INTRODUCTION 



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Fig. 123. Basidiomyceteae. Diploidization of monocaryon mycelium. (A) Two 

 monocaryon mycelia, mutually compatible, have united and diploidization has been 

 initiated in one cell. (B) Diagrammatic representation of the steps (1-6) in the 

 diploidization of a monocaryon mycelium by a dicaryon one. (Courtesy, Buller: 

 Nature, 126(3183) :686-689.) 



experiments which showed that the rate of progression of the diploidizing 

 nuclei through the mycehum was 1.2 to 1.5 mm. per hour in Coprinus 

 lagopus Fr. When the introduced nucleus or one of its descendants arrives 

 in the terminal cell of the hyphal branch the two nuclei divide by con- 

 jugate division and thenceforth a typical dicaryon mycelium is produced 

 from this hypha. The initiation of the dicaryon phase does not depend 

 alone upon the oidia. Two monocaryon hyphae of opposite sexual phase 

 may unite and the result is the same as when an oidium unites with a 

 hyphal cell. Brodie demonstrated that the oidia of Coprinus lagopus are 

 capable of germinating and forming a mycelium made of very slender 

 monocaryon hyphae. From these arise very numerous oidiophores and 

 heads of oidia. When two such oidial mycelia of opposite sexual phase 

 meet diploidization occurs. Also the oidia from one mycelium may 

 fertilize the oidial mycelium of the opposite sexual phase. Possibly the 

 oidia and the oidial mycelium may represent a residual male sexual 

 structure while any cell of the normal monocaryon vegetative mycelium 

 possesses a female tendency, this not being restricted merely to an oogone 

 as in many of the Ascomyceteae. Vandendries and Brodie (1933) find 

 however that in some Basidiomyceteae the oidia are also capable of func- 

 tioning as conidia, producing a typical monocaryon mycelium which is 

 capable of diploidizing and being diploidized by a monocaryon mycelium 

 of appropriate sexual phase. (Fig. 123.) 



The disappearance of definite sexual organs has not done away with 

 the three fundamental phenomena of sexual reproduction, cytogamy, 

 caryogamy, and meiosis, nor with the modification into various types of 

 compatibility and incompatibility of sexual strains such as occur in many 

 Ascomyceteae. Indeed, it seems possible that this development of 

 sexually compatible and incompatible strains has become greatly in- 

 creased in the Basidiomyceteae. 



