The experiment was repeated, with the
sole difference that the plants were allowed to grow more crowded; and
now the twenty-four tallest of the crossed plants were to the
twenty-four tallest self-fertilised plants in height as 100 to 94, and
in weight as 100 to 97. Moreover, a larger number of the crossed than of
the self-fertilised plants grew to a moderate height. The
above-mentioned twenty crossed plants were also grown in competition
with twenty self-fertilised plants raised from the closed or cleistogene
flowers, and their heights were as 100 to 94. Therefore had it not been
for the first trial, in which the crossed plants were to the
self-fertilised in height only as 100 to 99, this species might have
been classed with those in which the crossed plants exceed the
self-fertilised by above five per cent. On the other hand, the crossed
plants in the second trial bore fewer capsules; and these contained
fewer seeds, than did the self-fertilised plants, all the capsules
having been produced by cleistogene flowers. The whole case therefore
must be left doubtful.
19. Pisum sativum (common pea).
Four-plants derived from a cross between individuals of the same variety
were in height to four self-fertilised plants belonging to the same
variety as 100 to 115. Although this cross did no good, we have seen
under Table 7/C that a cross between distinct varieties adds greatly to
the height and vigour of the offspring; and it was there explained that
the fact of a cross between the individuals of the same variety not
being beneficial, is almost certainly due to their having been
self-fertilised for many generations, and in each generation grown under
nearly similar conditions.
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