^ abP. H. Raven, R. F. Evert og S. E. Eichhorn: Biology of Plants, 7. udg.,2005 side 9, ISBN0-7167-1007-2. (engelsk)
^Evert, Ray Franklin Katherine Esau: Esau's Plant anatomy: meristems, cells, and tissues of the plant body - their structure, function and development, 2006, ISBN0-471-73843-3(engelsk)