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Show 240 ILLEGITIMATE OFFSPRING OF CIIAP. v. same heterostyled species, to~ethe: with their il!e~itimate offspring, resemble ~ybnd u.nions be~ween chstlnct species together with theu hybrid offs~r~ng. In both cases we meet with every degree of stenh ty, fro1n very slightly lessened fertility to abs?lute barrenness, when not even a sino-le seed-capsule IS produced. In both cases the facility of effecting the first union is much influenced by the conditions to which the plants are exposed.* Both with hyb:·i~s ~nd i!leg itin1at~ pla~ts the innate degree of stenhty Is highly vanable In plants raised from the same mother-plant. In both cases the n1ale organs are more plainly affected than the female; and we often find contabescent anthers enclosing shrivelled and utterly powerless pollengrains. The more sterile hy.brids, as Max Wichu~·a has well shown,t are sometunes much dwarfed In stature, and have so weak a constitution that they are liable to premature death; and we have seen exactly parallel cases with the illegitimate seedlings of Lyt?rum and Primula. Many hybrids are the most persistent and profuse :flowerers, as are some illegitimate plants. When a hybrid is crossed by either pure parent-form, it is notoriously much more fertile than when crossed inter se or by another hybrid ; so when an illegitimate plant is fertilised by a legitimate plant, it is ~ore fertile than when fertilised inter se or by another Illegitimate plant. When two species are crossed and they produce numerous seeds, we expect as a general rule that their hybrid offspring will be n1oderately fertile; but if the parent species produce extremely few seeds, we expect that the hybrids will be very * This has been remarked by many experimentalists in effecting crosses between distinct spec1es; and in regard to illegitimate unions I have given in the first chapter a striking- illus.tration in the case of Primula verzs. . t 'Die Bastardbefruclltung un Pflanzenreich,' 1865. CHAP. v. HETEROSTYLED PLANTS. 241 sterile. But there are marked excepti0ns, as shown by Gartner, to these rules. S@ it is 'with illegitimate unions and illegitimate offspring. Thus the midstyled form of Lythrum salicaria, when illegitimately fertilised with pollen from the longest stamens of the short-styled form, produced an unusual number of seeds; and their illegitimate offspring were not .at all, or hardly at all, sterile. On the other hand, the illegitimate offspring fro1n the long-styled form, fertilised with pollen from the shortest stamens of the same form, yielded few seeds, and the illegitimate offspring thus produced were very sterile; but they were more sterile than might have been expected relatively to the difficulty of effecting the union of the parent sexual elements. No point is more remarkable in regard to the crossing of species than their unequal reciprocity. Thus species A will fertilise B with the greatest ease; but B will not fertilise A after hundreds of trials. We have exactly the same case with illegitimate unions; fm; the mid -sty led Lythrum salicaria was easily fertilised by pollen from the longest stamens of the shortstyled form, and yielded many seeds; but the latter form did not yield a single seed when fertilised by the longest stamens of the mid -sty led form. ·Another i1nportant point is prepotency. Gartner has shown that when a species is fertilised with pollen from another species, if it be afterwards fertilised with its own pollen, or with that of the same species, this is so prepotent over the foreign pollen that the effect of the latter, though placed ·on the stigma some time previously, is entirely destroyed. Exactly the same thing occurs with the two fonns of a heterostyled species. Thus several long-styled flowers of Prirnulu veris were fertilised illegitin1ately with pollen from another plant of the same form, and twenty-four hours H |