Taking into consideration the number of
capsules together with the average number of seeds, the crossed plants
(spontaneously self-fertilised) produced seeds in comparison with the
self-fertilised plants (spontaneously self-fertilised) in the proportion
of 100 to 35. By whatever method the fertility of these plants is
compared, the crossed are more fertile than the self-fertilised plants.
I tried in several ways the comparative vigour and powers of growth of
the crossed and self-fertilised plants of this third generation. Thus,
four self-fertilised seeds which had just germinated were planted on one
side of a pot, and after an interval of forty-eight hours, four crossed
seeds in the same state of germination were planted on the opposite
side; and the pot was kept in the hothouse. I thought that the advantage
thus given to the self-fertilised seedlings would have been so great
that they would never have been beaten by the crossed ones. They were
not beaten until all had grown to a height of 18 inches; and the degree
to which they were finally beaten is shown in Table 2/4. We here see
that the average height of the four crossed plants is 76.62, and of the
four self-fertilised plants 65.87 inches, or as 100 to 86; therefore
less than when both sides started fair.
TABLE 2/4. Ipomoea purpurea (Third Generation, the self-fertilised
plants having had a start of forty-eight hours).
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