Mattoon, Wilbur R. (Wilbur Reed), 1875-1941 & Reed, C. A. (Clarence Arthur), 1880-1950. Black Walnut for Timber and Nuts., book, 1940; (https://digital.library.unt.edu/ark:/67531/metadc9514/m1/1/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .