TANNIC  ACID  IN  PLANTS. 
555 
rectness  of  this  opinion,  by  his  observations  made  upon  the  fruit 
of  musa  sapientum,  which  in  the  ripe  state  contains  a  very  large 
amount  of  sugar,  and  in  the  unripe  state  is  full  of  starch  gran- 
ules, with  the  exception  of  some  longitudinal  rows  of  wide  tun- 
shaped  cells,  lying  in  the  midst  of  the  starch  tissue,  similar  to 
sap  vessels,  and  arranged  concentrically  in  the  substance  of  the 
fruit.  These  wide  cells  contain  a  clear  juice,  with  small  floating 
transparent  vesicles,  which  give  a  fine  blue  color  with  perchloride 
of  iron  solution,  while  the  other  parts  of  the  fruit  do  not  give  any 
such  coloration.  He  considers  that  there  is  no  doubt  the  tannic 
acid  in  this  case  is  produced  in  the  midst  of  the  starch  tissue,  and 
not  in  parts  of  the  plant  that  were  subject  to  incipient  decay,  but 
in  those  parts  which  are  in  a  state  of  normal  development.  The 
leaves  of  this  plant  contain  tannic  acid  in  rows  of  cells,  and  in 
vessels  formed  of  the  union  of  such  cells.  Dr.  Karsten  has  ob- 
served the  same  fact  in  a  number  of  other  plants.  In  some  in- 
stances the  cells  and  vessels  containing  the  tannic  acid  become 
very  much  thickened,  which  would  seem  to  support  Pettenkofer'g 
opinion,  that  the  production  of  tannic  acid  is  closely  connected 
with  the  production  of  wood. 
The  parenchyma  of  leaves  also  contains  tannic  acid  in  the  cell 
juice.  In  gall-nuts  the  whole  tissue  is  saturated  with  this  sub- 
stance. It  would  seem  that  a  vessel  containing  tannic  acid, 
which  in  the  oak  is  produced  in  the  wood  cambium,  is  punctured 
by  the  insect,  and  in  this  way  an  opening  is  made,  through  which 
the  tannic  acid  is  poured  into  the  tissues,  and  gives  rise  to  the 
abnormal  condition  of  the  organs. 
According  to  Dr.  Karsten,  tannic  acid  does  not  occur  free  in 
plants,  but  combined  with  another  substance  that  is  coagulated 
by  alcohol  and  by  acids.  This  compound  is  decomposed  by  con- 
tact with,  atmospheric  air,  and  then  the  reaction  with  perchloride 
of  iron  takes  place.  This  is  shown  by  the  fact,  that  when  a  cut- 
ting of  a  plant  is  immersed  in  perchloride  solution,  the  tannic 
acid  does  not  enter  into  combination  with  the  iron  until  the  cut- 
ting, after  being  impregnated  with  the  solution,  is  exposed  for 
some  time  to  the  air.  It  is  only  in  those  tissues  of  plants  which 
are  exposed  to  the  atmosphere,  by  pores  or  otherwise,  that  the 
blue  coloration  indicative  of  tannic  acid  is  produced  immediately, 
by  the  application  of  perchloride  of  iron  London  Pharm.  Jour. 
September  1,  1857. 
