﻿O'Neal: 
  Microsporogenesis 
  in 
  Datura 
  Stramonium 
  235 
  

  

  proximating 
  threads 
  occasionally 
  seen 
  should 
  be 
  considered 
  splrem 
  

   threads 
  in 
  the 
  sense 
  that 
  Bonicke 
  uses 
  the 
  term 
  the 
  writer 
  is 
  unable 
  

  

  I 
  

  

  to 
  determine. 
  This 
  approximation 
  cannot 
  be 
  observed 
  in 
  every 
  

   cell 
  in 
  this 
  stage 
  of 
  development; 
  it 
  is 
  more 
  in 
  evidence 
  in 
  the 
  

  

  ^ 
  

  

  figure 
  than 
  Is 
  ordinarily 
  seen. 
  In 
  other 
  parts 
  of 
  the 
  same 
  nucleus 
  

   the 
  threads 
  seem 
  to 
  radiate 
  from 
  chromatin 
  masses, 
  and 
  in 
  still 
  

   other 
  places 
  the 
  threads 
  seem 
  to 
  be 
  formed 
  by 
  the 
  union 
  of 
  three 
  

   or 
  more 
  smaller 
  ones. 
  To 
  the 
  mind 
  of 
  the 
  writer 
  the 
  effect 
  is 
  so 
  

  

  ■ 
  

  

  confusing, 
  that 
  he 
  feels 
  that 
  anyone 
  with 
  a 
  bias 
  in 
  his 
  thinking, 
  no 
  

   matter 
  what 
  it 
  might 
  be, 
  could 
  find 
  an 
  apparent 
  basis 
  for 
  it 
  here. 
  

   Fig. 
  3 
  shows 
  a 
  stage 
  a 
  little 
  later 
  than 
  that 
  shown 
  in 
  Fig, 
  2. 
  The 
  

   linin-chromatin 
  mass 
  has 
  withdrawn 
  from 
  the 
  nuclear 
  membrane 
  

   and 
  is 
  enveloping 
  the 
  nucleolus. 
  In 
  case 
  two 
  nucleoli 
  are 
  present 
  

   one 
  of 
  them 
  may 
  be 
  left 
  out 
  of 
  the 
  synaptic 
  ball. 
  At 
  this 
  time 
  

   the 
  threads 
  and 
  chromatin 
  masses 
  have 
  increased 
  greatly 
  in 
  thick- 
  

   ness 
  and 
  stain 
  sharply. 
  On" 
  account 
  of 
  the 
  contracted 
  condition 
  

   the 
  arrangement 
  can 
  not 
  be 
  made 
  out 
  so 
  readily 
  as 
  in 
  the 
  stage 
  

   just 
  preceding. 
  

  

  Synapsis, 
  — 
  ^This 
  term 
  is 
  used 
  in 
  botanical 
  literature 
  for 
  the 
  

   , 
  condition 
  shown 
  in 
  Fig. 
  4. 
  The 
  nucleolus 
  is 
  closely 
  enveloped 
  in 
  

   . 
  the 
  chromatin 
  mass, 
  but 
  its 
  outline 
  as 
  well 
  as 
  that 
  of 
  the 
  threads 
  

   may 
  be 
  distinguished. 
  The 
  details 
  of 
  the 
  threads, 
  however, 
  can 
  not 
  

   be 
  made 
  out 
  even 
  in 
  the 
  most 
  carefully 
  stained 
  preparations. 
  This 
  

   stage 
  occurs 
  so 
  regularly 
  and 
  the 
  sequence 
  is 
  so 
  evident 
  that 
  it 
  is 
  

   hard 
  to 
  believe 
  that 
  it 
  is 
  an 
  artifact, 
  as' 
  Schaffner 
  (14) 
  asserts 
  for 
  

   Agave. 
  In 
  it 
  the 
  formation 
  of 
  the 
  spirem 
  thread 
  is 
  consummated. 
  

  

  Hollow 
  spirem. 
  — 
  Fig.' 
  5 
  shows 
  the 
  spirem 
  thread 
  as 
  it 
  emerges 
  

   from 
  the 
  synaptic 
  ball. 
  At 
  this 
  time 
  it 
  is 
  rather 
  thin 
  and 
  when 
  

  

  J 
  

  

  stained 
  w^th 
  suitable 
  density 
  it 
  appears 
  granular 
  in 
  nature. 
  If 
  

   the 
  stain 
  is 
  dense, 
  it 
  appears 
  as 
  a 
  fairly 
  smooth 
  thread 
  without 
  

   any 
  internal 
  differentiation 
  whatever. 
  At 
  this 
  stage 
  no 
  evidence 
  

   of 
  the 
  double 
  nature 
  of 
  the 
  thread 
  could 
  be 
  made 
  out. 
  ■ 
  Later 
  

   the 
  thread 
  becomes 
  more 
  loosely 
  arranged 
  in 
  the 
  nuclear 
  cavity 
  

   as 
  shown 
  in 
  Fig. 
  6. 
  So 
  far 
  as 
  it 
  has 
  been 
  possible 
  to 
  determine, 
  it 
  

  

  is 
  endless. 
  

  

  bivalents 
  

  

  contraction 
  

  

  and 
  consequent 
  thickening^ 
  of 
  the 
  strand. 
  The 
  slightly 
  thickened 
  

  

  