16 INTRODUCTORY [OH. i 



Willstatter did not in any case extract the flavone accompanying the 

 anthocyanin he isolated. The second line of evidence, i.e. the formation 

 of a very small quantity of a purple pigment, as a by-product, during 

 the reduction of a large quantity of quercetin, might quite well involve 

 reactions other than reduction. 



Willstatter's views 1 provide a very different interpretation of Men- 

 delian factors for coloration from that of Keeble & Armstrong and the 

 author. For we must suppose, should Willstatter be correct, that the 

 factors for colour are the chromogen (flavone) and the power to reduce 

 the chromogen with a complete change of structure from the pyrone 

 grouping of the flavone to the quinonoid structure of anthocyanin. 

 A purple flower would contain the pigment in its neutral form; a 

 reddening factor would be the power to produce acid cell-sap ; con- 

 versely, a blue variety must have alkaline sap. Thus we have a reversion 

 to the ideas of the earliest writers, and it is less easy to correlate such 

 a view with the results of cross-breeding. But there is no doubt that 

 Willstatter's researches, whether his interpretation prove to be the 

 right one or not, have brought the whole problem of soluble pigments 

 within measurable distance of explanation. Such a solution, moreover, 

 will provide what is perhaps of greater importance, namely, a chemical 

 basis for one series, at any rate, of Mendelian phenomena. 



1 See also Appendix. 



