130  Frangula  and  Cascara  Barks.  {^y^SE™1, 
(4)  In  each,  the  relative  amount  of  cork,  of  collenchyma  and  of 
parenchyma  is  about  the  same. 
These  structural  similarities  would  seem  to  make  the  distinction 
between  the  pulverized  barks  quite  difficult,  but  fortunately,  for  this 
purpose,  there  are  a  very  few  points  of  dissimilarity  revealed  by  the 
compound  microscope  and  reagents,  which  may  serve  the  pharma- 
cologist. 
Fig.  <f,  Rhamnus  Frangula,  longitudinal  section.  A,  epidermis  ;  b,  collen- 
chyma ;  c,  sclerenchyma  ;  e,  medullary  ray  ;  f,  bast  bundle  ;  g,  parenchyma  ; 
hy  crystals  of  calcium  oxalate. 
Rhamnus  Frangula  contains  no  stone  cells,  while  the  Rhamnus 
Californica  and  the  Rhamnus  Purshiana  contain  a  large  number  of 
them,  scattered  in  large,  irregular  groups  below  the  cork,  and  usually 
outside  the  region  of  bast.  The  presence  or  absence  of  stone  cells 
is  very  easily  noted  by  one  familiar  with  vegetable  tissues,  and  this 
one  characteristic  is  suggested  as  a  means  of  distinction  between 
Rhamnus  Frangula  and  the  other  two  barks. 
In  the  case  of  Rhamnus  Purshiana  and  Rhamnus  Californica,  it 
