Am.  Jour.  Pharm.  \ 
October,  1897.  / 
Aralia  Nudicaulis. 
537 
cylindrical,  with  many  concave  leaf-scars,  corresponding  in  shape  to 
the  swollen  end  of  the  petioles.  The  outer,  very  thin,  grayish, 
somewhat  glossy  layer  of  the  bark  is  easily  detachable,  and  the 
lower,  thick,  fibrous  layer  can  readily  be  peeled  off  the  white  or 
slightly  yellowish  wood,  as  long  as  the  rhizome  is  fresh  and  moist. 
A  white  and  spongy  pith  forms  the  interior  of  the  wood.  On  drying, 
the  rhizome  becomes  wrinkled  and  brittle,  and  is  from  %  to  ^4  inch 
in  diameter.  The  taste  of  the  fresh  rhizome  is  peculiarly  aromatic, 
similar  to  that  of  ginseng,  leaving  no  bad  after-taste. 
MICROSCOPY. 
A  cross-section  of  a  segment  of  the  rhizome  shows  under  the 
microscope  three  distinct  parts,  the  pith,  the  wood  and  the  bark. 
The  pith  consists  of  rather  large,  granular  cells,  containing  starch 
with  occasional  crystals  of  oxalate  of  calcium. 
The  pith  is  surrounded  by  a  wood  zone  which  varies  in  thickness 
according  to  the  age  of  the  specimen.  In  old  rhizomes  the  wood  is 
about  twice  as  thick  as  the  bark,  while  in  very  young  specimens  a 
cross-section  shows  a  large  pith,  a  thick  bark,  and  very  little  wood. 
The  thick-walled  woody  edges  of  irregular  size  are  separated  by 
medullary  rays  of  one  or  two  rows  of  cells.  Sometimes  these  rays 
are  prolonged  into  the  bark.  A  layer  of  cambium  cells  in  a  double 
row  surrounds  the  wood. 
The  bark  consists  of  a  fibrous  layer,  a  corky  layer  and  an  epidermis. 
The  parenchyma  cells  are  rich  in  starch  and  contain,  like  the  pith, 
crystals  of  calcium  oxalate.  The  characteristic  part  of  the  fibrous 
layer  of  the  bark  is  the  great  number  of  oil  or  resin  cells,  the  largest 
cells  of  the  plant,  resembling  tubes  that  can  often  be  traced  quite  a 
distance  in  longitudinal  sections.  They  are  intrenched  by  a  wall  of 
small  cells  that  undoubtedly  secrete  oil  and  resin,  while  the  large 
inner  cells  serve  as  reservoirs.  The  medullary  rays  often  extend 
into  this  layer,  taking  an  irregular,  somewhat  tortuous  course,  and 
sometimes  their  two  rows  of  cells  separate  and  encase  one  of  these 
large  oil  cells.  The  resin  is  probably  held  in  solution  by  the  oil. 
Between  the  fibrous  and  corky  layers  of  the  bark,  a  double  row  of 
peculiarly  shaped  cells  are  observable,  probably  a  layer  of 
phellogen. 
The  corky  cells  are  empty  and  rather  large,  presenting  no  points 
of  particular  interest.  A  thin  epidermis  covers  the  corky  layer, 
easily  detachable  and  often  wanting. 
