PAPERS BY MEMBERS 99 



IV. Sumraary. 



This paper presents evaporation and soil moisture rec- 

 ords from the edaphic prairie association of the Chicago 

 region for the growing season of 1911. 



The data shows a very high rate of evaporation in May, 

 before the grass covering has become developed. 



The summer maximum rate of evaporation (i. e. when 

 the grass covering is present) seems lower than that which 

 one might expect, when compared with corresponding data 

 trom forest associations. 



The mean daily rate of evaporation for the season places 

 the prairie association between the pine and the cottonwood 

 dunes, as regards the atmospheric condition. 



Through the summer months the water content of the 

 soil is uniformly low. especially in the surface layer where it 

 often falls below that percentage designated as the wilting 

 coefficient. 



On the whole, the data seems to indicate decidely severe 

 mid-summer conditions in the prairie association. 



Grateful acknowledgement is made of helpful suggestions 

 from Drs. H. C. Cowles and Geo. D. Fuller dviring the progress 

 of the study- 

 Literature cited : 



1. Cowles. H. C. The physiographic ecology- of Chicago and 



vicinity. Bot. Gaz. 31:>3-108, 145-182, 1901. 



2. Fuller. Geo. D. Evaporation and plant succession. 

 Trans. 111. Acad. Sci. 4: 119-125. 1911 and Bot. Gaz. 52: 

 193-208, 1911. 



3. McNutt. Wade and Fuller, Geo. D. The range of evapora- 



tion and soil moisture in the oak-hickory forest as- 

 sociation of Illinois. 

 Trans. 111. Acad. Sci. 5: Feb. 23-24. 1912. 



4. Livingston, B. E. Operation of the porous cup atmometer. 



Plant World 13: 111-118. 1910. 



5. Livingston. B. E. A rain-correcting atmometer for eco- 



logical instrumentation. Plartt world 13: 79-82. 1910. 



6. Briggs, L. J. and Shantz, H. L. The wilting coefficient 



for different plants and its indirect determination. 

 U. S. Dept. Agri. Bur. of Pt. Ind. Bull. Xo. 230, 1912. 

 Leeend to fis:ures : 



