"Not just in that shape, dear, but they are made from its bark. The outside bark, or _epidermis_, consists of a thin, transparent, tissue-like substance, which covers not only the bark, but the whole of the tree, stem, leaves and branches, and beneath the epidermis is found a layer of cellular tissue, generally green. It covers the trunk and branches, fills up the spaces between the veins of the leaves and contains the sap, which flows in canals arranged for it in the most beautiful and wonderful manner. In one species of oak this layer--which is called the _suber_--assumes a peculiar character and is of remarkable thickness. When the tree is some five years old, its whole energy is directed toward the increase of the suber. A mass of cells is formed with great rapidity, and layer upon layer is added, until that part of the trunk grows so unwieldy that it would crack and split of its own accord. But such a thing is rarely allowed to happen: the suber is of too much value to man. After it is taken from the tree and has undergone due preparation, it appears in our shops and houses under the name of _cork_"