. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. NAIADACEAE 507 2949. P. natans L. (Knuth, op. cit., p. 137.)—In this species the closely- crowded spike consists of some 50 flowers about 4-5 mm. in diameter. In the first (female) stage it is about 4 cm., in the second (male) one about 6 cm. long, and just projects from the water. The four green perianth-like connectives are at first closed like an envelope, with only the four brush-shaped stigmas projecting. These are dusted by means of the wind with polle
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. NAIADACEAE 507 2949. P. natans L. (Knuth, op. cit., p. 137.)—In this species the closely- crowded spike consists of some 50 flowers about 4-5 mm. in diameter. In the first (female) stage it is about 4 cm., in the second (male) one about 6 cm. long, and just projects from the water. The four green perianth-like connectives are at first closed like an envelope, with only the four brush-shaped stigmas projecting. These are dusted by means of the wind with pollen from adjacent flowers already in the male stage. The connectives then diverge, and the eight sessile anther-lobes dehisce and empty their abundant y\g.^\t. Poiamogeton natans, J , 1, (from nature). Flower in the dusty pollen. g^^^ (f^^^,^, 3,^^^ ,^,„ f„„, 2950. P. perfoliatus L. (Wamstorf, Verb. bot. t::\ t' '^:^ ~a' Ver., Berlin, ., 1896.)—The stalks of the connec- (x about 6). tive-plates of the protogynous wind flowers belonging to this species are vertical to the ovary when the pollen is mature, while their ex- panded parts are parallel to it. In this way is constituted an excellent arrangement for catching the pollen carried by the wind. The pollen-grains are ovoid to ellipsoidal, white in colour, slightly transparent, dehcately retiform-tuberculate, about 44-50 /a long and 37-5 /j, broad. 2951. P. crispus L. (Wamstorf, op. cit., xxxviii, 1896.)—The flowers of this species are protogynous and the anthers extrorse. The pollen-grains are white, spheroidal to ovoid, almost glabrous, from 37-47 /a in diameter. MacLeod (Bot. Jaarb. Dodonaea, Ghent, v, 1893, pp. 284-5) gives a detailed description of the flower mechanism, corresponding for the most part with my account of P. natans. 2952. P. lucens L. (Wamstorf, op. cit.)—The pollen-grains in this species are whitish in colour, irregularly tetrahedral, from 25-8 /«, in diameter. 2953. P. gramineus L.,
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