ON  THE  STRUCTURE  OF  THE  STARCH  GRANULE.  135 
around  the  starch  granule ;  and  I  believe  it  will  be  generally  ad- 
mitted, that  the  action  I  am  about  to  describe  can  only  be  ac- 
counted for  on  the  premise  that  such  membrane  really  exists, 
I  took  a  small  quantity  of  the  starch  of  Canna  edulis,  and 
having  completely  saturated  it  with  pure  glycerine  on  a  glass 
slide,  I  covered  it  with  a  disc  of  thin  microscopic  glass. 
It  occurred  to  me,  that  if  the  granules  were  surrounded  by  a 
membrane,  and  the  glycerine  allowed  to  penetrate  to  their  con- 
tents, the  subsequent  addition  of  a  little  water,  by  diminishing 
the  gravity  of  the  external  fluid,  would  call  the  principle  of  en- 
dosmose  into  play  ;  that  the  fluid  contents  of  each  granule  would 
increase  in  volume  by  endosmotic  action,  and  therefore,  that  un- 
less the  surrounding  membrane  were  very  distensible  it  would  be 
ruptured. 
On  examination  by  the  microscope  I  found  this  to  have  been 
the  case.  The  granules  had  split  open,  and  bore  on  their  exter- 
nal surfaces  distinct  evidence  of  a  membrane  that  had  been  cor- 
rugated by  release  from  unusual  tension  ;  the  membrane  around 
some  of  the  granules  being  visible  in  distinct  longitudinal  wrin- 
kles, from  the  hilum  downwards. 
Were  the  starch  granules  composed  of  superposed  laminse 
only,  as  some  observers  have  maintained,  it  is  not  comprehensi- 
ble why  the  addition  of  water,  as  before  described,  should  rup- 
ture them  ;  and  even  admitting  the  possibility  of  this  occurring, 
through  some  agency  not  understood,  the  conclusion  is  almost 
irresistible,  that  the  rupture  w ould  then  have  been  in  the  direction 
of  the  laminar  surfaces,  whereas,  being  from  the  hilum  down- 
wards, it  was,  of  course,  at  right  angles  to  those  surfaces. 
The  fact  of  the  fracture  always  occurring  in  the  direction  of 
the  axis  may  be  readily  accounted  for,  by  adopting  the  supposi> 
tion  that  the  concentric  lines,  observable  upon  the  surface  of 
the  granules,  are  simply  plications  of  the  membrane,  admitting 
thus  of  its  extension  from  one  extremity  to  the  other,  but  not 
laterally.  This  would,  of  course,  necessitate  the  fracture  being, 
as  I  have  observed,  in  the  direction  of  the  axis,  and  this  view 
derives  much  support  from  the  circumstance  of  the  concentric 
lines  having  disappeared  during  the  progress  of  the  experiment. 
From  these  observations  then  it  would  appear,  that  starch  con- 
sists of  granular  matter,  enclosed  in  a  membraneous  vesicle,  of 
