﻿336 
  Farr: 
  Pollen-mother-cell 
  of 
  Cobaea 
  scandens 
  alba 
  

  

  the 
  pollen-mother-cell 
  ^in 
  Nicotiana, 
  while 
  in 
  Cohaea 
  it 
  thickens 
  

   to 
  only 
  one 
  fifteenth 
  of 
  the 
  mother-cell 
  diameter. 
  

  

  If 
  the 
  cell-wall 
  material 
  is 
  colloidal 
  in 
  nature, 
  the 
  degree 
  of 
  its 
  

   plasticity 
  would 
  be 
  related 
  to 
  the 
  amount 
  of 
  swelling 
  due 
  to 
  

  

  ( 
  * 
  

  

  imbibition. 
  This 
  suggests 
  a 
  possible 
  relation 
  between 
  the 
  amount 
  

   of 
  thickening 
  in 
  the 
  wall 
  and 
  the 
  breadth 
  of 
  the 
  furrow. 
  If 
  in 
  a 
  

   pollen-raother-cell 
  such 
  as 
  that 
  of 
  Nicotiana 
  there 
  is 
  an 
  almost 
  

   negh'gible 
  degree 
  of 
  resistance 
  of 
  the 
  cell-wall 
  to 
  the 
  forms 
  assumed 
  

   by 
  the 
  protoplast, 
  as 
  suggested 
  by 
  C. 
  H. 
  Farr, 
  the 
  pollen-mother- 
  

   cell-wall 
  of 
  Cohaea, 
  which 
  thickens 
  less, 
  might 
  be 
  conceived 
  of 
  

   as 
  producing 
  a 
  greater 
  resistance 
  to 
  the 
  cell 
  within. 
  The 
  relative 
  

   surface 
  tension 
  of 
  the 
  protoplast, 
  together 
  with 
  the 
  less 
  plastic 
  

   cell-wall, 
  might 
  prevent 
  the 
  early 
  rounding 
  up 
  of 
  the 
  lobes 
  of 
  the 
  

   mother-cell 
  of 
  Cohaea, 
  and 
  thus 
  decrease 
  the 
  breadth 
  of 
  the 
  furrow- 
  

  

  The 
  conditions 
  reported 
  in 
  the 
  microspore 
  formation 
  of 
  

   Drosera, 
  by 
  Levine,* 
  suggest 
  a 
  further 
  application 
  of 
  this 
  idea. 
  

   In 
  that 
  case 
  no 
  cell-plates 
  could 
  be 
  determined 
  during 
  the 
  division 
  

   of 
  the 
  cells, 
  and 
  they 
  did 
  not 
  present 
  the 
  marked 
  characteristics 
  

   of 
  a 
  process 
  of 
  division 
  by 
  furrowing. 
  Levine 
  states: 
  **if 
  furrows 
  

   are 
  present 
  in 
  Drosera 
  they 
  must 
  be 
  extremely 
  narrow 
  like 
  those 
  

   shown 
  in 
  the 
  slime 
  moulds 
  by 
  Harper 
  ('oo, 
  '14), 
  which 
  proceed 
  

   from 
  the 
  periphery 
  to 
  the 
  center 
  of 
  the 
  cytoplasm." 
  The 
  cell- 
  

   wall 
  of 
  the 
  pollen-mother-cell 
  of 
  Drosera 
  thickens 
  to 
  only 
  one- 
  

   twenty-second 
  of 
  the 
  diameter 
  of 
  the 
  protoplast, 
  and 
  if 
  the 
  previous 
  

   suggestions 
  are 
  assumed, 
  would 
  exert 
  an 
  even 
  greater 
  degree 
  of 
  

   resistance 
  to 
  the 
  protoplast 
  than 
  that 
  of 
  Cobaea. 
  This 
  may 
  per- 
  

   haps 
  be 
  great 
  enough 
  to 
  account 
  for 
  an 
  extremely 
  narrow 
  furrow. 
  

   The 
  fact 
  that 
  the 
  pollen-mother-cells 
  do 
  not 
  separate 
  after 
  cell- 
  

   division 
  is 
  completed, 
  but 
  form 
  a 
  tetrahedral 
  pollen-grain, 
  may 
  

   also 
  be 
  of 
  significance 
  in 
  this 
  relation. 
  

  

  It 
  has 
  been 
  observed 
  that 
  some 
  forms 
  of 
  amoeba 
  before 
  making 
  

   contact 
  with 
  a 
  food 
  particle 
  send 
  forth 
  strands 
  of 
  protoplasm, 
  or 
  

   pseudopodia, 
  and 
  surround 
  the 
  food. 
  A 
  fusion 
  of 
  these 
  pseudo- 
  

   podia 
  at 
  their 
  free 
  ends 
  or 
  edges 
  results 
  in 
  the 
  complete 
  enclosure 
  

   of 
  the 
  food. 
  In 
  Cobaea, 
  as 
  has 
  been 
  previously 
  stated, 
  the 
  ad- 
  

   vancing 
  tips 
  of 
  the 
  furrows 
  are 
  seen 
  first 
  

  

  between 
  

  

  * 
  Levine. 
  M. 
  Somatic 
  and. 
  reduction 
  divisions 
  in 
  certain 
  species 
  

   N. 
  Y. 
  Bot. 
  Gar. 
  Mem. 
  6: 
  127-147. 
  pi, 
  16-IQ. 
  1916. 
  

  

  