62 



(iirecl pioportionality between the CO.^ supply and assimilation in 

 Ihe cases given only holds good approximately, but that the melhod 

 of experiment does not pennit of an estimation of the extent of 

 Ihe deviation. 



In other cases, however, the deviation from proporlionality may 

 quite weil be measured. My experiments with Oxalis and Stellaria 

 nemorum at about { lighl make this clear. flere the values for 

 ihe assimilation al abnormal CO.^ concentrations' proved lower than 

 was to be expected. 



5 



(> 



I ^ 6 8 10 1£ 14 



Fig. 6. Diagram showing the influence of CO^ supply on the CO.^ assimilation of 

 Stellaria nemornm at different intensities of light. For Melandrium, see table VIII. 



The experiments with low lighl-intensities show a very interesting 

 deviation from Blackmans theory. As appears from the curves 

 for Ihe influence of light (fig. 2, p. 55), in the shade-plants the 

 light at intensities under jV— 2V works as the limiling faclor. 

 Only wilh intensities above ^ — ^^ does the carbon dioxide appear 

 as limiting factor. Thus, according to Blackman's theory it ought 

 to be expected that with a light-intensily of e. g. ^^^ an increase 

 in the COg percentage of the air över O.57 mg. per litre would 

 not result in any rise in the assimilation. The experiments however 

 show that a rise aclually does take place, wilh the same regularity 

 as with light-intensity I (see figs. 5, 6). In Stellaria nemorum and 

 Melandrium tjie maximum increase in the assimilation constituled 



