ORIGIN OF ASCOMYCETEAE 637 



higher fungi are much like the lower fungi in cell wall composition. In the 

 Florideae cellulose is present usually accompanied by a considerable 

 amount of pectic substances but there is no evidence of fungus chitin 



The hypothesis of Floridean ancestry of the higher fungi requires that 

 the phylogenetic evolution of the latter must be assumed to progress from 

 complex forms (Pezizales, Sphaeriales, etc.) to simpler forms such as 

 Taphrina, Endomyces, Saccharomyces, etc., contrary to the usual direction 

 of evolution accepted for most groups of fungi. On the contrary from the 

 relatively simplj^-built Phycomyceteae the rather simple Endomycetaceae 

 may be assumed to have arisen without too great difficulty. 



The chief arguments for a Floridean ancestry lie in the similarity 

 between the sexual reproduction in the simpler Florideae and in many of 

 the Ascomyceteae, including: 



1. Nonmotile, naked or at most very thin-walled, spermatia, with a 

 relatively large nucleus, mostly produced one or more at a time endog- 

 enously in scattered or crowded antherids. These depend for distribution 

 in the Florideae upon water currents and in the Ascomyceteae upon 

 streaming surface layers of water or upon insects. 



2. The production of a receptive filament (trichogyne) projecting 

 from the oogone. 



3. The multiplication within the oogone of the zygote nucleus (or of 

 the paired but not united gamete nuclei) and their passage through out- 

 growths from the oogone to terminal cells which become carpospores or 

 asei in the Florideae or Ascomyceteae respectively. 



4. Usually, but not always, the formation of enclosing envelopes of 

 various types around the oogone, sometimes before but more often after 

 fertilization. 



Aside from these reproductive similarities the vegetative structure 

 shows similarities. 



5. The filaments (hyphae) of both groups of organisms mostly grow in 

 length by the elongation and division of the terminal cells, which however 

 occurs also in the Phycomyceteae. 



6. The septa which arise by circular shelf-like growth from the lateral 

 wall of the cell do not entirely close in the Ascomyceteae as they do in 

 the Phycomyceteae (according to Buller, 1933) but leave a central pore 

 through which the protoplasmic continuity of adjacent cells is main- 

 tained, a condition which also occurs in the Florideae. 



In the Phycomyceteae in general each sexual act results in the produc- 

 tion of a single zygote: zygospore or oospore (e.g., Monohlepharis, Sapro- 

 legnia, Peronospora, Mucor, Entomophthora, Zoopage, etc.) but in the 

 Ascomyceteae in which sexual reproduction occurs by the union of non- 

 motile sperm cells with a trychogyne the one sexual act leads to the pro- 

 duction of many asci borne on ascogenous hyphae and usually surrounded 



