there is no special tendency to abuse or over-use the sex
instincts. In man, on the contrary, just because we can
remember and think and anticipate gratification, men do
give way to these desires and impulses in ways that
animals do not. An animal that is not deprived of food
is not likely to overeat, though it may give nearly its
whole time to eating; so it is with its sex gratification.
Man, however, because he can dwell on the pleasures of
food, can talk about the things he eats, and can do various
things to make our food more pleasant, is constantly
falling into over-indulgence in the matter of eating. His
continued consciousness and imagination of the pleasure
is a temptation to him. This same tendency in man is seen
in gratifying the sex impulses, and some most serious
dangers to our society and to our morals and our
civilization are connected with sex.

8. The Need of Education. It has long been the custom
to say little to young people about the facts of sex and
reproduction. It has been felt that knowledge of these
matters might make more of wrong doing, but human
sentiment is changing with respect to this. It is coming to
be felt that young people will be helped and not harmed
by knowing the wonderful facts of reproduction.

You should know that the sex impulses are natural and,
if not wrongly used, build us up in all the qualities which
each sex admires in the other. But you should also clearly
understand that these impulses are selfish, and must be
self-controlled. They are in danger of leading us into
wrong that is likely to destroy health and morals, respect
for each other, self-respect, and happiness. It is certainly
true that instincts and impulses that have all these
possibilities of both good and evil can be better guided
and controlled if we know about them than if we are
ignorant. Nature has shifted the responsibility to us.

With his powers of reasoning and of imagination, there

REPRODUCTIVE INSTINCTS 115

has come to man responsibility for his own guidance. It

is these powers of reasoning and imagination which tempt
him to indulgences which are destructive. It must be the
same powers of reasoning and imagination which will
reveal to him that he must be his own master and control
his instincts. By reason he must judge which of his
feelings are good and which are bad, and by his will power
he must control his acts. Otherwise he travels a path
which leads to destruction.

It is surely true that instincts which have such
wonderful power for good or evil can be better controlled
and guided if we understand them than if we are
ignorant of their meaning. You have an instinct for
what is right as well as for what is wrong. Your happiness
and real success in life can be won only by standing
firmly by what you know to be right.

CHAPTER TWENTY-TWO.
HOMES AND HOME MAKING.

1. Homes and Homes. There are all sorts of homes
among animals, and it is necessary for us to try to define
what we mean by a home. Many animals burrow in the
ground or in wood or even in stone, and thus form a den
into which they may retreat as a protection. This is a
very simple kind of home, if we can call it a home at all.
The burrows of the earthworm or the mole or the
burrowing beetles illustrate this type of home. Some
animals make or find places in which they store food for
winter. We see this in squirrels, ants, etc. The desire for
protection and for storing of food is thus the motive for
home-making of a simple sort.

There is, however, another factor, which may be found
alongside these, that is more important than both of
these in insuring the making of homes. This is the care
and rearing of offspring. Many animals seek or prepare
a specially protected place in which they rear their brood.
Indeed so important is this factor that we can scarcely
give the name of home in those cases where young are not
cared for.

2. Homes for the Rearing of Offspring. We have seen
that increasing care for offspring tends to hold together
the parents while the young are immature. This is not
always true. Very often one sex is left alone to care for
the young, but usually where such instinct exists at all,
both father and mother give some attention to the young.

116

HOMES AND HOME-MAKING 117

This common tie inevitably leads to closer and more
permanent relations between the parents. We see this in
many birds. In most of the song birds those of a pair
remain faithful during the whole season; indeed in some it
seems that they are faithful through several years, or even
through life. The nest of such birds is a real, though
temporary, home in the very strongest sense of the word.
In those animals that have homes in which the young
are reared it is true, also, that there is a better opportunity
for the growth of the sympathetic instincts between
parents and offspring. The home becomes a center of
attraction. It is easy to see, therefore, that home making
for care of offspring is a great step in the development of
social instincts as against the purely selfish instincts.
Many illustrations might be mentioned, but it is among
the birds and man that we find this idea developed at its
best. In many species of ants and bees we have most
elaborate homes, but these are the homes of societies or
colonies rather than of families. Such social insects
illustrate a very striking form of home, therefore. The
termites, or white ants, most of the wasps, some of the
spiders, and some of the burrowing mammals as moles,
rodents, etc., extend the list of those animals that make
homes.

3. The Home Idea Among Men. The earliest traces
we have of hum.an homes on the earth are caves, which
man found and adapted to his needs. Later he made
excavations of his own in the hillsides, as did the cliflf
dwellers of the western United States. Thatched cabins
and other primitive forms of structure have been known
in all parts of the world. The physical structure of the
home, however, is not an essential. It may be a cave or
a tree or a hut or a palace — the biological facts underlying
it are the same. These facts are — protection from the
elements, and from wild beasts; defense from other men;
a place to keep food and other essential property; a

118 REPRODUCTION

place for sleep and rest and for companionship with
mates; conditions suitable for the protection and rearing
of the children.

