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Show 268 .OONOL UDING REl\fARKS CHAP. VI. iirst crossed and of their hybrid offspring must also be looked at as merely an incidental result, following from the special co-adaptation of the sexual elements of the same species. We can thus understand the st1·iking parallelism, which has been shown to exist between the effects of illegitimately uniting heterostyled ·plants and of crossing distinct spocios. rrhe great difference ill. the degree of sterility betwoon the various heterosty led species when illegi tim a tol y fertilised, and between the two forms of the same species when similarly fertilised, harmonises well with the view that the result is an incidental one which follows from changes gr.adually effected in their reproductive systems, in order that the sexual elements of the distinct forms should act perfectly on one another. Transmission of the Two Forms by Heterostyled Plants. -The transmission of the two forms by heterosty led plants, with respect to which n1any facts were given in the last chapter, may perhaps be found hereafter to throw some light on their manner of development. Hildebrand observed that seedlings from the longstyled form of Primula Sinensis when fertilised with pollen from the sa1ne form were 1nostly long-styled, and many analogous cases have since been observed by me. All the known cases are given in the two following tables. that, jui!ging from the remarkable power with which abruptly changed conditions of life act on the reproductive system of most organisms, it is probable that tile close adaptation of the male to the female elements in the two forms of the same heterostyled specieB, or in all the individuals of the s~me ordinary species, could be acqmr~J only undc:r l~n~-con t~n_ued ueaily uniform conditiOns of hfu. CHAP. VI. ON HETEROSTYLED PLANT& r TABLE 36. 269 Nature of the . Offspring from Illegitimately fertilised Dimorphic Plants. -------------------------------------- Number I NumbPr of Lung- of Short-sty led sty led Offspring . 1 Offspring. Primula veris I own-form pollen during five 156 (Long-sty led form, fertilised byJ · ~ successive generations, pro- 6 " " Primula vulgaris Primula auricula Primula Sinensis • " " " " l duced. . • . • • . { Short-styled form, fertilised by}' · own-form pollen, produced • f Long-styled form, fertilised by} own-form pollen· during two · successive generations, pro-duced. • . • • • . (Short-styled form, fertilised byt I own-form pollen, is sa.iJ to •i produce during successive generations offspring in aboutj l the following proportions • { Long-styled form, fertilised byJ own-form pollen during two • successive generations, pro-duced. . • • • • • / Long-styled form, fertilised by) . own- form pollen (Hilde-brand), produced. • • • { Short-styled form, fertilised by) • own-form pollen, produced . J Pulmonaria 0 ffi . 1. {Long-styled form, fertilised by} cma IS own-fol'm pollen, produced . p ] f: {Long-styled form, fertilised by} o ygonum agopyrum own-form pollen, produced . " " { Short-styled form, fertilised by} own-form pollen, produced . 5 9 69 0 25 75 52 0 14 3 1 24 11 0 45 4 13 20 |