A STUDY IN PLANT ADAPTATION. 



489 



It is probable that the thick covering of spines is of some value to 

 the plant in protecting it from the full force of the intensely bright 

 sunlight and also of some value in cheeking transpiration. These ever 

 present and formidable, barbed spines are well illustrated in Fig. 5. 

 They serve their greatest usefulness to the cholla in preventing its 

 destruction by animals and in the important part which they play in 

 the dissemination of the species. All the younger branches of the 

 cholla are soft and succulent and, were it not for their efficient armor 



Fig. 4 A Large Cholla moved frosi the JNIesa to the Garlen. 



of barbed spines^ would be quickly destroyed by herbivorous animals. 

 In acquiring a condensed and succulent plant body in order to fit 

 itself to a desert environment the cholla would have courted its own 

 ruin were it not that it acquired a full equipment of spines at the 

 same time. From every standpoint it is, as an individual, admirably 

 equipped for its desert home. It is, however, more than this; it is the 

 best equipped of all desert plants for rapid and wide dissemination. It 

 makes ample provision for its offspring. 



