OCR Text |
Show 208 ILLEGITIMATE OFFSPRING OF C HAP. v. of a long-styled plant fertilised with pollen from its own-form shortest stamens, and these plants were the most sterile of all. The remaining plants in Class I. and II. were · almost certainly the product of pollen from the mid-length stamens, and although very sterile, they were less so than the first set. None of the plants i~ the first four classes attained their full and proper stature; the first seven, which were the most sterile of all (as already stated), were by far the rnost dwarfed, several of them never reaching to half their proper height. These same plants did not flower at so early an age, or at so early a period in the season, as they ought to have done. The anthers in 1nany of their flowers, and in the flowers of son1e other p] ants in the first six classes, were either contabescent or included numerous small and shrivelled pollen-grains. As the suspicion at one time occurred to me that the lessened fertility of the illegitimate plants might be due to the pollen alone having been affected, I n1ay remark that this certainly was not the case ; for several of them, when fertilised by sound pollen from legitimate plants, did not yield the full complement of seeds; hence it is certain that both the fmnale and male reproductive organs were affected. In each of the seven classes, the plants, though descended from the same parents, sown at the same time and in the same soil, differed much in their average degree of fertility. Turning now to the fifth, sixth, and seventh classes, and looking to the right-hand column of the table, we find nearly as many plants with a percentage of se~ds above the normal standard as beneath it. As w1th most plants the number of seeds produced varies much, it might be thought that the present case was one merely of variability. But this view must be rejected, CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 209 as far as' the less fertile plants in these three classes are concerned: first, because none of the plants in Class V. attained their proper height, which shows that they were in some manner affected; and, secondly, because many of the plants in Classes V. and VI. produced anthers which were either contabescent or included small and shrivelled pollen-grains. And as in these cases the male organs were manifestly deteriorated, it is by far the most probable conclusion that the female organs were in some cases likewise affected and that this was the cause of the reduced number of' seeds. With respect to the six plants in these three classes which yielded a very high percentage of seeds, the thought naturally arises that the nonnal standard of fertility for the long-sty led and short-sty led forms (with which alone we are here concerned) may have been fixed too low, and that the six illegitimate plants are merely fully fertile. The standard for the longstyled form was deduced by counting the seeds in twenty-three capsules, and for the short-styled form ~rom twenty-five capsules. I do not pretend that this Is a sufficient number of capsules for absolute accuracy; but my experience has led me to believe that a very. fair result may thus be gained. As, however, the maximum number observed in the twenty-five capsules of the short-sty led form was low, the standard in this case may possibly be not quite high enough. But it should be observed, in the case of the illegitimate plants, that in order to avoid over-estimating their infertility, ten very fine capsules were always selected ; ~nd the years 1865 and 1866, during which the plants I~ the three latter classes were experimented on, were highly favourable for seed-production. Now, if this p |