Michael Heinrich1, Robert Verpoorte2. 1. Center for Pharmacognosy and Phytotherapy/Research Cluster Biodiversity and Medicines, UCL School of Pharmacy, University of London, 29-39 Brunswick Sq., London WC1N 1AX, UK. Electronic address: m.heinrich@ucl.ac.uk. 2. Natural Products Laboratory, Institute of Biology, Leiden University, P.O. Box 9505, 2300RA Leiden, The Netherlands. Electronic address: verpoort@chem.leidenuniv.nl.