290 
Mucilage  in  Plants. 
Am.  Jour.  Pharm 
June,  18S8. 
secretion  hairs.  These  may  possess  a  head-like  portion  alone,  or 
may  have  in  addition  a  stalk.  They  arise  very  early,  especially  upon 
the  stipulae.  They  serve  some  function  in  the  developing  lamina 
and  then  disappear.  Later  are  formed  similar  hairs  upon  the  crenate 
margins  of  the  lamina.  When  not  fully  mature,  the  epidermal  cells 
of  the  secretion  hairs  possess  a  relatively  large  amount  of  protoplasm, 
a  large  nucleus  and  a  few  rather  large  vacuoles  {Fig.  12).  When 
fully  matured  the  secretion  hair  usually  resembles  that  shown  in 
Fig.  13.  The  upper  portion  or  head  is  rounded  and  consists  of  two 
kinds  of  cells,  those  upon  the  periphery  being  larger  and  of  irregular 
shape,  those  below  these  being  smaller  and  nearly  isodiametric.  The 
cells  of  the  stalk  resemble  closely  those  of  the  remaining  portion  of 
the  leaf.  The  epidermis  of  the  upper  portion  or  head  is  thicker  than 
that  of  the  stalk  and  consists  of  lamellae  of  cutin  and  cellulose  be- 
tween which,  however,  later  arises  the  mucilage.  If  a  hair  that  is 
about  to  discharge  its  mucilage  is  removed  from  the  leaf  and 
mounted  in  a  few  drops  of  picronigrosin  or  basic  lead  acetate  solu- 
tion, or  glycerin  methylene  blue  solution  and  slight  pressure  brought 
to  bear  upon  the  cover-glass,  the  cutin  layer  is  ruptured,  the  mucil- 
age is  discharged,  becoming  faint  blue  with  picronigrosin  or  methy- 
lene blue  solution,  or  granular  and  almost  colorless  with  basic  lead 
acetate  solution. 
The  use  of  methylene  blue  as  a  reagent  for  mucilage  in  plants,  as 
outlined  by  the  author,  has  the  advantage  that  it  is  decisive,  as  only 
some  lignified  cell- walls  otherwise  take  up  this  color,  and  it  may  be 
applied  by  proper  manipulation  to  dry  as  well  as  fresh  plant  material. 
DESCRIPTION  OF  ILLUSTRATIONS. 
(1)  Surface  section  of  the  epidermis  of  the  under  surface  of  the  leaf  of  Viola 
tricolor,  L- 
(2)  Surface  section  of  the  epidermis  of  the  upper  surface  of  the  leaf  Viola  • 
tricolor,  L- 
(3)  Surface  section  from  the  under  surface  of  the  spurred  petal  of  Viola  tri- 
color, L.,  var.  vulgaris,  Koch. 
(4)  Transverse  section  of  leaf  of  Viola  tricolor,  L.,  showing  epidermal  cell 
and  sub-epidermal  mucilage  cell. 
(5)  Surface  section  of  sub-epidermal  mucilage  cell  of  Viola  tricolor,  L., 
treated  with  alcoholic  iodine  and  sulphuric  acid  solution. 
(6)  Longitudinal  section  through  a  commercial  specimen  of  a  fleshy  scale  of 
bulb  of  scilla,  showing  mucilage  layer  around  acicular  crystals  of  calcium 
oxalate. 
