﻿Farr: 
  Pollen-mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  329 
  

  

  plant 
  at 
  least 
  presents 
  for 
  study 
  an 
  instance 
  of 
  quadripartitlon 
  

   with 
  no 
  conclusive 
  evidence 
  concerning 
  the 
  presence 
  or 
  absence 
  

   of 
  a 
  cell-plate 
  during 
  the 
  process 
  of 
  division. 
  

  

  Material 
  and 
  methods 
  

  

  The 
  material 
  for 
  study 
  was 
  collected 
  from 
  plants 
  of 
  Cobaea 
  

   scandens 
  alba 
  growing 
  in 
  the 
  greenhouse 
  of 
  Columbia 
  University. 
  

   The 
  large 
  size 
  of 
  the 
  pollen-mother-cells 
  made 
  it 
  possible 
  to 
  deter- 
  

   mine 
  the 
  stages 
  of 
  their 
  development 
  in 
  the 
  fresh 
  mounts. 
  Upon 
  

   examination 
  it 
  was 
  found 
  that 
  the 
  cells 
  in 
  all 
  of 
  the 
  anthers 
  of 
  

   the 
  same 
  bud 
  were 
  in 
  approximately 
  the 
  same 
  stage 
  of 
  develop- 
  

   ment. 
  The 
  material 
  for 
  fixation 
  was 
  then 
  selected 
  by 
  examinmg 
  

   one 
  anther 
  from 
  the 
  bud 
  and 
  fixing 
  the 
  four 
  remaining 
  anthers 
  of 
  

   those 
  which 
  were 
  found 
  to 
  be 
  in 
  the 
  desired 
  stages. 
  

  

  Flemming^s 
  strong 
  chromic-acetic-osmic 
  fixing 
  solution 
  was 
  

   used 
  in 
  the 
  preparation 
  of 
  the 
  materiaL 
  The 
  sections 
  were 
  made 
  

   3-5 
  PL 
  in 
  thickness, 
  and 
  were 
  stained 
  with 
  Flemming's 
  triple 
  stain. 
  

  

  Observations 
  

  

  The 
  mother-cell 
  at 
  the 
  close 
  of 
  the 
  second 
  nuclear 
  division 
  is 
  

   ver^'* 
  nearly 
  spherical 
  in 
  form. 
  The 
  four 
  nuclei 
  are 
  arranged 
  at 
  

   this 
  stage 
  and 
  through 
  all 
  of 
  the 
  succeeding 
  stages 
  of 
  microspore 
  

   formation 
  in 
  a 
  tetrahedral 
  manner 
  within 
  the 
  celL 
  They 
  are 
  

   ellipsoidal 
  in 
  form. 
  Their 
  diameter 
  immediately 
  after 
  reorganiza- 
  

   tion 
  is 
  about 
  one-seventh 
  of 
  the 
  diameter 
  of 
  the 
  mother-cell, 
  or 
  

   6 
  ju. 
  An 
  enlargement 
  of 
  the 
  nucleus 
  also 
  takes 
  place 
  during 
  the 
  

   division 
  of 
  the 
  cell, 
  which 
  results 
  in 
  a 
  diameter 
  of 
  about 
  one-fifth 
  of 
  

   the 
  mother-cell, 
  or 
  8.4 
  /x. 
  The 
  chromatin 
  is 
  at 
  first 
  appressed 
  to 
  

   the 
  nuclear 
  membrane 
  (Fig. 
  i.). 
  During 
  the 
  later 
  stages 
  of 
  cell- 
  

   division 
  it 
  is 
  found 
  scattered 
  throughout 
  the 
  nucleus 
  (Figs. 
  3, 
  4, 
  7), 
  

   The 
  nuclei 
  contain 
  one 
  or 
  more 
  larger 
  and 
  several 
  smaller 
  nucleoli, 
  

   which 
  are 
  usually 
  spherical. 
  Occasionally 
  an 
  oval 
  one 
  may 
  be 
  

   found 
  among 
  the 
  larger 
  nucleoli. 
  In 
  some 
  sections 
  they 
  are 
  seen 
  

   to 
  be 
  appressed 
  to 
  the 
  nuclear-membrane 
  (Figs. 
  1,2). 
  

  

  The 
  spindles, 
  of 
  which 
  there 
  are 
  six, 
  a 
  spindle 
  connecting 
  every 
  

   nucleus 
  with 
  every 
  other 
  one, 
  appear 
  to 
  be 
  inflated 
  (Fig. 
  i). 
  

   Spindle-fibers 
  may 
  be 
  found 
  to 
  run 
  along 
  apparently 
  the 
  entire 
  

   distance 
  from 
  one 
  nucleus 
  to 
  another, 
  and 
  they 
  are 
  quite 
  uniform 
  

  

  