I908J 



HARVEY— PRA IRIE-GRASS FORMATION 



89 



by the slow and progressive flowering of six 

 forms, extending up to the last week in April, 

 when an apparent break in floral continuity 

 occurs, no forms flowering for a week or ten 

 days. This break very naturally segregates 

 the prevernal floral aspect. 



In addition to the floral forms this aspect 

 is conspicuous as the time of appearance of 

 the rosettes of the vernal, serotinal, and 

 autumnal perennials, and seedling annuals 

 of these same aspects. No facies is estab- 

 lished, and the tone of the formation is that 

 of winter and early spring, mainly produced 

 by the standing brown stalks of Solidago 

 rigida, Helianthus scaberrimus, and Verbena 

 stricta of the autumnal aspect, which gives 

 everything a brownish cast, enlivened here 

 and there by the mats of Antennaria cam- 

 pestris and A. neodioica, and at the base of 

 slopes and in depressions by the green of 

 Poa pratensis sod. At the base of slopes 

 now and then are to be seen clumps of 

 green produced by the unfolding leaves of 

 colonies of Symphoricarpus occidentalis. To 

 complete the aspect, dotted here and there 

 are the floral forms which characterize it. 

 Ruderal species are noticeably absent. 



The pertinent climatological conditions 

 of the prevernal floral aspect may be obtained 

 directly from the adjacent table. On only 

 63 per cent, of the days does the mean 

 average temperature rise above 6° C, with a 

 range between -6° and 29 C. Coupling 

 this with an average soil temperature of 

 13 C, growth conditions are seen to be 

 far from favorable. The prevailing wind 

 direction is northwest and with a mean 



