Glossary of "Lichens" by Purvis (2000)
- A protective layer of compacted fungal cells usually present on the upper surface above the photobiont layer and occasionally also on the lower surface.
Glossary of "Plant Biology (1st ed.)" by Graham et al. (2003)
- The tissue in roots and stems lying between the epidermis and the vascular tissues.
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- The outer, mostly parenchymatous tissue inner to the epidermis and external to the vasculature. (root part, stem/shoot parts)
- Graham, L. E., Graham, J. M. & Wilcox, L. W. 2003. Plant Biology. -xxxv + 497 pp. Pearson Education, Inc., Upper Saddle River.
- Purvis, W. 2000. Lichens. 112 pp. Smithsonian Institution Press, Washington.