(2) The cambium. Inside of the rind and between it and the wood, there is, on living trees, a slimy coat called cambium (Med. Latin, exchange). This is the living, growing part of the stem, familiar to all who have peeled it as the sticky, slimy coat between the bark and the wood of a twig. This is what constitutes the fragrant, mucilaginous inner part of the bark of slippery elm. Cambium is a tissue of young and growing cells, in which the new cells are formed, the inner ones forming the wood and the outer ones the bark.
Fig. 5. Young Stem, Magnified 18½ Diameters, Showing Primary and Secondary Bundles. By Courtesy of Mrs. Katharine Golden Bitting.
E, epidermis, the single outside layer of cells.
C, cortex, the region outside of the bundles.
HB, hard bast, the black, irregular ring protecting the soft bast.
SB, soft bast, the light, crescent-shaped parts.
Ca, cambium, the line between the soft bast and the wood.
W, wood, segments showing pores.
MR, medullary rays, lines between the bundles connecting the pith and the cortex.