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An elongate, spindle-shaped xylem cell, lacking protoplasm at maturity, and having secondary walls laid in various thicknesses and patterns over the primary wall.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a dead lignified plant cell that functions in water conduction. Tracheids are found in the xylem of all higher plants except certain angiosperms, such as cereals and sedges, in which the water-conducting function is performed by vessels, or tracheae. Tracheids are usually polygonal in cross section; their walls have annular, spiral, or scalene thickenings or rimmed pores. The cells range in length from fractions of a millimeter to 3–5 mm (pine, larch) and even 10 mm (agave). In the process of evolution, tracheids developed into fibrous tracheids with limited water-conducting ability and into specialized mechanical elements known as libriform fibers.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Axial wood parenchyma cells are not in contact with axial phloem parenchyma once a layer of tracheids has formed to separate them from the cambium, whereas wood rays are intercontinuous with phloem rays via living cells of the cambium.
Abbreviations used in the figures of this study: A = aperture; AP = appressorium; B = pit border; F = fiber; H = hyphae; L = lipid bodies; M = margo of pit membrane; P = parenchyma cell; PA = perforation in end wall of vessel element; T = torus; VT = vascular tracheid. All wood anatomy images are of Osmanthus armatus, except for Figure 6, which is from O.
The long tapering tracheids constitute the dominant cell type of the conifer axial system and ensure both water conduction and tree support.
Tracheids also function in water transport but are less efficient in doing so because they are smaller in diameter, and the end walls are not totally dissolved as the cell reaches maturity.
Xylem conducting elements include tracheids and vessels.
Lignin appeared to be completely removed from the cell corner middle lamella regions, but tracheids were still joined in other parts of the middle lamella.
Although three samples exhibited helical checking on the tracheids, none exhibited spiral thickenings.
Norway spruce wood consists to 90% of small water-conducting elements with a diameter of about 10-40 [micro]m and a length of 1-4 mm (tracheids, Fig.
Everyone has seen these tubes, which biologists call "vessels" and "tracheids." They help form the grain in wood.
Green, "The Effect of Pulping Upon the Dimensions of Wood Tracheids," Wood Fiber 7 (3), 226-233 (1975).
The crown core is composed of an intertwining series of vascular bundles, fibers, and tracheids interspersed with parenchyma cells in a generally inverted cone shape.