PETER BELL is Emeritus Professor of Botany at University College London. He has spent many years studying plants, particularly the reproductive cells of land plants, and has travelled extensively throughout the world in his capacity as a botanist. He is author of The Diversity of Green Plants (1968, 1983, 1992), co-translator of Strasburger's Textbook of Botany (8th English edition, 1976) and editor of and contributor to Darwin's Biological Work (1959).
ALAN HEMSLEY is a Royal Society, University Research Fellow in the Department of Earth Sciences at the University of Wales Cardiff where his research focuses on the evolution of pollen and spore morphology and vascular plant evolution.