Oct. 6, 1923 
Temperature of the Leaves of Crop Plants 
21 
RELATION OF LEAF TEMPERATURE TO THE RATE OF TRANSPIRATION 
It is commonly stated that the temperature of a wilted leaf exposed to 
the direct rays of the sun is higher than that of a turgid leaf exposed to 
the same conditions, but very little quantitative work has been done on 
the subject. 
23 
g 22 
§21 
d 
P.M&20 :2I :22 .*23 :24 :25 :20 :27 :28 :2Q 30 IQ!0p.K:II -.12 :!3 :I4 :I5 :!S :I7 :!8 :!9 :20 
~PU( 
PIPKIN LEAVES 
r emperature of air 
* turbid leaf 
TIM 
E IN 
MINI/ 
ES 
— 
f 
..... 
— 1 
— 
— 
. % 
Fig. 2.—Graphs showing that there is only slight fluctuation in the temperature of the air and of turgid 
leaves during any given period when there is little or no breeze and when the temperature of the air is 
relatively low. Pumpkin leaves, 8.20 to 8.30 p. m. and 10.10 to 10.20 p. m., July 26, 1922. 
Darwin (4) in the observation of withered detached leaves and normal 
attached leaves of Tropaeolum majus found in intermittent sunshine 
and relatively low humidity that the temperature of the withered leaves 
was from 1.2 0 to 3.9 0 C. higher than that of the attached leaf. Smith 
Fig. 3.—Fluctuations in the temperature of the air and of the leaves of wilted and unwilted plants during 
a 15-minute period when the temperature was relatively high and when a brisk breeze was blowing. 
July 28, 1922. 
(14) observed that when two leaves of Amherstia mobilis were so placed 
that the surfaces containing the stomata were in direct contact, the 
temperature of the leaves was 2.5 0 C. above that of the same leaves 
when the surfaces bearing the stomata were placed facing outward. 
