1908] HARVEY—PRAIRIE-GRASS FORMATION 
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 pre- 
vernal 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 Symphoricar pus 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 flora] 
omy from the adjacent table. On only 
el cent. of the days does the mean 
ns age temperature rise above 6° C., with a 
— between —6° and 29°C. Coupling 
a oe an average soil temperature of 
7) Srowth conditions are seen to be 
om favorable, The prevailing wind 
8 3S northvest and with a mean 
PREVERNAL CLIMATOLOGY 
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