An account is given of uredosori and haustoria of 6 genera of the Pucciniastreae. Heretofore, the uredospores have been described in 3 genera of the group as arising catenulately, but they are now shown to be pedicellate throughout. The spores bud out singly from a layer of sporogenous cells at the base of the sorus. A uredoperidium occurs in all 6 genera. It consists of the terminal cells of 3-celled columns which arise in the young sorus. These terminal (peridial) cells are liberated by the disorganization of the subterminal or intercalary cells. The latter are disrupted by the upward growth of the first spore ''buds'' from the basal sporogenous cells. Germ pores characterize the uredospores ot the group. Although Melampsorella and Milesina are not unlike in respect of development of uredosori, they exhibit other characteristics which justify their retention as distinct genera. Hyalopsora and Uredinopsis are not dissimilar in regard to those features by which Magnus originally differentiated these genera; however, their retention as distinct genera is justified on the basis of other differences. The uredo stage provides no criteria for a division of the Pucciniastreae into 2 groups[long dash]those on ferns and those on flowering plants. Haustoria are of common occurrence throughout the group. They are similar in general organization, but vary greatly in size and shape, and exhibit''certain generic and specific differences.