The three lots of
plants in each case were left freely exposed to the visits of insects,
and their flowers without doubt were cross-fertilised by them.
Table 9/E further shows us that in all four cases the intercrossed
plants of the same stock still have a decided though small advantage in
fertility over the self-fertilised plants.
With respect to the state of the reproductive organs in the
self-fertilised plants of Tables 9/D and 9/E, only a few observations
were made. In the seventh and eighth generation of Ipomoea, the anthers
in the flowers of the self-fertilised plants were plainly smaller than
those in the flowers of the intercrossed plants. The tendency to
sterility in these same plants was also shown by the first-formed
flowers, after they had been carefully fertilised, often dropping off,
in the same manner as frequently occurs with hybrids. The flowers
likewise tended to be monstrous. In the fourth generation of Petunia,
the pollen produced by the self-fertilised and intercrossed plants was
compared, and they were far more empty and shrivelled grains in the
former.
RELATIVE FERTILITY OF FLOWERS CROSSED WITH POLLEN FROM A DISTINCT PLANT
AND WITH THEIR OWN POLLEN. THIS HEADING INCLUDES FLOWERS ON THE
PARENT-PLANTS, AND ON THE CROSSED AND SELF-FERTILISED SEEDLINGS OF THE
FIRST OR A SUCCEEDING GENERATION.
I will first treat of the parent-plants, which were raised from seeds
purchased from nursery-gardens, or taken from plants growing in my
garden, or growing wild, and surrounded in every case by many
individuals of the same species.
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