Preston, R. J. (1961). North American trees (2nd ed.). Iowa State University press.
Dyfyniad Arddull ChicagoPreston, Richard J. North American Trees. 2nd ed. Iowa: Iowa State University press, 1961.
Dyfyniad MLAPreston, Richard J. North American Trees. 2nd ed. Iowa State University press, 1961.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.