34 8 
The Ohio Naturalist. 
[Vol.XI, No. 7 ; 
well shaded. The undergrowth is quite sparse and the soil is 
covered with a thick layer of leafy litter. 
The instruments were the porous cup atmometers similar to 
those used in previous experiments. A graduated cylinder served 
the purpose of a reservoir. The cups were loaned by the Carnegie 
Desert Laboratory at Tucson. Four instruments were installed, 
one on the ground, at the three-inch level, one at one foot above 
the soil, another on an upright support at 6 feet, and a fourth 
resting on a light framework which was raised to a height of 
thirty-five feet. The instruments were set up on May 28, and 
weekly readings were begun on May 30, and continued until 
June 27. At this time, the cups at the one foot, and six foot levels 
were removed, and returned to the laboratory to be used in other 
investigations. The remaining instruments were read for three 
weeks longer. The sixth reading, June 27 to July 12, is for a 
period of two weeks, and cannot be compared with the other 
readings. It was the intention to supplement the evaporation 
readings with the temperature, and humidity data, but unfortu- 
nately, the instruments were not available at the time. The 
data are indicated in the following table: 
Table To Show The Evaporation Gradient In A Woodlot. 
Date 
3 Inches 
1 Foot 
6 Feet 
35 Feet 
May 28-30 
30.6 
29.8 
61.6 
May 30 to June 6 
41.5 
36.5 
77.0 
56 0 
June 6-13 
36.7 
38.2 
75.9 
54.0 
June 13-20 
91 1 
74.7 
154.0 
126.0 
June 20-27 
83.1 
73.8 
140.8 
116.0 
June 27 to July 12 ... . 
74.2 
198.0 
July 12-18 
54.4 
88.0 
It will be seen by comparison of the readings at the various 
levels, that the greatest evaporation has occurred in every case at 
the six foot level, pointing to a decrease in relative humidity from 
below upwards. The thirty-five foot reading exhibits a modifica- 
tion of this relation, which is due to the moisture given off in the 
transpiration of the leaves in the forest crown. Contrary to 
results obtained from similar investigations on Cranberry Island 
at Buckeye Lake, 1. c. 2 and also to the observations of Yapp in an 
English marsh,* the data do not show a uniform increase of the 
*Yapp, R. H. On Stratification in the vegetation of a marsh, and its 
relations to evaporation, and temperature. Annals of Botany 23:275-320. 
1909. 
