CHAPTER XIII 



THE OXIDASES IN RELATION TO PIGMENTATION, AND 

 THE ANTHOCYAN PIGMENTS 



IT has been known for a considerable time that there is a 

 connection between the occurrence of oxidases and sap 

 pigments in stems and the veins of leaves. Reinke in- 

 vestigated the chromogens as far back as 1882, and he was 

 by no means the first in the field. More recently they have 

 been studied by Wheldale (1910), Molisch (1905), Wffl- 

 statter (1913), Combes (1913), Keeble, Armstrong and 

 Jones (1913), Bartlett (1913), Everest (1914), Tswett (1914), 

 and others. 



SECTION I W HELD ALE'S THEORY OF ANTHOCYAN IN 

 FORMATION. 



The sap-soluble anthocyan pigments are regarded by 

 Wheldale as oxidation and condensation products of 

 colourless or light-coloured chromogens which are present 

 in living cells as part of a glucoside molecule. The hydro- 

 lysis of the glucoside is considered to be a reversible enzyme 

 action, effected possibly by an emulsin, and only the 

 chromogen thus liberated (which may itself be still a 

 glucoside owing to the retention of one or more sugar 

 groups) can be attacked by the oxidase. The chromogens 

 are by this author supposed to be either flavones or 

 xanthones, which are yellow colouring matters known to 



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