CHAPTER IV. 



THE SOIL AS RELATED TO PLANTS. 



A. USES OF THE SOIL TO PLANTS. 



I. The Soil Serves as a Foothold. 



The roots penetrate the soil and brace the 

 plants against the wind, and hold them erect so 

 that they more readily obtain air and light. 

 The necessity for this support is made greater 

 by the elongation of the stem in the struggle for 

 light. 



II. It Affords Important Food Elements. 



Although but 5 per cent, of the food supply of 

 plants is obtained from the soil, it does not fol- 

 low that this 5 per cent, may be omitted. On 

 the contrary, many of the soil-furnished ele- 

 ments are absolutely necessary to the life and 

 development of plants. 



III. The Soil Acts as a Storehouse for Water, 



so that the plant may draw upon its supply con- 

 tinuously, or much more nearly so than if it de- 

 pended only upon the moisture obtained from 

 the air and from that obtained for immediate 

 use from rains. This soil water is invaluable 

 both as a food and as a solvent for other con- 

 stituents of plant-food, since plants can only 

 take up substances which are soluble in the soil 



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