From the viewpoint of these studies we are chiefly
interested in the home as one of the factors in human
mating and reproduction. This long period of helplessness
in the human child makes it essential that the parents
remain together and work more or less as a unit in the
task of care and education. As society improves and the
child needs to know more in order to succeed, this need
becomes still more real.

The increase in efficiency in homes makes it unnecessary
to produce so many offspring, since the better they are
cared for in the dangerous period of infancy, the more
will survive. Furthermore, those that do survive profit in
the effectiveness of their own life by the improved life and
attention of the parents.

4. Development of Marriage. The various kinds of
relations that have existed between men and wome^n in
what we know of human history are closely related to this
matter of homes. The mother who bears the children and
nourishes them in infancy is naturally the very center of
the home. The parental instinct is proverbially strong in
her. Primitive man resorted often to violence to secure
a woman for his home. She was kept in a sort of slavery
or serfdom. She bore the children and did much of the
work for their support. As time went on, all sorts of
experiments in sex relationship were tried by the human
race, depending on the supply of food and on the social
and moral advancement of the people. For example, the
race has tried several husbands for one wife (polyandry),
several wives for one husband (polygamy), one husband
and one wife (monogamy), capture marriages, marriage
by consent of parents, marriage by consent of mates.
political marriages, religious marriages, romantic or love
marriages.

HOMES AND HOME-MAKING .119

A great many biological as well as social and moral
considerations point to the permanent monogamous
marriage as the most successful possible solution of this
relation, from the point of view of producing and
protecting and educating offspring. This test is the real
final test of its rightness. True permanent homes are
essential to proper rearing and development of children.
Real homes cannot be developed other than by full
devotion of both parents to the task and to each other.

5. The Ideals of the Human Home. It is clear that a
real home means a permanent, faithful devotion of the
parents to the task of producing and rearing children. It
means that each must deserve and have the complete
confidence of the other. Such close relations demand
confidence. The welfare of the children equally demands
it. It is not enough that the mother should be faithful and
pure. It is just as bad and vicious for a man to be
unfaithful to this ideal of the home as it is for the mother
to be. Unless both are faithful, it is not possible to raise
children in an atmosphere of truth and social and moral
health.

To get right homes it is not enough that parents merely
be true to their home and to one another; they must
educate their children in the same ideals. One day these
children will be making homes of their own and it is very
essential that pure homes continue in the next and later
generations. Young people who are not pure and clean
before marriage are not true to this ideal of a home, for
neither a man nor a woman who before marriage indulges
in sexual intercourse can be an honest and perfect unit in
a home. This is condemned by our history, by our laws,
by morals, by religion, and by science.

6. Chivalry in Man. Men as a whole have not taken a
manly position in this matter of sex purity. Men have
said: "We insist that the woman we marry shall be pure
and clean; but it is not so bad for a man to be impure as

120 REPRODUCTION

for a woman to be. We, therefore, will allow ourselves
more freedom than we will allow to our wives and
mothers and sisters."

In the olden days it was the ambition of the real knight
to use every opportunity to befriend and aid and protect
the weak. The good old word chivalry has come down
to us from those times. There is no boy with the instincts
of a man who would not protect his sister or his
sweetheart from a licentious man. Any knightly man
would die to defend the honor of any woman who, in any
way, looks to him for protection. Does not this same
spirit say to us as young men that we in our turn will
protect every woman just as we would our mother or
sister, even from ourselves? Is it not a part of the honor
of every boy in school to protect the honor of every girl
in school just as though she were his own sister? Can we
really be men and do any less?

The purity and fineness of the families of the next
generation depend on the chivalry of the boys of today
and the purity of the girls of today. The quality of the
family life determines the whole social and moral structure
of the nation.

CHAPTER TWENTY-THREE.
GROWING UP.

1. In the Simplest Forms. Thus far we have spoken
about the process of reproduction and the work of the
parents. There is another very interesting side to the
matter. This is the growing up or development of the
young individual into the form of the parent.

In the simplest forms this has been seen to be a rather
easy thing. In the case of bacteria, or Paramecium, when
the parent divides, each of the progeny has to double its
size. In the bacteria this requires only a half-hour or so
under favorable conditions. In Paramecium it takes a
little longer. Where the parent differs from the offspring
only in size the problem is merely one of growth.

2. How About the Higher Organisms? When we come
to a higher plant or animal, in which there are numerous
different kinds of organs in the adult, we see that the
work of the embryo in growing up is very much
complicated. The one-celled fertilized egg has in it
absolutely none of the leaves and roots, or brain and
muscles and bones which the parent organism has. The
most marvelous thing of all to the biologist is that a cell
with nothing of any of these tissues or organs in it, with
only a little mass of protoplasm, can develop these
complex structures. The wisest biologist has no final
answer to this question, and yet every egg that develops
answers the question in its own practical way. Of course
the student sees that it is no answer to the question to say

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122 REPRODUCTION

that the egg inherits the power and the tendencies from
its parents. This only gives a name to the process. Where
and how do these powers and tendencies reside in the
embryo?

Development is much more interesting and difficult in
the higher animals and plants because it means a great
deal more than merely growing. It means becoming
different.

