1. Faculty of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan
2. Kobe City University of Foreign Studies, Gakuen Higashi‐Machi, Nishi‐ku, Kobe 651‐21, Japan
3. Department of Botany, University of Glasgow, Glasgow G12 8QQ, UK
4. Department of Biology, Faculty of Science, Tokyo Metropolitan University, Minami‐Ohsawa, Hachioji 192‐03, Japan