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Show 114 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III. h . shows that p bistorta is so strongly pro- ~!r::a:~:~~(:he anthers ge~erally falling off before the sti. gmas are rna ture) that the flo. wers . m. usht be Ocrtohs s- ferti.1 .I se d b Y the many insects w. hich VISIt t emh." h er . b uch less conspicuous flowers w Ic se-speciesl. ttelar mno nectar and consequently are rarely crete I e or ' lf f .. l. V.I S.i te d b y I. nsec t s'. these are adapted for. .s e .- er ti AIsa - . th h ti"ll capable of cross-fertilisation. c- ~~ oog s ll cording to Delpino, the Polygonac~re are ge~era y fertilised by the wind, instead of by Insects as In the present genus. LE~COSMIA BURNETTIANA (THYMELilE). A p f Asa Gray has expressed his belief* that th_is species and 8 L ~~~minata as well as some species in the alhed gen~ Drymispermum, 'are dimorphic or heterostyled, I procu~e f Kew through the kindness of Dr. Hooker, two . drred ;~:rs of' the former species, an inhabitant of the Frrc~dly Islands in the Pacific. The pistil of the long-styled form _IS to that of the short-styled as 100 to 86 in lengt~; the stigma projects just above the throat of the corolla, and IS sur:ounde~ by five anthers, the tips of which reach up almost to 1ts based and lower down, within the tubular corolla, five other an rather smaller anthers are seated. In the short-styled form, the stigma stands some way down the tube of the coroll~, n~arly on a level with the lower anthers of the other form : 1_t d1~ers remarkably from the stig1na of the .long-style~ form, In bel~~ more papillose and in being longer 1n the ratiO of 100 to 0 · The anthers of the upper stamens in the short-styled form are supported on free filaments, and project above the throat of dt~e corolla, whilst the anthers of the lower stamens are seate . m the throat on a level with the upper stamens of the other form. The diameters of a considerable number of grains from both ~:ts of anthers in both forms were measured, but they did not dl er in. any trustworthy degree. The mean diameter of twenty-two * 'American Journal of Science,' 18G5, p. 101, and Seemann's ' Journal of Botany,' vol. iii. 1865, p. 305. CHAP. III. MENYANTHES TRIFOLIATA. 115 grains from the short-styled flower was to that of twenty-four grains from the long-styled, as 100 to 99. The anther of the upper stamens in the short-styled form appeared to be poorly developed, and contained a considerable number of shrivelled grains which were omitted in striking the above average. Notwithstanding the fact of the pollen-grains from the two forms not differing in diameter in any appreciable degree, there can hardly be a doubt from the great difference in the two forms in the length of the pistil, and especially of the stigma, together with its more papillose condition in the shortstyled form, that the present species is truly heterostylecl. Thjs case resembles that of Linum .<Jrandijlorum, in which the sole difference between the two forms consists in the length of tho pistils and stigmas. From the great length of the tubular corolla of Leucosmia, it is clear that the flowers are crosRfertilised by large Lepidoptera or by honey-sucking birds, and the position of the stamens in two whorls one beneath the other, which is a character that I have not seen in any other heterost.yled dimorphic plant, probably serves to smear tho inserted organ thoroughly with pollen. MENYANTHES TRIFOLIATA (GENTIANE2E). This plant inhabits marshes: my son William gathered 247 flowers from so many distinct plants, and of those 110 were long-styled, and 137 short-styled. The pistil of the long-style<l form is in length to that of the short-styled in the ratio of about 3 to 2. The stigma of the former, as my son observed, is decidedly larger than that of the short-styled; but in both forms it varies much in size. The stamens of the short-styled are almost double the length of those of the long-styled; so that their anthers stand rather above the level of the stigma of the longstyled form. The anthers also vary much in size, but seem often to be of larger size in the short-styled flowm·s. My on made with the camera many drawings of the pollen-grain~, and those from the short-styled flowers were in diameter jn nearly the ratio of 100 to 84 to those from the long-stylod flowers. I know nothing about the capacity for fertilisation in the two forms; but short-styled plants, living by themselves in the gardens at Kew, have produced an abundance of capRulcs, yet the seeds have never germinated; and this looks as if the short-styled form was sterile with its own pollen. I 2 |