[Envelope from Southern School-Book Depository to C. C. Cox, April 24, 1920], text, April 24, 1920; (https://texashistory.unt.edu/ark:/67531/metapth1246740/m1/1/: accessed July 8, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .