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.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)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, و Carl Schurz Vrooman. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. Washington, [D.C.]: National Archives, 1947.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)United States. Department of Agriculture, et al. Letters Sent by the Assistant Secretaries of Agriculture, 1889-1919. National Archives, 1947.