ared shows that the presence or absence of but two factors is
concerned, and at the same time provides the key to the nature of the
homostyled plants. These are potentially long styled, and the position of
the anthers is that of normal long-styled plants, but owing to some
interaction between the factors the style itself is unable to reach its
full development unless the factor for the small eye is present. For this
reason long-styled plants with the large eye are always of the homostyle
form. What the connecting-link between these apparently unrelated
structures may be we cannot yet picture to ourselves, any more than we can
picture the relation between flower {58} colour and hairiness in stocks. It
is evident, however, that the conception of the interaction of factors,
besides clearing up much that is paradoxical in heredity, promises to
indicate lines of research which may lead to valuable extensions in our
knowledge of the way in which the various parts of the living organism are
related to one another.

Short style } { Homo style
small eye } x { large eye
|
Short style
small eye
|
+-------------+----------+-----------+
Short style Short style Long style Homo style
small eye large eye ("pin") large eye
(9) (3) (3) (1)

* * * * *

{59}

CHAPTER VI

REVERSION

As soon as the idea was grasped that characters in plants and animals might
be due to the interaction of complementary factors, it became evident that
this threw clear light upon the hitherto puzzling phenomenon of reversion.
We have already seen that in certain cases the cross between a black mouse
or rabbit and an albino, each belonging to true breeding strains, might
produce nothing but agoutis. In other words, the cross between the black
and the white in certain instances results in a complete reversion to the
wild grey form. Expressed in Mendelian terms, the production of the agouti
was the necessary consequence of the meeting of the factors C and G in the
same zygote. As soon as they are brought together, no matter in what way,
the reversion is bound to occur. Reversion, therefore, in such cases we may
regard as the bringing together of complementary factors which had somehow
in the course of evolution become separated from one another. In the
simplest cases, such as that of t