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Show 8 INTRODUCTORY REMARKS. CHAP. I. truth and generality of the law, so as to insist on it and impress their belief on others. In 1862 I summed up my observations on Or hids by saying that nature "abhors perpetual self-fertilisation." If the word perpetual had been mi tted, the aphorism would have been false. As it stand~, I believe that it is true, though perhaps rath r too strongly expressed ; and I should hav add cl the self-evident proposition that the propagation of ihe species, whether by self-fertilisation or by cro -fertilisation, or asexually by buds, stolons, &c. is of paramount ilnportance. Hermann Miill r has d ne exc llent service by insisting repeatedly on this latter p int. It often occurred to me that it would b advisable to try whether seedlings from cross-fertili r<l flow rs were in any way superior to those from self-fertili cl flowers. But as no instance was known with animals of any evil appearing in a single generation fro1n the closest possible interbreeding, that is between brothers and sisters, I thought that the sa1ne rule w uld hold good with plants ; and that it would be n s ary at the sacrifice of too much time to s If-fertilise and intercross plants during several Ruccessive generation.·, in order to arrive at any result. I ought to have reflected that such elaborate provisions favourina crossfertili~ ation, as we see in innumerable plants~ would n?t have bee~ acquired for the Rake of gainino· a d1stan~ and s.hght advantage, or of avoiding a distant ~n~ shght ev1l. Moreover, the £ rtilisation of a. flower Y Its own pollen corresponds to a closer fonn of interbr:- eding than is possible with ordinary bi-sexual mumals; so that an earlier result might have b on expected. . I was at last l~d to make the experiments recorded In the present volume from the following circumstance. CHAP. I. INTRODUCTORY REMARKS. 9 For the sake of determining certain points with respect to inheritance, and without any thoug~t of the effects of close interbreeding, I raised close together two large beds of self-fertilised and crossed seedlings from the same plant of Linaria vulgaris. To my surprise, the crossed plants when fully grown were plainly taller and more vigorous than the self-fertilised ones. Bees incessantly visit the flowers of this Linaria and carry pollen from one to the other ; and if insects are exeluded, the flowers produce extremely few seeds ; so that the wild plants from which my seedlings were raised must have been intercrossed during all previous generations. It seemed therefore quite incredible that the difference between the two beds of seedlings could have been due to a single act of self-fertilisation ; and I attTibuted the result to the self-fertilised seeds not having been well ripened, improbable as it was that all should have been in this state, or to some other accidental and inexplicable cause. During the next year, I raised for the same purpose as before two large beds close together of self-fertilised and crossed seedlings from the carnation, Dianthus caryophyllus. This plant, like the Linaria, is almost sterile if insects are excluded; and we may draw the same inference as before, namely, that the parent-plants must have been intercrossed during every or almost every ·previous generation. Nevertheless, the self-fertilised seedlings were plainly inferior in height and vigour to the crossed. My attention was now thoroughly aroused, for I could hardly doubt that the difference between the two beds was clue to the one set being the offspring of crossed, and the other of self-fertilised flowers. Accordingly I selected almost by hazard two other plants, which happened to be in flower in the greenhouse, namely, |
