[Illustration: Fig. 49. Leafy branch of Bramble which has bent into the earth and given rise to a cluster of adventitious roots at the tip; ~l~, level of soil; P, point where the branch was cut from the parent plant.] In the case of the bramble notice how the leaves get smaller and smaller towards the tip of this branch as it bends down to the earth, and of course, they do not develop at all as true leaves under the soil (~see~ fig. 49). From these examples, and the many others you should be able to find for yourselves, you see that stems may take on other duties beyond their two chief ones, but that, however much they change their form and appearance, we can always find out that they are really stems by studying them with a little care. CHAPTER XIII. LEAVES The late spring and summer are the best times to study leaves, for, as you must have noticed, the woods begin to lose their green in the autumn, and the leaves have fallen in the winter. This tells us that the fresh greenness of the leaves (which you know is so important for the plant) does not last very long, and when they are no longer green the leaves are useless and drop away. As you know, =the chief work of leaves is to build starchy food=, for which they require their green colour. [Illustration: Fig. 50. Simple leaf of the Cherry.] When you go into the woods or gardens to study the leaves, first look at single ones, collecting as many kinds as you can. Though their shape varies very much, you will find that in almost all cases they are green, expanded, and flat. Let us first examine a single simple leaf, like that of a cherry. You will see that the expanded part (called the ~leaf blade~ or ~lamina~) narrows down to a small stalk, which connects the blade with the stem from which the leaf is growing; this stalk is called the ~leaf stalk~ or ~petiole~. Then at the base of it, just where it joins on to the stem, there are two little leaf-like structures which are not true leaves, but which belong to the leaf and are called ~stipules~; they are attached to the base of the petiole, which spreads out to clasp the stem, and is called the ~leaf base~ (~see~ fig. 50). Such a leaf shows us all the parts of a ~simple~ leaf; but some leaves have no stalks, others no stipules, and so on. [Illustration: Fig. 51. Compound leaf of the Rose.] Let us compare a rose leaf with the simple leaf of a cherry, oak, or beech. In the rose you will find five or seven small leaflets arranged on a single main stalk, and each of these leaflets separately is very much like a single leaf of the beech. Such a leaf as this we call ~compound~, for it is divided up into several parts, each of which looks like a whole leaf (~see~ fig. 51). Leaves are of very many different kinds and shapes, and special names have been given to each kind, which you can look up in a book if you want to classify them.