379 



As long as on aoconnt of insufficient constancy of the outward 

 circumstances or through inward causes, the growth already greatly 

 oscillates before the change in light-conditions, it may be easily 

 understood that a res[)onse of growth due to this one factor cannot 

 be accurately ascertained. 



As responses of growth of more than 50 7o are but rare, they 

 are not demonstrable when the growth shows such variations 

 beforehand. With the data in literature however this repeatedly 

 occurs. We repeat, tliat for our reactions ive only used organs, 

 showing as a rule no oscillations of groioth greater than 10°/,. 



The figures subjoined all represent the response of individuals, 

 approaching the average type as closely as possible. Only in the 

 case of Phycomgces nitens a schematical figuie of the process of 

 reaction was given. 



Just as in most of the previous curves published by Bi.aauvv such 

 figures, in which the reaction-type of a definite experimental series 

 is composed, are mainly based on the so-called cardinal points, to 

 be found in the reactions of all individuals. These cardinal points are: 



i. the average-point of time, at which the response of growth 

 begins ; 



2. the average-time, at which the reaction reaches its first climax 

 (either maximum or minimum of growth); 



3. the average-rate of growth at that moment in percents of 

 the original rate of growth ; and next again the average time, at 

 which eventually another maximum or minimum occurs and the 

 average-rate of growth at that moment. 



Dark- and light-growth-responses of Phycomyces nitens. 



The light-growth-responses are known from the results of Blaaüw, 

 published in "Licht u. Wachstum HI" (Med. d. Landb. Hoogesch. 

 1918) p. 108. The cardinal points for some intensities follow: 



TABLE 1. 



25 



Proceedings Royal Acad. Amsterdam. Vol. XXVI. 



