PLANT SOCIETIES 



447 



ground the " bunch " grasses, like buffalo grass, beard-grass, or 

 broom-sedge, etc., are dominant, and in the drier regions as one 

 approaches desert conditions the vegetation gradually takes on 

 more the character of the desert, so that in the plains, sage-brush, 



Fig. 408. 



Winter range in northwestern Nevada, showing open formations; white sage (Eurotia 

 lanata) in foreground, salt-bush (Atriplex confertifolia) and bud-sage (Artemisia spinescens) 

 at base of hill, red sage (Kochia americana) on the higher slope. (After Griffiths, Bull. 38, 

 Bureau Plant Ind., U. S. Dept. Agr.) 



the prickly-pear cactus, etc., occur. Besides the dominant vege- 

 tation of the society there are subordinate species, and the 

 societies are especially marked by a spring and autumn flora of 

 conspicuous flowering plants which are mixed with the grasses. 



634. Desert societies. These are composed of plants which 

 possess a form or structure enabling them to exist in a very dry 

 climate where the air is very dry and the soil contains but little 

 moisture. The true desert plants are perennial. The growth 

 and flowering period occurs during the rainy season, or those 

 portions of the rainy season when the temperature is favorable, 

 and the plants rest during the very dry season and cold. Charac- 

 teristic desert plants are the cacti with thick succulent green 

 stems or massive trunks, the leaves being absent or reduced to 

 mere spines which no longer function in photosynthesis; yuccas 



