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454 A TEXTBOOK OF GENERAL BOTANY 
Deserts are characterized by an open growth of comparatively — 
small plants many of which are thorny (Figs. 44, 512). Plants of 
desert regions are adapted in various ways to withstand adverse 
conditions. Some, particularly shrubs and shrubby trees, have 
long roots that reach down to subterranean water. The cacti 
have roots that spread near the surface of the soil. When the 

Fig. 509. Bush land in Australia in a region with an annual rainfall of ten 
to thirty inches 
soil is wet, considerable quantities of water are absorbed by the 
extensive root system and then stored in the enlarged stems. 
Deserts usually have a short rainy season when conditions are 
fairly favorable to vegetation and during which annuals spring 
up and pass through their whole development. Such annuals do 
not have a xerophytic structure. Other plants, with perennial 
underground portions, send up aérial shoots which disappear 
after the moist period. Some of the shrubs are leafless or have 
greatly reduced scale leaves; others have small, xerophytic, 
