Gregor Mendel’s work (see the chapter “Heredity, Natural Selection, and Evolution”) was really not appreciated until advances in cytology enabled scientists to better study cells. In 1900, Dutch botanist Hugo de Vries (1848–1935), German botanist and geneticist Carl Correns (1864–1933), and Austrian botanist Erich von Tschermak (1871–1962) examined Mendel’s original 1866 paper and repeated the experiments. In the following years, chromosomes were discovered as discrete structures within the nucleus of a cell. In 1917, American geneticist Thomas Hunt Morgan (1866–1945), while at Columbia University, extended Mendel’s findings to the structure and function of chromosomes. This and subsequent findings in the 1950s were the beginning of the modern era of genetics.