^pSefS.1'}     The  Structure  of  the  Starch  Grain.  417 
and  the  iodin  being  more  or  less  volatilized.  Also  the  facility  with 
which  soluble  starch  takes  up  the  iodin  in  a  chloroformic  solution 
indicates  that  the  affinity  of  starch  for  iodin  is  considerably  greater 
than  heretofore  supposed. 
STAINING  OF  THE  GRAIN. 
While  I  have  obtained  at  times  some  beautiful  results  by  the  use 
of  anilin  stains,  it  has  been  impossible  for  me  until  now  to  duplicate 
some  of  my  earlier  results.  I  have  succeeded,  however,  in  develop- 
ing a  method  in  the  staining  of  wheat  starch  which  yields  uniformly 
satisfactory  results.  It  is  as  follows:  to  0-500  gramme  of  wheat 
starch  add  2  c.c.  of  an  aqueous  iodin  solution  (containing  o-i  per 
cent,  of  iodin  and  0-5  per  cent,  of  potassium  iodid) ;  mix  well  and 
allow  the  mixture  to  stand  from  20  to  30  minutes  in  a  porcelain  dish 
or  watch  crystal ;  then  add  2  c.c.  of  a  saturated  aqueous  solution  of 
gentian-violet  (i  gramme  of  gentian-violet  to  100  c.c.  of  water)  ; 
allow  this  to  stand  from  12  to  24  hours,  examining  the  grains 
from  time  to  time  by  mounting  them  in  water.  When  the  grains 
are  satisfactorily  stained,  the  mixture  is  transferred  to  a  filter  and 
the  excess  of  stain  is  removed  as  quickly  as  possible  by  washing 
the  magma  with  water.  The  material  is  then  allowed  to  dry  spon- 
taneously or  between  pieces  of  bibulous  paper.  For  examination 
it  is  then  mounted  in  Canada  balsam,  the  preparation  being  per- 
manent for  years,  as  is  also  the  case  with  the  unmounted  material. 
Corn  starch  may  also  be  stained  by  the  use  of  this  method,  but 
in  the  staining  of  potato  and  maranta  starches  it  is  necessary  to  use 
weaker  iodin  solutions.  I  have  not  evolved  entirely  satisfactory 
methods,  however,  for  uniformly  staining  these  latter  starches. 
It  may  be  of  interest  to  state  that  the  foregoing  method  has 
certain  features  which  are  similar  to  those  of  the  gentian-violet 
method  used  in  demonstrating  the  so-called  continuity  of  proto- 
plasm in  the  vegetable  cell  wall  (15  ).  In  the  study  of  continuity  of 
protoplasm  a  swelling  reagent,  such  as  sulfuric  acid,  is  used  and  a 
comparatively  short  time  is  consumed  in  the  whole  operation ; 
whereas  in  the  method  proposed  for  the  staining  of  wheat  starch 
the  water  used  may  be  considered  a  swelling  agent  acting  on  the 
grain  during  a  longer  time.  The  analogy  in  the  results  are  so  strik- 
ing that  students  who  are  interested  in  the  study  of  the  continuity 
of  protoplasm  will  do  well  to  compare  their  results  on  the  cell  wall 
