In a young holly, and many other plants, we find growing out from the central stem smaller side branches which bear the leaves. As we have found already (Chapter VI.), the leaves are the active parts of the plant and do the food-building, so that the stem is chiefly useful as a support, which keeps them in a good position as regards the light and air. In general, we do not see much of the stem because it is largely hidden by the covering of leaves, so that if you want to study stems you should go to the woods in the winter when there are no leaves on the trees, and you can see the form of the branches themselves. In big trees, such as the oak and beech, the stems are very important, and the chief stem or ~trunk~ becomes very thick as it gets old. It is made of hard wood which is tough and strong, for such high trees have to bear great strain from the winds, as well as the weight of all the leaves. If you go into the woods when it is very windy, and watch the thick wooden boughs swaying, boughs which you could not move, you will see how much force the wind may sometimes have. The branches need all their strength in the summer to support the curtain of leaves which catches the wind. In a big tree we find the few chief branches thick and strong, but there are many hundred smaller ones, some of them dividing to quite delicate branchlets which bear the leaves, so that the whole tree body is very much complicated (~see~ fig. 43). [Illustration: Fig. 43. Much-branched stem of the Oak.] Each kind of tree has a way of branching which is characteristic of its species, so that even without leaves or flowers a woodman can tell what a tree is. This one can learn by practice in the woods, but to begin with it is rather difficult. Without going into detail, however, we may notice great family differences, such as exist between a larch or a Christmas-tree and an oak. In the first two there is one straight main trunk, with side branches at very regular intervals (~see~ fig. 44), and in the oak the main thick trunk soon bears several large branches nearly equalling the main stem; these divide again and again in a rather irregular fashion (~see~ fig. 43). [Illustration: Fig. 44. The Larch, showing its strong central trunk and more delicate side branches.]