258 



STRUCTURAL BOTANY 



by a few layers of conjunctive parenchyma (see 

 Fig. 104, ph). 



Even before the primary tissues are completely 

 developed, cambium begins to arise by tangential 



FIG. 106. Part of a transverse section of the root of Picea 

 excelsa, showing the completion of the cambium outside 

 the protoxylem by division of pericyclic cells, px, proto- 

 xylem ; x ly primary xylem -plate; x 2 , secondary xylem ; 

 6, bordered pits ; c, cambium ; pti^ primary phloem 

 (crushed); ph 2 , secondary phloem; r.c, resin canal; ^c, 

 pericycle ; pd, periderm. Magnified 165. (R. S.) 



divisions of the conjunctive cells lying just inside 

 the phloem groups. As usual, secondary wood is 

 formed on the inner side of the cambium and 



