472  Structure  of  Heuchera  Americana.  {Ao'ctober,Km' 
the  largest  grains  show  a  cross  by  polarized  light.  Even  then  the 
cross  is  very  faint.    The  cross  is  usually  somewhat  oblique. 
Old  or  mature  roots  contain  great  numbers  of  sphero-crystals  of 
calcium  oxalate,  and  these  are  frequently  so  arranged  that  when  the 
transverse  section  of  the  root  is  cleared  of  its  starch  and  proteids, 
it  presents  under  a  low  power  a  somewhat  annulate  appearance. 
The  rings  shown  in  the  woody  cylinder  in  Fig.  j  are  due  to  this 
annulate  arrangement  of  the  crystal  cells.  Not  all  sections,  how- 
ever, show  the  annulate  arrangement  so  distinctly  as  this  one. 
The  tannin  is  the  variety  which  produces  a  blue-black  precipitate 
with  ferric  salts,  and  it  occurs  abundantly  in  nearly  all  the  tissues  of 
the  root  and  rhizome,  and  more  abundantly  in  the  cell-walls  than 
among  the  cell  contents.  The  cork  cells,  especially  the  newer  ones, 
appear  to  contain  least  of  it.  Old  parenchyma  cells  that  contain 
large  quantities  of  starch  also  appear  to  contain  somewhat  less 
tannin  than  those  which  are  younger. 
The  alcannin  test  also  indicates  the  presence  of  small  quantities 
of  resin  in  the  cells,  sometimes  in  irregular  or  nodular  masses  of 
considerable  size,  more  commonly  in  trie  form  of  minute  particles 
imbedded  in  the  protoplasm  of  the  cells. 
DESCRIPTION  OF  FIGURES. 
Fig.  r. — A  rhizome  and  roots  of  Heuchera  Americana  about  natural  size. 
Drawing  made  from  living  plant. 
Fig.  2. — Transverse  section  of  the  rhizome  magnified  about  six  diameters. 
a,  corky  exterior  layer,  showing  its  friable  character  ;  b,  cortical  parenchyma  ; 
c,  cambium  zone  ;  dy  one  of  the  xylem  wedges  ;  e,  a  broad  medullary  ray ;  f, 
xylem  of  a  root  bundle,  the  section  having  passed  through  the  base  of  a  root ; 
g,  pith. 
Fig'  3- — Cross-section  of  one  of  the  older  roots  magnified  about  six  diameters. 
a,  cork ;  b,  cortical  parenchyma  ;  c,  end  of  one  of  the  secondary  xylem  rays  ; 
dy  faint  circle  caused  by  the  peculiar  arrangement  of  the  cells  containing 
calcium  oxalate  crystals  ;  e,  a  small  mass  of  tracheary  tissue  in  secondary 
xylem  ;  f,  cambium  ;  g,  soft  bast  layer. 
Fig.  4. — Root  as  seen  in  cross-section,  magnified  sixty-six  diameters,  ay 
cork ;  b,  cortical  parenchyma,  the  outer  cells  of  which  are  somewhat  collen- 
chymatous  •  c,  medullary  ray  ;  d,  d/,  d//,  dr/,y  original  xylem  rays  of  the 
tetrarch  radial  bundle  ;  e,  primary  phloem  ;  fy  meristem  ;  g,  one  of  the 
tracheids  in  the  secondary  xylem,  showing  scalariform  markings  on  the  oblique 
end- wall ;  hy  another  of  the  four  secondary  xylem  rays. 
Fig.  5.— Small  portion  from  xylem  region  in  longitudinal  section  of  root, 
showing  row  of  scalariform  tracheids  and  some  of  the  adjacent  parenchyma 
cells.  Magnification  330  diameters.  Two  of  the  parenchyma  cells  contain 
sphere-crystals  of  calcium  oxalate. . 
