Wakeman—Pigments of Flowering Plants. 
795 
colored or non colored, compounds is of much biochemical sig¬ 
nificance as will be pointed out in succeeding chapters. 
Pigments referable to hydrocarbons of the degree of sat¬ 
uration C n H 2n __ 6 . 
There exist in plants several compounds referable to hy- 
drocarbonss falling under this degree of saturation, being sub¬ 
stitution products of benzene, toluene and cymene, which though 
colorless in themselves are readily oxidized to pigments. More¬ 
over, being hydroquinones, they are capable of forming highly 
colored phenoquinones and quinhydrones by addition with their 
oxidation products the quinones. These compounds occur in 
a large number of plants either in the free state, as alkyl ethers, 
or in sugar ether combination as glucosides and they may be 
looked upon as pigment forming substances, commonly desig¬ 
nated chromogens in pigment literature. 
While no attempt is being made here at a discussion of the 
pigments of non-flowering plants it is interesting to note that 
there exist in several species of lichens pigments and pigment 
forming substances referrable to the hydrocarbons toluene, 
o-xylene, p-xylene and trimethyl 1, 2, 4 benzene. 
Benzene Hydroquinone 
The only known pigment, or pigment forming substance, 
referable to benzene as the underlying hydrocarbon is the or¬ 
dinary hydroquinone, or hydrobenzoquinone. The occurrence 
of hydroquinone as the glucoside arbutin in several species of 
Ericaceae and the possibility of its forming the corresponding 
quinone and quinhydrone through oxidation thus furnishing 
an explanation for the pigmentation of several species has been 
referred to under benzoquinone. 
Arbutin occurs in Ledum palustre 1 ) ; Rhododendron maxi - 
1 Am. Jr. Ph., 46, p. 314. 
