HEMIASCOAIYCETES 139 



Phylogeny of the Ascomycetes. Two \\idely divergent hy- 

 potheses have been advanced to account for the derivation of the 

 Ascomycetes: the rhodophycean or floridean hypothesis and the 

 phycomycetean hypothesis. The rhodophycean hypothesis, first 

 proposed by Sachs in 1875, is based on the similarities between 

 the reproductive structures of Ascomycetes and red algae, such 

 as {a) ascocarp and cystocarp, {b) the trichogyne apparatus in 

 each, {c) the non-motile spermatia of each, and {d) the resem- 

 blance of ascogenous hyphae and ooblastema filaments. The phy- 

 comycetean hypothesis was first proposed by de Bary in 1887, 

 who maintained that primitive Ascomycetes are those in which 

 the asci are directly formed from the zygote, as they are in Di- 

 podascus and Eremascus. Mortierella and Piptocephalis among 

 the Phycomycetes are regarded as in the Hne of origin. The ad- 

 herents of this hypothesis regard analogous structures among 

 Ascomycetes and Florideae as being parallel developments and 

 not as beine derived one from the other. Both of these hy- 

 potheses are elaborated in the accounts by Dodge (1941) and 

 Atkinson (1915). Both hypotheses emphasize morphology as a 

 basis for phylogenetic development and fail to stress physiology. 



LITERATURE CITED 



Atkinson, G. P., "Phylogeny and relationship in Ascomycetes," Ann. Botan. 

 Garden, 2; 315-376, 1915. 



Dodge, B. O., "The morphological relationships of the Florideae and the 

 Ascomycetes," Bull. Torrey Botan. Club, 41: 157-202, 1914. 



Orton, C. R., "Structural parallelism between spore forms in the Ascomy- 

 cetes," Mycol, 7:21-27, 1915. 



HEMIASCOAIYCETES 



The Ascomycetes are usually considered as composed of 2 sub- 

 classes: Hemiascomycetes, in which the asci arise singly or in 

 groups but ascocarps are lacking, and Euascomycetes, in which 

 the asci are aggregated and ascocarps are developed. According 

 to this classification, the Hemiascomycetes comprise tw^o Orders, 

 Endomycetales (Saccharomycetales) and Taphrinales (Exoas- 

 cales). Dodge (1935), however, includes both orders under the 

 name Endomycetales and divides them into 11 families. In the 



