28 



BURTON EDWARD LIVINGSTON 



used, each of which had a pair of very large primary leaves and 

 two or three leaves of the secondary form. It will be recalled 

 that the primary leaves of this plant are simple and that the others 

 have three leaflets. The average test times (for four tests in 

 each case), at 16 hours 30 minutes, September 9, 1911, are given 

 below, as well as the derived indices of transpiring power. 



Phaseolus vulgaris 





LEAF SURFACE 



TIME 



INDEX 







seconds 





f 



upper 



965 



0.031 



Large primary leaves ■ ' ■ | 



lower 



278 



0.108 





entire 





0.070 (average) 





upper 



570 



0.053 



Smaller secondary leaves | 



lower 



268 



0.112 





entire 





0.083 (average) 



Water test 



(free surface) 



30 





The lower surfaces of the two sorts of leaves have about the 

 same index, but the upper surface of the younger form is appar- 

 ently characterized by a transpiring power about 70 per cent 

 greater than that of the same surface of the primary leaves. It 

 is also to be noted that the difference between the indices for 

 the two leaf surfaces is greater in the case of the primary leaves 

 than in the others. 



Experiment V. This and the experiments to follow were per- 

 formed in the early autumn of 1912, with the assistance of Mr. 

 E. M. Harvey. The saturated paper standard was used. Exper- 

 iment V illustrates the differences in transpiring power, between 

 upper and lower leaf surfaces by day and night, for plants of 

 Ruellia tuherosa var. occidentalis A. Gray, growing in the open 

 ground near the Desert Laboratory, but partially shaded by 

 Acacia and Prosopis. The plants were rather mature at the time 

 of testing (September 12, 1912), having practically ceased flower- 

 ing. The tests represent hours 16 and 23/ 



The results are summarized on following page. 



