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
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Licence: Public Domain Mark

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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    In other cases, as in most Fumariacese, Canna indica, Salvia hirta, Limim nsita- tissimum, Draba ver?7a, Brassica Rapa, Oxalis micrantha and sensiliva, the pollen must also, according to Hildebrand, owing to the position of the sexual organs, fall on the stigma in the same flower, and is potent; but in such cases, since the flowers are visited by insects, an occasional crossing with other flowers is not impossible. Even among Orchidese, where we find the most wonderful contrivances to prevent self-fertilisation, Darwin found an instance in Cephalanthera grandiflora in which the pollen-tubes are emitted from the pollen-grains on to the stigma while the former are still in the anthers ; but according to Darwin’s experiments the number of good seeds produced is smaller when the plant is allowed to fertilise itself than when pollination is effected by foreign pollen with the help of insects. A clear comprehension of the phenomena of dichogamy, dimorphism, and the other contrivances for ensuring cross-fertilisation, can only be obtained by a careful study of numerous individual cases1. It is more clearly seen in the fertilisation of flowers than almost anywhere else how exactly the development of the organs is adapted to the fulfilment of a perfectly definite purpose. Each plant has its own peculiar contrivance for the conveyance of the pollen to the stigma of another flower. It is not possible to make many general remarks on this subject; the following may suffice here. It must be noted in the first place that insects2 carry pollen undesignedly while seek- ing the nectar of flowers which has been produced exclusively for their attraction. Flowers which are not visited by insects, and Cryptogams which do not require them, do not secrete any nectar. The position of the nectaries, usually concealed deep at the bottom of the flower, as well as the size, form, arrangement, and often also the movement of the parts of the flower during the time of pollination, are always of such a nature that the insect—sometimes of one particular species—must take up particular positions and make particular movements in obtaining the nectar, and thus cause the masses of pollen to fertilisation, smaller and less brightly-coloured, growing in situations where there are but few insects, the other adapted to cross-fertilisation, larger and more brightly-coloured, growing where insects abound. These two forms have occasionally been described as distinct varieties or even species. —Ed.] 1 See especially K. C. Sprengel, Das neu entdeckte Geheimniss der Natur, &c., Berlin, 1793.— Darwin, On the Fertilisation of Orchids, London, 1862.—Hildebrand, Die Geschlechterverthcilung bei den Pflanzen, u. das Gesetz der vermiedenen u. unvortheilhaften stetigen Selbstbefruchtung, Leipzig, 1867.—Strasburger in Jenaische Zeitschrift, vol. VI, 1870, and Jahrb. fiir wiss. Bot. vol. VII, where the mode of fertilisation of Gymnosperms, Marchantiere, and Ferns is described. [The most complete account of the phenomena of the reciprocal adaptation of flowers and insects to cross-fertilisation is contained in Herrmann Muller’s Befruchtung derBlumen durch Insecten u.die gegenseitigen Anpassungen beider, Leipzig, 1873, where also is a resume of the literature of the sub- ject. See also Kiilreuter, Vorliiufige Nachricht von einigen das Geschlecht betreffenden Versuchen, Leipzig, 1761.—Delpino, Ulteriori osservazioni sulla dicogamia, Milan, 1868-1870.—Axell, Om Anordningama for fanerogama vaxternas befruktning, 1869.—Darwin, On the Agency of Bees in the Fertilisation of Papilionaceous Flowers, Ann. and Mag. Nat. Hist. 3rd series, vol. II, p. 461. —Ogle in Pop. Sci. Rev. 1869, p. 261, and 1870, p. 45 (on Salvia).—Hildebrand in Leopoldina, 1869 (Composite) ; ditto, in Monatsber. der Berlin. Akad. 1872 (Grasses).—Farrer in Ann. and Mag. Nat. Hist. 1868; Nature, vol. VI, 1872, p. 478 et seq. (Papilionacere).—A. W. Bennett, in Pop. Sci. Rev. 1873, p. 337.—PI. Muller, in Nature, vols. VIII, IX, and X.—Sir J. Lubbock, On British Wild Flowers considered in relation to Insects, London, 1875.—Ed.] a J. G. Kolreuter first recognised the necessity of insect help, and described special contrivances for pollination, in his Vorlaufige Nachricht von einigen das Geschlecht der Pflanzen betreffenden Versuchen, 1761.