Part V—Leaves

HOW TO LOOK AT A LEAF

To-day we begin to learn what we can about the leaves of plants. I hope that enough fresh green leaves have been brought to school to allow every child here to have one on the desk before him, so that he may see, as far as is possible, just what is being talked about.

This picture (Fig. 133) shows you the leaf of the quince. Now, suppose you held in your hand a leaf fresh from the quince tree, and were asked to describe it to a blind person, how would you tell about it?

You would begin, I fancy, by saying, “This leaf is green,” for the color of an object is one of the things we notice first.

Next perhaps you would describe its shape. “This quince leaf is rounded, yet it is too long to be called a round leaf.” So you would use the word “oblong.”

Like most leaves, then, it is green; and like some other leaves, it is oblong.

Now look at this picture (Fig. 134) of the maple leaf. This, you see, is not oblong, but three-pointed.

What other differences do you notice between these two leaves?

You do not seem quite sure as to whether there are any other differences. But do you not notice that the edge of the maple leaf is cut into little teeth, like the edge of a saw, while the edge of the quince leaf is smooth?

And let me tell you here, that when I speak of a leaf, I speak not only of the enlarged flat surface we call the “leaf blade,” but also of the “leafstalk.” A leaf usually consists of a leafstalk and a leaf blade, though some leaves are set so close to the stem that they have no room for any stalks of their own.

“Oh! then,” you answer, “the leafstalk of the maple is much longer than that of the quince, and there are little bits of leaves at the foot of the quince leafstalk which the maple is without.”

You have done very well, and have noticed just those things which you should.

The shape of the leaf blade, whether the edge of this is toothed, the length of the leafstalk, and whether this has any little leaves at its foot where it joins the stem, are things always worth noticing.

Now take your leaves and hold them up against the light, or else look at the picture of the quince leaf, and study carefully the make-up of the blade.

You see that this is divided lengthwise by a heavy rib which juts out on the lower side. From this “midrib,” as it is called, run a great many smaller lines. These are called “veins.” And from these branch off still smaller veins that bear the name of “veinlets.” And somewhat as the paper is stretched over the sticks of a kite, so from the leaf’s midrib to its edge, and from vein to vein, is drawn the delicate green material which makes up the greater part of the leaf.

What I wish you to learn this morning is, how to look at a leaf.

Before using our brains rightly, we must know how to use our eyes. If we see a thing as it really is, the chances are that our thoughts about it will be fairly correct.

But it is surprising how often our eyes see wrong.

If you doubt this, ask four or five of your playmates to describe the same thing,—some street accident, or a quarrel in the playground, which all have seen, or something of the sort,—and then I think you will understand what I mean by saying that few people see correctly.

THE MOST WONDERFUL THING IN THE WORLD

It would be quite a simple matter to interest you children in plants and their lives, if always it were possible to talk only about the things which you can see with your own unaided eyes.

I think a bright child sees better than many a grown person, and I think that it is easier to interest him in what he sees.

And then plants in themselves are so interesting and surprising, that one must be stupid indeed if he or she finds it impossible to take pleasure in watching their ways.

But about these plants there are many things which you cannot see without the help of a microscope, and these things it is difficult to describe in simple words. Yet it is necessary to learn about them if you wish really to feel at home in this beautiful world of plants.

After all, whatever is worth having is worth taking some trouble for; and nothing worth having can be had without trouble. So I hope when you children come to parts of this book that seem at first a little dull, you will say to yourselves, “Well, if we wish really to know plants, to be able to tell their names, to understand their habits, we must try to be a little patient when we come to the things that are difficult.”

For even in your games you boys have to use some patience; and you are quite willing to run the risk of being hurt for the sake of a little fun.

And you girls will take no end of trouble if you happen to be sewing for your dolls, or playing at cooking over the kitchen stove, or doing something to which you give the name “play” instead of “work.”

I only ask for just as much patience in your study of plants; and I think I can safely promise you that plants will prove delightful playthings long after you have put aside the games which please you now.

So we must begin to talk about some of the things which you are not likely to see now with your own eyes, but which, when possible, I will show you by means of pictures, and which, when you are older, some of you may see with the help of a microscope.

Every living thing is made up of one or more little objects called “cells.”

Usually a cell may be likened to a tiny bag which holds a bit of that material which is the most wonderful thing in the whole world, for this is the material which has life.

Occasionally a cell is nothing but a naked bit of this wonderful substance, for it is not always held in a tiny bag.

This picture (Fig. 135) shows you a naked plant cell, much magnified, that swims about in the water by means of the two long hairs which grow from one end of the speck of life-giving material.

The next picture (Fig. 136) shows you a seed cut across, and so magnified that you can see plainly its many cells.

In the middle portion of the seed the cells are six-sided, and laid against one another in an orderly and beautiful fashion, while the outer ones are mostly round.

All animals, we ourselves, all plants, began life as a single cell.

Sometimes a cell will spend its life alone. When the time comes for it to add to the life of the world, it divides into two or more “daughter cells,” as they are called. These break away from one another, and in like manner divide again.

But usually the single cell which marks the beginning of a new life adds to itself other cells; that is, the different cells do not break away from one another, but all cling together, and so build up the perfect plant or animal.

By just such additions the greatest tree in the forest grew from a single tiny cell.

By just such additions you children have grown to be what you are, and in the same way you will continue to grow.

Every living thing must eat and breathe, and so all living cells must have food and air. These they take in through their delicate cell walls. The power to do this comes from the bit of living substance which lies within these walls.

This strange, wonderful material within the little cell is what is alive in every man and woman, in every boy and girl, in every living thing, whether plant or animal.

We know this much about it, and not the wisest man that ever lived knows much more.

For though the wise men know just what things go to make up this material, and though they themselves can put together these same things, they can no more make life, or understand the making of it, than can you or I.

But when we get a good hold of the idea that this material is contained in all living things, then we begin to feel this; we begin to feel that men and women, boys and girls, big animals and little insects, trees and flowers, wayside weeds and grasses, the ferns and rushes of the forest, the gray lichens of the cliffs and fences, the seaweeds that sway in the green rock pools, and living things so tiny that our eyes must fail to see them,—that all these are bound into one by the tie of that strange and wonderful thing called life; that they are all different expressions of one mysterious, magnificent idea.

