122 PLANT LIFE. 



which the innermost layer differs from the rest. This 

 innermost layer of closely-set cells, " endoderniisl' 

 forms a cylinder which divides the cortex from the 

 inner water- conducting part. Very often a peculiar 

 dot may be noticed on the radial walls of these cells 

 (see figure) which is a ring of cork. It appears as a dot 

 in the transverse section but as a line in the tangential 

 section. Each of these endodermis cells is, in fact. 



Fig. 12. — Transvkkse Section of Root (Ranunculus repens). The xylem is 

 formed of four groups of vessels X which will eventually be united by the change 

 of the connecting cells into a central 4-spoked cross. The barbless arrows xy 

 show the path of water entering from the cortex. Phloem, P, is not in contact 

 with the xylem. Pe. Pericycle or rootlet- and cork-forming layer. E. Endo- 

 dermis with a dot on radial walls (cork). Co. Cortex, only a small part of which 

 is shown. The one-barbed arrow PHL shows the path of the food material 

 brought by the supply pipes of Phloem (three-barbed arrow at /*). The four- 

 barbed arrow is the main water pipe through .\" passing up the stem. 



separated from its neighbours by a piece of cork, which 

 is placed between them, or all round each cell. The 

 reason for this arrangement is given below. The central 

 or conducting system of the root contains three distinct 

 kinds of cells, (i) Unmodified or not yet specialised 

 cells. (2) Water-conducting vessels, or tracheids, the 

 *"' Xylemy (3) Food-conducting tubes and cells, the 

 " Phloemr 



In old roots the xylem is often arranged in 



