. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. LEMNACEAE 501 (5) There is also a possibility of pollination by small water-spiders, water- beetles, and snails (Planorbis). Thus in the pollination of species of Lemnaceae, wind, water, and animals perhaps play equal parts; cross-pollination without outside help, however, and even autogamy are in no way excluded, as a result of the gregarious habits of plants of the species. 2938. L. polyrrhiza L. (= Spirodela polyrrhiza Schleid.). (G. Engelman, Bull. Torre
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. LEMNACEAE 501 (5) There is also a possibility of pollination by small water-spiders, water- beetles, and snails (Planorbis). Thus in the pollination of species of Lemnaceae, wind, water, and animals perhaps play equal parts; cross-pollination without outside help, however, and even autogamy are in no way excluded, as a result of the gregarious habits of plants of the species. 2938. L. polyrrhiza L. (= Spirodela polyrrhiza Schleid.). (G. Engelman, Bull. Torrey Bot. CI., New York, 1870, pp. 42-3 ; H. Gillman, Amer. Nat., Boston (Mass.), XV, 1881, pp. 896-7.)—Engelman describes this species as protandrous. Gillman observed that the stamens, which dehisce about 4 , move back at night, and open again the next morning between 7-9 ORDER ALISMACEAE JUSS. ' Bl. u. Insekt. a. d. nordfr. Ins.,' p. 133. CXXII. Literature.—Knuth, Flowers hermaphrodite or monoecious, rarely dioecious. The inner or both perianth whorls are petaloid, and therefore serve to attract insects. 957. Alisma L. Flowers hermaphrodite and homogamous, white or reddish in colour ; with half-concealed nectar secreted by a ring at the base of the stamens. 2939. A. Plantago L. (Herm. Miiller, ' Fertlsn.,' p. 565 ; Kirchner, ' Flora v. Stuttgart,' p. I S3; Knuth, 'Bl. u. Insekt. a. d. nordfr. Ins.,' p. 133 ; Warns- torf, Verb. bot. Ver., Berlin, xxxviii, 1896.) — The homoga- mous flowers of this species are arranged in pyramidal panicles, and possess a yellow nectar-guide at the base of each of the three white or reddish petals; they expand to form a surface about 10 mm. in diameter. Hermann Miiller says that nectar is secreted in twelve small drops by the inner side of a fleshy ring formed by the union of the broadened bases of the six filaments. The stamens are directed obliquely upwards and outwards, and turn their pollen- covered surface outwards, while the s
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