CHAPTER XVI 



THE SACCHAROMYCETACE.E 



The Pathogenic Blastomycetes Yeasts and Fermentation 



The Yeasts 



THE Saccharomycetacese or Yeasts are characterised by a vegeta- 

 tive reproduction by budding or gemmation. If a cell of ordinary 

 brewer's yeast be watched under conditions favourable to growth 

 and reproduction, it will be found that a slight protuberance makes 

 its appearance at one pole of the organism ; this increases in size, 

 and ultimately a daughter-cell resembling the parent is reproduced 

 and separates off. 



The true yeasts also reproduce by spore -formation by ascospores 

 (p. 465) ; in some there is a fusion of cells before sporulation, in 

 others the first cell formed by germination of the spore undergoes 

 fission, forming what is known as a pro-mycelium, after which the 

 cells multiply by gemmation. The Saccharomycetaceae may there- 

 fore be divided into : 



1. Zygosaccharomyces, in which pairs of cells fuse before sporula- 

 tion. 



2. Saccharomyces, in which there is no fusion of cells before 

 sporulation, and in which the spores germinate by ordinary budding. 



3. Saccharomycoides, in which the spores germinate by means of 

 a promycelium. 



Besides the true yeasts, there are a number of budding forms 

 known which do not spore. These have been termed " Torulse " 

 (any yeast-like cell is frequently called a " torula "). Some form 

 films on saccharine li quids and are known as Mycoderma. Organisms 

 are also known having a yeast-like form and multiple spores but 

 multiplying by fission ; these have been termed Schizosaccharo- 

 myces. The position of these forms is uncertain and they are 

 classed by the botanist among the Fungi Imperfecti (p. 470). 



In addition to reproduction by gemmation, the Saccharomyce- 



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