278 



BOTANICAL GAZETTE 



[OCTOBER 



vernal and estival aspects, only thirteen 

 new forms appearing during the aspect. 

 It is moreover the aspect of the sod- 

 formers, "floral" forms being represented 

 by only six species. Several ruderals make 

 their floral appearance in the formation dur- 

 ing this aspect but, with the exception of 

 Cassia chamaecrista, attain no conspicuous- 

 ness. 



The serotinal is markedly a period of 

 extremes, bringing about a change to which 

 one is generally sensible. During the early 

 days of July the weather settles and there 

 is a long succession of long and intensely 

 hot and dry days, which condition char- 

 acterizes the entire serotinal aspect. Relative 

 evaporation (table) is at an extreme, though 

 sHghtly less (0.81) than in the estival, find- 

 ing its explanation in the lower (0.4) hourly 

 wind velocity and higher (8.5) relative 

 humidity; the hot dry winds from the south 

 and southeast are now coexistent with the 

 highest mean temperature, the lowest mean 

 daily precipitation, a low relative humidity, 

 and a high light intensity. Thus evapora- 

 tion and transpiration are augmented to a 

 precarious degree. 



The chresard shows a continued decrease 

 from the estival, being 6.5 per cent, on July 

 6 and 4 per cent, on July 24; while the aver- 

 age chresard is 5.2 per cent., the lowest 

 yet reached. The holard of crest (8.2 

 per cent.), slope (12 per cent.), and 

 base (12.2 per cent.) are now (July 28) 

 more nearly approximate than in earHer 

 aspects. 



Relative evaporation at a maximum and 



