Part 5

But perhaps the amœba has an unsocial nature and does not care whether it is recognized or not.

Because it changes its shape so often the amœba has received its pretty name. For “amœba,” you must know, comes from a Greek word meaning “change.”

It is sometimes called “Proteus” for the same reason. Of course you know all about Proteus, the sea god who lived at the bottom of the ocean and paid homage to the great god Neptune, who was ruler of the seas. Proteus took care of the sea calves, and he had a queer way of changing his shape whenever he chose. He used to go to sleep on the rocks while the calves were sunning themselves, and because he was very wise and could help people who were in trouble, they used to go there and catch him. But he was not as friendly as he was wise, and would never tell anything unless forced to; and when he found himself a prisoner, he would at once change his form, and so try to escape by frightening his captors. He had a pleasant habit of all at once changing into an enormous serpent and opening a mouth full of frightful teeth; then, if _that_ did not frighten badly enough, he would all at once turn into a bull or a raging fire or a fierce torrent. He has been known to change into a dozen dreadful things in as many minutes, so no wonder his name has come to mean “something that changes.” And no wonder the amœba is called “proteus,” not that it indulges in any such outrageous transformations as the sea god, for it never does anything worse than change the shape of its own little jelly-like body.

Although it can move along, I do not think it would amount to much in a race, as it only moves a few inches in the course of a day; still that is a good deal, considering its size.

A great deal depends upon size in this world.

You could go as far in ten seconds as a snail could in as many hours. The distance would not count for much as far as you are concerned, but it would be a good day’s work for the snail. So when an amœba travels a few inches, that counts for as much in its life as a long day’s walk of a good many miles would in yours, or as a few hundreds of miles on a railway train.

The amœba can do more than travel. If you touch one it will shrink together, showing that this little bit of protoplasm has a sort of _feeling_ power.

When it is hungry it eats. For an amœba can get as hungry as anybody.

Hunger does not depend upon size. You can get as hungry as an elephant, although you cannot eat as much. You would starve to death, too, as soon as an elephant, perhaps sooner. An amœba no doubt gets as hungry as you do, and it certainly would starve to death if it did not have something to eat.

How can it eat without a mouth? Just as easily as it can travel without feet. You do not know protoplasm if you think it cannot eat when it is hungry. Very likely the reason it travels about is because it wants to find something good to eat. It does not care for roast turkey and cranberry sauce, nor for apple pie and plum pudding.

_That_ is not what it is looking for. It is looking for some tiny speck of food smaller than itself.

It lives in the water, of course. It would dry up if it were out in the air. You should think it would _melt_ in the water? Well, it does not, any more than a jellyfish melts. When it comes to some little speck of dead plant or animal, or, for all I know, to some living speck small enough, it proceeds to eat it.

It glides over it in the way you know about, and wraps the food speck up in its body. Then it draws out all the good part of the food into its own substance and goes on, leaving behind the waste particles.

Do you not think that is a good deal for an amœba to be able to do? But it can do more than this; it can divide itself in two and make two amœbæ out of one.

The little amœba is called a “cell.” After awhile you will see why. The whole amœba is just one cell.

As to whether it is a plant or an animal you will have to ask the amœba, for I cannot tell you. Some think it is a plant and some say it is an animal.

I do not think it makes much difference which you say it is.

A bit of protoplasm living by itself is called a “cell.”

Many plants and animals have, like the amœba, only one cell. Very often the little one-celled being has a thick outside wall. The protoplasm changes part of the food into a hard substance, that is, it builds itself a wall.

Very often cells live together in colonies instead of living alone. In such cases, the first cell divides into two cells, but the two stay together instead of entirely separating. Then each of these two cells divides again, and the four cells stay together, and so it goes on until a large body is built up of many cells.

The truth is, plants are only collections of cells which have agreed to work together. Where there is but one cell, it has to do all sorts of work; but where there are many, some do one kind of work, some another,—just as Robinson Crusoe, living all alone on the island of Juan Fernandez, had to do all sorts of things for himself: make his own shoes and clothes, get his own food and cook it, build his own house, and gather his own wood. But in a town one set of men makes shoes, another chops wood, another raises vegetables and grain, another grinds the grain, and another bakes the bread; then they all exchange with each other, and everybody has enough—or ought to have.

So in the plant made of many cells. One set of cells makes hard walls to protect the plant. Another set draws up water from the earth for all the cells in the plant, for living things require a great deal of water. Another set takes gas from the air and changes it into food. Another set makes tubes for the sap to flow through. Other sets do other things. Each set of cells does something for the whole plant.

