ASSIMILATION. 



231 



which contain chlorophyll, and it is the energy of light absorbed 

 by this colouring substance which effects the decomposition of 

 carbon dioxide. It is found that the assimilation of carbon 

 dioxide is most active in just those rays of the spectrum of 

 white light which are absorbed by a solution of chlorophyll. 

 This is well shown in the accompanying diagram, which gives 

 the relative assimilation by plants in different parts of the 

 spectrum (continuous line), and also the relative absorption by 

 a solution of chlorophyll (dotted line). It will be seen that the 

 two curves correspond very closely*: 



The following diagram gives the distribution of the intensi- 

 ties of the various rays of the solar spectrum as regards 



assimilation of carbon (continuous line - ), brightness as 



measured by the eye (broken line ), heating effects 



(dotted line ), and chemical action on silver salts (broken 



and dotted line ..._ )-j- : 



Kngehnann, Hot. Zeitnng, 1884, SO. f Sachs, Plant Physiology, p. 305. 



