294 BOTANICAL GAZETTE [October 



extends up to and even dominates the prevernal and vernal floral 

 aspects. 



Summary of the structure of the formation 



The formation is strictly of the prairie-grass type, its facies being 

 determined mainly by six species: Bouleloua oligostachya, B. curti- 

 pendula, B. hirsuia, Koeleria cristata, Andropogon furcaius, and A. 

 scoparius, to which must be added Poa pratensis in valleys and on 

 lower slopes. The Andropogons are the main sod-formers of crests 

 and ridges, while the Boutelouas characterize the higher slopes, 

 working up to the crest and ridges. Koeleria seems to be more 

 closely associated with the Boutelouas, occurring on middle slopes 

 mainly. With these are associated three sedges and seven other 

 grasses, which are all important as cooperating sod-formers, some of 

 them ranking as primary species in the formation. We may mention 

 Carex pennsylvanica, C. festucacea, and Sporobolus hrevifolius as 

 perhaps the more important of these. It is to be remarked that the 

 sedges are all pre-estival, while the grasses are all estival or post- 

 estival in their floral activity; the first facies to bloom is Koeleria in 

 the estival aspect, while the Boutelouas are serotinal and the Andro- 

 pogons autumnal. 



Upon this facial background of grasses there progressively appear 

 several conspicuous flowered forms of primary importance, which 

 with numerous secondary and tertiary species serve to impart a 

 bizarre aspect to the formation when considered as a whole and a 

 kaleidoscopic shift with seasonal succession. In passing it is well to 

 note that species primary in their own floral aspect may be of only 

 secondary or tertiary importance when the formation is considered 

 as a unit. Among these primary species we may note the ubiquitous 

 Antennaria campestris; the Spesias and Sisyrinchium of middle 

 slopes; Amorpha canescens upon upper slopes and ridges; Ratibida 

 upon lower, and Verbena and Erigeron ramosus upon upper slopes; 

 Symphoricarpus in valleys and on lowest slopes; the Kuhnisteras 

 upon slopes, K. purpurea occupying the upper slopes, while K. 

 Candida extends downward upon lower slopes; Solidago rigida and 

 Helianthus scaherrimus of great frequency and abundance; and finally 

 Aster sericeus upon isolated knolls. 



