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Show 312 FERTILITY OF CROSSED CIIAP. IX. CHAPTER IX. THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION ON THE PRODUCTION OF SEEDS. l!..,ertility of plants of crossed and self-fertilised parentage, both lots being fertilised in the same manner-Fertility of the parent-plants when first crossed and self-fertili::;ed, and of their crossed and selffertilised offspring when again crossc<l and self-fertilis d-Oomparison of the fertility of fl0wers fertilised with their own pollert and with that from other flowers on the same plant-Self-sterile plants-Causes of self-sterility-The nppearanre of l1 igltly ~elffertile val"ieties-Self-fertili sation apparently in some respects beneficial, independently of the assured production of secds.-Relative weights and rates of germination of seeds from crossed mul ~elffertilised flowers. THE present chapter is devoted to the F ertility of plants, as influenced by cross-fertilisation and selffertilisation. The subject consists of two distinct branches; firstly, the relative productiveness or fertility of flowers crossed with pollen from a distinct plant and with their own pollen, as shown by the proportional number of capsules which they produce, together with the number of the contained seeds. Secondly, the degree of innate fertility or sterility of the seedlings raised from crossed and self-fertilised seeds; such seedlings being of the same age, grown .under the same conditions, and fertilised in the same manner. These two branches of the subject correspond with the two which have to be considered by any one treating of hybrid plants; namely, in the first place the con1parative productiveness of a species when fertilised with pollen fro1n a distinct species and with its own pollen ; and CHAP. IX. AND SELF-FERTILISED PLANTS. 313 in the second place, the fertility of its hybrid offspring. These two classes of cases do not always run pa:rallel; thus some plants, as Gartner has shown, can be crossed with great ease, but yield excessively sterile hybrids ; while others are crosseu with extreme difficulty, but yield fairly fertile hybrids. 'The natural order to follow in this chapter would have been first to consider the effects on the fertility of the parent-plants of crossing then1, and of fertilising them with their own pollen ; but as we have discussed in the two last chapters the relative height, weight, and conRtitutional vigour of crossed and self-fertilised plants-that is, of plants raised from crossed and self-fertilised seeds-it will be convenient here first to consider their relative fertility. The cases observed by me are given in the following table, D, in which plants of crossed and self-fertilised parentage were left to fertilise themselves, being either crossed by insects or spontaneously self-fertilised. It should be observed that the results cannot· be considered as fully trustworthy, for the fertility of a plant is a most variable element, depending on its age, health, nature of the soil, amount of water given, and temperature to which it is exposed. The number of the capsules produced and the nu1nber of the contained seeds, ought to have been ascertained on a large nun1ber of crossed and selffertilised plants of the same age and treated in every respect alike. In these two latter respects my observations may be trusted, but a sufficient number of capsules were counted only in a few instances. The fertility, or as it may perhaps better be called the productiveness, of a plant depends on the number of capsules produced, and on the number of seeds which these contain. But from various causes, chiefly from the want of time? I was often compelled to rely on the |