13 



f. Détermination of the intensity of the light. 



In the experiments with varying quantities of light the 

 light of the lamp was mcasured by W e b e r's photo- 

 meter, différent résistances having been put in. As the 

 intensity of the electric current could be considered to be 

 constant, the intensity of the light could be deduced 

 from the résistance that was put in during the experiment. 

 In ail our experiments the lamp was placed at the same 

 distance from the Helodea-shoots, so that at that point 

 the intensity of the light was changing proportionally to 

 that of the lamp. 



§ 4. Intensity of light and velocity of assi- 

 milation. 



Àccording to what has already been pointed out in the 

 Introduction it is necessary to work with an excess of 

 light-energy when studying the influence of température 

 on the velocity of the assimilation. At least this is the 

 view that is most accepted since B 1 a c k m a n's theory 

 about limiting factors. 



Therefore when presently discussing some experiments 

 about the connection between the intensity of the light 

 and the velocity of assimilation, we do not in the least 

 mean to give an explanation of this interesting problem, 

 which would require much more accurate investigations. 

 We hâve only tried to find out which intensity of light 

 was required in our way of arranging the experiments, 

 to be sure of an excess of light-energy. 



The experiments were performed at two températures, 

 namely 24° C. and 36° C. The latter température, as will 

 be évident later on, was not noxious to the assimilation 

 function, though it was very near the injurious température. 



It might be noted hère that it was not sufficient to 

 establish the required excess of light at a low température. 

 It is possible that a quantity of light- energy which means 



