The Red and Blue Colouring Matters of Flowers. 



By P. Q. Keegan, LL.D. 



In my previous paper (see Natural Science, 1898, xii. pp. 194-199) it 

 was maintained that the tannic ehromogen of the blue colouring matter 

 of flowers is not the same as that of the red pigment. The old in- 

 vestigators of this attractive subject were not all of one mind in the 

 matter. The great majority unequivocally held that the blue was 

 the original colour, and that the red was merely a derivative thereof, 

 i.e. merely an unessential modification, or a product of further deoxida- 

 tion or dehydration. The French chemist Filhol was for a time evi- 

 dently in a state of considerable doubt and hesitancy. In his last 

 contribution on the subject, dated 25th June 1860, he states that in 

 examining the colouring matter of red, rose, or blue flowers he had 

 been struck with the differences which it presents according as it is 

 taken from such or such a flower ; he noticed that a great number of 

 flowers become blue in contact with alkalis, while others become green, 

 and, moreover, that the pigment of the former enjoys a greater stability 

 than that of the others. " At first," he says, " he thought he could 

 conclude that in deep red flowers there exist two distinct colouring 

 matters, one more stable than the other, but he soon saw that it was 

 not so when he operated on solutions of pure cyanine ; there are not 

 two kinds of cyanine." It is all the more remarkable, therefore, that 

 the illustrious Berzelius, who had chemically examined the red pig- 

 ments of cherry and gooseberry fruits and leaves, should conclude that 

 their colouring matter is not, as had been thought, a combination of a 

 blue pigment with an acid. " What had given occasion for this error," 

 he says," " is that by treating the juice of the berries with acetate of 

 lead blue precipitates are obtained, but this blue colour is due to the 

 impurity of the juice in consequence of the presence of citric and malic 

 acids." It is hardly necessary to observe that for a very long time 

 it was well known to chemists that the blue colours of flowers were 

 reddened by acids, and even that the tint of flowers naturally red was 

 made more vivid and brilliant by the addition of a trace of acid. But 

 this fact, remarkable as it is in its way, seemed comparatively trifling 

 so long as the various and divers pigments of plants were regarded as 



143 



