Xylem
Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The word xylem is derived from the Greek word ξύλον (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant.
The basic function of xylem is to transport water, but it also transports some nutrients.
Structure
The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels.
Xylem also contains two other cell types: parenchyma and fibers.
Xylem can be found:
in vascular bundles, 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 stelar arrangement not divided into bundles, as in many ferns.
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.
