It is, on the contrary, an astonishing fact, that the
crossed plants should have been victorious, even to a slight degree,
over the self-fertilised plants of the later generations.
The much greater constitutional vigour of the crossed than of the
self-fertilised plants, was proved on five occasions in various ways;
namely, by exposing them, while young, to a low temperature or to a
sudden change of temperature, or by growing them, under very
unfavourable conditions, in competition with full-grown plants of other
kinds.
With respect to the productiveness of the crossed and self-fertilised
plants of the successive generations, my observations unfortunately were
not made on any uniform plan, partly from the want of time, and partly
from not having at first intended to observe more than a single
generation. A summary of the results is here given in a tabulated form,
the fertility of the crossed plants being taken as 100.
TABLE 2/18. Ratio of productiveness of crossed and self-fertilised
plants. Ipomoea purpurea.
FIRST GENERATION OF CROSSED AND SELF-FERTILISED PLANTS GROWING IN
COMPETITION WITH ONE ANOTHER.
Sixty-five capsules produced from flowers on five crossed plants
fertilised by pollen from a distinct plant, and fifty-five capsules
produced from flowers on five self-fertilised plants fertilised by their
own pollen, contained seeds in the proportion of : 100 to 93.
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