536 THE STRUCTURE OF ECONOMIC PLANTS 



Fig. ^85. Stages in development of tuber: A, transection through periderm, cortex 

 pericyclic region, and vascular ring of mature tuber; B, same region as in A, ^"^er 1° mm in 

 diameter; C, same as in ^ and B, tuber ^.^ mm. in diameter: ^-.cambium; ^o^cone., en 

 endodermis; .p, epidermis ; .• />A, inner phloem ; . /,A, outer phloem; ^ pericycle. pa, 

 periderm; pi, pith; x^, xylem. (After Artschwager, 7o«r. /f^r R«.; 



