Therefore the number of dioecious species which owe their origin
to the transformation of heterostyled plants is probably not so large as might
have been anticipated from the facilities which they offer for such conversion.
In searching for cases like the foregoing ones, I have been led to examine some
dioecious or sub-dioecious plants, which are worth describing, chiefly as they
show by what fine gradations hermaphrodites may pass into polygamous or
dioecious species.
POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS.
Euonymus Europaeus (CELASTRINEAE).
(Figure 7.12. Euonymus Europaeus
Left: Hermaphrodite or male.
Right: Female.)
The spindle-tree is described in all the botanical works which I have consulted
as an hermaphrodite. Asa Gray speaks of the flowers of the American species as
perfect, whilst those in the allied genus Celastrus are said to be "polygamo-
dioecious." If a number of bushes of our spindle-tree be examined, about half
will be found to have stamens equal in length to the pistil, with well-developed
anthers; the pistil being likewise to all appearance well developed. The other
half have a perfect pistil, with the stamens short, bearing rudimentary anthers
destitute of pollen; so that these bushes are females. All the flowers on the
same plant present the same structure. The female corolla is smaller than that
on the polleniferous bushes.
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