This collection contains correspondence addressed to Kelso from M.L. Fernald (1873–1950), George A. Hardy (?), H.D. Harrington (1903–1981), A.S. Hitchcock (1865–1935), W.L. Jensen (?), Theodor Just (1904–1960), Paul E. Klopsteg (1889–1991), G.H.M. Lawrence (1910–1978), Bertil Lindquist (1904–1963), Otto C. McCreary (1879–1944), Robert P. McIntosh (1920–2017), J. Paul Miller (?), Wilfred H. Osgood (1875–1947), M. Walter Pesman (1887–1962), Reed C. Rollins (1911–1998), Ruth D. Sanderson (?), N. Savelev (?), B.O. Savile (1909–2000), Marjorie W. Stone (1917–1967), Emerson Stringham (?), Robert M. Underhill (1893–1988), J.T. Vassilczenko (1903–1995), U.T. Waterfall (1910–1971), and Henrietta L. Zobel (?).

A handwritten letter dated June 24 (no year) from an unknown correspondent from the Ùstav Biológie Krajiny (Institute of Landscape Ecology) at the Solvenskej akadémie vied (Slovak Academy of Sciences).

A handwritten and undated letter from an unknown correspondent who signed their name as Eva W. (?).

Also included is a typed essay published as Biological Leaflet No. 106 and dated November 1974. It is a translation into English from Russian by Kelso of Alexandrova's (spelled "Aleksandrova") "Classification of Vegetation, Principles of classification and classification systems of various phytocenological schools", Nauka Publishing House, Leningrad, 1969.