Wakeman—Pigments of Flowering Plants. 
799 
along with thymoquinone in several species of Monarda, also in 
Thuja articulata. Its occurrence as dimethyl ether 28 ) in the 
oils of Eupatorium triplinerve and Eupatorium capillifolium , 
as well as in the oil from Arnica Montana has also been noted. 
Pigments referable to hydrocarbons of the formula of 
SATURATION C n H 2n - 8 . 
The only plant pigments of known constitution referable to 
hydrocarbons falling under this degree of saturation are sub¬ 
stitution products of phenyl ethene and phenyl propene, allyl 
benzene. 
Pigments referable to phenyl ethene. 
CH CH 
Phenyl ethene 
Indoxyl 
CH 
Indican 
Indican occurs in indigo bearing plants almost exclusively 
in the form of the glucoside indican,* a sugar ether of indoxyl, 
referable to phenyl ethene. Upon treatment of the herb, or the 
indigo producing part thereof, with water the glucoside is ex¬ 
tracted. This is hydrolized by an enzyme present in the plant. 
By contact with the air the indoxyl thus produced is oxidized 
to indigotin. 
28 See references to preceding chapter. 
29 Ann. Chem. f 170, p. 345. 
•For references to indican and indoxl see Indigotin, formula of satura¬ 
tion CnH2n-16. 
