CHAPTER XXIV 



PUNGI 



249. Fungi. — The Fungi are of importance to us be- 

 cause: (1) some can be used as food (the so-called mush- 

 rooms); (2) one of them, the yeast plant, is used in 

 making bread, beer, and wine ; (3) others spoil our food 

 when they grow on bread and cake; (4) they cause many 

 diseases in plants. 



Fungi differ from the higher plants in two respects. 

 They are colorless, or nearly so, chiefly because they have 

 no chlorophyll. They are dependent for food on plant or 

 animal substances, either dead or alive, because they lack 

 chlorophyll and hence cannot make their own foods as the 

 green plants do. 



Fungi which live on the substances or juices of live 

 plants or of animals are called parasites (Greek, para, be- 

 side ; sitos, food) ; and those that live on dead objects 

 are called saprophytes (Greek, sapros, rotten; phyton, 

 plant). 



250. The Yeast Plant. — This plant is a unicellular fungus, 

 too small to be seen by the naked eye. It is oval or almost 

 round in shape, and is nearly colorless. It has all the 

 parts of a typical cell, although the nucleus cannot be seen 

 without a special stain. Because it lives upon dead vege- 

 table matter, it is a saprophyte. 



The Work of the Yeast Plant. — In the making of 

 bread, we know that: (1) yeast secretes an enzyme which 

 breaks up sugar into simpler substances; (2) in this pro- 



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