Notwithstanding the evil which many plants suffer from
self-fertilisation, they can be thus propagated under favourable
conditions for many generations, as shown by some of my experiments, and
more especially by the survival during at least half a century of the
same varieties of the common pea and sweet-pea. The same conclusion
probably holds good with several other exotic plants, which are never or
most rarely cross-fertilised in this country. But all these plants, as
far as they have been tried, profit greatly by a cross with a fresh
stock. Some few plants, for instance, Ophrys apifera, have almost
certainly been propagated in a state of nature for thousands of
generations without having been once intercrossed; and whether they
would profit by a cross with a fresh stock is not known. But such cases
ought not to make us doubt that as a general rule crossing is
beneficial, any more than the existence of plants which, in a state of
nature, are propagated exclusively by rhizomes, stolons, etc. (their
flowers never producing seeds), (12/3. I have given several cases in my
'Variation under Domestication' chapter 18 2nd edition volume 2 page
152.) (their flowers never producing seeds), should make us doubt that
seminal generation must have some great advantage, as it is the common
plan followed by nature. Whether any species has been reproduced
asexually from a very remote period cannot, of course, be ascertained.
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