'218 CHLOROPHYLL 



In haematin, on the other hand, where iron replaces magnesium, 

 the function of the substance is to act as a carrier of oxygen from the 

 free oxygen of the air to the carbonaceous matter in the tissues of the 

 animal. This property of carrying oxygen is possessed by many iron 

 compounds and is, perhaps, not difficult to explain. 



Chlorophyll and its derivatives give characteristic absorption 

 spectra, the black bands formed in the continuous spectrum of white 

 light which has been filtered through a solution of chlorophyll show- 

 ing the particular rays which are absorbed and whose energy is util- 

 ised in the assimilative processes of the plant (vide next chapter). 



Many other coloured or colour-yielding substances occur in plants, 

 but their importance in reference to the life of the plant in most cases, 

 is small or not understood. 



