EPIDERMIS. 181 
While the outer walls of the epidermal cells, as a rule, are 
thick, the lateral walls are mostly thin. The Figs. 63, 109, 129 
and 155, therefore, reproduce the type of epidermal cells. 
Upon surface sections, the lateral walls appear in many cases 
sinuous, as, for instance, in all leaves of the Graminee (Figs. 88 
B, 90, 154, 15%, 158), so that the individual epidermal cells 
which are provided with many protuberances fit into each other 
in a tooth-like manner (many corolla leaves, and the epidermis 
of Semen Stramonii, Fig. 90). 
As a rule, the contents of the epidermal cells are colorless, 
Fre. 90. Fie. 91. 
Fie. 90.—Tangential section through the epidermis of Semen Stramonii. 
Fie. 91.—Transverse section through Chinese galls; a, epidermis, the cells of which 
frequently grow out in the form of simple hairs; b, lacticiferous cells, 
without chlorophyll; occasionally, however, coloring matters 
appear in them, dissolved in the cell-sap. Colored epidermal 
cells produce, for example, the red color of many stems (buck- 
wheat, Ricinus) and other organs (the apple). In the red 
potatoes, the coloring matter is contained in cells lying beneath 
the cork. 
It has already been mentioned (page 180) that the epidermal 
cells often project outward. If these protuberances become — 
