More seed
will then be produced, and the seedlings being the product of
cross-fertilisation will be vigorous, so that the species will tend to
increase in number, to be again checked, as soon as the plant again
grows in crowded masses.
CHAPTER XII.
GENERAL RESULTS.
Cross-fertilisation proved to be beneficial, and self-fertilisation
injurious.
Allied species differ greatly in the means by which cross-fertilisation
is favoured and self-fertilisation avoided.
The benefits and evils of the two processes depend on the degree of
differentiation in the sexual elements.
The evil effects not due to the combination of morbid tendencies in the
parents.
Nature of the conditions to which plants are subjected when growing near
together in a state of nature or under culture, and the effects of such
conditions.
Theoretical considerations with respect to the interaction of
differentiated sexual elements.
Practical lessons.
Genesis of the two sexes.
Close correspondence between the effects of cross-fertilisation and
self-fertilisation, and of the legitimate and illegitimate unions of
heterostyled plants, in comparison with hybrid unions.
The first and most important of the conclusions which may be drawn from
the observations given in this volume, is that cross-fertilisation is
generally beneficial, and self-fertilisation injurious. This is shown by
the difference in height, weight, constitutional vigour, and fertility
of the offspring from crossed and self-fertilised flowers, and in the
number of seeds produced by the parent-plants.
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