3] 



PHYSIOLOGICAL REACTIONS 



85 



. , i«A' ^jt^im^Df^-^ 



BLACK GRAMA 



PMKRLV ORAtCO 



Fig. 20. — Features aiding water conservation or absorption. A, branch of a 

 desert plant, Hakea, with the leaves modified as spines ( :< i); B, stems of 

 Euphorbia tinicalli, specialized for photosynthesis and water storage ( ■: about g); 

 C, Arizona desert with large Cacti (phot. F. Shreve); D, cut bank on Jornada 

 Experimental Range, New IMexico, showing deep rooting of low desert plants — 

 in particular a ^lesquite bush about 12 inches (30 cm.) in diameter and only 

 6 inches high but with roots about 8 feet (nearly ai metres) deep (phot. U.S. 

 Forest Service); E, ' bisect ' diagram of above- and below-ground parts of forbs 

 and Grasses in the Palouse prairie grassland association of western central Idaho, 

 U.S.A. (courtesy of U.S. Soil Conservation Service) ; F, BlackGrama Grass 

 {Boiiteloiia eriopoda) grown under three degrees of grazing, showing effect on root 

 system (courtesy of U.S. Soil Conservation Service). 



