1. Dep. of Plant, Food, and Environmental Sciences, Faculty of Agriculture; Dalhousie Univ.; Truro NS B2N 5E3 Canada
2. Dep. of Botany; Univ. of British Columbia; Vancouver BC V6T 1Z4 Canada
3. Donald Danforth Plant Science Center; St. Louis MO 63132-2918 USA
4. Dep. of Biology; Saint Louis Univ.; St. Louis MO 63103-2010 USA