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many of the common genera. Gaumann (11, 12) includes keys to 

 families with characters that perhaps are more nearly indicative of 

 the evolutionary development of the families, but they are rather 

 difficult to use. 



Hemiascomycetes (Yeasts) 



The subclass Hemiascomycetes contains the orders Taphrinaies and 

 Endomycetales and seven families (22). The Taphrinaies, with two 

 families and six genera, are plant parasites with no known industrial 

 application. The genus Taphrina contains most of the 125 species 

 and will grow in culture. 



The order Endomycetales contains the other five families: Peri- 

 cystaceae, Ascoideaceae, Saccharomycetaceae, Endomycetaceae, and 

 Spermophthoraceae. Except for the Spermophthoraceae, which con- 

 tains the riboflavin-producers AsKbya and Eremothecium, the only 

 two families containing organisms of known technological importance 

 are the Saccharomycetaceae and the Endomycetaceae, which contain 

 the ascosporogenous or so-called true yeasts. The nonascosporogenous 

 or false yeasts are in the class Fungi Imperf ecti, since they apparently 

 form no sexual states and are contained in the two families Crypto- 

 coccaceae and Sporobolomycetaceae. Inasmuch as these two families 

 are generally discussed along with ascosporogenous yeasts, they are 

 so treated here. 



Yeast is a rather general, indefinite term. It refers to the unicellu- 

 lar-growth form of true fungi, which develop moist, rather mucoid 

 colonies. Yeasts have no true mycelium, but on certain media some 

 form pseudomycelia made up of chains of vegetative cells. 



The two most comprehensive treatments of yeasts are the monograph 

 by Lodder and Kreger-van Bij (19) and The Chemistry and Biology 

 of Yeasts edited by Cook (7). The latter volume contains a classi- 

 fication by Lodder et al. (20) of both the ascosporogenous and the 

 anascosporogenous yeasts. All the ascospore-forming yeasts are 

 treated by Lodder et al. (20) in the single family Saccharomycetaceae, 

 which includes the Endomycetaceae of Gaumann (11) and Martin 

 (22). Lodder et al. differentiate among 17 genera, of which Eremascus 

 and Endomyces are not considered yeasts because they form true 

 mycelia. The most important genus of the ascosporogenous yeasts 

 is Saccharomyces, which contains the so-called brewing and bakers' 

 yeast strains so important to the food and fermentation industries. 



The two families of anascosporogenous yeasts contain 13 genera, 

 2 of which are not yeasts in the strict sense. These families have 

 some strains that are undoubtedly imperfect states or heterothallic 

 forms of the true yeasts, some strains that are probably imperfect 

 states of Basidiomycetes, and several human pathogens. The most 

 important genus for technological purposes is Torulopsis, which is a 

 convenient source of protein. 



Euascomycetes 



The subclass Euascomycetes is characterized by its asci being formed 

 in or on a specialized fruiting body called an ascocarp. Ascocarps 

 range from a few strands of sterile hyphae incompletely covering the 



