6 



the influence of one of thèse factors, e. g. the amount of 

 of CO2 available, the amouut of radiant energy is insuffi- 

 cient, an increase of the amount of CO2 will not be fol- 

 lowed by a proportional increase of the assimilation, for 

 the amount of available radiant energy does not allow a 

 further rise of assimilation. In that case the conclusion 

 is obvions, that assimilation is independent of the amount 

 of CO2 available, but in reality the influence of the amount 

 of CO2 available has not been observed, because the amount 

 of available radiant energy was acting as a limiting factor. 

 The following diagram 2, reproduced from Black- 

 man's paper, represents graphically the results to be 

 expected in such a case. 



/n 



VL 



' '"/« i% J% '•% s'/^ 6%rûg 



Fig. 2. Assimilation-curve, after Blackman. 



The assimilation-curve A B, rising at first with the 

 amount of COj available, becomes horizontal in B as soon 

 as the amount of available radiant energy does not allow 

 any further increase of assimilation. Had the amount of 

 radiant energy been greater, the curve would hâve gone 

 on rising to D and would hâve run horizontally from D 

 to E. Thèse horizontal lines however do not give us any 

 idea of the relation between assimilation and the amount 

 of CO2 available. 