3. What is Development in Higher Forms? There are
three important elements in this mysterious process, and
while we cannot explain why it takes place by describing
these steps, it does make the process seem somewhat
clearer to us.

a. Growth. In the first place growth is important, as
it was in the lowly forms. Indeed the larger plants
and animals grow more in becoming mature than
the simpler ones. Often the increase is a million-
fold. The great redwoods of California, which
are among our largest plants, and whales, which
are about as large animals as have ever lived, arise
from eggs that require the microscope to enable us
to see them.

b. Cell Division. When a bacterium divides it makes
two bacteria, and thus the individual is kept small.
When the egg of a whale divides the daughter cells
remain together and we have a two-celled whale
embryo. These continue to divide, and since they
continue to remain together the embryo comes to
have more and more cells. This makes the
organism complex. As these cells grow it becomes
larger as well as more complex.

c. Differentiation. Growth and cell division are not
easy to explain, but the most difficult thing about
development is differentiation. This means that
these cells, all derived from one parent cell, are not
alike. They may seem to start alike, but great-
grand-daughters of the same cell may give rise to

GROWING UP - 123

cells as different as nerve cells, skin cells, bone

cells, blood cells, and many others.
The young of the higher plants and animals have a long,
difficult, and wonderful road to travel before they come to
be like their parents. It is "natural" for them to do it,
and we fully expect it to happen, but it is a marvel, none
the less.

4. Direct Developmient. The tgg of no one of the
higher organisms looks in the least like the parent. If we
take the chick, for example, the egg when fertilized has
no resemblance to the chicken. Yet when the chicken
hatches, in twenty-one days, the young chicken looks very
much like the adult. It still needs to grow, and to
differentiate a few things, like feathers, etc., before it is
just like the parent. Now if we go back in the egg to the
eighteenth or nineteenth day it still looked like a chick,
but a little less so. By studying it thus we can find that
it came very gradually to take on its likeness to the
parent. There- are no sudden or sharp changes in its
development. We call this sort of development direct.
This is a very common method of development. It is
found in mammals, in birds, in reptiles, in most fishes, and
in many lower forms.

5. Metamorphosis. Not all animals, however, develop
in this way. We have already seen in the frog that the
thing that hatches out of the egg does not look at all like
a frog. It must make more changes after hatching than
the chick does. This tadpole, which looks more like a fish
than like a frog, may grow as a tadpole and live an
independent life for quite a period before it begins the
changes that make it appear as a frog. We see it as three
different things: egg, tadpole, and frog. This indirect
development is called a metamorphosis. It differs from
the direct development in this: in a metamorphosis the
organism becomes like the adult by passing through one
or more somewhat sharp or sudden changes or stages.

124 REPRODUCTION

Between these points of sudden change there are periods
during which there is little or no change but growth.

Some of the most beautiful illustrations of metamor-
phosis in the growing up of offspring are found in the
insects. Very many of the insects undergo a profound and
striking metamorphosis. In the moths and butterflies we
have a story something like this:

(1) There is considerable food in the egg, and when
it hatches the animal that comes out is a small
worm-like object which we call a caterpillar
(larva).

(2) This feeds on leaves and the like and grows, but
remains a caterpillar for weeks or months, during
which time it stores up a large quantity of food.

(3) At the close of this period the caterpillar becomes
quiet and inactive, often secreting about itself a
protecting case.

(4) In this cocoon the whole structure is gradually
but profoundly changed within, though there is no
difference in the outside appearance of the cocoon.
Old organs are taken up by the blood and new
ones, suitable to the mature life, are developed
from the stored-up material. Wings, of which
there was no trace in the larva, long legs instead
of the poor, stumpy ones, and different eyes and
mouth parts appear.

(5) When this has all happened the changed animal
breaks from the cocoon in the adult form of the
butterfly. In this form it reproduces by eggs and
sperms, and mating takes place. Thus the cycle
is complete.

6. Possible Advantages in Metamorphosis. Without
doubt this round-about development has both its
advantages and disadvantages to the species, but on the
whole it looks as though it aids the process of successful
reproduction more than it hurts it. The adult butterflies

GROWING UP

125

are adapted to taking nectar from flowers. But their
caterpillars, which are able to eat voraciously of the
leaves of early spring, can get a much more successful
and early start than the nectar-living adult could do.
Furthermore, the adults of all such forms, flies, butterflies,
beetles, etc., appear full grown. They could not grow
except by moulting all the complex outside covering and

Figure 26. Stages in the life history of the Monarch butterfly. Above, at the
left, is shown a mass of eggs. These the mother usually attaches to the under side
of a leaf. From them the caterpillars hatch. At the right is shown the chrysalis
or cocoon stage into which the adult caterpillar is transformed. From this chrys-
alis the butterfly emerges.

its organs. It is economy therefore for them to do their
growing during the larval stages when they are simpler,
and moulting is more easy. During this time they store
up food enough to provide for the metamorphosis and the

126 REPRODUCTION

making of all the adult parts. It is possible therefore to
see that the metamorphosis may help make reproduction
and individual development more successful. It makes the
species rather more adjustable to the conditions of life.

