THE recognition of the + and - strains in rust fungi and the way in which the bi-nucleate aecial condition must be preceded by myeelial fusion of + and - strains or the introduction of pycniospore-containing nectar of the opposite strain, has led to the possibility of the study of inbred physiologic races. Johnson and Newton (Can. J. Res., 16 ; 1938) have made a study of the effects produced in Puccinia graminis Tritici Erikss. and Henn. Cultures have been started from a single urediospore and these have been followed through their cycle, selfing being brought about by mixing pycniospore-containing nectar of pustules of the isolated race.