(botany) The principal conductive cells of the xylem associated with the conduction of water and minerals from roots to the other parts of the plants
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 vessels.
The tracheary elements of the xylem are the tracheids and the xylem vessels. A tracheid is a tubular cell whose primary function is to conduct water and mineral salts, provide structural support, and prevent air embolism in vascular plants. A xylem vessel is a series of cells arranged in a way that enables rapid and more efficient water and mineral conduction in most angiosperms. Not all vascular plants have xylem vessels. In pteridophytes and most gymnosperms, the tracheid is the major conductive tissue and xylem vessel is absent. Most angiosperms have both tracheids and xylem vessels, and the xylem vessels are their main conductive tissue. The water flows rapidly in a xylem vessel due to its wider lumen (diameter) than that of a tracheid. Gymnosperms lacking vessels are a source of a type of wood referred to as softwood. In turn, the angiosperms with both tracheids and xylem vessels are source of the so-called hardwood.