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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 It might be outdated or ideologically biased.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 ?
If cellulosic fibrils are present in pit membranes of tracheid end walls, pit membranes may be retained as a result of gene action, resulting in absence of lysis of the pit membrane, rather than (as is typical for perforations in vessel elements), swept away in the flow of xylem sap.
(41.) Evans, R, "Rapid Measurement of the Transverse Dimensions of Tracheids in Radial Wood Sections from P.
Tangential double wall thickness of adjacent tracheids and lumen diameters were measured by means of a Leica DM4000M microscope interfaced with a digital camera and Leica image analysis software (Leica Microsystems Wetzlar GmbH, Germany).
Lamellation in the S2 layer of softwood tracheids as demonstrated by scanning transmission electron microscopy.
Bailey & Tupper (1918) offered a muchreproduced drawing schematizing the tracheid as a primitive type of tracheary element in angiosperms; from this, vessels (first with scalariform, ultimately simple perforation plates) were progressively derived on the one hand, whereas on the other hand, imperforate tracheary elements progressively lost pit borders and changed (by implication, gradually) from conductive to mechanical cells.
The classic method to quantify the extent of embolism is the determination of the native hydraulic conductivity in relation to the hydraulic conductivity after artificially refilling all embolized tracheids. Cavitation events can also be detected directly by recording acoustic emission (AE) in the high-frequency range of 100 kHz to 2 MHz (Tyree and Dixon, 1983, Jackson and Grace, 1996, Kikuta et al., 2003).
Based on Figures 6a and 6b, the modified nanoparticles impregnated in the tracheid and attached to the cell walls through chemical bonds or physical interactions (Wang 2012).
e Avascular tracheid from the terminal latewood, from a radial section, f Metaxylem vessel with an associated strand of axial parenchyma (left), g Oreopanax steinbachianus Harms, cult.
The spread of the fungal mycelium into the sapwood might have caused damage to the tracheid walls [34].
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.