1908] 
peared and those of the following aspect are 
now all ready to bloom. Much growth has 
taken place in the summer perennials and they 
have apparently outstripped the autumnal 
forms. Together they overtop the majority 
of the vernal group, and toward the end of 
the aspect the large cauline leaves of Solidago 
and Helianthus of the autumnal aspect render 
many of the low-statured bloomers quite 
hidden, except in the very open associations 
on the highest slopes and crests. Four 
ruderals bloom in this aspect but have little 
influence on the formation. 
The summary clearly indicates the sig- 
nificant climatological facts. Physiological 
activity ensues practically throughout the 
aspect; the temperature range of 31° C. to 
2° C., with a mean of 16° C., rarely inhibit- 
ng growth. The wind is dominantly from 
the south and east quarters. It reaches 
during this aspect a less total movement 
and so a less mean hourly velocity than in 
the prevernal, but the atmosphere has a 
much lower relative humidity; the relative 
‘vaporation is thus nearly twice as great. 
Couple this with the highest light intensity 
(-704) and the beneficial results of 8.19°™ of 
Precipitation on twelve days are much re- 
duced. -- The. chresard shows a marked 
decrease from 14.1 per cent. on May to to 
7-4 per cent. on May 22, though the average 
chresard for the aspect is 10.7 percent. The 
base (1 2.7 per cent.), slope (14.6 per cent.), 
and crest (8.8 per cent.) on May 22 still 
Showed a 
distinction of position is less marked than in 
~ the prevernal aspect. 
gradation in holard, though the. 
VERNAL CLIMATOLOGY 
HARV EY—PRAIRIE-GRASS FORMATION 
93 
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