Bark
the exterior covering of the stems of exogenous plants. It is composed of cellular and vascular tissue, is separable from the wood, and is often regarded as consisting of four layers: (1) The epidermis, or cuticle, which, however, is scarcely regarded as a part of the true bark; bark; (2) the epiphlœum, or outer cellular layer of the true bark or cortex; (3) the mesophlœum, or middle layer, also cellular; (4) an inner vascular layer, the liber, or endophlœum, commonly called bast. Endogenous plants have no true bark. Bark contains many valuable products, as gum, tannin, etc.