1. Postdoctoral fellow in the Department of Plant Pathology, University of Wisconsin, Madison 53706.
2. Staff of Agrigenetics Advanced Research Laboratory, Madison, Wisconsin 53716, and with the University of Wisconsin.
3. Staff of Agrigenetics Advanced Research Laboratory. Address correspondence to T. C. Hall, Agrigenetics Advanced Research Laboratory, 5649 East Buckeye Road, Madison, Wisconsin 53716.