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
Michalet says that short, thin, twisted branches are developed from the buds in
the axils of the lower leaves, and that these bury themselves in the ground.
(8/12. ‘Bulletin Soc. Bot. de France’ tome 7 1860 page 468.) They there produce
flowers not offering any peculiarity in structure, excepting that their
corollas, though properly coloured, are deformed. These flowers may be ranked as
cleistogamic, as they are developed, and not merely drawn, beneath the ground.
Ononis columnae.
Plants were raised from seeds sent me from Northern Italy. The sepals of the
cleistogamic flowers are elongated and closely pressed together; the petals are
much reduced in size, colourless, and folded over the interior organs. The
filaments of the ten stamens are united into a tube, and this is not the case,
according to Von Mohl, with the cleistogamic flowers of other Leguminosae. Five
of the stamens are destitute of anthers, and alternate with the five thus
provided. The two cells of the anthers are minute, rounded and separated from
one another by connective tissue; they contain but few pollen-grains, and these
have extremely delicate coats. The pistil is hook-shaped, with a plainly
enlarged stigma, which is curled down, towards the anthers; it therefore differs
much from that of the perfect flower. During the year 1867 no perfect flowers
were produced, but in the following year there were both perfect and
cleistogamic ones.
Ononis minutissima.
My plants produced both perfect and cleistogamic flowers; but I did not examine
the latter. Some of the former were crossed with pollen from a distinct plant,
and six capsules thus obtained yielded on an average 3.66 seeds, with a maximum
of 5 in one. Twelve perfect flowers were marked and allowed to fertilise
themselves spontaneously under a net, and they yielded eight capsules,
containing on an average 2.38 seeds, with a maximum of 3 in one. Fifty-three
capsules produced by the cleistogamic flowers contained on an average 4.1 seeds,
so that these were the most productive of all; and the seeds themselves looked
finer even than those from the crossed perfect flowers. According to Mr. Bentham
O. parviflora likewise bears cleistogamic flowers; and he informs me that these
flowers are produced by all three species early in the spring; whilst the
perfect ones appear afterwards, and therefore in a reversed order compared with
those of Viola and Oxalis. Some of the species, for instance Ononis columnae,
bear a fresh crop of cleistogamic flowers in the autumn.
Lathyrus nissolia.
Public-domain text, read in full here on John Shaqi.
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