48 



A TEXT-BOOK OF BOTANY. 



of the original cell, from which it is then separated by the forma- 

 tion of a transverse wall. The cells are spherical, ellipsoidal, or 

 egg-shaped, and in some cases somewhat elongated and hypha- 

 like. In the protoplasm are one or more large vacuoles. In 

 certain of the cells, which may be considered to be asci, two to 

 eight spherical or ellipsoidal spores are produced (Fig. 26). 

 There are a number of different species of Yeasts, some of which 



Fig. 26. Formation of ascospores in a number of diflFerent species of Yeasts, i, Sac- 

 charomyces cerevisia; 2, S. Pastorianus; 3, 5. inter medius; 4, 5". validus. — After Hansen. 



are cultivated ; and these latter are of great economic importance 

 on account of their property of inducing alcoholic fermentation. 

 They are also of use in the making of bread, changing the carbo- 

 hydrates in part into carbon dioxide and alcohol, both of which 

 are driven off in the baking. 



The property of yeast causing the fermentation of a solution 