While writing that last sentence, I almost forgot that I was writing for boys and girls, or indeed for any one but myself; and I am afraid that perhaps you have very little idea of what I am talking about.

But I will not cross it out. Why not, do you suppose?

Because I feel almost sure that here and there among you is a girl or boy who will get just a little glimmering idea of what I mean; and perhaps as the years go by, that glimmer will change into a light so bright and clear as to become a help in dark places.

But the thought that I hope each one of you will carry home is this,—that because this strange something found in your body is also found in every other living thing, you may learn to feel that you are in a way a sister or brother, not only to all other boys and girls, but to all the animals and to every plant about you.

HOW A PLANT IS BUILT

Now we know that the plant, like yourself, began life as a single cell; and we know that the perfect plant was built up by the power which this cell had of giving birth to other cells with like power.

Suppose that a brick were laid upon the earth as the foundation of a wall; and suppose that this brick were able to change into two bricks. Suppose that the new brick were able to form another brick in the same manner, and that this power should pass from brick to brick; and suppose that all these bricks were able to arrange themselves one upon another in an orderly fashion, so that they could not easily be moved from their places.

Now, if you can see this brick wall growing up, you can see something of how the cells of a plant grow up and arrange themselves.

But though it is fairly easy to see how the plant cells form one from another, that does not explain how they come to make a plant, with its many different parts, with its root and stem, its branches, leaves, and flowers.

One thing can divide and make two things of the same sort; but it is not easy to see how it can make things that are quite different from itself.

Now, if this difficulty as to the building-up of plants and animals has come into your minds, you are only puzzled by what has puzzled hundreds of people before you; and all these hundreds of people have found the puzzle quite as impossible to solve as the king’s horses and the king’s men found it impossible to put Humpty Dumpty together again.

A good many questions that we cannot answer come into our minds; but if we look honestly for the answers and do not find them, then we can be pretty sure that for the present it is safe to leave them unanswered.

As cell is added to cell in the building-up of plant life, some wonderful power forces each new cell to do the special work which is most needed by the growing plant.

Sometimes this new cell is needed to help do the work of a root, and so it begins to do this work, and becomes part of the root; or else it is needed to do stem work, and goes to make up the stem, or leaf work, and is turned over into the leaf.

A healthy cell is born with the power to do whatever is most needed.

HOW A PLANT’S FOOD IS COOKED

Some time ago we learned that the little root hairs, by means of their acid, are able to make a sort of broth from the earthy materials which they could not swallow in a solid state.

But before this broth is really quite fit for plant food, it needs even more preparation.

Why do we eat and drink, do you suppose?

“Because we are hungry.” That is the direct reason, of course. But we are made hungry so that we shall be forced to eat; for when we eat, we take into our bodies the material that is needed to build them up,—to feed the cells which make the flesh and bone and muscle.

And this is just why the plant eats and drinks. It needs constantly fresh nourishment for its little cells, so that these can live, and grow strong enough to make the new cells which go to form, not bone and flesh and muscle, as with you children, but fresh roots and stem and leaves and flowers and fruits.

If these little cells were not fed, they would die, and the plant would cease to live also.

And now what do you think happens to the broth that has been taken in from the earth by the root hairs?

As we have said, this broth needs a little more preparation before it is quite fit for plant food. What it really wants is some cooking.

Perhaps you can guess that the great fire before which all plant food is cooked is the sun.

But how are the hot rays of the sun to pierce the earth, and reach the broth which is buried in the plant’s root?

Of course, if it remains in the root, the earth broth will not get the needed cooking. It must be carried to some more get-at-able position.

Now, what part of a plant is usually best fitted to receive the sun’s rays?

Its leaves, to be sure. The thin, flat leaf blades are spread out on all sides, so that they fairly bathe themselves in sunshine.

So if the broth is to be cooked in the sun, up to the leaves it must be carried.

And how is this managed? Water does not run uphill, as you know. Yet this watery broth must mount the stem before it can enter the leaves.

Water does not run uphill ordinarily, it is true; yet, if you dip a towel in a basin of water, the water rises along the threads, and the towel is wet far above the level of the basin.

And if you dip the lower end of a lump of sugar in a cup of coffee, the coffee rises in the lump, and stains it brown.

And the oil in the lamp mounts high into the wick.

Perhaps when you are older you will be able somewhat to understand the reason of this rise of liquid in the towel, in the lump of sugar, in the lamp wick. The same reason accounts partly for the rise of the broth in the stem. But it is thought that the force which sends the oil up the wick would not send the water far up the stem. And you know that some stems are very tall indeed. The distance, for example, to be traveled by water or broth which is sucked in by the roots of an oak tree, and which must reach the top-most leaves of the oak, is very great.

Yet the earth broth seems to have no difficulty in making this long, steep climb.

Now, even wise men have to do some guessing about this matter, and I fear you will find it a little hard to understand.

But it is believed that the roots drink in the earth broth so eagerly and so quickly, that before they know it they are full to overflowing. It is easier, however, to enter a root than it is to leave it by the same door; and the result is, that the broth is forced upward into the stem by the pressure of more water or broth behind.

Of course, if the stem and branches and leaves above are already full of liquid, unless they have some way of disposing of the supply on hand, they cannot take in any more; and the roots below would then be forced to stop drinking, for when a thing is already quite full to overflowing, it cannot be made to hold more.

But leaves have a habit of getting rid of what they do not need. When the watery broth is cooked in the sun, the heat of the sun’s rays causes the water to pass off through the little leaf mouths. Thus the broth is made fit for plant food, and at the same time room is provided for fresh supplies from the root.

If you should examine the lower side of a leaf through a microscope, you would find hundreds and thousands of tiny mouths, looking like the little mouths in this picture (Fig. 137).

Some of the water from the earth broth is constantly passing through these mouths out of the plant, into the air.

A STEEP CLIMB

It is all very well, you may think, to say that the pressure from the root sends the water up through the stem; but when we cut across such a stem as a tree trunk, one finds it full of wood, with a little tightly packed soft stuff in the center, and not hollow like a water pipe, as one would suppose from all that has been said about the way the water rises in the stem.

