Anyhow, it is certain that the differences are
not of an external nature, for two plants which resemble each other as
closely as the individuals of the same species ever do, profit in the
plainest manner when intercrossed, if their progenitors have been
exposed during several generations to different conditions. But to this
latter subject I shall have to recur in a future chapter.
TABLE 7/A.
We will now turn to our first table, which relates to crossed and
self-fertilised plants of the same stock. These consist of fifty-four
species belonging to thirty natural orders. The total number of crossed
plants of which measurements are given is 796, and of self-fertilised
809; that is altogether 1,605 plants. Some of the species were
experimented on during several successive generations; and it should be
borne in mind that in such cases the crossed plants in each generation
were crossed with pollen from another crossed plant, and the flowers on
the self-fertilised plants were almost always fertilised with their own
pollen, though sometimes with pollen from other flowers on the same
plant. The crossed plants thus became more or less closely inter-related
in the later generations; and both lots were subjected in each
generation to almost absolutely the same conditions, and to nearly the
same conditions in the successive generations. It would have been a
better plan in some respects if I had always crossed some flowers either
on the self-fertilised or intercrossed plants of each generation with
pollen from a non-related plant, grown under different conditions, as
was done with the plants in Table 7/C; for by this procedure I should
have learnt how much the offspring became deteriorated through continued
self-fertilisation in the successive generations.
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