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Show 142 LAWS OF V .A.RI.A.TION. CHAP. v. tious in transposing animals from one district to another ; for it is not likely that man should have succeeded in selecting so many breeds and sub-breeds with constitutions specially fitted for their own districts: the result must, I think, be due to habit. On the other hand, I can see no reason to doubt that natural selection will continually tend to preserve those individuals wbieh are born with constitutions best adapted to their native countries. In treatises on many kinds of cultivated plants, certain varieties are said to withstand certain climates better than others: this is very strikingly shown in works on fruit trees published in the United States, in which certain varieties are habitually recommended for the northern, and others for the southern States ; and as most of these varieties are of recent origin, they cannot owe their constitutional differences to habit. The case of the Jerusalem artichoke, which is never propagated by seed, and of which consequently new varieties have not been p:r;oduced, has even been advanced-for it is now as tender as ever it was-as proving that acclimatisation cannot be effected ! The case, also, of the kidney-bean has been often cited for a similar purpose, and with much greater weight ; but until some one will sow, during a score of generations, his kidney-beans so early that a very large proportion are destroyed by frost, and then collect seed from the few survivors, with care to prevent accidental crosses, and then again get seed from these seedlings, with the same precautions, the experiment cannot be said to have been even tried. Nor let it be supposed that no differences in the constitution of seedling kidney-beans ever appear, for an account has been published how much more hardy some seedlings appeared to be than others. On the whole, I think we may conclude that habit, CHAP. v. CORRELATION OF GROWTH . 143 use, and disuse, have, in some cases 1 . able part in the d'fi . ' P ayed a consider-of the structure ofmo ~ cation of the constitution, and vanous organs . b t th t h of use and dI' suse h ave often b ' uI a t e effects ~th, a~d sometimes overmasteredeen argely combined twn of Innate differen ces. by, the natural selecCorrelation oif Growt z I th n.- mean by th · . at the whole organisat' . . JS expression growth and developmen~o~~s tso tied t~gether· during its any one part occur and ' a when slight variations in selection, other p;rts bare accumu!ated through natural . ecome modified Thi . Important subject mo t . · s IS a very most ob . ' . s Imperfect! y understood Th VIous case IS that di . . e solely for the good of' th mo fications accumulated safely be concluded a:ffi et ~~ung or larva, will, it may in the same manner' ec e structure of the adult . as any mal t · ' the early embryo seriou I con ormation affecting tion of the adult ' Th s y affects the whole organisa- . e several part f th b are homologous and hi h s 0 e ody which . ' w c , at an early b · are alike seem li'abl t . em ryoniC period ' e 0 Vary I 11' d ' ~ee this in the right and left . n an a Ie manner : we In the same manner. I·n th sfides of the body varying even m· the jaws an'd 1' b e ront and hin d 1e gs, and lower jaw is believed ti bm hs, varying together, for the Th o e omolog 'th ese tendencies' I d o no t d oubt ous WI b the limbs· more or less complete! b ' may e master d family of t Y Y natural selection · thu . sags once existed with .· s a one Bide . and if thi. h d b an antler only on b ' s a een of reed it might probabl h b any great us to the by natural selection. y ave een rendered p !'man nt Homologous part h authors, tend to coh:~e ~s th ~s .been remarked by som plants; and nothing . ' IS Is often s n in monstrous h Is more commo th h omologous parts in I n an t e union of norma structures as th u . f ' niOll 0 |
