﻿332 
  Farr: 
  Pollem-mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  

  

  After 
  the 
  completion 
  of 
  the 
  second 
  nuclear 
  division, 
  the 
  most 
  

   striking 
  change 
  in 
  the 
  pollen-mother-cell 
  is 
  its 
  lobed 
  appearance- 
  

   Upon 
  the 
  plasma-membrane, 
  midway 
  between 
  the 
  polar 
  regions 
  

   of 
  the 
  three 
  nuclei, 
  there 
  appear 
  sharp 
  indentations 
  pointing 
  toward 
  

   the 
  center 
  of 
  the 
  cell. 
  In 
  a 
  section, 
  three 
  of 
  these 
  may 
  be 
  in 
  view- 
  

   Fig. 
  2 
  clearly 
  shows 
  two 
  such 
  indentations. 
  The 
  absence 
  of 
  the 
  

   third 
  one 
  is 
  due 
  to 
  the 
  plane 
  in 
  which 
  the 
  section 
  is 
  cut. 
  The 
  

   view 
  of 
  the 
  adjoining 
  spindle 
  shows 
  that 
  it 
  is 
  not 
  a 
  median 
  section, 
  

   such 
  as 
  we 
  have 
  in 
  the 
  two 
  other 
  spindles. 
  The 
  cell-wall 
  conforms 
  

   to 
  these 
  indentations 
  and 
  the 
  fibers 
  through 
  which 
  the 
  furrows 
  

  

  4 
  

  

  pass, 
  aside 
  from 
  being 
  separated 
  in 
  the 
  center, 
  are 
  apparently 
  

   undisturbed 
  by 
  it. 
  

  

  During 
  the 
  succeeding 
  stages 
  of 
  division 
  there 
  appear 
  in 
  some 
  

   of 
  the 
  sections, 
  first 
  at 
  the 
  periphery 
  of 
  the 
  spindle 
  equators, 
  

   later 
  at 
  different 
  points 
  in 
  the 
  equators, 
  small 
  masses 
  of 
  material 
  

   which 
  vary 
  in 
  their 
  staining 
  reactions 
  according 
  to 
  their 
  size. 
  

   The 
  smaller 
  ones 
  stain 
  very 
  darkly, 
  almost 
  black, 
  with 
  gentian 
  

   violet 
  (Fig. 
  3). 
  The 
  larger 
  ones 
  stain 
  the 
  same 
  as 
  the 
  cell-wall, 
  

   with 
  a 
  narrow, 
  dark-stained 
  layer 
  of 
  material 
  upon 
  the 
  outside, 
  

   apparently 
  a 
  membrane 
  (Fig. 
  7). 
  These 
  bodies 
  do 
  not 
  appear 
  in 
  

   all 
  of 
  the 
  sections, 
  but 
  they 
  occur 
  in 
  short 
  rows 
  directly 
  in 
  front 
  of 
  

   the 
  furrow 
  tips, 
  as 
  shown 
  before 
  one 
  furrow 
  in 
  Fig. 
  5. 
  They 
  are 
  

   not 
  seen 
  at 
  this 
  time 
  either 
  along 
  the 
  centers 
  of 
  the 
  spindles 
  or 
  in 
  

   the 
  center 
  of 
  the 
  cell. 
  If 
  any 
  such 
  bodies 
  were 
  present, 
  beyond 
  

   these 
  short 
  rows, 
  they 
  would 
  be 
  clearly 
  visible 
  because 
  of 
  the 
  

   regions 
  of 
  less 
  dense 
  cytoplasm 
  across 
  the 
  equators 
  of 
  the 
  spindles. 
  

  

  A 
  careful 
  examination 
  of 
  the 
  sections 
  in 
  which 
  these 
  masses 
  of 
  

   material 
  appear 
  has 
  resulted 
  in 
  the 
  conclusion 
  that 
  they 
  are 
  never 
  

   upon 
  the 
  spindle-fibers, 
  but 
  that 
  they 
  are 
  between 
  them; 
  and 
  that 
  

   the 
  spindle-fibers 
  have 
  no 
  direct 
  relation 
  to 
  their 
  formation. 
  

   They 
  are 
  believed 
  to 
  be 
  sections 
  of 
  the 
  furrows 
  which 
  are 
  cutting 
  

   into 
  the 
  cytoplasm 
  of 
  the 
  pollen-mother-celL 
  In 
  a 
  section 
  such 
  

   as 
  that 
  shown 
  in 
  Fig. 
  3, 
  for 
  instance, 
  there 
  has 
  been 
  cut 
  a 
  portion 
  

   from 
  one 
  of 
  the 
  faces 
  of 
  the 
  tetrahedral 
  mother-cell, 
  and 
  in 
  it 
  are 
  

   median 
  sections 
  of 
  three 
  nuclei. 
  If 
  in 
  the 
  unsectioned 
  mother-cell 
  

   every 
  one 
  of 
  the 
  spindles 
  is 
  cut 
  by 
  a 
  furrow, 
  it 
  can 
  be 
  seen 
  that 
  in 
  

   cutting 
  off 
  this 
  portion 
  from 
  the 
  mother-cell, 
  three 
  half-furrows 
  

   have 
  been 
  removed. 
  If 
  this 
  severed 
  portion 
  is 
  viewed 
  upon 
  the 
  

  

  