Brown, James Milton. Anon.1968. The Photosynthetic Regime of Some Southern Arizona Ponderosa Pine. Biological Science. Biological Science. University of Arizona. http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=756120291&sid=2&Fmt=1&clientId=43922&RQT=309&VName=PQD.