Osthoff, R. [Letter from R. Osthoff to F. Pfotenhauer, June 15, 1927], letter, June 15, 1927; (https://texashistory.unt.edu/ark:/67531/metapth606249/m1/1/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .