282 



Sir F. Darwin. 



to keep the relative humidity (i/r) as constant as possible. The rates of trans^ 

 piration are given as corrected. North light. 



Time. 



Rate corrected. 



T. 









C C. 



per cent. 



10.42 A.M. 



24 -8 



14-2 



65 



10.54 „ 



24 7 



14 -2 



64 



11.1 „ 1 

 11.5 „ J 



Covered bell-jar with a black hi 





11.21 „ 



27-1 



14 -6 



62 



12.5 P.M. 



22-1 



14 -6 



63 



12.30 „ 



Light : cloth b 



ig removed. 





12.41 „ 



24 -9 



15 -2 



62 



2.46 „ 



25 -8 



15 -7 



63 



3.10 „ 



28 -0 



15 7 



63 



3.27 „ 



Dark : cloth ba 



g replaced. 





3.43 „ 



25 -0 



15 "9 



63 



3.57 „ 



25 -4 



15 -8 



63 



4.11 „ 



26 '0 







Result. — The fall in transpiration-rate between 11.21 a.m. and 12.5 p.m. is 

 27-1 to 221 or 123/100. The rise in the next period is from 221 to 28-0 or 

 100/127 ; the diminution in the final dark period is 108/100. The average 

 proportion between the transpiration in light and darkness (L/D) is 

 119/100. 



Experiment 2. — April 11, 1911. P. laurocerasus. 

 Potometer: T 15'0-16-2° C. yfr 46-56 per cent. Transpiration corrected. 



Time. 



Rate. 



Time. 



Rate. 



11.17 A.M. 



164 



11.55 A.M. 



107 



11.33 „ 



140 



11.58 „ 



103 



11.37 „ 



122 



12.13 P.M. 



108 



11.41 „ 



116 



12.28 „ 



95 





In dark room. 



4.10 „ 



109 



11.45 „ 



115 



4.12 „ 



110 



Transpiration was falling (in the light) from 11.17 to 11.41 ; the effect of 

 darkness was to diminish rather than to increase the rate of fall. The total 

 change in the dark is a fall from 115 to 110, or L/D = 105/100. 



