DESERT VEGETATION. 



571 



ward while new shoots are developed. Peucephyllum schattii, 

 on the other hand, is tree-like in habit, having a common trunk, 

 and thus in old age dies. These two shrubs, according to Co- 

 ville, represent the two types in the Death's Valley. 



The perennial vegetation, aside from the true shrubs, is pecu- 

 liar. Only a few species have enlarged roots for water storage 

 during the dry season. In these the aerial stems die down to 

 the ground. A large number of them, however, are suff rules- 

 cent, i.e., the lower portion of the aerial shoots is shrubby. These 

 remain green, and slow transpiration goes on during the dry 

 period, as in the case of the true shrubs, while the roots are not 

 thickened for water storage, but find enough hygroscopic water 

 to supply the reduced shoot system. 



Fig. 509. 

 Desert society, chiefly yucca. 



Cacti, Yuccas, etc. Trees are not present in the true desert 

 portions of the regions, while around springs or along streams, 

 or in the vicinity of basins where there is ground-water through- 



