"'The _cork_ oak'!" exclaimed Clara, quite as much surprised as she was expected to be. "Do the corks that come in bottles grow on it?"
"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_"
"I should like to see how they get it," said Malcolm.
"The trunk is regularly marked around in deep cuts, which begin close to the branches and go down almost to the roots. A ladder is used to mount to the upper part of the trunk, and the cuts, or incisions, are made with a long knife or with an axe. Then they strip off the sheets of cork between the circles. This operation is a very delicate one, and requires much care and skill lest the inner part should be injured. If the operation is carried out successfully, the cork-like substance will grow again and become as abundant as ever.
"The next thing to be done to the pieces of bark is partially to burn, or char, them, and also to make them quite flat, as they come from the trunk in a rounded shape. The burning makes the pores close up, so that the liquid in a vessel for which it is used as a stopper cannot come through; and this is done over a brisk fire, in what is called a _burning-yard_. Another process, called _rounding_, removes every trace of the fire, unless the cork has been too much burned, and then, having already been flattened by the pressure of heavy stones, it is ready for the cork-maker, who cuts the material first into strips and then into squares according to the size of corks wanted.