No, a stem is not a hollow pipe, or even a bunch of hollow pipes, it is true; and it does seem something of a question, how the water can force its way through all this wood; and even if one hears how it is done, it is not an easy thing to make clear either to grown people or to children. But I will see what I can do; and I know that you really love these plants and trees, and will try to be a little patient with them and with me.

The water, or liquid, when it mounts a stem or tree trunk, takes a path that leads through the new-made cells. Each young cell wall is made of such delicate material that it allows the water, or broth, to filter through it, just as it would pass through a piece of thin cloth. And so it makes its way from cell to cell, along the stem, more slowly than if it were passing through a hollow tube, but almost as surely. It is true, the earth broth does not reach the leaves above without having given up something to the little cells along the road. These seem to lay hold of what they specially need for their support, while the rest is allowed to pass on.

I want your teacher to prove to you by a little experiment that water makes its way up a stem.

If she will place in colored water the stem of a large white tulip, cutting off its lower end under the liquid, those parts whose little cells are in closest connection with the stem will soon begin to change color, taking the red or blue of the water; for a freshly cut stem has the same power as the root to suck in water eagerly and quickly.

HOW A PLANT PERSPIRES

We cannot see the water as it passes from the tiny leaf mouths into the air. Neither can we see the water that is being constantly carried from the surface of our bodies into the air. But if we breathe against a window pane, the scattered water in our breath is collected by the cold of the glass in a little cloud; and if we place the warm palms of our hands against this window pane, in the same way the cold collects the water that is passing from the little mouths in our skin, and shows it to us as a cloud on the glass.

Heat scatters water so that we cannot see it, any more than we can see the lump of sugar when its little grains are scattered in hot water; but cold gathers together the water drops so that we are able to see them.

This is why you can “see your breath,” as you say, on a cold day. The cold outside air gathers together the water which was scattered by the heat of your body.

If you place against the window pane the under side of the leaves of a growing plant, the water passing from the tiny leaf mouths collects on the glass in just such a damp cloud as is made by the moist palms of your warm hands.

When water passes from your hands, you say that you are perspiring; and when water passes away from the plant, we can say that the plant perspires. Some plants perspire more freely than others. A sunflower plant has been known to give off more than three tumblers of water a day by this act of perspiration.

There is a tree, called the Eucalyptus, whose leaves perspire so freely that it is planted in swampy places in order to drain away the water.

Of course, the more quickly the leaves throw off water, the faster the fresh supply pushes up the stem.

If the leaves do their work more quickly than the roots make good the loss, then the plant wilts.

When a leaf is broken from a plant, it soon fades. Its water supply being cut off, it has no way of making good the loss through the leaf mouths.

Just as the air in a balloon keeps its walls firm, so the water in the leaf cells keeps the cell walls firm.

As a balloon collapses if you prick it with a pin, and let out the air, so the cell walls collapse when the cells lose their water; and when the cell walls of a leaf collapse, the leaf itself collapses.

HOW A PLANT STORES ITS FOOD

We see that the water is drawn away from the earth broth into the air by the heat of the sun, just as water is drawn from the broth we place on the stove by the heat of the fire; and that when this has happened, the plant’s food is cooked, and is in condition to be eaten.

But this broth does not lose all its water. There is still enough left to carry it back through the leaf into the branches and stem, and even down into the root once more.

In fact, the prepared food is now sent to just those parts of the plant which most need it.

Perhaps it is laid up beneath the bark, to help make new buds which will burst into leaf and flower another year.

Or perhaps it goes down to help the roots put out new branches and fresh root hairs.

Or possibly it is stowed away in such an underground stem as that of the lily, or the crocus bulb, and is saved for next year’s food. Once in a while some of this prepared food is stored in the leaf itself.

When a leaf is thick and juicy (“fleshy,” the books call it), we can guess that it is full of plant food.

Do you recall the Bryophyllum,—the plant we talked about a few days ago? Its wonderful leaves, you remember, gave birth to a whole colony of new plants.

You may be sure that these leaves had refused to give up all the food sent to them for cooking in the sun. You can guess this from their thick, fleshy look, and you can be sure of this when you see the baby plants spring from their edges; for without plenty of nourishment stored away, these leaves could never manage to support such a quantity of young ones.

LEAF GREEN AND SUNBEAM

But the earth broth which the roots supply is not the only article of importance in the plant’s bill of fare.

The air about us holds one thing that every plant needs as food.

This air is a mixture of several things. Just as the tea we drink is a mixture of tea and water, and milk and sugar, so the air is a mixture of oxygen and nitrogen, and water and carbonic-acid gas.

Oxygen, nitrogen, and carbonic-acid gas,—each one of these three things that help to make the air is what we call a gas, and one of these gases is made of two things. Carbonic-acid gas is made of oxygen and carbon.

Now, carbon is the food which is needed by every plant. But the carbon in the air is held tightly in the grasp of the oxygen, with which it makes the gas called carbonic-acid gas.

To get possession of this carbon, the plant must contrive to break up the gas, and then to seize and keep by force the carbon.

This seems like a rather difficult performance, does it not? For when a gas is made of two different things, you can be pretty sure that these keep a firm hold on each other, and that it is not altogether easy to tear them apart.

Now, how does the plant meet this difficulty?

You cannot guess by yourselves how this is done, so I must tell you the whole story.

Certain cells in the plant are trained from birth for this special work,—the work of getting possession of the carbon needed for plant food. These little cells take in the carbonic-acid gas from the air; then they break it up, tearing the carbon from the close embrace of the oxygen, pushing the oxygen back into the air it came from, and turning the carbon over to the plant to be stored away till needed as food.

Only certain cells can do this special piece of work. Only the cells which hold the green substance that colors the leaf can tear apart carbonic-acid gas. Every little cell which holds a bit of this leaf green devotes itself to separating the carbon from the oxygen.

Why this special power lies in a tiny speck of leaf green we do not know. We only know that a cell without such an occupant is quite unable to break up carbonic-acid gas.

But even the bit of leaf green in a tiny cell needs some help in its task. What aid does it call in, do you suppose, when it works to wrench apart the gas?

In this work the partner of the bit of leaf green is nothing more or less than a sunbeam. Without the aid of a sunbeam, the imprisoned leaf green is as helpless to steal the carbon as you or I would be.

