(12/6. Dr. Engler 'Botanische Zeitung' 1868 page 833.) Several
genera include both heterostyled (dimorphic or trimorphic forms) and
homostyled species. Ophrys offers a remarkable instance of one species
having its structure manifestly adapted for self-fertilisation, and
other species as manifestly adapted for cross-fertilisation. Some
con-generic species are quite sterile and others quite fertile with
their own pollen. From these several causes we often find within the
same genus species which do not produce seeds, while others produce an
abundance, when insects are excluded. Some species bear cleistogene
flowers which cannot be crossed, as well as perfect flowers, whilst
others in the same genus never produce cleistogene flowers. Some species
exist under two forms, the one bearing conspicuous flowers adapted for
cross-fertilisation, the other bearing inconspicuous flowers adapted for
self-fertilisation, whilst other species in the same genus present only
a single form. Even with the individuals of the same species, the degree
of self-sterility varies greatly, as in Reseda. With polygamous plants,
the distribution of the sexes differs in the individuals of the same
species. The relative period at which the sexual elements in the same
flower are mature, differs in the varieties of Pelargonium; and Carriere
gives several cases, showing that the period varies according to the
temperature to which the plants are exposed.
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