Ihis relalively high iiilensily tlie advanlage of incrca.sed (X).^ tension 

 is verv greal. 



The resulls obtaiiied can therefore only l)e explained on Ihe 

 assumplion tlial llie decisive factors for Ihe assimilation infhience 

 each olher's degree of activity. Wilh light-intensilies under j\,— ^^q ^"^ 

 a carhon dioxide conceiitralion of 0..->7 mg. per Htre, bolh Ihe light 

 and Ihe carbon dioxide therefore work as »controlHng factors». 



It is worthy of note that the same result \vas obtained in the 

 case of all three of the plants examined wilh intensity ^\|, which 

 seems to indicate that we have here to do with a state of atTairs 

 that is of general a])plication, at least for shade-plants. That the 

 phenomenon is of the greatest ecological importance follows from 

 the fact, demonstrated below, that the supply of CO., is usually 

 more abundant in the undergrowlh of the forest than in Ihe open 

 lield. The shade-plants live their lives in great measure under 

 light-inlensities below j\, — ^f,, hut with higher CO.^ concentrations 

 than 0..-.7 mg. ])er litre. The following figures show the increase in 

 assimilation with low and high light-intensity for two shade-plants. 



Oxalis. 



Stellaria nemorum. 



