The following paper was written after I had prepared a revised account of the Cyperaceae of the Malay Peninsula. I can not claim first hand acquaintance with Cyperaceae of other regions, nor to have consulted all the literature. I have, however, been impressed with the need to investigate more fully the tropical members of the family, and I have been led to the conclusion that the Hypolytreae (of Bentham) are the most primitive element in Cyperaceae. I have argued this thesis below and have given a general survey of the inter-relationships of the spikelet-form in the various tribes. I suggest that here, as in many other families of plants, the tropical members are, on the whole, the most primitive, and a full understanding of them is, therefore, of great importance in a comparative morphological study of the family. Such a full understanding is still lacking, and I would commend the subject to anyone who may be interested. It is a small example of the wealth of significant information waiting to be extracted from the astounding variety of plant life in the tropics. In Cyperaceae there are five main spikelet-forms: 1. Hypolytreae (of Bentham, not of Pax). Within each glume an arrangement usually considered as a partial inflorescence, by Bentham ("Genera Plantarum") as a flower, consisting of a terminal ovary and a varying number of scales around it, some or all of them with a single axillary stamen, the scales more or less distinctly arranged in whorls of 3 (usually 1-4 whorls), the two lateral scales of the outer whorl keeled and sometimes more or less completely joined laterally. 2. Scirpeae and Rhynchosporeae. Spikelets with many or few flower-bearing glumes, each glume enclosing a hermaphrodite flower consisting at fullest development of 6 (rarely to 10) perianthsegments or bristles, 3 stamens and an ovary with 3 stigmas. Various reductions from this condition occur, and some flowers may be male only; in some cases a spikelet may have only a single apparently terminal flower.