4 2 
Journal of Agricultural Research 
Vol. XXVI, No. I 
(5) The temperature of the leaves during the day and night. —(a) During 
the hours of early morning and evening and when the general climatic 
conditions are relatively mild, the temperature of the turgid leaves of 
the plants examined is slightly below the temperature of the surrounding 
air. The temperature of the leaves during the night is approximately 
that of the surrounding air, according to the observations made. During 
the day, however, from 9 a. m. to 4 p. m., under the general climatic 
conditions prevailing during the growing season in Kansas, different 
species of plants show a different behavior of the temperature relation¬ 
ship of their turgid leaves and the surrounding air. 
(b) The temperature of the turgid leaves of corn, sorghum, pumpkin 
and watermelon in direct sunlight may fluctuate slightly above or below 
air temperature, but the average temperature of the leaves is approx¬ 
imately that of the surrounding air. In the case of com, the average 
of over 1,000 determinations of leaf temperature under a wide range of 
conditions was 30.64° C., while the average air temperature for an equal 
number of determinations during that time was 30.58° C. A thousand 
observations on the temperature of leaves of sorghum and the surrounding 
air showed an average of 30.64° C. for the former and 30.66° C. for the 
latter. 
(c) The average temperature of the turgid leaves of soybeans in 500 
observations was 33.66° C., while the average temperature of the air 
was 33.13 0 C. The temperature of the leaves of soybeans was thus, 
under the conditions of this experiment, approximately 0.5° C. higher 
than that of the air. 
{d) The average of 500 temperature observations on the leaves of 
cowpeas was 0.2° C. lower than the average temperature of the surround¬ 
ing air, while the leaves of alfalfa consistently showed a temperature 
somewhat less than 1 0 C. below the temperature of the air. 
(6) Temperature of different portions of the leaf. —The experiments 
with the leaves in direct sunlight showed that the temperature of the 
base of the leaf is always lower than the temperature of the tip region. 
This temperature difference varies from 1° to 1.5° C., depending upon the 
nature of the leaf and upon the available water supply. 
(7) Temperature of leaves in direct and in diffuse sunlight. —The data 
obtained show that in diffuse sunlight the temperature of attached turgid 
leaves of the plants studied is always lower than that of the surrounding 
air. The average difference between the temperature of the leaves and 
that of the air varied from 0.1° to 3° C., while the maximum difference 
observed was 5 0 C. In direct sunlight the temperature of the turgid 
leaves of most plants fluctuates above and'below 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 and remains there 
until the leaf is again exposed to direct sunlight. 
LITERATURE CITED 
(1) Askenasy, E. 
1875. UEBER DIE TEMPERATUR, WELCHE PFLANZEN IM SONNENLICHT ANNEHMEN. 
In Bot. Ztg., Jahrg. 33, p. 441-444- 
(2) Blackman, F. Frost, and Matthaei, Gabrielle L. C. 
1905. EXPERIMENTAL RESEARCHES IN VEGETABLE ASSIMILATION AND RESPIRA¬ 
TION. IV. A QUANTITATIVE STUDY OF CARBON-DIOXIDE ASSIMILATION 
AND LEAF-TEMPERATURE IN NATURAL ILLUMINATION. In Proc. Roy. 
Soc. [London] Ser. B. v. 76, o. 402-460, 6 fig. 
