INFLUENCE OF THE ORIGIN OF THE CELLS ON FERTILISATION. 909 



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 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^ 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 

 become attached to its hairs, feet, or proboscis, and afterwards, when assuming similar 

 positions, to be applied to the stigmas of other flowers. In dichogamous plants the 

 movements of the stamens, styles, or branches of the stigmas assist this end, taking place 

 frequently in such a way that at one time the open anthers occupy the same position 

 in the flower that the receptive stigmas do at another time, so that the insect, when 

 taking up the same position, touches the open anthers in one flower and the receptive 

 stigmas in another flower with the same part of its body. The same result is also ob- 

 tained in dimorphic flowers, the pollination being in these ca^es efficacious when anthers 

 and stigmas which occupy the same position in different flowers are made mutually to 

 act on one another. But there are besides many other contrivances, most variable in 

 their nature and often perfectly astonishing, for effecting the conveyance of pollen by 

 insects. ^ few examples may suffice. 



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

 Darwin, On the Fertilisation of Orchids, London 1862. — 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, Marchantieae, 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 Kolreuter, Vorlaufige Nachricht von einigen das Geschlecht betreffenden Versuchen, 

 Leipzig 1761. — Delpino, Ulteriori osservazioni suUa dicogamia, Milan 1868-1870. — 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. 1869, p. 261, and 1870, p. 45 (on Salvia). — Hildebrand in Leopoldina, 

 1869 (Compositae) ; 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.— H. Muller, in Nature, vols. VIII, IX, and X.— Sir J. Lubbock, On British 

 Wild Flowers considered in relation to Insects, London 1875.] 



2 J Q 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. 



