Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- Growth in height or length of a stem or root, brought about by the elongation and differentiation of cells derived from the apical meristem.
Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- In plants, growth that is characterized by the lengthening of roots and shoots and by the proliferation of new roots and shoots through branching. (Contrast with secondary growth.)
- 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.