118 Chemt'Mri/ of McnfleUan Factors for Flower-Colonr 



If there is excess of acid in the cell-sap an oxonimn salt with an 

 organic plant acid is formed: 



0-X 



FiR. 3. 



and crystalline salts, which the pigment readily forms with hydrochloi-ic 

 acid, are regarded as artificial compounds of a similar kin<l : 



O-CI 



HO 



Fig. 4. 



In the presence of excess of water, both the red and the blue forms 

 will also pass to the colourless isomer, but when a neutral salt, such as 

 sodium nitrate or chloride, is present the isomeric change is prevented 

 by the formation of additive compounds: 



O-NO3 



NaO 



Fig. 5. 



For preparing the pigment, the methods are long and elaborate, but 

 consist mainly in extracting the pigment from dried flowers by means 

 of water, sodium nitrate being added to jDrotect the pigment, and finally 

 precipitating the pigment with alcohol. 



The blue pigment — cyanin — is a glucoside. On hydrolysis it is 

 decomposed into glucose and a pigment, cyanidine. Both cyanin and 

 cyanidine readily form crystalline compounds with hydrochloric acid. 

 Analyses of cyanidine chloride gave as simplest formula Q,^Ji.ySd.. HCI 

 but no account is given of any determination of the molecular weight. 



The hypothesis advanced by Willstatter as regards the constitution 

 of anthocyanin is not at present based on any experimental evidence 

 beyond the existence of the salts with acids. The chief argument 



