Fig. 17.1-4a and b. Tangential section of bark. These two sections were cut with a paradermal orientation, that is, parallel to (tangential to) the surface of the trunk. The upper section passed through a layer of cork cells, the other passed through a layer of sclereids. The cells do not have any special size or shape, nothing similar to the precise shapes of the vessel elements, fibers or ray cells produced by the cells of the vascular cambium. And whereas the vascular cambium consists of fusiform initials and ray initials, the cork cambium just has one type of nondescript cell.

            Both sections of tissue were taken from the same block of bark, from a cactus, Leptocereus quadricostatus.