born Oct. 19, 1856, Geneva, Ill., U.S.
died March 3, 1939, New York, N.Y.
U.S. cell biologist.
He joined the Columbia University faculty in 1891, where he became established as a pioneer in work on cell lineage (tracing the formation of different kinds of tissues from individual cells). His interests later extended to internal cellular organization and the problem of sex determination, leading to a series of papers (1905) on the role of chromosomes. Recognizing the importance of Gregor Mendel 's findings, he realized that the role of chromosomes went far beyond the determination of sex and envisioned their function as important components in heredity as a whole, ideas that were a powerful force in shaping future genetic research.