CHAPTER XI.

ROOTS

If you have a garden of your own, or have even watched another person gardening, you must have found out that it is not always an easy thing to get rid of the weeds, and that when one tries to “pull them up by the roots,” they often resist it very strongly indeed. If you have never done this, try to pull up a large grass tuft or a hedge mustard, or any fairly big common plant, and you will find that often when it does not look very strong it may be extremely difficult to get it completely out of the soil, and even when it comes out you may find that you have not got it quite whole, for the finer branches of the root will generally break off. Now this shows us one of the uses of its roots to a plant; they keep it firmly in the soil, and prevent the wind from blowing it away, and people or animals from overturning it too easily.

To see the form of a complete root it is wise to choose a fairly small plant, let us say a daisy, wallflower, candy-tuft, or young holly; then loosen the earth all round it and pull it very gently from the soil. Shake off the mud and then wash it clean and spread it out on a sheet of white paper so that you can examine it properly. Notice that there is a central chief root, with many side branches which have again finer and finer branchlets (~see~ fig. 36). At the tip of the very finest you should see a number of delicate hairs, the root hairs, but it is very possible that you will have torn these off with the soil. To see them best, look at some of your seedlings which have grown in moist air, where they are very well developed (~see~ fig. 8). In any of these plants you will notice that the main root seems to be a downward continuation of the main stem, and that the side roots come off all round it, just as was the case in your bean seedlings (~see~ figs. 36 and 7). Such a root is called a ~tap root~.

Now dig up a small grass plant and compare its root with these, and you will see that there is no main root, but very many roots coming off in a tuft from the base of the stem, just as was the case in your corn seedlings (~see~ fig. 37). The difference between these roots and tap roots is not of much importance as regards the actual work they do but is one of difference in form; the finer branches in both are very similar and have the same work to do.

If you leave the plants you have pulled up lying in the air for an hour or two, you will find that they will wither, the leaves becoming quite limp and the whole plant drooping. Now place them with their roots only in water, and you will soon find that they are beginning to revive. They will revive fully and live a long time if their roots are kept in water. This reminds us of the second very important use of its roots to a plant, which we have already found out (~see~ Chapter IV.), and shows us again that the roots absorb water and keep the whole plant supplied with it. Of course you know that cut flowers can drink up water with their stems, but that is only for a short time, and is not quite natural. The special part of the rootlet, which does the actual absorption, is the part near the tip which is covered with root hairs. You have already seen these root hairs in the course of your work (~see~ pp. 13 and 15).

There are then =two chief duties of roots=, ~to absorb water from the soil for the whole plant, and to hold it firmly in the ground~. The fine fibres of the root, which are so much divided and run in the soil, serve both these purposes, as they expose a large area to contact with the soil, and so can absorb much from it, as well as getting a good hold of it.

As well as these two chief functions, =there are many other pieces of work which roots may do=, and according to the special work they take up, so they become modified and look different from usual roots.

One thing they often do is to act as ~storehouses of food~. For example, examine the root of a carrot. The part we commonly call the carrot and which we eat, you will see is really the main axis of the tap root, and has the little side roots attached in the usual way. The unusual thickness of the main root is due to the large quantities of food which it stores. Just in the same way radishes and many other plants have their main roots very thick and packed with food, while dahlias have their side roots thickened in a similar way (~see~ fig. 39). Such modified roots, which look quite different from ordinary ones, are called ~Storage roots~, and if you examine many of them you will find them packed with starch (~see~ p. 11 for iodine test).

Although it is general for the roots to hold the plant firmly in the ground, ~in some cases they grow out of the stem in the air~ and help to hold it up against a tree or wall, or some support, as in the case of ivy. If you pull off a branch of ivy which is climbing up a tree you will find that all along the back of the stem there are tufts of short thick rootlets which often come away holding a piece of the bark of the supporting tree. These roots, you will see, do not come out in the usual way from the main root or base of the stem, but come out all along the stem itself (~see~ fig. 40). Such special roots are called “Adventitious,” and they grow from the stem wherever they are needed.

~Adventitious roots~ may also come out from a wounded plant which has had its true roots cut away. For example, take a piece of Forget-me-not stem without any roots, and slit it at the base, and put it in a glass of fresh water. After a week or so you should see little white roots growing out from the stem into the water, and if you let them get strong you may then plant the sprig and get a new forget-me-not plant from it. In this and all “cuttings” adventitious roots growing out from the stem do the usual work of roots. There are many other kinds of adventitious roots, but we must only mention the orchids, some of which have long tufts of roots which grow out irregularly from the stem and hang in the air. These are special ~air-roots~, and grow on many orchids, but also on some other plants which live attached to trees and absorb the water out of the air instead of from the soil (see fig. 41).

There are many other curious roots, particularly in plants which grow in tropical countries, ~e.g.~, the ~stilt roots~ which come out from the base of the stems of many palms and make tripod-like supports (~see~ fig. 42), and others which grow from the high branches to the ground like pillars, and prop up the heavy trunks. However, we do not need to go so far to find very many different kinds of roots, and if you examine carefully those of the plants growing in our woods and lanes, you will find what a number of extra pieces of work they can do, in addition to their two chief duties of drawing in water from the soil, and holding the plant in its position in the earth.