Mostly concerned with Blakeslee's studies on beans, blood groups, colchicine, Datura, embryo cultures, and horticulture. Many letters relate to the support and direction of the Smith College Genetics Experiment Station, which he headed. Other letters are about the Carnegie Institution of Washington, "Biological Abstracts," American Association for the Advancement of Science, American Philosophical Society, Institut de France, University of Connecticut. Also contains travel letters from Germany and miscellaneous lectures.

The maize geneticist Barbara McClintock (1902-1992) is credited with the discovery of "jumping genes," that is chromosomal "crossing over" and translocation. She received the Nobel Prize in Physiology or Medicine in 1983. The collection is organized into six series: I. Correspondence, 1931-1991; II. Subject files, 1938-1989; III. Works by McClintock, 1944-1989; IV. Works by others, 1927-1991; V. Research notes, notebooks, and card files, 1930s-1990s ; VI. Photographs, 1928-1991.