420 COMPARATIVE MORPHOLOGY OF FUNGI 



Thus plasmogamy is suppressed and the haplont is limited to a short 

 period in the basidiospore, from the entrance of the spore nucleus until its 

 first division. In this type, where imperfect forms appear, they are 

 binucleate, in contrast to Corticium. 



Comparing these three types of life cycle with the diagrams of the 

 Ascomycetes, we observe that the haploid mycelium (the thallus in the 

 Ascomycetes) is much reduced ; it is usually ephemeral and in the Gastero- 

 mycetous type is entirely suppressed; the conidia and the other 

 imperfect forms, as they occur in some Ascomycetes, are unknown in 

 the Basidiomycetes. 



Parallel with this recession of the haplont, there is a complete disap- 

 pearance of functional sexual organs in the Basidiomycetes known at 

 present. Consequently plasmogamy takes place (as in the higher Asco- 

 mycetes) pseudogamously between two hyphae ; but it is transferred from 

 the hyphae of the fructifications into the vegetative mycelium; subse- 

 quently it is shifted forward into the basidiospores {Tilletia Tricici) and 

 is finally suppressed, i.e., replaced by a nuclear division which is 

 no longer followed by septal formation (G aster omycetous type). In 

 contrast to the Ascomycetes, the rhythm of development is relaxed, 

 plasmogamy has become labile in time and place, and the Basidiomycetes 

 are diffusely fruiting (perittogamous sensu Killian, 1924). 



Because of the insignificance of plasmogamy, its products exhibit no 

 new important characteristics, i.e., after plasmogamy the diplont contin- 

 ues to develop vegetatively (in contrast to the ascogenous hypha of the 

 Ascomycetes, which cannot nourish itself). It is so well adapted to the 

 vegetative function that it develops simple imperfect forms which are 

 not fundamentally different from the imperfect forms of the haplonts. 



Long after plasmogamy and fixation of the binucleate character, the 

 diplont forms fructifications, which (in contrast to many Ascomycetes) 

 bear no direct relation to plasmogamy. Because of their diploid charac- 

 ter, they attain to a much higher differentiation than the haploid fructifi- 

 cations of the Ascomycetes. In most cases, their basidia occur in special 

 layers just as do the asci of the Ascomycetes. Similarly in the young 

 stages of these basidia, caryogamy immediately followed by meiosis occurs. 

 In spite of the labile character or entire absence of plasmogamy, the 

 position of caryogamy and meiosis remains unaltered in the basidia. 

 The tetracytes are not individualized within the mother cells but arise 

 exogenously on sterigmata. 



After this exposition of the course of development of Basidiomycetes, 

 we approach the question of their origin. In this respect there are two 

 historical schools. The school of Bary considers the Basidiomycetes as 

 members of the Ascomycetous series, and the school of Brefeld, Tavel and 

 Moller regards the Basidiomycetes as polyphyletic derivations of the 

 Phycomycetes (and eventually of the Ascomycetes). The Brefeld- 



