400 



COMPARATIVE MORPHOLOGY OF FUNGI 



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upon a minimal quantatitive difference of sex factors. These differences 

 generally change, and may thereafter be fixed as genotypes (multiple 

 allelomorphs) (Kniep, 1923). It is always possible to explain these 

 forms of heterothallism as different stages of self sterility. According 

 to this explanation, the Coprinus fimetarius type might be called homo- 

 thallic with a sterility factor, the Corticium type homothallic with two 

 sterility factors (Brunswik, 1924). The difficulty in this second inter- 

 pretation lies in the frequent alteration in 

 1 (T^S Z resulting fixation of the genotype of the sex 



"A factors of Schizophyllum commune. 



The cytological processes which take place 

 in the further development of the primary 

 mycelia have been studied for the heterothallic 

 forms only, e.g., for Coprinus fimetarius and Pen- 

 iophora Sambuci (Corticium serum) (Bensaude, 

 1918; Lehfeld, 1923). There were observed 

 anastomoses between the + and — mycelia 

 whereby the nucleus of one cell passed through 

 the clamp connection into the corresponding 

 cell of the other hypha (Fig. 266, 1). This 

 anastomosis may also take place, instead of be- 

 .£ tween two vegetative primary hyphae, between 

 one vegetative hypha and the germ tube of an 

 oidium which has arisen elsewhere in the culture 

 Salbuci. 2 l 6 : Two yoZTserZ and has been brought to the place in question, 

 tubes anastomosing and form- Generally the entire uninucleate mycelium is 

 "^m Cla TwobranrhTs^fseT- exhausted in the formation of binucleate cells, 

 ondary hyphae, A, B, have so that at a certain stage one finds no more nor- 



apptaring! 16 W^™ LehjlTd, mal uninucleate hyphae in the culture. The 

 1922; Bensaude. 1918.) binucleate cells develop laterally into binucleate 



hyphae. 

 The dicaryons which have resulted from these processes normally 

 keep on dividing conjugately throughout the entire life cycle, until the 

 formation of the fructification and the hymenial fundaments (as 

 the equivalents of the paired nuclei in the ascogenous hyphae of 

 the ascomycetes). The processes which led to their formation must 

 consequently be interpreted as the remains of a pseudoagamous 

 sexual act (plasmogamy) ; for hybrids may be formed between two differ- 

 ent species as between Panaeolus campanulatus and P. fimicola (Vanden- 

 dries, 1923). In the homothallic forms, the binucleate condition arises 

 in some way by an autogamous process, which is apparently pushed back 

 into the basidiospores as in the Corticium bombycinum type and in the 

 Gasteromycetes. This last type approximates apogamy; pure apogamy, 

 however, is found only in the Uredinales. 



