[Chap. XXIX ROOTS: DEVELOPMENT AND STRUCTURES 



303 



Region of 

 elongation 



Region of _J^ 

 cell division |^^ I j^^^ ^^p 



Fig. 122. Enlarged view 

 of the end of a root, show- 

 ing root cap, growing re- 

 gion, and root hairs. Cour- 

 tesy of World Book Co. 



Growing 



point 



Root cap 



Fig. 123. Diagram of a root tip, 

 showing the tissues and their ar- 

 rangement. Courtesy of World 

 Book Co. 



division and cell differentiation. Farther up the young root, differentiated 

 cells become more and more conspicuous. The epidermal cells elongate 

 parallel to the axis of the root. As elongation slows down, root hairs 

 begin to appear as tubular extensions of some of the epidermal cells, and 

 within a few hours they attain their complete elongation at right angles 

 to the surface of the root. 



Near the center of the vascular cylinder rows of cells extending length- 

 wise in the root become conspicuously large. These cells are the fore- 

 runners of the primary xylem vessels. The cross walls disintegrate, and 

 spiral thickenings are formed along the longitudinal walls before the 

 protoplasm disintegrates. Other strands of cells in the vascular cylinder 



