1. Business Unit Cell Cybernetics, Plant Research International, P.O. Box 16, 6700 AA, Wageningen, The Netherlands
2. Business Unit Biometry, Plant Research International, P.O. Box 16, 6700 AA, Wageningen, The Netherlands
3. Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
4. Department of Biochemistry, Beckman Center, Stanford University Medical Center, Stanford, California 94305