Lastly, with Pisum, Primula, the three generations of Canna,
and the three of Nicotiana (which together complete the twelve cases), a
cross between two plants certainly did no good or very little good to
the offspring; but we have reason to believe that this is the result of
these plants having been self-fertilised and cultivated under nearly
uniform conditions for several generations. The same result followed
with the experimental plants of Ipomoea and Mimulus, and to a certain
extent with some other species, which had been intentionally treated by
me in this manner; yet we know that these species in their normal
condition profit greatly by being intercrossed. There is, therefore, not
a single case in Table 7/A which affords decisive evidence against the
rule that a cross between plants, the progenitors of which have been
subjected to somewhat diversified conditions, is beneficial to the
offspring. This is a surprising conclusion, for from the analogy of
domesticated animals it could not have been anticipated, that the good
effects of crossing or the evil effects of self-fertilisation would have
been perceptible until the plants had been thus treated for several
generations.
The results given in Table 7/A may be looked at under another point of
view. Hitherto each generation has been considered as a separate case,
of which there are eighty-three; and this no doubt is the more correct
method of comparing the crossed and self-fertilised plants.
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