Carrière[193] says that a plant of _Stauntonia latifolia_ which for some years produced stamens only, now produces flowers of both sexes; it was dioecious, but is now monoecious. The same author alludes to a similar occurrence in _Juniperus Virginiana_. The hops is also said to vary in sexual characteristics from time to time.[194] In addition to the genera, already named, in which this production of flowers of both sexes has been observed may be mentioned _Taxus! Gunnera! Urtica! Mercurialis! Restio! Cannabis! Salix! Humulus!_ as well as others in which the change is less frequent.
Among cryptogams a similar change occurs. As an illustration may be cited _Leucobryum giganteum_, as quoted from Müller in Henfrey's 'Botanical Gazette,' i, p. 100.
As to androgynous willows, in addition to the references given under the head of Substitution of stamens for pistils, see Schlechtendal, 'Flora Berol.,' ii. p. 259. Tausch, 'Bot. Zeit.,' 1833, i. p. 229. Koch, 'Synops. Flor. Germ.,' 740. Host, 'Flor. Aust,.' ii, p. 641 (_S. mirabilis_). See also Hegelmaier, 'Württemberg Naturwissenshaft Jahreshefte,' 1866, p. 30. Other references to less accessible works are given in 'Linnæa,' xiv, p. 372.
=Change from hermaphroditism to unisexuality.=--Many flowers ordinarily hermaphrodite as to structure, become unisexual by the abortion or suppression of their stamens, or of their carpels, as the case may be. This phenomenon is lessened in interest since the demonstration of the fact by Darwin and others, that many plants, structurally hermaphrodite, require for the full and perfect performance of their functions the cooperation of the stamens and pistils, belonging to different individuals of the same species.
Some of the _Ranunculaceæ_ constantly exhibit a tendency towards the dioecious condition, and the rarity with which perfect seeds of _Ranunculus Ficaria_ are formed is to be attributed, in great measure, to the deficiency of pollen in the anthers of these flowers. _Ranunculus auricomus_ also is frequently sterile. Specimens of _Ranunculus bulbosus_ may be met with in which every flower is furnished with carpels, most of which have evidently been fertilised, although there are no perfect stamens in the flowers.