Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- The outer protective covering of seed, developing from one or two integuments. Syn: testa. (seed part)
Glossary of "The Evolution of Plants (2nd ed.)" by Willis & McElwain (2014)
- Outer layer of the seed developed from the integuments of the ovule.
- 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.