﻿220 
  Dr. 
  R. 
  E,. 
  Gates. 
  Meiotic 
  Phenomena 
  in 
  ike 
  Pollen 
  

  

  In 
  the 
  study 
  of 
  large 
  numbers 
  of 
  pollen 
  mother-cells 
  in 
  diakinesis, 
  occasional 
  

   departures 
  from 
  the 
  normal 
  nine 
  pairs 
  are 
  found. 
  In 
  one 
  such 
  case 
  two 
  of 
  the 
  

   longest 
  chromosomes 
  had 
  obviously 
  fused 
  together 
  end 
  to 
  end, 
  forming 
  one 
  

   enormously 
  long 
  chromosome. 
  The 
  fusion 
  was 
  complete, 
  and 
  there 
  was 
  not 
  

   the 
  slightest 
  indication 
  of 
  a 
  line 
  of 
  separation 
  between 
  them. 
  This 
  nucleus, 
  

   therefore, 
  contained 
  eight 
  separate 
  chromosome 
  bodies, 
  the 
  other 
  seven 
  pairs 
  

   being 
  unaltered. 
  In 
  certain 
  other 
  nuclei 
  where 
  only 
  eight 
  bivalent 
  chromo- 
  

   somes 
  were 
  present, 
  there 
  had 
  probably 
  been 
  a 
  fusion 
  of 
  two 
  pairs, 
  but 
  it 
  was 
  

   not 
  possible 
  to 
  identify 
  with 
  certainty 
  which 
  pairs 
  had 
  amalgamated. 
  In 
  at 
  

   least 
  one 
  case 
  it 
  would 
  appear 
  that 
  some 
  other 
  process 
  than 
  fusion 
  may 
  have 
  

   brought 
  about 
  the 
  diminution 
  in 
  number. 
  Ten 
  chromosome 
  bodies 
  were 
  

   found 
  in 
  diakinesis 
  in 
  a 
  limited 
  number 
  of 
  cases. 
  Whether 
  they 
  have 
  arisen 
  

   through 
  a 
  transverse 
  segmentation 
  of 
  one 
  of 
  the 
  bivalent 
  chromosomes 
  or 
  by 
  

   the 
  separation 
  of 
  the 
  members 
  of 
  a 
  pair 
  can 
  perhaps 
  not 
  be 
  determined 
  with 
  

   certainty, 
  owing 
  to 
  variations 
  in 
  chromosome 
  width. 
  In 
  any 
  case, 
  however 
  

   these 
  alterations 
  come 
  about 
  they 
  can 
  be 
  looked 
  upon 
  as 
  temporary 
  or 
  

   permanent 
  germinal 
  changes 
  according 
  to 
  their 
  later 
  behaviour. 
  They 
  serve 
  

   merely 
  to 
  emphasise 
  the 
  remarkable 
  constancy 
  in 
  the 
  history 
  of 
  the 
  chromo- 
  

   somes 
  in 
  the 
  germ-cell 
  cycle. 
  Probably 
  all 
  organisms 
  will 
  show 
  such 
  

   occasional 
  alterations 
  when 
  large 
  numbers 
  of 
  their 
  germ 
  cells 
  in 
  the 
  same 
  

   stage 
  of 
  their 
  development 
  are 
  critically 
  studied 
  and 
  compared. 
  

  

  Another 
  phenomenon 
  of 
  much 
  interest 
  in 
  the 
  meiotic 
  chromosomes 
  of 
  

   lettuce 
  is 
  the 
  tendency 
  which 
  appears 
  for 
  certain 
  of 
  the 
  bivalent 
  chromo- 
  

   somes 
  to 
  coalesce 
  more 
  or 
  less 
  completely 
  on 
  the 
  equatorial 
  plate 
  of 
  the 
  

   heterotypic 
  spindle. 
  At 
  this 
  stage 
  the 
  chromosome 
  pairs 
  become 
  even 
  

   more 
  condensed 
  than 
  in 
  the 
  late 
  diakinesis, 
  assuming 
  finally 
  an 
  almost 
  

   globular 
  shape. 
  They 
  frequently 
  show 
  at 
  this 
  time 
  their 
  point 
  of 
  attach- 
  

   ment 
  to 
  the 
  spindle, 
  as 
  a 
  thread-like 
  prolongation 
  from 
  one 
  end 
  of 
  the 
  chromo- 
  

   some. 
  All 
  indications 
  of 
  their 
  bivalent 
  nature 
  have 
  now 
  completely 
  

   disappeared. 
  In 
  counting 
  the 
  chromosomes 
  at 
  this 
  stage, 
  either 
  in 
  polar 
  

   view 
  or 
  in 
  side 
  view, 
  I 
  was 
  at 
  first 
  able 
  to 
  find 
  only 
  seven 
  bodies. 
  It 
  was 
  

   necessary, 
  of 
  course, 
  to 
  assure 
  oneself 
  that 
  such 
  chromosome 
  groups 
  were 
  

   uncut 
  in 
  sectioning. 
  Then 
  cases 
  were 
  found 
  where 
  two 
  of 
  the 
  bivalent 
  

   chromosomes 
  were 
  more 
  or 
  less 
  completely 
  coalesced, 
  and, 
  finally, 
  cases 
  in 
  

   which 
  all 
  nine 
  could 
  clearly 
  be 
  counted. 
  The 
  diminution 
  in 
  number 
  at 
  this 
  

   time 
  is 
  thus 
  found 
  to 
  be 
  due 
  to 
  the 
  temporary 
  coalescence 
  of 
  two 
  bivalent 
  

   chromosomes, 
  probably 
  end 
  to 
  end, 
  giving 
  eight 
  bodies, 
  or 
  of 
  two 
  more, 
  

   diminishing 
  the 
  number 
  to 
  seven 
  bodies. 
  

  

  So 
  far 
  as 
  I 
  know, 
  the 
  literature 
  of 
  cytology 
  contains 
  no 
  similar 
  instance 
  of 
  

   chromosome 
  behaviour, 
  either 
  in 
  plants 
  or 
  animals. 
  It 
  can 
  hardly, 
  I 
  think, 
  

  

  