1. Donald Danforth Plant Science Center, St. Louis, Missouri 63132
2. Department of Mathematics, Florida State University, Tallahassee, Florida 32306
3. Independent Scientist, Santa Rosa, California 95409
4. Department of Horticulture, Michigan State University, East Lansing, Michigan 48824
5. Department of Computational Mathematics, Science and Engineering, Michigan State University, East Lansing, Michigan 48824