Water-conducting cells are a category of plant cells found in xylem in the vascular tissue system which facilitate the vertical and lateral movement of water through the plant. At maturity, they can be classified into two types: tracheids and vessel elements. All land plants possess water-conducting cells. However, most bryophytes and gymnosperms will only possess tracheid-type water-conducting cells; angiosperms can possess either or both tracheids and vessel elements.
All water-conducting cells begin as live cells and are killed similarly. They begin as protoxylem, then mature into metaxylem. As this occurs, their cell walls and organelles are degraded and removed to increase the efficiency of water transport across the cell. By maturity, water-conducting cells are dead, elongate cells which have been fully hollowed out, save for thick secondary cell walls which were deposited as it died.