The Formation of the Anthocyan Pigments of Plants. 117 



or flaking of flowers is due, in some cases, to local inhibition of oxydase, and 

 in others to a local defect of chromogen. 



That the pale yellow or cream xanthein sap pigment of the wallflower is 

 in some way related with the red and purple anthocyans is rendered probable 

 from a study of the curious behaviour of a hybrid wallflower Gheiranthus 

 kewensis, the issue of a cross between Cheiranthus cheiri and C. mutdbjlis. 

 When the flowers of C. kewensis open they are of a pale yellow or cream 

 colour, and of that colour they remain for a long time. Gradually, however, 

 a faint reddish hue steals over them, deepens, and finally replaces the 

 original colour. Experiments now to be described make it probable that 

 what is witnessed here is a gradual formation of red anthocyan at the expense 

 of the cream-yellow xanthein pigment. 



If petals of the " primrose " race of the common wallflower, G. cheiri. or the 

 soluble yellow extract therefrom be heated in aqueous alcoholic solution 

 with a little concentrated hydrochloric acid and zinc dust a red pigment is 

 formed. In the first phase of the reaction the xanthein glucoside is hydro- 

 lysed to a reducing sugar and to a yellow compound which is insoluble in 

 water. For example, a solution of the pigment was divided into two parts, 

 and the reducing power of the solutions was determined by the Bertrand 

 method, in the one before and in the other after hydrolysis. The results 

 were : — 



Before hydrolysis = sugar equivalent to 6'5 c.c. of permanganate. 

 After „ „ „ 13'5 „ „ 



The glucoside is also hydrolysed slowly by the emulsin of almonds. After 

 the yellow insoluble compound produced during hydrolysis has been dissolved 

 in 50-per-cent. alcohol and reduced by zinc dust and an acid it undergoes 

 reoxidation to an intense red pigment. The red pigment passes through 

 green to yellow on the cautious addition of alkali. It is reduced to a 

 colourless state by zinc dust and acetic acid or by zinc dust and ammonium 

 chloride, the colour recovering on oxidation. 



The solution of hydrolysed pigment separated by filtration from the yellow 

 product gives no red colour when reduced. Thus we have chemical evidence 

 that the yellow glucoside of the wallflower undergoes hydrolysis, and that 

 its product is converted by reduction and oxidation into a red pigment. 

 Since reduction and oxidation may take place in any plant cell we may 

 infer that the pale yellow wallflower owes its lack of red or purple anthocyan 

 to the absence of the agent for glucoside hydrolysis, and it may be predicted 

 that the pale colour of the primrose (yellow-cream) race of wallflower is 

 recessive to the anthocyan colour of red or purple races. 



