1913.] Formation of the Anthocyan Pigments of Plants. 31-5 



identical with that of the petals from which it was made ; but sooner or 

 later the colour fades and the solution becomes colourless. The fading is 

 rapid in concentrated alcohol and slow in alcohols of somewhat weaker 

 grades. The agent responsible for the fading is resistant to high tem- 

 peratures. Thus if alcoholic extracts be evaporated to dryness and the 

 residues be taken up with water, the fading of the solutions still takes place 

 Further evidence in favour of the view that decolorisation is due to reduction 

 is offered by the results of experiments on the effect of extracts in inhibiting 

 and in reversing oxydase-action. 



The experiments were made in the following ways : — 



1. Extracts made from Stocks by Grinding the Petals with Alcohol. — A 

 solution of the peroxydase of bran is rendered of such a strength that it 

 just gives the characteristic blue reaction with benzidine and hydrogen 

 peroxide. Petals of a coloured variety of stock are ground with alcohol, the 

 extract is evaporated to dryness, and the residue dissolved in water. If a 

 few drops of the latter solution be added to the solution of peroxydase, and if 

 the benzidine-hydrogen peroxide test be applied, no colour-reaction ensues. 

 The oxydase is prevented by the reducing agent from bringing about the 

 oxidation of benzidine. Only if it be increased very considerably in amount 

 is the oxydase able to overcome the opposing influence of the reducing agent, 

 and to bring about the oxidation of the benzidine. 



2. Extracts obtained by Immersing Intact Petals in Strong Alcohol. — The 

 use of extracts made by grinding petals with strong alcohol is open to 

 obvious objections. We have, therefore, used extracts obtained by the 

 immersion of intact petals in strong alcohol. 



For this purpose petals of purple stocks are immersed in alcohol of 

 99 per cent. When the alcohol is decanted from the tube containing the 

 petals, its colour (pale purple) disappears in the course of a few minutes. 

 On evaporation over a water-bath it yields a purple residue. For the 

 purposes of control an equal volume of alcohol of the same strength as that 

 used for the extraction of the petals is also evaporated to dryness. A 

 bran peroxydase is prepared of such a strength that when a given volume 

 of it is added to a given volume of a weak solution of benzidine containing 

 one drop of hydrogen peroxide a definite but pale blue colour is produced. 

 The addition of similar volumes of peroxydase, hydrogen peroxide and 

 benzidine to the purple residue results in the production of no blue colour, 

 whereas the colour develops normally when the reagents are added to the 

 vessel in which the alcohol alone has been evaporated to dryness. The 

 alcohol which has been in contact with the petals, like the alcoholic extract 

 obtained by maceration, prevents the action of oxydase. 



