﻿328 
  Farr 
  Pollex-mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  

  

  spindle-fibers 
  of 
  the 
  first 
  division 
  entirely 
  disappear. 
  After 
  the 
  

   four 
  nuclei 
  resulting 
  from 
  the 
  second 
  division 
  have 
  been 
  fully 
  

   reorganized, 
  they 
  assume 
  a 
  tetrahedral 
  arrangement 
  in 
  the 
  cell, 
  

   and 
  a 
  spindle 
  is 
  formed 
  betv\'een 
  every 
  tw^o 
  nuclei, 
  making 
  a 
  total 
  

   of 
  sk 
  spindles. 
  "These 
  spindles, 
  "as 
  Farr 
  states, 
  "are 
  indistin- 
  

   guishable 
  from 
  each 
  other, 
  in 
  other 
  words 
  it 
  is 
  not 
  possible 
  to 
  tell, 
  

   either 
  from 
  the 
  nuclei 
  or 
  from 
  the 
  spindles, 
  which 
  of 
  the 
  four 
  nuclei 
  

   are 
  sister 
  nuclei/' 
  A 
  migration 
  of 
  the 
  nuclei 
  occurs 
  resulting 
  in 
  

   their 
  appression 
  to 
  the 
  plasma-membrane. 
  The 
  cell 
  cavity 
  then 
  

   becomes 
  lobed. 
  This, 
  it 
  is 
  further 
  shown, 
  appears 
  to 
  be 
  "due 
  

   to 
  furrowing 
  of 
  the 
  plasma-membrane 
  along 
  the 
  plane 
  midway 
  

   between 
  each 
  pair 
  of 
  nuclei. 
  The 
  first 
  indication 
  of 
  the 
  furrowing 
  

   is 
  to 
  be 
  found 
  in 
  the 
  flattening 
  of 
  the 
  protoplast 
  on 
  four 
  sides, 
  each 
  

   of 
  which 
  is 
  parallel 
  to 
  the 
  plane 
  of 
  three 
  nuclei, 
  so 
  that 
  the 
  entire 
  

   protoplast 
  assumes 
  the 
  form 
  of 
  a 
  tetrahedron, 
  the 
  nuclei 
  lying 
  

   near 
  the 
  corners." 
  The 
  furrowing 
  of 
  the 
  plasma-membrane 
  and 
  

   the 
  invagination 
  of 
  the 
  mother 
  wall 
  take 
  place 
  simultaneously. 
  

   The 
  furrowing, 
  however, 
  progresses 
  more 
  rapidly 
  at 
  some 
  places 
  

   than 
  at 
  others. 
  C. 
  H. 
  Farr's 
  description 
  continues 
  as 
  follows: 
  

  

  It 
  is 
  evident 
  that 
  if 
  there 
  are 
  four 
  nuclei 
  arranged 
  tetrahedrally 
  and 
  equidistant 
  

   from 
  each 
  other 
  within 
  a 
  sphere, 
  there 
  wiH 
  be 
  four 
  points 
  upon 
  the 
  surface 
  of 
  that 
  

  

  spherewhichareequidistantfromeachof 
  three 
  of 
  the 
  nuclei. 
  . 
  . 
  . 
  By 
  the 
  transform- 
  

   ation 
  of 
  the 
  sphere 
  into 
  a 
  tetrahedron 
  the 
  plasma-membrane 
  has 
  been 
  brought 
  closer 
  

   to 
  the 
  nuclear-membrane. 
  At 
  these 
  four 
  points 
  above 
  mentioned, 
  on 
  the 
  plasma- 
  

   membrane, 
  the 
  constriction 
  of 
  the 
  mother-cell 
  continues 
  to 
  proceed 
  more 
  rapidly 
  

   than 
  elsewhere. 
  . 
  . 
  . 
  These 
  projections, 
  or 
  invaginations, 
  continue 
  to 
  elongate 
  toward 
  

   the 
  center 
  of 
  the 
  cell, 
  and 
  consequently 
  in 
  the 
  direction 
  of 
  the 
  fourth 
  nucleus, 
  keeping 
  

   at 
  all 
  times 
  equidistant 
  from 
  the 
  three 
  nuclei. 
  As 
  a 
  result 
  the 
  four 
  projections 
  meet 
  

   in 
  the 
  center 
  of 
  the 
  tetranucleate 
  cell, 
  and 
  fusion 
  of 
  their 
  tips 
  occurs. 
  . 
  . 
  - 
  Thus 
  there 
  

   are 
  organized 
  four 
  protoplasmic 
  masses 
  each 
  with 
  a 
  single 
  nucleus 
  and 
  connected 
  

  

  witheachof 
  the 
  otherfour 
  by 
  an 
  isthmus 
  of 
  cytoplasm, 
  at 
  first 
  quite 
  broad. 
  . 
  . 
  . 
  Ap- 
  

   parently 
  each 
  isthmus 
  constricts 
  independently 
  of 
  the 
  bthers. 
  . 
  . 
  . 
  Upon 
  the 
  com- 
  

   pletion 
  of 
  the 
  division 
  each 
  of 
  the 
  four 
  cells 
  is 
  separated 
  from 
  the 
  other 
  three 
  by 
  a 
  

   lateral 
  wall 
  which 
  is 
  thicker 
  in 
  its 
  periphery 
  and 
  thinner 
  at 
  its 
  center. 
  

  

  The 
  figures 
  of 
  Cobaea 
  scandens, 
  drawn 
  by 
  Lawson, 
  show 
  the 
  

   absence 
  of 
  division 
  of 
  the 
  cell 
  after 
  the 
  first 
  nuclear 
  division 
  ; 
  the 
  

   disappearance 
  of 
  the 
  spindle 
  of 
  the 
  first 
  division 
  before 
  the 
  begin- 
  

   ning 
  of 
  the 
  second 
  division 
  ; 
  the 
  thickening 
  of 
  the 
  cell 
  wall 
  ; 
  the 
  

   tetrahedral 
  arrangement 
  of 
  the 
  four 
  nuclei; 
  and 
  a 
  furrow-like 
  

   indentation 
  of 
  the 
  plasma-membrane. 
  These 
  characteristics 
  

   suggest 
  a 
  type 
  of 
  cytokinesis 
  similar 
  to 
  that 
  of 
  Nicotiana. 
  The 
  

  

  