A THERMO-ELECTRICAL METHOD FOR THE DETER- 

 MINATION OF LEAF TEMPERATURE 



EDITH BELLAMY SHREVE 



Desert Laboratory, Tucson, Arizona 



During the past year I have obtained successful results in 

 determining the surface temperature of plant leaves by means 

 of a thermo-electrical method. The method differs from pre- 

 viously used ones in the fact that the leaves are not wounded 

 and in the consequent avoidance of the temperature complica- 

 tions which have been shown to result from the wounding of 

 plant tissues. 



The essential part of the apparatus is a thermo-couple, 1 one 

 junction of which is so fastened to a light spring clip that it is 

 held in position on the surface of the leaf. The other junction 

 is placed beside a mercury thermometer in a small thermos 

 bottle. A portable galvanometer and a damping key complete 

 the main parts of the apparatus. 



The details of the instruments are shown in figure 1. A, B, 

 and C are diagrams representing the top, side and end views of 

 the spring clip. The clip is made of brass spring wire, the ends 

 of which pass through small pieces of cork at the points marked 

 a and b. The size of the clip and strength of the spring vary 

 somewhat with the size and thickness of the leaf to be measured. 

 I found No. 00 wire to be most universally useful. A single turn 

 of wire is made around one pair of the cork-tipped ends. From 

 c to e the wire is No. 40 copper and from e to d No. 40 "Ideal" 

 wire. The joint at e is made by the cold soldering process and 

 must be very little thicker than the wires. The wire is insulated 

 on the top and sides but not on the bottom, where it touches the 



1 In response to my request the design of construction of the thermo-couple 

 was made by Mr. M. S. Van Duesen, of the U. S. Bureau of Standards, and I 

 am also indebted to him for helpful suggestions. 



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