CHAPTER XVI 



THE SACCHAROMYCETACEJE 

 The Pathogenic Blastomycetes Yeasts and Fermentation 



The Yeasts 



THE Saccharomycetacese or Yeasts are characterised by a 

 vegetative reproduction by budding or gemmation. If a cell oi 

 ordinary brewer's yeast be watched under conditions favourable 

 to growth and reproduction, it will be found that a slight pro- 

 tuberance 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 asco- 

 spores (p. 563) ; in some there is a fusion of cells before sporula- 

 tion, 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 Saccharomy- 

 cetacese may therefore be divided into : 



1. Zygosaccharomyces, in which pairs of cells fuse before 

 sporulation. 



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 liquids and are known as Mycoderma. Organ- 

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

 but multiplying by fission ; these have been termed Schizosaccha- 

 romyces. The position of these forms is uncertain, and they are 

 classed by the botanist among the Fungi Imperfecti (p. 568). 



