FUNGI, SAC FUNGI 295 



shallow depressions separated by ridges. The surface of these 

 depressions is the fruiting surface. It is formed of countless 

 numbers of cylindrical sacs (asci) standing side by side. Each 

 sac contains eight spores. Each morel, therefore, produces 

 myriads of spores, but very few of them ever succeed in pro- 

 ducing mycelium to form another morel. The morels (Mor- 

 chella) appear in damp places in early spring and are prized as 

 edible fungi. They are sometimes called mushrooms, but do 

 not belong to the true mushroom group. 



Fig. 243. 



Sclerotina fructigena, the trumpet-shaped fruit bodies growing from old peach mummies 

 which were affected with the rot. Natural size. 



445. The yeast fungi. The yeast fungi, or sprouting fungi, 

 as they are often called, are by some classed among the sac fungi 

 as degenerate forms. The yeast plant is remarkable for its 

 activity in producing fermentation especially of solutions con- 

 taining sugar, giving off carbon dioxide and forming alcohol; 

 one yeast (Saccharomyces cerivisece) is used both in bread-rising 

 and in brewing beer. The yeasts usually consist of single cells, 

 oval or ellipitcal in form, and in this condition they are single- 

 celled plants. They multiply by a process of budding or sprout- 

 ing. Near either end of a cell a small bud appears as a sprout 

 or protuberance of the wall, which has only a frail connection 

 with the parent yeast cell. This bud increases in size, and soon 

 separates, forming a new yeast plant. Sometimes these buds 

 remain connected for a time, forming small colonies, which 



