1913.] Formation of the Anthocyan Pigments of Plaids. 311 



The petals of stocks decolorised by strong alcohol contain oxydase. The 

 reproduction of the original colour by the immersion of decolorised petals 

 in water is hastened by the addition of hydrogen peroxide. When a pink 

 and a purple petal decolorised in the same alcohol are transferred to water 

 to which a drop or two of hydrogen peroxide is added, the petals recover 

 pink and purple respectively. Therefore it follows that the activating action 

 of the peroxide is due to its provision of oxygen and not to its acidity. 



In water which has been boiled for a long time in order to remove the 

 oxygen, the recovery of colour, if it take place at all, occurs more slowly 

 than in unboiled water. The addition of dilute hydrogen cyanide — a 

 substance known to inhibit oxydase-action — prevents the recovery of colour. 

 The results of other experiments designed to decide between the indicator 

 and oxidation hypotheses lend further support to the latter. Thus 

 decolorised petals in which the pigment has been caused to reform may be 

 again decolorised either by leaving them in water till the pigment has 

 diffused away or by transferring them to alcohol. Petals treated in this 

 manner, if placed in hot water, produce once again their natural pigments. 



Again, the restoration of pink colour to decolorised petals of a pink 

 variety may be brought about in an alkaline medium ; for example by 

 transferring the petals from alcohol to water containing a small quantity of 

 hydrogen peroxide which has been rendered faintly alkaline. The pink 

 colour which is thus induced changes subsequently to purple. Conversely 

 the purple colour returns to a petal of a purple variety even though the 

 medium in which the change is effected be acid. In this case the recovered 

 purple soon becomes pink owing to the action of the acid. 



The last experiment is rendered still more conclusive if the procedure be 

 modified in the following manner. Petals of purple stocks are incubated 

 with 99-per-cent. alcohol to which enough citric acid has been added to 

 render the alcohol distinctly acid to litmus. The petals became almost 

 decolorised, retaining only a faint pink colour. When transferred to 

 distilled water — which is not acid to litmus — pigment is produced in con- 

 siderable quantities and the colour of the pigment is at first red but soon 

 becomes purple. If the colour were of the type of an indicator reaction the 

 effect of the water would be not to intensify but to dilute the tint. 



The conclusion which we have reached as the result of these observations 

 is that, although indicator changes run parallel with the changes involved in 

 the formation of anthocyanic pigments, the latter arise as the result of the 

 oxidation of chroniogens. 



It remains to mention the remarkable acceleratory effect which high 

 temperature has on the reproduction of the natural pigments of stocks. As 



