I.H'I" CYCLES, SL-.XUALHV, and sexual iMLCHANlSAlS 75 



of hcrcrothallisni. Species of indeterminate sexuality can be cited in 

 abundance, but thev can be more easily rationalized as intermediate 

 betw een the various types of heterothallism and homothallism. 



The fungi, viewed from this particular bias, present many 

 admittedly puzzling features that offer, however, no recognized out- 

 right contradiction to the essential idea of homo-^hetero^'homothal- 

 lism. The lack of heterothallic species in a few large and long-estab- 

 lished groups — the AspergUhis-Pemcill'mm, etc., complex — is a case 

 in point. Here, ho\\ever, there is a majority of sexually sterile species, 

 and the entire group may well represent a vestige of the primitive 

 homothallic stem, well along its degenerative course toward unequiv- 

 ocal inclusion in the Fungi Imperfecti. 



Further speculation along these lines for the present time, ho\t^- 

 ever intriguing, cannot produce a wholly satisfactory answer to the 

 problem. There is as yet insufficient information to permit the postu- 

 lation of a completely feasible system that would account for the 

 complicated sexual situation now existing in the fungi. For the time 

 being, we can only recognize the situation for what it is, and marvel. 



SUMMARY 



Sexual reproduction in fungi displays a tremendous range of 

 variability. Recognition of three distinct features is necessary ade- 

 quately to describe the role of sex in any single species. These facets 

 are: (1) the life cycle, in which the critical events are synonymous 

 with the initiation, the progression, and the termination of the essen- 

 tial sexual process; (2) the pattern of sexuality, which determines 

 self-fertility or self-sterility, and in the latter case the exact pattern of 

 inter-individual fertility; and (3) the sexual mechanism, the means 

 by which sexual fusion is accomplished within the restrictions 

 imposed by the life cycle and pattern of sexuality. Seven types of 

 life cycles, seven distinct patterns of sexuality, and about a dozen or 

 more basic kinds of sexual histories allow, in combination, a be\\'il- 

 dering array of distinct sexual types. 



Although there is a very loose correlation between morpholog- 

 ical specialization and each of the three major facets of sexuality, no 

 rigid correlation appears to exist between phylogenetic groupings 

 and the various combinations of sexual features. A possible scheme to 

 rationalize the sexual situation as now existing rejects the simple der- 



