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3*7 



Inocul 



en fixing bacteria, 

 lligan). 



found in acid soils release the nitrogen in the soil to 

 the air. Are these useful or harmful? Why? In some 

 soils, a little one- 

 celled animal is 

 found which feeds 

 upon useful bac- 

 teria, thus de- 

 stroying the fer- 

 tility of the soil. 

 Many insects in 

 the larval or pu- 

 pal form (page 

 134) make their homes in the earth, and sometimes do much 

 harm by eating the roots of plants. Earthworms, however, 

 are useful animals in the garden, for they plow up the 



ground by boring their holes, thus 

 passing much soil to the surface of 

 the garden through their bodies. 

 This loosens the compact soil 

 and allows water to make its way 

 through the ground. Sometimes 

 we find moles and other boring 

 animals which do harm. 



Other harmful plants. While 

 green plants make food for them- 

 selves, and for the world about 

 them, other little plants do a great 

 deal of harm. Some of these are 

 called fungi. Among them are 



Corn smut. Black knot. * 6 



(After Mayne and Hatch.) molds, TUStS, Smuts, SCabs, and 



many other plant diseases. We find, for example, rust on 

 asparagus, beans, and some other plants* Black rot is an- 



