274 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



contains two hydroxyl, three carboxyl, and two aldehyde 

 groups. It may be dialyzed, and gives no reducing sugar 

 when hydrolyzed. An amorphous deep brown pigment was 

 also obtained from the same flowers. This may be repre- 

 sented by the formula C 24 H 44 20 , is non-dialyzable, and 

 gives glucose when hydrolyzed. The analyses of the pro- 

 ducts obtained by Willstatter and by Grafe from Pelar- 

 gonium are not in good agreement. Possibly they were 

 dealing with different substances. In any case, the com- 

 plete removal of water of crystallization constitutes a 

 difficulty. Grafe ascertained that a colourless addition 

 product of anthocyanin may be isolated by means of 

 sodium hydrogen sulphite, whilst Tswett (1913, 1914) found 

 phenylhydrazine and hydrogen cyanide to behave similarly. 

 This shows that the free carbonyl group forms part of the 

 chromophoric complex, or possibly the compounds may 

 resemble the colourless isomer in structure. The addition 

 of a mineral acid decomposes the addition product; con- 

 sequently the red colour of the anthocyanin in acid solution 

 again appears. 



Tswett, too, has prepared pure anthocyanin from red 

 cabbage, and found that it was decolorized by the addition 

 of methyl alcohol or of acetone, as well as by ethyl alcohol. 

 This, he very justly points out, cannot be a reducing action, 

 but is rather one of isomerization, as suggested by Will- 

 statter, or due to the formation of compounds between 

 the alcohols and anthocyanin analogous to the formation 

 of acetal with acetaldehyde. 



Another research of this class is that undertaken by 

 Bartlett (1913) upon the chromogen isolated from the 

 aerial tubers of the Hawaiian bitter yam, a species of Dios- 

 corea. This was considered by its investigator to have 

 possible chemical and physiological relationships with the 

 ammonia-greening anthocyanin of that plant, as it forms 



