1896.] water currents on the assimilation of aquatic plants. 77 



added to the water in the funnel the rate of bubbling became 

 about eight times as quick, returning after two minutes to about 

 its previous rate. 



5 p.c. spirit added 



A similar striking effect was obtained by adding 10 p.c. after a 

 few minutes. Later in the day the effect was not so marked, 

 the rate of bubbling was doubled when alcohol was added to the 

 water in the funnel. The result is what might have been ex- 

 pected since the escape of gas varies with the pressure at the 

 cut end of the stalk. This well-known fact may be simply demon- 

 strated by cementing the cut stalk with gelatine into the lower 

 end of a vertical tube which is filled with water to various heights 

 by means of a side opening and rubber tube, and thus exposes the 

 cut end of the stalk to varying pressures. 



The following table shows a diminution in, and final cessation 

 of, the bubbling as the pressure rises, and a rise as it is allowed to 

 fall again. 



27th June, 1895. Elodea canadensis. 