It sounds a good deal like a fairy story, does it not,—this story of Leaf Green and Sunbeam?

Charcoal is made of carbon. About one half of every plant is carbon.

The coal we burn in our fireplaces is the carbon left upon the earth by plants that lived and died thousands of years ago. It is the carbon that Leaf Green and Sunbeam together stole from the air, and turned over into the plant.

If one looks at a piece of coal with the eyes which one keeps for the little picture gallery all children carry in their heads, one sees more than just a shining, black lump. One sees a plant that grew upon the earth thousands of years ago, with its bright green leaves dancing in the sunlight; for without those green leaves and that sunlight, there could be no coal for burning to-day. And when we light our coal fire, what we really do is to set free the sunbeams that worked their way so long ago into the plant cells.

It is more like a fairy story than ever. Sunbeam is the noble knight who fought his way into the cell where Leaf Green lay imprisoned, doomed to perform a task which was beyond her power. But with the aid of the noble Sunbeam, she did this piece of work, and then both fell asleep, and slept for a thousand years. Awakening at last, together they made their joyful escape in the flame that leaps from out the black coal.

In truth, a sunbeam and a flame are not so unlike as to make this story as improbable as many others that we read.

And because I have told it to you in the shape of a fairy story, you must not think it is not true. It is indeed true. Everywhere in the sunshiny woods and fields of summer, the story of Leaf Green and Sunbeam is being lived. But when the day is cloudy or the sun sets, then there is no Sunbeam to help the Princess, and then no carbon is stolen from the air.

PLANT OR ANIMAL?

Did you ever stop to ask yourself, “What is the difference between a plant and an animal?” because this is the place where that question should be answered.

“Why, an animal is altogether different from a plant,” you answer, perhaps a little scornfully. “I have no trouble in telling which is which.”

It is very natural that you should feel this way. A cow or a horse, for example, is not at all like a tree; and when you think of animals, you think of the ones you know best, and likewise of plants.

But wise men have discovered plants that look and act so much like animals, and animals that look and act so much like plants, that at one time they say, “Now, these are animals, surely,” and a little later exclaim, “No, after all, these are plants;” and they take a long time to make up their minds as to whether certain objects are plants or animals.

And already even you children have discovered that the plants you know best belong to families, and have children, and care for them in a very motherly fashion; that they drink earth food with their roots, and eat carbon food with their leaves; and soon you will find that they do many other things which once upon a time you would have thought it a great joke to be told a plant could do.

You remember my telling you of one little plant cell that could swim; and there are some animals, you know, that are rooted to one spot as we usually think only a plant is rooted.

What, then, is the difference between a plant and an animal?

Leaf Green and Sunbeam between them put life into what had no life before; and the living plant matter, which they help to make, is that which animals cannot make themselves, yet which they cannot live without, for this living matter is absolutely necessary to them as food.

And the one real difference between a plant and an animal is this,—a plant can make out of certain dead substances the living matter that all animals must have for food; an animal cannot do this.

HOW WE ARE HELPED BY LEAF GREEN AND SUNBEAM

The cell in which Leaf Green lives has no little mouths such as we saw in the picture some time ago.

Its walls are so delicate that the carbonic-acid gas passes through them quite easily,—as easily as the gas escaping from an unlighted jet in the schoolroom could pass to your nose even if you wore a veil, or as easily as water would pass through a piece of muslin.

But between Leaf Green’s cell and the outer air are other cells,—those which make up the outer covering or skin of the leaf. These are arranged so as to form the openings or mouths about which we have read. By means of these mouths the gas makes its way through the leaf’s thick skin.

The plant needs as food the carbon in this gas, and so keeps fast hold of it; but the oxygen is not needed for this purpose, and so it is pushed back into the air.

Now, we learned in the last chapter of one very great service rendered to animals by plants. We learned that plants took carbon from the air, and turned this into food for animals.

But there is still another way in which plants serve animals. And once more it is the work of Leaf Green and Sunbeam that is of such importance to us; for when they take hold of the carbon, making it into living food for man and beast, they take from the air the gas that is poisonous, and send back into the air the gas which gives life and health.

This poisonous gas which they lay hold of, you remember, is carbonic-acid gas; and carbonic-acid gas is what we animals send out of our bodies with every breath, for it is the part of the air which poisons us. When the schoolroom is so close that our heads ache, it is because so many children have been breathing out this gas, and we are forced to take it back into our bodies again.

But when this gas is stolen by the plant, and robbed of its carbon, it is no longer carbonic-acid gas. Nothing of it is left but the oxygen which is pushed out through the cell walls; and this oxygen is as good to breathe as the other gas (carbon and oxygen mixed) is bad.

So the plant finds good what we find poisonous. It takes in and keeps that which hurts us (the carbon), and sends out that which helps us (the oxygen).

So you see that our lives depend on the lives of plants in two ways:—

1. The plants give us the food we need for life.

2. The plants take from the air the gas that poisons us, and give to the air the gas which we need for life and health.

And in both cases it is Leaf Green and Sunbeam who are making life possible for us.

Remember the great services of these two fairies when next you pass a green tree which is bathing itself in sunshine.

HOW A PLANT BREATHES

Perhaps you have heard people say that it is not good to sleep in a room with plants.

They say this, because they have heard that at night the plant does not give out oxygen, but that it does give out the poisonous carbonic-acid gas.

Now, you children know that part of this statement is true.

You know that the plant cannot give out oxygen at night, because at that time there is no Sunbeam about to help Leaf Green tear apart carbonic-acid gas and send the oxygen back into the air.

But how about the other part of the statement?

Is it true that at night plants give out the poisonous carbonic-acid gas?

Both day and night, plants give out carbonic-acid gas; for though plants, save in the sunlight, cannot eat by means of their little green cells, they can breathe through the tiny mouths (Fig. 137) on the under side of the leaf by night as well as by day.

And when either a plant or an animal breathes, it takes the life-giving oxygen from out the air mixture, and keeps it for its own use. But poisonous carbonic-acid gas is sent back into the air. Now, the question is, whether a plant does most good or most harm to the air by taking in and sending out the different gases.

Of course, it does good when it lets the oxygen out through its cell walls, and stores away the carbon within itself; and it may seem to do harm when through its leaf mouths it breathes in oxygen and breathes out carbonic-acid gas.

