A COMPARISON OF THE RATES OF EVAPORATION IN 
CERTAIN ASSOCIATIONS IN CENTRAL ILLINOIS* 
HENRY ALLAN GLEASON AND FRANK CALEB GATES 
(WITH SIX FIGURES) 
During the session of the Biological Summer School of the 
University of Illinois, held at Havana, IIl., during June and July 
1910, a series of measurements of the relative rates of evaporation 
within certain plant associations was made. In view of the growing 
interest in the study of evaporation and its relation to vegetation, 
the results obtained are here presented. 
The greater part of our knowledge of evaporation in relation to 
tation has been given to us through the work of Livincston and 
TRANSEAU. One of the most suggestive papers is that of TRAN- 
SEAU,? in which he determined the relative rates of evaporation for 
a number of habitats about Cold Spring Harbor, Long Island, N.Y. 
He has summarized his results in a diagram which clearly shows 
the marked difference in the amount of evaporation in areas close 
to each other but differently vegetated. While TRANSEAU worked 
with habitats, as he expresses it, in the work at Havana certain 
definite plant associations were selected in which to determine the 
rate of evaporation. 
Havana is located on the east bank of the Illinois River in central 
Illinois. The climate may be briefly characterized by the following 
statements: an average temperature during June and July of about 
24° C., with warm nights and hot days, and a yearly rainfall of 
about 90 cm., of which considerably more than half falls during 
the growing season. Strong winds are frequent, as is usually the 
case in the central states. Except on the alluvial river bottoms, 
the soil of the area is sandy with a slight admixture of humus. Most 
of the area was originally occupied by associations of the Prairie 
Contribution no. 125 from the Botanical Laboratory of the University of 
Michigan. 
2 TRANSEAU, E. N., The relation of plant societies to evaporation. Bor. Gaz. 
45° 217-231. 1908. 
Botanical Gazette, vol. 53] 478 
