176 



EDITH BELLAMY SHREVE 



Following is a list of plants for which indices of transpiring 

 power have been calculated, 8 using first the temperatures as 

 read from a shaded mercury thermometer standing in the foliage 

 of the plant, and second, the temperatures obtained by the 

 thermo-couple. In the second case the reading which showed 

 the maximum difference from air temperature was always used. 



GKOWING IN THE OPEN 



Encelia farinosa 

 Prosopis velutina 

 Fouquieria splendens 

 Amaranthus palmeri 

 Bahia absinthifolia 

 Streptanthus arizonicus 

 Malva borealis 



GKOWING IN POTS 



Encelia farinosa 

 Lantana sp. 

 Poinsettia sp. 

 Phaseolus sp. 

 Rumex hymenosepalus 

 Nasturtium sp. 

 Ricinus officinale 

 Tradescantia sp. 

 Amaranthus palmeri 

 Streptanthus arizonicus 



In no case does the second result differ from the first more than 

 10%, and in the majority of cases it is under 2%. Now the 

 maximum difference between the indices of 10 different leaves of 

 the same apparent age on the same plant is frequently over 20% 

 and never under 10%. Consequently this work has established 

 the fact that the temperature of the air may be safely used for 

 the temperature of the cobalt slip. A sample of the results is 

 given in table 3. 



It is of course just as important to know whether or not the air 

 temperature may be used instead of the temperature of the slip, 

 in the calculations for the standardization of the slips over a 

 porous evaporating surface. By fastening the thermal couple to 

 a microscopic slide in the same manner that it is fastened to the 

 glass of the spring clip in figure 1, the temperature of the slip as it 

 lies over the evaporating surface was read. The porous evapo- 

 rating surface used was similar to the one described by Livingston 

 and Shreve 9 with the exception that a thermometer bulb was not 

 inserted in the side. In table 4 are given the times required for 



8 For method of calculation see Livingston and Shreve, loc. cit. p. 306. 



9 Livingston and Shreve, loc. cit. p. 294. 1916. 



1916. 



