Root Action in Plants. 



149 



soil aside, and the setting of fence posts proves how large 

 this space is. A 6-inch post set in the hole dug for it seldom 

 occupies so much of the space but that all of the soil re- 

 moved may be returned by thorough ramming. It is the 

 existence of such large amounts of open space in the soil 

 which makes the movements of water, air and roots 

 through it possible and the absence of it which makes a 

 puddled soil so uncongenial to plant growth. 





FIG. 47. Method by which root-hairs advance through the soil. 

 (Adapted from Sachs.) 



In Fig. 47 is represented a section of the tip of a root 

 growing and advancing through the soil. It has been 

 found that at 1, a short way back from the tip, there is a 

 center of growth. Here new cells are forming by division 

 and subsequent enlargement. On the forward side of this 

 cell the new ones build the root cap, which acts as a shield 

 and wedge, while those in the rear are finally transformed 

 to make the various structures found in the root. 



At the center of growth new cells are forming and ex- 

 panding under the intense power of osmotic pressure and, 

 as the root is anchored behind, the root cap is pushed for- 

 10 



