398 
Rhamnus  Purshiana. 
f  Am.  Jour.  Pharm. 
(  September,  1914. 
The  corky  layer  consists  of  an  outer  epidermis  of  dark  brown 
weathered  cells,  then  several  rows  of  cells  filled  with  a  dark  red 
coloring  matter,  and  in  the  more  recent  bark  a  row  or  two  of  cells 
containing  chlorophyll. 
The  middle  bark  is  made  up  of  parenchymatous  cells,  which  are 
filled  with  small  starch  grains.  There  are  visible,  also,  in  the  trans- 
verse section,  several  groups  of  cubical  crystals  and  in  the  longitudinal 
section  groups  of  very  thick-walled  yellow  cells. 
The  inner  bark  consists  principally  of  yellow  medullary  rays, 
Fig.  5- — Transporting  Cascara  bark  on  pack  horses  to  wagon  road. 
separated  by  bast  parenchyma,  through  which  are  scattered  numerous 
yellow  bast  fibres.  As  seen  in  the  longitudinal  section,  these  fibres 
are  frequently  surrounded  by  small  cubical  crystals.  (Parke,  Davis 
and  Company,  "  New  Preparations,"  Feb.  5,  1879;  "  Proc.  of  Amer. 
Pharm.  Assoc.,"  vol.  27,  1879,  p.  262.) 
Microscopical  Examination  of  the  Bark. — The  corky  layer 
is  about  0.045  mm-  thick,  and  consists  of  eight  or  twelve -rows,  some- 
what flattened,  rather  thick-walled,  but  not  sclerotic  cells.  The 
parenchyma  of  the  primary  bark  is  tangentially  elongated,  partly  of  a 
collenchymatic  character,  free  from  secondary  cork,  and  contains 
