Fig. 65. A series of bud scales from a Horse Chestnut; (a) and (b) are entirely hard and brown; (c) and (d) are brown at the tips and green at the base, where the others cover them; (e) is quite green, soft, and leaf-like.
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, a1, and a2). 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.
Fig. 66. Branch of Sycamore, showing leaf stalk (l) with bud (b) in its axil. Scars of leaf stalks (s) and large terminal bud (t) with scars (a), (a1), and (a2) left by the terminal buds of past years.