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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 ?
faster filling of the near-surface tracheids by penetrating liquids) was virtually eliminated.
4a), wood of Tropaeolum appears to have fibers as a background cell type, but these cells, when seen in longitudinal section and in macerations, prove to be both narrow vessel elements and vasicentric tracheids.
1991 "Variation in wood and tracheid properties of Pinus maximinoi, P.
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.
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.
We assume that the cumulated AE energy is a more reliable measure for PLC than the AE number per se, because the hydraulic conductivity is proportional to the 4th power of the radius of a capillary (Hagen-Poiseuille equation) and tracheid diameters are variable within a wood specimen.
In plants, xylem vessels or tracheids exhibit capillary action.
The best preserved examples are assigned to Dadoxylon recentium, a wood characterized by biseriate, alternate, bordered tracheid pitting (Fig.
Mauseth JD, Uozumi Y, Plemons B J, Landrum JV (1995) Structural and systematic study of an unusual tracheid type in cacti.
AE signals are supposed to be induced by elastic oscillations of conduit cell walls following the cavitation event, because the pressure rises rapidly in the tracheid lumen as liquid water at negative pressure is replaced by water vapor very near vacuum pressure.
A zone of tracheid cells with opaque cell walls in this region may suggest that part of the surface of the growth interruption was partially charred.
Fingerprint traceability of logs using outer shape and the tracheid effect.