lit* 



KLK.MKNTS <l- CKNKIJAL SCI KMT, 



220. The soil and its significance. It is customary to speak 

 of the soil as including the top layer of earth material. The 

 term is sometimes used to apply to whatever earth materials 

 there are upon the solid rock. In agriculture and gardening the 

 term applies to the more nutrient layer in which plants grow. 



The soil is the natural growing place of most plants and 

 many animals. The roots of plants are usually embedded in 



FIG. 98. Action of plants upon rocks 



The roots of plants enter crevices and break the rock. Here there is not enough 



soil to cover the rock, and the pine trees are rooted in the sandstone. (Mogollon 



Mountains, Arizona) 



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 in the soil, sometimes 

 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 



