CHAPTER XY. 



UNICELLULAR PLANTS (Continued}. 



B. Yeast. 



{Saccharomyces. ) 



UNDER the general name of yeast are included some of the 

 simplest forms of vegetal life. Some yeasts are ' ' wild, ' liv- 

 ing upon fermenting fruits or in fruit juices, and commonly 



FIG. 93. Yeast-cells. Brewer's (top) yeast actively vegetating. The large internal 

 vacuoles and the small fat-drops are shown, as are also buds, in various stages of 

 development, and the cell-wall. Nuclei not visible. (Highly magnified.) 



occurring in the air; others are "domesticated,' 1 or cultivated, 

 such as those regularly employed in brewing and in baking. 



If a bit of ' ' yeast-cake ' ' (either ' ' compressed ; ' or " dried ' 

 yeast) is mixed with water, a milky fluid is obtained which 



closelv resembles the so-called baker's or brewer's yeast. 



/ / 



184 



