24 



BURTON EDWARD LIVINGSTON 



special conditions may have been operative on one plant and not 

 upon another. 



Figure 2 presents the graphs for the three series of indices 

 (table 4, column 4, 7 and 9) and for the two series of average 

 relative transpiration ratios (table 5, columns 4 and 7). Figure 

 3 repeats the graph representing the indices for the entire leaf 

 surface, and also shows the graphs for the four series of relative 

 transpiration ratios for the individual plants. 



Inspection of the graphs brings out the fact that there is a 

 much greater uniformity and consistency in the march of the 

 index of transpiring power derived from the standardized hygro- 

 metric paper than is found in the march of the ratio of relative 

 transpiration. W'Mle the minor irregularities in the ratio graphs 

 may safely be related to non-uniformities in the fluctuation of the 

 surrounding conditions of the weighed plants and of the instru- 

 ments, the more pronounced discrepancies between the results of 

 the two methods with which we are dealing must have some other 

 explanation. Perhaps the most striking of these greater dis- 

 crepancies lies in the fact that, while the index remains low and 

 almost constant throughout the night hours, the ratio shows an 

 unmistakable tendency to increase in value after the early attain- 

 ment of its minimum. No explanation of this condition can now 

 be offered. 



Another striking discrepancy between the graphs of the ratio, 

 on the one hand, and of the index, on the other, manifests itself 

 in the early fall of the values of the ratio in the case of plant 2. 

 This appears probably to be related to incipient drjdng,^^ which 

 may have occurred in plant 2 while it had not yet been sensibly 

 induced either in plant 1 or in the plants used in the hygrometric 

 tests. 



It is also remarkable that the relative transpiration ratio of 

 plant 1, by either atmometer, presents a much flatter graph than 

 that exhibited by the hygrometric index of transpiring power. 



In spite of discrepancies, however, the conclusion is forced upon 

 us that the results obtained by means of the two methods are 



11 Livingston and Brown. Loc. cii. 



I/ivingston, B. E., Incipient drying in plants. Science N. S., 35 : 394-395, 1912. 



