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



Experiment 41 ; July 12, 1910.— Nicotiana glauca (in pot). 



The chamber was fixed to the leaf by plasticine, a method subsequently 

 abandoned because it appeared to injure the leaves. Diffused light. 



The rate of flow (E) is given in full, the square root of E is only given for 

 the salient points. The actual observations, i.e., the number of seconds in 

 which the column fell through 6 cm., are given for the extreme points. 







K (reciprocals). 



a/R. 



A M 



Seconds. 









20 



50 



7 1 



P M 









12.9 





57 -1 



7-5 







52-6 





24 





51 -8 





25 



Leaf stalk cut, cut surface not creased 



28 



1 47-8 



6-9 



30 





50 





33 

 36 





53 -8 

 62 -5 





41 





80 





46 





120 -5 





53 



6-4 



156 -3 



12 -5 



1.1 





128-2 





5 





108 -7 





10 





86 "9 





25 





51 -5 



7-2 



2.7 





26 -9 





26 





18-9 



4-3 



56 





14 -1 







Vaselined cut stalk 





3.3 





12 -2 



3-5 



47 





7-4 



2-7 



4.12 





5-9 . 



2-4 



6.37 



295 



3-4 



1 -8 



The details of the stomatal change are best seen in the larger curve 

 constructed from E (reciprocals of times and therefore proportional to rate 

 of flow). Within five minutes of the severance of the leaf-stalk the stomata 

 had begun to open with great rapidity ; the opening continued for 28 minutes, 

 when it was replaced by rapid closure, which gradually became slower, 

 the curve between 4 and 7 p.m. (not shown in the diagram) being a very 

 flat one. 



The temporary effect of cutting off water-supply was to increase the 

 rate E in the proportion 50 : 156 or 1 : 31. This is much greater than was 

 ever observed with the horn hygroscope. Thus* with Campanula vidalii 

 the rise was from 20 to 33, i.e., as 1 : T65, and in Tropaeolum from 40 to 60, 

 i.e., as 1 : 1*5. 



