274 Sir F. Darwin. 



40 





1 1 1 



30 





/ 



20 





/ • 



10 



,/ 







110 100 90 80 70 60 

 Fig. 1 (Experiment 1). 



In the figures the ordinates represent transpiration rates, while the relative 

 humidity (-vjr) is given on the horizontal axis. Thus if transpiration varies 

 directly as the relative humidity, the diagram should give a straight diagonal 

 line. The fact that the diagonal does not pass through the intersection of 

 the axes will be discussed later. 



Experiment 2. — November 8, 1909. P. laurocerasus. Fig. 2. 



Time. 



Period. 



Eate. 



T. 











° C. 



per cent. 



11.48 A.M. 



i 



56 



15 -8 



53 



12.3 p.m. 



ii 



56 



15 -4 



57 





Bell-jar over plant. 







12.24 „ 



iii 



35 



15 -1 



89 



12.35 „ 



iv . 



32 



15 -2 



92 



12.44 „ 



V 



27 



15 -4 



93 



2.7 „ 



vi 



17 



15 -6 



94 



60 





1 







50 









y / 

 / / 



40 







s 



s 



.S j 





30 





1 



r y 



1 / 







20 





; / 







/ 







—1 



i i 



* 1 ■ j ' 



110 100 90 80 70 60 50 



Fig. 2 (Experiment 2). 



It will be seen that the dots representing transpiration for various values 

 of are by no means in a straight line. This I take to be " lag," that 



