scientific study of the genetics of color inheritance. These studies have
developed certain interesting facts with reference to the chemistry of the
development of these ornamental pigments, which may be briefly mentioned
here.

In many of the plants which have been studied, the color of the flowers
depends upon several different factors, as follows:

_C_, a chromogen (or color-producing substance) which is generally a
flavone or xanthone glucoside, and which may be either yellow or
colorless.

_E_, an enzyme which acts upon _C_, to produce a red pigment.

_e_, another enzyme which acts upon the red pigment, changing it to some
other anthocyanin color.

_A_, an antioxidase, or antienzyme, which prevents the action of _E_.

_R_, an enzyme which changes reds to yellows.

Thus, if a plant whose flower contains only the factor _C_ be crossed with
one which contains the factor _E_, a red blossom will result, or if it
contains the factor _e_ more intense pigments are developed. But if either
_A_ or _R_ are present, no change in the color of the original parents will
result from the crossing.

THE PHYSIOLOGICAL USES OF PIGMENTS

The vegetative pigments undoubtedly serve as agencies for regulating the
rate of metabolic processes. At the same time, it is extremely difficult to
determine whether the presence of a pigment in any given case is the cause
or the effect of the changes in the plant's activities which result from
changes in its external environment.

The chlorophylls are, of course, the regulator of photosynthesis, absorbing
solar energy with which the photosynthetic process may be brought about.
The simultaneous presence of carotinoids in varying amounts undoubtedly
serves to modify the amount and character of the radiant energy absorbed,
as these pigments absorb a different part of the spectrum of light and
hence undoubtedly produce a different chemical activity or "actinic effect"
of the absorbed energy. The variations in depth of color of foliage during
different growing conditions, from a pale yellow when conditions are
unfavorable and growth is slow to the rich dark green of more favorable
conditions, is a familiar phenomenon. Whether this change in pigmentation
is the result of an adjustment of the plant protoplasm, so that it can
absorb a more highly actinic portion of the light, or is a direct effect of
the lack of conditions favorable to chlorophyll-production and active
phot