﻿'238 
  O'Neal: 
  Microsporogexesis 
  in 
  Datura 
  Stramonium 
  

  

  their 
  separation 
  the 
  nucleus 
  of 
  each 
  divides 
  to 
  form 
  the 
  generative 
  

   and 
  tube 
  nuclei. 
  Meanwhile 
  the 
  cell 
  has 
  increased 
  in 
  size 
  greatly 
  

   and 
  a 
  large 
  central 
  vacuole 
  has 
  been 
  formed. 
  A 
  plasma 
  membrane 
  

   is 
  formed 
  about 
  a 
  portion 
  of 
  the 
  cytoplasm 
  containing 
  the 
  gener- 
  

   ative 
  nucleus, 
  thus 
  forming 
  the 
  generative 
  cell 
  and 
  completing 
  

   the 
  development 
  of 
  the 
  pollen 
  grain. 
  . 
  . 
  

  

  I 
  

  

  Discussion 
  

  

  It 
  is 
  felt 
  that 
  anyone 
  giying 
  a 
  cytological 
  paper 
  on 
  a 
  field 
  so 
  

   well-worn 
  as 
  that 
  of 
  the 
  reduction 
  divisions 
  should 
  have 
  a 
  distinct 
  

  

  ■ 
  

  

  purpose 
  in 
  so 
  doing. 
  It 
  is 
  evident 
  that 
  such 
  work 
  can 
  not 
  reveal 
  

   much 
  that 
  is 
  strikingly 
  new. 
  A 
  consideration 
  of 
  the 
  literature 
  of 
  

   plant 
  cytology 
  shows 
  that 
  while 
  many 
  plants 
  have 
  been 
  investi- 
  

   gated 
  few 
  of 
  the 
  results 
  have 
  been 
  correlated 
  with 
  the 
  results 
  of 
  

  

  experimental 
  work. 
  M 
  

  

  cytologically 
  

  

  have 
  been 
  monocotyledonous 
  and 
  not 
  readily 
  amenable 
  to 
  Men- 
  

   delian 
  investigation. 
  Blakeslee 
  (2) 
  has 
  shown 
  that 
  Datura 
  has 
  at 
  

   least 
  two 
  pairs 
  of 
  characters 
  that 
  show 
  Mendelian 
  behavior 
  with 
  

   almost 
  mathematical 
  exactness. 
  Such 
  a 
  result 
  must 
  be 
  due 
  to 
  a 
  

   precise 
  handling 
  of 
  the 
  hereditary 
  substance 
  and 
  to 
  the 
  selection 
  

   of 
  unmistakeable 
  characters 
  by 
  the 
  plant 
  breeder. 
  The 
  present 
  

   work 
  shows 
  that 
  there 
  is 
  a 
  very 
  definite 
  apportionment 
  of 
  the 
  

   chromatin 
  material 
  In 
  the 
  reduction 
  divisions 
  of 
  Datura. 
  After 
  

   the 
  chromosomes 
  are 
  cut 
  oflF 
  from 
  the 
  the 
  spirem' 
  thread 
  they 
  may 
  

   be 
  traced 
  as 
  distinct 
  individuals 
  till 
  the 
  telophase 
  of 
  the 
  second 
  

   division. 
  It 
  is 
  evident 
  that, 
  if 
  the 
  factors 
  representing 
  the 
  parental 
  

   characters 
  are 
  segregated 
  in 
  the 
  two 
  halves 
  of 
  the 
  spirem 
  thread, 
  

   they 
  would 
  become 
  equally 
  distributed 
  in 
  the 
  formation 
  of 
  the 
  

   four 
  microspores. 
  

  

  It 
  has 
  long 
  been 
  known 
  that 
  in 
  the 
  insects 
  certain 
  definite 
  

   characters 
  like 
  sex 
  may 
  be 
  traced 
  to 
  a 
  specific 
  chromosome 
  or 
  

   part 
  of 
  a 
  chromosome 
  In 
  the 
  reproductive 
  cells. 
  Recently 
  Allen 
  

   (1) 
  has 
  reported 
  that 
  a 
  similar 
  basis 
  for 
  sex 
  may 
  be 
  made 
  out 
  in 
  

   Sphaerocarpos, 
  one 
  of 
  the 
  liverworts.' 
  To 
  one 
  who 
  has 
  studied 
  

   the 
  cells 
  of 
  Datura 
  it 
  is 
  clear 
  that 
  there 
  is 
  no 
  visible 
  evidence 
  of 
  

   such 
  a 
  basis 
  for 
  the 
  Mendelian 
  characters 
  with 
  which 
  Blakeslee 
  

   and 
  Avery 
  worked. 
  The 
  determinants 
  of 
  these 
  characters 
  must 
  

   be 
  chromosomes 
  or 
  parts 
  of 
  chromosomes 
  that 
  are 
  for 
  the 
  present 
  

  

  