SUMMARYFurther evidence is presented thatUstilago AvenaeandU. perennanswill hybridize.Crosses betweenUstilago AvenaeandU. perennanswere made which involved four sorus characters, namely, covered, naked, powdery, and indurate.The naked and powdery characters were found to be dominant over covered and indurate, respectively.Independent inheritance of these characters is indicated by the fact that naked powdery, naked indurate, covered powdery, and covered indurate segregates were produced in the F2generation. These segregates broke up in the F3generation as follows: the naked powdery segregate gave rise to all four of the above-mentioned segregates; the naked indurate segregate produced naked indurate and covered indurate types; the covered powdery segregate produced covered powdery and covered indurate types; and the covered indurate segregate proved to be doubly homozygous in yielding only the covered indurate type of sorus. In crosses ofU. perennanswith a race ofU. Avenaehaving normal powdery sori, only the covered vs. the naked sorus characters were studied. Again it was found that the naked sorus character is dominant over the covered sorus character.The susceptibility of cultivated oats toUstilago perennanswas demonstrated, but tall oatgrass has not been found to be susceptible toU. Avenaenor to the hybrids between these two smuts.ThatUstilago AvenaeandU. perennansare synonymous is indicated by the morphological identity of their chlamydospores, their genetic relationship, and host range.A consolidated species would, by priority, be designated asUstilago Avenae(Pers.) Jensen.