There is only one key to unlock the matter, and that is this,—to find out whether the plant does most towards poisoning or towards purifying the air.

And that has been found out already.

Wise men say that Leaf Green and Sunbeam do much more good to the air than the little breathing mouths do harm. The two good fairies take away a great deal of poison, and send back a great deal of the helpful oxygen; while the tiny mouths neither rob the air of much oxygen nor give it much poison. Indeed, the harm they do is so small compared with the great good accomplished by Leaf Green and Sunbeam, that even at night you need not worry at the thought that you have plants in your room.

Perhaps you wonder that a plant does these two things that are so exactly opposite to each other.

But a plant must breathe as well as eat; for when it breathes, it takes in the precious oxygen which is just as necessary to its life as to ours.

In summer, by the dusty roadside, you see plants almost white with dust, looking quite ill and lifeless.

And they are both ill and lifeless; for their little leaf throats are so choked that they cannot breathe in the oxygen they need, and in consequence they are being slowly suffocated.

THE DILIGENT TREE

Now we have learned three things about plants, and especially about leaves. We have learned—

1. That they perspire.

2. That they eat and drink.

3. That they breathe.

They perspire when the water passes through the leaf mouths into the air.

They eat when Leaf Green and Sunbeam together manage to take the carbon out of the carbonic-acid gas which has made its entrance through the leaf mouth and the cell wall. They drink when the roots suck in water and earth broth.

They breathe when the leaf mouths take from the air the oxygen, and give back to it carbonic-acid gas.

The veins and veinlets, of which you see so many running through a leaf, act in something the same way as the water pipes of a city; for through these veins the watery food, the earth broth, is carried to the different cells.

When one knows all that we know even now about a plant, one looks at a tree covered with leaves with a good deal of admiration.

Just think of what is being done inside that quiet-looking tree! Think of the millions of cells that go to make it up, each cell having its own work to do! Think of the immense amount of business being carried on within the trunk, inside the branches, and especially in each green leaf! And when you have the chance, notice how hard each leaf tries to get just as much sun and air as it possibly can.

In the first place, the thin, flat leaf blades are so spread out that every part is exposed to the light and air.

Then notice how the leaves are placed in reference to one another.

Almost every single one is fastened to the tree so as to get its fair share of sunshine.

When you think of the many thousands of leaves borne by one tree, it astonishes you to see how seldom one leaf gets in another’s light.

And the shapes of leaves are always suited to their arrangement on the tree.

If you should take the leaves of a chestnut tree and replace them by the leaves of a maple, you would find the maple leaves all getting in each other’s way, or else you would see that they were taking up a great deal more room than necessary.

But when a leaf is studied on its own tree, one sees that its shape is the very best that could be imagined for its position.

And in the smaller plants we notice this same thing.

And when you remember that Leaf Green cannot feed the plant unless Sunbeam comes to her assistance, you realize how necessary it is that each leaf be within the reach of Sunbeam’s visits.

LEAVES AND ROOTS

You will be surprised to learn that the way in which a plant’s leaves grow tells us something of the way in which its roots grow.

Many of you have been overtaken far from home in a rainstorm, and have sought shelter under a spreading tree. The ground directly beneath the tree has kept almost dry even after some hours of rain, but the earth just under the tips of the spreading branches got very wet: for the great tree acted like a large umbrella; and when the raindrops fell upon the smooth leaves, which sloped outward and downward, they rolled from leaf to leaf till they reached the very lowest, outermost leaves of all. From these they fell to the ground, just as the drops that gather upon your umbrella run outward and downward to the umbrella’s edge, and then off upon the ground.

So you can see that the circle of earth which marks the spread of the branches above must be specially wet, as it received a great part of the rain which fell upon the whole tree.

And whenever you see a tree which sheds the rain water in such a circle, you can be pretty sure that, if you should dig into the earth a ditch which followed this circle, you would soon reach the tips of the new root branches of the tree.

You know that the root does the drinking for the plant; and only the newest parts of the root, the fresh root tips, are really good for work of this sort. You remember that the earth food is carried up the stem to the leaves in a watery broth; and that if the water supply should give out, the new plant cells would not get the broth which helps them to grow, and to put out other cells, and so to build up the plant.

Now, as only the new root branches, near their tips, are able to drink, if the water should leak through the earth in equal quantities everywhere, much of it would be wasted; but when this water is collected in certain spots within reach of the new root branches, there is good reason to believe that these will be able to satisfy their thirst.

By the shedding of the rain from the tips of the spreading branches above, the water is collected in a ring, and so sinks into the earth; and the root branches below spread out in just the same direction as the tree branches above, till they find what they need, and drink their fill.

So by the way in which a tree sheds the rain, you can tell just where its root branches reach out underground.

In smaller plants you see much the same thing. Fig. 138 shows a plant called the Caladium. You can see that the raindrops must roll outward down these leaves, and fall upon the earth just above the tips of the root branches.

Fig. 139 shows you the rhubarb plant. This has quite a different sort of root. Now, if the rhubarb leaves were like those of the Caladium, unless the rhubarb root-branches changed their direction, these root-branches would grow very thirsty indeed.

But as it is, the water pours down these leaves toward the center of the plant, and reaches the ground almost directly over the straight, fleshy root, with its downward-growing branches; and we see that these root-branches are watered by the leaves above just as carefully as are those of the Caladium.

By knowing one thing about a plant, often you can guess that another thing is so.

You understand now that when the leaves of a plant shed rain water after the fashion of the Caladium, the chances are that its root-branches spread out as far as the drip of the water; and that the root of the rhubarb points almost straight downward, is told you by the drip of water from the rhubarb leaves.

LEAF VEINS

Some time ago you learned that from the stem of a plant you could guess the number of seed leaves which it brought into the world, and that in the same way from the seed leaves you could guess what kind of a stem it would build up.

From the way in which a leaf is veined you can guess both of these things. You can guess what sort of a stem belongs to the plant, and with how many seed leaves it began life.

When the little veins run in and out, forming a sort of network, we say that the leaf is “net-veined.”

These leaves of the quince (Fig. 140), the maple (Fig. 141), and the basswood (Fig. 142) are all net-veined.

