This collection includes letters between Ingenhousz and European and American scientists.

The plant physiologist and historian Rodney H. True (1866-1940) divided his career relatively evenly between the Bureau of Plant Industry in United States Department of Agriculture and the Department of Botany and Morris Arboretum of the University of Pennsylvania. A specialist in the physiological function of mineral nutrients in plants, True was active in his later career in the Philadelphia Society for Promoting Agriculture, the Pennsylvania Horticulture Society, and the Agricultural History Society. The True Papers consist of 6 linear feet of material relating primarily to the period of his career spent at the University of Pennsylvania. The collection contains roughly equal proportions of personal and professional correspondence, with a few diaries and research notebooks documenting his involvement with professional organizations and his interests in the history of his discipline.

This collection contains correspondence, drafts of papers, the manuscript of an unpublished book, and photographs. Osterhout's interest in the electrophysiology of plants is documented, as well as his professional career at the University of California, Berkeley; Harvard University; and the Rockefeller Institute.

William Jacob Robbins (1890-1978, APS 1941) was a botanist and physiologist. From 1937 to 1957 he was director of the New York Botanical Garden. His research focused on culture methods of plants in relation to biochemistry and nutrition, especially on the synthetic abilities of fungi. His studies paralleled the scientific agenda of the Rockefeller Foundation, an agency with which he was closely associated for years as adviser and trustee. He was perhaps the most influential botanist in the National Academy of Sciences (NAS) during the early postwar era, and a principal participant in the plans for the global reconstruction of science. Robbins served as president of the American Philosophical Society from 1956 to 1959.