210 



FIRST YEAE SCIENCE 



habitable. Some of them are injurious to plants and 

 animals, but a large number are most beneficial. 



These plants cause the decay of dead animal and vege- 

 table matter. If it were not for them, all the plants and 

 animals that die upon the earth \\ould encumber its surface 

 indefinitely with their bodies, and none of the material 

 that they have taken from the soil would return to fertilize 



it. These plants make 

 possible the manufacture 

 of vinegar, some cheeses 

 and a great many other 

 things which we use 

 daily. 



On the other hand, the 

 decay in fruit, the mold 

 on bread, the corn smut, 

 the smut on oats and 

 barley, the potato blight, 

 the scabs of apples and 

 potatoes, the rusts on 

 grains and many other 

 common plant diseases 

 are simply fungus plant 

 growths. The wheat rust 

 alone costs the United 

 States many millions of dollars each year. Thousands of 

 feet of timber are destroj^ed yearly by the wood-destroying 

 fungi. Dry rot of timber, as it is called, is due to a fun- 

 gus growth. The fight against these harmful fungi costs 

 millions of dollars each year. 



But some fungi are exceedingly useful. The fungus 

 most commonly made use of is the yeast plant. In bread 

 making, yeast which contains the little yeast plants is 

 mixed thoroughly into the material which is to compose 



MISTLETOE GROWING ON AN OAK. 

 An interesting parasitic plant. 



