. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. e development of a bordered pit. b, The original, thin,primary wall; a, the overhanging border formed as the wall thickened. . ofthe wall has continued and extended the border; the primary wall has thickened at c,forming the torus. C, the border and the torus are finished. in wood, namely the wood parenchyma and the tracheal tubes,are, respectively, almost and entirely lacking. Considered asstrengthening elements the fiber-tracheids are in all essentialrespects like
. Plant anatomy from the standpoint of the development and functions of the tissues, and handbook of micro-technic. e development of a bordered pit. b, The original, thin,primary wall; a, the overhanging border formed as the wall thickened. . ofthe wall has continued and extended the border; the primary wall has thickened at c,forming the torus. C, the border and the torus are finished. in wood, namely the wood parenchyma and the tracheal tubes,are, respectively, almost and entirely lacking. Considered asstrengthening elements the fiber-tracheids are in all essentialrespects like wood fibers. They are long and tapering cells,their ends interlace, their walls are thickened and lignified. io8 TRANSPORT OF WATER AND SOIL SOLUTES But in one noteworthy detail they are very unlike wood fibers,namely, their walls have numerous and large bordered pits, andit is this that fits them for water highways (Fig. 51). The bordered pit is a thin area in the wall with an overhang-ing border. The thin place is clearly to facilitate the passageof water and solutes, and the border serves the double purpose. FIG. 52.—Diagrammatic representation of a block of pine wood highly magnified, a,Early growth; b, late growth; c, intercellular space; d, bordered pit in tangential wall of lategrowth; TO,/and e, bordered pit in radial wall of early growth from different points of view;h, row of medullary cells for carrying food; g, row of medullary ray cells for carrying water;k, thin place in radial wall of ray cells that carry food. THE TRACHEIDS 109 Windward
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