CHAPTER VII 



ORGANS OF NUTRITION. ROOTS IN RELATION 

 TO THE SOIL 



Problems : What is soil and what does a plant get from it? 

 What determines the direction of growth of roots f 

 How is a root fitted for the work it has to do f 

 How do roots absorb water and soil salts? 

 What is diffusion? What is osmosis? 



Laboratory Suggestions 



Laboratory or Home Experiment. How to determine the presence of organic 

 matter in soil. 



Laboratory demonstration. To test the capacity of soils for holding moisture. 



Home experiment. To show the effect of gravity on a growing root. 



Laboratory demonstration. Structure of a root in cross section. 



Laboratory exercise. Roots and root hairs. 



Laboratory demonstration. To show that roots give off acid. 



Laboratory demonstration. To show diffusion and osmosis. 



Use of the Root. — If one of the seedlings of the bean is allowed 

 to grow in sawdust and is given light, air, and water, sooner or 

 later it will die. Soil is part of its natural environment, and the 

 roots which come in contact with the soil are very important. It 

 is the purpose of this chapter to find out just how the young plant 

 is fitted to get what it needs from this part of its environment; 

 namely, the soil. 



Composition of Soil. — As any one knows, the soil is composed 

 of different substances in different localities. Contrast the black 

 soil of Minnesota or Illinois with the sandy soil of Maine or 

 California, or the red clay of Virginia. If we examine a small 

 mass of garden soil carefully, we find that it is composed of numer- 

 ous particles of varying size and weight. Between these particles, 

 if the soil is not caked and hard packed, we can find tiny spaces, 

 which are formed and enlarged when the soil is tilled. They allow 

 the penetration of air and water. If we examine soil under the 



63 



