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Show 242 ILLEGITIMATE OFFSPRING OF CHAP. v. afterwards legitimately with pollen from a short-styled dark-red polyanthus which is a variety of !· veris; and the result was that every one of the thnty seed~ lings thus raised bore flowers mor~ ?r less rod, show~ ing plainly how prepotent the legrt1mato pollen from a short-styled plant was over the illegitimate polleu from a long-styled plant. In all the severaL foregoing points the parallelism is wonderfully close between the effects of illegitimate and hybrid fertilisation. It is hard~y an. e.xaggoration to assert that seedlings from an 1llogttnnately fertilised heterostyled plant are hybrids for1ned within the lirnits of one and the same species. This conclusion is important, for we thus learn that the difficulty in sexually uniting two organic forms and tho sterility of their offspring, afford no sure criterion of so-calleu specific distinctness. If any one were to ?ross two varieties of the same· form of Lythrum or Pnmula for the sake of ascertaining whethe1, they were specifically distinct, and he found that they could be united onJy with some difficulty, that their offspring were extremely sterile, and that the parents and their offspring ~·esembled in a whole series of relations crossed speCies and their hybrid offspring, he n1ight maintain that.his varieties had been proved to be good and true speCies; but he would be completely deceived. In the seco~<l place, as the forms of the same trimorphic or dirnorphw heterostyled species are obviously identical in gene:·al structure, with the exception of the reproduc~Ive organs, and as they are identical in general constitl~tion (for they live under precise! y the sa1ne condi· tions ), the sterility of their illegitimate unions and that of their illegitimate offspring, must depend ex· elusively on the nature of the sexual elemen~s anc: on their incornpatibility for uniting in a partwulaJ CnAP. V. HETEROSTYLED PLANTS. 243 manner. And as we have just seen that distinct species when crossed resemble in a whole series of relations the forms of the same species when illegitimately united, we are led to conclude that the sterility of the former must likewise depend exclusively on the incompatible nature of their sexual elements, and not on any general difference in constitution or structure. We are, indeed, led to this same conclusion by the impossibility of detecting any differences sufficient to account for certain 'species crossing with the greatest ease, whilst other close I y allied species cannot be crossed, or can be crossed only with extreme difficulty. We are led to this conclusion still more forcibly by considering the great difference which often exists in the facility of crossino- . l b remproca ly the same two species; for it is manifest in this case that the -result must depend on the nature of the sexual elements, the male elernent of the one species acting freely on the female element of the other, but not so in a reversed direction. And now we see that this same conclusion is independently and strongly fortified by the consideration of the illegitimate unions of trimorphic and dimorphic heterosty led plan~s .. In so complex and obscure a subject as hybridIsm It Is no slight gain to arrive at a definite conclus~ on, na~ely, that we must look exclusively to functional drfferences in the sexual elements, as the cause of the sterility of species when :first crossed and of their hybrid offspring. It was this consideration which led me to make the many observations recorded in this chapter, and which in my opinion make them worthy of publication. R 2 |