en. xiv.] YEAST FUNGI. 137 



become free Jby finally bursting the membrane of the mother- 

 celL On sowing these new cells into sugar-containing fluids 

 they multiply by the process of gemmation. 



Classifying them according to physiological function there 

 are various species of torula or saccharomyces. They all have 

 the power to split up sugar into alcohol and carbonic acid, but 

 this power is not possessed by all to the same degree. 



Fio. 99. TORULA, OR SA.CCHAROMYCFS. 

 In the lower part of the figure an ascospore and four isolated spores (after 



Rees) are shown. 

 Magnifying power about 700. 



(a) Saccharomyces ceremsicR (torula cerevisice). This is the 

 ordinary yeast used in the production of beer. The individual 

 full-grown cells vary in diameter from O'OOS to O'Ol mm. ; 

 they form beautiful long chains. They produce ascospores. 



() Saccharomyces vini is very common in the air, and pro- 

 duces alcoholic fermentation of grape-juice ; it is therefore the 

 proper yeast of wine-production. Its cells are elliptical, slightly 

 smaller than the former ; it forms ascospores. 



(c) Saccharomyces pastorianus is of various kinds (Hansen) : 

 in some the cells are about 002 to O'OOS mm. in diameter, in 

 others larger. Some form ascospores, others do not. Most of 

 them can be found in wine -fermentation and in cider-fermen- 

 tation, but only after the first alcoholic fermentation is com- 

 pleted. They are very common in the air. I have sown a 

 saccharomyces, which was contained in ordinary water, on 

 solid nourishing media (gelatine, and gelatine and broth). It 

 grew up copiously and formed groups of a distinct pink colour. 



