Não informado. (1933). Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania. University of Pennsylvania.
Chicago-referens (17:e uppl.)Não informado. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania. Philadelphia, Pa: University of Pennsylvania, 1933.
MLA-referens (8:e uppl.)Não informado. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania. University of Pennsylvania, 1933.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.