CRITERIA OF MALE AND FEMALE IN BREAD MOULDS (MUCORS).

The Mucors, commonly called bread moulds, are a group of fungi apparently simple in structure and in their methods of reproduction. All are able to multiply rapidly, perhaps indefinitely, by means of nonsexual spores. We have still in cultivation, for example, the sexual races of the common Rhizopus which were isolated in 1904. A few species are hermaphroditic (homothallic) and produce sexual spores (zygospores) through the interaction of branches from the same individual. The great majority, however, are dioecious (heterothallic) and require for sexual reproduction the interaction of individuals of the two opposite sexes provisionally designated as (+) and (-). Which of these two sexes is male and which is female is the problem of our present discussion. The process of zygospore formation in dioecious species can be illustrated by figure 1, a-e. Two filaments of opposite sex (a) produce, at the point