vn] THE FORMATION OF ANTHOCYANINS 113 



3. Artificial pigments identical with natural products can be 

 prepared from flavones. From the flavone glucosides (except in the 

 case of quercitrin, a glucoside of quercetin) anthocyanins are formed, 

 and from the flavones themselves, anthocyanidins. 



4. When anthocyanins are prepared artificially from flavone gluco- 

 sides, no anthocyanidin stage is passed through. This may be shown 

 by conducting the experiment under amyl alcohol, in which the antho- 

 cyanidins are soluble, should they be formed. 



5. When flavone glucosides are hydrolysed, and the flavone 

 converted artificially into anthocyanidins without removal of sugars, 

 the latter do not again combine with anthocyanidins to form antho- 

 cyanins. 



On the basis of the above statements Everest maintains that the 

 glucoside hypothesis is untenable. For (1) precludes the possibility of 

 the reacting substances being, as a rule, in the glucosidal state throughout 

 the reaction ; (2) makes it essential for the final product to be a gluco- 

 side, whereas (5) appears to make it impossible for such a recombination, 

 i.e. between anthocyanidin and sugar, to take place. Finally (3) and 



(4) render hydrolysis unnecessary. 



Let us now consider these points. As regards (1), it is by no means 

 proved that flavones in the living plant have at most two hydroxyls 

 replaced by sugar. It is quite conceivable that in the living cell more 

 hydroxyls are replaced, and that only stable glucosides containing one 

 or two molecules of sugar have been isolated, and this by virtue of their 

 stability. No definite investigations have been made as to how many 

 hydroxyls are replaced in the flavone in the plant, and in absence of 

 further evidence, no conclusive statements can be made. With (2) 

 the author is in agreement (Wheldale, 244). Again, it is not yet deter- 

 mined whether the artificial products mentioned in (3) and (4) are 

 anthocyanins, and the matter is discussed later in the chapter. But, 

 for the moment, grant them to be so. Then, with regard to statement 

 (3), that it is not essential for hydrolysis to precede the formation of 

 anthocyanin, it may be pointed out that nothing is known of the reactions 

 giving rise to the artificial pigment ; nor is there any reason for supposing 

 the artificial and natural reactions to be the same. As regards (4), 

 the glucoside hypothesis is still in agreement with a mode of formation 

 which does not involve complete hydrolysis at any moment. Criticism 



(5) is of no value since it is well known that glucosides are not synthesised 

 in vitro in the absence of an enzyme. Moreover, in the presence of 

 an enzyme, synthesis only takes place to a small extent under special 



w. p. 8 



