INFLUENCE OF THE ORIGIN OF CELLS ON FERTILISATION. 8ll 



In Other cases, as in most Fumariaceae, Caji7ia indica, Salvia hirta, Linwn tisita- 

 tissimiim, Draha vetiia, Brassica Rapa, Oxalis viicraiitha and seiisifiva, 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 Orchidecc, where we find the most wonderful contrivances to prevent 

 self-fertilisation, Darwin found an instance in Cephahmthera 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 experim.ents 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 cases ^. 



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 insects 2 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.] 



^ See especially K. C. Sprengel, Das neu entdeckte Geheimniss der Natur, &c., Berlin, 1793. — ■ 

 Darwin, On the Fertilisation of Orchids, London, 1S62. — Hildebrand, Die Geschlechtervertheilung 

 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 Mliller's Befruchtung der Blumen durch Insecten u. die 

 gegenseitigen Anpassungen beider, Leipzig, 1873, where also is a resume of the literature of the sub- 

 ject. See also Kolrcuter, Vorliiufige Nachricht von einigen das Geschlecht betreffenden Versuchen, 

 Leipzig, i;6i. — Delpino, Ulteriori osservazioni sulla dicogamia, Milan, 1S68-1870. — Axell, Om 

 Anordningarna 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. 1S69, p. 261, and 1870, p. 45 (on Salvia). — Hildebrand in Leopoldina, 

 1869 (Compositce) ; ditto, in Monatsber. der Berlin. Akad. 1872 (Grasses).— Farrer in Ann. and Mag. 

 Nat. Hist. 1868; Nature, vol. VI, 1872, p. 478 et seq. (Papilionaceae). — A. W. Bennett, in Pop. Sci. 

 Rev. 1873, p. 337.— H. Miiller, in Nature, vols. VIII, IX, and X.— Sir J. Lubbock, On British Wild 

 Flowers considered in relation to Insects, London, 1875. — Ed.] 



^ J. G. Kolreuter first recognised the necessity of insect help, and described special contrivances 

 for pollination, in liis Vorlnufige Nachricht von einigen das Geschlecht der Pflanzen betreffenden 

 Versuchen, 1761. 



