

394 



BOTANICAL GAZETTE 



[NOVEMBER 



THE STIPA-ARISTIDA ASSOCIATION 



Stipa formation of high prairies— Pound and Clements 13, p. 3 8l « 

 Wire-grass association. — Shantz 18, p. 48. 



domi 



tuft growth-form, with moderately ( 

 usually in coarse sterile soil, more 

 slopes and crests. 



common 



They are found 

 on south-facing 



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Fig. 8 .—Primitive grassland on a gravelly terrace left by Gregory Creek, which 

 lies across the picture in a slanting position, and is marked by the large tree, a narrow- 

 leaf cottonwood; the growth consists of Bouteloua hirsute, Artemisia frigida, and a 

 few mat plants, and is very open; July 191 3. 



The Stipa comata consocies, dominated by Stipa comata Tnn. 

 and Rupr., occurs in the region on gravelly slopes and on wind- 

 swept tops and crests of mesas. In it are occasionally found 



tenuiftora Pursh, Helianthus 



Chrysopsis villosa Nutt., Psoralea tenu 



pumilus Nutt., Aristida lonziseta Steud., and Sitanion brevifoli 



J. G. Smith. A pure 

 railroad embankment. 



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