1. Research Chemist, U. S. Department of Agriculture, Agricultural Research Service, Department of Botany, North Carolina State University, Box 7625, Raleigh, NC 27695-7625
2. Professor, Department of Statistics, North Carolina State University, Box 8203, Raleigh, NC 27695-8203
3. Associate Professor, Crop and Soil Environmental Sci., Res. Div., Virginia Polytechnic Inst. and State Univ., Tidewater Agricultural Experiment Station, P. O. Box 7099, Suffolk, VA 23437-0099