"Available space theory". Dictionary of Botany. Retrieved 2012-05-24. http://botanydictionary.org/available-space-theory.html ↩
Romberger, John (1963). Meristems, Growth, and Development in Woody Plants: An Analytical Review of Anatomical, Physiological, and Morphogenic Aspects. U.S. Government Printing Office. p. 37. ↩