manifest or latent in the ancestry. Changes in the environment during
the embryonic stage, it is true, seem sometimes to be registered in the
growing form; but it has never yet been proved that these induced
changes can ever amount to a unit character or genetic factor that will
maintain itself and segregate as a distinct factor after hybridization.
Ancestry alone furnishes the material for the factor, and no amount of
induced change can get itself registered in the organism so as to come
into this charmed circle of ancestral characters which alone seem to be
passed on to posterity.

A quotation from Bateson ought to set this point at rest:

"The essence of the Mendelian principle is very easily expressed. It is,
first, that in great measure the properties of organisms are due to the
presence of distinct, detachable elements [factors], separately
transmitted in heredity; and secondly, that _the parent cannot pass on
to offspring an element, and consequently the corresponding property,
which it does not itself possess_."[28]

[Footnote 28: _Scientific American_ Sup., January 3, 1914.]

Heredity we now see is a method of analysis, and the facts brought to
light by Mendelism help us very much toward an understanding of living
matter. Especially does it help us to understand the complexity
underlying the facts of heredity, which until now have seemed so strange
and capricious. As Professor Punnett of Cambridge remarks:

"Constitutional differences of a radical nature may be concealed beneath
an apparent identity of external form. Purple sweet peas from the same
pod, indistinguishable in appearance and of identical ancestry, may yet