subhirtella and Prunus x yedoensis, then back-crossed the resulting hybrid with P. subhirtella, and named his cross Prunus x 'Hally Jolivette' in honor of his wife. A cultivar of Forsythia bred by Sax was named 'Karl Sax' by a nurseryman. In 1946 he was appointed acting director of Harvard's Arnold Arboretum, in 1947 becoming the director – a post he held until 1954. Demography Sax was also interested in human demography. In 1955 he wrote Standing Room Only: The Challenge to Overpopulation, on the consequences of uncontrolled human population growth. Sax became associated with Planned Parenthood and was a member of the Population Association of America. Honors Sax was an elected member of the National Academy of Sciences and the American Academy of Arts and Sciences. In 1966, he and Hally were co-recipients of the Mary Soper Pope Memorial Award in botany. In 1959 he retired and moved to Media, Pennsylvania where he continued his work on plant breeding. Karl Sax died on October 8, 1973. References "Dr. Karl Sax Dies; Botanist Was 81". New York Times, Oct. 10, 1973. Smocovitis, V. B. Sax, Karl. 'American National Biography Online. Oxford University Press Swanson, C. P. 1988. Cytogenetics and Karl Sax. Genetics'' 119:5–7 External links Biographical Memoir of Karl Sax written by Carl P. Swanson and Norman H. Giles for the U.S. National Academy of Sciences, a superb source of information about Sax and his work 1892 births 1973 deaths People from Spokane, Washington American botanists Arnold Arboretum American geneticists Washington State University alumni Bussey Institution alumni University of California, Berkeley faculty Members of the United States National Academy of Sciences United States Army soldiers United States Army personnel of World War I People from Colville, Washington