14 



an excess at a low température, becomes a limiting factor at 

 high température in conséquence of the increase of velocity. 



The results of the experiments with various intensities 

 of light are given in the tables I and II. The period of 

 exposition of the shoots to the différent intensities of Hght 

 is mentioned in the 3rcl column. At each of the applied 

 intensities two or more flasks were filled with water, 

 which had been conducted along the Helodea-shoots. The 

 indication and the contents of thèse flasks are given in the 

 4th column. The fîrst flask of each séries was filled with 

 water, which had not flowed along the shoots, but had 

 been collected directly. 



Notwithstanding the inévitable errors in the observations, 

 the results show that at both températures the rate of 

 assimilation becomes independent of the light-intensity 

 when this is more than about 2000 Hefner-candles. 



From thèse results it seems right to suppose that the 

 intensity of light might be a limiting factor. Further on it 

 will appear whether this conclusion is to be considered correct. 



At our further experiments an intensity of 2482 candies 

 was applied, which was obtained by putting in a résis- 

 tance of 1.1 n. 



When the ligth is less than 2000 candies the velocity 

 of assimilation seems to dépend very much on the light- 

 intensity. Hven from our (rather rough) data one would 

 draw the conclusion of a proportionality between thèse 

 values. It should be noticed that the results of both tables 

 are not to be compared, as they were obtained with dif- 

 férent shoots. 



§ 5. The velocity of the assimilation when 

 the circumstances are constant and when 

 the velocity of the watercurrent is change d. 



It seemed not improbable that noxious influence would 

 be efFected by an action of the light during a longer 



