28o BOTANICAL GAZETTE [October 



xerophytic relict along the crest of prairie knolls, where it mingles 

 with the gramas as they advance upon the bunch-grass stage, yet 

 usually as a secondary element among these sod-formers. In our 

 area, however, it is lacking. 



Bouteloua hirsuta seems to be the pioneer of the gramas as they 

 encroach upon Bulbilis, or upon the bunch-grasses where Bulbilis 

 is absent, as is the case in our formation. It is in turn apparently 



Fig. i. — Serotinal aspect: Bouteloua curtipendula sod on upper slope; Solidago 

 rigida to the left; Helianthus scaberrimus to the right; admixture in the background. 



followed by B. oligostachya, which seems to occur more abundantly 

 and to occupy the most prominent place of the sod-formers. Fre- 

 quently it alone encroaches upon the bunch-grasses, B. hirsuta being 

 absent. Next comes B. curtipendula (Jig. i), which also contributes 

 largely to the early prairie sod. In many places the Poa sod is the 

 next to follow. The gramas are thus largely confined to the crests, 

 decreasing in abundance downward, where they not infrequently 

 rise to facial prominence. Contrary to the serotinal floral forms, 

 the Boutelouas are of low stature, B. curtipendula alone rising above 



