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.
Παραπομπή σε μορφή Chicago (17η εκδ.)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, και Carl Schurz Vrooman. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. Washington, [D.C.]: National Archives, 1947.
Παραπομπή σε μορφή MLA (8th εκδ.)United States. Department of Agriculture, et al. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. National Archives, 1947.