Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- (a) A specialized, permanent opening in the upper epidermis of the thallus of some liverworts, functioning in gas exchange. (b) A single hole in the primary cell wall of sieve elements that is lined with callose and through which solutes flow in sugar conduction. (c) Vernacular term for a wood vessel, used in the wood industry.
Glossary of "The Evolution of Plants (2nd ed.)" by Willis & McElwain (2014)
- A circular opening in the wall of pollen grains or all elliptical opening in the epidermis surrounded by two guard cells.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.
- Willis, K. J. & McElwain, J. C. 2014. The Evolution of Plants, 2nd ed. -ix + 398 pp. Oxford University Press, Oxford.