sTptembef,11!™'}       Gelsemium  Sernpervirens,  Ait.  .427 
entirely  fill  the  former  pith  area,  except  a  very  small  space  in  the 
centre,  where  a  shrunken  thread  of  dead  tissue  represents  all  that 
remains  of  the  pith.  The  patches  by  this  time  are  composed  al- 
most wholly  of  "  Hornbast."  Only  a  few  sieve  tubes  are  distin- 
guishable, and  these  are  more  or  less  distorted.  The  contrast  be- 
tween the  large  cells  of  the  phloem  sheath  and  the  dark  crushed 
masses  is  very  striking. 
The  breadth  of  the  external  phloem,  which,  during  the  first  few 
years,  was  less  than  that  of  the  internal  patches,  increases  greatly 
in  older  stems.  In  a  six-year-old  stem  its  breadth  almost  equals 
that  of  the  patches  ;  in  a  ten-year-old  stem  it  exceeds  them.  The 
same  alternation  of  bands  of  "  Hornbast  "  with  parenchyma  cells 
occurs  as  in  the  internal  patches,  but  as  the  pressure  conditions  are 
different  here  the  bands  are  narrower  and  less  marked.  As  the 
growth  has  been  centripetal,  the  newly  formed  tissue  lies  internal  to 
the  old. 
The  widening  of  the  medullary  rays  is  very  noticeable  in  older 
stems.  The  width  of  a  ray  at  the  periphery  of  the  wood  is  six  or 
eight  times  greater  than  at  the  centre.  Elongated  cells,  that  are 
continuations  of  the  rays,  separate  the  cone-like  masses  of  the  ex- 
ternal phloem  zone, 
HISTOLOGY  OF  A  NODAL  SECTION. 
Near  a  node  the  circle  of  wood  and  external  phloem  becomes 
elliptical,  and  the  patches  of  internal  phloem  lie  at  the  ends  and 
sides  of  the  ellipse.  The  end  patches  are  considerably  larger  than 
the  side  ones  and  are  further  divided  into  a  central  and  lateral  por- 
tion, the  former  for  the  petiole,  the  latter  to  remain  in  the  stem. 
Higher  up,  the  ends  of  the  ellipse  curve  out  more  and  more,  and 
soon  separate  from  the  sides  to  form  the  petiolar  bundles.  Each 
bundle  is  accompanied  by  a  portion  of  the  internal  phloem,  so  that 
at  first  the  petiolar  bundle  is  composed  of  external  phloem,  wood 
and  two  small  masses  of  internal  phloem.  Left  in  the  stem  are  the 
two  long  lateral  curves  of  wood  and  external  phloem  as  before. 
The  two  small  groups  of  internal  phloem  that  remained  behind  at 
each  end  now  move  together  to  reconstitute  the  end  patches. 
Above  the  node  the  wood  reunites  into  a  continuous  ring,  while  at 
the  next  node  above,  the  leaf  bundles  will  be  given  off  from  the 
opposite  sides  of  the  stem. 
