Self-sterile plants.
Causes of self-sterility.
The appearance of highly self-fertile varieties.
Self-fertilisation apparently in some respects beneficial, independently
of the assured production of seeds.
Relative weights and rates of germination of seeds from crossed and
self-fertilised flowers.
The present chapter is devoted to the Fertility of plants, as influenced
by cross-fertilisation and self-fertilisation. The subject consists of
two distinct branches; firstly, the relative productiveness or fertility
of flowers crossed with pollen from a distinct plant and with their own
pollen, as shown by the proportional number of capsules which they
produce, together with the number of the contained seeds. Secondly, the
degree of innate fertility or sterility of the seedlings raised from
crossed and self-fertilised seeds; such seedlings being of the same age,
grown under the same conditions, and fertilised in the same manner.
These two branches of the subject correspond with the two which have to
be considered by any one treating of hybrid plants; namely, in the first
place the comparative productiveness of a species when fertilised with
pollen from a distinct species and with its own pollen; and in the
second place, the fertility of its hybrid offspring. These two classes
of cases do not always run parallel; thus some plants, as Gartner has
shown, can be crossed with great ease, but yield excessively sterile
hybrids; while others are crossed with extreme difficulty, but yield
fairly fertile hybrids.
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