1896.] water currents on the assimilation of aquatic plants. 79 



In our later experiments the gas yielded during half-an-hour 

 was collected and measured in the modification of Timiriazeff's 

 Eudiometer described and figured in Darwin and Acton's Prac- 

 tical Physiology 1 . 



As the times involved were short, and the temperature re- 

 mained fairly steady during the experiments, we dispensed with 

 barometric and thermometric corrections, and we believe that 

 the readings of the eudiometer are fairly comparable inter se 

 during any given experiment : although they certainly do not 

 give absolute amounts with accuracy. It will be seen that the 

 variations in the yield of gas as given by the eudiometer do 

 not always agree with the rates obtained by timing the bubbles 

 given off. When this is the case, we are inclined to trust the 

 eudiometer readings rather than those of the stop-watch. 



To stir the water uniformly, we hung a microscopic slide 

 to an ordinary bottle-jack, such as is used for roasting meat. The 

 glass slide makes five turns in about four seconds, and then reverses 

 and rotates in the opposite direction. 



Experiments with Elodea. 



In the following experiments we have given the average 

 rate of bubbling during periods in which the water was alter- 

 nately left quiet and disturbed. Where the amount of gas 

 yielded during the same period was measured the rate of yield 

 per minute is given in terms of a graduation of the eudiometer : 

 each graduation is equal to 001 c.c, and is of such a length that 

 the quantity of gas can be roughly read to 0*002 c.c. 



A single experiment is given in full, in order that it may be 

 seen that the effect of stirring is fairly well kept up for a period of 

 half-an-hour. 



1 Edition n. p. 45. 



