Die Formation of the Anthocyan Pigments of Plants. 127 



than that which arises when a-naphthol and oxydase interact with one 

 another. If j9-cresol be added to the red solution produced by the action of 

 oxydase on guaiacol a brown colour appears. Saligenin, on the other hand, 

 does not modify the normal deep red colour given by guaiacol and oxydase. 



Search in chemical literature brings to light a few records of similar 

 observations. Thus Schoenbein, in 1856 * observes that guaiacum blue 

 oxidises other oxidisable substances, and in doing so becomes reduced and 

 decolorised. Kastle and Porchf find that the oxidation of ^-phenylene 

 diamine, guaiacum, and phenolphthalein, by means of an oxydase, is accele- 

 rated greatly by phenol, the cresols and /8-naphthoL They recognise that 

 these accelerators act probably as auxiliary oxygen carriers, and that 

 they are themselves more or less completely oxidised in the process. 

 Miss Wheldale* suggests that oxidised catechol acts as a peroxide. 



jp-Phenylene diamine (^-diainino-phenyl, XH 2 C 6 H 4 iSTE[2) exhibits a some- 

 what different behaviour. Together with a-naphthol it constitutes the 

 indophenol reaction for oxydase, which reaction is used largely by animal 

 physiologists. In it the oxidised amine arid phenol are coupled to an 

 indophenol. 



We find that phenylene diamine gives much the same violet-blue 

 coloration with all phenols, including methyl quinol ; but that benzidine 

 and oxydase give with each phenol a distinct colour, similar to that produced 

 when the phenol in question is oxidised by oxydase. It would appear, 

 therefore, that nothing analogous with the indophenol reaction takes place 

 when benzidine and phenols are acted on by oxydase. 



It is to be noted that ^-phenylene diamine is oxidised by atmospheric 

 oxygen to a garnet red (tetra-aminodiphenyl-2>azophenylene), whereas it 

 gives a dark brown product when oxidised by oxydase. The indophenol 

 reagent is ill-adapted for the localisation of plant oxydases because of the 

 readiness with which it oxidises spontaneously. Petals of recessive white 

 Primula sinensis give a general purple reaction with it, and a brown with 

 phenylene diamine, but solutions of these reagents become strongly coloured 

 even without the addition of hydrogen peroxide, whereas this is not the 

 case with benzidine and the other reagents which we use for the investigation 

 of plant oxydases. 



We have not used «s-dimethyl-2>phenylene diamine (XH^CeELtNMea), 

 which substance is oxidised readily to quinone imine, the salts of which 



* ' Journ. Prakt. Chem.,' vol. 57, p. 496. 

 t 'Journ. Biol. Chem.,' 1908, vol. 4, p. 301. 

 % ' Boy. Soc. Proc., ! 1911, B, vol. 84. 



