— 237 — 



according to Pantanelli an optimum curve. The position of the 

 optimum is influenced by the C0 2 content of the water. 



In a series of papers Blackman (1905, 1911) and his students 

 have investigated the influence of C0 2 supply, light intensity and 

 temperature on G0 2 assimilation in land and water plants. The 

 result of his experiments is that "the magnitude of this function 

 in every combination of these factors is determined by one or other 

 of them acting as a limiting factor". For instance let us consider 

 the influence of light on the G0 2 assimilation at a temperature of 

 20° and a G0 2 content in the air of 5 %. The curve representing 

 the relation between light intensity and C0 2 assimilation will at 

 first be a straight line, the G0 2 assimilation rising in proportion to 

 the intensity of light. At a certain point the curve will attain a 

 maximum and further it will be parallel to the abscissa line. Here 

 the temperature and not the light intensity is acting as limiting 

 factor and only a rise of the temperature will produce a rise in the 

 G0 2 assimilation. Hence it appears that the position of the maxi- 

 mum is influenced by the temperature: at lower temperatures the 

 maximum will also lie at a lower intensity of light. An "optimum" 

 of light intensity according to Blackman does not exist. 



An investigation of the influence of light on the G0 2 assimila- 

 tion in light and shadow plants is carried out by Weis (1903). The 

 leaves were enclosed in a test tube in air supplied with G0 2 . 

 After the exposure of the plant the air was analysed by the 

 method of Bonnier-M angin. The intensity of light was measured 

 with photographic paper. The result of the experiments was as 

 follows (G0 2 assimilation in cm 3 G0 2 pr. 1 cm 2 pr. hour). 



In sunlight the C0 2 assimilation is 2 — 3 times greater in Oeno- 

 thera than in Polypodium; in sunlight the C0 2 assimilation is 

 higher in Polypodium. That agrees very well with the results obtai- 

 ned in my experiments. 



The investigations of Combes and several others on the in- 

 fluence of light on the production of matter will be referred to later. 



Oenothera. 



Polypodium. 



Sunlight . . . 

 gL sunlight 

 zjL sunlight 



0.1660 

 0.0517 

 0.0270 



0.0650 

 0.0705 

 0.0420 



