The Different Forms of Flowers on Plants of the Same SpeciesDarwin, Charles
Science
The Different Forms of Flowers on Plants of the Same Species
Darwin, Charles
Fertilization of plants; Heterostylism; Plant physiology; Plants -- Variation; Pollination
Mr. Thiselton Dyer remarks that this tree, an inhabitant of Malacca and Borneo,
appears to be heterostyled. (3/21. ‘Journal of Botany’ London 1872 page 26.) He
sent me dried flowers, and the difference between the two forms is conspicuous.
In the short-styled form the pistils are in length to those of the short-styled
as 100 to 40, with their globular stigmas about twice as thick. These stand just
above the numerous anthers and a little beneath the tips of the petals. In the
short-styled form the anthers project high above the pistils, the stigmas of
which diverge between the three bundles of stamens, and stand only a little
above the tips of the sepals. The stamens in this form are to those of the long-
styled as 100 to 86 in length; and therefore they do not differ so much in
length as do the pistils. Ten pollen-grains from each form were measured, and
those from the short-styled were to those from the long-styled as 100 to 86 in
diameter. This plant, therefore, is in all respects a well-characterised
heterostyled species.
Aegiphila elata (Verbenaceae).
Mr. Bentham was so kind as to send me dried flowers of this species and of Ae.
mollis, both inhabitants of South America. The two forms differ conspicuously,
as the deeply bifid stigma of the one, and the anthers of the other project far
above the mouth of the corolla. In the long-styled form of the present species,
the style is twice and a half as long as that of the short-styled. The divergent
stigmas of the two forms do not differ much in length, nor as far as I could
perceive in their papillae. In the long-styled flowers the filaments adhere to
the corolla close up to the anthers, which are enclosed some way down within the
tube. In the short-styled flowers the filaments are free above the point where
the anthers are seated in the other form, and they project from the corolla to
an equal height with that of the stigmas in the long-styled flowers. It is often
difficult to measure with accuracy pollen-grains, which have long been dried and
then soaked in water; but they here manifestly differed greatly in size. Those
from the short-styled flowers were to those from the long-styled in diameter in
about the ratio of 100 to 62. The two forms of Ae. mollis present a like
difference in the length of their pistils and stamens.
Aegiphila obdurata.
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