Am.  Jour.  Pharm. 
June,  1898. 
Mucilage  in  Plants. 
289 
The  origin  of  "  cell-wall  mucilage"  may  be  best  studied  in 
the  young  roots  and  stems  of  althaea.1  In  the  very  young  elements 
the  mucilage  cells  are  found  to  be  much  larger  than  in  the 
surrounding  parenchyma.  If  in  this  stage  sections  of  fresh  material 
are  treated  with  alcohol,  there  is  no  indication  of  any  of  the  cells 
containing  mucilage.  A  little  later,  however,  we  find  in  older  speci- 
mens that,  in  addition  to  the  protoplasm  and  nucleus,  there  is  a 
granular  layer  formed  on  the  inside  of  the  wall.  Upon  the  addition 
of  water  this  layer  swells,  and  upon  subjecting  it  to  the  methylene  blue 
treatment  it  is  found  to  be  a  mucilage  layer.  The  cell  wall  grows 
in  thickness  by  the  successive  depositions  of  lamallae  of  mucilage, 
and  finally  in  old  cells  we  observe  only  a  small  lumen  with  a  little 
protoplasm,  the  mucilage  wall  occupying  the  remainder. 
The  study  of  these  mucilage  cells  may  be  performed  on  commer- 
cial specimens  of  althaea  root.  If  the  latter  are  first  washed  in 
water  until  softened,  and  then  put  into  strong  alcohol,  we  have  mate- 
rial that  may  be  easily  sectioned.  Sections  are  made  and  are  put 
into  an  alcoholic  methylene  blue  solution  for  several  hours  or 
longer.  These  are  then  mounted  on  a  slide  in  a  glycerin  methy- 
lene blue  solution.  In  the  course  of  a  few  hours  the  mucilage  cells 
have  taken  on  a  prominent  blue  color  and  are  distinct  from  the 
other  parenchyma  cells  (Fig.  8).  The  lamellae  are  pronounced,  and 
in  the  centre  a  small,  irregular  lumen  with  a  small  amount  of  proto- 
plasm is  observed. 
If  a  specimen  of  elm  bark  of  commerce  is  treated  similarly  to 
that  of  althaea  root,  equally,  if  not  more,  characteristic  are  the  blue 
colored  mucilage  cells  (Fig.  p). 
Mucilage  occurs  as  a  secondary  thickening  beneath  the  cuticle  of 
a  number  of  seeds,  as  Sinapis  alba  (Fig.  10)  and  Linum  (Fig.  n), 
etc.  If  sections  of  the  dry  seeds  are  mounted  first  in  a  solution 
of  glycerin  and  water  and  then  a  glycerin  solution  of  methylene 
blue  added,  the  mucilage  layer  becomes  a  permanent  blue  color, 
stronger  in  Sinapis  alba  than  in  Linum. 
The  secretion  hairs  (or  glands,  as  they  are  sometimes  called)  which 
we  find  at  the  apex  of  the  divisions  of  the  leaves  of  Viola  tricolor,  L., 
and  other  plants,  yield  a  mucilage.  In  the  leaves  of  Viola  tricolor,  L., 
at  the  apex  of  the  divisions  of  the  lamina  and  stipulae,  we  find  large 
1  See  Tschirch,  Anatomiscber  Atlas,  Lief.  VI,  S.  128. 
