1. Department of Chemistry, Iowa State University, Ames, Iowa 50011; PWA, WRRC, BCE, Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, California 94710; Department of Wood and Paper Science, North Carolina State University, Raleigh, North Carolina 27695; and University of British Columbia, 4034-2424 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada