SUMMARYThis paper deals with the comparative morphology and taxonomic relationships of the smuts of barley grasses, brome grasses, and wheat grasses in the Northwest heretofore known under the namesUstilago Lorentziana, U. bromivora, andU. bullata, respectively.Examination of 19 current collections, and 41 herbarium specimens of these three smuts revealed that they are morphologically similar. There is more variation in the morphology of the spores of collections ofU. bromivora, than exists betweenU. bromivora, as a species, and eitherU. bullataorU. Lorentziana.The modes for the diameter of the spores of various collections ofU. bromivoraranged from 6μin collection M-K to 10μin collections M-J and M-H. The mode for spore diameter ofU. bullatawas 7μin 3 collections and 8μin a fourth; forU. Lorentzianait was 8μin all collections.InU. bromivorathe epispore also varied according to collection from very minutely echinulate-verrucose in collection M-K to rather coarsely verrucose in collection M-L. Most collections were distinctly echinulate-verrucose.U. bullataandU. Lorentzianashowed less variation, from finely echinulate-verrucose to minutely verrucose.It is considered that the smuts under the namesUstilago bromivora, U. bullata, andU. Lorentzianareally represent one composite species, probably containing numerous well-defined physiologic races. SinceU. bullatahas priority over the other two names and is descriptive of the sori, it is proposed that that name apply to this species.An emended description ofUstilago bullatais accordingly given, with a list of the hosts in North America. Thus, 5 species ofAgropyron, 23 species ofBromus, 1 ofElymus, 7 ofHordeum, and 1 ofSitanionare recognized as hosts toU. bullata, in the new concept of this species. Ten of this total of 37 grasses are herein reported for the first time.