— 239 — 



above may rise to about dz 5 % of the value ; partly, that the plant 

 material used in the experiments is not uniform. Certainly the shape 

 of the curve varies with the surrounding conditions, especially with 

 the intensity of light, in which the plants are grown. As a matter 

 of fact the irregularity in the estimations can be made less by using 

 uniform material. I have not laid stress on this point. It was more 

 important for me to get the extreme values also. 





















- v. 





















y 















§ ^ 



















r > 





Sam 



hucus 













































Intensify t 





m 4 



i 





? / 



6 2 



0 2 



4- 2 



a 3 



2 36 



Fig. 4. C0 2 assimilation in Senecio silvalicus, Rumex acetosella and 

 Sambucus nigra. 



The shape of the assimilation curves in the 4 plants is as follows : 

 The curves begin below the axis of abscissae, which is crossed 

 at some distance from the zero point; the first part of the curves 

 is about linear, next they bend gradually and become finally about 

 parallel to the axis. On the whole the curves are identical with those 

 found of Blackman for the influence of light on the C0 2 assimilation. 

 In the first part, light is the limiting factor and in the last part an 

 other factor (temperature or C0 2 supply) is limiting. Between these 

 two parts there is a third part of considerable extent where the 

 C0 2 assimilation is neither constant nor proportional to the light 

 intensity; here the different factors interact. According to the 

 investigations of Mitscherlich (1909, p. 537 and 1911 p. 231) 

 similar curves are obtained from studying the influence of nutritive 



