i8o Science of Plant Life 



angled soil particles. If a root tip or a longitudinal section 

 of one is examined under a microscope, it may readily be seen 

 that the growing point is not at the very end, as in stems, 

 but is covered by a root cap. The growing region of the root 

 extends a few centimeters back from the growing point (Fig. 98) . 

 Therefore, as the root elongates, the root cap is pushed for- 

 ward and is abraded by the soil particles. This injures the 

 outer cells of the cap, but as they are being renewed from 

 within, the cap is always present as a protection for the grow- 

 ing point. 



At the growing point the cells are small, similar in form, and 

 filled with protoplasm. They are constantly dividing and 

 forming new cells. As the cells grow older and enlarge, they 

 assume the mature cell form of the particular tissue to which 

 they belong. The protoplasm of mature cells is merely a 

 lining inside the cell wall. Most of the cell space is occupied 

 by a water solution of sugar, soluble proteins, salts, and acids. 

 Sometimes starch grains are present (Fig. 99, page 170). 



The three stages of growth are characterized by cell division, 

 cell enlargement, and the fixation or thickening of the cell 

 walls. They are very similar in all plant organs. But no- 

 where can they be seen so readily as in the longitudinal section 

 of a young root. 



