Tracheid

Tracheids (unique: tracheids ) [ tʁaχe ' ˀ i: dən ] are for water supply and consolidation formed, usually strongly lignified, elongated in the axial direction cells. You find yourself V.A. in the xylem of the vascular bundles of the stem axis of plants.

In contrast to the evolutionary modern vessels ( tracheae ), tracheids have not resolved transverse walls, but direct the water on so-called bordered pits from cell to cell. In the upper region they are tapered and therefore have a greater connection area to the next cell; Here are i.d.R. also most wells.

Gymnosperms ( gymnosperms ) and vascular spore plants ( Pteridophyta ) usually have only tracheids for water conduction, while angiosperms ( Angiospermae) have predominantly, tracheae, the guarantee of a larger diameter and resolved transverse walls an even better water management. However, in hardwoods also increases the risk of embolism in presence of air.

After they have reached their final size, shape and function, die from the tracheids and woody by Lignineinlagerung in the cell wall. So in contrast to the tracheae they also take on firming function. V.A. the narrow lumen, darker late wood in coniferous trees is almost exclusively formed to consolidate purposes why fine-grained softwood with high latewood units in general more stable and is more valuable than rough year.

In deciduous trees the consolidation is taken, however, from Libri form fibers.

Should also be noted, the radial Holzstrahltracheiden which occur in some softwood species. They flank the existing parenchyma cells of wood beam up and down and are responsible for water management in the radial direction.