CHAPTER III.

SEEDS AND SEEDLINGS

If we wish to follow the whole life of a plant, we cannot do better than begin by watching the baby plant “hatching” out from its seed at the beginning of its active life.

There are many seeds which would be good to begin work on, any kind would be interesting, but it is best to use some nice big ones which allow us to see the parts easily. Good ones to choose would be broad beans or peas. Notice first the size and shape of the dry seed of the bean, make a drawing of it, and then place it in water. After a few hours you will see that the outside skin wrinkles up; this is because the skin absorbs water and increases in size, and so becomes too big for the rest of the seed (~see~ fig. 3, A, B). After the water has soaked right into the substance of the seed you will find that the outer skin fits again and is once more smooth, and that the whole seed is larger than it was before it was soaked (~see~ fig. 3, C).

Take one of these soaked beans and examine its structure. Notice the black mark where it was attached to the parent pod, and the little triangular ridge pointing towards it (~see~ fig. 4, A). Now carefully peel off the skin, noticing that there are two skins, an outer thick one and an inner thin one, which protect the parts within. When you have removed the skin, you will find that the inner portions of the seed split very readily into two thick fleshy parts, and that lying between them is a tiny young plant. Notice how this young plant is connected on either side with the fleshy parts, so that to separate them you must tear one side or the other as in fig. 4 B, where at (~a~) we see the scar left where the tiny plant (~p~) was torn from the side. The two big fleshy parts are really portions of the young plant, and are in fact its two first leaves, but they are very different from ordinary leaves, and are packed with food substances, and are called the ~cotyledons~, or “nurse-leaves.” Notice also the tiny root of the baby plant or ~embryo~, as it is called; it bends a little to the outer side, and fits into a kind of pocket in the skin of the coat. You can see the shape of the root even from the outside of the dry bean (~see~ fig. 4, A (~r~)). You will find in the pea, cucumber, and many other seeds, that there is also the tiny embryo with its two nurse leaves, the whole being protected by strong coats. The differences between the bean, pea, and cucumber seeds are only in the details of shape and colour, not in the actual ~parts~ of the seed.

In the case of maize and corn, however, you will find that the seed does not split into two equal parts like the bean, but that the young plant lies at one side of the seed, and a solid white mass fills the rest of the space (~see~ fig. 5). There are also differences in the seedlings which you will notice when they begin to grow.

Now that you have examined some seeds, you should start a number growing, so as to have plenty to watch. They will grow more quickly if you soak them in water for a night before you plant them in damp sawdust, and keep them moist and fairly warm all the time. You should have a number of seeds of each kind planted together to provide enough for you to dig up one of them every day and examine it fully, inside as well as out. Make a drawing of each one so that you will have a complete series of drawings showing how the young plants grow. This will kill them, so that you must leave at least one seedling which is never touched, and which you can watch all through its life.

As the young plant grows, notice how it breaks away from the protection of its nurse leaves; first the root comes out and bends downwards into the sawdust (~see~ fig. 6 A), then the little shoot which bends up into the air.

Whichever way you plant the seeds you will find this is always the case, for even if you start with the root pointing up, it will bend round and grow downwards while the shoot bends up (~see~ p. 41).

As the plant gets bigger, side roots grow out from the main one, and the little leaves of the shoot begin to open out--the whole plant is growing (~see~ fig. 7).

=Now we may perhaps begin to find out something about the question of feeding in plants.= What are the nurse-leaves doing all the time the plant is growing? You will find in the bean that the seed coats may split open a little, but that on the whole the cotyledons remain all the time enclosed in them, and attached to the young shoot (~see~ fig. 7). Examine the nurse leaves of seedlings of different ages, and you will see that they are much less thick and fleshy in the older seedlings. As the plant gets bigger the nurse-leaves get thinner and less until they become merely dry shrivelled remnants.

Now, ~what use could the cotyledons be if they only shrivel away~?

Take a freshly soaked seed and cut a thin slice of the nurse-leaves and drop it into a little solution of iodine;[1] the tissue will go a violet blue colour. Then drop iodine on a piece of bread, a piece of potato, and some boiled rice, and you will find that they also go blue, or almost black. The food in the nurse-leaves is in some ways the same as that in bread, potato, and rice, and in many other things we eat.

[1] Get a chemist to make a solution of iodine and potassium iodide, which should be a bright, clear, orange colour.

The part of the food which goes blue with iodine is ~starch~, and this blue colouring of starch with iodine is an easy and safe test for it. You will see the same colour if you take some ordinary laundry starch and stir it up with hot water and a little iodine. Look now at the corn seed; the white solid mass in the seed contains starch, as you can prove with iodine, and although it is not in the cotyledon, yet it is quite near the young plant, which can get at it easily.

We have found, therefore, that ~young plants have a store of food in their nurse-leaves, or near them in the seed~, and that this food is the same as very much of our own food, that is, it is starch. There are other food substances present, too, but they are more difficult to find. The seed, therefore, contains not only the young living plant itself, but also a storehouse of food for its use, ~and as the plant grows we see this store getting less and less~ in the shrivelling cotyledons. This shows that the young plant uses up this food in the course of its growth.

But you must not forget that, although we find the young plants provided with food in this way, we have not yet settled the question of the food supply for all plants. As we see, the cotyledons shrivel up and are emptied of their store long before the plant is full grown. Remember that baby calves have milk for food, while old cows have grass. And when the store of food supplied in the seed is finished the older plants must find new supplies for themselves.

In growing seedlings you must always keep them well supplied with water, the soil or sawdust in which they grow ~must~ be kept moist. If you take one out of the sawdust and try to grow it only in the air, you will find that it soon dies. Even for the seedling the storehouse of food is not enough; it requires to have water too.

You can keep seedlings growing quite well, however, if you place them in glass jars so that their roots are in water, or even in closed glass jars standing over water, so that the air is thoroughly moist. You will then be able to see very well numbers of fine white hairs on the roots (~see~ fig. 8). These hairs are very important and absorb the water which keeps the whole plant moist.

You have now seen that seedlings require ~water~ for their life just as animals do; and also that young plants are provided by their parents with a store of ~food~ which is largely ~starch~, and which they use up during their early growth.