Net-veined leaves are borne by plants which brought into the world more than one seed leaf; and with the net-veined leaf we can expect to find that stem which comes with more than one seed leaf,—a stem where the skin or bark, the woody rings, and the soft central pith, are clearly separated one from another.

But a leaf such as that in Fig. 143 or that in Fig. 144, where the veins do not branch off in a network, but run in unbroken lines side by side,—such leaves as these tell you that they are borne by plants which started life with only one seed leaf, and which have such a stem as the cornstalk, where you see no woody rings or central pith.

These leaves are called “parallel-veined.”

I fear that you find all this a little difficult to understand and to remember; but if you read it patiently, when you study the botany for older children, I think it will come back to you and make your lessons easier.

LEAF SHAPES

As I told you before, we should notice always the shape of a leaf.

It is much easier to describe some new plant we have met on our walks if we remember the shape of its leaves.

Next summer I hope you will make a collection of leaves, pressing and keeping them. I think you will be amazed at their great variety in shape.

Some you find long and narrow, others almost round. Some are arrow-shaped, others star-shaped, others needle-shaped (Fig. 145). Some are three-pointed like the maple leaf (Fig. 146); others deeply-parted, like the oak leaf (Fig. 147).

Sometimes a large leaf is cut up into several little leaves. These little leaves are called “leaflets.”

The clover leaf (Fig. 148) has three leaflets.

The locust leaf (Fig. 149) is cut into a great many leaflets.

The edge of one leaf (Fig. 150) is smooth, while that of another is cut into little teeth (Fig. 151) like the teeth of a saw.

I should like to know how many of you children, without looking even at a picture save such as you carry in that little gallery in your head, could describe correctly the shapes of some of our common leaves. I should like to ask you to draw on the blackboard the rough outlines of any leaves that you remember. If you think you could not do this, will you not try, when next you see a leaf, to carry off in your mind such a picture of it as to enable you to outline it on the blackboard when you go back to the school room?

Really it does not take any more time to see a thing correctly than to see it incorrectly. It takes a little more sense, that is all.

It takes some sense to give even one minute of honest thought to the thing you are looking at.

You know some children who never seem to have all their thoughts in one place at a time, and who in consequence never see anything really well.

It is better to stop doing a thing altogether than to do it in a foolish sort of way; and it is foolish to start to do even the smallest thing, and yet not do it.

The child who looks at even a leaf in a way to make it possible for him to draw the outline of that leaf five minutes later, is likely to be the child who goes in for both work and play with all his heart, and who comes out as far ahead on the playground as he does in the schoolroom.

Now, after that lecture, which some of you need badly enough (and which I will tell you, as a great secret, I need not a little myself), I want to point out a few more of the things that are worth noticing in a leaf.

But perhaps it is better to save them for another chapter.

HAIRY LEAVES

Notice always whether a leaf is smooth or hairy. Do you remember the mullein that sends up its tall spires over the hill pasture? The grayish leaves of this mullein are so hairy that they feel almost like wool. What is the use of all this hair? It is not likely that a plant would wrap itself in this hairy coat except for some good reason.

It is believed that this coating of the mullein prevents animals from eating the leaves, and so destroying the plant. In the mouth, these hairs slip from the leaf blade, and cause a most unpleasant sensation.

But usually the hairs on a leaf are helpful because they prevent too much perspiration or giving-off of water. The more freely the hot sun beats upon a leaf, the more quickly the water is drawn away from it. You can see just how this is by hanging a wet towel in front of the fire. In a very short time the heat from the burning coals draws the water from the towel. But put a screen between the fire and the towel, and the water passes off more slowly.

Now, the hairs on that side of the leaf which faces the sun act as a screen from its fierce heat. We have learned how important it is that the leaf should not part with its water more quickly than the roots can make up the loss. We know that when a leaf does this, it wilts just as a leaf wilts when it is picked and cut off from its water supply, on account of the collapse of the walls of the many little cells which are emptied of water.

So you can understand that plants which grow in dry, sunny places, where there is little drinking water for the roots, and where the sun beats constantly on the leaves, must take every care that there is no waste of water.

And if you keep your eyes open, you will discover that many of the plants which grow in such places screen themselves from the full heat of the sun by a coat of hairs.

The plant called “life everlasting” is one which grows in dry, open, sunny places. It clothes its leaves with silky hairs, and so prevents them from throwing off too quickly the small amount of water its roots are able to provide. Without this silky coat, the sun would suck its leaves quite dry of water.

Sometimes a leaf has only a few of the little leaf mouths through which most of the water passes. As these mouths are wide open only in the sunlight, and as often the rest of the leaf is covered with a thick skin which prevents the water from slipping away (as a little of it nearly always does) through the cell walls, such a leaf will hold its water supply and keep fresh for a long time. Such leaves as these we find on what we call “evergreen” plants. The pines and hemlocks which light up the woods all winter have these thick-skinned, few-mouthed leaves, which throw off so little water that even when the ground is frozen hard, and gives no drinking water to the roots, they are able to keep fresh by the careful way in which each one hoards its own little supply.

WOOLLY AND “DUSTY” LEAVES

Curiously enough, some plants put on a hairy coat for just the opposite reason from the one which makes life everlasting clothe itself in that fashion. Life everlasting fears lest its leaves throw off their water, or perspire too quickly.

Down by the stream that runs through the meadow grow great clusters of the pink-flowered steeple bush. If you look at the lower sides of the leaves of the steeple bush, you see that they are very woolly. As this wool is not between the sun and the leaf blade, it cannot be meant to protect the leaves from the heat of the sun; and indeed in this wet meadow, close to the river, never mind how quickly the leaves throw off their water, the roots can have no difficulty in finding close by more than enough to make good the loss. No, the fact is that these leaves need to throw off water very freely indeed to make room for the ever-fresh supply that is pushing up the stem, and their woolly covering is intended to help them do this very thing. Its object is to aid perspiration. In swampy places the moisture rises every night from the wet ground, and settles on the plants about. The little mouths on the under surfaces of the leaves of the steeple bush would soon be clogged with the moisture rising from below, if they were not protected in some way; and if they became so clogged, they could not throw off the water with which the whole plant is charged. Thus, by having this thick coat of hair, the water that otherwise would cling to the outer surface of the leaf blade is kept at a distance from the little mouths, and these are not interrupted in the performance of a duty so necessary to the health of the plant.

