1914] 



VES TA L—PRA TRIE VEGE TA TION 



39 1 



slopes of the foothills. Narrow zones of this growth are frequently 

 found bordering Symphoricarpos and Prunus shrub associations of 

 the foothills, which appear to be increasing in area on the slopes, 

 at the expense of the grassland. In such meadow-like zones are 



seen Frasera sp 



m 



xiosa Griseb., Thermopsis divaricarpa A. Nels., 

 Nutt., and Aster Geyeri (Gray) Howell, with other 

 oohytes. Such meadow-like zones border scrub 



•«** 



Fig. 6. — Society of Arnica, in a prairie-grass growth of moist alluvium at the 

 base of a steeper slope, south of Boulder; dominant plants are Poa and Koeleria; 

 May 1913. 



oak associations farther south, at Castle Rock, Perry Park, near 

 Larkspur, and at Palmer Lake. 



The prairie-grass locally found west of the plains belt has many 

 features in common with eastern black-soil prairie as represented 

 along the border of the eastern deciduous forest. The secondary 

 species, however, are mostly different, and the growth found along 

 the mountain-front would probably be considered a separate asso- 

 ciation, which may be called the western mesophytic prairie-grass 



