Chapter 15 



BIOLOGY OF HIGHER PLANTS- 

 ANATOMY AND PHYSIOLOGY 



I. THE ROOT 



General Regions. — Very important parts of the roots are the tips of 

 the finest branches. The surface of these branches is covered for a 

 considerable distance, from a point slightly behind the tip, with fine, 

 transparent, hairlike root hairs. Each root hair is really a continuous 

 extension from one of the outer flattened, epidermal cells of the root. 

 Each root hair contains a nucleus and a vacuole within the cytoplasm. 

 The extreme tip of the root is protected by a root cap, the outer cells 

 of which are constantly destroyed as the root is pushed through the soil. 

 Some of the growth of the root occurs in the formative region just above 

 the root cap and is known as the embryonic region. The cells of this 

 region are small, closely packed, angular, filled with protoplasm, and fre- 

 quently dividing by mitosis. Just above this region is the elongation 

 region in which the cells grow in length by taking water into the vacuoles 

 distributed in their cytoplasm. The next region is the maturation region 

 (cell differentiation region) in which different cells begin to undergo 

 specialization and differentiation. In this region the cells of the epi- 

 dermis form root hairs, and the cells of the central axial part of the root 

 form conduction tissues for the transportation of plant materials. The 

 fourth region includes the remainder of the root and is known as the 

 mature region. The cells here are differentiated into various tissues of 

 the mature root (Figs. 57 and 70). 



The mature root consists of primary and secondary tissues. The 

 former develop from differentiated cells which arise directly by cell 

 division from the embryonic region of the root tip. The secondary tis- 

 sues are produced from the cambium, which develops from undiffer- 

 entiated cells that retain their embryonic character. 



219 



