This communication reports on an anatomical study of Xanthium strumarium Linn., with respect to the receptacle, the bur, its spines, and septum between the two flowers of a female inflorescence. The anatomical details, presented here, support Farr's view (1915), which was based entirely on ontogenical studies, that the bur is a continuation of the receptacle, and that the spines it carries are modified floral bracts.