noun, plural: xylem vessels
(botany) One of the tracheary elements of xylem that is characterized by being made up of a series of cells arranged in a way that enables water and mineral conduction in many angiosperms
The xylem is the vascular tissue responsible for the upward conduction of water and nutrients from the roots. The xylem tissue moves water and nutrients to various parts of the plant such as shoots and leaves. Its major components include xylem parenchyma, xylem fibers, tracheids, and xylem vessels.
The xylem vessel is one of the two cell types of tracheary elements, the other is the tracheid.These two are the water conducting elements in vascular plants. However, Pteridophytes and most Gymnosperms have only tracheids. Most angiosperms (flowering plants) have both xylem vessels and tracheids but the xylem vessels serve as the major conductive element.
Both xylem vessels and tracheids lose their protoplast at maturity and therefore become non-living components of the xylem eventually. Both of them form a secondary cell wall in between the primary cell wall and the plasma membrane that is lignified. The most common patterns of secondary cell wall thickenings are annular, spiral, scalriform, reticular, and pitted. However, the xylem vessels have thinner secondary walls. Both xylem vessels and tracheids have pits on their lateral walls.
The xylem vessel is a series of cells and each cell is referred to as a vessel member (vessel element). In contrast, a tracheid is an individual cell. The vessel is made up of vessel members with common end walls that are partly or wholly dissolved. The end walls may have perforations. The presence of perforation plate distinguishes xylem vessels from tracheids.
The typical length of xylem vessel is 10 cm. However, a typical vessel member is shorter than a tracheid cell. Nevertheless, the former is broader in diameter than the latter, enabling water to flow rather rapidly through xylem vessels than tracheids. This makes the xylem vessel more efficient in conducting water. When viewed from the top, the xylem vessels are circular in contrast to the tracheids that are polygonal.
Woody angiosperms, particularly trees, form secondary xylem (with xylem vessels being referred to as wood vessels). The type of wood they produce is called hardwood.
- xylem vessel
- xylem trachea