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CHAPTER V. 

 YEASTS. 



ACCORDING to modern usage the word " yeast " is used to 

 describe those alcohol-forming fungi which are formed, as a 

 rule, by a process of budding, and which under special con- 

 ditions form spores in the interior of the budding cells. The 

 old name Saccharomycetes has been retained to describe these 

 fungi, which are of such great technical importance. 



It has already been stated that both the bacteria and 

 mould-fungi possess alcohol-forming species, whilst among 

 the moulds certain bud-forming species also occur. 



Mycelium formation has been shown to exist in not a few 

 Saccharomycetes, and since an endogenous spore-formation 

 also occurs in certain of the moulds, it would appear doubtful 

 whether it is correct to class the yeasts as an independent 

 group of fungi. The direct observation of genetic connection 

 between typical Dematium-like mould-fungi on the one hand, 

 and Saccharomycetes on the other, makes it difficult to accept 

 the earlier view. This observation at ,all events proves that 

 species exist which cannot be classed in an independent group. 

 Doubtless future investigations will bring to light further 

 instances of species which represent stages in the development 

 of higher fungi. 



The genera Mycoderma and Torula, which include no 

 members exhibiting endogenous spore-formation, but include 

 a number of species known only in the budding stage, will be 

 dealt with in an appendix to this section. 



The Nutrition of Yeasts. 



Some account of the nutrition of fungi in general has 

 already been given in the chapter on moulds. In the following 



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