CHAPTER TWENTY-FOUR.
THE RATE OF REPRODUCTION.

1. How Fast Must Organisms Propagate? Reproduction
is to keep the species going. To accomplish this, as we
have seen in former chapters, each pair must during their
life bring to maturity at least two individuals. If they
succeed in doing more than this the species increases in
numbers; if they do less the species diminishes. On the
average this is what each species does. Some may be
gaining, but if they do, it is probably at the expense of
other species. If a certain species of birds temporarily
increases in a locality, the insects on which they feed will
grow fewer there. On the other hand, if the birds
should decrease the insects are likely to increase. The
sum of life on the earth probably does not increase or
decrease greatly from generation to generation. Man, at
present, is increasing in numbers; and so, perhaps, are
those plants and animals that he cultivates for his uses.
But the forest trees, the wild plants, the song and game
birds, and the larger wild animals are decreasing with his
progress. Thus the total life remains about the same.

2. What Determines the Rate of Reproduction? How
many offspring a plant or animal must produce that two
may come to maturity will depend on the favorable or
unfavorable conditions through which the young must go
to reach maturity. Among these are the climatic
conditions which favor or endanger the young, the amount
of the food supply and the ease of getting it, and the

127

128 REPRODUCTION

enemies that prey upon the young. But most of all it
depends on the protection and care which the parents
give to their eggs and their young. How many must
be produced depends on such things as those just
mentioned. How rapidly the parents must reproduce in
order to bring forth this number will depend on the length
of life of the parents.

In general, we may say that the rate of reproduction
in any species that has stood the test of time and has
proved successful does meet these conditions. Those that
care for their young need not produce so many; those
that have few enemies need not produce so many. But a
pair must on the average produce rapidly enough, live
long enough, and care for their offspring enough to bring
two to maturity during their own life. Otherwise the
species is doomed.

3. Some Examples of the Rate of Reproduction. While
all organisms must thus produce more offspring than can
hope to survive, they differ greatly in the actual number
and in the rate of reproduction, because the other factors
enter in so differently. For example, an organism that
produces offspring which are large at birth, as the
mammals, do not meet so many failures in bringing
offspring to maturity as does a fern plant in which the
reproductive body is a small and delicate spore. In
general, there are two ways to increase the output of
offspring: either by more frequent reproduction, or by
increasing the number produced at a time, or by a
combination of these.

a. Bacteria. Some species of bacteria may divide in
half an hour. There are here only two offspring
resulting, but the divisions may come so frequently
that the bacteria multiply right up to the limit of
their food in a short while. Because of poisons
which they produce, and because the food at any
one place soon gives out, they are unable to keep

THE RATE OF REPRODUCTION . 129

up this rate long at a time. This rapidity of
reproduction is very valuable to them, since the
decaying food in which they thrive does not last
very long. This power enables them to make the
most of it. At this rate of increase, multiplying
by two every half hour, in one day it would
require twenty-eight figures to represent the
individual bacteria resulting from one parent; the
total would be two raised to the forty-eighth power.
Paramecium. Many of the one-celled animals live
on the same kind of decaying material as bacteria.
Some of them multiply at a rate nearly equal to
that in bacteria. Most, however, are not so rapid.
Paramecium, under favorable conditions, requires
from twelve to thirty hours to divide and grow to
maturity, but if its food held out and it could keep
up this rate, it would require only a few weeks for
the descendants of one Paramecium to make a
mass of protoplasm as big as the earth itself.

Ferns. The fern produces spores only once a year,
but it produces millions at each season. If every
spore out of a million should succeed in producing
one mature fern plant, on the tenth year we would
have 1,000,000 to the tenth power of new fern
plants, to say nothing of all the old ones that lived
over from previous years. A single fern plant
could populate the earth with ferns alone in a few
years.

The House Fly. Chancellor Jordan, of Leland
Stanford University, says concerning the reproduc-
tive power of this pest: "If all the eggs of a common
house fly should develop, and each of its progeny
should find the food and temperature it needed,
with no loss and no destruction, the people of a
city in which this might happen could not get away
soon enough to escape suffocation by a plague of

130 REPRODUCTION

flies." With the rapid rate of reproduction in flies,
one fly living all summer and producing a hundred
or more of eggs, and one-half of her progeny being
females, and coming to maturity in two weeks with
the same powers, the swarm of flies centering in
the city would overtake the fleeing man by sheer
increase in number.*^.

e. Sparrows. This is a bird rather more prolific than
is usual. It breeds several times in one season,
thus giving it the advantage over birds that nest
only once. If we start the season with one pair and
assume that they nest three times with four young
at each nesting, and live five years, and that one-
half are females, we can compute how many young
there would be in ten years.

First year 2 12 young 14

Second year 14 84 " 98

Third year 98 588 " 686

Fourth year 686 4116 " 4802

Fifth year 4802 28812 " 33614

And for the remaining five years each pair of these
would produce as many as this first pair.

