﻿334 
  Farr: 
  

  

  ALBA 
  

  

  of 
  Figs. 
  4 
  and 
  5. 
  These 
  are 
  adjoining 
  sections 
  of 
  the 
  same 
  

   pollen-mother-celL 
  Fig. 
  4 
  is 
  drawn 
  from 
  a 
  section 
  cut 
  

  

  between 
  

  

  Fig, 
  5 
  and 
  the 
  fourth 
  nucleus 
  of 
  the 
  cell. 
  Fig. 
  4 
  is 
  consequently 
  

   nearer 
  to 
  the 
  furrows 
  which 
  are 
  advancing 
  from 
  the 
  sides 
  of 
  the 
  

   lobes, 
  nearer 
  to 
  the 
  fourth 
  nucleus. 
  The 
  projections 
  are 
  very 
  

   distinct 
  in 
  Fig. 
  4, 
  but 
  they 
  have 
  not 
  advanced 
  far 
  enough 
  into 
  

   the 
  cytoplasm 
  to 
  be 
  seen 
  in 
  the 
  section 
  from 
  which 
  Fig. 
  5 
  is 
  drawn. 
  

   In 
  the 
  center 
  of 
  the 
  cell 
  section, 
  Fig. 
  6, 
  at 
  the 
  point 
  toward 
  

   which 
  the 
  tips 
  of 
  the 
  three 
  furrows 
  are 
  pointing, 
  is 
  shown 
  the 
  

   first 
  appearance 
  of 
  that 
  which 
  will 
  develop, 
  at 
  an 
  even 
  later 
  stage, 
  

   into 
  the 
  central 
  triangular 
  area 
  of 
  wall 
  material. 
  No 
  straightening 
  

   of 
  the 
  fibers 
  may 
  be 
  observed 
  to 
  precede 
  it. 
  Fig. 
  7 
  represents 
  a 
  

   very 
  late 
  stage 
  in 
  the 
  process 
  of 
  cell-division, 
  in 
  which 
  the 
  central 
  

   triangular 
  area 
  may 
  be 
  seen. 
  The 
  furrows 
  have 
  pushed 
  through 
  

   in 
  other 
  places 
  along 
  the 
  equators 
  of 
  the 
  spindles. 
  Some 
  of 
  the 
  

   fibers 
  in 
  their 
  paths 
  are 
  not 
  yet^surrdunded, 
  as 
  can 
  be 
  seen 
  from 
  

   ■ 
  the 
  drawing. 
  These 
  observations 
  show 
  that 
  except 
  for 
  these 
  

   slight 
  irregularities 
  the 
  advance 
  of 
  the 
  furrows 
  in 
  Cobaea 
  is 
  quite 
  

   uniform, 
  as 
  has 
  been 
  suggested 
  in 
  connection 
  with 
  their 
  appearance 
  

   first 
  at 
  the 
  outer 
  portions 
  of 
  the 
  spindle 
  equators. 
  This 
  uniform 
  

  

  I 
  J 
  

  

  advance 
  accounts 
  for 
  the 
  appearance 
  of 
  the 
  central 
  triangular 
  

   section 
  of 
  the 
  furrow 
  at 
  a 
  much 
  later 
  stage 
  than 
  it 
  was 
  found 
  to 
  

   appear 
  In 
  Nicotiana. 
  The 
  daughter 
  cells 
  become 
  almost 
  spherical 
  

   in 
  form 
  before 
  their 
  complete 
  separation 
  (Fig. 
  7). 
  

  

  Discussion 
  

  

  The 
  pollen-mother-cells 
  of 
  Cobaea, 
  then, 
  present 
  another 
  

   instance 
  in 
  the 
  microspore 
  formation 
  of 
  dicotyledons, 
  in 
  which 
  the 
  

   cell-plate 
  is 
  not 
  apparent 
  during 
  cytoplasmic 
  division. 
  The 
  

   process 
  concerned 
  is, 
  in 
  its 
  general 
  characteristics, 
  like 
  that 
  found 
  

   by 
  C. 
  H. 
  Farr 
  in 
  Nicotiana 
  and 
  other 
  dicotyledons. 
  It 
  differs 
  

   from 
  Nicotiana, 
  however, 
  in 
  possessing 
  some 
  cytoplasmic 
  char- 
  

   acteristics 
  similar 
  to 
  those 
  observed 
  in 
  the 
  study 
  of 
  cleavage 
  

   furrows 
  in 
  the 
  fungi. 
  Mention 
  has 
  already 
  been 
  made 
  of 
  the 
  

   less 
  dense 
  areas 
  in 
  Cobaea 
  which 
  appear 
  across 
  the 
  equators 
  of 
  

   the 
  spindles 
  during 
  the 
  process 
  of 
  furrowing. 
  Now 
  Harper* 
  found 
  

  

  ♦Harper. 
  R. 
  A. 
  Cell 
  and 
  nuclear 
  division 
  in 
  Ftiligo 
  varians. 
  Bot. 
  Gaz. 
  30: 
  

   217-251. 
  pl^ 
  14' 
  1900. 
  

  

  