60 EASY LESSONS IN VEGETABLE BIOLOGY. 



wood of Exogens. Chap. VI. Sec. 8. In the root, 

 the multiplying cells are not quite at the extremity. 

 A sort of cap is formed, which receives additions to 

 its interior and pushes out the layers external to 

 them. Thus the new-formed tissue is protected from 

 the rough soil. (Fig. 26, B, C.) Sometimes the ab- 

 sorbing activity of the points of the root-hairs is so 

 great that particles of soil actually unite with them, 

 to be afterward dissolved by the cell-sap. 



5. The primary root is that which is formed by 

 the downward elongation of the axis. It is in a line 

 with the stem. It is called a tap-root when it is 

 thicker than the branches which spring from it, and 

 may be fusiform or spindle-shaped like the carrot, 

 napiform or turnip-shaped as the radish or turnip, 

 filiform or threadlike, or cylindrical. Secondary or 

 lateral roots are those which spring laterally from the 

 stem or primary root, as the clasping roots of ivy. 

 Sometimes the primary root is undeveloped, or dies, 

 and is replaced by secondary roots. In grasses these 

 are filiform, and are called fibrous roots. Sometimes 

 secondary roots become tuberous or fasciculated, 

 (swollen in the middle, or at intervals,) as in the 

 dahlia, etc. All roots are more or less branched, and 

 are covered with delicate root-hairs. If the branches 

 of the root run near the surface of the ground, they 

 are called creeping roots. 



6. The stem is that part of the plant which bears 



