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
on both stigmas is ascertained. Several other species of Rhamnus are said to be
dioecious or sub-dioecious. (7/10. Lecoq ‘Geogr. Bot.’ tome 5 1856 pages 420-
26.) On the other hand, R. frangula is an ordinary hermaphrodite, for my son
found a large number of bushes all bearing an equal profusion of fruit.
Epigaea repens (ERICACEAE).
This plant appears to be in nearly the same state as Rhamnus catharticus. It is
described by Asa Gray as existing under four forms. (7/11. ‘American Journal of
Science’ July 1876. Also ‘The American Naturalist’ 1876 page 490.) (1.) With
long style, perfect stigma, and short abortive stamens. (2.) Shorter style, but
with stigma equally perfect, short abortive stamens. These two female forms
amounted to 20 per cent of the specimens received from one locality in Maine;
but all the fruiting specimens belonged to the first form. (3.) Style long, as
in Number 1, but with stigma imperfect, stamens perfect. (4.) Style shorter than
in the last, stigma imperfect, stamens perfect. These two latter forms are
evidently males. Therefore, as Asa Gray remarks, “the flowers may be classified
into two kinds, each with two modifications; the two main kinds characterised by
the nature and perfection of the stigma, along with more or less abortion of the
stamens; their modifications, by the length of the style.” Mr. Meehan has
described the extreme variability of the corolla and calyx in this plant, and
shows that it is dioecious. (7/12. “Variations in Epigaea repens” ‘Proc. Acad.
Nat. Soc. of Philadelphia’ May 1868 page 153.) It is much to be wished that the
pollen-grains in the two male forms should be compared, and their fertilising
power tried on the two female forms.
Ilex aquifolium (AQUIFOLIACEAE).
In the several works which I have consulted, one author alone says that the
holly is dioecious. (7/13. Vaucher ‘Hist. Phys. des Plantes d’Europe’ 1841 tome
2 page 11.) During several years I have examined many plants, but have never
found one that was really hermaphrodite. I mention this genus because the
stamens in the female flowers, although quite destitute of pollen, are but
slightly and sometimes not at all shorter than the perfect stamens in the male
flowers. In the latter the ovary is small and the pistil is almost aborted. The
filaments of the perfect stamens adhere for a greater length to the petals than
in the female flowers. The corolla of the latter is rather smaller than that of
the male. The male trees produce a greater number of flowers than the females.
Asa Gray informs me that I. opaca, which represents in the United States our
common holly, appears (judging from dried flowers) to be in a similar state; and
so it is, according to Vaucher, with several other but not with all the species
of the genus.
GYNO-DIOECIOUS PLANTS.
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