Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- A generally elongate cell that is dead at maturity, has a lignified, secondary cell wall, and is positioned end-to-end with other tracheary elements, forming a continuous tube that functions in water and mineral conduction; the major component of xylem tissue.
Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- Either of two types of xylem cells - tracheids and vessel elements - that undergo apoptosis before assumuing their transport function.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.
- Sadava, D., Hillis, D. M., Heller, H. C. & Berenbaum, M. R. 2011. Life: The Science of Biology, 9th ed. -xliv + 1266 pp. Sinauer Associates, Inc., Sunderland.