ROOTS 



73 



nodes, and such secondary roots may be the only roots of 

 many plants (Fig. 46). In propagating plants by layering 

 ( 23) or by cuttings, the roots are necessarily all secondary 

 roots. Even erect stems 

 sometimes send down 

 secondary roots into the 

 soil from the lower joints 

 (Fig. 77), as is very com- 

 mon in corn. 



35. Root-cap. The 

 growing tip of each root 

 and rootlet is protected 

 by a cap of cells called 

 the root-cap (Fig. 70). 

 This root-cap consists of 

 several layers of cells, 

 the outer ones gradually 

 dying or being worn away 

 as the tip of the root 

 pushes through the soil, 

 and being replaced by 

 new layers which are 

 continually forming be- 

 neath. In some plants 

 the root-cap is very 

 easily seen as a conical 

 thickening at the tip of 

 the root; in others it 

 can 



only by examining un- 

 der the microscope lon- 

 gitudinal sections through the root-tip. The presence of 

 such a protective cap in the root is in strong contrast with 

 the stem, whose growing tips are protected by overlapping 

 leaves. 



i j i FIG. 70. Longitudinal section through root- 



be demonstrated tip of 8piderwortt showing central vascular 



axis (pi), cortex (p), epidermis (e), and 

 root-cap (c). 



