138        ON  THE  STRUCTURE  OF  THE  STARCH  GRANULE. 
while  the  latter  combated  the  notion  that  the  markings  in  starch  granules 
were  due  to  the  existence  of  a  succession  of  layers  or  sfcrata  without  any 
distinct  covering  or  envelope,  contending  that  there  was  an  outer  mem- 
brane which  was  permeated  by  a  dilute  solution  of  glycerine ;  the  latter 
admitted  the  existence  of  the  membrane,  although  denying  the  endosmotic 
action  of  solution  of  glycerine,  and  at  the  same  time  contended  that  the 
markings  were  due  to  concentric  layers  within.  He  had,  himself,  in  sub- 
mitting starches  to  microscopic  examination,  observed  certain  phenomena, 
some  of  which  were  in  favor  of  one  and  some  of  the  other  of  these  views. 
Thus,  dilute  acetic  acid,  while  it  caused  a  swelling  of  the  granules,  ren- 
dered the  markings  more  distinct.  On  the  other  hand,  gelatine  and  most 
of  the  media  employed  for  mounting  microscopic  objects,  sooner  or  later, 
caused  the  entire  disappearance  of  the  markings.  So  much  indeed  was 
this  the  case  that  a  good  medium  for  mounting  the  starches  so  as  to  show 
the  markings  was  still  a  desideratum. 
Mr.  Bentley  said  the  structure  of  the  starch  granule  had  always  been 
an  interesting  subject,  that  it  was  more  particularly  so  at  the  present  time, 
when  starch,  or  at  least  a  substance  almost  identical  with  it,  had  been 
found  in  animal  structures,  and  thus  its  presence  could  no  longer  be  relied 
upon  as  an  absolute  distinctive  character  between  an  animal  and  a  vegeta- 
ble. With  regard  to  the  structure  of  the  starch  granule,  he  had  always 
been  a  firm  believer  in  Sehleiden's  views  in  all  their  essential  points,  and 
he  had  been  strengthened  in  this  belief  by  repeating  the  experiment  of  Mr. 
Busk  and  Dr.  Allman.  That  the  starch  granules  consisted  of  a  series  of 
hollow  scales  or  shells  placed  over  one  another,  appeared  to  him  to  be  sup- 
ported by  the  results  of  many  experiments  and  observations.  Thus,  if  the 
cells  of  the  potato  were  examined  when  very  young,  the  contained  starch 
would  be  seen  to  consist  chiefly  of  minute  granules  scattered  amongst  lar- 
ger ones,  whilst  in  the  cells  of  old  potatoes  the  two  different  sized  granules 
were  observed,  but  here  the  smaller  granules  were  comparatively  few  in 
proportion  to  the  larger.  The  smaller  granules  were  nearly  spherical  in 
form,  while  the  larger  were  ovate  or  more  or  less  irregular  in  their  outline  ; 
but  it  was  observed  that  the  inner  zones  of  the  larger  granules  were  nearly 
spherical,  corresponding  in  appeai*ance  with  the  small  granules.  From 
these  facts  it  was  inferred  that  the  small  granules  became  the  nuclei  of  the 
larger,  and  that  they  were  augmented  in  size  by  successive  depositions  of 
concentric  layers  from  within  outwards,  the  outer  layers  becoming  gradu- 
ally more  irregular.  The  experiments  of  Dr.  Allman  tended  to  show,  that 
if  starch  be  left  for  several  weeks  in  a  dilute  solution  of  iodine  and  then 
examined  by  the  microscope,  the  appearance  of  concentric  layers  became 
more  evident ;  and  that  on  the  addition  of  a  drop  of  dilute  sulphuric  acid 
the  granules  immediately  began  to  swell,  and  when  the  swelling  had  ceased 
the  scales  were  found  to  be  more  or  less  separated  from  one  another.  It 
had  also  been  found  that  when  starch  was  heated  on  a  metallic  plate  until 
