CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 293 



This distribution is not the same everywhere. In the north, 

 Koeleria and Stipa appear in the uplands, and Poa and Sorghastrum 

 do not appear at all. In the central region, Panicimi virgatum, Birt- 

 bilis dactyloides, and Boutelona hirsnta are added to the uplands 

 and Sporobolus heterolepis and S. cryptandrus to slopes. The 



Fig. 156. Mixed grass prairie in which Bouteloua gracilis, Stipa co?nata, 

 and Calamovilja longifolia are the principal species. Colorado.— Photo by R. 

 B. Livingston. 



southern faciation, sometimes regarded as a separate association, is 

 even more distinct, especially because of added species in the up- 

 lands, such as Stipa leucotricha, Andropogon saccharoides, A. 

 tener, and A. ternarius. 



There has been much discussion and study of the eastern mar- 

 gin of Tall Grass Prairie, its extension as a "peninsula" into Illinois 

 and Indiana, and the isolated areas farther east, particularly in 



