CH. iv] PROPERTIES AND REACTIONS OF ANTHOCYANINS 45 



Later, N. J. C. Miiller (169), on the basis of spectroscopic examina- 

 tion, announced that the red and blue pigments were of various kinds, 

 but it is doubtful whether his materials were pure. Wiesner (135) also 

 appeared to be uncertain as to whether all anthocyanins are alike, 

 whereas Weigert (179) definitely distinguishes two groups of anthocyanin 

 of which more will be said later. From this time onward, as investi- 

 gations increased, there seemed to be little doubt that a number of 

 substances are responsible for the different colours. Overton (333) 

 held this point of view, and we may quote the words of Molisch (104) 

 to the same effect: "dass der Begriff Anthokyan, wie er bisher in der 

 Literatur gefasst wurde, kein einheitliches chemisches Individuum 

 darstellt, sondern eine Gruppe von mehreren verschiedenen, wahr- 

 scheinlich verwandten Verbindungen." The more recent suggestion 

 of Grafe (209) comes nearer the truth, for he says we must regard 

 anthocyanin as a term to be used for a whole series of pigments, which 

 may have a similar fundamental nucleus, but which differ in the com- 

 plexes attached to the nucleus. Colour and other chemical reactions 

 would then depend on a particular grouping common to all or most of 

 the pigments. This view has been supported by the recent researches 

 of Willstatter (245, 256, 257) ; he has isolated anthocyanin from the 

 flowers or fruits of ten (or more) plants, and has shown that, in all 

 probability, they have the same fundamental structure. Some of the 

 number, though derived from plants quite unrelated, appear to be 

 identical; others differ in the number of their hydroxyl groups; others 

 again, he suggests, have their hydroxyls replaced by different radicals. 

 Thus we may now correctly consider the word anthocyanin to stand, 

 as a collective term, for a class of substances comparable to the sugars, 

 tannins, fats, proteins, etc. 



Hence, in giving an account of the reactions of anthocyanin, one is 

 always dealing with a large group of substances of which the properties 

 may differ considerably. Therefore to make any general statement 

 in some cases is difficult, and there is always the further consideration 

 that the substances examined have rarely been obtained pure. 



The appearance of anthocyanin as crystals in the living tissues 

 has been discussed in Chapter in. Outside the cell anthocyanin has 

 also been obtained in undoubted crystalline form. Molisch (104) 

 prepared crystals very readily from the petals of the scarlet Geranium, 

 Pelargonium zonale, by placing a petal in distilled water under a cover- 

 slip on a slide. The pigment diffuses out, and on slow evaporation 

 deposits groups of beautiful needle-shaped crystals. By a similar 







