138 ROOTS 



easily permeable. The cells are much alike in shape and 

 size. It is in these cells of the cortex that food is prin- 

 cipally stored. It is the cortex which is principally en- 

 larged in tap-roots. 



The stele of roots is also called the central axis, or the 

 vascular cylinder. It is a part of that vascular system 



Fig. 47. — Cross section of a young root showing root-hairs, epidermis, cortex, and 

 stele. The stele or central region is chiefly composed of xylem and phloem. 

 The cells of the xylem have heavy walls ; the cells of the phloem are shaded. 



which extends throughout the whole body of the plant. 

 The veins of the leaves and the vascular bundles of the 

 stem are also parts of this system. You are already 

 familiar with xylem and phloem. The vascular system is 

 principally composed of these tissues. Xylem is also called 

 wood, and phloem is also called bast. 



You note that in the stele of the root the tissue xylem 

 (heavy-walled) occupies the center. It also radiates from 

 the center. Between the radiating arms of the xylem are 

 groups of cells which are phloem. The xylem or wood 

 and the phloem or bast lie along alternating radii. This ar- 



