The Study of Plant Life

CHAPTER I.. Introductory

INTRODUCTORY

Many people do not realise that plants are alive. This mistake is due to the fact that plants are not so noisy and quick in their ways as animals, and therefore do not attract so much attention to themselves, their lives, and their occupations.

When we look at a sunflower, surrounded by its leaves and standing still and upright in the sunlight, we do not realise at first that it is doing work; we do not connect the idea of work with such a thing of beauty, but look on it as we should on a picture or a statue. Yet all the time that plant is not only living its own life, but is doing work of a kind which animals cannot do. Its green leaves in the light are manufacturing food for the whole plant out of such simple materials that an animal could not use them at all as food. Even its beautiful flower is creating and building up the seeds which will form the sunflowers of the future. All animals directly or indirectly make use of the work done by plants in manufacturing food, for they either live on plants themselves, or eat other animals which do so.

Plants are living, and therefore require food of some kind as well as air and water in the same way, and for the same purposes as do animals. As a rule, we cannot see them breathing and eating, but that is because we do not look in the right way. In our study of plants we must first learn how to see and question them properly, and when we have done this they will show themselves to us and tell us stories of their lives which are quite as interesting as any animal stories.

Now the sunflower we have just thought of is probably growing in a garden well looked after by a gardener, who sees that it gets all the light and water and just the kind of soil it needs. It is therefore protected and cared for to a certain extent, but who looks after the wild plants which manage to grow everywhere? These have not only their own lives to live, but by their own efforts must overcome difficulties which are not even felt by the cultivated ones.

They succeed in a wonderful way, and some plants manage to grow under very difficult conditions, even in places where they get no water for months under a burning sun, or in forests where the overshadowing trees cut off the light and rain, or under the water where they get no direct air. They have to do all the usual work of plants, and at the same time struggle against the hardships of their surroundings. They are like men fighting for their lives with one hand and doing a piece of work with the other.

The result of this is that they sometimes make themselves strange-looking objects, and in some plants which have had a very hard struggle it is difficult to know which part of the plant is which. Look, for example, at a Cactus (~see~ fig. 48), which grows in the desert; it appears to have neither stem nor leaves like an ordinary plant, and to consist merely of a roundish green mass covered with needle-like prickles. Yet when you come to study the Cactus you will find out that the thick, fleshy mass is really its stem, and the prickles its leaves which have taken on these strange shapes. By means of its unusual form the Cactus can live where our common plants would die of the dry heat in a day or two. The power plants have of changing their bodies so as to fit themselves to live under all kinds of conditions is one of the strongest proofs that they are alive.

All the parts of plants have some special life-work, just as we have legs and arms for different purposes, and every part is formed in some way to suit the needs of the plant and help it to get on well in its home.

The main thing to realise at the beginning of the study of plants is that they are living things, and therefore to try to discover the importance of the shape and arrangement of all their parts and their relation to the life of each plant as a whole.

We will begin by looking carefully for all the signs of life in them, and noting how often these are the same as those of the animals, even though the whole plant-body is so different from that of an animal.

CHAPTER II.. Signs of Life

SIGNS OF LIFE

If you were asked to give =the signs of life in an animal=, it is likely that you would think at once of =its power of breathing, eating, growing, and moving=. Now when we ask the same question about plants the answer does not appear to be quite so easy to find, because at first sight plants do not seem to do any of these things except the growing. However, ~the same answer would be quite correct for plants~, as well as animals, for they are really able to breathe, eat, grow, and move; all you have to do is to watch them in the right way to see that this is the case.

We are not in the habit of treating dry seeds as though they were alive; beans are stored away in sacks all the winter and may be left for months in dry cellars, and the precious seeds which will give us our beautiful flowers in the summer are put away in boxes through the winter. Yet you know that if you place seeds in the earth and keep them warm and moist, little plants will come up and will grow. What gives them the power of growth which is not possessed by the stones and earth around them? Warmth and moisture alone could not put this power into the seeds when we planted them. This power, which only belongs to living things, was there all the time, but was lying asleep, shut in and protected so that it was not easily disturbed till suitable conditions made it time for it to wake.

You know when you are asleep that you do not eat or run about, but simply lie still and breathe. This is what the seed was doing before the baby plant began to break through its protecting coat and show itself to the world as a living thing.

Let us watch some of these young plants just waking up to activity, and see if we can find in them the four signs we take as being the tests of animal life.

First let us see if we can show that they =breathe=.

You know that when you breathe you take air into your lungs, use some of it, and give the rest out. You can show that plants also use up some part of the air. If you would actually prove this to yourself or anyone else, take some peas or beans, soak them in water, and leave them in damp sawdust for a day or two till the tiny plant has just begun to show. Then put them on wet blotting-paper in a jar which has a very well-fitting cork with no leakage, and through which a fine bent glass tube is fitted. Place a small tube of caustic potash in the jar. Then place the end of the bent tube in a dish of water, which acts better if you have dissolved some caustic potash in it (~see~ fig. 1). Once it has begun to rise in the tube, mark the level of the water with a small label. If then you mark it daily the labels will show how much water has risen each day, and the amount of water rising in the tube shows us the amount of air which has been absorbed by the growing beans.

This tells us, therefore, that ~air is absorbed by plants~ in the course of their growth. But there is another thing we must notice about breathing which is equally important.

You will find that you yourself, as well as all animals, not only use up a part of the air, but also give out a waste product which we call carbonic acid gas. You can see one of the characters of this gas from your lungs if you take a jar of lime water and breathe into it for some time. Compare this with a similar jar of lime-water through which ordinary air has been pumped at about the same rate for the same time, and you will see that the one you have breathed into has gone very much more cloudy-white than the other (~see~ fig. 2). The cloudiness in jar A is caused by the waste gas (carbonic acid gas) which you breathe out, and which combines with the lime in the lime-water to make solid grains of chalk. Fine white chalk grains always form in lime-water when this gas is present, so that a jar of clear lime-water is a very good test for the presence of the gas.

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