orm, which can rarely and obscurely be detected during one
individual life, become apparent after several generations: the slight
differences, often hardly describable, which characterize the stock of
different countries, and even of districts in the same country, seem to
be due to such continued action.

{189} Here, as in the MS. of 1842, the author is inclined to
minimise the variation occurring in nature.

{190} This is more strongly stated than in the _Origin_, Ed. i. p.
30.

_On the hereditary tendency._

A volume might be filled with facts showing what a strong tendency there
is to inheritance, in almost every case of the most trifling, as well as
of the most remarkable congenital peculiarities{191}. The term
congenital peculiarity, I may remark, is a loose expression and can only
mean a peculiarity apparent when the part affected is nearly or fully
developed: in the Second Part, I shall have to discuss at what period of
the embryonic life connatal peculiarities probably first appear; and I
shall then be able to show from some evidence, that at whatever period
of life a new peculiarity first appears, it tends hereditarily to appear
at a corresponding period{192}. Numerous though slight changes, slowly
supervening in animals during mature life (often, though by no means
always, taking the form of disease), are, as stated in the first
paragraphs, very often hereditary. In plants, again, the buds which
assume a different character from their stock likewise tend to transmit
their new peculiarities. There is not sufficient reason to believe that
either mutilations{193} or changes of form produced by mechanical
pressure, even if continued for hundreds of generations, or that any
changes of structure quickly produced by disease, are inherited; it
would appear as if the tissue of the part affected must slowly and
freely grow into the new form, in order to be inheritable. There is a
very great difference in the hereditary tendency of different
peculiarities, and of the same peculiarity, in different individuals and
species; thus twenty thousand seeds of the weeping ash have been sown
and not one come up true;--out of seventeen seeds of the weeping yew,
nearly all came up true. The ill-formed and almost monstrous "Niata"
cattle of S. America and Ancon sheep, both when bred together and when
crossed with other breeds, seem to transmit their peculiarities to their
offspring as truly as the ordinary b