vn] THE FORMATION OF ANTHOCYANINS 115 



No flavone is present in the white variety, but it must nevertheless 

 contain a factor which, in some way, acts upon the chromogen, apigenin, 

 with the production of magenta anthocyanin. The magenta flowers 

 contain apigenin in the inner tissues of the corolla, and anthocyanin 

 in the epidermis. This anthocyanin, isolated according to methods 

 given elsewhere and purified from apigenin, gave on combustion the 

 following percentages as compared with apigenin 1 : 



C H O 



From anthocyanin 50-50% 5-11% 44-39% 



From apigenin 66-66 % 3-70 % 29-64 % 



from which it will be seen that anthocyaniu in Antirrhinum is a more 

 highly oxidised substance than apigenin. Determinations of the 

 molecular weight of this anthocyanin gave results of the order of 700 

 showing that the red pigment has a much larger molecule than apigenin, 

 the molecular weight of the latter being 270. Hence it is possible that 

 in the formation of anthocyanin, either two or three molecules of flavone 

 condense with oxidation, or the flavone condenses with some other 

 aromatic substance present in the plant. 



2. Evidence from analogous reactions. It has been suggested above 

 that sugar is first split off from certain hydroxyl groups of the flavones 

 (which we know to occur as glucosides), and only then can changes, 

 such as oxidation and condensation, take place at these points the 

 hydroxyl groups. Co-ordinated reactions of this kind are known to 

 be common in plant metabolism, the most familiar case being that of 

 indigo which may be represented: 



C 14 H 17 6 N (indican) + H 2 - C 8 H 7 ON (indoxyl) + C 6 H 12 6 

 2C 8 H 7 ON + 2 = C 16 H 10 2 N 2 (indigo) + 2H 2 



The first reaction is brought about by a glucoside-splitting enzyme, 

 indimulsin, which hydrolyses the glucoside indican ; the second by an 

 oxidase which oxidises the colourless indoxyl to the pigment indigo. 



The development of a bright red pigment which rapidly appears 

 when flowers and leaves of Schenckia blumenaviana are placed in chloro- 

 form vapour has led Molisch 2 to form the opinion that the reactions 



1 It should be noted that in preparation, the glucosides of both the anthocyanin and 

 apigenin are split up, and the pigments obtained for analysis free from sugar. Any 

 sugar present in the molecule would naturally raise the percentage of oxygen to a con- 

 siderable extent. 



2 Molisch, H., 'Ueber ein neues, einen carminrothen Farbstoff erzeugendes Chromogen 

 bei Schenckia blumenaviana^ Ber. D. hot. Ges., Berlin, 1901, xix, pp. 149-152. 



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