though it may be complicated by
the existence of several factors which may also react upon one another. Nor
must it be forgotten that in so far as these different factors are
concerned the whites themselves may differ in constitution without showing
any trace of it in their appearance. Before the case can be regarded as
settled all these different possibilities will have to be definitely
tested. With the dark Eastern races as with the negro we cannot {132} hope
to come to any conclusion until we have evidence collected by critical and
competent observers.

Though for the present we must regard the case of the negro as not proven,
there are nevertheless two others in which the heredity would appear not to
follow the Mendelian rule. Castle in America crossed the lop-eared rabbit
with the normal form, and found that the F_1 animals were intermediate with
respect to their ears. And subsequent experiment showed that, on the whole,
they bred true to this intermediate condition. The other case relates to
Lepidoptera. The speckled wood butterfly (_Pararge egeria_) has a southern
form which differs from the northern one in the greater brightness and
depth of its yellow-brown markings. The northern form is generally
distinguished as var. _egeriades_. Bateson crossed the southern form from
the south of France with the paler British form, and found that the
offspring were more or less intermediate in colour, and that in subsequent
generations the parental types did not recur. These cases at present stand
alone. It is possible that further research may reveal complications which
mask or interfere with an underlying process of segregation. Or it may be
that segregation does not occur owing to some definite physiological reason
which at present we do not understand.

And here it is impossible not to recall Mendel's own experiences with the
Hawkweeds (_Hieracium_). This {133} genus of plants exhibits an
extraordinary profusion of forms differing from one another sometimes in a
single feature, sometimes in several. The question as to how far these
numerous forms were to be classified as distinct species, how far as
varieties, and how far as products of chance hybridisation, was even at
that time a source of keen controversy among botanists. There is little
doubt that Mendel undertook his experiments on the Hawkweeds in the hope
that the conception of unit-characters so brilliantly demonstrated for the
pea would serve to explain the gre