If you look at a leaf or a bit of skin from a stem under a microscope, you will see they are built up of cells, as a house is built of bricks. Only the cells are not placed regularly like the bricks in a house, and they are not solid like bricks. The walls of these cells are sometimes hard and sometimes soft, sometimes tough and sometimes tender; but the walls were all built by the protoplasm that lived in them. Sometimes the protoplasm leaves the little house it has built and goes somewhere else.

Then the empty, wall-surrounded space is left like a cell of honeycomb before the honey is put in, or an anther cell after the pollen has fallen out and left nothing in it.

Before microscopes were as perfect as they are now, these empty spaces with their surrounding walls were discovered. Even where the cells contained protoplasm the microscope was not strong enough to reveal it, so only the cell walls were seen.

It was soon known that plants were built up of these little compartments, and because they resembled cells in being small and shut in by walls, they were called “cells.” After awhile it was discovered that the living part of the plant was the colorless, jelly-like protoplasm which lived in the cells. Yet later, particles of wall-less protoplasm were found building up plants and animals. What were these soft little protoplasmic atoms to be called?

The plant was really built up by them, and only part of them had walls, so they were called by the name the people had already given to the walled spaces which they supposed built up the plant, and so got the name of “cells,” which is not at all an appropriate name.

There is nothing quite so easy as to be mistaken, you see, and the botanists, having seen that the plant was built of little compartments, and never suspecting the presence of the living protoplasm lurking in some of them, had called the compartments “cells”; later, when the protoplasm was discovered to be the real builder, the old name was kept. So you see how the amœba came to be called a “cell.”

There are a great many different kinds of cells in one plant.

But every living cell has very much the same powers as the amœba, though in many of them some one power is developed at the expense of all the rest. In this way different sets of cells are able to perform different kinds of work, and do it very well indeed.

The amœba is not the only single-celled creature. There are a great many different kinds of single-celled plants or animals, and some of them take very curious and beautiful forms, with streamers floating about them.

Such are not protean, like the amœba; they do not change their shapes.

Plants are not the only things that have cells. Animals, too, are built up of them. Animal cells are usually softer than plant cells, because they very often have no hard walls. Bone cells of course have hard walls, and there are others, but most of the animal cells are without walls.

So you see all living things are built of cells, and the living part of the cells is the protoplasm.

You yourself are built up of millions of cells, and without the help of protoplasm you would not be living, for protoplasm made your cells, and protoplasm is the only thing in you that is alive. Your muscles are made of muscle cells, and the protoplasm in them moves, and when the muscle cells all move together, that moves your arm or your leg or your head or some other part of your body.

Since your muscle cells devote themselves to moving, they do not try to do much else; so other cells digest the food which the blood carries to the muscle cells. Yet other cells build a good thick skin to protect the soft muscles, and yet another set of cells _thinks_ for the muscles, and tells them where and when and how to move. Each set of cells has its own work.

Your brain is made up of nerve cells, and the protoplasm in them in some way enables you to think and feel. Your bone cells are hard and resisting, your sinew cells strong and flexible. So each part of your body is made up of different kinds of cells.

But what has all this to do with football and parties and picnics you would like to know?

Why, a great deal, to be sure. If it were not for cells and protoplasm there would be no people.

And how could you have football games and picnics without people, _I_ should like to know?

POLLEN CELLS.

In the dark little dungeon cells of the anthers, the pollen grains lie. Hundreds, and sometimes thousands of them, are packed in there as closely as they can be. But they do not mind it, not in the least. They grow and get ripe, and as soon as this happens, their prison door opens and out they pour.

They are funny little things, not at all what they seem to be. For you would think they were just little specks of dust of almost no shape at all. But that is your fault, or rather the fault of your eyes.

You see your eyes were not meant to look at things so tiny as pollen grains. You can see a common ball or even a small shot very well indeed; but when it comes to pollen grains you are as blind as a mole. You will have to put on your spectacles to see _that_, I can tell you, and very powerful spectacles they will have to be, too. The best spectacles for you to look through are the ones we call a microscope. Just put your eye to that tube and you will see what you will see, for there are pollen grains at the other end—pollen grains from several kinds of flowers; there are some in the corner from our friend the morning-glory. And now you know what I meant when I said you could not see a pollen grain; for those little specks of dust have all at once become large and important objects. Some are round and some are not, and all are creased or pitted or ridged or covered with little points or marked in some other way. Now you see why they stick so easily to the hairs on the bee or the butterfly or whatever comes visiting the flowers for nectar. They are not smooth, but all roughened over by these ridges and points.

