CHAPTER VII 



REACTIONS INVOLVED IN THE FORMATION OF ANTHOCYANINS 



Nehemiah Grew (1) evolved, as a result of his observations, an 

 elaborate scheme to explain the origin of the various pigments in plants. 

 It is expressed in the scientific language of the period and is difficult to 

 translate into modern conceptions, but it is clear that he believed the 

 presence of air to play an important part in the process. Speaking 

 of colours in roots, he says these organs show less variety in this respect 

 than leaves and flowers 'The Cause hereof being, for that they are 

 kept, by the Earth, from a free & open Aer; which concurreth with 

 the Juyces of the several Parts, to the Production of their several 

 Colours. And therefore the upper parts of Roots, when they happen 

 to stand naked above the Ground, are often deyed with several Colours." 



A publication by Schiibler & Franck (117) in 1825 perhaps contains 

 the first definite hypothesis as to the origin of red and blue pigments. 

 These investigators treated extracts from coloured flowers and leaves 

 with acids and alkalies, and the results led them to the view that green 

 pigment of leaves occupies a mean position, from which an oxidised 

 yellow-red series is formed, on the one hand, by the action of acids, 

 and a deoxidised blue-violet series, on the other hand, by the action 

 of alkalies. The hypothesis was further reinforced in 1828 by Macaire- 

 Princep (3), who maintained that chlorophyll, when treated with acids, 

 becomes oxidised first to yellow, then to red and orange pigments, and 

 this oxidised chlorophyll can be turned green again by alkalies. The 

 red plant pigments are, in his opinion, oxidised chlorophyll, and the 

 blue, a mixture of red chlorophyll with a vegetable alkali. All colours 

 may thus be looked upon as simple modifications of chlorophyll. 



These erroneous ideas were accepted, without any real experimental 

 basis, by plant physiologists of the day as Von Mohl (7, 8) very clearly 

 points out in 1838. "Les physiologistes s'occupaient plutot generale- 

 ment de faire des speculations sur les couleurs des plantes, de les 



