348 



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 instruinents 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 supi^lement the evaporation 

 readings with the temperature, and htunidity data, but unfortu- 

 nately, the instruments were not available at the time. The 

 data are indicated in the following table: 



Table To Show The Evapor.'Mion Gradient In A Woodlot. 



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 unifonn 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. 



