Wakeman—Pigments of Flowering Plants. 
811 
Authorities differ somewhat as to what part or parts of the 
molecule the coloring properties are due. All seem to agree, 
however, that it depends largely upon the number of hydroxy 
groups. A study of the formulae reveals the fact that the 
property of color appears to depend upon the number of free 
hydroxy groups, or their oxide equivalent, rather than upon 
the number originally introduced into the molecule, the chang¬ 
ing of the hydroxy groups into methoxy groups appears to 
diminish both the color of the compound and its dyeing proper¬ 
ties. On the other hand the elimination of the elements of 
a molecule of water from two hydroxy groups to form the xan- 
thone grouping appears to intensify both pigmentation and dye¬ 
ing quality. 
Most writers, in treating of these pigments, distinguish be¬ 
tween diphenyl ketone and xanthone derivatives. However, 
since whether or not a compound falls into the xanthone group 
depends merely upon the position of hydroxy groups and the con¬ 
sequent elimination of the elements of a molecule of water and 
the formation of a heterocycle and not upon any more basal 
constitutional difference, there appears to be no sufficient point 
to this distinction. Therefore for the sake of simplicity as well 
as for observing genetic relationships, all of the members of 
this group, referable to diphenyl methane, will here be regarded 
as hydroxy derivatives of diphenyl methanone. 
II. A. 1. Pigments referable to diphenyl methane. 
a. Trihydroxides. 
Cotoin. 
b. Tetrahydroxides. 
Euxanthone. 
Euxanthonic acid. 
c. Penthydroxides. 
Maclurin. 
Kinoin. 
d. H exhydroxides. 
Gentiseine. 
Gentisin. 
Datiscetin. 
