BOTANY 



PIG. 17. Transverse section of root to show 

 a rootlet at two stages of development. 

 rh, root hairs ; ec, cortex ; d, cells in pro- 

 cess of absorption; en, endodermis; pe, 

 pericycle; co, conjunctive tissue; ph, 

 bast ; g, cambium ; x, wood ; c, derma- 

 togen of rootlet ; p, its periblem ; pi, its 

 plerome. (After Scott.) 



original one. This 

 corky formation con- 

 tinues as long as the 

 root lives and adapts 

 itself to its increasing 

 girth. Its outer part 

 is composed of dead 

 cells, and together 

 with the remains of 

 the layers originally 

 outside it, constitutes 

 the bark of the root. 

 The cortex and epi- 

 blema continue for a 

 very short time, so 

 that in an old root the 

 bark consists of peri- 

 cycle tissue and layers 

 of cork. 



We must again re- 

 turn to the young root 

 to trace the manner 

 of formation of its 

 branches. The latter 

 originate when it is 

 quite young, as we 

 have seen already. 

 They arise in the peri- 

 cycle, in very many 

 cases opposite to the 

 protoxylem of each 

 wood bundle, gener- 

 ally before the strands 

 are lignified through- 

 out. There are con- 

 sequently usually as 



