CHAPTER XIV.
BUDS
The proper time to study buds in nature is the spring, but then you will have to wait long to see all the different stages of their slow unfolding. But they can be made to open artificially, and it is really wise to study buds in winter, when there are not so many other things to do. You can arrange this very well if in the late autumn you cut off fairly big branches with buds on them (horse chestnut is particularly good for this) and keep them in a warm room. You must, of course, keep the cut ends of their stalks in water, which you should change every three or four days, sometimes cutting off a piece from the ends of the branches so that they have a fresh surface exposed to the water. In this way they should live for months, and may just begin to unfold and show fresh young green leaves about Christmas time, when the buds on the trees out in the cold are still tightly packed up.
Watch the buds as they unfold, and you will find that round each bud are several dry brown scales; these drop off, and within them are more green, leaf-like scales enclosing the true young leaves, which are still curled up and very small when they first come out.
If you examine a big bud which has not yet begun to unfold, and carefully pull off all the parts separately with the help of a needle and knife, you will see how the outer scales fold over one another like a coat of mail, and where they are exposed to the outside air they are hard and shiny, and in many plants are covered over by a sticky waterproof substance like tarpaulin. These outer scales keep off the rain and snow, and keep the inner parts dry and unharmed. Within them the scales are softer and often quite green, and they, too, wrap round each other, so that there is no crack left which could allow the cold rains to enter to the little leaves within. In many cases also the young leaves are wrapped up in soft, long hairs which look almost like cotton wool. These hairs grow on the leaves themselves, and you can see them after they have opened out, but as the leaves are then much bigger, the hairs are scattered further apart and do not show so much.
If you cut right through the length of a bud with a sharp knife, you will see how all these scales and young leaves are packed together, as in fig. 64.
Take another bud and carefully pull off all the scales one by one and lay them in a row, beginning with those right outside; you will see that they get less scale-like and more like real leaves as you go in towards the centre of the bud (~see~ fig. 65). The outside simple brown scales scarcely look like leaves at all, but the inner ones are green and soft, and in some plants, those right inside have quite a leaf-like appearance.
This helps us to see that ~bud scales are really only modified leaves, which are altered for their special work of protection~ of the young leaves through the winter.
Of course, you know that the buds are already on the trees in the late autumn after the leaves have fallen; but have you seen the buds already there in the summer while the leaves are still fresh and green? If you look for buds you will be sure to find them, and at the same time you will learn where they grow on the stem. You must look right at the base of the leaf stalk, in the angle made by the leaf stalk where it joins the main stem; this is called the ~axil~ of the leaf, and it is in the axil of the leaf that you will find the small green buds in summer-time. These buds grow out in the following year, so that a new leaf comes in very nearly the same place as the old one, or, what is more usual, there grows out a new branch which may bear several new leaves. Now examine a twig of horse chestnut or sycamore from which the leaves have dropped; notice that, where the ~buds~ are to be seen on the stem, they ~lie immediately above scars~ of a definite shape, ~which are the scars left by the fallen leaf stalks~, as you can see by comparing them in the autumn with leaf stalks which are just falling away (~see~ fig. 66, ~l~, ~b~, and ~s~).
On the stem there are other scars, which are different from the ordinary leaf scars, and which are like bands of fine lines round the stem. What are these? Now if the single big leaf stalk leaves its scar so clearly on the stem, what kind of scar would a number of thin scales lying close together be likely to leave? Will it not be a number of narrow scars in a band, just such a scar as we have here (fig. 66, ~a~, ~a~^1, and ~a~^2). If you mark a bud on a tree or one of the branches in your room and watch it unfold, and keep a note of it till the autumn, you will find at its base where the bud scales were, that there is then a scar just like this. Whenever you see such a scar you will know that it has been left by a bud. Now you know that, as a rule, trees have buds only once a year, so that each of the bud scars along the stem must represent a past year’s bud, and if you count these scars along the length of the stem it will tell you the number of years the stem has been growing. For example, in fig. 66 the twig shows us five years’ growth if you count the last bud which will grow out to form a shoot.
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).
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~).
Sometimes little bulb-like structures grow in the axils of ordinary leaves, for example, in the tiger lily; these drop off when they are ripe, and can grow into whole new plants. They are really half-way between bulbs and true buds.