﻿Stork: 
  Studies 
  in 
  the 
  genus 
  Tailvxacum 
  207 
  

  

  commenced 
  in 
  191 
  6 
  were 
  interrupted 
  during 
  the 
  two 
  years 
  of 
  

   the 
  war 
  but 
  are 
  being 
  resumed 
  now. 
  

  

  Megasporogenesis 
  in 
  Taraxacum 
  erythrospermum 
  

  

  The 
  megaspore-mother-cell 
  is 
  a 
  hypodermal 
  cell 
  at 
  the 
  apex 
  of 
  

   the 
  nucellus 
  and 
  is 
  easily 
  distinguished 
  by 
  its 
  denser 
  staining. 
  

   It 
  rapidly 
  increases 
  in 
  size, 
  assuming 
  an 
  elongated 
  form, 
  and 
  its 
  

   large 
  round 
  nucleus 
  attains 
  a 
  diameter 
  not 
  much 
  less 
  than 
  that 
  

   of 
  a 
  cross 
  section 
  of 
  the 
  cell. 
  In 
  the 
  resting 
  state, 
  the 
  nucleus 
  

   show 
  a 
  large 
  nucleolus 
  (not 
  more 
  than 
  one 
  was 
  ever 
  observed) 
  

   and 
  a 
  finely 
  reticulate 
  linin 
  with 
  densely 
  staining 
  chromatin. 
  

   When 
  entering 
  the 
  prophase, 
  this 
  reticulum 
  becomes 
  coarser 
  by 
  

   the 
  merging 
  of 
  its 
  elements, 
  and 
  the 
  irregular 
  strands 
  soon 
  contract 
  

   into 
  a 
  dense 
  mass 
  — 
  a 
  typical 
  synapsis 
  (Fig. 
  i). 
  Usually 
  there 
  

   are 
  at 
  the 
  edges 
  of 
  the 
  mass 
  suggestions 
  of 
  threads, 
  as 
  appears 
  in 
  

   Fig. 
  I. 
  Since 
  this 
  synaptic 
  condition 
  is 
  encountered 
  frequently 
  

   in 
  the 
  preparations, 
  it 
  is 
  reasonable 
  to 
  assume 
  that 
  it 
  lasts 
  a 
  

   relatively 
  long 
  time. 
  The 
  spireme 
  then 
  loosens 
  up 
  until 
  it 
  is 
  

   distributed 
  again 
  throughout 
  the 
  entire 
  nuclear 
  cavity. 
  Figs. 
  

   2 
  and 
  3 
  show 
  stages 
  in 
  this 
  process 
  of 
  loosening 
  up, 
  and 
  Fig. 
  4 
  is 
  

   drawn 
  from 
  a 
  thin 
  section 
  of 
  the 
  nucleus 
  when 
  this 
  stage 
  is 
  com- 
  

   pleted. 
  The 
  relatively 
  thick 
  thread 
  appears 
  to 
  be 
  of 
  a 
  finely 
  

   granular 
  nature. 
  Nowhere 
  in 
  the 
  preparations 
  is 
  there 
  any- 
  

   thing 
  to 
  suggest 
  that 
  the 
  thread 
  could 
  be 
  double 
  at 
  this 
  stage. 
  

   If 
  it 
  is 
  a 
  double 
  thread, 
  the 
  two 
  halves 
  are 
  so 
  intimately 
  merged 
  

   as 
  to 
  be 
  indistinguishable. 
  In 
  this 
  stage 
  T. 
  platycarpum, 
  which 
  

   is 
  a 
  normally 
  sexual 
  species, 
  is 
  reported 
  by 
  Osawa 
  (6) 
  to 
  present 
  a 
  

   clearly 
  parallel 
  spireme, 
  while 
  the 
  ooapogamous 
  species, 
  T. 
  alhidum 
  

   has 
  a 
  single 
  spireme; 
  neither 
  does 
  Juel 
  (5) 
  figure 
  or 
  describe 
  a 
  

   parallel 
  spireme 
  for 
  T. 
  vulgar 
  e 
  at 
  this 
  stage. 
  Osawa's 
  figures 
  

   seem 
  very 
  clear 
  and 
  definite 
  In 
  demonstrating 
  the 
  double 
  spireme 
  

   for 
  T. 
  platycarpum, 
  and 
  from 
  the 
  present 
  known 
  cases 
  * 
  

   appear 
  that 
  the 
  normal 
  sexual 
  Taraxacum 
  species 
  

  

  exhibit 
  

  

  ooapogamous 
  

  

  spireme 
  

  

  It 
  is 
  Interesting 
  to 
  note 
  in 
  this 
  connection 
  

  

  that 
  Beer 
  (i) 
  doubt's 
  the 
  existence 
  of 
  a 
  double 
  spireme 
  at 
  the 
  hollow 
  

  

  reme 
  stage 
  in 
  any 
  of 
  the 
  Compositae 
  that 
  he 
  has 
  studied. 
  

  

  The 
  thread 
  now 
  becomes 
  shorter 
  and 
  thicker, 
  the 
  thickenings 
  

  

  _ 
  , 
  J- 
  -^. 
  : 
  t.^^ 
  +^ 
  +V.O 
  t-pciiltincr 
  number 
  of 
  chromosomes. 
  

  

  