ORIGIN OF ASCOMYCETEAE G39 



myceteae. H. S. Jackson (1944) gives very convincing arguments for the 

 hypothesis that the closely parallel life histories of the Uredinales and 

 Florideae indicate something more than a mere convergence, probably 

 true relationship. 



From the Pezizales it is usually considered that the Tuberales have 

 arisen and possibly the Hysteriales. The fructifications of the Asco- 

 corticiaceae may be looked upon as representing much reduced apothecia, 

 thin and without a definite margin. They still retain the characteristic 

 hook or crozier mode of formation of the asci. The family Taphrinaceae 

 might be looked upon as producing a much further simplified apothecium 

 in which the hook or crozier are lacking and where the whole vegetative 

 mycelium is dicaryotic, perhaps representing the ascogenous hyphae of 

 the usual types of Pezizales. 



The Sphaeriales show in the genus Mycosphaerella numerous cases of 

 the production of rounded oogones with unbranched, nonseptate, apical, 

 usually uninucleate trichogynes which are fertilized by sperm cells pro- 

 duced internally (sometimes in fours) in the spermogonial structure. In 

 this order as in the Pezizales the union of oogone and antherid may take 

 the place of spermatization of a trichogyne. The Erysiphales represent 

 mostly Sphaeriaceous forms with usually superficial, nonostiolate peri- 

 thecia. Probably the Pseudosphaeriaceae arose from typical Sphaeriaceae 

 as also did the Aspergillales and Myriangiales. The Gymnoascaceae 

 represent a development in the Aspergillales toward the loosening up of 

 the perithecial wall which is entirely lacking in the Endomycetaceae as 

 are the ascogenous hyphae, so that a single sexual act produces but one 

 ascus. (Fig. 206.) 



B. O. Dodge (1914) gave a very scholarly exposition of the similarities 

 in the sexual reproductive structures of the Ascomyceteae and Florideae 

 with special reference to the probable origin of the former from the latter. 

 This should be read in connection with the excellent explanation (by 

 Atkinson, 1914) of the origin of the simpler Ascomyceteae from the 

 Phycomyceteae. 



For those who look to the Phycomyceteae as the possible source of 

 the higher fungi several hypotheses have been proposed. For many years 

 that of Brefeld (1889) was the prevalent one. He started from the assump- 

 tion that sexuality among the fungi was confined to the Phycomyceteae 

 and was entirely lacking in the Ascomyceteae and Basidiomyceteae. He 

 assumed that the ascus is a sporangium homologous to that of the Muco- 

 rales. Accordingly he considered the polysporous asci to represent a more 

 primitive stage and the fungi with the standard eight-spored asci as more 

 advanced. The basidium he considered to be a conidiophore bearing a not 

 standardized number of conidia in the more primitive forms (the Usti- 

 laginales), the number finally becoming fixed at four per conidiophore 



