Miss Wheldale, On the nature of anthocyanin. 143 



resembles that of an acid-alkali indicator. With heavy metals, 

 such as copper and lead, insoluble coloured salts are formed. 



There appears to be evidence, as will be discussed later, that 

 the production of pigment in anthocyanic species is brought about 

 through the agency of an oxydase so that anthocyanin may be 

 regarded as a coloured oxidised product of an aromatic chromogen 

 and moreover, like the unaltered chromogen, as an acid capable 

 of producing salts. In the acid state the molecule of anthocyanin 

 is red but the addition of alkali produces a blue salt. 



We may suppose that there is usually unaltered chromogen 

 present in the plant in addition to anthocyanin, and the simul- 

 taneous existence of these two bodies would account for the green 

 colour given by alkalis and the green precipitate by basic lead 

 acetate, i.e. a mixture due to the blue salt of the oxidised product 

 and the yellow salt of the chromogen. The stronger — more 

 oxidised — acid would probably react first with bases; hence the 

 blue colouration with a slight amount of alkali. 



On this supposition, the green precipitates prepared and 

 analysed by Heise^^ and Gautier" represents a mixture of the 

 salts of both anthocyanic acid and its chromogen. 



An alternative explanation is that offered by Overton^", who 

 regards anthocyanin as a di- or poly-basic acid, the blue colour 

 given by a small amount of alkali being due to the acid salt, the 

 green colour with excess of alkali to the neutral salt. 



Grafe^^ too, is of the opinion that one of the pigments 

 isolated by him from Althaea rosea is a di-basic acid; he regards 

 the green colour with alkalis as a specific reaction of anthocyanin 

 and not one due to admixture with any other substances giving 

 a yellow reaction. 



Evidence for the assumption that the aromatic chromogen 

 forms a component of anthocyanin has been arrived at through 

 experiments in cross-breeding*. It appears, from this source, 

 that the components of anthocyanin can be represented by various 

 Mendelian factors, the loss of which gives rise to derivative 

 varieties. In Antirrhinum majus, an ivory-white variety exists, 

 which is free from anthocyanin, but contains a chromogen such 

 as those described above. The magenta type contains anthocyanin. 

 It has been proved experimentally that the factor representing 

 the chromogen is essential to the constitution of the magenta 

 type. 



Cross-breeding with Antirrhinum shows moreover that the 

 so-called xantheic pigment of the yellow variety is essential to 

 the constitution of the ivory-white and is hypostatic to it. In 

 fact xanthein appears to be a yellow aromatic chromogen in a 



* Wheldale 19. 



