United States. Department of Agriculture, United States. National Archives and Records Service, Willits, M., Dabney, C. W., Brigham, J. H., Hays, W. M., . . . Vrooman, C. S. (1947). Letters sent by the assistant secretaries of agriculture, 1889-1919. National Archives.
Chicago-referens (17:e uppl.)United States. Department of Agriculture, United States. National Archives and Records Service, Mr Willits, Charles William Dabney, Joseph H. Brigham, W. M. Hays, B. T. Galloway, och Carl Schurz Vrooman. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. Washington, [D.C.]: National Archives, 1947.
MLA-referens (8:e uppl.)United States. Department of Agriculture, et al. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. National Archives, 1947.