770 



TEXTBOOK OF BOTANY 



In all semi-arid and arid regions there are undrained basins where 

 continued evaporation of water that flows into them from adjacent up- 

 lands leads to the accumulation of salts. These accumulations var\" all 

 the wav from common salt, basic carbonates, sulfates, to borax. These 

 salts are variously toxic, and when concentrated exclude all plants, but 

 when dilute max not interfere with the growth of a limited number of 

 plants such as grease wood, several species of salt bush, salt grass and 

 the succulents: seepweed, pickleweed, and samphire. 



Desert (Figs. 397-400). The driest areas of North America are in 

 Lower California, adjacent parts of California, and parts of the Sonora 



Fig. 396. A sagebrush desert near Nephi, Utah. The plants pictured here are 

 about 4 feet high and range in age from 30 to 50 years. The associated species 

 are mostly annuals which grow only during the rainy periods. Sagebrush is the 

 characteristic natural vegetation on the better soils of the Great Basin region. 

 Photo bv H. L. Shantz. 



and Chihuahua deserts. The region as a whole has about 10 inches of 

 rainfall, but local areas ha\e as low as 3 inches and in some vears no 



