Chapter X. 



Yeasts, Morels, Cup-fungi and Truffles* 



All of the higher fungi which have been described, enjoy 

 one character in common ; their spores are produced upon 

 stalks. No matter how various the form of the fruit-body may 

 be, in this one respect all the different varieties agree. The 

 group of higher fungi now to be considered is marked by the 

 production of spores in sacs, hence they all pass under the gen- 

 eral name of sac-fungi. 



Yeasts. One of the most simple forms is the yeast plant, 

 familiar to housewives and brewers the world over. Yeast, as 

 most people know, is a culture of fungi developed upon malt 

 and hops and then transferred to various substances for 

 purposes which differ in the different arts. In bread-making 

 the value of the yeast lies in its power of liberating carbonic- 

 acid-gas while it is growing in the dough. When a cupful of 

 yeast is placed in a baking of bread and the dough is set away 

 in a warm place beside the stove, the yeast-plants feed upon the 

 substance in the dough and as they grow and reproduce they 

 create among other waste products, carbonic-acid-gas and alco- 

 hol. When the bread is kneaded and allowed to stand again 

 before placing in the oven, the kneading serves to distribute the 

 yeast-plants evenly through the loaf and they continue to grow, 

 forming bubbles of gas and small amounts of alcohol. When 

 the lightness of the bread is assured the loaves are placed in the 

 oven and the heat which is applied kills all the yeast plants, but 

 the bubbles of gas have done their part in leavening the loaf. 



In brewing, it is not the gas which is deemed so desirable, 

 but the alcohol, and the yeasts are permitted to develop until 

 the proper percentage of alcohol has been introduced. The 

 hardening of cider, the fermentation of wine, and a variety of 

 other processes are equally the result of fungus growth. Yeasts 



