154 On the Formation of Anthocyanin 



These results show that there is some connection between pro- 

 duction of pigment and the capacity for forming starch from the sugar 

 provided. As a rule, the leaves which turn red are those which form 

 least starch from the sugar solution and several, in fact, form very 

 little or no starch even under normal conditions. 



Hence experiments on sugar-feeding further strengthen the view 

 that reddening is due to an increase in the concentration of sugar 

 which ultimately leads to an increase in concentration of glucosides ; 

 the latter, being formed from sugar, naturally accumulate in excess 

 since there can be no translocation from the severed leaf 



Palladin(14) also maintains that the amount of aromatic chromogen 

 is increased by sugar-feeding. In his experiments equal portions of 

 leaves of Rumex imierttia were placed in water and 20"/„ cane-sugar 

 respectively. After four days the pieces in cane-sugar had developed 

 anthocyanin, those in water none. The sugar-fed and the control portions 

 were then heated with water and equal amounts of the extracts treated 

 with horse-radish peroxidase and hydrogen peroxide. The extract from 

 the sugar-fed portions produced considerably more pigment than that 

 from the control portions. This view is quite in accordance witii my 

 suggestion that sugar-feeding leads to increase of free aromatic chro- 

 mogen. 



With Vicia Faba leaves in sugar-cultures Palladin obtained a 

 different result. In this case the extracts gave less not more pigment 

 with peroxidase and hydrogen peroxide, whereas cultivation in water 

 only increased the amount of free chromogen. As an explanation 

 Palladin suggests that the free chromogen combines with sugar to form 

 a glucoside— prochromogen — and as siich cannot be oxidised by the 

 oxidase. 



I should suppose the explanation to be as follows : — The chromogen 

 in Vicia Faba is of a different nature from that in most plants in that 

 it is oxidised by tyrosinase, and we may therefore suppose it to be a 

 tyrosin-like compound and not capable of being syuthesised from sugar 

 alone. The increased concentration of sugar would only form a gluco- 

 side from the existing chromogen and thereby decrease the amount of 

 free chromogen and would not increase the total amount of glucoside. 

 Cultivation in water would tend if anything to decrease the amount of 

 sugar and hence the amount of free chromogen would increase. It may 

 be also added that sugar-culture does not produce colour in Vicia 

 Faba leaves. 



The question as to whether sugar-feeding does or does not directly 



