214 ANTHOCYANINS AND GENETICS 



or purple, as the case may be, is determined by the nature of the accom- 

 panying substances in the cell-sap. This idea is further corroborated 

 by the fact that anthocyanin outside the cell is modified in colour 

 by acids, alkalies and inorganic and organic salts of various kinds. 

 When we see in one and the same flower a number of shades of red 

 and purple, or red and blue, it is difficult to avoid accepting this explana- 

 tion, especially as we know that various products of metabolism, such 

 as organic acids, are produced locally. 



This point of view has been recently advocated by Willstatter. 

 As a result of his researches on the anthocyanin of the Cornflower, he 

 maintains that the blue flower pigment is the potassium salt of a neutral 

 purple pigment (itself an acid), and the red pigment is an acid salt of 

 the purple, with some organic acid. If all three pigments are present 

 in one flower, we must suppose that the blue cells have alkaline contents, 

 the purple, neutral, and the red, acid. That the pigment of a plant 

 may be modified in colour in different regions of the plant according, 

 to the chief organic and inorganic substances present in the cells, seems 

 reasonable, but the difficulty lies in finding some explanation for the 

 existence of red and blue varieties. Thus, for instance, Willstatter 

 maintains that the pigments of the blue Cornflower, the magenta 

 Rosa galliea and the red fruits of the Cranberry are one and the same 

 substance. If so, its colour must be modified by other substances in 

 the cell-sap. But in the Cornflower there is the blue type, having blue 

 outer and purple inner florets; there is a variety in which the outer 

 florets are bright pink ; another in which they are purple-red. According 

 to Willstatter, in the ray floret cells of the type, the cell-sap is alkaline ; 

 in the pink variety, acid, and in the purple, neutral. How can this be 

 expressed in Mendelian terms? We must imagine that the blue type 

 loses some factors which either inhibit acidity, or produce alkalinity. 

 These are the blueing factors ; let them be B x , B 2 , etc. Loss of these 

 will give rise to the purplish-red and pink varieties. Without further 

 evidence, such as would be derived from analysis of the pigments 

 extracted from the purple and pink varieties (which has not so far been 

 accomplished), it is difficult to arrive at any satisfactory explanation. 

 But even if the above hypothesis fits the case of Centaurea, it can 

 scarcely be adapted to the case of Antirrhinum. In this genus, there 

 are two forms of anthocyanin, a red and a bluish-red, or magenta. 

 There is certainly no evidence at present for regarding the magenta 

 as the potassium, or alkaline salt, of the red, nor for considering the 

 red to be the acid salt of the magenta. 



