204 PLANT RELATIONS. 



trate or creeping habit is a much less exposed one in such 

 regions than the erect habit. In the same manner, the very 

 characteristic rosette habit, with its cluster of overlapping 

 leaves close against the ground, tends to diminish loss oi 

 water through transpiration. 



One of the most common results of xerophytic conditions 

 upon body habit is the development of thorns and spiny 



Fig. 171. Young plants of BupJwrhia splendevs^ showing a development of thorne 

 characteristic of the plants of dry regions. 



processes. As a consequence, the vegetation of dry regions 

 is characteristically spiny. In many cases these spinv pro- 

 cesses c;in !)(• niii(h"' to dcveldp into ordinary stems or leaves 

 in the presence of nioi'c favorable water conditions. It is 

 }>robable, therefore, that such structure's represent redac- 

 tions in the growth of certain regions, caused by the unfavor- 

 alile conditions. Incidentally tliese thorns and si)iny pro- 

 cesses are prolialjly of great service as a protection to plants 

 in regions where vegetation is peculiarly exposed to the 



