CHAPTER XXII 

 LIFE IN THE SOIL 



241 . Living things in the soil. We have already mentioned 

 some of the living things of the soil, but there are others, 

 chiefly microscopic, which need further discussion. There are 

 many small animals, as the earthworms already discussed, the 

 larva of many kinds of insects, many adult insects, and many 

 microscopic animals of the lower forms of life. In addition to 

 the roots of living plants there are many kinds of lower micro- 

 scopic plants, chief of which are the bacteria. These animals 

 and plants live upon organic and mineral matter in the soil, 

 and through their life processes or by means of their bodies 

 when they die they are constantly contributing to the organic 

 matter available for the growth of higher plants. 



242. Interrelationship of living things in the soil. The dif- 

 ferent things living in the soil may prey upon one another 

 quite as do things that live above the ground. The soil is 

 often filled with a dense population of living things, some 

 living upon mineral matter in the soil, some upon dead organic 

 matter, some upon other living things. 



An instructive illustration of the extent to which these 

 interrelations may go is seen 'in the case of the roots of the 

 corn plant and certain animals that may often be found upon 

 or near these roots. Extremely small insects, known as plant 

 lice, or aphides, bite into the tender roots of the corn and suck 

 out the nourishing juices. These aphides are almost stationary 

 animals and cannot ordinarily make their way from one plant 

 to another without assistance. When well nourished, they 

 excrete small drops of a glistening, sweetish solution some- 

 times called honeydew. This honeydew is an article of food 



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