1911.] New Method of Estimating the Aperture of Stomata. 147 



Thus on June 23 the rate of air-flow changed considerably in the day, 

 becoming slower on the whole, but not showing any marked effect of light or 

 darkness. On the following day there is irregularity which is not clearly 

 connected with changes in illumination. 



It was formerly found* that the stomata of Caltha palustris close in darkness. 

 This, however, is not always the case; no closure could be detected in a 

 porometer experiment of June 25, 1910. Further work is needed on this species. 



Nocturnal Closure. — The following two experiments illustrate the closure 

 and opening of stomata when exposed to diurnal change of illumination. The 

 experimental plants Nicotiana glauca (Experiment 67) and P. laurocerasus 

 (Experiment 68) were in flower-pots and placed close together in a greenhouse 

 on the roof of the laboratory. The sky was cloudy, except between 5 and 

 6.30 p.m., when there was occasional faint sunshine. The temperature (T) and 

 relative moisture (ty) of the air are given under Experiment 67. Only the 

 square root of the air flow (^/R) is given. 



Experiment 67 ; August 9, 1910. — N. glauca. 





</K. T. 







P.M. 











2.22 



30-4 









54 





20 -3 



72 





3.6 



33 -7 









56 





. 20-2 



70 





4.24 



26 -9 









5.5 









Faint sun for about \ hour. 



12 



25 -2 



20 -4 



74 





6.16 



26 







Sun obliquely on leaf. 



45 



25 -7 







7.47 



3-7 









59 



2-7 • 



17 -0 



84 





8.12 



2-3 









27 



2-1 









31 



2-0 









54 





3.6 -0 



87 





9.9 











10.27 





15 -2 



91 





29 



2-1 









37 





14 -4 



91 





12.10 



2-8 









1.58 



3-7 



13 5 



91 





3.30 



4-5 



12 -8 







39 



4-6 









51 









Notes easily legible ; eastern sky red. 



4.45 



6-1 



12 -4 



90 



5.55 





13 -0 



90 



Light clouds, no sun on plant. 



6.5 



18 -3 







7.37 



34 -7 



15 -4 



85 





9.1 



43 -4 



19 2 



72 



Bright : not sunshine. 



* F. Darwin ('98), p. 580. 



