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
which had not been artificially fertilised, produced capsules containing 5, 1,
and 5 seeds; and it is quite possible that pollen may have been brought to them
by insects from the long-styled plant growing in the same garden. Nevertheless,
as they did not yield half the number of seeds compared with the other flowers
on the same plant which had been artificially and legitimately fertilised, and
as the short-styled plants of the two previous species apparently evince some
slight capacity for fertilisation with their own-form pollen, these three
capsules may have been the product of self-fertilisation.
Besides the three species now described, the yellow-flowered L. corymbiferum is
certainly heterostyled, as is, according to Planchon, L. salsoloides. (3/6.
Hooker’s ‘London Journal of Botany’ 1848 volume 7 page 174.) This botanist is
the only one who seems to have inferred that heterostylism might have some
important functional bearing. Dr. Alefeld, who has made a special study of the
genus, says that about half of the sixty-five species known to him are
heterostyled. (3/7. ‘Botanische Zeitung’ September 18, 1863 page 281.) This is
the case with L. trigynum, which differs so much from the other species that it
has been formed by him into a distinct genus. (3/8. It is not improbable that
the allied genus, Hugonia, is heterostyled, for one species is said by Planchon
(Hooker’s ‘London Journal of Botany’ 1848 volume 7 page 525) to be provided with
“staminibus exsertis;” another with “stylis staminibus longioribus,” and another
has “stamina 5, majora, stylos longe superantia.”) According to the same author,
none of the species which inhabit America and the Cape of Good Hope are
heterostyled.
I have examined only three homostyled species, namely, L. usitatissimum,
angustifolium, and catharticum. I raised 111 plants of a variety of the first-
named species, and these, when protected under a net, all produced plenty of
seed. The flowers, according to H. Muller, are frequented by bees and moths.
(3/9. ‘Die Befruchtung der Blumen’ etc. page 168.) With respect to L.
catharticum, the same author shows that the flowers are so constructed that they
can freely fertilise themselves; but if visited by insects they might be cross-
fertilised. He has, however, only once seen the flowers thus visited during the
day; but it may be suspected that they are frequented during the night by small
moths for the sake of the five minute drops of nectar secreted. Lastly, L.
Lewisii is said by Planchon to bear on the same plant flowers with stamens and
pistils of the same height, and others with the pistils either longer or shorter
than the stamens. This case formerly appeared to me an extraordinary one; but I
am now inclined to believe that it is one merely of great variability. (3/10.
Planchon in Hooker’s ‘London Journal of Botany’ 1848 volume 7 page 175. See on
this subject Asa Gray in ‘American Journal of Science’ volume 36 September 1863
page 284.)
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