CHAPTEE XV. 



UNICELLULAR PLANTS {Continued). 



B. Yeast. 



{Saccharomyces.) 



Under tlie 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.) 



oecurring in the air ; others are ' ' domesticated, ' ' or cultivated, 

 such as those regularly employed in bremng and in baking. 



If a bit of "yeast-cake " (either "comj^ressed "or " dried" 

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



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



184 



