132         The  Rhubarbs  and  a  Probable  Adulterant,  {AVa?S£ffi!ra,• 
irregularity  of  the  fibro-vascular  tissue  in  certain  areas,  as  shown  in 
the  half-tone  reproduction  of  a  photomicrograph  {Frontispiece,  Fig. 
2).  This  doubtless  corresponds  to  the  stellate  structures  of  the 
Russian,  but  it  is  not  carried  out  to  the  same  extent. 
The  Rhaponticum  (Frontispiece,  Fig.  j)  in  the  particular  just  men- 
tioned, presents  an  entirely  different  aspect,  as  is  easily  distin- 
guished from  either  variety  of  the  Chinese  rhubarb.  There  is  a 
distinct  and  plainly- marked  radiate  structure,  unbroken  by  such  an 
arrangement  of  the  vascular  tissue  as  is  so  apparent  in  the  true 
rhubarb.  As  will  also  be  observed,  the  paring  of  the  rhizome  did 
not  extend  down  to  the  cambium  line,  which  appears  as  a  dark 
line  in  the  figure.    The  parenchyma  here  is  also  thin-walled. 
Under  higher  magnification,  the  cell  contents  of  the  tissues 
become  manifest.  In  both  the  Rheum  officinale  and  the  rhaponti- 
cum the  elements  observed  are  starch  grains  and  calcium  oxalate 
crystals.  Of  these  more  extended  mention  will  be  made  when  the 
powdered  form  of  the  substances  is  considered.  Rumex  hymeno- 
sepalus  in  the  gross  and  in  section  offers  no  points  of  comparison  to 
the  species  of  Rheum.  The  roughly-wrinkled  root  is  of  a  dark, 
krameria-red  color,  and  possesses  no  trace  of  the  characteristic 
rhubarb  odor.  The  taste  is  sharply  astringent,  and  in  no  wise 
mucilaginous  and  disagreeable  like  Rheum.  The  gritty  feeling 
when  ground  between  the  teeth  is  also  absent.  In  section  (Frontis- 
piece, Fig.  Is)  it  presents  the  typical  form  of  a  simple  root.  The 
thin-walled  parenchyma  occupying  the  whole  extent  of  the  section 
is  marked  off  into  two  areas  by  the  concentric  cambium  line,  in 
such  a  manner  that  the  inner  central  one  occupies  about  two-thirds 
the  diameter  of  the  section.  Radiating  from  the  center  to  the 
cambium  line  are  about  twelve  groups  of  tracheary  vessels. 
In  the  form  of  powders  the  Rheums  and  the  canaigre  are  not  eas- 
ily differentiated,  yet  a  careful  examination  will  not  fail  to  show  the 
presence  of  the  latter,  even  when  mixed  with  other  drugs.  The 
distinction  of  R.  officinale  and  R.  rhaponticum,  however,  is  a  different 
matter,  and  the  author  was  not  able  to  select  any  salient  micro- 
scopical feature  that  would  serve  to  distinguish  them  apart,  either 
individually  or  in  mixtures.  But  a  chemical  test  was  found,  which 
will  be  described  later  on. 
In  a  No.  60  powder  of  either  rhubarb  the  most  striking  elements 
observed  are  the  starch  grains  and  calcium  oxalate  crystals,  to 
