According to Torrey and Gray, the North American species
of Helianthemum, when growing in poor soil, produce only cleistogamic flowers.
The cleistogamic flowers of Specularia perfoliata are highly remarkable, as they
are closed by a tympanum formed by the rudimentary corolla, and without any
trace of an opening. The stamens vary from 3 to 5 in number, as do the sepals.
(8/17. Von Mohl 'Botanische Zeitung' 1863 pages 314 and 323. Dr. Bromfield
'Phytologist' volume 3 page 530, also remarks that the calyx of the cleistogamic
flowers is usually only 3-cleft, while that of the perfect flower is mostly 5-
cleft.) The collecting hairs on the pistil, which play so important a part in
the fertilisation of the perfect flowers, are here quite absent. Drs. Hooker and
Thomson state that some of the Indian species of Campanula produce two kinds of
flowers; the smaller ones being borne on longer peduncles with differently
formed sepals, and producing a more globose ovary. (8/18. 'Journal of the
Linnean Society' volume 2 1857 page 7. See also Professor Oliver in 'Natural
History Review' 1862 page 240.) The flowers are closed by a tympanum like that
in Specularia. Some of the plants produce both kinds of flowers, others only one
kind; both yield an abundance of seeds. Professor Oliver adds that he has seen
flowers on Campanula colorata in an intermediate condition between cleistogamic
and perfect ones.
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