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
Finally, although P. veris and vulgaris, when crossed legitimately, and
especially when their hybrid offspring are crossed in this manner with both
parent-species, were decidedly more fertile, than when crossed in an
illegitimate manner, and although the legitimate cross effected by Mr. Scott
between P. auricula and hirsuta was more fertile, in the ratio of 56 to 42, than
the illegitimate cross, nevertheless it is very doubtful, from the extreme
irregularity of the results in the various other hybrid crosses made by Mr.
Scott, whether it can be predicted that two heterostyled species are generally
more fertile if crossed legitimately (i.e. when opposite forms are united) than
when crossed illegitimately.
SUPPLEMENTARY NOTE ON SOME WILD HYBRID VERBASCUMS.
In an early part of this chapter I remarked that few other instances could be
given of a hybrid spontaneously arising in such large numbers, and over so wide
an extent of country, as that of the common oxlip; but perhaps the number of
well-ascertained cases of naturally produced hybrid willows is equally great.
(2/19. Max Wichura ‘Die Bastardbefruchtung etc. der Weiden’ 1865.) Numerous
spontaneous hybrids between several species of Cistus, found near Narbonne, have
been carefully described by M. Timbal-Lagrave (2/20. ‘Mem. de l’Acad. des
Sciences de Toulouse’ 5e serie tome 5 page 28.), and many hybrids between an
Aceras and Orchis have been observed by Dr. Weddell. (2/21. ‘Annales des Sc.
Nat.’ 3e serie Bot. tome 18 page 6.) In the genus Verbascum, hybrids are
supposed to have often originated in a state of nature (2/22. See for instance
the ‘English Flora’ by Sir J.E. Smith 1824 volume 1 page 307.); some of these
undoubtedly are hybrids, and several hybrids have originated in gardens; but
most of these cases require, as Gartner remarks, verification. (2/23. See
Gartner ‘Bastarderzeugung’ 1849 page 590.) Hence the following case is worth
recording, more especially as the two species in question, V. thapsus and
lychnitis, are perfectly fertile when insects are excluded, showing that the
stigma of each flower receives its own pollen. Moreover the flowers offer only
pollen to insects, and have not been rendered attractive to them by secreting
nectar.
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