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Show 108 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III. We see in this table that the fertility of the two legitimate unions to th~t of the two illegit~mate together is as 100 to 35, J~dged by the propor.tion of flowers which produced fruit; and as 100 t_o 32, Judged by the average number of seeds per fruit. But the small number of fruit yielded by the 18 long-styled flowers in the first line was probably accidental, and if so, the difference in the proportion of legitimately and illegitimately fertilised flowers which yield fruit is really greater than that represented by the ratio of 100 to 35. The 18 long-~tyled flowers illegitimately fertilised yielded no seeds,-not even a vestige of one. Two long-styled plants which were placed under a net produced 138 flowers, besides those which were artificially fertilised, and none of these set any fruit ; nor did some plants of the same form which were protected during the next summer. Two other longstyled plants were left uncovered (all the short-styled plants having been previously covered up), and humble-bees, which had their foreheads white with pollen, incessantly visited the flowers, so that their stigmas must have received an abundance of pollen, yet these flowers did not produce a single fruit. We may therefore conclude that the long-styled plants are absolutely barren with their own-form pollen, though brought from a distinct plant. In this respect they differ greatly from the long-sty led English plants of P. ojfwinalis which were found by me to be moderately self-fertile; but they agree in their behaviour with the German plants of P. officinalis experimented on by Hildebrand. Eighteen short-styled flowers legitimately fertilised yielded, as may be seen in Table 20, 15 fruits, each having on an average 2 · 6 seeds. Four of these fruits contained the highest possible number of seeds, namely CHAP. III. PULMONARIA ANGUSTIFOLIA. 109 4, and four other fruits contained each 3 seeds. The 12 illegitimately fertilised short-styled flowers yielded 7 fruits, including on an average 1 · 86 seed; and one of these fruits contained the maximum number of 4 seeds. This result is very surprising in contrast with the absolute barrenness of the long-styled flowers when illegitimately fertilised; and I was thus led to attend carefully to the degree of self-fertility of the short-sty led plants. A plant belonging to this form and covered by a net bore 28 flowers besides those which had been artificially fertilised, and of all these only two produced a fruit each including a single seed. This high degree of self-sterility no doubt depended merely on the stigmas not receiving any pollen, or not a sufficient quantity. For after carefully covering all the long-styled plants in my garden, several short-styled plants were left exposed to the visits of humble-bees, and their stigmas will thus have received plenty of short-styled pollen; and now about half the flowers, thus illegitimately fertilised, set fruit. I judge of this proportion partly from estimation and partly fTom having examined thTee large bTanches, which had boTne 31 floweTs, and these produced 16 fruits. Of the fruits produced 233 were collected (many being left ungathered), and these included on an average 1· 82 seed. No less than 16 out of the 233 fruits included the highest possible number of seeds, namely 4, and 31 included 3 seeds. So we see how highly fertile these short-styled plants were when illegitimately fertilised with their own-form pollen by the aid of bees. The great difference in the fertility of the long and short-styled flowers, when both are illegitimately fertilised, is a unique case, as far as I have observed with heterosty led plants. The long-sty led flowers when thus fertilised are utterly barren, whilst about half of the |
