146 ROOTS 



way the absorptive zone moves along just behind the advancing 

 tip. The root hairs grow out more or less at right angles to the 

 surface of the root, and are able on account of their flexible 

 slimy walls to push through small openings and around the soil 

 particles against which they flatten and to which they become 

 glued fast, thereby coming in close contact with the water films 

 around the soil particles. Why the region of elongation is near 

 the tip is now clear, for, if behind the absorptive zone, the hair 

 region would be pushed ahead and the root hairs thereby torn 

 away. 



FIG. 130. Cross section of a root through the absorbing region, x, 

 xylem; p, phloem; a, pericycle; e, endodermis; c, cortex; h, root hairs. 

 Highly magnified. 



The cortex, consisting of many layers of parenchyma cells, 

 transports the substances absorbed by the root hairs to the con- 

 ductive tissues, and in fleshy roots also serves as a storage region. 



The vascular cylinder contains the conductive tissues, notably 

 the xylem and phloem. The xylem and phloem and their posi- 

 tions in reference to each other are best seen in a cross section of 

 a root, as shown in Figure 130. The xylem occupies the cen- 

 ter and has strands radiating from the center like the spokes of 

 a wheel. Between the spokes of the xylem and near their outer 

 ends are the phloem strands. Inasmuch as the absorbed sub- 

 stances are carried to the shoot by the xylem, this alternate ar- 



