i8 
Journal of Agricultural Research 
Vol. XXVI, No I 
The time, however, that elapsed during the recording of the deflection 
and the return of the galvanometer to equilibrium amounted to approxi¬ 
mately 10 to 12 seconds, so that an interval of about 15 seconds occurred 
between any two consecutive temperature observations. 
Since it was observed that the temperatures of the leaves and the sur¬ 
rounding air were subject to rapid and marked fluctuations, it was con¬ 
sidered that the average of several determinations would more nearly 
represent the general temperature relations of the leaves and the 
surrounding air than would a single observation. On that account, each 
temperature value reported in the following tables is the average of from 
10 to 20 different determinations usually taken during a 15 to 20 minute 
period. The manner in which the temperature values reported in the 
tables were obtained can best be illustrated by the following example: 
If Table IV, part 3, is examined, it is observed that the temperatures 
recorded on July 18, 1922, from 11.15 to 11.30 a. m. for the air, corn 
leaves, and milo leaves are 29.3 0 , 29.9 0 , and 29.6° C., respectively. Each 
of these temperatures is the average of the 20 consecutive determinations 
of the temperatures of the air, com leaf, and milo leaf, shown in Table I. 
Table I.— Deflections on the galvanometer scale in 20 temperature determinations of 
the air and of the leaves of corn and milo from 11.15 to 11.30 a. m., July 18 , 1Q22 
Air. 
Corn. 
Milo. 
Air. 
Corn. 
Milo. 
7-5 
6-5 
7.0 
6. 1 
6.4 
5-4 
6.5 
7.0 
7-5 
5-5 
5-7 
5-7 
7.0 
7-5 
7.2 
5 -o 
5-5 
5-8 
6.8 
7.2 
7.2 
6. i 
6.7 
5.8 
5 -1 
6. 1 
6.8 
6-3 
8.1 
7.2 
6. 0 
6.4 
6-5 
6.3 
7.0 
6. 0 
6. 0 
6.0 
5-8 
6.4 
8.0 
6.6 
5-7 
6-5 
7.0 
6.5 
7-5 
6.5 
6.4 
5-8 
5 -i 
5-5 
7-3 
6. 6 
5-2 
4.6 
4.8 
6.8 
8. 1 
7.0 
Average deflection on the 
scale 
6. 1 
6. 7 
6.4 
Temperature of constant... 
23. 2 
23. 2 
23. 2 
Temperature (° C.). 
1 
29- 3 ° 
29.9 0 
29. 6° 
During this experiment the air was clear, a slight breeze was blowing, 
and the reading of the constant temperature junction was 23.2 0 C. 
Since the deflections were to the right on the galvanometer scale, and 
since a deflection of one scale division indicates a difference in tempera¬ 
tures of i° C. between the two thermojunctions, the temperature of the 
air and of the leaves in question was obtained by adding each of the 
average*deflections to the constant temperature 23.2 0 C. 
determination oE transpiration 
The transpiration experiments were performed upon normal plants 
which were grown in large metal containers after the manner previously 
reported by Miller and Coffman (9). The soil used in the containers 
was a sandy loam in good tilth, and had a moisture content ’of 23.3 per 
cent and a wilting coefficient of about 12 per cent. In order to determine 
