The Cytological Basis for Homothallism and Heterothallism in the Agaricaceae
American Journal of Botany
STATEMENT OF PROBLEM In most of the previous studies on sexuality in the Hymenomycetes, cytological work has been a minor feature. Furthermore, in practically all studies on sex in this group, the basidia of the fungi used were four-spored. The sex reactions of the four-spored species are explainable in terms of sex factors and the distribution of these factors is explicable on the basis of known nuclear events. A number of species or forms among the agarics are known to have twospored basidia.
... In such cases there are theoretically possible a number of variations from the typical nuclear cycle found in four-spored forms. The problem then presented itself of determining, in these two-spored forms, which of the theoretical possibilities existed in fact; what cytological phenomena underlie homothallism and heterothallism in these fungi; and to what extent additional light could be thrown on the detailed nuclear phenomena in the agarics. HISTORICAL SKETCH The discovery in 1918-1919 of heterothallism in the Hymenomycetes opened up a fertile field of investigation in the higher fungi, and during the following decade our knowledge of sex phenomena has been extended to include a considerable number of Hymenomycetes and a few Ascomycetes. The recent discovery of heterothallism in important pathogens, the rusts and smuts, has added a new and vital emphasis to the problem of sexuality in fungi. Gaumann's (7) excellent review of this subject is now available in English as well as German and the present writer will therefore limit the following review to the most pertinent items in the older literature and to the recent developments in the field. It seems desirable to subordinate chronological sequence to a convenient grouping of related phases of. the subject. Mlle. Bensaude (2), who first announced the discovery of heterothallism in the Hymenomycetes, isolated two haploid (primary) mycelia of Coprinus fimetarius Fr. and showed that these mycelia conjugate, giving rise to a diploid (secondary) mycelium. The work of Mlle. Bensaude, especially her cytological studies, established clearly the existence of heterothaIIism. Her