And this is not the end of it. You have not yet seen a pollen grain. You have only seen the outside of one.

For it has an inside. You think it is too small to have anything inside of it?

I can tell you things _much_ smaller than that have something inside of them. The truth is, these things seem so small because we are so large. If we were as small as they, they would not seem small at all. They would seem a very ordinary size indeed, and we would expect them to have an outside and an inside.

The truth is, pollen grains are hollow. They are as hollow as the baby’s rubber ball. But they are not _empty_. The baby’s rubber ball is not empty; it is full of air. These pollen grains are not full of air. If you were to see what is in them, you might not think it very important, but that would be a great mistake, for they are full of—protoplasm!

The truth of the matter is, the pollen grain is a _cell_; it has a wall outside and is made of protoplasm inside.

Protoplasm, you remember, is the material out of which every living thing is made. You are made from protoplasm yourself; flowers are made from it, too, and leaves and birds and _everything that lives_.

So you see if a pollen grain is filled with protoplasm, that is rather a serious matter.

This pollen grain, small as it is, has a tough outer skin. It is not as tough as leather, but it is tough for so small a grain, and is strong enough to keep the protoplasm from running out.

The protoplasm in the pollen grain is what the ovule needs to nourish it and make it able to grow. The ovule, too, is a cell filled with protoplasm, and the protoplasm of the pollen and of the ovule must somehow come together before the ovule can do any more growing.

You know how the bees and butterflies and all sorts of insects carry the pollen from flower to flower and dust the stigmas with it. You may think that when a pollen grain is safely landed on a stigma then the rest is easy enough. But if you suppose the pollen grain can pass through the style you are _very_ much mistaken. It cannot even pass through the stigma. It is true, the tissues of both style and stigma are rather loose, and that the style is sometimes hollow. But, as far as I know, the pollen _never_ passes through. Small as it is, it is too large to get through the tiny openings in the stigma, and then, you know, the stigma is sticky and holds it fast.

Here is an interesting state of affairs! The ovule cell is waiting for protoplasm, and the pollen cell is anchored safe and fast at the stigma.

But you may be sure there is a way out of this difficulty.

To begin, the pollen grain has two coats, a tough outer one and a delicate inner one. There are openings, or at least weak places, in the outer coat, and after the pollen has lodged on the moist stigma, the protoplasm inside swells and comes bulging through these weak places. The inner coat is forced out, as though some _extremely_ small fairy had stuck her finger through the wall from the inside and pushed out a part of the inner lining. Well, this finger-like part that comes through the wall does not break open, but begins to grow. It grows longer and longer until a tube is formed, a tube so small that only the microscope can enable us to see it.

This tube pushes its way through the stigma into the style; there it continues to grow like a long root, only it is _not_ a root, and it is hollow; and the protoplasm from the inside of the pollen grain runs down this tube.

You can guess what happens next. The tube grows and grows; it finds plenty of nourishment in the tissue of the style, which is made of material suitable to feed it. Of course, it grows down the style into the ovary, because the style opens into the ovary.

When it reaches the ovary it finds its way to an ovule, and goes in at a little door which the ovule keeps open for it.

Now, you see, there is an open path between the pollen grain and the ovule, and the protoplasm from the pollen grain which has run down the tube enters the ovule. Here it passes out of the tube by breaking through the delicate wall, and unites with the protoplasm of the ovule.

Thus the ovule is fertilized. It is nourished and strengthened, and at once begins to grow into a seed.

Meantime the shell of the pollen lies on the stigma, a little dried-up, empty thing. Its work is done. Thanks to the bee or the butterfly or some other flower-loving friend, it has been taken to the right place, and all that was living in it, its protoplasm, goes on living in the little ovule.

The pollen grains the bees carry home have a very different fate. They are crushed and soaked and kneaded with honey and fed to baby bees.

But the flowers are willing the bees should have some to live on, and so each flower makes thousands more than it needs. You see, if it did not give the bees something to eat, they would not come and they could not live on honey alone; they, too, need the protoplasm in the pollen to nourish them.

Some kinds of flowers use their own pollen. They do not need the bees and do not want them. So they keep their pollen shut up tightly and do not make any honey to coax the bees to come. But nearly all flowers wish to have other pollen than their own. And this they can only get by the help of other people’s wings, as they have none of their own.

THE POLLEN.

What does the pollen do?

It helps the ovule change to a seed.

It feeds the bees and the wasps and the flies.

But above all, it helps the ovule change to a seed.

THE ANTHERS.

