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
All the species hitherto mentioned which produce cleistogamic flowers are
entomophilous; but four genera, Juncus, Hordeum, Cryptostachys, and Leersia are
anemophilous. Juncus bufonius is remarkable by bearing in parts of Russia only
cleistogamic flowers, which contain three instead of the six anthers found in
the perfect flowers. (8/22. See Dr. Ascherson’s interesting paper in ‘Botanische
Zeitung’ 1871 page 551.) In the genus Hordeum it has been shown by Delpino that
the majority of the flowers are cleistogamic, some of the others expanding and
apparently allowing of cross-fertilisation. (8/23. ‘Bollettini del Comizio
agrario Parmense.’ Marzo e Aprile 1871. An abstract of this valuable paper is
given in ‘Botanische Zeitung’ 1871 page 537. See also Hildebrand on Hordeum in
‘Monatsbericht d. K. Akad Berlin’ October 1872 page 760.) I hear from Fritz
Muller that there is a grass in Southern Brazil, in which the sheath of the
uppermost leaf, half a metre in length, envelopes the whole panicle; and this
sheath never opens until the self-fertilised seeds are ripe. On the roadside
some plants had been cut down, whilst the cleistogamic panicles were developing,
and these plants afterwards produced free or unenclosed panicles of small size,
bearing perfect flowers.
Leersia oryzoides.
It has long been known that this plant produces cleistogamic flowers, but these
were first described with care by M. Duval-Jouve. (8/24. ‘Bulletin Bot. Soc. de
France’ tome 10 1863 page 194.) I procured plants from a stream near Reigate,
and cultivated them for several years in my greenhouse. The cleistogamic flowers
are very small, and usually mature their seeds within the sheaths of the leaves.
These flowers are said by Duval-Jouve to be filled by slightly viscid fluid; but
this was not the case with several that I opened; but there was a thin film of
fluid between the coats of the glumes, and when these were pressed the fluid
moved about, giving a similarly deceptive appearance of the whole inside of the
flower being thus filled. The stigma is very small and the filaments extremely
short; the anthers are less than 1/50 of an inch in length or about one-third of
the length of those in the perfect flowers. One of the three anthers dehisces
before the two others. Can this have any relation with the fact that in some
other species of Leersia only two stamens are fully developed? (8/25. Asa Gray
‘Manual of Botany of the United States’ 1856 page 540.) The anthers shed their
pollen on the stigma; at least in one instance this was clearly the case, and by
tearing open the anthers under water the grains were easily detached. Towards
the apex of the anther the grains are arranged in a single row and lower down in
two or three rows, so that they could be counted; and there were about 35 in
each cell, or 70 in the whole anther; and this is an astonishingly small number
for an anemophilous plant. The grains have very delicate coats, are spherical
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