1. L. G. Firbank is at the Centre for Ecology and Hydrology, Merlewood, Grange-over-Sands, Cumbria LA11 6JU, UK.
2. F. Forcella is at the USDA Agricultural Research Station, Morris, MN 56267, USA, and Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108-6026, USA.