2.66 THE STRUCTURE OF ECONOMIC PLANTS 



a general agreement as to the subsequent development of tissues 

 derived from them. There are commonly five or six relatively v^ide 



-^ca 2 



>xy 3 



- — int par 



--ph3 



I 



ph2-^ 



ca — - 



xy 2— I 



Fig. 131. A-E, sectors of successive secondary cambiums from peripheral one, A, to one 

 of innermost rings, E, showing progressive development of rings ; F, sector of central portion 

 of stele showing primary cambium and secondary tissues derived from it : ca, primary cam- 

 bium ; ca 2., secondary cambium ; int par, interzonal parenchyma ; pf> i, secondary phloem ; 

 ph 3, tertiary phloem ; xy t., secondary xylem , xj 3, tertiary xylem. 



