144 Dr. F. Darwin and Miss D. F. M. Pertz. [June 15, 



The period of darkness is indicated on the diagrams by a black bar on the 

 time scale. 



In the tables, R stands for the proportional rate of air-flow obtained from 

 the reciprocals of the second column. The fourth column gives the square 

 root of the rate of flow. 



Experiment 38 ; July 8, 1910. — Tropaeolum (in a pot). North window. 

 Temp., 15-16°. -f, 72-75 per cent.* 



1429 

 1515 

 1429 



35 -4 

 23 -6 

 13 -6 



f The symbol <1> is used for the relative humidity of the a 



Fig. 4.— Experiment 38. Partial closure of 



It will be seen that there is a rapid fall in the curve at about 5 minutes 

 after the beginning of the dark period, and that the curve gradually 

 flattens until, at 3 p.m., it is approaching steadiness. 



