The same
conclusion holds good, as we have already seen, in the analogous cases
of Ipomoea, Mimulus, and Dianthus, with respect to height.
10. Nicotiana tabacum.
My plants were remarkably self-fertile, and the capsules from the
self-fertilised flowers apparently yielded more seeds than those which
were cross-fertilised. No insects were seen to visit the flowers in the
hothouse, and I suspect that the stock on which I experimented had been
raised under glass, and had been self-fertilised during several previous
generations; if so, we can understand why, in the course of three
generations, the crossed seedlings of the same stock did not uniformly
exceed in height the self-fertilised seedlings. But the case is
complicated by individual plants having different constitutions, so that
some of the crossed and self-fertilised seedlings raised at the same
time from the same parents behaved differently. However this may be,
plants raised from self-fertilised plants of the third generation
crossed by a slightly different sub-variety, exceeded greatly in height
and weight the self-fertilised plants of the fourth generation; and the
trial was made on a large scale. They exceeded them in height when grown
in pots, and not much crowded, in the ratio of 100 to 66; and when much
crowded, as 100 to 54. These crossed plants, when thus subjected to
severe competition, also exceeded the self-fertilised in weight in the
ratio of 100 to 37.
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