| OCR Text |
Show 320 DARWINISM CHAP. Chile, where humming-birds are especially plentiful, ~ve find. great numbers of rod tubular flowers, often of large size and. apparently adapted to these. li~tle creatures. . Su~h are the beautiful Lapageria and Philesia, the. grand Pitca~rneas, and the genera Fuchsia, Mitraria, Embothrmm, Escalloma, D~sfontainea, Eccremocarpus, and many Gesneracere. Amono tho most extraordinary modifications of flower structure adapted. FIG. 31.-Humming-bird fertilising Marcgravia nepenthoidcs. to bird fertilisation are the species of Marcgravia, in which the pedicels and bracts of the terminal porti~n of a pen~ent bunch of flowers have been modified into pitchers whiCh secrete nectar and attract in ects, while birds feeding on the nectar, or insects, have the pollen of the overhanging flowers dusted on their backs, and, carrying it to other flowers, thus crossfertilise them (see Illustration). , In Australia and New Zealand the fine " glory peas (Clianthus), the Sophora, Loranthus, many Epacrid.on' :md Myrtacere, and the large flowers of the New Zealand flax XI THE SPECIAL COLOURS OF PLANTS 321 (Phormium ton ax), are cross-fertilised. by birds ; w hilo in Natal the fi~e trumpet-creeper (Tocoma capensis) is fertilised by N ectanncas. The great extent ~o which insect and bird nPcncy is necessary to flowers 1s well shown by the ca c of New Zca_land. The c?tire ~ountry is comparatively poor in species of msccts, especially m bees and butterflies which arc the chief flower fertilisers ; yet according to the rescn.rchcs of local botanists no less than one-fourth of all the flowerirw plants are incaJ?able of sel~-ferti1isation, and, therefore, wholl; dependent on msect or bircl agency for the continuance of the species. The facts as to the cro s-fertilisation of flowers which Jmvc now been very briefly summarised, taken in connection with Darwin's experiments proving the increased vicrour and fertility _given by cross-fertilisation, seem amply to justify his aphonsm that "Nature ahhors self-fertilisation," and his more precis,~ statcn:ent~ that, "No plant is perpetually self-fertilIsed; and this v1ew has boon upheld by Hildebrand Delpino and other botanists. I ' ' Self-Fertilisation of Flowers. But all this time we have been only looking n.t one side of the question, for thet'c exists an abundance of facts which seem to imply, just as surely, the utter uselo sness of cro - fertilisation. Let us, then, see what tho o facts arc before proceeding further . . . 1. An imm~nse variety o~ plants are habitunJly self-fertilised, and thmr numbers probably far exceed those which are habitually cross-fertilised by insects. Almost all tho very small or obscure flowered plants with hermaphrodite flowers are . ~f this kind. Most of these, however, may be insect fertilised occasionally, and may, therefore, come under the rule that no species are perpetually self-fertilised. 2. There ar~ many plants, however, in which special arrangements exist to secure self-fertilisation. Sometimes the ?orolla closes and brings the anthet's and stigma into contact; m others the. anthers cluster round the stigmas, both maturing together, as m many buttercups, stitchwort (Stellaria meuia), 1 See H. Muller's Fe1·tilisation of Flcnvers, p. 18. y |
