Wakeman—Pigments of Flowering Plants. 
783 
material has been collected and studied for the purpose of mak¬ 
ing comparisons and verifying conclusions. 
PLANT PIGMENTS. 
Pigments referable to hydrocarbons of the formula of 
Saturation C n H 2n -- 4 . 
All of the known plant pigments of this degree of saturation 
are quinones or more particularly their quinhydrone or pheno- 
quinone addition products, and metallic derivatives of the lat¬ 
ter, and are referable to dihydro benzene, dihydro toluene and 
dihydro cymene. 
Pigments referable to dihydrobenzene. 
H 
C 
CH 
H 2 C Iv y^CH 
0=C \/ CH 
CH 
Dihydro benzene 
only plant pigment 
H 
Benzo quinone 
referable to dihydro benzene, of 
whose existence in plants we have any evidence, is the ordinary 
quinone, or benzoquinone. However, its occurrence is purely 
hypothetical. Though benzoquinone has never yet been iso¬ 
lated from a plant, its dihydro derivative, hydroquinone, is 
known to occur in several species and under such conditions as 
would suggest the formation of quinone and quinhydrone as a 
possible explanation of the pigmentation which exists there. 
For example, the glucosides arbutin and methyl arbutin occur in 
the leaves of Gaultheria procumbens, Uva ursi, and several other 
species of the Ericaceae. Arbutin upon hydrolysis yields hydro¬ 
quinone. Hydroquinone by the action of oxidases, known to occur 
in Gaultheria and, no doubt, present in the other arbutin contain¬ 
ing plants, is readily converted into quinone with the forma¬ 
tion of quinhydrone as an intermediate product. The pres¬ 
ence of benzoquinhydrone, which is brownish-red in color, would 
afford an explanation of the reddish tint commonly acquired 
by the leaves and stems of these plants in the fall. It might 
also account for the remarkable colorations of the Madrones 
and Manzanitas so well known upon the Pacific coast, since both 
are species of Arbutus and closely related to the above named 
plants. Arbutin has been isolated from the leaves of at least 
one of the manzanitas, Arctostaphlos glauca. 
