Não informado. (1919). Department circular. U.S. Department of Agriculture.
Chicago-referens (17:e uppl.)Não informado. Department Circular. Washington: U.S. Department of Agriculture, 1919.
MLA-referens (8:e uppl.)Não informado. Department Circular. U.S. Department of Agriculture, 1919.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.