DEVELOPMENT OF PLANTS 



249 



freed by the decay of the ascus and when conditions are favorable 

 grow into the characteristic yeast cells, as shown in Fig. 161, F. 



(a) Fermentation. — These microscopic plants must be num- 

 bered among those plants that are of the greatest economic value. 

 Their importance is due to the fact that they decompose sugars 

 upon which they feed into CO2 and alcohol, a change called fer- 

 mentation. The extensive brewing and distilling industries all 



Fig. 161. The yeast plant, Saccharomyces: A, single plant, B, plant 

 producing three buds. C, section of two plants showing buds and nuclear 

 division. D, chain of plants due to rapid budding and growth. E, forma- 

 tion of ascospores. F, germination of an ascospore and the formation of 

 new plants by budding. — After Wager. 



over the world are dependent upon the growth and peculiar action 

 of these microscopic plants. When yeast plants are placed in 

 solutions containing sugar in the form of molasses or prepara- 

 tions of rye, corn, barley, potatoes, etc., and slightly warmed, the 

 growth of the yeast produces a vigorous fermentation. Carbon 

 dioxide rises to the surface, forming a frothy scum while the alco- 

 hol accumulates in the fluid. Beers and ales are fermented bever- 

 ages of this nature, while whiskies, brandies, alcohol, etc., are 

 obtained from the fermented mass by removing a part of the 

 water by distillation. Wines and cider are weak alcoholic bev- 



17 



