factor not only produces a white streak in the hair, but affects the
pigmentation of the skin as well, usually resulting in one or more white
spots on some part of the body. It is really a factor for "piebaldism."

For the sake of clear thinking, then, the idea of a unit character due
to some unit determiner or factor in the germ-plasm must be given up,
and it must be recognized that every visible character of an individual
is the result of numerous factors, or differences in the germ-plasm.
Ordinarily one of these produces a more notable contribution to the
end-product than do the others; but there are cases where this statement
does not appear to hold good. This leads to the conception of _multiple
factors_.

In crossing a wheat with brown chaff and one with white chaff, H.
Nilsson-Ehle (1909) expected in the second hybrid generation to secure a
ratio of 3 brown to 1 white. As a fact, he got 1410 brown and 94 white,
a ratio of 15:1. He interpreted this as meaning that the brown color in
this particular variety was due not to one factor, but to two, which
were equivalent to each other, and either one of which would produce the
same result alone as would the two acting together. In further crossing
red wheat with white, he secured ratios which led him to believe that
the red was produced by three independent factors, any one of which
would produce red either alone or with the other two. A. and G. Howard
later corroborated this work,[48] but showed that the three factors were
not identical: they are qualitatively slightly different, although so
closely similar that the three reds look alike at first sight. E. M.
East has obtained evidence from maize and G. H. Shull from
shepherd's-purse, which bears out the multiple factor hypothesis.

[Illustration: WHITE BLAZE IN THE HAIR

FIG. 19.--The white lock of hair here shown is hereditary and
has been traced back definitely through six generations; family
tradition derives it from a son of Harry "Hot-Spur" Percy, born in 1403,
and fallaciously assigns its origin to "prenatal influence" or "maternal
impression." This young woman inherited the blaze from her father, who
had it from his mother, who had it from her father, who migrated from
England to America nearly a century ago. The trait appears to be a
simple dominant, following Mendel's Law; that is, when a person with one
of these locks who is a child of one normal and one affected parent
marries a normal individual, half