The innate power of the crossed plants to resist unfavourable conditions
far better than did the self-fertilised plants, was shown on two
occasions in a curious manner, namely, with Iberis and in the third
generation of Petunia, by the great superiority in height of the crossed
over the self-fertilised seedlings, when both sets were grown under
extremely unfavourable conditions; whereas owing to special
circumstances exactly the reverse occurred with the plants raised from
the same seeds and grown in pairs in pots. A nearly analogous case was
observed on two other occasions with plants of the first generation of
Nicotiana.
The crossed plants always withstood the injurious effects of being
suddenly removed into the open air after having been kept in the
greenhouse better than did the self-fertilised. On several occasions
they also resisted much better cold and intemperate weather. This was
manifestly the case with some crossed and self-fertilised plants of
Ipomoea, which were suddenly moved from the hothouse to the coldest part
of a cool greenhouse. The offspring of plants of the eighth
self-fertilised generation of Mimulus crossed by a fresh stock, survived
a frost which killed every single self-fertilised and intercrossed plant
of the same old stock. Nearly the same result followed with some crossed
and self-fertilised plants of Viola tricolor. Even the tips of the
shoots of the crossed plants of Sarothamnus scoparius were not touched
by a very severe winter; whereas all the self-fertilised plants were
killed halfway down to the ground, so that they were not able to flower
during the next summer.
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