Charles Elmer Allen (October 4, 1872 in Horicon, Wisconsin - June 25, 1954) was an American botanist and cell biologist whose discoveries include the first documentation of sex chromosomes in plants.[1] He was a member of the United States National Academy of Sciences and the American Philosophical Society,[2] [3] and held presidencies of the Botanical Society of America (1921), the Wisconsin Academy of Sciences, Arts and Letters (1931-1933), the American Society of Naturalists (1936), and the American Microscopical Society (1948). Allen was a professor at the University of Wisconsin for over 20 years.[4]