302 



MEDICAL MYCOLOGY 



in shape to a dumb-bell, is an aseus (Pig. 58, 4-5). In some cases, at least in 

 Zygosaccharomyces Priorianus, copulation is absent, and the individual sprout 

 cells develop parthenogenetically to asci. Rarely, in small colonies where the 

 mother cell lacks other cells, it may copulate with a daughter cell in pseudogamy. 

 That which is anomalous in Zygosaccharomyces Priorianus becomes increas- 

 ingly common in other species ; as sexual tendencies weaken, copulation becomes 

 more and more difficult. Thus in some species, such as Z. niongolicus, although 

 copulation does occur, most of the asci develop parthenogenetically after put- 

 ting forth copulation tubes which fail to function. 



Fig-. 59. — Torulaspora Rosei. Development of asci (XI, 800). (After Guilliermond 1912.) 



Fig. 60. — Saccharomyces cerevisiae. 1-i, formation of spi-out cell with amitosis of nucleus 

 (XloOO); 5-10, development of sprout cell to ascus and g;ermination of ascospore (X750). 

 (After Guilliermond 1902, 1904.) 



Torulaspora shows still further degeneration toward parthenogenesis. On 

 favorable media, the sprout cells of T. Delhrucki form numerous sprout cells 

 which attempt fusion (Fig. 59). Occasionally this is successful and ascospores 

 are formed, but generally the separating wall is not dissolved, and each cell 

 forms 1-4 ascospores parthenogenetically. AVhile copulatory processes are 

 formed in T. Rosei and T. fermentaii, they ntver fuse, and parthenogenesis is 

 complete. 



Finally complete parthenogenesis witli no morphologic suggestion of sex 

 is reached in the large genus Saccharomyces (Fig. 60). This genus furnishes 

 most of the common yeasts used in alcoholic fermentation, such as S. cerevisiae, 



