The natural order to follow in this chapter would have been first to
consider the effects on the fertility of the parent-plants of crossing
them, and of fertilising them with their own pollen; but as we have
discussed in the two last chapters the relative height, weight, and
constitutional vigour of crossed and self-fertilised plants--that is, of
plants raised from crossed and self-fertilised seeds--it will be
convenient here first to consider their relative fertility. The cases
observed by me are given in Table 9/D, in which plants of crossed and
self-fertilised parentage were left to fertilise themselves, being
either crossed by insects or spontaneously self-fertilised. It should be
observed that the results cannot be considered as fully trustworthy, for
the fertility of a plant is a most variable element, depending on its
age, health, nature of the soil, amount of water given, and temperature
to which it is exposed. The number of the capsules produced and the
number of the contained seeds, ought to have been ascertained on a large
number of crossed and self-fertilised plants of the same age and treated
in every respect alike. In these two latter respects my observations may
be trusted, but a sufficient number of capsules were counted only in a
few instances. The fertility, or as it may perhaps better be called the
productiveness, of a plant depends on the number of capsules produced,
and on the number of seeds which these contain.
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