This same habit of coating its lower leaf surfaces with hair, you notice in the speckled or swamp alder, a shrub which grows also in wet places, and therefore runs the same risk of having its leaf mouths clogged with water.

So when you see only the upper surface of a leaf covered with hair, you can guess that the object of the plant is to prevent too much perspiration; but when you see only its lower side clothed in this same way, you can guess that the plant fears too little perspiration.

Sometimes you find a plant with leaves which have a coating of what looks almost like dust on one or both of their surfaces. This dust we call “bloom.” We see it in apples and grapes, as well as on leaves. It is made up of a waxy material which is put forth by the plant just as it puts forth hair. This bloom the plant uses also as a help to free perspiration. By thus clothing its leaves it shields the little mouths from water clogging; and so you can be sure that the little mouths have not been filled with water, and thus prevented from doing their work.

The cabbage leaf has mouths on both of its surfaces, and so both sides are covered with this protecting bloom. If you dip a cabbage leaf in water and then shake it, the drops roll off and leave it quite dry.

PRICKLES AND POISON

Leaves need to protect themselves from other enemies than too great heat and too much water.

We found that the prickly armor of the thistle enabled it to live in pastures where the cattle had killed most of the other plants.

Many animals like to eat green leaves, so we are not surprised to find that plants invent different ways of protecting themselves.

One look at the leaf of the thistle is enough to persuade us that it would not be very good eating.

The red-berried holly, with which we decorate our churches and houses at Christmas time, is another plant with prickly leaves.

Some plants cover their leaves with bristles, which the cattle dread almost as much as the stout prickles.

As we read before, the mullein defends its leaves by a fuzzy coat of hair. Such an armor as this is less warlike than that of the thistle, but quite as effective.

Other plants fill their leaves with juices which are either poisonous or unpleasant.

It seems as if animals guessed the presence of these unfriendly juices by the plant’s smell, for they will munch the different growing things all about such a plant as this, and leave the harmful leaves severely alone.

The nettles cover their leaves with stinging hairs. These stiff hairs break off when handled, burying themselves in the flesh, and sending out a burning acid that punishes severely the meddler, man or beast, as it may happen to be.

By this time I think you realize that leaves are well worth noticing. And when you have looked at a leaf so fully as to be able to carry in your mind its outline, I hope you will then discover whether it wears a coat of hair, or a dusty bloom, or a prickly armor, or a thick, evergreen skin, and that you will decide what enemies it is trying to escape.

SOME CRUEL TRAPS

Have you ever seen a leaf like the one in this picture (Fig. 152)?

It is shaped something like a pitcher; and the plant on which it grows has been named the “pitcher plant.”

The pitcher plant lives in low, wet place, such as the shaded swamp, or the marsh down by the lake.

On account of its curious leaves it is brought to the cities, and is sold on the street corners or at the florists’.

In June comes the great flower of the pitcher plant. Sometimes this is a dull red; again it is a delicate pink or perhaps a light green; and it has faint, pleasant fragrance.

Next June I hope that some of you children will find these beautiful flowers and these curious leaves.

Why should a leaf be shaped like a pitcher, do you suppose?

These leaves are not only pitcher-like in shape, but also in their way of holding water; for if you succeed in discovering a settlement of pitcher plants, you will find that nearly every pitcher is partly filled with rain water. Usually this water is far from clear. It appears to hold the remains of drowned insects; and sometimes the odor arising from a collection of these pitcher plants is not exactly pleasant.

Perhaps you wonder how it happens that dead insects are found in every one of these pitchers; and possibly you will be surprised to learn that apparently these curious leaves are built for the express purpose of capturing insects.

It is easy to understand that these odd leaves are not so well fitted as more simple ones to cook the plant’s food in the sun, or to take carbon from the air; but if they are unfitted to provide and prepare ordinary food, possibly they are designed to secure food that is extraordinary.

It seems likely that the pitcher plant is not content to live, like other plants, upon the simple food that is taken in from the earth and from the air. We are led to believe that it wishes something more substantial; that it needs a meat diet; and that to secure this, it teaches its leaves to capture flies and insects in order that it may suck in their juices.

These leaves are veined in a curious and striking fashion. The bright-colored veins may convince the insects of the presence of the sweet nectar in which they delight. At all events, in some way they are tempted to enter the hollow leaf; and, once they have crawled or tumbled down its slippery inner surface, they find it impossible to crawl back again, owing to the stiff hairs, pointing downward, which line the upper part of the pitcher.

Even if they have wings, it is difficult for them to fly upward in so straight a line as would be necessary to effect their escape.

When tired out in their efforts to get out of this cruel trap, they fall into the water at the bottom of the pitcher, and are drowned. Their bodies decay and dissolve; and it is thought that this solution is taken in by the leaf, and turned over to the plant as food.

It is just the old, sad story of the spider and the fly, you see, only now it is the pitcher and the fly.

But be sure to examine one of these pitchers if you possibly can, and then you will understand better how the whole thing is managed.

The leaf in this picture (Fig. 153), for it is a leaf, you cannot find in our North American swamps. It grows on a plant called Nepenthes, a plant which lives in hot countries far from the United States.

The leaf in the picture is full grown, and all ready for its work of trapping animals. Before it was old enough to do this, the lid which is now lifted was laid nicely across the opening to the pocket, and so prevented any unseasonable visits.

Sometimes these pockets are so large as to be able to hold and to hide from sight a pigeon. They are gayly colored, and the rim around their border is covered with a sugary, tempting juice. So you can guess that the animals in search of nectar are not slow in accepting the invitation offered by color and sweets, and that some of these are imprudent enough to venture across the sticky edge. In this event they are pretty sure to lose their footing on the slippery inner surface of the pocket, and to fall into the watery liquid with which it is filled. Even if they do not slip immediately, their efforts to crawl back over the rim are defeated by a row of teeth such as you see in the picture.

The liquid at the bottom of the leaf is not rain water, as in the pitcher plant. It is given out by the leaf itself; and it contains an acid which dissolves the animals’ bodies, so that their more nourishing parts can easily be taken in by certain little cells which line the lower part of the pocket, and which have been brought up to this work.