Anthers, anthers, full of pollen, Cunning cupboards of the bee, Stamen flour amply hiding, What have you for me, for me? What have you for me?

Pollen have I, plenty of it, Pollen for my darling bee; Pollen every day I blossom For my bee, but none for thee, For thee, none for thee.

OVULE CELLS.

You will be glad to know that the little ovules at the heart of the morning-glory and of all other flowers are single cells.

They have an outside wall and are filled with protoplasm.

When a pollen cell is formed from the inside of the anther, it separates and is no longer connected with anything. This is not the case with the ovule. It is fastened to the ovary by a little stem, for it will stay there and grow; and it must have a way to get food from its parent plant. It gets the food through this little stem.

You know what happens when the flower opens.

The bees bring pollen, and the protoplasm of the pollen joins that of the ovule. As soon as this happens the ovule begins to change. We say it _grows_. It gets the food to grow on from the mother plant through the little stem which is fastened to the inside of the ovary.

The protoplasm in the ovule first divides and makes two cells instead of one. These two cells do not entirely separate from each other. They stay together to do their work. Soon each of them divides into more cells. These cells again divide, and this continues until a great many cells are formed. Meantime the ovule has increased in size as well as complexity, and its cells do several different kinds of work. In the morning-glory, for instance, some build a hard outer wall about the young plant; this is the seed-case. Other cells form two little leaves; others make a little stub of a stem. So the change goes on until the single-celled ovule becomes a many-celled seed with a young plant rolled up under its walls. If you open a morning-glory seed you can see this little baby plant, only you will have to soak the seed first to soften the food that is stored about the young plant.

The cells made this food to nourish it, and it stays dry and hard until the rain moistens it in the spring, when it gets soft, like boiled starch, and is then ready for the little plant to use. When the ovules grow on one plant and the pollen comes from another, the seeds will contain the protoplasm of two different plants.

Now protoplasm remembers the plant it came from, and tries to make the new plant like it.

The ovule protoplasm tries to make the seed remember the plant it grows on, and the pollen protoplasm tries to make the pollen remember the plant it comes from.

So if the pollen comes from a plant bearing white flowers, it wants the seeds to grow into white-flowered plants. But if the ovules which fertilizes it grow on a pink-flowered plant, they try to make the seeds grow into pink-flowered plants. Now what happens? Very likely some of the flowers will be white and some of them pink. Some will take after the plant the pollen came from and some after the one the ovule came from. But sometimes the flowers will be a mixture of both plants and will be pink and white.

The ovule is the mother part of the plant and the pollen is the father part, and sometimes the seed-children take after the mother, sometimes after the father, and sometimes after both.

This is very strange and we cannot quite understand it. How can the protoplasm remember the exact shade and color of the plant it came from? How can it make seeds that grow into plants just like the old plants?

Protoplasm, you are a great, a very great mystery!

By knowing about pollen and ovules we are able to help form a great many lovely new flowers and fruits.

We get variegated flowers by fertilizing a flower of one color with pollen from a flower of another color.

When we do this we must cover over the plant with a piece of netting just before it blossoms, so the bees and butterflies cannot get ahead of us and fertilize the plant. Then we must put a bit of pollen from one flower on the stigma of the flower we want to experiment with.

We must always use the pollen from the same kind of a plant, however.

It would be of no use to put nasturtium pollen on a morning-glory stigma, for instance, for it could not affect the ovule in the least. The protoplasm knows in some way its own plant and will not fertilize any other.

This is a very good thing, otherwise we might have a funny mixture of all sorts of plants.

Many delicious fruits have been produced by fertilizing one plant with pollen from another.

New varieties of grapes and berries are constantly obtained in this way.

If you live on a farm or have a garden, you might try to develop some new kinds of berries or fruits. You might not succeed, but it would do no harm to try.

CHLOROPHYLL.

Chlorophyll is plant green.

That is what the word means.

We are so used to seeing green leaves that we think very little about it.

It probably never has occurred to most of us that the green coloring matter of plants can be of much importance. Yet it is one of the most important things in the world.

Like many other things, it is not what it seems. It is not merely a dye as one might suppose, but much more than that.

We cannot really see what it is without a microscope, and when we look at a piece of green leaf through the microscope we are surprised to find the leaf is not green at all.

It is colorless like glass, but in the cells just behind the skin cells we see little roundish green bodies packed away. These are the chlorophyll grains, and when there are a great many of them close together they show through the skin and make the whole plant green.

The skin protects them, you see, and yet it is transparent and allows the light to get to them, which is a matter of great importance to the chlorophyll grains, for they are hard workers, but cannot do a single thing without sunlight.