View source for Tracheid

'''Tracheids''' are elongated [[cell (biology)|cell]]s in the [[xylem]] of [[vascular plant]]s, serving in the transport of water. The build of tracheids will vary according to where they occur. 

Tracheids are one of two types of tracheary elements, [[vessel element]]s being the other. All tracheary elements will develop a thick lignified cell wall, and at maturity the [[protoplast]] has broken down and disappeared. The presence of tracheary elements is the defining characteristic of vascular plants to differentiate them from [[non-vascular plant]]s. 

The two major functions that tracheids may fulfill are 
* as part of the transport system
* in structural support

In most cases, the prime function of tracheids is that of transporting water. They occur in [[vascular bundle]]s throughout the non-woody parts of the vascular plant and provide water and minerals collected by the roots to leaves and other parts of the plant (stem, flowers, fruits etc).  

A good example of structural support is in [[softwood]]s where tracheids are the major cell type. Tracheids give softwood its strength. 

Because tracheids have a much higher surface to volume ratio compared to vessel elements, they serve to hold water against gravity (by [[adhesion]]) when [[transpiration]] is not occurring. This is likely one mechanism that helps plants prevent air emboli.

==See also==
* [[vessel element]]
* [[xylem]]

==References==
* Wilson, K. & D.J.B. White (1986). ''The Anatomy of Wood: its Diversity and variability.'' Stobart & Son Ltd, London 

==External links==
*Pictures of softwood tracheids [http://botweb.uwsp.edu/anatomy/images/gymnospermwood/pages/Anat0288.htm in cross section] and [http://botweb.uwsp.edu/anatomy/images/xylemdevelopment/pages/Anat0182.htm  in maceration]; both in pine.

[[Category:Plant anatomy]]
[[Category:Plant physiology]]