The great difficulties arising in the identification of a number of plants belonging to the genus Evolvulus, which plants were found in several recent collections of Convolvulaceae and were kindly entrusted to me for study, induced me to submit this genus to a further examination. It soon proved how great the prevailing confusion was, both in literature and in the herbaria. Various species were again and again wrongly interpreted and this especially concerns those which had been described by the older authors. Thanks to the invaluable help of a great number of herbaria I was in a position to bring about some order in the genus. Still numerous questions remain unsolved. A close study of living material, preferably on the habitat itself, will often be of great value here. I had a great quantity of material at my disposal, kindly lent me by the following herbaria. (These herbaria are indicated in the taxonomical part by the abbreviations in parentheses.) Botanischer Garten und Botanisches Museum, Berlin— Dahlem. (B) ’s Lands Plantentuin, Buitenzorg, Java. (Bog) Institut de Botanique et Herbier Boissier, Genève. (Boiss) Jardin Botanique de l’Etat, Bruxelles. (Br) Institute Biologico de Defeza Agricola e Animal, São Paulo. (Bu) Universitetets Botaniske Museum, Copenhagen. (C) Royal Botanic Gardens, Sibpur, Calcutta. (Calc) Conservatoire et Jardin Botaniques de la Ville, Herbier de Candolle, Genève. (DC) id., Herbier Delessert, Genève. (Del) Field Museum of Natural History, Department of Botany, Chicago. (F) Botanisches Institut und Botanischer Garten der Universität, Göttingen. (G) Gray Herbarium, Harvard University, Cambridge, Mass., U.S.A. (Gr) Hortus Botanicus en Botanisch Laboratorium van de Rijksuniversiteit, Groningen. (Gro) Botanisches Institut der Universität, Halle a. Saale. (H) Herbarium E. Hassler, San Bernardino, Paraguay. (Hassl) Royal Botanic Gardens, Kew, Surrey. (K) Rijks Herbarium, Leiden. (L) Botanischer Garten (Glawnij botanitscheski sad), Leningrad. (Len) Linnean Society of London, London. (Linn) Botanisches Museum, München. (M) British Museum (Natural History), London. (NH) New York Botanical Garden. (NY) Museum national d’Histoire naturelle, Herbier et Laboratoire de Botanique, Phanérogamie, Paris. (P) Jardim Botanico, Rio de Janeiro. (R) Naturhistoriska Riksmuseet, Stockholm. (S) Botanic Garden, Singapore. (Sing) Musee du Congo Belge, Tervueren. (T) Botanisch Museum en Herbarium van de Rijksuniversiteit, Utrecht. (U) United States National Herbarium, Smithsonian Institution, Washington, D.C., U.S.A. (US) Naturhistorisches Museum, Botanische Abteilung, Wien. (V) Here I wish to express my best thanks to the directors of these herbaria for their great assistance and especially to the directors and staff of the herbaria and libraries I have personally visited, viz. the “Jardin Botanique de l’Etat”, Brussels, the Royal Botanic Gardens, Kew, the Linnean Society of London, the British Museum of Natural History, London, the “Muséum national d’Histoire naturelle”, Paris and the “Musée du Congo Belge”, Tervueren. Further my gratitude to the director and staff of the “Rijks Herbarium” at Leyden, the collections and library of which I have so often consulted, and finally my most sincere thanks to Professor Dr. A. Pulle, Director of the “Botanisch Museum en Herbarium van de Rijks Universiteit” at Utrecht, under whose direction this work was completed. His great assistance, his continual interest in the work and his advice in the composition thereof have been of inestimable value to me.