and, though the oaken logs are corroded by the weather, they are still
sound, and, having been beaten by the storms of a thousand winters, bid
fair to defy those of a thousand more."

"I should think, then," said Malcolm, "that people would always build
their houses with oak if it lasts so long."

"Yet they do not do this even in England," was the reply, "where the
trees grow to such an immense size and the ancient buildings still in
existence prove the great endurance of the oak. Now brick and stone and
iron are used, which outlast any wood. And now," continued Miss Harson,
"I am going to tell you something about a foreign species of this tree
which I am sure will surprise you. It is found in the South of Europe
and in Algeria, and is called the _cork oak_."

"'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