﻿O'Neal: 
  Microsporogenesis 
  in 
  Datura 
  Stramonium 
  233 
  

  

  paratively 
  few 
  chromosomes 
  are 
  formed 
  and 
  the 
  cells 
  stain 
  readily 
  

   with 
  the 
  usual 
  laboratory 
  dyes. 
  ^ 
  

  

  Anthers. 
  — 
  When 
  the 
  sporogcnous 
  cells 
  are 
  developing, 
  the 
  

   anthers 
  range 
  from 
  two 
  to 
  four 
  millimeters 
  in 
  length; 
  those 
  six 
  

   millimeters 
  long 
  almost 
  invariably 
  contain 
  mature 
  pollen. 
  Each 
  

   anther 
  has 
  four 
  loculi, 
  the 
  walls 
  of 
  which 
  are 
  composed 
  of 
  four 
  

   layers 
  of 
  flat 
  cells. 
  As 
  the 
  anthers 
  mature 
  the 
  cell 
  walls 
  of 
  the 
  

   two 
  middle 
  layers 
  of 
  these 
  cells 
  become 
  thickened 
  in 
  the 
  fashion 
  

   usual 
  for 
  mechanical 
  tissue 
  and 
  finally 
  aid 
  in 
  the 
  liberation 
  of 
  the 
  

   pollen 
  grains. 
  The 
  fourth 
  layer 
  becomes 
  modified 
  to 
  form 
  the 
  

   tapetum 
  which 
  immediately 
  surrounds 
  the 
  sporogenous 
  cells. 
  

  

  Tapetal 
  cells, 
  — 
  The 
  cells 
  of 
  the 
  tapetum 
  are 
  about 
  the 
  same 
  

   size 
  as 
  the 
  pollen 
  mother 
  cells 
  when 
  the 
  latter 
  are 
  in 
  the 
  resting 
  

   condition. 
  At 
  this 
  time 
  they 
  are 
  uninucleate, 
  but 
  by 
  the 
  time 
  

   the 
  mother 
  cells 
  have 
  reached 
  the 
  spirem 
  stage, 
  they 
  usually 
  

  

  i 
  

  

  contain 
  two 
  or 
  more 
  nuclei, 
  which 
  have 
  arisen 
  from 
  the 
  original 
  

   one 
  by 
  fragmentation. 
  The 
  tapetal 
  cells 
  increase 
  in 
  size 
  as 
  the 
  

   spore-producing 
  tissue 
  develops, 
  sometimes 
  attaining 
  a 
  diameter 
  

   two 
  or 
  three 
  times 
  that 
  of 
  the 
  sporogenous 
  cells. 
  During 
  this 
  

   development 
  the 
  cytoplasm 
  of 
  most 
  of 
  the 
  cells 
  becomes 
  decidedly 
  

   vacuolated 
  and, 
  as 
  it 
  continues, 
  the 
  majority 
  of 
  the 
  cell 
  walls 
  break 
  

   down, 
  and 
  the 
  cell 
  contents 
  are 
  allowed 
  to 
  escape 
  into 
  the 
  pollen 
  

   cavity. 
  Some 
  of 
  the 
  cells 
  apparently 
  become 
  reduced 
  in 
  size 
  

   without 
  any 
  evident 
  breaking 
  of 
  the 
  walls, 
  and 
  still 
  others 
  seem- 
  

   ingly 
  persist 
  unchanged 
  until 
  the 
  pollen 
  is 
  matured. 
  

  

  The 
  periplasm 
  was 
  carefully 
  searched 
  for 
  *' 
  wandering 
  cells" 
  

  

  ■ 
  

  

  such 
  as 
  were 
  found 
  by 
  Duggar 
  (6) 
  In 
  Symplocarpus 
  and 
  more 
  

   recently 
  in 
  Galium 
  by 
  Juel 
  (8), 
  but 
  no 
  positive 
  evidence 
  of 
  such 
  was" 
  

   found. 
  Occasional 
  cells 
  were 
  observed 
  which 
  had 
  apparently 
  

   broken 
  loose 
  from 
  the 
  anther 
  wall. 
  These 
  were 
  always 
  angular 
  in 
  

   outline 
  and 
  were 
  attributed 
  to 
  faulty 
  manipulation 
  rather 
  than 
  

   to 
  any 
  evidence 
  of 
  vital 
  phenomena. 
  Tapetal 
  nuclei 
  are 
  not 
  

   abundant 
  in 
  the 
  periplasm; 
  sometimes 
  they 
  may 
  be 
  seen 
  as 
  elon- 
  

   gate, 
  irregularly 
  shaped 
  structures, 
  similar 
  to 
  those 
  described 
  by 
  

   Pickett 
  (13) 
  for 
  Arisaema, 
  but 
  more 
  frequently 
  as 
  mere 
  darkly 
  

  

  * 
  

  

  staining 
  fragments. 
  No 
  amoeboid 
  forms 
  were 
  found. 
  

  

  Sporogenous 
  cells, 
  — 
  The 
  pollen 
  mother 
  cells 
  arise 
  directly 
  from 
  

   the 
  primary 
  sporogenous 
  cells 
  without 
  division 
  (Coulter 
  & 
  Cham- 
  

  

  