Wakemaw—Pigments of Flowering Plants. 793 
lower surfaces of the leaves, and often of the entire shoots of 
Monarda fistulosa, and the general reddish appearance of the 
young plants of Monarda punctata in spring can readily be 
accounted for by the greater oxidase content of the vigorous 
young tissue and the consequent greater chemical activity. 1 A 
similar phenomenon in the young plants or shoots after the fall 
rains may be explained in the same way. 
On the other hand, the fall coloration of arbutin containing 
foliage may be explained by assuming that as the synthetic 
life process of the plant grow sluggish, the reserve carbohy¬ 
drates stored away in the glucoside are rendered available as 
food material by hydrolysis. This latter process would set 
free the hydroquinone as well as the sugar. The former (chro¬ 
mogen) in turn would be oxidized to pigment. If this line of 
reasoning may be applied to the madrones as well as to the 
other species of arbutus, the brilliant coloration of both the 
enormous leaf buds in spring and of the leaves and the freshly 
peeled trunk in autumn may be accounted for. 
It has been pointed out above that the diethers of the hydro- 
thymoquinone, being deprived of their phenolic hydrogen are 
no longer prone to oxidation, hence to quinhydrone pigment 
formation. It is, therefore, not surprising that plants char¬ 
acterized by the presence of the dimethyl ether of hydrothy- 
moquinone are not conspicuously colored. The only pigmenta¬ 
tion of the Eupatorium species which could be attributed to 
quinhydrone formation is the occasional purplish coloration of 
the stems. 
This purplish stem coloration though not conspicuous de¬ 
serves special notice since most of the plants considered in this 
chapter are remarkable at some period of their development, 
generally late in the season, for conspicuously colored stems, 
the members of the Ericaceae, trailing arbutus, winter green, 
manzinitas, and mandrones for red or red brown stems, the 
characteristic color of benzo quinhydrone, while the stems of 
the Monardas are often conspicuously purple, the color of thy- 
moquinhydrone. 
Many investigators have inferred that ferments—hydrolases, 
oxidases, and reductases—play an important role in pigment 
1 The oxidase content of the Monardas has been studied both quantita¬ 
tively and qualitatively by F. Rabak, Ph. Rev., 22, p. 190; Swingle, Ph 
Rev., 22, p. 193; Wakeman, Ph. Rev., 26, p. 314. 
