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A vessel element or vessel member (also called a xylem vessel) [1] is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in most angiosperms ( flowering plants ) and in some gymnosperms such as cycads and Ephedra , but absent in conifers .
Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels. [6] Xylem also contains two other type of cells: parenchyma and fibers. [7] Xylem can be found: in vascular bundles, present in non-woody plants and non-woody parts of woody plants
After this, the water moves up the xylem vessels to the leaves through diffusion: A pressure change between the top and bottom of the vessel. Diffusion takes place because there is a water potential gradient between water in the xylem vessel and the leaf (as water is transpiring out of the leaf). This means that water diffuses up the leaf.
In the stems of some Asterales dicots, there may be phloem located inwardly from the xylem as well. Between the xylem and phloem is a meristem called the vascular cambium. This tissue divides off cells that will become additional xylem and phloem. This growth increases the girth of the plant, rather than its length.
The xylem typically lies towards the axis with phloem positioned away from the axis . In a stem or root this means that the xylem is closer to the centre of the stem or root while the phloem is closer to the exterior. In a leaf, the adaxial surface of the leaf will usually be the upper side, with the abaxial surface the lower side.
Root pressure may be important in refilling the xylem vessels. [3] However, in some species vessels refill without root pressure. [4] Root pressure is often high in some deciduous trees before they leaf out. Transpiration is minimal without leaves, and organic solutes are being mobilized so decrease the xylem water potential.
Angiosperms have both tracheids and vessel elements. [1] A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of conductive cell, called vessel elements, to transport water through the xylem.
Xylem is the water-conducting tissue, and the secondary xylem provides the raw material for the forest products industry. [25] Xylem and phloem tissues each play a part in the conduction processes within plants. Sugars are conveyed throughout the plant in the phloem; water and other nutrients pass through the xylem.