Thus the proposition that the
benefit from cross-fertilisation depends on the plants which are crossed
having been subjected during previous generations to somewhat different
conditions, or to their having varied from some unknown cause as if they
had been thus subjected, is securely fortified on all sides.
Before proceeding any further, the view which has been maintained by
several physiologists must be noticed, namely, that all the evils from
breeding animals too closely, and no doubt, as they would say, from the
self-fertilisation of plants, is the result of the increase of some
morbid tendency or weakness of constitution common to the closely
related parents, or to the two sexes of hermaphrodite plants.
Undoubtedly injury has often thus resulted; but it is a vain attempt to
extend this view to the numerous cases given in my Tables. It should be
remembered that the same mother-plant was both self-fertilised and
crossed, so that if she had been unhealthy she would have transmitted
half her morbid tendencies to her crossed offspring. But plants
appearing perfectly healthy, some of them growing wild, or the immediate
offspring of wild plants, or vigorous common garden-plants, were
selected for experiment. Considering the number of species which were
tried, it is nothing less than absurd to suppose that in all these cases
the mother-plants, though not appearing in any way diseased, were weak
or unhealthy in so peculiar a manner that their self-fertilised
seedlings, many hundreds in number, were rendered inferior in height,
weight, constitutional vigour and fertility to their crossed offspring.
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