i9o8] HARVEY— PRAIRIE-GRASS FORMATION 283 



herb from a tuberous structure, terminating in a spike bearing 

 numerous heads of purphsh flowers. The abundant plumose pappus 

 assures a widespread distribution. 



Autumnal floral aspect 



No marked ch mat ©logical change is to be noted in passing from 

 the serotinal to the autumnal aspect, but simply one of gradually 

 decreasing favorableness. Hence the latter has been set off partly 

 for convenience of discussion, though it seems more or less distinctly 

 characterized by definite floral activity; yet possibly it might be more 

 accurately designated as late serotinal. Beginning in early August 

 and marked by the estivation of such very conspicuous forms as 

 Helianthns scaherrimus, Solidago rigida, and the bunch-grasses 

 {Andropogon furcatus and ^. scoparius), it extends into early October, 

 when vegetative activity comes to an end. Its floral activity is 

 terminated, however, in middle September by the flowering of Gentiana 

 puherula and Solidago rigidiiiscida, while florally the aspect is at its 

 best during late August and early September, when the prairie is a sea 

 of yellow from the Solidagos, mainly S. rigida, dotted here and there 

 by the blue of Asters. Rising sentinel-Hke along higher slopes and 

 crests are the rose-purple spikes of the blazing-stars, while on isolated 

 knolls associations of Aster sericeus with their purplish flowers and 

 white tomentose leaves reHeve the sea of yellow. The bunch-grasses 

 impart a very characteristic tone to the higher and more xerophytic 

 knolls. 



In earher aspects marked restriction of forms was noted, less 

 apparent in the serotinal it is here scarcely evident. On the other 

 hand there is a marked identity of the controlhng species on base, 

 slope, and crest, the entire formation presenting an unbroken and 

 identical covering, undoubtedly to be associated with the noticeable 

 equality of the chresard throughout these various situations. 



Eighteen of the twenty-two forms (82 per cent.) are composites, 

 and all but one of these (Kuhnistera villosa) are wind-distributed. 

 Like the prevernals the autumnals are pronouncedly xerophytic, 

 fitting into uncertain, that is unfavorable, ecological conditions, the 

 former at the initiation, the latter at the dechne of floral activity. 

 Just as prevernals have come to possess the spring period of not 



