The author would like to thank FAO for commissioning this work, in particular Prof. Raffaele Mattioli for his encouragement and support, as well as other friends and colleagues for taking the time to discuss the issues involved, especially Dr David Bourn for allowing the author access to his working library and for his editorial comments, and Dr Issa Sidibe and Dr Victorin Codjia for providing the author with up-to-date price information.
