Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.

Date:: 1875

Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$While in the very numerous diclinous, dichogamous, dimorphic, and trimorphic flowers, insects carry pollen from one flower to another, it is comparatively rare for cross-pollination to take place without the help of insects. This occurs in some Urticacese, as Pilea and Broussonelia, where the anthers emerge suddenly from the bud and scatter their light pollen in the air like a fine cloud of dust, which is then blown to the female organs of other flowers. In the rye the arrangement is still simpler; the flowers open separately, usually in the morning; the filaments elongate rapidly and push the ripe anthers out of the pales ; the anthers then hang down at the end of the long filaments, open, and allow the heavy pollen to fall down, thus reaching the stigmas of other flowers lower down in the same spike or in neigh- bouring spikes, being assisted in this by the oscillations of the haulm under the influence of the wind1. In connection with the tendency so clearly evidenced even among Cryptogams, and still more among Phanerogams, to prevent self-fertilisation within the same hermaphrodite flower, it is a very remarkable fact that there are a number of plants among Angiosperms which form two kinds of hermaphrodite flowers, viz. large flowers which can generally be fertilised by the pollen of other flowers, and small, more or less depauperated flowers, sometimes underground, which never open \Clei- stogavious Flowers], the pollen emitting its tubes immediately from the anthers and thus fertilising the ovules. There occur therefore in these cases different kinds of flowers on the same individual, one kind being adapted for cross-, the other kind exclusively for self-fertilisation2. This occurs, for example, in Oxalis Acelosella, where the small flowers are formed close to the ground when the larger flowers have already ripened their fruit ; in Impaiiens Noli-me-tangere, Lamium amplexicaule, Specularia perfoliata, many species of Viola, as V. odorata, elatior, canina, mirabilis, See., Ruellia clandesiina, many Papilionaceae, as Amphicarpaea, and Voandzeia, Com- melyna bengalensis, Sec. When in these cases the large typically developed flowers are fertile, cross-fertilisation with other flowers of the same species must happen occasionally in the course of generations, and the small depauperated self-fertilised flowers then seem to be a subsidiary contrivance whose purpose is altogether un- known. It is however remarkable, and apparently in contradiction to the general rule, that the large normal flowers sometimes exhibit a tendency to infertility (as in species of Viola) or are altogether unfruitful (as in Voandzeia), so that reproduction depends in such cases mainly or entirely on the cleistogamous self-fertilised flowers. But since there are many questions in connection with this subject that are not yet solved, these rare exceptions cannot overthrow the general law3. 1 [For a detailed account of the very remarkable phenomena connected with the pollination of rye and other cereals, see Hildebrand in Gardener’s Chronicle, March 15 and 22, and May 24, 1873; also A. S. Wilson, Trans. Bot. Soc. Edin. XI, 506 and XII, 84. Flowers the pollination of which is effected by the wind are termed anemophilous, in contradistinction to the entomophilous, or those pollinated by the agency of insects.—Ed.] 2 H. v. Mohl, Einige Beobachtungen iiber dimorphe Bliithen, Bot. Zeit. 1863, Nos. 42, 43. [See also A. W. Bennett on the closed self-fertilised flowers of Impatiens in Journ. Linn. Soc. 1872, p. 147; ditto, Pop. Sci. Rev. 1873, p. 337. In Juncus bufonius the pollen-tubes are emitted while the pollen-grains are still enclosed in the anther, perforating the wall of the latter.—Ed.] 3 [Herrmann Muller (Nature, vol. VIII, p.433 et seq.) has pointed out the existence of another kind of dimorphism, in which a species presents two different forms of flowers, one adapted to self-$