The student may be interested to find how many
there would be in that time.

f. Man. Man produces much more slowly than any
of the forms mentioned. Physically it would be
possible for the healthy aboriginal man to reproduce

'about once in fifteen or eighteen months on an
average. Or during the possible reproductive

•period of about thirty years one pair might produce,

say, twenty offspring. Before the last one was
produced, the oldest would be in its reproductive
period, and thus the generations would overlap. As
a matter of fact, we do not find families of this size.
Marriages take place much later than the beginning
of the reproductive period. The lack of strength

THE RATE OF REPRODUCTION 131

on the part of civilized women, the trouble and

cost of rearing large families of children, the

impossibility of rearing that many children wisely,

and many other such considerations make it out of

the question for human beings to reproduce up to

the animal limit. Parents are not willing to make

this much sacrifice, and it would not be wise if

they did.

In new countries the average rate of increase in a single

generation is between three and four children to the family.

In old countries it is less, going down close to two

children for each family, or in some countries a fraction

less than two. This means gradual "race suicide," for a

species can not be kept going if a pair brings less than a

pair to maturity. Eet us assume the higher number for

the new country, or four children to each home. It is

clear that at this rate each generation doubles the native

population, and that if all the human beings lived, a very

few generations would stock the earth up to its utmost

limit of support. Some parts of the world, as the more

populous parts of China, seem to have reached this

condition now.

4. The Difference between the Rate of Reproduction
and the Real Increase. Any one of the species of plants
and animals would become a pest to us if they really
multiplied at the high rates indicated as theoretically
possible. The human race itself would soon find life
intolerable if it reproduced to its full limit. But no species
ever does. The winters and the drouths, starvation and
internal weakness and disease, parasites and other enemies,
— such things sweep off countless millions of all these
species. It is a great struggle that goes on all the time
among all the animals and plants that are born; for, in the
long run, if a million are produced by two parents, only
two can come to maturity. Many students think that it
is out of this severe struggle that improvement has come

132 REPRODUCTION

to plants and animals, for generally in the struggle the
weakest are destroyed and those survive that for some
reason or other are best adapted to all the important
factors in the environment. The rate of reproduction in
this way seems to be a matter of considerable value in
determining progress.

CHAPTER TWENTY-FIVE.
CROSSING BREEDS.

1. Reproduction without Union. In reproduction such
as fission in bacteria, budding in yeast, spore production
in molds, and stolons, buds, grafts, or tubers in the higher
plants, only one parent takes part in the formation of the
new individual. In such cases the offspring is likely to be
just like the single parent, because it is simply a portion
of it. The single parent stamps its nature most strongly
upon the offspring. It is frequently found that such stock
gradually "runs down" if continued indefinitely, as in the
case of Irish potatoes.

2. Union of Similar Gametes from the Same Parent.
In cases where one kind of gamete is formed and the union
takes place between cells that have the same parent, we
have two nuclei taking part in the union, but they, having
the same ancestry, are likely to be very similar. Never-
theless it appears that such a union as this tends to
restore and strengthen the vitality of the embryo, as
compared with organisms in which no union occurs. This
is known as self-fertilization.

3. Union of Unlike Gametes from the Same Parent. We
have seen that there are a good many hermaphrodite
parents, in which one parent produces both eggs and
sperm. The gametes are different, but the parent is one.
This is found, for example, in tapeworms, in earthworms,
in snails, in many plants. Doubtless self-fertilization
occurs in many of these cases. It is similar to the self-

133

134 REPRODUCTION

fertilization described in the preceding section, except that
the gametes are distinctly different, are formed in different
parts of the body, and their union introduces a little more
possibility of newness and variety in the result.

4. Union of Dissimilar Gametes from Different Parents.

While self-fertilization is possible in the case of some of
the animals and plants which produce both kinds of
gametes in the same parent, it is not the rule. In a form
such as the earthworm or snail there are interesting
adjustments that tend to prevent the sperm of one animal
reaching and fertilizing the eggs of the same animal. In
both of these cases, when copulation between two animals
takes place, each animal transfers sperms to the other, and
later the sperms are brought into union with eggs of other
parentage. This is cross-fertilization. But the most
common and sure kind of cross-fertilization in the animal
kingdom is in the mating of parents which produce only
one kind of gamete, exclusively male parents mating with
exclusively female parents. In such case cross-fertilization
is insured by making self-fertilization impossible.
Separate maleness and femaleness is a device which
insures cross-fertilization.

In the common seed-plants we have something quite
similar. Most of the plants produce both kinds of spores
in the same flower, and if the sperms produced by the
pollen of a flower fertilize the eggs produced by the
gametophytes in the ovary of the same flower, we might
call it self-fertilization. We call it self-pollination, when
the pollen of one flower acts on the pistil of the same
flower. Self-pollination, however, seems to be the
exception in higher plants rather than the rule. Just as
in animals, there are many devices which prevent self-
fertilization, and secure cross-fertilization. In plants
there is a most wonderful series of adaptations tending to
insure cross-pollination and to discourage self-pollination.
Sometimes, as in the gametes in animals which have

CROSSING BREEDS 135

separate sexes, a flower produces only pollen or only-
ovules. In other cases, as in the hermaphrodite animals,
the two kinds of gametes in an individual flower do not
ripen at the same time. All of these facts show that nature
appears to favor cross-fertilization over self-fertilization.

