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Show ..._ - - - 4• ~ .. 272 DEFINITE ACTION OF TilE CHAP. XXIII. following chapter. vVe know, however, far too littl~ of .the causes and laws of variation to make a sound classific~twn. The direct action of the conditions of life, whether leadmg to definite or indefinite results, is a totally distinct consideration from the effects of natural selection ; for natural selection depends on the survival under various and complex circ~mstances of the best-fitted individuals, but has no relatwn whatever to the primary cause of any mo~fication of structure. I will first give in detail all the facts whwh I have been able to collect, rendering it probable that climat~, fo_od, &c., have acte~ so definitely and powerfully on the orgamsatwn of our domesticated productions, that they have sufficed t.o form new subvarieties or races, without the aid of selectwn by man or of natural selection. I will then give the facts and considerations opposed to this conclusion, and finally we will weigh, as fairly as we can, the evidence on both sides. When we reflect that distinct races of almost all our domes-ticated animals exist in each kingdom of .Europe, and formerly even in each district of England, we are at first strongly inclined to attribute their origin to the definite action of the physical conditions of each country; and this has ?een ~he conclusion of many authors. But we should bear m mmd that man annually has to choose which animals shall be preserved for breeding, and which shall be slaughtered. vVe have also seen that both methodical and unconscious selection ·were formerly practised, and are now occasionally practised by the most barbarous races, to a much greater extent than might have been anticipated. Hence it is very difficult to judge bow far the difference in conditions between, for instance, the several districts in England, could have sufficed without the aid of selection to modify the breeds which have been reared in each. It may be argued that, as numerous wild animals and plants have ranged during many ages throughout Great Britain, and sWI retain the same character, the difference in conditions between the several districts could not have modified in so marked a manner the various native races of cattle, sheep, pigs, and horses. rrhe same difficulty of distinguishing between selection and the definite effects of the conditions of life, is encountered in a still higher degree when we compare closely allied natural CI IAP. XXIII. CONDITIONS OF LIFE. 273 forms, inhabiting two countries, such as North America and Europe, which do not differ greatly in climate, nature of soil, &c., for in this case natural selection will inevitably and rigorously have acted during a long succession of ages. From the importance of the difficulty just alluded to, it will be advisable 1o give as large a body of facts as possible, showing that extremely slight differences in treatment, either in different parts of the same country, or during different seasons, certainly cause an appreciable effect, at least on varieties which arc already in an unstable condition. Ornamental flowers are good for this purpose, as they are highly vaTiablc, and are carefully observed. AU floriculturists are unanimous that certain varieties are affected by very slight differences in the nature of the artificial compost in which they are grown, and by the natural soil of the distTict, and by the season. Thus, a skilful judge, in writing on Carnations and Picotees/ asks "where can Admiral Cmzon be seen possessing the colour, size, and " sb·ength which it has in Derbyshire? Where can Flora's Garland be " found equal to those at Slough? Where do high-coloured flowers revel "better than at Woolwich and Birmingham? Yet in no two of these " districts do the same varieties attain an equal degree of excellence, "although each may be receiving the attention of the most skilful culti" vators." The same Wl'iter then recommends every cultivator to keep five different kinds of soil and manure, " and to endeavour to suit the "Tespective appetites of the plants you are dealing with, for without such " attention all hope of general success will be vain." So it is with the Dahlia: 2 the Lady Cooper rarely succeeds near London, but does admirably in other districts; the reverse holds good with other varieties; and again, there are others which succeed equally well in various situations. A skilful gardener 3 states that he procured cuttings of an old and well-known variety (pulcbella) of Verbena, which from having been propagated in a different situation presented a slightly different shade of colour ; the two varieties were afterwards multiplied by cuttings, being carefully kept distinct; but in the second year they could hardly be distinguished, and in the third year no one could distinguish them. The nature of the season has an especial influence on certain varieties of the Dahlia : in 1841 two varieties were pre-eminently good, and the next year these same two were pre-eminently bad. A famous amateur 4 asserts that in 1861 many varieties of the Rose came so untrue in character, "that it was hardly possible to recognise them, and the thought " was not seldom entertained that the grower had lost his tally." The same amateur 5 states that in 1862 two-thirds of his Auriculas produced central trusses of flowers, and these are remarkable from not keeping tnw; 1 'Gardener·:; Chronicle,' 1853, p. 183. 2 Mr. Wildman, 'Floricultural Soc.,' Feb. 7, 1843, reported in' Gard. Chron.,' 1843, p. SG. VOL. II. 3 Mr. Robson, in 'Journal of Horticulture, · Feb. 13th, ~SGG, p. 122. 4 ' J ournal of Horticulture,· 1861, p. 24. s Ibid., 1802, p. 83. ·r |
