1. Laboratoire de Biologie Moléculaire des Plantes Supérieures, Sciences III, Université de Genève, 1211 Genève 4, Switzerland (A.V.B., W.J.D., N.M.B., W.J.B., C.S.); Department of Microbiology, Centre of Legume Research, M409 Walters Life Science Building, University of Tennessee, Knoxville, TN 37996 (C.B.M., G.S.); and Federal Agronomy Research Station, Changins, 1260 Nyon, Switzerland (P.M.)