With the present publication, the structural studies of the ROLLET-Collection in Venezuelan Guiana are completed. Hundreds of tree species were studied concerning their bark structure, their leaf anatomy and fruit structure. The picture is now rounded off by the investigation of the leaf venation described in detail in this book, accompanied by many instructive figures. Interest in tropical medicinal wild plants is now growing rapidly, as there may be plants which cure dangerous viral infections, and North-American pharmaceutical companies have already started a multimillion dollar business on this expectation. But who knows all the species and can identify them? The key developed for this book may help to assist with the identification of the tropical flora though these keys are pioneer work. The book will be of interest not only to anatomists, taxonomists and ecologists but also to the teachers explaining the extraordinary tropical flora.