ON  VEGETABLE  MUCILAGE. 
37 
ON  VEGETABLE  MUCILAGE,  AND  SUBSTANCES  ALLIED 
THERETO. 
By  Dr.  Ku'tzing. 
Having  sliced  off  with  the  razor  a  very  thin  piece  of  the  white, 
broad  sort  of  tragacanth,  and  placed  it  in  a  drop  of  water  under 
the  microscope,  it  swelled  up  instantaneously,  and  showed  a  dis- 
tinctly cellular  structure,  and  much  larger  starch-grains  than 
usual.  The  cells  consisted  of  a  very  thick  membrane,  and  partly 
of  several  concentric  layers.  The  starch  grains  were  round  and 
crowded  in  the  cells,  which  were  but  loosely  connected,  and  of  va- 
rious sizes,  some  of  1-10 "diameter. 
No  reaction  was  produced  on  the  thick  cell-walls  by  tincture  of 
iodine,  but  the  starch  grains  became  blue.  On  adding  one  drop 
of  concentrated  sulphuric  acid,  the  cells  swelled  up  still  more,  and 
the  concentric  layers  became  more  distinctly  visible,  and  at  the 
same  time,  assumed  a  yellow  or  brownish-orange  color.  The  in- 
ner cell-wall  now  appeared  to  be  coated  with  a  delicate  blue  mem- 
brane, wThich  enclosed  the  starch-grains  in  the  form  of  a  sac.  The 
starch-grains,  by  continued  application  of  sulphuric  acid,  were 
converted  into  dextrine,  and  at  last  disappeared,  as  well  as  the 
blue  membrane,  but  the  thick  cells  still  remained,  though  they  lost 
the  property  of  becoming  orange  or  yellow  by  iodine;  they  re- 
mained at  last  entirely  colorless  by  tincture  of  iodine,  but  upon 
the  application  of  heat  also  dissolved. 
These  results  induced  the  author  to  examine  various  other  gums, 
and  to  watch  the  process  of  their  formation  in  the  plum-tree  gum, 
which  exudes  from  the  trees  belonging  to  Drupaceae,  and,  by  the 
aid  of  iodine  and  sulphuric  acid,  he  discovered  that  the  cellulose 
of  phanerogamic  cells  are  colored  blue,  while  that  of  all  lichens 
and  fungi  which  he  examined,  are  colored  orange  or  yellowish- 
brown  by  the  application  of  sulphuric  acid  and  iodine.  All  the 
kinds  of  natural  gums  of  commerce  present  the  same  appearances, 
but  with  this  difference,  that  those  which  contain  more  bassorine 
than  arabine,  present  the  iodine  reaction  with  the  aid  of  sulphuric 
acid  for  a  longer  time,  whereas  in  gum  arabic  it  disappears  sooner. 
To  the  phanerogamia,  which  present  a  blue  coloration,  belong 
cotton,  the  cells  of  endive  leaves,  of  cucumbers,  and  the  wood  of 
the  cruciferae. 
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