1. School of Biology and Environmental Science, Agriculture and Food Science Centre, Univ. College Dublin; Belfield Dublin 4 Ireland
2. Dep. of Plant Ecology; Justus-Liebig-Univ.; Heinrich-Buff-Ring 26-32 D-35392 Giessen Germany
3. The Glenside Group, Block 2, Unit 4, Bandeath Industrial Estate, Throsk; Stirling FK7 7XY Scotland
4. School of Agriculture, Food Science, and Veterinary Medicine, Univ. College Dublin; Belfield Dublin 4 Ireland