472  Rhizome  and  Roots  of  Phlox  Carolina,  j 
Am.  Jour.  Pharm. 
October,  1910. 
The  stems  are  cylindrical,  smooth,  and  the  diameter  is  from  2.y2 
to  3}^  mm.  Thus,  they  are  seen  to  be  slender  stems,  and  in  order 
to  maintain  their  perpendicular  position  would  need  to  be  quite 
woody,  especially  in  the  lower  portion,  which  they  are.  The  so- 
called  rhizome,  which  is  merely  an  extension  of  the  over-ground 
stem,  is  usually  vertical,  comprising  from  two  to  four  nodes,  and 
usually  I  to  2  cm.  long.  From  the  nodes  arise  from  two  to  four 
comparatively  thick  roots,  which  are  sometimes  nearly  2  mm.  in 
diameter  in  the  fresh  state,  from  1  to  2  decimetres  long,  unbranched, 
and  produce  a  large  number  of  fine  rootlets,  especially  near  the 
free  ends  (Fig.  A).  The  commonly  vertical  character  of  the 
rhizome  of  Phlox  ovata  is  one  of  the  features  which  distinguishes 
it  from  the  rhizomes  of  both  Spigelia  and  Ruellia,  although  it 
should  be  stated  that  occasionally  decumbent  stems  are  found  which 
produce  roots  at  the  nodes.  In  neither  case  is  that  part  of  the  stem 
producing  roots  a  true  rhizome. 
The  rhizome,  or  underground  part  of  the  stem,  is  character- 
ized, by  a  strong  development  of  woody  tissue,  which  in  trans- 
verse section  occupies  about  one-half  of  the  radius.  The  bark  is 
about  0.5  mm.  in  diameter,  the  xylem  and  phloem  together  are 
about  0.9  mm.  in  diameter,  and  the  radius  of  the  pith  is  0.3  mm. 
Histological,  Characters  of  Rhizome. — The  epidermis  in 
transverse  section  is  made  up  of  rounded  tabular  cells  and  is 
surrounded  by  a  cuticle  which  is  more  or  less  lignified  and  8  to 
10  microns  in  thickness.  Beneath  the  epidermis  are  two  to  four 
rows  of  collenchymatous  cells,  the  remainder  of  the  cortex  being 
made  up  of  about  twelve  rows  of  parenchyma  cells,  the  walls  of 
which  are  about  5  microns  thick,  the  cells  themselves  being  from 
40  to  80  microns  in  diameter.  All  of  the  cells  of  the  cortex  are 
rich  in  protoplasmic  contents,  and  sometimes  contain  a  consider- 
able number  of  small  starch  grains,  1  to  3  microns  in  diameter. 
Beneath  the  cells  of  the  cortex  there  is  usually  a  well-defined  ring 
of  endodermal  cells,  which  may  be  more  or  less  lignified,  and 
which  may  also  contain  a  few  small  starch  grains.  Beneath  the 
endodermis  is  a  layer  of  pericambial  cells,  which  show  one  or  two 
tangential  divisions.  Next  beneath  is  the  sieve,  which  is  made  up 
either  of  thin-walled,  somewhat  tabular  cells,  or  of  oval,  very  thick- 
walled  cells.  The  sieve  cells  are  rich  in  protoplasmic  contents,  and 
frequently  contain  a  number  of  starch  grains.  The  xylem  portion 
of  the  fibro vascular  bundles  (Fig.  C)  is  made  up  of  at  least  two, 
