310 



Mendelian Factors for Floiver- Colour. 



Since we find that the return of colour in water is always accelerated by 

 acid or alkali, we suggest that the acceleration by hydrogen peroxide is 

 merely a function of the amount of acidity or alkalinity of the medium in 

 which the hydrogen peroxide is dissolved. Moreover, although the exceed- 

 ingly small amount of acid or alkali which at first diffuses into the petal from 

 the very dilute solution may be sufficient to accelerate the actual return of 

 colour, it is not sufficient to give the usual acid or alkaline coloration with the 

 anthocyanin present. Further addition of the hydrogen peroxide solution 

 would, and in fact does, bring about this result. In support of this, we 

 observe that the extract, which at once comes into contact with the full 

 amount of acid or alkali, immediately gives the acid or alkali colour, and not 

 the original purple, pink, etc., of the petals. 



To confirm this suggestion we carefully neutralised some laboratory 

 hydrogen peroxide, which is, of course, always decidedly acid, and found that 

 this neutral reagent actually retarded the recovery of colour as compared 

 with control experiments on decolorised petals in cold, hot, or very faintly 

 acidified water. 



This result is not surprising in view of the decolorisation of petals by 

 hydrogen peroxide and colloidal platinum, already described in this paper, 

 and, we think, clearly demonstrates that the oxidising properties of hydrogen 

 peroxide have nothing to do with the recovery of colour by the use of this 

 reagent when it has not been neutralised. 



Secondly, the same authors state that the purple coloration of a petal can 

 be restored by re-oxidation in an acid medium. For this purpose purple 

 petals of Stocks are incubated with 99-per-eent. alcohol with just enough 

 citric acid to render the alcohol acid. The petals become almost decolorised, 

 but retain a faint pink colour. When transferred to distilled water the 

 pigment is reproduced in considerable quantity, at first red and then purple. 



We should explain the phenomenon as follows : The purple pigment is 

 rendered colourless by the alcohol, but, owing to the presence of a small 

 quantity of citric acid (which is very slightly dissociated in alcohol), the 

 colour does not entirely disappear, and the solution remains pink. Trans- 

 ference to water restores the colour, which is at first red, owing to the 

 increased ionisation of the citric acid by the water that soaks into the petal. 

 After a time the acid diffuses away into the surrounding water, leaving the 

 liquid in the petals practically neutral, when the pigment becomes purple. 



Finally Keeble, Armstrong, and Jones note that when the colour is 

 restored to petals by immersion in water, and the colour is allowed to diffuse 

 out of them, coloration is again restored by transferring them to hot water, 

 and this process may be repeated two or three times. 



