The correspondence includes determinations of specimen types, exchanges, botanical society business, critiquing of journal articles, recommendations for Martin's many students, and inquiries from the general public. Correspondents include botanical garden personnel, herbarium curators, professors at other universities, government agencies dealing with the study of fungi, foreign mycologists, and his former students. Significant correspondents include Constantine John Alexopoulos, Ruth McVaugh Allen, Gladys Elizabeth Baker, Robert Joseph Bandoni, Ernst Athearn Bessey, Henry Shoemaker Conard, William Bridge Cooke, Richard William George Dennis, Bernard Ogilvie Dodge, Marie Leonore Farr, Joseph Charles Gilman, William Dudley Gray, Clifford William Hesseltine, Herbert Spencer Jackson, Theodor Karl Just, Lorene Louise Kennedy, Donald T. Kowalski, Paul Lewis Lentz, David Hunt Linder, Marcel V. Locquin, Josiah Lincoln Lowe, Bernard Lowy, Thomas Huston Macbride (no letter from Macbride is in the Martin Papers), Donald Phillip Rogers, Fred Jay Seaver, William C. Sturgis, Kartar Singh Thind, Arthur Luna Welden, and Kenneth Wells.