Chlorophyll Content. 93 



Leaves poor in chlorophyll {Yellow Varieties). 



Leaves poor in chlorophyll, e.g., yellow varieties with a chloro- 

 phyll content of from 15% to 3%, or even less, of that of the leaves 

 of the normal green varieties, exhibit a marked deviation in the 

 proportionality between chlorophyll and assimilation. The numbers 

 given in Table XXII for the yellow varieties are not maximal values 

 of the assimilation, for it was found impossible to use the maximum 

 light intensity without injuring the leaves. Under cei'tain conditions 

 it was found that at 15''C instead of 25''C the absolute amount of 

 carbon dioxide absorbed by equal surfaces of yellow and green 

 varieties can in the former reach a value as high or even higher 

 than that taken in by the leaf of the normal variety. 



Table XXII. 



Assimilation Numbers of Leaves of Green and Yellow 



Varieties of Elm.. 



Ulmus, 5% CO2, 3000 candle power at 35 cm. distance (24,000 lux). 



Willstatter points out that from this table it may be observed 

 that the assimilation of chlorophyll-poor and chlorophyll-rich leaves 

 is very similar at lower temperatures, but that the quantity of 

 assimilation per unit quantity of chlorophyll is much greater in the 

 yellow varieties. 



Willstatter seems to indicate that the conditions in the yellow 

 varieties are of great importance in judging the factors which 

 influence the assimilation. As temperature variations do not 

 influence the assimilation in such leaves, while decrease in light 

 decreases the assimilation, he concludes that in this case the 

 enzymatic system is more developed than the chlorophyll system, 

 which thus controls the rate of assimilation. The reaction of the 

 chlorophyll system being photochemical it may be assumed to have 

 a temperature coefficient not far from unity, while the enzymatic 

 process has a temperature coefficient of a magnitude of 2 to 3. In 

 the normal leaf the chlorophyll system is more developed and the 

 enzymatic process limits the rate of assimilation, Consequently 



