van der Water, Peter. 1999. ?Delta(13)C And Stomatal Density Variability In Modern And Fossil Leaves Of Key Plants In The Western United States?. Geosciences. Geosciences. University of Arizona. http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=731687391&sid=11&Fmt=2&clientId=43922&RQT=309&VName=PQD.