The Netherlands is to be congratulated in having available within its borders such an outstandingly important collection of historical botanical material as that preserved in the Rijks Herbarium at Leiden. To a greater and greater degree the importance of this great assemblage of botanical specimens becomes manifest as critical work is done on it and on the corresponding collections in other botanical centers, and as various natural groups are treated monographically. In many groups of plants, particularly those represented in the Netherlands East Indies, the Rijks Herbarium is the court of last resort in determining the exact status of many hundreds of described species, because in this collection are deposited the actual types of the very numerous species described by REINWARDT, BLUME, KORTHALS, MIQUEL, BÜSE and other pioneer botanists who did the original basic work on the exceedingly rich flora of Malaysia. In addition to these early botanical collections the institution contains a most important series of specimens collected within the past half century in all parts of Malaysia, extending from Sumatra to New Guinea and including the Philippines. It is an almost hopeless task accurately to indentify these recent collections without reference to the vast stores of historical material preserved in Leiden. While it is true that extensive collections of Malaysian plants are to be found in other botanical centers, such as Kew, the British Museum, the Paris Museum, the Berlin Botanical Garden, the Natural History Museum, Vienna, the New York Botanical Garden, the United States National Herbarium, and at such distant centers as Buitenzorg, Singapore, Calcutta, and Manila, not one of these institutions has such great wealth of historical Malaysian material as is to be found in the archives of the Rijks Herbarium. In extent, that is in the actual number of specimens of Malaysian plants, disregarding the historical aspects of the collection, no botanical institution in the world contains such a mass of Malaysian material as that preserved in Leiden. While it is true that in the past some monographs have been prepared on the basis of an actual examination of material in several institutions, much such work has been done solely on the basis of collections available in one center. The modern tendency is for botanists to go farther afield and in doing really critical work to examine the historical material preserved in the larger botanical centers. This may and usually does involve more or less travel, but many centers now provide for inter-institutional loans, while it is usually possible to secure photographs of really important specimens. Through such cooperation monographic work is rendered much more inclusive, more valuable, and more accurate than in those cases where a monographer has based his work largely or wholly on the collections in one institution; and where his knowledge of those species not represented in his own institution was gained from the descriptions alone. It is axiomatic that no monographic treatment is fully satisfactory unless it is actually based on comprehensive collections where the author, through one means or another, has been able critically to examine actual specimens of most or all of the species considered by him, including as far as possible the actual types on which the original descriptions were based.