SOME OBSERVATIONS ON THE TEMPERATURE OF 
THE LEAVES OF CROP PLANTS 1 
By Edwin C. Miller, 2 Plant Physiologist , Department of Botany , Kansas Agricultural 
Experiment Station , and A. R. Saunders, Senior Student, Kansas State Agricultural 
College 
INTRODUCTION 
In investigating the water relations of various crop plants at the 
Kansas Agricultural Experiment Station it was thought advisable to 
study the temperature of leaves of these plants under natural field con¬ 
ditions. Especially it seemed desirable to consider the temperature- 
relationships of leaves under conditions of a limited water supply, since 
a lack of moisture is the limiting factor in crop production in the Great 
Plains area and in regions adjoining it. It is commonly stated that 
transpiration under conditions that furnish a sufficient supply of water to 
the roots of plants prevents the temperature of the leaves from becoming 
so high as to interfere with their normal life activities, but experimental 
evidence on this point is rather limited and fragmentary. In order to 
obtain some information on this question, investigations were undertaken 
to study the temperature of leaves along the following lines : 
(1) The relation of leaf temperature to the rate of transpiration. 
(2) Leaf temperatures during the day and night. 
(3) Temperature of different portions of the leaf under like conditions. 
(4) The temperature of leaves in direct and in diffuse light. 
The data reported in this paper were obtained at Manhattan, Kans., 
during the growing season of 1922. The literature in regard to the tem¬ 
perature of leaves has been thoroughly reviewed by Ehlers (5) 3 and will 
be mentioned here only in the discussion of the various phases of these 
experiments. 
METHODS OF EXPERIMENTATION 
DESCRIPTION OF APPARATUS 
In these experiments the temperature of the leaves was measured by 
a modification of the method reported by Shreve (11, p. 12 , 13, 50-57), 
a diagram of the apparatus used being shown in figure 1. It consisted 
of two thermo junctions TC and T'C', approximately 5 mm. in length, 
which were formed by braiding the two wires and then uniting them by 
an acid-free solder. The wires used were No. 36 copper and No. 36 con- 
stantan, with insulated connecting length A, B, and B', totaling approxi¬ 
mately 3 feet. 
1 Accepted for publication June 25, 1923. Published with the approval of the Director. Contribution 
from the department of botany, Kansas Agricultural Experiment Station, paper No. 200. 
2 Acknowledgments are due Prof. E. V. Floyd and G. E. Raburn, of the department of physics, Kansas 
State Agricultural College, for their aid and advice in regard to the temperature measurements. 
* Reference is made by number (italic) to “Literature cited,” p. 43-44. 
Journal of Agricultural Research, 
Washington, D. C. 
agw 
Vol. XXVI, No. 1 
Oct. 6, 1923 
Key No. Kans. -38 
(15) 
