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Show 32G FERTILITY OF CROSSED CHAP. IX. fertilised flowers in the second table, G, being prouuced by self-fertilised par~nts, and the cro~sed flowers by crossed parents, which .In the later generations hacl become son1ewhat closely Inter-related, and had been subjected all the tin1e to nearly the same conditions. These two tables include fifty cases relating to thirty-two species. The flowers on Inany other species wero crossed and self-fertilised, but as only a few were thus treated, the results cannot be trusted, as far as fertility is concerned, and are not here given. Son1e other case:· have been rejected, as the plants were in an unhealthy condition. If we look to the figures in the two tables expressing the ratios between the n1ean relative fertility o( the crossed and self-fertilised flowers, we see that in a majority of the cases (i.e., in thirty five out of fifty) flo·wers fertilised by pollen fron1 a dis~inct plant yield more, son1etimes many Inore, f-3cccls than flowers fertilised with their own pollen ; and they commonly set a larger proportion of capsules. rrhe degree of infertility of the self-fertilised flowers differs cxtren1ely in the different species, and even, as we shall sec in the section on self-sterile plants, in the individuals of the saine species, as well as under ~lightly changed conditions of life. Their fertility ranges from zero to fertility equalling that of the erossecl flowers; and of this fact no explanation can be offered. There are fifteen cases in the two tables in which the number of seeds per capsule produced by the self-fertilised flowers equals or even exceeds tha,t yielded by the crossed flowers. Some few of these eases are, I believe, accidental ; that is, would not recur on a second trial. rrhis was apparently the ease with the plants of the fifth generation of Ip01nooa, and in one of the experiinents with Dianthus. Nicotiana offers the most anoinalous case of any, CHAP. IX. AND SELF-FERTILISED l!'LOWERS. 327 as the. self-fertilised flowers on the parent-plants, and o? theu descendants of the second and third generations, produced more seeds than did the crossed flowers ; but we shall recur to this case when we treat of highlv self~fertile varieties. It 1night have been expected that the difference in fertility between the crossed and self-fertilised flowers would have been more strongly marked in Table G, in which the plants of one set were derived from selffertilised parents, than in Table F, in which flowers on the parent-plants were self-fertilised for the first time. But this is not the case, as far as my scanty n1aterials allow of any judg1nent. There is therefore no evidence at present, that the fertility of plants goes on din1inishing in successive self-fertilised generations, although there is son1e rather weak evidence that this does occur with respect to their height or growth. But we should bear in mind that in the later genera~ ions the crossed plants had becoine n1ore or less closely Inter-related, and had been subjected all the time to nearly uniform conditions. It is remarkable that there is no close correspondence, either in the parent-plants or in the successive generations, between the relative number of seeds produced by the crossed and self-fertilised flowers, and the relative powers of growth of the seedlings raised fron1 such seeds. Thus, the crossed and self-fertilised flowers on the parent-plants of Ipomrea, Gesneria, Salvia, Limnanthes, Lobelia J~~lgens, and Nolana prodt~ ced a nearly equal nuinber of seeds, yet the plants ra~secl from the crossed seeds exceeded considerably in he1ght those raised from the self-fertilised seeds. r~he crossed flowers of Linaria and Viscaria yielded far n1ore seeds than the self-fertilised flowers ; and although the plants raised from the former were taller |
