Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- Opening in the integument(s) of a seed plant ovule through which pollen grows to reach the female gametophyte within.
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- A small pore at the distal end of the integument of a seed, functioning as the site of entry of pollen grains, or in angiosperms of pollen tubes.
Glossary of "The Evolution of Plants (2nd ed.)" by Willis & McElwain (2014)
- An opening in the integument (seed coat) through which the pollen usually enters.
- 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.
- 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.