vii] THE FORMATION OF ANTHOCYANINS 121 



Palladin's 'respiration pigments' at once makes it clear that Jones' 

 chromogens are identical with these pigments. Class (a) contains some 

 substance which can act as an organic peroxide, class (6) no such sub- 

 stance, so that hydrogen peroxide must be added in order to give a 

 pigment. Class (c) apparently contains no substance which can act 

 as a respiration pigment. There is no evidence whatever that the 

 chromogens of the respiration pigments are in any way the chromogens 

 of anthocyanin, and hence their absence has no bearing on albinism 

 with regard to anthocyanin (see footnote on p. 109). 



More recently Combes (234, 235, 620) has brought forward evidence 

 which he considers to be in complete contradiction to the oxidation 

 hypothesis of the formation of anthocyanin. Combes' work may be 

 summed up under three headings : 



1. The isolation of two pigments from leaves of Ampelopsis 

 hederacea : namely, a brownish-yellow pigment crystallising in rosettes 

 of needles and having the properties of a flavone, and a purple pigment 

 also crystallising in rosettes of needles and having the properties of 

 an anthocyanin. 



2. The transformation of the flavone into a purple pigment identical 

 with anthocyanin by reduction. 



3. The transformation of anthocyanin into a flavone by oxidation. 

 The method employed by Combes of obtaining anthocyanin from 



flavone (from Ampelopsis) is to dissolve the flavone in alcohol, acidify 

 with hydrochloric acid and add sodium amalgam. The solution thus 

 treated with nascent hydrogen becomes violet-red and increases in 

 intensity of coloration. After neutralisation and filtration, the solution 

 obtained gives a purple substance on evaporation. The latter crystal- 

 lises in needles grouped in rosettes like the natural anthocyanin and 

 has the same melting point and properties as the natural product. 

 Combes also obtained crystalline anthocyanin from a crystalline flavone 

 isolated from leaves of the Privet (Ligustrum vulgare) and from a similar 

 substance extracted from a variety of Vine which does not redden in 

 autumn. From these results he concludes that the phenomena observed 

 for Ampelopsis are not confined to that plant. And, moreover, though 

 the variety of Vine (Chasselas dore) does not redden in autumn, yet 

 its leaves produce a substance capable of being reduced to form an 

 anthocyanin. In addition, he employed flowers of Narcissus incom- 

 parabilis. The genus Narcissus, as is well known, contains a readily 

 crystallisable flavone, and from this substance he also prepared an 

 anthocyanin-like product by reduction. 



