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Show 146 LAWS OF VARIATION. CHAP. v. . so far-fetched, as it may at first these two orders, Ish d ntageous natural selection d if it e a va ' . appear : an . la But in regard to the differ-may have come I~to p Yl· d external structure of the b h · the mterna an . ences ot ill 1 correlated with any differ-seeds, which are not ~ way~s impossible that they can ences in the flowers, I see to the plant : yet in the . ay advantageous . be In any w diffi ces are of such apparent Im- Umbelliferro thesed ber~n in some cases, according to t e-the see s eillg . d por anc . the exterior flowers an coo- Tausch, ort~ospermo::t:l flowers,-that the elder De lospermous In dth; ~· main divisions of the order on Oandolle fo~ e IS H ce we see that modifica- 1 s differences. en hi h ana ogou . ed by systematists as of g tions of structure,llVIedw t unknown laws of correlated 1 ay be who y ue o h vgaro uwet,h m, a nd W.i thout b ei.l lg, ~s far as we can see, of t e 1' ht t service to the spemes. h s IgW es ft n falsely attribute to correlation of gro~ ' e may o e 1 f species structures which are commo~ to ~h~:e grt~u1:{eritance ; and which in truth are simp y . d tt..-·ough . ·t ay have acqurre ru for an anmen~ progeni or m dification in structure, natural selection some one m? other and in· d after thousands of generations, some . . an ' . d th two modificatiOns, dependent modification ; an h ~e of descendants having been transmitted to a w o e group h ht to be with diverse habits, would naturally beSt oug . I do correlated i·l l some necessar· y manner. . o, agoacmcu, n·ing t d bt that some apparent correlations, no ou . 1 due to the manner throughout whole orders, are ~ntrre y For instance, alone in which natural selection can act.. d seeds are Alph. De Oandolle has re:narked that ~g: should exnever found in fruits which do not ope . t adually plain the rule by the fact that seeds c?uld no ~rin fruits become winged through natu.radl.s~~ect~opni::~se·~roducing which opened; so that the m IVl ua CHAP. v. CORRELATION OF GROWTH. 147 seeds which were a little better fitted to be wafted further, might get an advantage over those producing seed less fitted for dispersal ; and this process could not possibly go on in fruit which did not open. The elder Geoffroy and Goethe propounded, at about the same period, their law of compensation or ba1ancement of growth ; or, as Goethe expressed it, "in order to spend on one side, nature is forced to economise on the other side." I think this holds true to a certain extent with our domestjc productions: if nourishment flows to one part or organ in excess, it rarely flows, at least in excess, to another part ; thus it is difficult to get a cow to give much milk and to fatten readily. The same varieties of the cabbage do not yield abundant and nutritious foliage and a copious supply of oil-bearing seeds. When the seeds in our fruits become atrophied, the fruit itself gains largely in size and quality. In our poultry, a large tuft of feathers on the head is generally accompanied by a diminished comb, and a large beard by diminished wattles. With species in a state of nature it can hardly be maintained that the law is of universal application; but many good observers, more especially botanists, believe in its truth. I will not, however, here give any instances, for I see hardly any way of distinguishing between the effect.s, on the one hand, of a part being largely developed through natural selection and another and adjoining part being reduced by this same process or by disuse, and, on the other hand, the actual withdrawal of nutriment from one part owing to the excess of growth in another and adjoining part. I suspect, also, that some of the cases of compensation which have been advanced, and likewise some other facts, may be merged under a more general principle, namely, that natural selection is continually trying to economise in every part of the organisation. If under H2 |