294 Physiologie. 



tion of the Anthocyan Pigments of Plant s. Part VI- 

 (Proc. Roy. Soc. B. LXXXVI. p. 113—131, 1913.) 



The object of the series of papers to which this belorgs is the 

 .elucidation of the biochemistry aud genetics of flower pigmentalion, 

 to achieve which it is necessary 1) to ascertain the nature of the 

 Chemical processes that determine the formation of the anthocyan 

 pigments, 2) to discover the chemical nature of the Mendelian cha- 

 racters to which the several varieties of a given species owe their 

 power of forming and breeding true to definite types of flower 

 colour. The working hypothesis used in the investigation may be 

 expressed in the form of two equations. A) Prochromogen (? a glu- 

 coside) -|- enzyme (? emulsin) = chromogen. B) Chromogen -[- oxy- 

 dase (Peroxydase -|- organic peroxyde) = anthocyan pigment. The 

 present and previous Communications are concerned with B, the 

 consideration of equation A being reserved for a later occasion. 

 The authors' previous work has shown that the presence of oxydase 

 in flowers can be demonstrated by means of benzidine, «-naphthol, 

 or similar "artificial chromogens" which when acted on by oxydase 

 yield pigments; that the distribution of oxydase coincides with that 

 of anthocj'^an; and that in white flowers oxydase may be present 

 in an active or an inhibited State — in the former case some other 

 pari of the pigment-forming mechanism is absent from the flower. 

 in the latter case the whole of the mechanism is present but its 

 action is prevented by the inhibition of the oxydase. 



The present paper deals with the chromogens of the flower, 

 and the following are the chief conclusions arrived at. In concen- 

 trated alcohol the anthocyan pigments are reduced to colourless 

 chromogens by reducing agents the nature of which is unknown — 

 they may be specific chemical substances, they may perhaps be ot 

 the nature of catalysts, but they are probably not enzymes (reduc- 

 tases). When the alcohol is replaced by water the oxydases. which 

 are not destroyed by the alcohol, resume their activity and colour- 

 less chromogen is converted into anthocyan pigment. The colours 

 of the pigments thus produced are identical with those of the 

 natural petals, indicating either that chromogens of more than onc 

 kind exist in the different colour varieties of Matthiola or that one 

 chromogen is present and associated with it are substances which 

 determine the coloration of the oxidised products of the chromogen. 

 The petals of Matthiola, etc., contain much larger quantities ot 

 chromogen than are used in the natural flower — not only may the 

 original depth of colour be recovered but the pigment so formed 

 may be removed from the tissues and further instalments of pigment 

 may be produced ~ but whether the reserves of chromogen in the 

 flower occur as such or (more probably) in the form of prochromo- 

 gen cannot at present be determined. The factor which determines 

 the direction in which the pigment-producing reaction shall go is 

 the amount of active water present in the cells — as the amount ot 

 water decreases the reducing agents of the cell become active and 

 oxydase becomes inert, as the amount of water increases oxydase 

 action comes into play and the reducing agents are either destroyed 

 or, if they persist, any action they exert is masked by the superior 

 and opposed activity of oxydase. The relations may be expressed 

 diagrammatically by the following scheme: 



