252 



Dr. A. E. Everest. 



Both Willstatter and the author have noticed that when flavonols are 

 reduced as described by them, with formation of anthoeyans, a considerable 

 proportion of the yellow compound remains unacted upon — as the result of 

 quantitative estimation Willstatter found, in one case, only 4 per cent, of 

 anthocyan present after reduction — but this is, to some extent at least, due 

 to the difficulty in regulating the reduction of the pigment, and it is quite 

 conceivable that in Nature conditions may be more favourable to anthocyan 

 formation than in the experiments thus far described. 



It would appear desirable that evidence should be collected upon which 

 conclusions might be drawn as to whether the anthocyan pigments are 

 produced in plants vid flavonols, or, as the result of direct synthesis, inde- 

 pendent of the presence of flavonols. 



If they are produced vid flavonols, then, unless the conditions present in 

 Nature allow the reaction causing the conversion of the flavonol into 

 anthocyan to proceed to completion, and the reaction proceeds more rapidly 

 than that whereby the flavonol is synthesised, and, further, that there is no 

 reconversion from anthocyan to flavonol as the result of re-oxidation, it is 

 to be anticipated that flowers, fruit, etc., containing an anthocyan pigment 

 will also contain some quantity, great or small, of a flavonol, and indeed of 

 the particular flavonol that corresponds to the anthocyan present. Thus, 

 where the anthocyan pigment is one of the cyanidin glucosides, a corre- 

 sponding quercetin glucoside would be expected, whereas if the anthocyan 

 were a glucoside of pelargonidin, then a corresponding glucoside of kaempferol 

 should be found, and so forth. It is, indeed, possible that if these pigments 

 are produced vid flavonols, there is a more or less regular relationship 

 existing between the amount of flavonol and of the corresponding anthocyan 

 present in a normal full-grown flower of any particular species when grown 

 under normal conditions. 



There remains a further possibility which should not be overlooked, viz.^ 

 that where two flavonols are present under conditions which give rise to 

 production of anthocyans from flavonols, one of the yellow pigments may be 

 preferentially reduced, passing completely to an anthocyan before the second 

 is attacked. This seems, at first sight, rather unlikely, but if such were the 

 case, the result would be that not a flavonol corresponding to the anthocyan 

 would be found, but one differing from it ; thus the investigations proposed 

 by the author would produce useful evidence in this case also, and, if 

 necessary, could probably be verified by independent methods. 



With respect to the presence of yellow sap-pigments, flavones or flavonols, 

 in flowers containing anthocyans, there is considerable evidence of their 

 GO-existence already available, and many of the early workers noted that the 



