132  Frangula  and  Cascara  Barks.  {^^*m?m' 
seems  that  no  microscopical  element  can  be  detected  sufficiently 
reliable  to  depend  upon  as  a  means  of  distinguishing  the  two  species, 
the  one  from  the  other.  However,  if  the  powder  be  macerated 
several  days  in  diluted  alcohol,  a  very  marked  difference  may  be 
noted ;  the  powder  of  Rhamnus  Purshiana  will  be  of  an  orange- 
yellow  color,  when  mounted  for  microscopical  examination,  and 
when  viewed  by  a  moderately  high  power  the  various  tissues  will 
come  out  clearly,  while  the  powder  of  Rhamnus  Californica,  sub- 
jected to  the  same  treatment,  assumes  a  purplish  color,  and  when 
viewed  through  the  lens  the  tissues  seem  to  be  obscured  more  or 
less  by  a  dark  coloring  matter.  If  to  a  small  quantity  of  the 
powdered  barks  an  alkaline  solution  be  added,  the  color  developed 
in  the  Rhamnus  Californica  is  a  deep  red,  while  that  of  the  Purshi- 
ana is  orange.  This  test  may  be  briefly  stated  as  follows :  If  0-2 
gramme  of  the  powdered  bark  be  placed  in  a  small  test  tube,  and 