5. Evidence from Experiment. Charles Darwin was the
first to prove by actual experiment that cross-fertilization
has, at least in some forms, advantages over self-
fertilization. He took plants of one species and subjected
them to the same general conditions. Some he forced to
be self-pollinated if at all. He cross-pollinated others. As
a result he found that those that were cross-pollinated set
more seed, the seed weighed more, and the plants coming
from them were more thrifty, on the average, than those
produced by self-pollinated flowers. Other observers have
found the same thing to be true. There is thus some
advantage in crossing plants and animals, and the devices
that we have seen that aid in crossing are expressions of
this advantage. Some plants, however, seem to do quite
as well with self-fertilization as with cross-fertilization.

6. Why is Cross-Fertilization Advantageous? This
question is not easy to answer. We have not yet reached
the place where the biologist can say just what is gained
by mixing different strains in this way. It seems in some
way related to this mingling of protoplasms, nuclei,
and chromosomes, which have different history and
composition. It is possible that new and different
protoplasm coming in from the outside sperm is more
stimulative to the ^gg than that from the same parent. It
seems also that there is more chance for variety in the
offspring when two different strains are mixed than when
both cells are of the same strain.

From this last mentioned fact, whether or not this can be
regarded as an advantage to the plant or animal species,
we can readily see how it is of advantage to man. By
crossing different apples, or peaches, or daisies, or cattle

136 REPRODUCTION

and hogs, we get new strains. Sometimes these are of no
value, sometimes they result in a mingling of the charac-
ters of both parents, and sometimes they give a result
decidedly more perfect for our uses than either of the
parents. Very much of the improvement in most of our
cultivated animals and plants has been possible because
of this mixing of breeds, together with the selection of
what suits us best out of the results.

7. The Limits of the Crossing. We have seen that in
mingling gametes there seems to be some advantage in
having the gametes different, as in male and female
parents. Where nature lays so much emphasis we have
come to feel there must be something worth while. There
is, however, a limit to the difference that is possible in
gametes and in parents. If we select parents of different
varieties, or particularly of different species, the offspring
are quite certain to be different from either and often are
not so good as either.

The following rules may help the reader appreciate this:

a. The more different the parents are the less likely
their gametes are to unite. We may cross different
species of lilies or different species of roses, but we
cannot cross lilies with roses.

b. If fertilization succeeds, the more different the
parents are, the more likely is the offspring to be
imperfect. For example, we can cross the different
varieties of horses readily enough. We can also
cross the horse with the ass, and the result is the
mule. The mule has qualities that make it a better
animal for some human uses than either the horse
or the ass. The mule, however, is entirely unable
to breed. It cannot breed with either parent or with
other mules. Its gametes seem to be imperfect.
The horse and ass are of different, but related,
species. The individual plants or animals which
result from crossing different species are called
hybrids. Hybrids are not all sterile, as is the mule.

CROSSING BREEDS 137

In the human race the different varieties may cross. It
seems that there may be some gain in the crossing of
peoples nearly akin, as the English, German, French, etc.,
who are all branches of the Caucasian stock. The mixture
of these different, but kindred, types often produces
valuable results. There is, however, considerable evidence
for the view that crossing the different races, as negroes
with Indians, and negroes with whites, gives offspring
more of the nature of hybrids; and while they are not
necessarily infertile, they do not seem to have the vigor
of the original stocks.

CHAPTER TWENTY-SIX.
THE END OF THE CIRCLE.

1. Our Circuit. We have been studying in these
chapters one of the most wonderful of the many remark-
able things about life. I wonder if I have made it so that
you understand and appreciate it? I hope you may do
both. We have seen how reproduction thwarts death.
The parent would surely die sooner or later, but by
dividing it saves the species and makes itself immortal.
Gradually the process becomes perfected so the parents
live longer side by side with their offspring.

We have seen how the increasing helplessness of the
offspring makes the care of the parents more and more
necessary, and how this in turn binds the mates together
in the necessary task of caring for the young. This makes
home possible, and develops sympathy and love and the
finer qualities of sacrifice. The home relations become
more and more important, until, in humans of the more
advanced races, the home is looked upon as the very
picture of what human society ought some day to
become — a great family.

We have seen how family relations have built up in the
best men and women a sense of respect and chivalry; how
self-control is coming gradually to dominate the primitive
animal sex-qualities; how the mental and spiritual appre-
ciation of husband and wife for one another enlarge and
enrich and refine their lives more than any single factor in
all our conditions.

138

THE END OF THE CIRCLE . 139

We must appreciate that anything that has belonged in
this way to all life from the beginning, that has aided
evolution so much, that has itself unfolded and improved
so greatly, must be of great consequence in life.

It is because of this importance that this little book has
been written. All of us know about reproduction; but
often we do not stop to appreciate its beauty and import-
ance in human development. It means much more in
human life than anywhere among the animals.

