1914] 



VES TA L—PRA IRIE VEGE TA TION 



389 



pendulus (Michx.) Fourn. {Bouteloua curtipendula [Michx.] Torr.). 

 Secondary species include other grasses, rather xerophytic prairie 

 perennials, as Liatris punctata Hook., Gaillardia aristata Pursh, 

 Psoralea tenuiflora Pursh, Aster Porteri Gray, and Chrysopsis 

 villosa Nutt. The growth is shown in fig. 5. 



The bunch-grass association depends upon a constant water 



supply which endures 



through 



the latter part of the summer. 



As available soil moisture is constantly present in mesa-terrace 



Fig. 5. — Bunch-grass at the south crest of Horse Mesa (of the higher level): 

 Atidropogon, Sorghastrum, Artemisia, Carduus; next to the large rock a shrub of 

 poison ivy; on rock surfaces, lichens; September 1913. 



soils only till the middle of July, the association is limited to 

 moist slopes, the higher mesa- tops, and small depressions. 

 Scattered bunch-grasses occur beside surface rocks in the mesa- 

 terrace. 



The Andropogon furcatus consocies is a pure or nearly pure 

 growth of the big blue-stem. It is found in local areas of coarse 

 soil. There is also the Andropogon scoparius consocies, which is 

 synonymous with the bunch-grass association of Shantz (i8, p. 54). 

 The occurrence of a practically closed bunch-grass growth, made 



