The arrangement of the primary vascular system in Ranunculaceae offers several characters of taxonomic importance, relating to the number of foliar gaps and traces and especially to the nature of the axillary vascular supply. Five types of axillary vascularization are now recognized, two of which are here described for the first time. The family shows a greater range of variation in vascular construction than is known in any comparable group of genera. To a great extent the vascular evidence supports conclusions already widely accepted on other grounds, as, for example, in emphasizing the isolation of Paeonia, but elsewhere, and particularly in considering affinities with other families, the study of the vascular system seems likely to make an independent contribution.