MLA

Stieglitz, Alfred, 1864-1946. Apollinaire, Guillaume. Box 3, folder 51. 1916 Jan 29. https://collections.library.yale.edu/catalog/2111673.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 3, folder 51"])(1916 Jan 29)[Apollinaire, Guillaume]. https://collections.library.yale.edu/catalog/2111673.