1. Institute of Plant Nutrition and Soil Science, University of Kiel, Olshausenstraße 40, D‐24098 Kiel, Germany
2. E. S. E. Department, The Hebrew University, Givat Ram, Jerusalem 91904, Israel
3. Forschungs‐ und Technologiezentrum Westküste, Hafentörn, D‐25761 Büsum, Germany
4. Institute of Systematical Botany, University of Munich, Menzinger Straße 67, D‐80638 München, Germany