HOW BOCK BECOMES SOIL 287 



the soil. In the case of many plants the stem is also under- 

 ground, as is true of the dandelion, plantain, parsnip, and 

 radish. Plant roots spread more or less hi the soil, some- 

 times many feet from the rest of the plant, and may also 

 descend to considerable depths. From the soil these roots 

 secure various substances. The soil serves not only as a 

 source of supply of food materials but also gives anchorage 

 to the plants whose roots are embedded in it. Many animals 

 also live in the soil, and all of them are dependent directly 

 or indirectly upon the plants that grow within or upon the 

 soil. Animals such as the earthworm, the gopher, the fox, 

 and the hedgehog burrow in the soil, and thereby secure 

 food in the form of plant roots or decaying organic matter, 

 or secure homes that furnish them a measure of protection 

 from enemies or from extremes of temperature. 



