19 



From thèse results it is évident that the rate of assi- 

 milation is independent of the velocity of the watercurrent, 

 therefore it was of no conséquence that this velocity was 

 not entirely constant in our experiments. 



Still more important is a second conclusion which can be 

 drawn from this resuit, viz. that the COo was available in such 

 an excess that the amount of COo was not a limiting 

 factor. For, decrease of the velocity of the watercurrent 

 means a slower replacing of the water which is streaming 

 along the shoots and which is loosing its COo. When 

 this does not influence the rate of assimilation we may 

 conclude that the assimilation has reached its maximum 

 under the circumstances of our experiments. 



§ 6. The assimilation and the température. 



The way of arranging the experiments for différent 

 harmless températures needs no interprétation after the 

 previous remarks. As to the experiments at injurious 

 températures it is quite différent, as then the velocity of 

 assimilation is decreasing during the experiment. The only 

 thing to do hère is to détermine a mean velocity during 

 the period of filling the flask, which in our experiments 

 was 4.5 à 5 minutes, the flasks being changed every 6 

 minutes. Supposing however the change of the velocity 

 to be regular, then we might consider this mean velocity 

 to be the real velocity 3 minutes after putting on the 

 flask. So when changing the flasks every 6 minutes we 

 thus establish the velocity of the assimilation 3, 9, 15 

 and 21 minutes after putting on the fîrst flask. 



Moreover thèse experiments présent the difHculties that 

 fresh Helodea^shoots had to be used for every injurious 

 température, so the results could not be compared with 

 one another. This difiîculty can be removed by determining 

 the rate of assimilation of the shoots at a same harmless 

 température before the beginning of the actual experiment 



2* 



