M. Whbldalb 



117 



substance might produce red anthocyanin and a further condensation 

 with a second substance magenta anthocyanin, and the power to form 

 these substances would be represented by the red and blue factors. 



Hjrpotheses in this connection are, however, of little value until we 

 have more knowledge of the constitution of the pigments themselves. 

 Nothing, moreover, can be said at present of the nature of the factors 

 causing the deepening or dilution of anthocyanin characteristic of deep 

 and pale varieties. 



At this point some account must be given of the work of Will- 

 statter (36), on the anthocyanin of the Coi-nflower (Centaurea). The 

 author states that in the flower three pigments are present, a red, 

 a violet, and a blue. Willstatter is of the opinion that the anthocyanin 

 of Centaurea contains a nucleus of the type of Fig. 1, colour being due 

 to the presence of the quinonoid structure : 



OH 



Fig- 1. 



The above would represent the nucleus of the violet pigment, which 

 is also in itself an acid. Under certain conditions a change readily takes 

 place to a colourless isomer, the oxonium oxygen becoming divalent : 



Fig. 2. 



The isomer is really a flavone with an extra and unusual hydroxyl 

 group in position 2. 



The blue pigment in the flower, according to Willstatter, is the 

 potassium salt of the compound in Fig. 1, the position of the potassium 

 being uncertain. If the cell-sap is alkaline, the blue salt predominates 

 or is alone present. 



