in. PHARMACEUTICAL BOTANY 
that the walls of the cork cells are composed of three layers or 
lamella. The lamella next to the cell cavity is cellulose. 
Outside of this is a middle lamella which may be lignified and 
a lamella of suberin. Cork tissue is usually devoid of inter- 
cellular-air-spaces. It forms a protective covering to the roots 
of secondary growth, perennial stems (after the first season) 
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roseum. X50. ep, epidermis; co, primary cortex; fer, pericycle filled with peri- 
cyclic fibers; ph, phloem; ca, cambium (intrafascicular); x, xylem; mr, medullary 
ray; m, pith, composed of ordinary parenchyma. 
of Dicotyledons and Gymnosperms, and wounds of stems and 
branches. It protects the delicate underlying tissues from 
invasion by fungal parasites, from sudden changes in tempera- 
ture, and from loss of water. 
The suberized walls of cork cells resist the action of concen- 
trated sulfuric acid. They are colored green, when in contact 
with alcoholic extract of chlorophyll for several days in the dark. 
RHYTIDOME sometimes called “scale bark” or “shell bark” 
represents the outer crust of alternating cork and cortical or 
pericyclic and phloem tissues resulting when cork cambia arise 
