Thumbprints - Cork
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Cork oak (Quercus suber) with sections of cork removed. This tree is native to the Mediterranean region. Cork consists of the irregularly shaped, thin-walled, wax-coated cells that make up the peeling bark of the birch and many other trees, but, in the restricted commercial sense of the word, only the bark of the cork oak merits the designation of cork. The cork oak grows abundantly in Portugal, Spain, parts of southern France and Italy, and North Africa. The tree is usually about 18 m (60 feet) tall, with a broad, round-topped head and glossy green, hollylike leaves. Cork is obtained from the new outer sheath of bark formed by the inner bark after the original rough outer bark is removed. The outer sheath may then be stripped and will form again. Unlike the inner bark, the outer bark, or cork, is not vital to the tree's survival and functions merely to protect it from the heat and dry winds of the Mediterranean summer. The repeated stripping of cork is possible because the inner bark of the cork oak develops an especially uniform and continuous regenerative tissue. After the outer bark has been peeled, this tissue proliferates sufficient cork cells to the outside so that, in a healthy tree, 2.5-5 cm (1-2 inches) of a uniform new cork sheathing forms in from 3 to 10 years. Stripping this regenerated layer yields commercial cork slabs.