XEROPHYTIC SOCIFTIES 509 
Fic. 459.— A deciduous forest, a mesophytic society consisting of Bass- 
wood, Birches, Elms, Maples, and Oaks, under which grow many herbaceous 
plants. After C. M. King. 
Xerophytic Societies. — These are the societies adapted to 
drought. Among xerophytic plants there are various adapta- 
tions to drought, such as sunken stomaia, hairy epidermis, re- 
duction of leaf surface, deep tap-roots, reservoirs within the 
leaves or other parts of the plant for holding water, edgewise 
position or rolling of leaves, bridging over the period of drought 
in the form of seeds or subterranean structures, etc. 
Among the xerophytic societies are the rock societies, composed 
chiefly of Lichens (Fig. 460) and Mosses which grow on dry and 
exposed rocks; desert and dry plain societies (Fig. 461) where such 
plants as Cacti, Sage Brush, Agaves, and Yuccas dominate; zero- 
phytic thickets, composed of a dense mass of bushes and repre- 
sented by the chaparral of the Southwest; and the xerophytic 
forests, in which Pines, Spruces, and Firs, adapted to mountain 
slopes and gravel ridges, occur. 
