YEAST PLANTS 223 



little cells are Yeast-plants, and bear the name of 

 Saccharomyces cerevisiae. 



371. They reproduce by a kind of fission, called 

 "budding." Each cell pushes out a little projection 

 which grows larger and larger, and finally a cell-wall 

 forms between it and the old cell and these sooner or 

 later separate from one another. Under 

 favorable circumstances certain cells form 

 spores internally, and these are now re- 

 garded as asci, homologous with the asci 

 of the higher sac-fungi. Yeast-plants are, 

 ther.efore, to be considered as greatly sim- figT loe.— sac- 

 plified Sac-fungi, and they are members of " ^romyces. 

 the family Saccharomycetaceae (of the Order Hemiascales) 

 which has experienced what is probably the greatest 

 reduction suffered by any plants of the Ascosporeae. 



372. Yeast-plants are saprophytes, and live upon the 

 starch of flour. They break up the starch, and in the 

 process liberate considerable quantities of carbon dioxide 

 which appears as bubbles upon the surface of the yeast. 

 Another result of the breaking up of the starch is the 

 formation of alcohol; hence the growth of yeast-plants in 

 a starchy substance is always accompanied by what is 

 known as alcohoUc fermentation. The housewife and 

 baker use yeast-plants for the carbon dioxide gas which 

 they evolve; to give lightness to the bread, while the 

 brewer and distiller use the same plants for the alcohol 

 produced by their activity. (See Chapter IV, paragraph 

 139.) 



373. The Truffles (Order Tuberales) are well known 

 from their large underground spore-fruits, which are 

 edible. Internally there are narrow tortuous channels 

 on whose walls asci develop, each containing a number of 

 spores. Little is known of their round of hfe, and the 



