Am.  Jour.  Pharm. 
July,  1895. 
}     Structure  of  Oar  Hemlock  Barks. 
359 
some  characters  which  we  may  rely  on  for  distinguishing  them.  In 
both,  cork  formation  begins  early,  and  in  all  cases  where  the  bark 
has  been  taken  from  stems  more  than  a  few  inches  in  diameter,  the 
secondary  cork-formations  have  invaded  the  inner  layer  of  the  bark, 
and  bands  of  cork  will  be  observed  crossing  at  various  angles  the 
medullary  rays.  The  cork  in  both  is  colored  a  deep  purple,  and 
this  coloring  matter  is  bleached  out  only  with  difficulty,  even  by 
Labarraque's  solution.  This  coloring  matter  appears  to  differ  in 
composition  from  the  reddish-brown  coloring  matter  found  in  the 
tissues  between  the  bands  of  cork,  for  not  only  is  the  color  a  different 
shade  of  red,  but  it  bleaches  more  readily.  Tests  for  tannin  show 
that  in  both  species,  also,  the  white  or  colorless  younger  portions  of 
the  bark  contain  little  of  it,  while  the  older  portions,  particularly 
the  dead  sieve  and  parenchyma  tissues  between  the  bands  of  sec- 
ondary cork,  are  exceedingly  rich  in  it.  Stone  cells  of  large  size 
and  often  quite  irregular  shape  occur,  either  isolated  or  clustered  in 
groups  of  several  or  many,  throughout  all  except  the  youngest  por- 
tions of  the  inner  bark.  They  are  quite  numerous,  but  are  distrib- 
uted without  apparent  order.  They  are  marked  with  numerous 
very  fine  pore-canals,  and  very  numerous  and  fine  concentric  lines. 
Abundance  of  starch  was  found  in  the  bark  of  Tsuga  Canadensis. 
The  medullary  ray  cells  and  the  tangential  rows  of  large  parenchyma 
cells,  which  occur  at  frequent  and  regular  intervals  in  the  inner  bark, 
were  found  to  be  especially  rich  in  it ;  but,  strange  to  say,  no  starch 
was  observable  in  the  bark  of  Tsuga  JSIertensiana,  although  there 
were  a  similar  structure  and  arrangement  of  medullary  ray-cells  and 
there  were  the  tangential  rows  of  large  parenchyma  cells,  the  same 
I 
