) Many other
such facts could be adduced. In short, every alteration in the function
of a part is probably connected with some corresponding, though often
quite imperceptible change in structure or composition.
Whatever affects an organism in any way, likewise tends to act on its
sexual elements. We see this in the inheritance of newly acquired
modifications, such as those from the increased use or disuse of a part,
and even from mutilations if followed by disease. (12/9. 'Variation
under Domestication' chapter 12 2nd edition volume 1 page 466.) We have
abundant evidence how susceptible the reproductive system is to changed
conditions, in the many instances of animals rendered sterile by
confinement; so that they will not unite, or if they unite do not
produce offspring, though the confinement may be far from close; and of
plants rendered sterile by cultivation. But hardly any cases afford more
striking evidence how powerfully a change in the conditions of life acts
on the sexual elements, than those already given, of plants which are
completely self-sterile in one country, and when brought to another,
yield, even in the first generation, a fair supply of self-fertilised
seeds.
But it may be said, granting that changed conditions act on the sexual
elements, how can two or more plants growing close together, either in
their native country or in a garden, be differently acted on, inasmuch
as they appear to be exposed to exactly the same conditions? Although
this question has been already considered, it deserves further
consideration under several points of view.
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