vn] THE FORMATION OF ANTHOCYANINS 109 



and hence the term 'respiration pigments.' The chromogens, moreover, 

 are considered by Palladin to be present in the living plant as prochro- 

 mogens of the nature of glucosides, the hydrolysis and synthesis of which 

 are controlled by glucoside-splitting enzymes, and chromogen is only 

 produced as required for oxidation. After the death of the plant the 

 hydrolysis of the glucosides is rapidly increased, and the chromogen 

 becomes entirely oxidised: 



prochromogen (glucoside) + water -^- chromogen + sugar 

 chromogen + oxygen -*- ' respiration pigment ' 



Palladin includes anthocyanin 1 among the respiration pigments, 

 and explains its appearance in leaves fed on sugar, in young leaves 

 and autumnal leaves, as due to excess of carbohydrates: "Diese 

 Tatsache kann in der Weise gedeutet werden, dass durch Zuckerzugabe 

 die Atmungsenergie so gesteigert wird, dass ein Teil des oxydierten 

 Chromogens nicht momentan wieder reduziert werden kann." 



It was first suggested in 1909 by the present writer (212) that many 

 anthocyanins may be derived from the flavones or possibly xanthones 2 . 

 The flavones are a group of natural colouring matters, some of which 

 have been artificially synthesised by Kostanecki 3 . As a group they 

 are widely distributed, and the greater number have been isolated by 

 Perkin 4 from plants used commercially for dyeing. They may be 

 regarded as oxy-derivatives of /3-phenyl-benzo-y-pyrone : 



CO 



The flavones differ from each other in the number and position of 

 their hydroxyl groups. They are all substances coloured yellow, 



1 It must be clearly understood, however, that anthocyanins, apart from the fact that 

 they are aromatic substances, have very little in common with the respiration pigments. 

 The latter are formed only after death (unless we believe, with Palladin, that they are 

 reduced immediately in the living plant), the former only in living plants. It is possible 

 that the reactions taking place in the formation of the two sets of pigments are upon 

 similar lines, but there is no reason for thinking that they arise from the same chromogens. 



2 Later work, however, has not yet confirmed the origin of any anthocyanin from the 

 xanthones. 



3 See Abderhalden, E., Biochemi&ches Handlexikon, Berlin, 1911, Bd. vi. 



4 Perkin, A. G., various papers in Chem. Soc. Trans., 1895-1904. 



