CHLOROPHYLL 



43 



I per cent, of the activity subsequently developed. Carbon 

 assimilation thus begins only when the leaves are fully green 

 and develops very quickly ; wherefore it follows that the first 

 origin of this function is not correlative to the amount of 

 chlorophyll produced, or, in other words, that the amount of 

 chlorophyll is not a conditioning factor in the early stages of 

 carbon assimilation. 



Willstatter and Stoll * were the first to make quantitative 

 estimations of the amount of chlorophyll in leaves, by the 

 methods already outlined.f Also they measured the amount of 

 carbon assimilation of the leaves of different plants and of the 

 same plant in different conditions — normal, etiolated, autum- 

 nal, and so on — and thus arrived at the assimilation number 

 which is the ratio between the amount of carbon dioxide as- 

 similated per hour and the chlorophyll content, both expressed 

 in milligrams. A selection of the values obtained are tabulated 

 below. 



Willstatter and Stoll, whose experimental methods were 

 similar to Irving's, with the chief exception that they used 

 a 5 per cent, concentration of carbon dioxide, found that 

 leaves with but a small portion of their full chlorophyll content 

 developed can assimilate to a measurable degree. 



WILLSTATTER AND STOLL'S ASSIMILATION NUMBERS. 



Plant. 



Primula 

 Rubus 



Tilia 



Populus 

 Elm 



Kind of Leaf. 



Chlorophyll 



Content in 



Mgms. 



Normal 



Normal 



Young 



Older 



Dark green autumn leaves 



Yellow-green autumn 



leaves 



Yellow variety 



Green varietv 



n-4 



16-2 

 5-2 



22-5 



152 



39 



9-5 

 130 



This conclusion is contrary to that of Irving, a difference 

 probably due to the fact that Irving used young leaves whilst 



* Willstatter and Stoll : " Ber. deut. chem. Gesells.," 1915- 4 8 » *54°- 

 f See Vol. I., Section on Pigments. 



