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  330 
  Farr: 
  Pollen-mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  

  

  in 
  thickness 
  throughout 
  their 
  length. 
  Continuous 
  fibers 
  at 
  the 
  

   extreme 
  outer 
  portion 
  of 
  the 
  spindle 
  may 
  sometimes 
  be 
  found 
  

   appressed 
  to 
  the 
  plasma-membrane 
  at 
  about 
  their 
  middle 
  points. 
  

   In 
  the 
  center 
  of 
  the 
  cell 
  the 
  outer 
  fibers 
  of 
  the 
  spindles 
  are 
  seen 
  to 
  

   cross 
  one 
  another, 
  and 
  leave 
  no 
  inter-splndle 
  areas 
  except 
  a 
  small, 
  

   usually 
  triangular 
  space 
  at 
  the 
  center 
  of 
  the 
  cell, 
  due" 
  to 
  the 
  curva- 
  

  

  i 
  

  

  ture 
  of 
  the 
  fibers 
  (Fig. 
  i). 
  

  

  The 
  spindle-fibers 
  in 
  the 
  Cohaea 
  exhibit 
  a 
  very 
  different 
  behavior 
  

   during 
  cell-division 
  than 
  do 
  the 
  spindle-fibers 
  of 
  the 
  larch 
  and 
  

   onion, 
  as 
  shown 
  by 
  Timberlake,* 
  In 
  the 
  pollen-mother-cells 
  of 
  

   the 
  larch 
  and 
  in 
  the 
  vegetative 
  cells 
  of 
  the 
  onion, 
  whose 
  divisions 
  

   are 
  accompanied 
  by 
  the 
  formation 
  of 
  a 
  cell-plate, 
  the 
  continuous 
  

   fibers, 
  after 
  nuclear 
  division, 
  show 
  a 
  thickening 
  at 
  their 
  ends 
  near 
  

   the 
  nuclei. 
  This 
  apparently 
  marks 
  the 
  beginning 
  of 
  the 
  activity 
  

   of 
  the 
  fiber, 
  which 
  soon 
  develops 
  a 
  very 
  marked 
  thickening 
  in 
  the 
  

   equator. 
  These 
  enlargements 
  upon 
  the 
  fibers 
  seem 
  to 
  unite 
  and 
  

   form 
  a 
  layer 
  throughout 
  the 
  thickness 
  of 
  the 
  original 
  spindle. 
  

   This 
  is 
  accompanied 
  by 
  a 
  shortening 
  of 
  the 
  fibers. 
  The 
  central 
  

   fibers 
  then 
  continue 
  to 
  shorten 
  until 
  they 
  finally 
  disappear, 
  having 
  

   been 
  used 
  up 
  in 
  the 
  formaton 
  of 
  the 
  cell-plate. 
  While 
  these 
  

   activities 
  of 
  the 
  fibers 
  are 
  going 
  on, 
  there 
  appears, 
  in 
  the 
  onion, 
  a 
  

   zone 
  of 
  orange-staining 
  material, 
  presumably 
  carbohydrate 
  in 
  

   nature, 
  the 
  probable 
  function 
  of 
  which 
  is 
  to 
  serve 
  as 
  reserve 
  

   material 
  for 
  cell-wall 
  formation. 
  

  

  The 
  continuous 
  fibers 
  in 
  Cobaea, 
  in 
  some 
  cases, 
  show 
  a 
  certain 
  

   amount 
  of 
  thickening 
  throughout 
  about 
  two-thirds 
  of 
  their 
  length, 
  

   but 
  they 
  remain 
  attenuated 
  at 
  their 
  ends 
  (Figs. 
  2, 
  7). 
  Occa- 
  

   sionally 
  a 
  fiber 
  may 
  be 
  found 
  to 
  be 
  thickened 
  apparently 
  through- 
  

   out 
  its 
  length 
  (Figs. 
  5, 
  7, 
  8). 
  Tljis 
  thickening, 
  however, 
  is 
  almost 
  

   negligible 
  when 
  compared 
  with 
  that 
  found 
  in 
  cell-plate 
  formation. 
  

   In 
  no 
  instances 
  were 
  there 
  found, 
  in 
  any 
  spindle-fibers 
  of 
  the 
  Cohaea, 
  

   such 
  localized 
  enlargements 
  as 
  those 
  shown 
  by 
  Timberlake 
  and' 
  

   others 
  to 
  precede 
  the 
  formation 
  of 
  a 
  cell-plate. 
  No 
  shortening 
  or 
  

   disappearance 
  of 
  the 
  fibers 
  in 
  any 
  other 
  manner 
  could 
  be 
  found. 
  

   The 
  continuous 
  fibers 
  between 
  the 
  nuclei 
  are 
  apparently 
  unchanged 
  

   during 
  the 
  succeeding 
  stages 
  of 
  cell-division 
  (Figs. 
  2-7). 
  They 
  

  

  * 
  Timberlake, 
  H, 
  G. 
  The 
  development 
  and 
  function 
  of 
  the 
  cell 
  plate 
  in 
  higher 
  

   plants, 
  Bot. 
  Ga2. 
  30: 
  73~99. 
  1 
  54-170. 
  pL 
  8, 
  g. 
  1000. 
  

  

  