Anthocyanins and Anthocyanidins. 



151 



effects obtained by the presence of other plant colouring matters (flavonols, 

 carrotinoids, etc.) and of varying concentration of colour in the cell sap, is 

 capable of explaining all the lovely variations seen in plant life. 



Shibata, Shibata and Kasiwagi challenge the evidence of the existence of 

 the anthocyan pigments in the three forms suggested by Willstiitter and 

 Everest, and to replace the conclusions of Willstatter and Everest, and 

 Willstatter and Mallison, Shibata, Shibata and Kasiwagi put forward the 

 following as an explanation of the various flower colours : — 



(1) " The metal organic or complex compounds of reduced flavonal 



glucosides 



(Sugar) 



MeX 



I 



o 



I OH 

 O 

 H 



[MeXj] „ are the most important factor 



in the production of flower colours." 



(2) " The ' blue ' anthocyanins are the complex compounds of reduced 

 flavonol glucosides, which possess several hydroxyl groups belonging to the 

 flavonol nucleus besides those of sugar molecules, and the metal with which 

 they are coordinated is probably calcium or magnesium, for the salts of these 

 metals are always present in the plant cells." 



(3) " The ' violet,' ' violescent red ' or ' red,' pigments are either the 

 analogous metallic complex compounds of flavonol glucosides, which contain 

 fewer of the auxochromic hydroxyl groups, or a mixture of the blue pigments 

 and their decomposition products by excess of acids, i.e., the red oxonium 

 salts of E. Willstatter." 



They then add, " Our conception of the colour variation of the anthocyans 

 is, we believe, free from the objections raised in the preceding pages, and 

 moreover, the blue pigments are accessible, while the phenolates and inner 

 salts are wanting an experimental support." 



Before passing to observations concerning these new suggestions, it is 

 advantageous to consider carefully the experimental evidence that is available 

 in support of them, as compared with that upon which the earlier conclusions 

 of Willstatter and Everest were founded and developed. 



Willstatter and Everest's conclusions are supported by considerably more 

 experimental evidence than that referred to by Shibata, Shibata and Kasiwagi, 

 and it would appear that these authors have overlooked some of the later 

 work of Willstatter and his collaborators. 



Willstatter and Everest {loc. cit.) produced evidence that proved the forma- 

 tion of oxonium salts in red anthocyanins, and made it highly probable that 



