264 



FRANCIS RAMALEY 



In closing this brief account of the environmental conditions 

 it remains to be emphasized that extreme conditions wherein 

 only highly xerophytic species are found may result from differ- 

 ent causes. The texture of the soil is important and in a coarse 

 soil poor in humus extreme xerophytes will be found. But 

 exposure to drying effect of wind is also of consequence and may 



Fig. .5. View of dry grassland in which mountain sage, Artemisia frigida, 

 is prominent. Part of a fairy ring of mushrooms, Tricholoma praemagnum. is 

 seen inclosing the Ai-temisia. 



result in such high transpiration that even in fairly fine-grained 

 soil there will be little approach to a mesophytic vegetation 

 cover. 



GEOGRAPHIC RELATIONS 



Distribution maps (not reproduced in this paper) were made 

 of the 36 most important species of the dry grassland. They 



