76 SEX IN MICROORGANISMS 



ivation of heterothallism from homothallism, or vice versa, in favor 

 of an indirect derivation of homothallism from the various types of 

 heterothallism, each of which in turn was independently evolved 

 from primitive homothallic forms. Present understanding is insuffi- 

 cient, however, to permit the postulation of a completely feasible 

 system to account for the existing sexual complexity of the fungi. 

 The multiplicity of sexual types and forms which contribute to this 

 complexity, however, provides a wealth of material for those who 

 would seek exact specifications in the tools for the elucidation of 

 many basic phenomena of universal biological importance. 



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