Intercrossed
seedlings, raised in England from the Brazilian stock, compared with
self-fertilised seedlings of the corresponding second generation,
yielded seeds in number as 100 to 89; both lots of plants being left
freely exposed to the visits of insects. If we now turn to the effects
of crossing plants of the Brazilian stock with pollen from the English
stock,--so that plants which had been long exposed to very different
conditions were intercrossed,--we find that the offspring were, as
before, inferior in height and weight to the plants of the Brazilian
stock after two generations of self-fertilisation, but were superior to
them in the most marked manner in the number of seeds produced, namely,
as 100 to 40; both lots of plants being left freely exposed to the
visits of insects.
In the case of Ipomoea, we have seen that the plants derived from a
cross with a fresh stock were superior in height as 100 to 78, and in
fertility as 100 to 51, to the plants of the old stock, although these
had been intercrossed during the last ten generations. With
Eschscholtzia we have a nearly parallel case, but only as far as
fertility is concerned, for the plants derived from a cross with a fresh
stock were superior in fertility in the ratio of 100 to 45 to the
Brazilian plants, which had been artificially intercrossed in England
for the two last generations, and which must have been naturally
intercrossed by insects during all previous generations in Brazil, where
otherwise they are quite sterile.
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