﻿Farr 
  : 
  

  

  ALB 
  

  

  fibers, 
  and 
  later 
  they 
  appear 
  to 
  surround 
  them. 
  These 
  observa- 
  

   tions, 
  together 
  with 
  the 
  appearance 
  of 
  the 
  spindle-fibers 
  throughout 
  

  

  L 
  

  

  cell-division 
  and 
  after 
  division 
  is 
  completed, 
  lead 
  to 
  the 
  con- 
  

   clusion 
  that 
  the 
  fibers 
  are 
  first 
  surrounded 
  and 
  then 
  severed. 
  

   In 
  considering 
  such 
  a 
  progressing 
  furrow 
  with 
  relation 
  to 
  the 
  

   fibers, 
  the 
  behavior 
  of 
  the 
  atnoebae 
  toward 
  their 
  food 
  particles 
  

   suggests 
  itself 
  as 
  an 
  analogy. 
  The 
  apparently 
  very 
  elastic 
  plasma- 
  

   membrane 
  plays 
  a 
  prominent 
  part 
  in 
  both 
  instances. 
  In 
  the 
  

   process 
  of 
  furrowing 
  the 
  spindle-fiber 
  corresponds 
  to 
  the 
  food 
  

   particle. 
  It 
  does 
  not 
  seem 
  entirely 
  inconceivable 
  that 
  the 
  

   advancing 
  edge 
  of 
  the 
  furrow, 
  amoeba-like, 
  may 
  approach 
  a 
  

   fiber 
  to 
  within 
  a 
  certain 
  distance 
  and 
  then 
  send 
  forth 
  projections 
  

   which 
  first 
  surround 
  it 
  and 
  finally 
  cause 
  it 
  to 
  separate 
  at 
  its 
  middle 
  

  

  point. 
  

  

  The 
  cleavage 
  in 
  Cobaea, 
  as 
  has 
  been 
  shown, 
  is 
  directed 
  with 
  

  

  reference 
  to 
  the 
  distribution 
  of 
  the 
  nuclei. 
  It 
  seems 
  quite 
  possible, 
  

   as 
  was 
  suggested 
  by 
  Harper 
  for 
  FuUgo 
  and 
  Piloholiis, 
  that 
  the 
  

   nuclei 
  may 
  control 
  the 
  orientation 
  of 
  the 
  furrows, 
  and 
  that 
  the 
  

   formation 
  of 
  the 
  less 
  dense 
  zones 
  in 
  the 
  cytoplasm 
  is 
  a 
  visible 
  

   expression 
  of 
  the 
  activity 
  of 
  the 
  nuclei. 
  If 
  to 
  these 
  assumptions 
  

   are 
  added 
  the 
  suggestions 
  of 
  C. 
  H. 
  Farr, 
  concerning 
  the 
  diffusion 
  

   of 
  soluble 
  ions 
  from 
  the 
  nuclei 
  along 
  the 
  paths 
  of 
  the 
  fibers, 
  a 
  

   possible 
  explanation 
  for 
  an 
  amoeboid 
  activity 
  suggests 
  itself. 
  If 
  

   the 
  fibers 
  mark 
  the 
  paths 
  of 
  diffusion, 
  the 
  compounds 
  formed 
  by 
  

   the 
  meeting 
  ions 
  would 
  be 
  most 
  concentrated 
  around 
  the 
  fibers 
  

   in 
  the 
  exact 
  equatorial 
  planes. 
  It 
  does 
  not 
  then 
  seem 
  unthinkable 
  

   that 
  in 
  these 
  regions 
  of 
  highest 
  concentration 
  the 
  substances 
  may 
  

   be 
  in 
  the 
  necessary 
  condition 
  to 
  contribute 
  to 
  the 
  development 
  of 
  

   the 
  plasma 
  membrane, 
  and 
  that 
  in 
  this 
  manner 
  they 
  determine 
  

   the 
  position 
  and 
  direction 
  of 
  the 
  penetrating 
  furrows. 
  

  

  To 
  Dr. 
  R. 
  A. 
  Harper 
  I 
  wish 
  to 
  express 
  my 
  appreciation 
  for 
  

   advice 
  and 
  inspiration 
  during 
  the 
  progress 
  of 
  this 
  study. 
  

  

  Department 
  of 
  Botany, 
  

   Columbia 
  University 
  

  

  