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Show 110 HETEROSTYLED DIMORPHI@ PLANTS. CHAP. III. short-styled ones produce capsules, and these include a little above two-thirds of the number of seeds yielded by them when leo-itimately fertilised. The sterility of the illegitimate!; fertilised long-styled flowers is probably increased by the deteriorated condition of their pollen; nevertheless this pollen was highly efficient when applied to the stigmas of the short-sty led flowers. With several species of Primula the short-styled flowers are much more sterile than the long-styled, when both are illegitimately fertilised; and it is a tempting view, as formerly remarked, that this greater sterility of the short-styled flowers is a special adaptation to check self-fertilisation, as their stigmas are eminently liable to receive their own pollen. This view is even still more tern pting in the case of the longsty led form of Linum grandijlorum. On the other hand, with Pulrnonaria angustijolia, it is evident, from the corolla projecting obliquely upwards, that pollen is much more likely to fall on, or to be carried by insects down to the stigma of the short-sty led than ot the long-sty led flowers ; yet the short-sty led instead of being more sterile, as a protection against self-fertilisation, are far more fertile than the long-styled, when both are illegitimately fertilised. Pulmonaria azurea, according to Hilde brand, is not heterosty led.* From an examination of dried flowers of Amsinclda spectabilis, sent me by Prof. Asa Gray, I formerly thought that this plant, a member of the Boraginere, was heterostyled. The pistil varies to an extraordinary degree in length, being in some specimens twice as long as in others, and the point of insertion of the stamens likewise varies. But on raising many plants from seed, I soon beca1ne convinced that the whole case was one of mere variability. The first-formed flowers are apt to * ' Die Geschlechter-Vertheilung bei den Pflanzen,' 1867, p. 37. CHAP. III. POLYGONUM FAGOPYRUM. Ill have stamens somewhat arrested in development, with very little pollen in their anther. ; anl in such flowers tho stigma projects above the anther , whil t generally it stands below and sometimes on a level with them. I could detect no difference in the size of tho pollen-oTain or in the structure of the stio·ma in the plants which differed most in the above respects; and all of them, when protected frmn tho access of in. octs, yielded plenty of seeds. Again, from statements made by Vauchor, and from a ha ty inspection, I thought at first that the allied Ancltusa arvensis and Echittm vulgare were heterostyled, but soon saw my error. From information given me, I examined dried flowers of another member of the Boraginere, Anwbia hispidissima, collected frmn several sites, and though tho corolla, together with the included organs, differed much in length, tltere was no sjgn of heterostylism. POLYGONUM FAGOPYHUM (POLYGONACE~). Hildebrand has shown that this plant, the common Buck-wheat, is heterostyled. * In the long-styl d form (Fig. 7), the three stigmas project considerably above the eight short stamens, and stand on a level with the anthers of the eight long stamens in the short-styled form; and so it is conversely with the stig1nas and sta1nens of this latter form. I could perceive no difference in the structure of the stigmas in the two forms. The pollen -grains of the short-sty led form are to those of the long-styled as 100 to 82 in diameter. This plant is therefore without doubt heterosty led. I experimented only in an imperfect manner on the relative fertility of the two forms. Short-styled flowers were dragged several times over two heads of flowers on long-styled plants, protected under a net, which were thus legitimately, though not fully, fertilised. They produced 22 seeds, or 11 per flower-head. Three flower-heads on long-styled plants received * 'Die Geschlechter-Vertheiluug,' &c., 1867, p. 34. |