42 



BOTANY: PRINCIPLES AND PROBLEMS 



between these two main types. Others may sometimes depart 

 radically from the normal forms in response to certain special 

 and unusual functions which they have assumed. 



The Absorbing Region.^ — Absorption of water and nutrient 

 material is carried on only by the j^ounger portions of the root, 

 near its tip. The very tip itself is covered with a sheathing root- 





FiG. 23. — Tip of a root, showing root-cap (A), growth zone (B), and root-hair 

 zone (C). (From Ganong, "Textbook of Botany", copyrighted by the Macmillan 

 Company. Reprinted by permission) . 



cap of cells, which protects the delicate underlying tissues as the 

 root pushes its way through the soil (Fig. 71). Back of this is a 

 short region of growth, the only place where elongation of the 

 root occurs. Behind this, in turn, is the absorbing region, a 

 somewhat longer zone the surface of which is covered with 

 thousands of exceedingly delicate filaments, the root-hairs (Fig. 

 23). Each hair is an elongated projection growing out from one 

 of the surface cells of the root (Fig. 24), its sap-cavity and lining 

 of cytoplasm being continuous with those of the root-cell of 

 which it forms a part (Fig. 25) . The root-hair may reach a length 



