SummaryAsci from cultures in which strains Arl.6 and Arl.10 ofNeurospora sitophilaare mated are not all alike. Some asci produce spores which differ primarily only as to their sex. All 8 spores in the ascus develop mycelia which form monilioid conidia normally. Other asci produce four different kinds of spores, two of each kind. The spores differ not only as to sex but in the types of mycelia which they develop on germination. Two spores of each sex give rise to albinistic mycelia which are practically sterile as regards their ability to produce monilioid conidia. Two spores of each sex are typical and their mycelia develop masses of orange colored conidia. In such asci the spores may alternate two and two as to sex and four and four as to being albinistic as contrasted with typical; or the spores may alternate four and four as to sex, and two and two albinistic and typical. The particular distribution of the spores in the ascus depends upon whether the factors for sex and factors for conidia are segregated during the first or the second nuclear division in the ascus.A new race ofNeurospora sitophilawhich can be propagated indefinitely by sexual reproduction has been obtained by mating two albinistic haplonts of opposite sex.A culture of strain Arl. 10, originally derived from a single ascospore, now develops two kinds of monilioid conidia. Conidia of one kind produce typical mycelia which form conidia normally; other conidia, as the result of a saltation or some sort of somatic segregation develop albinistic mycelia, which are very much like the albinistic mycelia derived from ascospores following segregations during meiosis. Some of the former, however, do produce a few colorless and otherwise abnormal conidia. By selecting conidia from Arl. 10 through a few generations mycelia were obtained which appear to be typical and stable.Strain Arl.6 is a typical stable conidial strain.The albinistic races of both sexes develop true microconidia which are comparable to microconidia of species ofSclerotinia.These microconidia germinate and produce albinistic mycelia which can be mated. The perithecia are normal in every respect except that their ascospores will be albinistic. Microconidia ofNeurospora sitophilaare distinct morphological structures not to be confused with the monilioid conidia. Whether or not typicalMoniliastrains produce microconidia has not been determined.