VOLUME LX\III . NUMBER 3 



THE 



Botanical Gazette 



SEPTEMBER igig 



phytogeography of the eastern mountain- 

 front IN COLORADO 



I. PHYSICAL GEOGRAPHY AND DISTRIBUTION 

 OF VEGETATION 



CONTRIBUTIONS FROM TliE HULL BOTANICAL LABORATORY 251 



A R T H U R G. V E S T A L 

 (with SEVENTEEN FIGURES) 



Introduction 



The plant geography of a region is the effect of the working of 

 present and former environmental influences upon the floras and 

 vegetation-complexes which exist and have existed within the region 

 and in the regions adjoining. The region of present study, lying 

 as it does in the transition belt between two great geographic 

 divisions of North America, the Great Plains, or western part of the 

 prairie region, and the Rocky Mountains, has some of the char- 

 acters of both ; others of its physical and vegetational features are 

 transitional, intermediate; and it has certain pecuharities, differ- 

 ing thus from the regions on either side. Since climatic variation, 

 differences of soil and of topography, and multiformity of vegetation- 

 types are considerable, the plant-covering of the area is a complex 

 of many diverse types. Descriptive accounts of the plant associa- 

 tions of plains and foothills have already been published (17, 18), 

 so that the present article may deal more particularly with geo- 

 graphic description and geographic relations. 



153 



