Am  Jour.  Pharm.  \ 
September,  1899.  j 
Gelsemium  Sempervirens,  Ait. 
433 
ternal  phloem  and  pith  are  absent  in  the  root.  In  plants  like  Stry di- 
ttos, whose  roots  possess  medullary  phloem,  pith  is  always  present. 
The  view  may  be  advanced  that  to  utilize  the  pith  area,  either 
for  more  perfect  protection  of  the  phloem,  in  these  twisted  and  at 
times  contorted  stems,  or  to  increase  the  total  amount  of  it,  a  por- 
tion of  the  external  phloem,  during  the  evolution  of  the  plant, 
dipped  in  from  the  bases  of  the  petioles,  through  the  fissures  formed 
by  the  leaf  traces  in  the  vascular  cylinder,  and  became  internal  in 
position.  The  climbing  habit  of  this  plant  may  be  one  of  the  fac- 
tors in  its  evolution. 
SUMMARY  OF  RESULTS. 
(1)  The  internal  phloem  arises  primarily  as  four  longitudinal 
strands,  which  are  an  integral  part  of  the  leaf  trace  bundles. 
(2)  The  origin  of  the  internal  phloem  is  simultaneous  with,  or 
slightly  later  than,  the  protoxylem  and  external  phloem,  so  that  the 
leal  trace  bundles  are  bicollateral  from  the  first. 
(3)  The  internal  phloem  patches  are  bounded  internally  by  a  two- 
celled  phloem  sheath. 
(4)  The  internal  phloem  patches  grow  centrifugally  by  means  of 
a  medullary  cambium,  the  inner  and  older  layers  in  time  becoming 
crushed  and  obliterated. 
(5)  Death  of  the  pith  occurs  early  in  the  first  year, 
(6)  The  continued  disintegration  of  the  pith  and  growth  of  the 
internal  phloem  results  in  the  filling  up  of  the  pith  cavity  with  the 
latter. 
(7)  The  internal  phloem,  which  runs  into  the  petiole,  constitutes 
there  at  first  a  bicollateral  bundle  system,  but  at  the  base  of  the 
petiole  it  descends  through  the  xylem  as  two  strands,  and  from  this 
point  upward  the  primitive  collateral  bundle  system  prevails. 
(8)  No  internal  phloem  is  present  in  the  root. 
(9)  A  copious  fungoid  growth  is  found  in  the  cortex  of  the  root. 
Absorption  of  starch  usually  results  in  cells  inhabited  by  the  fungus. 
(10)  No  internal  phloem  is  present  in  the  lower  portion  of  the 
hypocotyl,  nor  in  the  cotyledons. 
(11)  Two  of  the  internal  phloem  patches  of  the  stem  arise  just 
below  the  cotyledonary  node,  the  other  two  just  below  the  node 
bearing  the  first  pair  of  leaves. 
(12)  Internal  phloem  is  an  acquired  characteristic  of  the  plant, 
and  has  probably  been  developed  in  these  long  and  at  times  twisted 
stems,  to  supplement  the  external  phloem. 
