Editing Xylem (section)

== Structure ==
{{plain image with caption|Xylem cells.svg|Diagrammatic structure of xylem cells|400px|right}}

The most distinctive xylem [[cell (biology)|cell]]s are the long tracheary elements that transport water. [[Tracheid]]s and [[vessel element]]s are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called ''vessels''.<ref>{{cite book |author1=Raven, Peter A. |author2=Evert, Ray F. |author3=Eichhorn, Susan E. |year=1999 |title=Biology of Plants |publisher=W.H. Freeman and Company |pages=576–577 |isbn=978-1-57259-611-5}}</ref>

Wood also contains two other type of cells: [[Ground tissue#Parenchyma|parenchyma]] and [[ground tissue#Fibres|fibers]].<ref>[http://www.britannica.com/EBchecked/topic/650951/xylem Xylem] {{webarchive |url=https://web.archive.org/web/20110916145301/http://www.britannica.com/EBchecked/topic/650951/xylem |date=2011-09-16 }}. Encyclopædia Britannica</ref>

Xylem can be found:
* in [[vascular bundle]]s, present in non-woody plants and non-woody parts of woody plants
* in secondary xylem, laid down by a [[meristem]] called the [[vascular cambium]] in woody plants
* as part of a [[stele (biology)|stelar arrangement]] not divided into bundles, as in many [[fern]]s.

In transitional stages of plants with [[secondary growth]], the first two categories are not mutually exclusive, although usually a vascular bundle will contain ''primary xylem'' only.

The branching pattern exhibited by xylem follows [[Murray's law]].<ref name="mcculloh">{{cite journal |last=McCulloh |first=Katherine A. |author2=John S. Sperry |author3=Frederick R. Adler |title=Water transport in plants obeys Murray's law |journal=Nature |doi=10.1038/nature01444 |volume=421 |pages=939–942 |year=2003 |pmid=12607000 |issue=6926 |bibcode=2003Natur.421..939M |s2cid=4395034}}</ref>