174 EDITH BELLAMY SHREVE 



The tripartite slip is placed between the glass and wire, so 

 that the thermal junction comes next to the leaf. On the 

 outside a rectangular hole is cut in the gummed cloth so that the 

 tripartite slip can be seen from the outside as usual. The 

 thermal-couple is made of copper and "Ideal" wires, both being 

 no. 40, the piece of soldering at the junction being no thicker 

 than the wires. The wires have such a small diameter that the 

 glass clip fits practically as tightly as without it. The gal- 

 vanometer and other parts of the apparatus for determining the 

 temperature have been previously described in detail. 7 



Fig. 1. Upper and lower views of cobalt chloride clip showing arrangement 

 for use of thermo-couple. 



Tests were made on widely different types of plants, growing 

 both in the greenhouse and in the open. The clip, arranged as 

 in figure 1, was placed on the leaves and left there while the 

 .cobalt paper turned from the light to the dark standard blue and 

 the temperature was read every ten seconds during this time. 

 Tables 1 and 2 give samples of the results obtained. The tem- 

 perature of the slip departs somewhat from the air temperature 

 by different amounts according to the species of plant, time of 

 day and the atmospheric and soil conditions. However the 

 greatest departure from air temperature, as read by a mercury 

 thermometer, which appeared in all the tests was 1.5°C. and this 

 .occurred only for temperatures above 28°C. 



7 Shreve, E. B., loc. cit. 1919. 



