. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. DISPERSAL BY WIND. 813 distributed in small detachments, and only at a suitable time, when a dry wind IS blowing. A similar contrivance is exhibited by the Muscineffi in the Mar- chantiaceae, Anthocerotace^, and JungermanniacejB. Peculiar filamentous, very hygroscopic cells with spiral bands of thickening on the cell-wall, are found with the spores in the receptacles of these plants (see p. 696). These have been called elaters, because it was thought that their movements caused the ejection of t
. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. DISPERSAL BY WIND. 813 distributed in small detachments, and only at a suitable time, when a dry wind IS blowing. A similar contrivance is exhibited by the Muscineffi in the Mar- chantiaceae, Anthocerotace^, and JungermanniacejB. Peculiar filamentous, very hygroscopic cells with spiral bands of thickening on the cell-wall, are found with the spores in the receptacles of these plants (see p. 696). These have been called elaters, because it was thought that their movements caused the ejection of the spores. Their significance, however, rather lies in the fact that they serve to hold the spores together after the opening of the receptacle, and only expose them by degrees to the wind. They also help to burst open the receptacles, but that hardly concerns us just now. Only three of the most striking of the varied contrivances for spore distribution by wind in Mosses (which are destitute of elaters) will be here described. First, those which are observed in the Andreseacese (see figs. 450 ^ and 450 2). Here the capsule opens by four longi- tudinal clefts which, however, do not extend quite to the free end, and the four pieces into which the wall is thus divided may be com- pared to the staves of a barrel joined together at the top. In damp weather they become approximated, so that the clefts are closed (fig. 450^). In dry weather the valves become arched, the clefts widen, and the spores may be blown out from the interior of the capsule by the dry wind (fig. 450 ^). The distribution of the spores is effected quite difierently in the Polytrichums, one species of which is illustrated in figs. 450 ^'*'^'^'^'^. After the roof (operculum) which formerly surmounted the cap- sule has fallen ofi" a delicate whitish membrane comes into view, which is held fast by the points of numerous sharp teeth, and is stretched like the skin of a drum over the mouth of the capsule with its
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
