496 THE STRUCTURE OF ECONOMIC PLANTS 



Somewhat later, secondary cambiums may arise in the tissue on 

 the inner face of the secondary xylem which remains active for a 

 limited period. (Fig. 2.57.) Still later, secondary cambiums may 

 be formed in the parenchyma of the root which are not related 

 spatially to any vascular elements; and these, in turn, may pro- 

 duce xylem centripetally and phloem centrifugally. (Fig. ^58.) 



Fig. 2.55. Transection of young fleshy root: ca, cambium, co, cortex; en, endodermis ; 

 ep, epidermis ; lac, lacuna ; rnx, metaxylem ; far, interstitial parenchyma ; pel, pericycle ; 

 /)/>, phloem; />x, protoxylem ; .vj i, secondary xylem. 



Less frequently, secondary cambiums may develop in the paren- 

 chyma of the original phloem groups. 



While the development of these anomalous secondary cambiums 

 is taking place, the primary cambium continues to function, form- 

 ing secondary xylem and phloem elements and a large amount of 

 storage parenchyma. The parenchyma around the secondary 

 xylem elements may in turn produce a secondary cambium which 

 forms new elements in the usual manner, and Artschwager (i) 



