i9o8] HARVEY— PRAIRIE-GRASS FORMATION 285 



SO largely accomplished. However, the climatological conditions 

 (table) of this aspect bear to its floral activity a relation analogous to 

 that existing in the prevernal, and the forms here occurring seem in 

 no less degree peculiarly adapted to the late seasonal conditions. 



In August the wind is dominantly from the south and east, but 

 in early September begins to swing to the northeast quadrant, where it 

 remains until the prevernal, then swinging round again to the south- 

 east. The average daily rainfall (0.26^™) remains about the same 

 as in the preceding aspect, though it falls on only 25 per cent, of the 

 days, while in the serotinal it falls on t,2, per cent, of the days. Relative 

 humidity, sunshine per cent., and relative light intensity are notice- 

 ably similar in these two aspects, while relative evaporation has 

 decreased almost a third. In the fact that the hourly wind velocity 

 has increased only a tenth, and in the 4° C. fall in the mean tempera- 

 ture must be sought an explanation of this lowered evaporation. 



Species of the autumnal floral aspect 



Facies. — Andropogon furcatus,t A. scoparius.t 



Principal species. — Solidago rigida,t Aster sericeus,t Helianthus scaberri- 

 muSjt Sporobolus brevifolius.f 



Secondary species. — Solidago rigidiuscula,t S. missouriensis, S. nemoralis, 

 Ratibida columnaris,*t Aster multiflorus, Artemisia gnaphaloides,* Verbena 

 stricta,*t Carduus undulatus.*t 



Tertiary species. — Aster oblongifolius, Solidago canadensis,! Kuhnia 

 glutinosa, Lacinaria scariola, Nabalus asper, Lygodesmia juncea,* Polygala alba,* 

 Dysodia papposa, Grindelia squarrosa, Kuhnia eupatorioides, Lacinaria punc- 

 tata, Gentiana puberula, Kuhnistera villosa, Meriolix serrulata.* 



RuDERAL SPECIES. — Salsola tragus, Meliotus alba,* Lactuca canadensis.* 



*From earlier aspect. fForming associations. 



During the early days of August four forms, destined later to be- 

 come very conspicuous, make their floral appearance in the following 

 order: Solidago missouriensis, Helianthus scaberrimus, Solidago 

 nemoralis, and 5. rigida. S. missouriensis, the first of the autumnal 

 bloomers, occurs in subcopious abundance and most abundantly 

 in the open association of the upper slopes and crests, where it is 

 quite noticeable, though it never becomes a prominent feature of the 

 tone because of its low stature and small panicles. It is distinctly 

 xerophytic, as is evident both by its structure and distribution, and, as 



