570 



RELATION TO ENVIRONMENT. 



leaves as well as the binding effect of the profusely branching 

 roots often holds the sand in place in the form of tall columns as the 

 wind moves the surrounding portion forward. Other charac- 

 teristic woody plants are Atriplex canescens, Yucca radiosa, etc. 

 This Yucca is sometimes buried by dunes and seems to have the 

 power of growing out at the top again as it is buried from time 

 to time with the increasing height of the dune. 



1059. The true desert flora. The shrubs have the compact 

 rounded growth, and small, thick, gray leaves peculiar to most 



Fig. 508. 



Sage-brush (Artemisia tridentata), showing open formation in desert, Arizona. 

 (After Schimper. ) 



perennial desert plants, since their relation is confined to the 

 physical forces of environment, not at all to the organic, because 

 the formation is an open one. The height of the shrubs is rarely 

 over i-i.5w (3-4^ feet), and is usually less. The sage-brush 

 (Artemisia tridentata), one of the largest shrubs, barring accidents, 

 never dies, for there are numerous shoots from the subterranean 

 stock, and as the older ones die they bend outward and down- 



