DESERT VEGETATION. 



573 



sisted of two branching stems q&cm (19 in.), which consist of 

 cylindrical to flattened, pear-shaped, thick, succulent portions 

 devoid of leaves, provided with a thick cuticle and large water- 



Fig. Si I- 



Desert vegetation Arizona, showing clump of prickly-pear cactus in foreground 

 with radiate shrubs in background. Open formation. (Photograph by Tuomey.) 



storage system. There were eight roots with an average length 

 of 2-$m (7-10 feet), each of which had numerous lateral branches. 



III. Other Desert Regions. 



1060. The greatest desert region in the world comprises the 

 great Sahara Desert, which extends across the northern part of 

 the continent of Africa between 20 and 30 north latitude, and 

 then extends over Arabia, then southward over south Persia 

 and Beluchistan and the northeast corner of farther India. 

 The next in size is in central Asia, from the Caspian Sea to the 

 mountains which separate Mongolia and Manchuria. The 

 largest one in the southern hemisphere is in central Australia; 

 there is a smaller one in southwest Africa, and a narrow desert 



