Jan., 1920] Resistance of Leaves to Transpiration 73- 



Conclusions. 



The conclusions from the experiments in this paper are 

 drawn from a comparison of the ratios given in the tables. 



The ratio — t^-- — from experiment 3 is taken as a standard 

 mullein 



. . . • T 1 ^1 ^- mullein^ , mullein^ 



for comparison m series i, and the ratio — ,, • » and — „ . , 



^ mullein' mullem* 



from experiments 5, G and 7 or sub-series-a as standard for 



comparison in series II. These represent the ratios of water 



loss in still air, and sunlight, or those conditions to which 



plants are more commonly subjected. For comparison, we 



assume that the numerator of the ratios does not change except 



in direct proportion to the environmental factors. For example, 



wind increases both the numerator and the denominator of the 



ratios or the transpiration of the two plants, but perhaps not 



to the same degree as when their rates are compared in still 



air. Under this assumption, any change in the ratios is due 



to an increase or a decrease in the transpiration rates of the 



plants used as the denominators as compared to the other 



plants. In the first series of experiments tobacco was used as a 



suitable plant with which to compare mullein, because of the 



very similar leaf structures of the two plants, except the absence 



of a hairy leaf covering on tobacco. In the second series normal 



mullein plants were compared with plants having the hairy 



covering of the leaves removed. These comparisons are made 



of daily results rather than hourly figures, because there is a 



great fluctuation in the hourly rates in some experiments and 



daily figures represent the average of these results. 



By comparing the ratio ff^' ( = 0.69) in still air and 



light with the ratio ( = 0.81) in still air and darkness it shows 

 that there was a greater resistance of the mullein leaves to 

 water loss in darkness than in light. A comparison of the 

 ratio ( = 0.69) in still air and light with the ratio ( = 0.65) in 

 wind and light shows that there was a very slight decrease in the 

 resistance of the mullein leaves to water loss in wind than in still 

 air. The comparison of the ratio (=0.85) from the still air 

 intervals of experiment 4 and the ratio ( = 0.57) from the wind 

 intervals of the same experiment and the ratio ( = 0.68) from 

 the still air intervals of experiment 2 and the ratio ( = 0.56) from 



