Many valuable fruits are quite sterile, or
produce extremely few seeds. This is notoriously the case with some of
the best pears and grapes, with the pine-apples, bananas, bread-fruits,
pomegranate and some members of the orange tribe. It is open to
discussion as to what may be the immediate cause of this sterility, but
it is quite evident, that all such sterile varieties must have
originated in a cultivated condition. Otherwise they would surely have
been lost.
In horticulture and agriculture the fact that new varieties arise from
time to time is beyond all doubt, and it is not this question with which
we are now concerned. Our arguments were only intended to prove that
cultivated species, as a rule, are derived from wild species, which obey
the laws discussed in a previous lecture. The botanic units are compound
entities, and [91] the real systematic units in elementary species play
the same part as in ordinary wild species. The inference that the origin
of the cultivated plants is multiple, in most cases, and that more than
one, often many separate elementary forms of the same species must
originally have been taken into cultivation, throws much light upon many
highly important problems of cultivation and selection. This aspect of
the question will therefore be the subject of the next lecture.
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