30 THE AMERICAN NATURALIST [Vol. XL V 



The removal of the higher types of plants from the 

 desert conditions with which they articulate, that is, ex- 

 treme forms with reduced shoots and swollen stems, is 

 followed by increased development of spines when grown 



under equable conditions, or in climates with greater 

 water supply as illustrated by Opinttia taut a rita and 

 other "spineless" forms. 



