The buds which come in the axils of the leaves along the stem may form new leaves, or may develop into side shoots with new stems and leaves. There is another bud, generally bigger than these, which grows at the end of the shoot (t, fig. 66). This has just the same structure as the others, but it will certainly grow out to form a stem and carry on the line of growth of the main shoot, unless it is injured.
The amount that the shoot grows in one year depends on very many things, on the light and warmth it gets, on its food and the growth of its neighbours. Hence, in the growth of different shoots in the same year, or the same shoot in different years, we find very great differences. Sometimes a number of bud scars lie very close together, showing that for several years it had only grown a small amount, while in the years following it may have added very much to its length. In some plants there are little side shoots which never grow much, and always remain quite short; for example, in the larch each tuft of leaves grows on a little stunted stem which represents several years’ growth, and which never reaches any length (see fig. 67).
Fig. 67. Larch, with tufts of leaves growing from short side shoots.
Not only do we get leaves and stems packed away in buds, but the flowers for next year are there also. For example, examine several of the big horse chestnut buds from the outer branches of the tree, and you will be sure to find tiny sprays of young flowers packed away in the hearts of some of them.
There are some quite special buds which we must notice, and which at first sight appear very different from real buds. They have been given a different name, and are called Bulbs. Cut right through a tulip or hyacinth bulb lengthways, and compare it with a horse chestnut bud to which you have done the same. The arrangement of the parts of the two things seems to be very similar. If you examine the bulb in detail, you will find that it is protected on the outside by brown, hard scales, and that the softer leaves within are folded over each other very much like those in the true buds. Now the bud of the horse chestnut is attached to the parent stem—is there nothing corresponding to the stem in the tulip bulb? Look carefully at the base, and you will see a little mass of tissue which holds the scales together (see S, fig. 68); this is the stem, which is short and very much reduced, being unlike a usual stem. There is also one great difference between the scales in the bud and the bulb. In the bud they are rather thin and dry, but in the bulb they are thick and white and very fleshy, and if you test them with iodine, you will find that they contain much starchy food. They form the storehouse of the tulip, and this food will be used by the plant when it begins to grow. In the axils of these thick fleshy leaves you may often find small buds, which will get large and fleshy by next year and form the new bulbs (see fig. 68 b).
Fig. 68. Bulb cut through, showing the overlapping scales (s) packed with food attached to the shortened stem S. B is the bud, which will grow out into the air, and (b) the bud which will form a new bulb next year; (r) adventitious roots growing from the base of the stem.