1911.] New Method of Estimating the Aperture of Stomata. 145 



Experiment 65 ; August 4, 1910. — Helianthus animus. Temp. 20-21°. 

 ■ty, 58-62 per cent. 



A cut leaf in water. In order to get a fairly readable fall of the water 

 column, it was found necessary to use a tube in which 1 cm. = 0"4 c.c. instead 

 of the usual - l tube. The square root only of rate of flow (v/R) is given. 





VR. 





VR. 



A.M. 





P.M. 





10.49 



3-7 



12.53 



4-8 



56 



4-0 



58 



Bark 



11.16 



5-2 



1.4 



3-3 



25 



Bark 



13 



2-3 



30 



4-1 



26 

 38 



1-9 

 1 -8 



P.M. 





2.10 



1-8 



12.6 



3 2 



15 



Light 



15 



Light 



25 



2-2 



22 



3-4 



36 



2-4 



29 



3 6 



49 



2-9 



39 



4-3 



3.11 



3 7 





































1 







































Fig. 5. — Experiment 65. Partial closure and reopening in darkness and light. 



It will be seen that from 10.49 to 11.25 a.m., when the first dark period 

 began, the stomata were opening ; the exact moment at which the fall in the 

 curve (i.e., the closure of the stomata) began is not shown, because the 

 observations are not numerous enough, but 6 minutes after the beginning of 

 darkness the rapid fall had begun. The first dark period, of about 50 minutes, 

 was not long enough to bring the stomata to rest, but later in the day, between 

 1 and 2 p.m., half-an-hour's darkness brings the curve to the horizontal. The 

 rapid opening of the stomata at 12.15 and 2.15 p.m. is well shown. 



