Asa Gray informs me
that Coprosma is dioecious, and that it is closely allied through Nertera to
Mitchella, which as we know is a heterostyled dimorphic species. In the male
flowers of Coprosma the stamens are exserted, and in the female flowers the
stigmas; so that, judging from the affinities of the above three genera, it
seems probable that an ancient short-styled form bearing long stamens with large
anthers and large pollen-grains (as in the case of several Rubiaceous genera)
has been converted into the male Coprosma; and that an ancient long-styled form
with short stamens, small anthers and small pollen-grains has been converted
into the female form. But according to Mr. Meehan, Mitchella itself is dioecious
in some districts; for he says that one form has small sessile anthers without a
trace of pollen, the pistil being perfect; while in another form the stamens are
perfect and the pistil rudimentary. (7/6. 'Proceedings of the Academy of
Sciences of Philadelphia' July 28, 1868 page 183.) He adds that plants may be
observed in the autumn bearing an abundant crop of berries, and others without a
single one. Should these statements be confirmed, Mitchella will be proved to be
heterostyled in one district and dioecious in another.
Asperula is likewise a Rubiaceous genus, and from the published description of
the two forms of A.
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