258 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



back to the chromogen. The relations were by these 

 writers expressed in the following scheme : 



\ 



Chromogen (2^2^) Anthocyan pigment 



f - Water \ 



\Reducing agent/ 



<r 



In support of it, they demonstrated that the restoration 

 of colour is accelerated by a moderate increase of tempera- 

 ture and by hydrogen peroxide; also that the action of 

 peroxidase is very feeble in strong spirit, though it can pro- 

 duce a slight browning of benzidine in the tissues (but not 

 in vitro), even when the solution contains as much as 95 

 per cent, alcohol. The possibility of the aiithocyan colour 

 change being of the indicator type was examined by Keeble, 

 Armstrong, and Jones, and dismissed as unsatisfactory. 



Wheldale and Bassett (1914, 1) have recently pointed 

 out that this fading and restoration of colour is exhibited 

 by most pigments of the anthocyanin class, and has been 

 recorded by Hansen (1884), Molisch (1905),andGrafe (1911), 

 in various plants. Furthermore, restoration of colour takes 

 place in boiled solutions on evaporation, and so cannot be 

 due to oxidase action. This criticism seems to the author 

 to be quite unanswerable. In addition it has been shown 

 by Wheldale that the acceleration of the return of colour 

 is due, not to hydrogen peroxide, but to the acid contained 

 in this reagent as usually prepared, and that when dry 

 hydrochloric or hydriodic acid is passed into absolute 

 alcohol containing decolorized petals, the usual red colour 

 is produced. This is also the case when hydrogen cyanide 

 gas is passed in. Thus, in spite of the fact that the latter 

 substance is an inhibitor of oxidase action, the reaction 

 still takes place. 



