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
Three long-styled and three short-styled plants were protected under separate
nets, and they produced altogether only 8 berries, containing on an average only
1.5 seed. Some additional berries were produced which contained no seeds. The
plants thus treated were therefore excessively sterile, and their slight degree
of fertility may be attributed in part to the action of the many individuals of
Thrips which haunted the flowers. Mr. J. Scott informs me that a single plant
(probably a long-styled one), growing in the Botanic Gardens at Edinburgh, which
no doubt was freely visited by insects, produced plenty of berries, but how many
of them contained seeds was not observed.
Borreria, nov. sp. near valerianoides (Rubiaceae).
Fritz Muller sent me seeds of this plant, which is extremely abundant in St.
Catharina, in South Brazil; and ten plants were raised, consisting of five long-
styled and five short-styled. The pistil of the long-styled flowers projects
just beyond the mouth of the corolla, and is thrice as long as that of the
short-styled, and the divergent stigmas are likewise rather larger. The anthers
in the long-styled form stand low down within the corolla, and are quite hidden.
In the short-styled flowers the anthers project just above the mouth of the
corolla, and the stigma stands low down within the tube. Considering the great
difference in the length of the pistils in the two forms, it is remarkable that
the pollen-grains differ very little in size, and Fritz Muller was struck with
the same fact. In a dry state the grains from the short-styled flowers could
just be perceived to be larger than those from the long-styled, and when both
were swollen by immersion in water, the former were to the latter in diameter in
the ratio of 100 to 92. In the long-styled flowers beaded hairs almost fill up
the mouth of the corolla and project above it; they therefore stand above the
anthers and beneath the stigma. In the short-styled flowers a similar brush of
hairs is situated low down within the tubular corolla, above the stigma and
beneath the anthers. The presence of these beaded hairs in both forms, though
occupying such different positions, shows that they are probably of considerable
functional importance. They would serve to guard the stigma of each form from
its own pollen; but in accordance with Professor Kerner’s view their chief use
probably is to prevent the copious nectar being stolen by small crawling
insects, which could not render any service to the species by carrying pollen
from one form to the other. (3/23. ‘Die Schutzmittel der Bluthen gegen
unberufene Gaste’ 1876 page 37.)
Public-domain text, read in full here on John Shaqi.
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