Rioux, D.; Nicole, M.; Simard, M.; Ouellette, G.B. (1998). "Immunocytochemical Evidence that Secretion of Pectin Occurs During Gel (Gum) and Tylosis Formation in Trees". Phytopathology. 88 (6). The American Phytopathological Society: 494–505. doi:10.1094/PHYTO.1998.88.6.494. PMID18944900.
Rioux, D.; Nicole, M.; Simard, M.; Ouellette, G.B. (1998). "Immunocytochemical Evidence that Secretion of Pectin Occurs During Gel (Gum) and Tylosis Formation in Trees". Phytopathology. 88 (6). The American Phytopathological Society: 494–505. doi:10.1094/PHYTO.1998.88.6.494. PMID18944900.
Van Sambeek JW, Dawson JO, Ponder F Jr, Loewenstein EF, Fralish JS (2003). "The Central Hardwood Forest: Its Boundaries and Physiographic Provinces". Proceedings of the 13th Central Hardwood Forest Conference. 234. U.S. Department of Agriculture, Forest Service, North Central Research Station.