62 The Ohio Journal of Science [Vol. XX, No. 3, 



no openings except into the halls of the building. While the 

 framework of the greenhouse cast shadows on the plants and 

 apparatus and produced unequal light conditions during the 

 course of a day. In order to produce equal light conditions, the 

 entire apparatus was arranged on a rotating table such as 

 described by Livingston (10) in Plant World for use in standard- 

 izing porous cup atmometers (Fig. 1). The table was rotated 

 by a small electric motor at a slow rate which was not fast enough 

 to produce an increase in water loss, although it insured proper 

 Hght and ventilation for the cups and plants. 



The electric current for operating the shot droppers was 

 taken from the electric light circuit in the greenhouse, and 

 transformed by means of a bell ringer from 116 volts to 16 

 volts, which did away with the use of dry cells. The electrical 

 connections for operating the recording and shot dropping 

 apparatus were made by means of two wires hung from the 

 roof of the greenhouse directly above the center of the table, 

 into two concentric mercury cups. Small wires led from the 

 mercury cups to the recording and shot dropping apparatus. 



In order to properly ventilate the room where the experi- 

 ments were performed and not to allow any direct air currents 

 to blow on the apparatus, the table was placed in the center 

 of the room and the ventilators directly above it were dis- 

 connected so that only those at the two ends of the room could 

 be raised. 



CALCULATION OF RESULTS. 



The results of these experiments are expressed on an hourly 

 basis. The time is recorded as hours, beginning with 1 for 

 1 A. M., and running up to 24 for 12 P. M., to correspond 

 to the 24 hours of each day. The temperature which is taken 

 from the thermographic record sheet, is the mean for each 

 hour, and is expressed in degrees Fahrenheit. The humidity, 

 taken in the same way, is recorded as saturation deficit (100% — • 

 humidity) and is expressed in percentages. The duration of 

 sunshine record, which begins at sunrise and ends at sunset, 

 was taken directly from the dial of the instrument, wind 

 velocity the same way, and needed no alteration; but the 

 hourly evaporation and transpiration rates had to be calculated. 



