86 



Mr Darwin and Miss Pertz, On the effect of [Feb. 10, 



Experiment 10 : 20th November, 1895. 

 Elodea in Tap-water which had stood 24 hours. 



Altogether eleven experiments were made with Elodea. 



The results are fairly uniform, that is to say, the rate of bubbling 

 as taken by the stop-watch is nearly always markedly increased. 

 Exceptions occur, however : for instance, in the " stirred " periods 

 of Experiment 8 stirring did not increase the rate of bubbling, 

 but in both cases the amount of gas actually yielded was greater. 

 The same thing is true of the final " stirred " period of Experi- 

 ment 9. Indeed there were no exceptions to the statement that 

 the actual yield of gas per minute was greater when the water was 

 stirred. We are inclined to believe that the results obtained by 

 measuring the gas are trustworthy because the amount of effect 

 due to change of condition does not vary greatly. The following 

 figures give, in round numbers, the effect of change from the 

 " stirred " to the " still " condition. 



180 

 140 

 175 

 161 

 155 

 165 



100 



