IPOMOEA BATATUS 



497 



reports that "when the amount of tissue produced by the secondary 

 cambium is considerable, as can best be seen in the region of the 

 large central cell of the young root, a tertiary cambium develops 



Fig. 156. Transection of portion of young fleshy root showing origin of cambiums. A 

 secondary cambium is being initiated around large metaxylem vessel at lower right-hand 

 corner of figure : w, primary cambium ; co, cortex ; en, endodermis ; pel, pericycle ; ph 

 phloem; px, protoxylem. (After Artschwager, /ow. A^r. Rw.) 



around a number of the secondary elements and increases in the 

 same way as did the group from which it arose." 



In roots which become ridged at maturity, the lobes are traversed 

 by vascular bundles which originate in the primary vascular ring 

 and are diverged into the cortex, continuing vertically through the 

 ridges. (Fig. 2.59.) Small bundles are occasionally present in the 



