PHYCOMYCETOUS AFFINITIES 309 



unfortunately not yet known. In the Ascomycetes genera such 

 as Eremascus, Endomyces, and Zijgosaccharomyces afford forms 

 intermediate in type between Dipodascus and the Euascomycetes. 

 In these genera also, the cell formed by the fusing gametangia 

 functions as the ascus, but the ascospores are of small and 

 definite number. In the multinucleate character of its gametangia 

 Dipodascus stands alone among these lower forms. Its nearest 

 known relative is perhaps Endomyces magnusii of the Endomycet- 

 aceae. In that species the ascus results from the fusion of 

 uninucleate cells and only four ascospores are formed, but the 

 cells of the mycehum and the oidia are multinucleate. In the 

 other species of Endomijces all the cells are uninucleate. In some 

 higher forms (e.g., Sphaerotheca) the mature ascogonium is 

 septate and one of its cells becomes the ascus. 



Though Dipodascus is clearly ascomycetous, the three other 

 genera, Ascoidea, Conidiascus, and Oscarhrefeldia, included 

 with it in the Ascoideaceae by Schroter and Lindau, are of doubt- 

 ful affinity. 



In Ascoidea the mycelium is abundantly septate, repeatedly 

 branched, and saprophytic, and a spore sac containing many 

 spores as in Dipodascus is formed. The genus has been inade- 

 quately investigated, and accounts based on cytological studies 

 are contradictory (Popta, 1899;Lohwag, 1926; Varitchak, 1928; 

 Walker, 1929). Apparently a fusion of sexual nuclei does not 

 occur, and the spores seem not to be delimited by the astral 

 rays. The spore sac is ovate to clavate-cylindrical, is formed 

 terminally, and dehisces by an apical pore. After the escape 

 of the spores it proliferates repeatedly as does the sporangium 

 in Saprolegnia. In the light of present knowledge there seems 

 to be Httle justification for regarding this sac as an ascus. How- 

 ever, in a discussion of the origin of the Ascomycetes Atkinson 

 (1915) takes the position that Ascoidea may be related to Dipo- 

 dascus, and that the spore sac may be merely the result of the 

 apogamous development of one gametangium in the absence 

 of the other. Perhaps from that point of view the term ascus 

 could be logically applied. Under certain conditions cells 

 morphologically equivalent to the spore sacs function as conidia, 

 falling off and germinating by germ tube. The first conidium 

 formed is terminal on the hypha, but further apical growth of 

 the hypha pushes it aside and causes it to have a lateral position. 

 Successive formation of conidia in this fashion results in a 



