Fig. 232. Cinchona rubra - Cross-section of bark.
A, Cork cells. B, Cortical parenchyma. C, Coloring matter, deposits between and within the cells. D, Medullary ray. (Black line from D should not extend beyond the first two rows of cells in the figure.) E, Bast fibers.
This image is from Cinchona in Sayre's Manual of Organic Materia Medica and Pharmacognosy, 1917.