And the bearing of these facts on the other problem of the transmission
of acquired characters is quite obvious. Mendelism provides no place for
any such transmission. Mendel's Law is sometimes called the law of
_alternative inheritance_, thus embodying in its name the thought that
offspring may show the characters possessed by one parent or by the
other, but that it cannot develop any characters whatever which were not
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_.
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