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
The hermaphrodite plants present nothing particular in the state of their
reproductive organs; and so it is in all the following cases. The females of the
present species produce rather fewer flowers and have somewhat smaller corollas
than the hermaphrodites; so that near Torquay, where this plant abounds, I
could, after a little practice, distinguish the two forms whilst walking quickly
past them. According to Vaucher, the smaller size of the corolla is common to
the females of most or all of the above-mentioned Labiatae. The pistil of the
female, though somewhat variable in length, is generally shorter, with the
margins of the stigma broader and formed of more lax tissue, than that of the
hermaphrodite. The stamens in the female vary excessively in length; they are
generally enclosed within the tube of the corolla, and their anthers do not
contain any sound pollen; but after long search I found a single plant with the
stamens moderately exserted, and their anthers contained a very few full-sized
grains, together with a multitude of minute empty ones. In some females the
stamens are extremely short, and their minute anthers, though divided into the
two normal cells or loculi, contained not a trace of pollen: in others again the
anthers did not exceed in diameter the filaments which supported them, and were
not divided into two loculi. Judging from what I have myself seen and from the
descriptions of others, all the plants in Britain, Germany, and near Mentone,
are in the state just described; and I have never found a single flower with an
aborted pistil. It is, therefore, remarkable that, according to Delpino, this
plant near Florence is generally trimorphic, consisting of males with aborted
pistils, females with aborted stamens, and hermaphrodites. (7/15. ‘Sull’ Opera,
la Distribuzione dei Sessi nelle Piante, etc’ 1867 page 7. With respect to
Germany H. Muller ‘Die Befruchtung etc.’ page 327.)
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