ROOTS: KINDS OF ROOTS 31 



root hairs are constantly being developed from newly formed 

 epidermal cells, while all the older root hairs behind are con- 

 stantly dying and disappearing. They are long, slender, tubular 

 cells, and since they serve the important purpose of absorbing 

 water and mineral food solutions from the soil, they must be fresh 

 and new. 



53. Internal structure of the root. Fig. 36 represents a cross 

 section of a root. The outer layer of cells is the epidermis from 

 which the root hairs arise. Just 

 inside of the epidermis is the 

 cortex, which consists of several 

 layers of cells more or less rounded 

 and with air spaces between where 

 they touch adjacent cells. Inside 

 of this is a ring of a single layer 

 of rather thin cells (the pericycle}. 

 This can be located by observing 

 that it lies just outside of groups 

 of cells so highly differentiated in 



the Center. These groups of Cells, Section of corn root, showing root hairs 

 .LI. -xu j.u xU' 11 j r formed from elongated epidermal cells. 



together with the thin-walled fun- 



damehtal cells which are between them, make the central cylinder 

 (fig. 37). There are often eight groups of special cells seen in cross 

 section of a young root. Four of these, the more prominent 

 ones, are the fibre-vascular bundles (paragraph 98). They are 

 broad inward and narrowed outward as seen in cross section. 

 The larger cells are the vessels or tubes through which the water 

 or " sap " flows in the root. Besides the vessels there are thick- 

 walled wood fibers, and on the outer side also some young thin- 

 walled living cells which divide and grow to form additional cells 

 for the bundle as the root increases in diameter. The tissue of 

 these bundles is woody and is the xylem (paragraph 98). Alter- 

 nating with these four radiating groups of wood cells are four other 

 groups of bast cells (or phloem), which lie near the pericycle. The 

 tissue of thin-walled cells lying between these groups is funda- 

 mental tissue, parenchyma (paragraph 94). 



