106 REACTIONS INVOLVED IN [CH. 



in cells which have become reddened with anthocyanin. In the course 

 of time, as investigations proceeded, it became clear that anthocyanin 

 is not derived from chlorophyll; Macaire-Princep and Marquart had 

 been led astray in their views by the close connection between the 

 disappearance of chlorophyll, and the appearance of anthocyanin, 

 and vice versa. Yet, in the light of the additional knowledge which 

 we now possess, it can still be stated with truth that there is a certain 

 relationship, though an indirect one, between the two pigments, or, 

 more strictly perhaps, between the spheres of their chemical activity. 

 The hypothesis of Wigand (136) in 1862 came very near to those 

 held at the present time. Wigand maintained that anthocyanin arises 

 by oxidation from a colourless substance which occurs in solution in 

 the cell, and which changes to red under certain circumstances, and 

 may, after a time, become colourless again. He considers it to be a 

 tannin on the grounds that: 



1. The red colouring of spring and autumn appears only in tannin- 

 containing plants, and though it is not always found in these, yet it 

 never develops in plants free from tannin. 



2. Only in those tissues or cells (especially the epidermal cells and 

 veins) in which the tannin was previously present does the colouring 

 matter develop later. 



3. The red sap, like the tannin, is turned green or blue with iron 

 salts, and yellow with potash or ammonia. 



The tannins of Wigand were very probably, in many cases, flavones, 

 from which it is now believed that the anthocyanins may arise. 



From analyses of pigments of wine and grapes, Gautier (149, 175), in 

 1893, also formed the opinion that anthocyanin is an oxidised product 

 of tannic acids, but no suggestions are made as to the particular reactions 

 involved. At a later date, in 1897, Overton (333) concluded, on the 

 basis of many observations and experiments, that red pigment is formed 

 when there is an accumulation of sugars, but beyond stating that antho- 

 cyanin is probably a tannin -like substance existing, in combination 

 with sugar, as a glucoside, Overton makes no definite statement as to 

 the mode of formation. Mirande (365) in 1907 suggested that the 

 appearance of anthocyanin when leaves are injured by insects is due 

 to an accumulation in the tissues of tannins and glucose, accompanied 

 by the presence of an oxidase. Laborde (199, 200, 201) in 1908 also 

 came to the conclusion that there is a relationship between tannins 

 and anthocyanins. To quote Combes: "1'auteur (i.e. Laborde) 

 assimile le phenomene du rougissement a une action diastasique qui 