In our study we have come around to ourselves. What
does all this mean to us? This is the important thing.
This is the end of all our circles.

2. Yourself. — I am thinking now especially of the young
people v/ho have been reading this little book. You are
yourself still near the beginning of the wonderful cycle.
It often makes us feel very small and unimportant when
we study the great facts of nature, but it is inspiring to
know that we ourselves are links in nature's endless chain.
Of course each of us may end the chain, but if we normally
perform our part in the cycle we are a part of this
immortal stream of life. In continuing it we can add to
it or subtract from it.

It is certainly a proper part of the ambition of every
person, if one is normal in body and mind, to continue the
good strains of inheritance that have come to him from
ancestors. The fact that you are alive now is proof that
the chain has been unbroken in your case for untold
ages. In order to make you, there have been all these
successions of individual, selfish upbuildings alternating
with unselfish division and sacrifice of parents; all this
crossing of strains; this manifold care of parents for
offspring; the weeding out of misfits and the saving of
fit; this marriage and building of homes; this developing
of fine ideals of sympathy, devotion, and self-control —
all these I say have been preserving and piling up and
mixing the characteristics that your friends call you. In

140 REPRODUCTION

one way or another you owe all your capacities and
powers to this wonderful thing we have been reading
about. If you are well and strong and normal, you have
blessings you cannot properly measure.

We human beings have come pretty generally to feel
that all such blessings and powers carry with them some
obligations. We say of a young fellow who inherits from
his parents property and a good name, and then through
recklessness or incompetence squanders both, that he is a
spendthrift — ungrateful and degenerate. What shall we
say of boys and girls who are the "heirs of all the ages"
in these finer human capacities, and who so barter them
that they are not carried on to future generations? The
whole race is robbed.

You then owe at least two things to society: (1) to give
your best qualities a chance, and (2) to try to see that
those who represent you in the next generation are the
best possible, and have the best possible chance.

3. The Lower and Higher Qualities in Sex and Repro-
duction. In this discussion we have been trying to make
clear that everything about reproduction is natural and
with meaning. The divisions, the unions, the attractions,
the impulses and desires, the satisfactions, the unselfish
care given by parents, these are all a part of it, and are all
sound and natural. You should know about them, and
they must be kept natural. But all the natural things
about reproduction and sex are not equally important to
us as humans. The mental and spiritual and social
states which we have developed in connection with these
things are even more important to us than reproduction
itself. The worst thing that could happen to us is that we
should be like the lower animals in reproducing. We
humans have all the lower qualities that the animals have,
but we have developed the power of controlling and
guiding these impulses of ours in loftier ways. Mating
means to the lower animals certain instinctive desires and

THE END OF THE CIRCLE 141

gratifications. With us it means marriage, faithfulness to
one another, the building of a home through sympathy,
mutual unselfishness, and helplfulness. In the lower
species the males often instinctively protect their females
and young in an emergency. So do we, but in addition we
feel that men should always protect and help and cherish
children and women. We feel that a man who is not thus
chivalrous is not quite a gentleman. In animals, the parents
instinctively guard and feed their offspring, but with us
the real mother and father do not only do this but help
the children get their education, try to provide for their
future, nurse and care for them when they are sick, sym-
pathize with them in their difficulties, give their very lives
for them in many ways. Courtship among the higher
animals is an instinctive and passionate series of ap-
proaches culminating in mating. With us the earlier
years of young manhood and womanhood are full of fine
friendships and companionships in which our minds and
spirits are developed in some of the finest ways we know,
and the period of courtship itself is full of high ideals and
devotions that make it one of the most charming times of
our lives in and of itself.

So what I want you to feel is this — that because men
and women control and guide and spiritualize these feel-
ings and states that belong to reproduction and sex, we
have built up around them a whole realm of human inter-
est and a portion of our personality that inspires all good
people more than the facts themselves. This is shown in
our finest poetry and other forms of literature dealing
with the love that exists between men and women.

4. Sex and Society. Much of the structure of our
modern society depends on our need of food and other
comforts. Thus our farming and the transportation and
distribution of crops is built up around the need of food;
our stores, manufactures, banks, and the industrial system
generally relate to food, the need of clothing, and the

142 REPRODUCTION

other comforts of life. But beneath all of this and equally-
important with the other needs is the need of reproduc-
tion and mating. This is what makes the home as we have
seen, and it is on the home and the family that our
modern society rests.

The monogamous home, where one man and one woman
live faithfully together and rear their children in sympathy
and sacrifice, this is the cornerstone of the particular form
of society that we know. No other forms of mating will
give us the home as we know it, nor society as we have it.
There are of course still many crude and wrong things
about our homes and our society, for we are still selfish
and animal in many ways, but we are sure that no other
form of marriage would furnish so good a means of rear-
ing children and of giving them a permanent home and a
start in life — and this is the prime work of society.
Possibly this little book has helped you appreciate how
much of your own happiness and chance you owe to the
principles we have studied. Surely then you will strive
to do your full part to keep the stream of life clear and
pure for your own sake and for those who are to come
after.

