146 Dr. R Darwin and Miss D. R M. Pertz. [June 15, 



It is well known* that aquatic and marsh plants do not close their stomata 

 in darkness. The following experiment illustrates the fact : — 



Experiment 30p.— Alisma sp. June 28, 1910. Temp. 17-18° 

 ■^r, 68-71 per cent. 



Porometer on lower surface, upper surface painted with vaseline. Fall of 

 column 12-8 cm., i.e., 4 cm., at an average pressure of 10 cm. The experiment 

 began in the dark room with the shutters open to a south light, but no 

 sunlight shone on the leaf. In this instance we have simply given the average 

 number of seconds required for the fall of the water column, because in this 

 way any change in the aperture is more strikingly obvious. 



June 28 





A.M. 1 





10.38—55 



6 2 



11.0 



Dark 



13—56 



6 5 



12 noon 



'Light 



■» 





12.2—50 



6-6 



51 



Dark 



3.45—46 



6-8 



June 29 





A.M. 1 





10.13—14 



7 



15 



Light 



16—50 



6-7 



In other experiments the result is not so simple. 

 Experiment 24p. — Alisma sp. June 23. Conditions as in Experiment 30p. 



Jun 



e23. 



June 24. 



A.M. 



Seconds. 



A.M. 



Seconds. 



11.0 



6 





Dark 



19 



10 



9.43 



26 



20 



Dark 



45 



27 



32 



10 



56 



27 



56 



13 



58 



Light 

 24 



P.M. 





10.7 



27 



12.13 



17 



11.3 



23 



32 

 32 -5 



22 

 Light 



39 

 40 



24-5 



Dark 



34 

 43 



23 

 21 



P.M. 





55 



21 



12.2 



25 -5 



1.8 



16 



4 



24 -5 



15 



20 



4.28 



44 



2.4 



26 



30 



45 -5 



3.31 



41 



Dark 







* F. Darwin ('98), p. 579, where references to the literature are given. 



