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Show 4 INTRODUO'rORY REMARKS. CIIAP. I. same stock two kinds of flowers. The flowers of tho one kind are minute and completely closed, so that they eannot possibly be crossed; but they are abundantly fertile, although producing an . extremely small quantity of pollen. The flowers ~f the other kind produce n1uch pollen and are open; and these can be, and often are, cross-fertilised. Hermann Mull r has also made. the remarkable discovery that there ar some plants . which exist under two forms; that is, produce on distinct stocks two kinds of hermaphrodite flowers. The one form bears small flowers constructed for self-fertilisation; whilst the other bears larg r and n1uch more conspicuous flowers plainly constructed for cross-fertilisation by the aid of insects; and without their aid these produce no seed. The adaptation of flowers for cross-fertilisation is a subject which has interested me for the last thirtyseven years, and I have collected a larae mass of ob- . b b servat1ons, ut these are now rendered superfluous by t~e many excellent works which have been lately pubhshed. In the year 1857 I wrote* a short pap r on the fertilisation of the kidney bean ; and in 1862 my work 'On the Contrivances by which British and Foreign Orchids are Fertilised by Insects' appeared. It seemed to me a better plan to work out one oToup o.f plants as_ ~arefully as I could, rather than tob pubhsh many miscellaneous and imperfect observations. ~Iy ~res~nt ":ork is the complement of that on Orchids, In whwh it was shown how admirably these plants are co:nstructed so as to permit of, or to favour, or to necessitate cross-fertilisation. The adaptations * 'Gardeners' Chronicle' 1857 p. 725, and 1858, pp. 824 a~d 844: 'Annals and Mng. of Nat. Hist.' 3rd series, vol. ii. 1858, p. 462. 0HAP. I. INTRODUCTORY REMARKS. 5 for cross-fertilisation arc perhaps more obvious in the Orchidere than in any other group of plants, but it is an error to speak of them, as some authors have done, as an exceptional case. The lever-like action of the stamens of Salvia (described by Hildebrand, Dr. vV. Ogle, and others), by which the anthers are depressed and rubbed on the backs of bees, shows as perfect a structure as can be found in any orchid. Papilionaceous flowers, as described by various authors-for instance, by Mr. T. H. Farrer-offer innumerable curious adaptations for cross-fertilisation. The case of Posoqueria fragrans (one of the Rubiacea: ), is as wonderful as that of the most wonderful orchid. The stamens, according to Fritz 1\fiiller, * are irritable, so that as soon as a moth visits a flower, the anthers explode and cover the insect with pollen ; one of the filaments which is broader than the others then moves and closes the flower for about twelve hours, after which time it resumes its original position. Thus the stig1na cannot be fertilised by pollen from the same flower, but only by that brought by a moth from some other flower. Endless other beautiful contrivances for this same purpose could be specified. Long before I had attended to the fertilisation of flowers, a remarkable book appeared in 1793 in Germany, 'Das Entdeckte Geheimniss der N atur,' by C. IC Sprengel, in which he clearly proved by innumerable observations, how essential a part insects play in the fertilisation of 1nany plants. But he was in advance of his age, and his discoveries were for a long time neglected. Since the appearance of my book on Orchids, many excellent works on the fertilisation of flowers, such as those by Hildebrand, Delpino, Axell, * 'Botanische Zeitung,' 1866, p. 129. |