The collection encompasses correspondence Hammond had received from Daniel I. Arnon (1910–1994), Siegfried Bellartz (1924– ), Alan Boyden (1897–1986), W.E. Bullard (?), Harold W. Chapman (1921–1962), Daniel G. Clark (?), R.A. Diettert (?), Marin S. Dunn (?), S.D. Elek (?), Morgan Evans (?), Herman S. Forest (?), David R. Goddard (1908–1985), Robert J. Hansen (?), George B. Hooper (?), M.A. Johnson (1901–1964), Hisakichi Kimura (?), Masao Kumazawa (?), Robert Lepper (1914–2010), Conrad B. Link (1912–2008), Hans Ferdinand Linskens (1921–2007), Alicia Lourteig (1913–2003), W.E. Martin (1908–1998), Herbert L. Mason (1896–1994), Yoshiharu Matsumura (?), William V. Mayer (1920–1989), Philip A. Munz (1892–1974), George L. McNew (1908–1998), Henry T. Northern (1932–1979), Theron O. Odlaug (1911–?), Theodore Payne (1872–1963), Walter S. Phillips (1905–1975), Harry J. Puller (?), Elmer C. Purdy (1889–1953), Maunell van Rensselaer (1897–1972), Donald D. Ritchie (1914–1987), John G. Seeley (1915–2007), Karl M. Silberschmidt (1903–1973), Carl Skottsberg (1880–1963), G. Fred Somers (1914–2000), John D. Spikes (1918–2006), John R. Squire (1915–1966), E.E. Stanford (1888–?), G. Ledyard Stebbins (1906–2000), Russell B. Stevens (1915–?), Ian M. Sussex (1927– ), Sam F. Trelease (1892–1958), Warren H. Wagner (1920–2000), Felix Widder (1892–1974), Wilbur E. Wright (?), and Cecil Yampolsky (1889–1970).