The next picture (Fig. 154) shows you a water plant. It is called the “bladderwort,” because of the little bags or bladders which you see growing from the branches under water. The little bladders are traps set for water animals, which swim into them in their wish, perhaps, to escape some enemy. But they are quite unable to swim out again; for the door into the bladder is transparent, and looks like an open entrance with a nice hiding place beyond. It opens easily from the outside, but is so arranged that it will not open from within. So when the poor little animal hurriedly swims into what seems to it a cozy resting spot, and draws a long breath of relief at getting safe inside, it is hopelessly caught, and must slowly starve to death, for there is no chance of escape. It may live for nearly a week in this prison; but at last it dies. Its body decays, and is taken in as food by the cells set apart for that purpose.

Strangely enough, though we ourselves do not hesitate to kill animals for food, and sometimes, I am sorry to say, for nothing but amusement, we give a little shiver of disgust when we find these plants doing the same thing. Some lines that came out in one of the magazines a few years ago express this feeling:—

“What’s this I hear About the new Carnivora? Can little plants Eat bugs and ants And gnats and flies? A sort of retrograding! Surely the fare Of flowers is air, Or sunshine sweet. They shouldn’t eat Or do aught so degrading.”

MORE CRUEL TRAPS

The plants about which we read in the last chapter do not take any active part in capturing insects. They set their traps, and then keep quiet. But there are plants which lay hold of their poor victims, and crush the life out of them in a way that seems almost uncanny.

This leaf (Fig. 155) belongs to a plant which lives in North Carolina. It is called Venus’s flytrap.

You see that the upper, rounded part of the leaf is divided by a rib into two halves. From the edges of these rounded halves run out a number of long, sharp teeth; and three stout bristles stand out from the central part of each half. When an insect alights upon this horrible leaf, the two halves come suddenly together, and the teeth which fringe their edges are locked into one another like the fingers of clasped hands.

The poor body that is caught in this cruel trap is crushed to pieces. Certain cells in the leaf then send out an acid in which it is dissolved, and other cells swallow the solution.

After this performance the leaf remains closed for from one to three weeks. When finally it reopens, the insect’s body has disappeared, and the trap is set and ready for another victim.

The next picture (Fig. 156) shows you a little plant which is very common in our swamps,—so common that some of you ought to find it without difficulty next summer, and try upon it some experiments of your own.

It is called the “sundew.” This name has been given to it because in the sunshine its leaves look as though wet with dew. But the pretty drops which sparkle like dew do not seem so innocent when you know their object. You feel that they are no more pleasing than is the bit of cheese in the mouse trap.

When you see this plant growing in the swamp among the cranberry vines and the pink orchids, you admire its little white flowers, and its round red-haired leaves, and think it a pretty, harmless thing. But bend down and pluck it up, root and all, out of the wet, black earth. Carry it home with you, and, if you have a magnifying glass, examine one of its leaves.

The picture (Fig. 157) shows you a leaf much larger than it is in life. The red hairs look like pins stuck in a cushion, and the head of each pin glistens with the drop that looks like dew.

But the ants and flies do not take these drops for dew. They believe them to be the sweet nectar for which they long, and they climb or light upon the leaves in this belief.

And then what happens?

The next two pictures will show you (Figs. 158, 159).

The red hairs close slowly but surely over the insect whose legs are already caught and held fast by the sticky drops it mistook for nectar, and they hold it imprisoned till it dies and its juices are sucked in by the leaf.

I should like you to satisfy yourselves that these leaves act in the way I have described. But a bit of fresh meat will excite the red hairs to do their work quite as well as an insect, and I hope in your experiments you will be merciful as well as inquiring.

So you see that the little sundew is quite as cruel in its way as the other insect-eating plants. But its gentle looks seem to have deceived the poet Swinburne, who wonders how and what these little plants feel, whether like ourselves they love life and air and sunshine.

“A little marsh-plant, yellow-green And tipped at lip with tender red, Tread close, and either way you tread, Some faint, black water jets between Lest you should bruise its curious head.

“You call it sundew; how it grows, If with its color it have breath, If life taste sweet to it, if death Pain its soft petal, no man knows, Man has no sight or sense that saith.”

THE FALL OF THE LEAF

You know that in autumn nearly all the leaves fall from the trees. To be sure, a few trees (such as the pines and hemlocks) and some plants (such as the laurel and wintergreen and partridge vine) do hold fast their leaves all winter; but these are so few as compared with the many plants which lose their leaves, that they hardly count.

Perhaps you never stopped to wonder why most plants get rid of their leaves before winter comes on; but you feel pretty sure now that there is some good reason for a habit that is adopted by nearly all the plants that live in this part of the country.

When we were talking about the way in which leaves defend themselves from different dangers, we found that evergreen leaves, the leaves which hold fast to the tree and keep fresh all winter, manage to keep their water safe inside their cells by wearing a very thick skin, and by not having too many little leaf mouths. For when a leaf has a thin skin and a great many mouths, its water leaks away very quickly. And if many such leaves should remain upon a plant into the winter, might it not happen that they would let off all its water at a time when its roots could not find any more in the frozen ground? And thus might not the leaves kill the plant by draining it quite dry?

So you can see why it is well for most plants to shed their leaves before winter comes on and the root’s drinking water is turned into ice.

But when a plant is about to shed its leaves, it takes care not to waste the precious food which they hold. This food it draws back into its stem and roots, laying it away in safe places beneath the buds which are to burst another year.

It is this action on the part of the plant which changes the color of the leaves every fall. That material which makes them green is broken up, and part of it is taken away. That which is left is usually yellow or brown or reddish, and gives the leaves the beautiful colors we see in our October woods.

So whenever you see the woods changing color, losing their fresh green and turning red and yellow, you can be sure that the trees have begun to prepare for winter. You know that they are stowing away their food in warmer, safer places than can be supplied by the delicate leaves. And when all the food has been drawn out of the leaves, and packed away in the right spots, then the plant finishes a piece of work it began some time before. This piece of work is the building-up of a row of little cells just where the leafstalk joins the stem or branch. When this row is complete, it acts almost like a knife, loosening the stalk from the stem.

Then the leaf’s life work is over; and with the first breeze, the empty shell, which is all that is left, breaks away from the parent plant, and drifts earthward.