1908] 



HA R VE V— PRAIRIE-GRASS FORMA TION 



93 



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 3i°C. to 

 2°C, with a mean of 16 C, rarely inhibit- 

 ing 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 

 evaporation is thus nearly twice as great. 

 Couple this with the highest light intensity 

 ( . 704) and the beneficial results of 8 . io cm of 

 precipitation on twelve days are much re- 

 duced. The chresard shows a marked 

 decrease from 14. 1 per cent, on May 10 to 

 7.4 per cent, on May 22, though the average 

 chresard for the aspect is 10 . 7 per cent. The 

 base (12.7 per cent.), slope (14.6 per cent.), 

 and crest (8.8 per cent.) on May 22 still 

 showed a gradation in holard, though the 

 distinction of position is less marked than in 

 the prevernal aspect. 



