At least 21 species of rusts have been recorded on Abies; 2 (possibly identical) belong to Melampsora, 2 are unconnected peridermia, and the rest are distributed among 6 genera of the Puccinias-treae; 14 in all parasitize Abies balsamea. A study is here made of the structure of the spermogonia of 13 species, representing all of the genera (Melampsora, Melampsorella, Pucciniastrum, Calyptospora, Hyalop-sora, Milesina, and Uredinopsis), as a contribution to morphology in relation to taxonomy. It has been found that the spermogonia are strikingly distinctive and in some cases they show species differences within the generic type.