152 



Practical Plant Biology. 



The outer layers of the fundamental tissue of the stem have 

 very thick, hard and brown cell-walls, forming a tissue known as 

 sclerenchyma. It forms a continuous coating over the bases of 

 the mature leaves and the stem, and is only penetrated by the 

 conducting strands entering from the roots. 



The roots have a comparatively simple structure. A single 

 conducting tract runs down the axis of each. It is covered by a 



_J 



FIG. 36. Aspidium filix-mas, root, transverse section, x 350. b, bast ; 

 , cortex; />, pericycle; pi, piliferous layer; r, root-hair; s, sheath of 

 conducting tract; x, wood. (From Evans' An Intermediate Textbook 

 of Botany.) 



thick coat of fundamental tissue the cortex. In the outermost layer 

 of the cortex certain isolated cells grow out at right angles to the 

 surface and develop into root-hairs which grow out among the 

 particles of the soil and absorb water and various dissolved sub- 

 stances. The inner layers of the cortex develop thick and brown 

 walls and form a sclerenchymatous sheath round the conducting 

 tract. An apical growing cell, like that of Funaria, adds to the 

 root at its tip. It is pyramidal in shape. Its apex points towards 



