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Show 94 DARWINISM CHAP. of the Rcutellro also vary. The eggs also vary somewhat in size and shape; and the amount of downy clothing on the young bird, when first hatched, differs very considerably. Finally, the attitude of the body, the manner of walking, the mode of flight, and the voice, all exhibit modifications of the most remarkable kind.1 A cclimatisation. A very important kind of variation is that constitutional change termed acclimatisation, which enables any organism to become gradually adapted to a different climate from the parent stock As closely allied species often inhabit different countries possessing very different climates, we should expect to find cases illustrating this change among our domesticated animals and cultivated plants. A few examples will therefore be adduced showing that such constitutional variation docs occur. Among animals the cases arc not numerous, because no systematic attempt has been made to select varieties for this special quality. It has, however, been observed that, though no European dogs thrive well in India, the Newfoundland doc.r originating from a severe climate, can hardly be kept aliv~~ A bet~er case, p~rhaps, is furnished by merino sheep, which, wh~n Imported directly from England, do not thrive, while tho e wluch have been bred in the intermediate climate of the Cape of Good Hope do much better. When geese were first introduced into Bogota, they laid few eggs at long intervals, and few of the young survived. By degrees, however, the fecundity ~ml?ro:ed, and in about twenty years became equal to what 1t IS m Europe. According to Garcilaso, when fowls were first introduced into Peru they were not fertile, whereas now they are as much so as in Europe. Plants furnish much more important evidence. Onr nursery~en distinguish in their catalogues varieties of frui ttrees _whwh a~e more or less hardy, and this is especially the case m ~menca, where certain va.r:etics only will stand the severe chm~te of Canada. There is one variety of pear, the Forelle, wh1ch both in England and France withstood frosts 1 This account of domestic pigeons is greatly condensed from Mr. Darwin's work already referred to. IV VARIA'l'ION UNDER DOMES'l'ICA'riON 95 that killed the flowers and lmcls of a.ll other kinds of pears. \Vhea.t, which i. grown over .·o brae a portion of. th world, has become ada.pted to special clima.tcs. Wheat Imported from Indi:~ and sown in good wheat soil in England produced the most meagre cars ; while wheat taken from France . to the \Vest Indian Islands produced either wholly barren sp1kes or spikes furnishQ(l with two or three miserable seed , while \Vest Indian seed by it: siue yielded an enormous harvest. The ora.nge was very tender when first introduced into Italy, and continued so as long as it was propagated by grafts, but when trees were raised from seed many of these were found to be hardier, and the orange is now perfectly acclimatised in Italy. wcet-pea.s (Lathyrus odoratus) imported from England to the Calcutta, Botanic Gardens produced few blossoms and no seed ; those from France ftowcr·ed a little better, but still produced no seed, but plants raised fr~~ seed bro.ught from Darjeelinrr in the Him:tbya., hnt ongmally denved from England, flower anJ seed _profusel:f in ~alcut~.1 An ob. erva.tion by Mr. Darwm lnmself 1s perhaps even more instructive. He says: "On 24th May 1864 there was a severe frost in Kent, and two rows of scarlet runners (Phaseolus multiflorus) in my ga.rclcn, containing 390 plants of the same arro and equally exposed, wore all blackened and killed except about a dozen pla.nts. In an adjoining row of Fulmer's dw<trf bean (Phaseolus vulgaris) one single plant escaped. A still more severe frost. occurred fo~r days afterwards, and of the dozen plants wh1ch had provwnsly ~scaped only three survived; these were not taller or more v1gorous than tho other young plant., but they escaped complet~ly, with not even the tips of their loaves browned. It was Impossible to behold these three plants, with their blackened, withered and dead brethren all n.rouud them, and not see a.t a glance 'that they differed widely in their constitutional power of resisting frost.' . . The preceding sketch of the vanat1on that occurs. am.on.g domestic animals and cultivated plants shows how Wide 1t 1s in range and how great in amount; and we have ~ood re~son to believe that similar variation extends to all orgamsed bemgs. In the class of fi hes, for example, we have one kind which has I Animals and Plants tmder Domestication, vol. ii. pp. 307-311. |