Oct. 6, 1923 
Temperature of the Leaves of Crop Plants 
39 
i° C., while in a few cases a maximum difference of 5 0 C. was observed. 
In direct sunlight the temperature of the turgid leaves of most plants 
fluctuates above and below the air temperature, but as soon as a cloud 
obscures the sun the temperature of the leaf almost immediately drops 
below the temperature of the air, as shown in figures 6 and 7. A study 
of these figures will also show that the difference in temperature between 
a wilted leaf and a turgid leaf is not nearly so great in diffuse light as in 
direct sunlight. 
P.K2.-00 :01 :02 :03 .-04 .05 G9 :07 .-08 .-00 :I0 :l I :l 2 :I3 :I4 :I5 :I6 :l 7 H 8 :I9 :20 
Fig. 8 .—Graphs showing the temperature of the air and of leaves in direct sunlight and in diffuse light 
from 2 .oo p. m. to 2.20 p. m., July 24 , 1922 . 
Table VIII .—Temperature changes of the air and of the leaves of turgid and wilted soybean 
plants in direct sunshine and in diffuse light caused by a heavy cloud obscuring the sun 
IN DIRECT SUNLIGHT 
Time. 
Temperature of— 
Air. 
Turgid leaf. 
Wilted leaf. 
P. m. 
1.10 . 
1.11 . 
1.12 ........ 
*•*3 . 
I-I 4 . 
. 
1.16. 
I - I 7 . 
1.18. 
0 C. 
32. 0 
72 . I 
3 2 * 7 
3 °- 7 
3 1 - 0 
3 i -3 
32. 8 
72 . 6 
32. 0 
° C . 
34 - O 
33-9 
33-3 
3 °- 7 
3 2 ’ 3 
31. 8 
32. 6 
33 - 2 
34 - 2 
°C. 
38.3 
38. 0 
38. 5 
34.3 
3 6 - 9 
36. 7 
35-8 
37 - 1 
37*3 
IN 
DIFFUSE LIGHT, 
CLOUD OVER SUN 
. 
3 °. O 
26. 3 
2 9 - 3 
1.20. 
28. O 
26.3 
27. 8 
1.21. 
27. 7 
26. O 
27.9 
1.22. 
26. 7 
2 5 - 3 
2 7 -3 
1-23. 
26.3 
2 5 * 3 
26. 7 
1-24. 
26. 8 
2 5 - 3 
2 7 * 3 
I - 2 5 . 
26.3 
2 5 * 1 
27. 0 
1.26. 
2 5 * 9 
25. 0 
26. 9 
1-27. 
25.8 
2 5 - 1 
26. 7 
1.28. 
254 
25. 0 
26. 4 
1.29. 
2 5 9 
2 5 - 3 
26.8 
