696 
Rhus  Venenata  DC. 
(  Am.  Jour.  Pharm. 
(October,  1920. 
DESCRIPTION  OF  PLANT. 
Rhus  venenata  De  CandoUe,  family  Anacardiaceae,  is  commonly 
known  as  swamp-sumac,  poison  sumac,  poison  elder  and  poison 
dogwood.  The  latter  synonym  must  not  be  confused  with  the 
flowering  dogwood,  which  is  a  member  of  the  Cornaceae  family. 
It  is  a  shrub  possessing  a  slender  clustered  stem,  which  some- 
times takes  a  tree-like  form,  reaching  to  a  considerable  height. 
The  stem  is  brittle,  showing  for  the  most  part  a  pithy  region  inter- 
nally. The  leaves  are  7-13  foliate,  with  slender  reddish  green  peti- 
oles. The  leaflets  are  obovate,  oblong,  dark  green  and  glossy  on 
the  ventral  surface,  paler  on  the  dorsal  side,  and  without  marginal 
teeth.  The  midrib  and  veins  are  prominent.  The  flowers  are  dioe- 
cious and  are  in  narrow  axillary  panicles,  yellowish  green  to  white 
in  color.  The  petals  are  slightly  reflexed.  The  stamens  appear 
nearly  twice  as  long  as  the  petals.  The  fruit  is  a  smooth,  white 
drupe,  often  remaining  on  the  branches  until  spring.  The  leaf 
scars  are  prominent,  alternate  and  of  a  somewhat  crescent  shape. 
The  bark  on  young  stems  is  mottled  with  conspicuous  lenticels. 
HISTOI.OGY  OF  STEM. 
We  find  the  epidermis  to  be  composed  of  a  single  layer  of  epi- 
dermal cells  with  a  thick  outer  cuticle.  The  subepidermal  region 
shows  a  couple  of  layers  of  cork  cells,  more  or  less  tangentially 
elongated.  The  cortex  region  is  compact  in  nature  and  consists 
for  the  most  part  of  sclerosed  parenchyma.  Numerous  rosette, 
aggregate  crystals  of  calcium  oxalate  are  found  in  this  region.  Resin 
canals  are  present  in  the  primary  cortex,  which,  according  to  Sole- 
reder^  is  common  in  the  Rhus  venenata.  The  structure  of  the  peri- 
cycle  varies  according  to  the  age  of  the  plant.  In  the  older  stems 
isolated  groups  of  sclerenchyma  fibers  occur  usually  in  the  form 
of  adjacent  arcs.  The  convex  side  of  each  of  these  is  directed 
towards  the  exterior.  The  inner  concave  side  of  each  arches  over 
a  dome-shaped  phloem  in  the  centre  of  which  is  a  single  resin  canal. 
In  younger  stems  the  arcs  (strands)  of  sclerenchyma  fibers  are  joined 
with  each  other  by  means  of  sclerosed  parenchyma.  In  this  way 
the  pericycle  constitutes  a  continuous  ring  of  stereomatic  structure, 
which  covers  the  phloem-containing  resin  canals  as  a  single  band.  A 
zone  of  cambium  cells,  more  or  less  collapsed,  is  found  separating 
the  phloem  region  from  the  xylem.  The  prosenchyma  forming 
the  structure  of  the  wood  has  simple  and  bordered  pores.  The 
