1. Notes on taxonomic techniques;Benson L.;Torreya,1939
2. Methods of collecting cacti for the herbarium and botanical garden;Clover E. U.;Cact. Succ. J. (US),1952
3. How to Collect Certain Plants
4. The study of Cactaceae;Fosberg F. R.;Cact. Succ. J. (US),1932