14-4 Miss Wheldale, On the nature of antliocyanin. 



lower stage of formation than the ivory-white, yet capable, like 

 the latter, of being acted upon by the oxydase with the productions 

 of anthocyanin, which in this case is mixed with unaltered yellow 

 chromogen and consequently produces the crimson colour of the 

 crimson variety. 



Antirrhinum is the type of a number of genera in which 

 the colourless chromogen of the ivory-white variety gives rise, 

 probably through loss of some factor, to a xanthe'ic pigment. 



Definite knowledge as to the nature and constitution of these 

 aromatic chromogens, from the oxidation of which anthocyanin 

 may arise, is a difficult chemical problem. I am inclined to 

 believe that they belong to the flavone and xanthone classes 

 of natural colouring matters*, which they closely resemble in 

 properties and reactions. The flavones and xanthones are chiefly 

 present in plants as glucosides or rhamnosides, most have fifteen 

 carbon atoms in their empirical formulae and on fusion with 

 caustic alkali many give protocatechuic acid and phloroglucin. 



The nucleus of these substances is 7-pyrone, which may be 

 regarded as an anhydride of a diolefine-dioxyketone : — 



CH = CH 

 CH = CH 



Xanthones and flavones are derived from pheno-7-pyrone : — 







CH 



CO 



Xanthone being a dibenzopyrone 



CO 



See Czapek, Biochemie der Pjianzen. 



