Bark

Bark, a term somewhat loosely applied to the outer part of an exogenous stem. By woodcrafts-men it is commonly employed for everything external to the cambium or growing-layer, which is the layer torn through in "barking" a tree, and they divide it into the two layers, the fibrous inner bark, or bast, and the outer bark or cork. Botanists employ the term rather to the dead tissues - whether in part composed of the epidermis, the hypoderm or other part of the primary cortex, the periderm or corky secondary cortex, or sometimes, in part, of bast - which are spontaneously thrown off by the tree, owing to the formation of cork below them by which they are cut off from all the vital juices of the plant. Medicinally the term is more especially applied to the bark of the Cinchonas, the source of quinine.