56 TRANSPIRATION IN A DESERT PERENNIAL. 
Proper substitution in equation 2 gives: 
[(20.66) (.41) + (2.23) (X) +6.80] [6.3] = (14.51) (7.24) 
.”. specific heat of leaves, X =.64. 
Proper substitution in equation 3 gives: 
[(20.66) (.41) +6.80] [.50] = (2.28) (.64) (X) .. X=5.3. 
Ss 
Therefore the temperature of the leaves was 
19.2°-++5.3° = 24.5°, or 5.5° above air-temperature. 
EXPERIMENTATION. 
EXPERIMENT XX. 
A series of leaf-temperature determinations was made from trees D and E. 
The samples were taken every 2 hours, a period of 2 to 3 minutes elapsing 
between the cuttings. The general appearance of the trees indicated that 
tree H was nearer the stage of dropping its leaves than was D. 
TasBLE 23.—Temperatures for leaves from two trees with the corresponding air-temperatures 
Experiment XX. 
‘Temperature. Difference from air. 
Date. Time. 
D EB Air. D E 
1912. °¢, °¢, °C, 
Sept. 16... 9500™p.m.| 26.7 27.6 27 -1.3 | +40.6 
11,59 pm.| 22.9 24:8 - 25 —2:1 | 0.2 
Sept.17...! 5 00Ta.m.| 19.6 16.0 | 20° 19° 0.4 | -3.0 
8 OOga.m.| 22.8 24:3 | 95.5 24.8 | 2.7 | —0.5 
10 00ja.m.| 32.9 35.8 33.5 —0.6 | 42.3 
12 00 m. 45.9 44.6 37.5 48.4 | 47.1 
2 00 p.m. | 38.0 43.7 39.0 —1.0 | 44.7 
400 p.m.| 35.1 35.9 | 39.5 39.0 | 4.4 -3.1 
6 00 p.m.| 29.1 27.9 32.5 3.4 | 46 
9 12 ce Ss ¢ 0 a a i 2S 4 oe 6 
Fic. 25.—Graph for leaf-temperature from_two adult trees, plotted with air-tempera- 
tures. Exp. XX. 
