File:The natural history of plants, their forms, growth, reproduction, and distribution; (1902) (14803286643).jpg

Identifier: naturalhistoryof01kern (find matches)
Title: The natural history of plants, their forms, growth, reproduction, and distribution;
Year: 1902 (1900s)
Authors: Kerner von Marilaun, Anton, 1831-1898 Oliver, Francis Wall, 1864- Macdonald, Mary Frances Ewart Busk, Marian Balfour, Lady
Subjects: Botany
Publisher: London, Blackie
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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exhibits a ridge of hairs of the kind, and the ridge alwaysterminates at the thickened node, whence springs a pair of opposite leaves. Thestalks of these leaves are somewhat hollowed out and have their edges beset withhairs like lashes. The hairy ridges on the segments of the stem are readily wetted 228 ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. by rain and retain a considerable quantity of water. The water that they cannothold they conduct downwards to the ciliate axils of the next lower pair of leaves,where it is drawn through the lash-like hairs in due course and collected into aring of water surrounding the node (see fig. 52^). If this accumulation of waterbecomes so voluminous and heavy that it cannot any longer be retained by thefringe of lashes, the surplus glides on to the unilateral ridge of hairs on the adjacentinternode down to the pair of leaves below. Accordingly, after a shower everynode from which leaves arise is seen to be inclosed in a water-bath, and the hairy
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Fig. 52.—Hairs and Leaves which retaiu Dew and Rain.Dwarf Gentian (Gentiana acaulis). * Ladys Mantle (Alchemilla vulgaris). 3 Chickweed (Stellaria media). ridges also are so soaked with water that they look like edgings of glass. All theindividual cells in each of the hairs are full of protoplasm and cell-sap, but only thelowest, which are very short, really act as absorption-cells. When these cellsbecome at all relaxed in dry air, the fact is indicated by the appearance on theexternal cell-wall of fine striae (see fig. 53 ^ and 53 2). The protoplasts inhabiting themattract water, and after being relaxed in the manner referred to the cells regaintheir turgidity on being wetted, whilst the fine wrinkles on the outer membrane arein consequence immediately smoothed out. Although the upper cells of the hairpossess a less thick cuticle, they, on the other hand, seem not to absorb any water,but to serve rather to conduct it by their surfaces. This case is, as we have said, comparatively r

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