INDEX

Adjustability, 5.

Alg-ae, 12, 28, 30, 31, 50, 72, 79

Alternation of generations, 58,

78, 79, 104.
Antheridium, 67, 74.
Aphids, 86.

Archegonium, 67, 74. 75.
Artificial fertilization, 65.
Assimilation, 10.

Bacteria, 17, 128.
Bee, 84.

Beginnings of life, 2.
Birds, 93.
Budding, 26.
Buds, 20.

Capsule, 75.
Cell, 15.

Cell division, 122.
Chlorophyll, 50.
Chromatin, 55.
Chromosomes, 55, 81.
Cilia, 30.
Circle of life, 1.
Cloaca, 95.
Cncnon, 124.
Coelenterates, 82.
Coluny, 22.
Conjugation, 48.
Copulation, 95, 98.
Cross fertilization, 134.
Crossing breeds, 133,
Cytoplasm, 55.

Darwin, Charles, 135.
Death, 6.
Determiners, 64.
Differentiation, 90, 122.
Differentiation of sex, 68, 96.
Direct development, 123.

Earthworm, 68.
Eggs, 53, 60.
Embryo, 89, 95, 98.
Environment, 7.

Female characteristics, 69.
Ferns, 72, 129.
Fertilization, 54, 59.
Fission, 20.
Flagellum, 57.
Flower, 102.
Fly, 129.

Foot of moss, 75.
Frogs, 88.

Gametes, 49, 98.
Gametophyte, 58, 75.
Gemmae, 26.
Genetics, 64.
Germination, 31.
Grafting, 26.
Growth, 2, 122.
Growth of plants, 2.

Habit, 112.
Hermaphrodite, 66.
Homes, 116.
Honey bee, 85.
House fly, 129.
Hybrids, 136.
Hydatina, 85.
Hydra, 23.
Hydroids, 40, 82.

Immaturity, 3.
Instinct, 112.
Internal cell division, 27.
Invertebrates, 88.

Jelly fish, 82.
Jordan, D. S., 129.

Larva, 4, 124.

Mammals, 97.
Man, 97, 130.
Marriage, 118.
Marsupials, 99.
Maturity, 4.
Megaspore, 105.
Metamorphosis, 123.
Milk, 100.

Monarch butterfly, 125.
Monogamy, 118.
Mosses, 72.
Mule, 136.

Nucleus, 55.

Oedogonium, 67.
Old age, 5.
Oogonium, 67.
Ova, 57.
Ovary, 67.
Oviduct, 94.

143

Paramecium, 51, 129.
Parasites, 17.
Parental care. 108.
Parthenogenesis, 84.
Petal. 101.
Pistil, 101.
Plant lice, 86.
Pleurococcus, 12.
Poisons, 5.
Pollen, 101.
Pollination, 102, 134.
Polyandry, 118.
Polygamy, 118.
Potato, 41,
Prothallia. 76.
Protonema, 73.
Protoplasm, 15.

Race suicide, 131.
Rate of reproduction, 127.
Reduction, division, 57, 81.
Reproductive instincts, 11.
Resting spores, 32.
Rhizoids, 76.
Root tip, 3.
Runners, 38.

Salmon, 46.
Self-fertilization, 133.
Self-pollination, 134.
Sepal, 101.
Seta. 75.

Sex, 58.

Sex dimorphism, 69, 71, 96.

Sparrow, 130.

Spermary, 67.

Sperms, 53, 57, 74.

Spirogyra, 50.

Spores, 27.

Sporogonium, 76.

Sporophyte, 58, 75.

Stamen, 101.

Stigma, 101.

Stolon, 38.

Strawberry, 38.

Tadpole, 90.
Testis, 67.
Tubers, 40.

Ulothrix, 28, 48.
Uterus, 98.

Vagina, 98.
Vaucheria, 67.
Vertebrates, 88.
Vivipary, 86.

Walter, H. E., 64.
Wheat rust, 30.

Yeast, 21.

Zoophytes, 24.

144

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146

SCHOOL SCIENCE SERIES, NUMBER FIVE

Involution, Heredity, and
E.\igenics

By JOHN MERIvK COUIvTER. Ph. D.

Head of the Department of Botany

University of Chicago

This little book is the result of an expressed need on the
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147

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9 Evidences of Natural Selection.

10 Objections to Natural Selection.

11 Mutation.

12 Objections to Mutation.

13 Orthogenesis.

14 The Problem of Heredity.

15 Machinery of Heredity.

148

16 Some Facts of Heredity.

17 Methods of Plant Breeding.

18 Results of Plant Breeding.

19 The Evolution of Non-Vascular Plants.

20 The Evolution of Vascular Plants.

21 The Beginning of Animal Life.

22 Appearance of Air-Breathers and Vertebrates.

23 The Evolution of Various Organs.

24 Reptiles, Birds, and Mammals.

25 Eugenics.

26 Lessons from Evolution.

Cloth bound, 144 pp. Illustrated. 50 cents.

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Bloomington, 111.

If, IT^-U

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