|tracheid (trā'kē-ĭd, -kēd') Pronunciation Key
An elongated, water-conducting cell in xylem, one of the two kinds of tracheary elements. Tracheids have pits where the cell wall is modified into a thin membrane, across which water flows from tracheid to tracheid. The cells die when mature, leaving only their lignified cell walls. Tracheids are found in all vascular plants. Compare vessel element.