1908] 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 33 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 
Factes.—Andropogon furcatus,} A. scoparius.t 
PRINCIPAL SPECIES.—Solidago rigida,t Aster sericeus,} Helianthus scaberri- 
mus,t Sporobolus brevifolius.+ 
SECONDARY SPECIES.—Solidago rigidiuscula,t S. missouriensis, S. nemoralis, 
Ratibida columnaris,*} Aster multiflorus, Artemisia gnaphaloides,* Verbena 
Stricta,*} Carduus undulatus.* ; 
TERTIARY SPEcIES.—Aster oblongifolius, Solidago canadensis,t Kuhnia 
glutinosa, Lacinaria scariola, Nabalus asper, Lygodesmia juncea,* Polygala alba,* 
papposa, Grindelia squarrosa, Kuhnia eupatorioides, Lacinaria punc- 
tata, Gentiana puberula, Kuhnistera villosa, Meriolix serrulata.* 
UDERAL SPECIES.—Salsola tragus, Meliotus alba,* Lactuca canadensis.* 
* : . ase 
From earlier aspect. {Forming 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 
"emoralis, and S. rigida. SS. missouriensis, the first of the autumnal 
bloomers, occurs in subcopious abundance and most abundantly 
Eg 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 
