Stránka:book 1922.djvu/456

426 The Book of Woodcraft shedding its bark as well as its leaves. Leaves 4 to 9 inches long. Canada to the Gulf. When a tree is a mere sapling, the bark is thin and soft; it stretches each year with the annual growth of the trunk. But it becomes thicker and harder with age and then it cracks with the expansion of the trunk. This process continues each year till the segments of the first coat are widely separated by gaping fissures. This is well seen in the Elm, and each of the bark ridges shows the annual layers, from the widely sep- arated outer one to the united inmost one. But some trees, notably the Sycamore, burst their bark, yet do not retain the fragments. These are dropped each year, hence the smooth green surface of the trunk, hence also its success as a tree of grimy cities, for it has an annual cleaning of the skin and thus throws off mischievous accumulations that would kill a tree that retained its bark indefinitely. The Shagbark Hickory will be remembered as a halfway shedder.