FUNGI 303 



therefore, make their own food (c/. 310). They live by 

 attaching themselves to living plants or animals; or they 

 feed upon dead or decaying materials. An organism that 

 feeds upon other living organisms is called a parasite ; the 

 organism upon which a parasite feeds is called the host. 

 A fungus feeding upon decaying organic material is called 

 a saprophyte. 



A yeast plant is a fungus having one cell. It is repro- 

 duced by budding (cf. Fig. 103, 129). Many centuries 

 ago "wild yeasts" were cultivated by man, and the result 

 is our ordinary bread yeast, or leaven. While feeding 

 upon the sugar of the dough, the yeast plant' produces 

 carbon dioxide. This causes the dough to rise, and 

 makes bread porous and light. 



Bacteria, also called microbes, or germs, are very small, 

 one-celled fungi found everywhere in air, water, and soil 

 (Fig. 247), and in the bodies of ^ 



plants and animals. They are re- < x-p ff)J 



produced by cell-division, like pro- *' 



tococcus. The cell walls of bacteria 

 usually have projections, called 

 cilia, by means of which the cells 

 swim about. It is bacteria that 

 make milk and fruit juices "sour/' 

 and cause meat to decay. These 

 changes are fermentations, like the TuPh ' c 



Fl 



teria, greatly magnified. 



+ r irooof Fl - 247 - Six Kinds of Bac- 



tO 



Most of the bacteria that live about us are harmless, but others 

 cause diseases like typhoid fever, diphtheria, cholera, and consump- 

 tion, and must be looked upon as our worst enemies. Bacteria that 

 are of great importance to us are those that grow upon the roots of 



