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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.



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.

References in periodicals archive ?
Yang and Hazenberg (1994) applied TSLR to tracheid length to determine the transition point of 10 black spruce trees harvested near Thunder Bay, Ontario.
It is not uncommon to find hyphae growing along the length of both vessel members (Figure 14) and vascular tracheids.
These parenchymous materials do not originate from conifers, for the xylem tissue directly associated with them is comprised predominately of the vessel dements of angiosperms, with few tracheid structures observed.
We have focused on the possible existence of thin areas or porosities in tracheid primary walls, and whether or not cellulosic fibrils are visible with SEM in primary walls of tracheids.
Secondary walls of internodal tracheids are thin, with thickenings that are annular, looplike, or of some intermediate form.
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.
It is expected that as the tree matures, the proportion of latewood tracheids with thicker walls and higher SG increases compared with the initial stages of growth where thin-walled earlywood cells are predominant.
No end walls of sectioned roots lack pit membranes or pit membrane remnants of some kind, so on a functional as well as a morphological basis, the tracheary elements of roots are closer to the tracheid end of the gamut than to the vessel element end.
Although there were different magnitudes of anatomical change under different forest management regimes, with a corresponding increment in growth ring number, the density, tracheid length, latewood percentage, and the ratio of cell wall thickness to cell diameter from earlywood and latewood increased; ring width, however, decreased (Jeong and Zink-Sharp 2012, 2013).
Tracheids have intact primary membranes, so the more primary membrane remains in perforations, the more tracheid like the cell could be considered.
Protoxylem tracheids, 6-12 [micro]m in diameter, are characterised by annular and spiral thickening with scalariform and transitional pitting seen on the 9-15 [micro]m diameter metaxylem tracheids (Fig.
As the tracheid cytoplasm undergoes autolysis, the matrix materials in pit membranes of Metasequoia are removed from both torus and margo regions.