Ihe lighl-inlensilies oflered in Xalure for our disposal, hul. in com- 

 mon with all lighl-measuiemenls given in Ihe lileralure. Ihey art- 

 ([uite insufficient to be made Ihe basis of a calculalion of Ihe 

 daily process of assimilalion in the foivst-planls. The only i)ossi- 

 bility of obtaining information as to Ihe variations in Ihe condi- 

 tions of light in the forest is by a conlinuous regislering, and Ihc 

 lack of suitable apparatus has hitherto rendered this impossible 

 to carry out. 



If the curves for the shade-planls are comparcd with one anolhei-. 

 it will be seen that the maximum assimilation varies. The con- 

 ditions are most favourable for Oxalis. This circumstance is nalu- 

 rally of ecological importance, since it gives a dilTerenl degree of 

 productive power under favourable conditions. The rise of the 

 curves in their left-hand sections also probabh' indicales variations 

 which point to specifically dilTerent powers of assimilation, due 

 possibly to different chlorophyll percentages or to dilVerenl inten- 

 silies in the protoplasm factor. The experiments however are too 

 few in number to give a sufficiently exact delermination of Ihe 

 steepness of the curve in the strong individual variation. 



4. The influence of the carbon dioxide concentration on the assimilation. 



The influence of the (^03 concentration upon the assimilation 

 has already been examined by Godlewski (1874)'. The Pfkffkk 

 apparatus used by him (Pfeffer 1874) certainly does not give any 

 great degree of accuracy. Godlewski also used very high (^Oo 

 concentrations (l.-2%—A2%). He found that the assimilalion rises 

 with an increase of the COg concentration up to 5 — K) "o. and that 

 the rise becomes more pronounced the stronger the light is. 



In view of Bro\vn's experiments il9()2), and of my own as 

 described below, it seems as though it may be doubted whelher 

 the rise in the assimilalion really runs up to such high (X)., con- 

 centrations. For the same reason it seems to me that a number 

 of Kreusler's values (1885) ought to b.e revised. Krkisi-er however 

 employed a much better method than Godlewski, namely an air- 

 current with a comparatively low CA)., concentration and gravi- 

 metric estimalion of CO.^. An average of the values obtained by 

 him for dilTerent plants gives a strikingly low and extended curve. 



* For earlior, incomplete observations see Cz.xpek 1913, p. .v27}. 



