﻿Farr: 
  Pollen 
  -mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  333 
  

  

  side 
  opposite 
  to 
  the 
  cut 
  surface, 
  there 
  are 
  seen 
  the 
  three 
  lobes 
  of 
  

   the 
  mother-cell 
  and 
  the 
  three 
  half-furrows 
  meeting 
  at 
  a 
  point 
  

   equidistant 
  from 
  the 
  centers 
  of 
  the 
  three 
  lobes. 
  These 
  furrows 
  

   are 
  cutting 
  sharply 
  into 
  the 
  cytoplasm. 
  It 
  has 
  been 
  stated 
  before 
  

   that 
  the 
  equatorial 
  regions 
  through 
  which 
  these 
  furrows 
  are 
  

   advancing 
  are 
  composed 
  of 
  very 
  clear 
  cytoplasm. 
  There 
  are 
  then 
  

   no 
  visible 
  structures 
  in 
  the 
  line 
  of 
  advance 
  of 
  the 
  furrows 
  except 
  

   the 
  spindle-fibers. 
  An 
  examination 
  of 
  the 
  cut 
  surface 
  of 
  the 
  

   section 
  will 
  show 
  that 
  the 
  furrows 
  work 
  in 
  between 
  the 
  fibers 
  in 
  

   their 
  paths, 
  and 
  later 
  surround 
  them. 
  A 
  cross-section 
  of 
  such 
  a 
  

   furrow 
  would, 
  present 
  a 
  wavy 
  appearance 
  upon 
  its 
  advancing 
  edge 
  . 
  

   The 
  masses 
  of 
  material 
  which 
  appear 
  in 
  the 
  equatorial 
  regions, 
  as 
  

   shown 
  in 
  Figs. 
  3, 
  5 
  and 
  7, 
  are 
  the 
  severed 
  portions 
  of 
  this 
  edge. 
  The 
  

   smaller 
  portions 
  consist 
  of 
  the 
  plasma-membrane, 
  while 
  the 
  larger 
  

   portions 
  are 
  of 
  wall 
  material 
  surrounded 
  by 
  plasma-membrane. 
  

   It 
  may 
  also 
  be 
  observed 
  that 
  these 
  penetrating 
  tips 
  appear 
  first 
  

   at 
  the 
  peripheral 
  regions 
  of 
  the 
  equators 
  of 
  the 
  spindles. 
  This 
  Is 
  

   what 
  might 
  be 
  expected 
  if 
  the 
  furrow 
  advances 
  uniformly 
  through- 
  

   out 
  its 
  length. 
  

  

  C. 
  H. 
  Farr 
  found 
  in 
  Nicotiana 
  that 
  the 
  furrows 
  advance 
  much 
  

  

  more 
  

  

  six 
  furrows. 
  As 
  he 
  states, 
  

  

  It 
  is 
  thus 
  apparent 
  that 
  these 
  four 
  projections 
  finall}- 
  meet 
  in 
  the 
  center 
  of 
  the 
  

   tetranucleate 
  cell, 
  before 
  the 
  furrows 
  have 
  completed 
  the 
  division 
  on 
  the 
  equator 
  of 
  

  

  each 
  spindle 
  The 
  first 
  indication 
  of 
  the 
  growth 
  of 
  thes 
  eprojections 
  toward 
  the 
  

  

  center 
  of 
  the 
  cell 
  is 
  in 
  the 
  straightening 
  of 
  the 
  spindle-fibers 
  This 
  straightening 
  

  

  results 
  in 
  the 
  fibers 
  pulling 
  away 
  from 
  the 
  center 
  of 
  the 
  mother-cell, 
  leaving 
  a 
  sjfece 
  

   which 
  is 
  triangular 
  in 
  section, 
  but 
  is 
  really 
  pyramidal, 
  in 
  the 
  center 
  of 
  the 
  cell. 
  

  

  The 
  projections 
  in 
  his 
  plant 
  are 
  also 
  triangular 
  in 
  section 
  and, 
  in 
  

   his 
  /. 
  J2, 
  are 
  shown 
  as 
  they 
  appear 
  during 
  the 
  earlier 
  stages 
  of 
  

  

  furrowing. 
  

  

  In 
  the 
  corresponding 
  stages 
  of 
  Cobaea 
  no 
  traces 
  of 
  such 
  pro- 
  

   jections 
  from 
  the 
  intersections 
  of 
  the 
  furrows 
  could 
  be 
  found 
  

   (Figs. 
  3, 
  4, 
  5). 
  While 
  in 
  the 
  tobacco 
  th 
  ' 
  

  

  more 
  

  

  t 
  four 
  points, 
  the 
  furrows 
  of 
  Cobaea 
  may 
  be 
  

   conceived 
  of 
  as 
  advancing, 
  in 
  general, 
  more 
  regularly, 
  pene- 
  

   trating 
  only 
  slightly 
  deeper 
  at 
  many 
  points 
  upon 
  their 
  edges. 
  

   That 
  the 
  appearance 
  of 
  these 
  furrow 
  tips 
  In 
  the 
  sections 
  is 
  due 
  

   to 
  the 
  planes 
  in 
  which 
  they 
  are 
  cut 
  may 
  be 
  seen 
  from 
  a 
  comparison 
  

  

  