Allard, R. W. 1., Alvim, P. d. T. 1., Ashri, A., Barton, J. H. 1., & Buttel, F. H. 1. (1991). The U.S. National Plant Germplasm System. Washington, D.C.: National Academy Press.

Allard, Robert Wayne 1919-2003, Paulo de Tarso 1919-2011 Alvim, Amram Ashri, John H. 1936-2009 Barton, and Frederick H. 1948-2005 Buttel. The U.S. National Plant Germplasm System. Washington, D.C.: National Academy Press, 1991.

Allard, Robert Wayne 1919-2003, et al. The U.S. National Plant Germplasm System. Washington, D.C.: National Academy Press, 1991.