82  Structure  of  Iris.  { x^^m^ 
• 
of  the  rhizome  are  unlignified.  The  cortex  and  fundamental  tissues 
of  the  central  cylinder  consist  of  loosely  arranged  parenchyma. 
The  cells  of  this  parenchyma  are  notably  unequal  in  size,  and  the 
intercellular  spaces,  though  often  large,  are  not  regular  either  in 
size  or  in  arrangement  as  they  commonly  are  in  the  stems  of  other 
aquatic  and  marsh  plants. 
The  parenchyma  cells  abound  in  rounded  granular  particles  which 
look  remarkably  like  starch  grains,  but  which  do  not  polarize  light,  and 
which  stain  brownish  instead  of  blue  with  potassium-iodide  iodine.  In 
chloral-hydrate  iodine  they  swell  and  gradually  disappear,  but  with- 
out acquiring  the  blue  color  of  ordinary  starch.  If  sections  be 
treated  with  a  1 5  per  cent,  solution  of  alpha-naphthol,  afterwards 
with  sulphuric  acid,  and  then  heated,  the  grains  disappear  and  an 
intense  violet  color  will  be  gradually  developed  in  the  tissues.  This 
test  justifies  the  suspicion  that  the  grains,  though  behaving  in  some 
respects  like  proteid,  may  really  be  carbohydrate  in  their  character, 
related  to,  if  not  in  fact  a  modification  of  starch.  But  this  matter 
requires  further  investigation. 
There  occur  in  the  parenchyma,  both  of  the  cortex  and  of  the  central 
cylinder,  rather  numerous  isolated  crystals  of  calcium  oxalate  in  the 
form  of  large-sized,  mostly  elongated  and  pointed  prisms,  which, 
between  the  crossed  Nicols,  show  beautiful  polarization  effects. 
The  cross-section  of  a  rootlet  shows  a  structure  so  characteristic 
that  it  might  be  employed  readily  in  the  identification  of  the  drug. 
The  epidermis  consists  of  two  or  three  layers  of  rather  small  and 
thickish-walled  cells.  The  cortical  parenchyma  consists  of  very 
unequal-sized,  quite  loosely  arranged  cells,  with  irregular  intercellu- 
lar spaces.  The  central  bundle  is  from  ten  to  fifteen  rayed.  The 
rays  terminate  interiorly  in  about  six  or  eight  large  ducts,  which 
form  a  circle  about  a  small  pithy  central  portion.  The  endodermis 
is  composed  of  cells  very  distinct  from  those  of  the  adjacent  tissues. 
Its  cells  are  of  nearly  equal  size  and  excessively  thickened  in  their 
inner  and  radial  walls,  which  are  also  lignified,  while  their  exterior 
walls  remain  thin  and  unlignified. 
DESCRIPTION  OF  FIGURES. 
Fig.  j. — Diagram  of  cross-section  of  rhizome  of  Iris  versicolor,  the  section 
passing  through  near  the  base  of  one  of  the  joints  ;  a,  a  vasal-bundle  in  the 
cortex;  b,  cylinder-sheath  ;  r,  a  vasal-bundle  in  the  central  cylinder.  Magnifi- 
cation, 6  diameters. 
