But we should bear in mind that in the later
generations the crossed plants had become more or less closely
inter-related, and had been subjected all the time to nearly uniform
conditions.
It is remarkable that there is no close correspondence, either in the
parent-plants or in the successive generations, between the relative
number of seeds produced by the crossed and self-fertilised flowers, and
the relative powers of growth of the seedlings raised from such seeds.
Thus, the crossed and self-fertilised flowers on the parent-plants of
Ipomoea, Gesneria, Salvia, Limnanthes, Lobelia fulgens, and Nolana
produced a nearly equal number of seeds, yet the plants raised from the
crossed seeds exceeded considerably in height those raised from the
self-fertilised seeds. The crossed flowers of Linaria and Viscaria
yielded far more seeds than the self-fertilised flowers; and although
the plants raised from the former were taller than those from the
latter, they were not so in any corresponding degree. With Nicotiana the
flowers fertilised with their own pollen were more productive than those
crossed with pollen from a slightly different variety; yet the plants
raised from the latter seeds were much taller, heavier, and more hardy
than those raised from the self-fertilised seeds. On the other hand, the
crossed seedlings of Eschscholtzia were neither taller nor heavier than
the self-fertilised, although the crossed flowers were far more
productive than the self-fertilised.
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