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 dimmish loss of 

 water through transpiration. 



One of the most common results of xerophytic conditions 

 upon body habit is the development of thorns and spiny 



PIG. 171. Young plants of Euphorbia splendens, showing a development of thorns 

 characteristic of the plants of dry regions. 



processes. As a consequence, the vegetation of dry regions 

 is characteristically spiny. In many cases these spiny pro- 

 cesses can be -made to develop into ordinary stems or leaves 

 in the presence of more favorable water conditions. It is 

 probable, therefore, that such structures represent reduc- 

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

 able conditions. Incidentally these thorns and spiny pro- 

 cesses are probably of great service as a protection. to plants 

 in regions where vegetation is peculiarly exposed to the 



