462 THE AMERICAN NATURALIST. [Vol. XXXV II. 



The red pigment is probably a glucoside, or a very closely 

 related compound, of which the constituents are a sugar and a 

 tannic acid. Since in many plants, the provision of the cells 

 with sugar increases the tendency to form red cell sap, there 

 can be little doubt that a sugar forms part of the raw material 

 out of which the pigment is built up. Tannins are also con- 

 tained in the cells in which the red color has been formed by the 

 artificial increase of sugar. The red color stuff is thrown down 

 by the tannin reagents coffein and antipyrin, and the precipitate 

 closely resembles those of the tannins. The behavior of the red 

 pigment indicates that it is a tannin compound. The supposition 

 that tannin is connected with the formation of the red and blue 

 pigments of flowers is not new, but was first suggested by Wig- 

 and in 1862. It was observed that red color was formed only in 

 cells that contained tannin. "If we examine," says Overton, 

 "the reaction of the red color stuff upon different bases we 

 obtain support for the opinion, that this pigment represents a 

 weak bivalent or multivalent acid. For we find that its tinge is 

 almost unnoticeably changed by very weak bases as coffein, 

 antipyrin, etc., that with stronger bases, however, the color 



explanation of these phenomena is that the free acid is only 

 little dissociated electrolytically and that the red color is peculiar 

 to the molecules of the acid that has not been dissociated, the 

 blue color would belong to the univalent, and the green color to 

 the bivalent ions of the acid. On account of the weakness of 



