In my seventh chapter some
observations will be given on the gradual conversion of heterostyled and of
ordinary hermaphrodite plants into dioecious or sub-dioecious species.
The fourth and last Class consists of the plants which were called polygamous by
Linnaeus; but it appears to me that it would be convenient to confine this term
to the species which coexist as hermaphrodites, males and females; and to give
new names to several other combinations of the sexes--a plan which I shall here
follow. Polygamous plants, in this confined sense of the term, may be divided
into two sub-groups, according as the three sexual forms are found on the same
individual or on distinct individuals. Of this latter or trioicous sub-group,
the common Ash (Fraxinus excelsior) offers a good instance: thus, I examined
during the spring and autumn fifteen trees growing in the same field; and of
these, eight produced male flowers alone, and in the autumn not a single seed;
four produced only female flowers, which set an abundance of seeds; three were
hermaphrodites, which had a different aspect from the other trees whilst in
flower, and two of them produced nearly as many seeds as the female trees,
whilst the third produced none, so that it was in function a male. The
separation of the sexes, however, is not complete in the Ash; for the female
flowers include stamens, which drop off at an early period, and their anthers,
which never open or dehisce, generally contain pulpy matter instead of pollen.
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