iv] REACTIONS OF ANTHOCYANINS 49 



of substances known as flavones which are almost universally distri- 

 buted in plants. The flavone pigments in bulk are yellow, but exist 

 in the cell-sap in such small quantities as to be inconspicuous except 

 when treated with alkali, when an intense yellow colour is developed; 

 with ferric chloride solution they give a green or brown coloration. 

 They, moreover, occur in the plant largely as glucosides, in which form 

 they are readily soluble in alcohol and water, and hence they are present 

 in all crude aqueous and alcoholic extracts of anthocyanin. Extracts 

 of white flowers, or in fact of any non-anthocvanic parts, give as a 

 rule yellow or orange-yellow precipitates with lead acetate, which are 

 insoluble flavone salts of lead. 



That there is some substance in white flowers which turns yellow 

 with ammonia was noticed by Boyle (107): "we thought fit to make 

 Trial upon the Flowers of Jasmin, they being both White as to Colour, 

 and esteem'd to be of a more Oyly nature than other Flowers. Where- 

 upon having taken the White parts only of the Flowers, and rubb'd 

 them somewhat hard with my Finger upon a piece of clean Paper,... 

 a strong Alcalizate Solution, did immediately turn the almost Colour- 

 less Paper moisten'd by the Juice of the Jasmin, ...a, Deep, though 

 somewhat Greenish Yellow,... when we try'd the Experiment with the 

 Leaves of those purely White Flowers that appear about the end of 

 Winter, and are commonly call'd Snow drops, the event, was not much 

 unlike that, which, we have been newly mentioning." Later in the 

 Comptes Rendus of 1854 and 1860, Filhol (125, 132) published papers 

 of considerable interest in connection with this point. Filhol found 

 that when white flowers of Viburnum Opulus, Philadelphus coronarius 

 and other plants were exposed to ammonia, they turned yellow ; as 

 yellow, he says, as the flowers of Laburnum. The same results he 

 observed in leaves in the parts free from chlorophyll. When the 

 flowers, after treatment with alkali, were placed in acidified water, 

 they became white again. The substance which gives the yellow 

 colour was found to be soluble in water and alcohol and slightly so in 

 ether, and Filhol terms it xanthogene.' When coloured, red or purple, 

 flowers were treated with ammonia, they turned green as a rule, but 

 in some cases blue (Papaver, Pelargonium, Salvia splendens}. In one 

 particular experiment when he added aluminium hydroxide to an 

 extract of Vervain flowers, the aluminium hydroxide became yellow 

 but the supernatant liquid retained the purple colour. Thus he comes 

 to the conclusion that the green coloration with alkalies in Viburnum 

 and other flowers is due to a mixture of a blue colour given by 



w. P. 1 



