1. D. W. Meinke is in the Department of Botany, Oklahoma State University, Stillwater, OK 74078, USA. J. M. Cherry is in the Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA. C. Dean is in the Department of Molecular Genetics, John Innes Centre, Norwich, NR4 7UH, UK. S. D. Rounsley is at The Institute for Genomic Research, Rockville, MD 20850, USA. M. Koornneef is at the Laboratory of Genetics, Wageningen Agricultural University, Wageningen, 6307 HA, Netherlands.