﻿Farr: 
  Pollen-mother-cell 
  of 
  Cobaea 
  scaxdens 
  alba 
  331 
  

  

  seem 
  to 
  be 
  some 
  of 
  the 
  last 
  structures 
  in 
  the 
  cytoplasm 
  to 
  be 
  

   severed 
  before 
  the 
  separation 
  of 
  the 
  daughter-cells 
  (Figs. 
  6, 
  7). 
  

   Even 
  after 
  this 
  separation 
  finally 
  occurs 
  the 
  halves 
  of 
  these 
  

   fibers 
  are 
  found 
  to 
  extend 
  from 
  the 
  nuclei 
  to 
  the 
  plasma- 
  

   membranes 
  of 
  the 
  two 
  microspores 
  separated 
  by 
  the 
  furrows. 
  

   The 
  behavior 
  of 
  the 
  fibers 
  in 
  connection 
  with 
  the 
  formation 
  of 
  the 
  

   cell-plate 
  led 
  Timberlake 
  to 
  say, 
  "the 
  whole 
  process 
  seems 
  to 
  

   indicate 
  a 
  somewhat 
  plastic 
  character 
  of 
  the 
  fiber." 
  The 
  behavior 
  

   of 
  the 
  fibers 
  of 
  Cohaea, 
  as 
  shown 
  by 
  the 
  present 
  study, 
  suggests 
  

   that 
  such 
  a 
  statement 
  would 
  not 
  apply 
  to 
  them, 
  but 
  that 
  they 
  are 
  

   more 
  permanent 
  in 
  nature. 
  

  

  Across 
  the 
  equators 
  of 
  the 
  spindles 
  a 
  less 
  dense 
  region 
  of 
  cyto- 
  

   plasm 
  appears 
  at 
  about 
  the 
  time 
  of 
  thickening 
  of 
  the 
  fibers 
  (Fig. 
  2). 
  

   This 
  also 
  is 
  evident 
  during 
  the 
  remaining 
  stages 
  of 
  division 
  (Figs. 
  

   3-7). 
  It 
  is 
  apparently 
  made 
  more 
  conspicuous 
  by 
  a 
  denser 
  area 
  

   around 
  the 
  nuclei, 
  which 
  does 
  not 
  extend 
  into 
  the 
  equatorial 
  

   regions. 
  The 
  peripheral 
  cytoplasm 
  is 
  fibrillar 
  in 
  nature. 
  The 
  

   fibrillae 
  show 
  at 
  first 
  no 
  tendency 
  to 
  radiate 
  from 
  the 
  nuclei 
  

   (Fig. 
  i). 
  The 
  beginning 
  of 
  such 
  a 
  radiation 
  can 
  be 
  seen 
  in 
  Fig. 
  2. 
  

   This 
  continues 
  until 
  a 
  distinct 
  radiation 
  is 
  found 
  in 
  the 
  stage 
  

   represented 
  by 
  FiG. 
  4, 
  and 
  the 
  condition 
  is 
  maintained 
  throughout 
  

   the 
  succeeding 
  stages 
  of 
  division. 
  Scattered 
  irregularly 
  through 
  

   the 
  cytoplasm 
  are 
  many 
  spherical, 
  red-stained 
  bodies 
  which 
  vary 
  

   greatly 
  in 
  size. 
  In 
  Fig. 
  3 
  five 
  such 
  bodies 
  are 
  shown, 
  which 
  appear 
  

   to 
  be 
  arranged 
  along 
  a 
  fiber, 
  but 
  in 
  general 
  they 
  have 
  no 
  definite 
  

   arrangement 
  with 
  reference 
  to 
  any 
  other 
  structures 
  in 
  the 
  cell. 
  

  

  Very 
  soon 
  after 
  the 
  completion 
  of 
  the 
  second 
  nuclear 
  division 
  

   the 
  cell-wall 
  becomes 
  thickened 
  to 
  about 
  one-fifteenth 
  of 
  the 
  

   diameter 
  of 
  the 
  mother-cell. 
  This 
  thickening 
  is 
  approximately 
  

   uniform 
  over 
  the 
  entire 
  surface 
  of 
  most 
  of 
  the 
  cells 
  examined. 
  

   The 
  loose 
  arrangement 
  of 
  the 
  cells 
  in 
  the 
  pollen-chamber 
  may 
  

   account 
  for 
  this 
  uniform 
  enlargement. 
  The 
  interceHular 
  spaces 
  

   are 
  usually 
  large 
  enough 
  to 
  prevent 
  the 
  touching 
  of 
  the 
  different 
  

  

  cells. 
  

  

  tw 
  

  

  with 
  the 
  walls 
  of 
  the 
  different 
  cells 
  appressed. 
  At 
  this 
  eariy 
  

   stage 
  in 
  division 
  the 
  cell-wall 
  has 
  reached 
  almost 
  its 
  maximum 
  

   thickness. 
  Cells 
  were 
  rarely 
  found 
  whose 
  wall-thickness 
  exceeded 
  

   one-fourteenth 
  to 
  one-thirteenth 
  of 
  the 
  diameter 
  of 
  the 
  mother-cell. 
  

  

  