ORIGIN OF ASCOMYCETEAE 635 



conjugation tube is formed, there being developed simply an opening 

 through the antherid and oogone walls which permits the entry of the 

 male nucleus. However, the supposed isogamy in the Mucorales is more 

 apparent than real. Even where the gemetangia are equal in size the 

 nuclei and part of the cytoplasm of one pass through an opening in the 

 walls into the other so that we actually have a functioning antherid 

 although it is equal in size with the oogone. In Dicranophora one game- 

 tangium is very large and the other very small and the "zygospore" wall 

 includes the oogone alone or rarely part of the antherid also. So we can 

 perhaps with justification look to some soil-inhabiting member of the 

 Saprolegniales for the ancestral form of the Mucorales. It must be noted 

 that Jaczewski (1929-30) suggested that these latter fungi arose directly 

 from some of the Chy tridiales (in the wider sense) . Others have suggested 

 the Monoblepharidaceae or the Cladochytriaceae as the ancestral stock 

 of the Mucorales. 



Within the Mucorales the evolution has apparently been in various 

 directions of modification of the sporangium, terminating in small in- 

 dehiscent sporangioles or portions of elongated sporangia. The Ento- 

 mophthorales appear to be terminal lines of evolution in which the 

 mycelium is much reduced, and the "conidia" represent usually violently 

 discharged, mostly indehiscent, sporangioles (but in Basidiobolus these 

 produce internal aplanospores). The sexual reproduction of the various 

 genera represents modifications of some of the different types found in 

 the Mucorales. 



In the Zoopagales the sporangia are reduced to indehiscent sporan- 

 gioles (or "conidia") and the sexual reproduction is sometimes isogamous 

 and reminiscent of some of the Mucorales or more often heterogamous. 

 Not enough is known of their cytology, the chemical composition of the 

 cell walls etc., to permit more definite suggestions as to their phylogeny. 



Origin of Ascomyceteae 



There are two main schools of thought regarding the phylogenetic 

 origin of the Higher Fungi (Ascomyceteae, Basidiomyceteae, etc.). In the 

 one it is held that the fungi as a whole form a monophyletic series and, 

 consequently, it is believed that the Ascomyceteae and other higher fungi 

 arose from the Phycomyceteae. There is no general agreement as to the 

 definite paths along which such derivation occurred, nor whether the 

 higher fungi are monophyletic or polyphyletic in their origin from the 

 lower fungi. The other school holds that the fungi are not necessarily 

 monophyletic and that some, if not all, of the higher fungi arose from 

 algae that had some of the characteristics of the simpler Florideae. In 

 both theories the points of connection between the Ascomyceteae and the 

 Rusts and Smuts and the more characteristic Basidiomyceteae are not in 



