﻿O'Neal: 
  Microsporogenesis 
  in 
  Datura 
  Stramonium 
  239 
  

  

  indistinguishable. 
  In 
  this 
  study 
  no 
  irregularity 
  of 
  chromatin 
  

   behavior 
  has 
  been 
  found 
  that 
  could 
  explain 
  the 
  origin 
  of 
  mutants, 
  

   but 
  1this 
  could 
  scarcely 
  be 
  expected 
  since 
  their 
  occurrence 
  is 
  

   comparatively 
  rare. 
  It 
  is 
  conceivable 
  that 
  such 
  might 
  result 
  from 
  

   the 
  distribution 
  of 
  the 
  chromatin 
  substance 
  in 
  megasporogenesis. 
  

   If 
  such 
  is 
  the 
  case, 
  it 
  must 
  for 
  the 
  present 
  remain 
  a 
  closed 
  book 
  on 
  

   account 
  of 
  technical 
  difficulties 
  and 
  the 
  laboriousness 
  of 
  the 
  

   investigation. 
  \ 
  , 
  

  

  The 
  most 
  striking 
  thing 
  about 
  the 
  chromosomes 
  of 
  Datura 
  Is 
  

   their 
  uniformity 
  of 
  size. 
  This 
  is 
  especially 
  evident 
  in 
  the 
  second 
  

   division. 
  In 
  the 
  first 
  . 
  division 
  this 
  uniformity 
  is 
  somewhat 
  

   obscured 
  by 
  the 
  shapes 
  assumed 
  by 
  the 
  blvalents 
  until 
  they 
  appear 
  

   in 
  the 
  metaphase. 
  ' 
  . 
  , 
  

  

  Interpretation 
  of 
  the 
  prophase, 
  — 
  The 
  behavior 
  of 
  the 
  chromatin 
  

   material 
  in 
  the 
  formation 
  of 
  the 
  spirem 
  thread 
  has 
  been 
  a 
  much 
  

   mooted 
  question 
  and 
  it 
  seems 
  that 
  the 
  present 
  study 
  of 
  Datura 
  

   can 
  not 
  shed 
  much 
  light 
  upon 
  it. 
  In 
  the 
  resting 
  condition 
  the 
  

   nucleus 
  presents 
  such 
  a 
  maze 
  of 
  threads 
  and 
  granules 
  that 
  almost 
  

   any 
  interpretation 
  might 
  be 
  given. 
  Bonicke 
  (4) 
  claims 
  that 
  the 
  

   spirem 
  thread 
  is 
  formed 
  by 
  the 
  union 
  of 
  two 
  smaller 
  threads. 
  

   The 
  writer 
  came 
  to 
  the 
  present 
  problem 
  with 
  a 
  similar 
  theory. 
  

   As 
  shown 
  elsewhere 
  the 
  confirmatory 
  evidence 
  is 
  not 
  wholly 
  con- 
  

  

  .♦ 
  

  

  vincing. 
  

  

  No 
  satisfactory 
  theory 
  has 
  been 
  formulated 
  as 
  to 
  how 
  the 
  

  

  chromosomes 
  control 
  growth 
  t>r 
  impart 
  the 
  parental 
  characters 
  

   to 
  the 
  offspring. 
  It 
  was 
  purposed 
  to 
  make 
  a 
  comparative 
  study 
  

   of 
  the 
  chromosomes 
  of 
  plants 
  showing 
  the 
  dominant 
  characters 
  

   and 
  of 
  the 
  chromosomes 
  from 
  plants 
  displaying 
  the 
  recessive 
  

   characters. 
  Since 
  the 
  rate 
  of 
  growth 
  in 
  the 
  two 
  types 
  is 
  quite 
  

   different 
  it 
  was 
  conceived 
  that 
  there 
  might 
  be 
  a 
  physical, 
  deter- 
  

   minable 
  basis 
  for 
  it 
  in 
  the 
  chromatin 
  substance 
  of 
  the 
  cells. 
  

   Through 
  an 
  unfortunate 
  misunderstanding 
  the 
  plants 
  showing 
  

   the 
  recessive 
  characters 
  were 
  destroyed 
  before 
  material 
  was 
  

   collected 
  for 
  study. 
  Seeds 
  have 
  been 
  planted, 
  'however, 
  and 
  it 
  is 
  

  

  > 
  

  

  soon 
  

  

  1 
  

  

  Summary 
  

  

  I. 
  As 
  a 
  dicotyledonous 
  plant 
  Datura 
  Strarhoninm 
  is 
  favorable 
  

  

  M 
  

  

  behavior. 
  

  

  