794 Wisconsin Academy of Sciences, Arts, and Letters. 
formation. No where would this part seem more conspicuous 
than in the formation of quinhydrone and pheno-quinone pig¬ 
ments. Indeed one of the first questions which arises in the 
biochemical study of any such series of related compounds as 
the cymene, thymol, carvacrol, hydrothymoquinone, monohy¬ 
droxy thymoquinone and dihydroxy thymoquinone series in the 
Monarda species is which of these complex cyclic substances 
was first formed from the simple chain products of photo syn¬ 
thesis? Being accustomed for purposes of classification to 
look upon the hydrocarbons as basal compounds and to con¬ 
sider all other compounds as being derived from the hydro¬ 
carbons, it is easy to regard such a series as being formed in 
this order. However, it is highly improbable that the plant 
works in this way. An oxidase which oxidises hydrothymo¬ 
quinone to thymoquinone exists in several species of Monarda, 
but up to the present time no oxygen conveyer has been found 
which oxidizes thymol or carvacrol to hydrothymoquinone, all 
attempts in this direction having been attended with negative 
results, or in the case of thymol, sometimes, with the formation 
of dithymol. It is not at all improbable that the monatomic 
phenols and the hydrocarbons are reduction products, possibly 
by products of autoxidation. The large amounts, however, 
in which the monatomic phenols are found in comparison with 
the amounts of thymoquinone and its oxidation products pres¬ 
ent does not encourage this assumption. 
Of almost equal interest with the thymoquinone series of 
compounds in the Monarda species are the less complete, pos¬ 
sibly because less closely investigated, series of carvacrol, hy¬ 
drothymoquinone, and thymoquinone in Callistris quadrivalvis 
(Thuja Articulata) and the cymene, hydrothymoquinone series 
of Foeniculum vulgare. Another similar example which should 
be mentioned here is Thymus vulgaris. The oil of thyme is 
known to contain cymene, thymol, and sometimes carvacrol. 
Other members of the series, if not present in the original oil, 
are possibly produced upon standing, since oil of thyme, quite 
colorless when freshly distilled, often, upon standing, takes on 
a red color quite similar to the color of the oil from Monarda 
fistulosa from which dihydroxythymoquinone has been separ¬ 
ated. 
The fact that so frequently the pigment forming substance 
does not occur alone but is associated with other closely related, 
