CHAPTER III. 



YEASTS; BUDDING FUNGI; SACCHAROMYCES. 



THE yeasts are known also as the blastomyces group of 

 fungi. They, like the bacteria, contain no chlorophyll. The 

 yeast-cells are slightly round, and multiply by budding like 

 a tuber on a potato. They are the cause of alcoholic fermen- 

 tation in sugar. The bud looks like a small sprout, and is 

 detached finally from the parent cell to take on the functions 



FIG. 65. 



a 



a. Saccharomyces. b. Cell with four spores. (Lehmann.) 



of a matured cell (Figs. 65 and 66). Under certain condi- 

 tions some of the yeasts may form hyphse and mycelia. This 

 usually occurs when the medium has an alkaline reaction or 

 when it is deficient in sugar. The yeasts grow best at the 

 room temperature and in the presence of oxygen. In fact, 

 most of the budding fungi are strongly aerobic. The culture- 

 medium must contain sufficient organic matter and must have 

 an acid reaction. Putrefaction inhibits their growth. They 

 are cultivated like the mould fungi. They can be examined 

 in water or bouillon, or mounted in glycerin. 



The most common and best known yeast is Saccharomyces 



156 



