“Because we are hungry.” That is the direct reason, of course. But we are made hungry so that we shall be forced to eat; for when we eat, we take into our bodies the material that is needed to build them up,—to feed the cells which make the flesh and bone and muscle. And this is just why the plant eats and drinks. It needs constantly fresh nourishment for its little cells, so that these can live, and grow strong enough to make the new cells which go to form, not bone and flesh and muscle, as with you children, but fresh roots and stem and leaves and flowers and fruits. If these little cells were not fed, they would die, and the plant would cease to live also. And now what do you think happens to the broth that has been taken in from the earth by the root hairs? As we have said, this broth needs a little more preparation before it is quite fit for plant food. What it really wants is some _cooking_. Perhaps you can guess that the great fire before which all plant food is cooked is the sun. But how are the hot rays of the sun to pierce the earth, and reach the broth which is buried in the plant’s root? Of course, if it remains in the root, the earth broth will not get the needed cooking. It must be carried to some more get-at-able position. Now, what part of a plant is usually best fitted to receive the sun’s rays? Its leaves, to be sure. The thin, flat leaf blades are spread out on all sides, so that they fairly bathe themselves in sunshine. So if the broth is to be cooked in the sun, up to the leaves it must be carried. And how is this managed? Water does not run uphill, as you know. Yet this watery broth must mount the stem before it can enter the leaves. Water does not run uphill ordinarily, it is true; yet, if you dip a towel in a basin of water, the water rises along the threads, and the towel is wet far above the level of the basin. And if you dip the lower end of a lump of sugar in a cup of coffee, the coffee rises in the lump, and stains it brown. And the oil in the lamp mounts high into the wick. Perhaps when you are older you will be able somewhat to understand the reason of this rise of liquid in the towel, in the lump of sugar, in the lamp wick. The same reason accounts partly for the rise of the broth in the stem. But it is thought that the force which sends the oil up the wick would not send the water far up the stem. And you know that some stems are very tall indeed. The distance, for example, to be traveled by water or broth which is sucked in by the roots of an oak tree, and which must reach the top-most leaves of the oak, is very great. Yet the earth broth seems to have no difficulty in making this long, steep climb. Now, even wise men have to do some guessing about this matter, and I fear you will find it a little hard to understand.