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  Genetic 
  Segregation. 
  

  

  about 
  20 
  per 
  cent, 
  is 
  type-bearing 
  and 
  the 
  proportion 
  diminishes 
  rapidly 
  in 
  

   each 
  successive 
  flower 
  above 
  that 
  level. 
  

  

  In 
  all 
  the 
  examples 
  given 
  hitherto 
  the 
  segregation 
  is 
  in 
  diploid 
  tissues, 
  but 
  

   a 
  comparable 
  phenomenon 
  has 
  been 
  proved 
  by 
  Collins 
  to 
  occur 
  in 
  the 
  haploid 
  

   axis 
  of 
  a 
  moss 
  (Funaria). 
  In 
  a 
  dioecious 
  moss, 
  as 
  the 
  Marchals 
  have 
  shown, 
  

   wex-segregation 
  occurs 
  at 
  spore-formation, 
  the 
  division 
  in 
  which 
  reduction 
  is 
  

   effected. 
  This, 
  of 
  course, 
  agrees 
  with 
  cytological 
  expectation, 
  though 
  so 
  far 
  

   as 
  I 
  know, 
  the 
  details 
  have 
  not 
  been 
  observed. 
  But 
  from 
  the 
  leaves 
  of 
  

   mosses 
  placed 
  in 
  nutrient 
  fluids 
  new 
  plants 
  may 
  be 
  raised 
  without 
  great 
  

   difficulty, 
  and 
  Collins 
  found 
  that 
  the 
  (perigonial) 
  leaves 
  surrounding 
  the 
  male 
  

   organ 
  thus 
  propagated, 
  produce 
  exclusively 
  male 
  axes.* 
  He 
  has 
  since 
  raised 
  

   similar 
  cultures 
  from 
  the 
  (perichaetial) 
  leaves 
  surrounding 
  the 
  female 
  organ, 
  

   and, 
  as 
  related 
  in 
  the 
  paper 
  following 
  this, 
  from 
  them 
  monoecious 
  plants 
  

   resulted. 
  The 
  proof 
  is 
  thus 
  complete 
  that 
  in 
  a 
  haploid 
  tissue 
  a 
  segregation 
  of 
  

   sex 
  can 
  occur. 
  

  

  The 
  inference 
  may 
  be 
  drawn 
  that 
  the 
  factors 
  for 
  other 
  characters 
  may 
  

   similarly 
  be 
  liable 
  to 
  segregate 
  in 
  the 
  haploid 
  state. 
  In 
  this 
  connexion 
  I 
  

   may 
  mention 
  a 
  case 
  which 
  though 
  as 
  yet 
  obscure, 
  perhaps 
  fulfils 
  this 
  

   expectation. 
  In 
  botanic 
  gardens 
  a 
  variegated 
  maiden-hair 
  fern 
  (Adiantum 
  

   capillus- 
  Veneris) 
  is 
  grown 
  which 
  has 
  wedges 
  of 
  white 
  tissue 
  irregularly 
  

   distributed 
  in 
  the 
  segments. 
  This 
  plant 
  produces 
  spores 
  freely,f 
  and 
  these 
  

   give 
  rise 
  to 
  prothallia 
  which 
  in 
  several 
  cultures 
  raised 
  here 
  have 
  always 
  been 
  

   entirely 
  green. 
  But 
  when 
  ferns 
  arise 
  from 
  these 
  green 
  prothallia 
  by 
  the 
  

   sexual 
  process, 
  they 
  are 
  of 
  three 
  kinds, 
  green, 
  white 
  or 
  variegated 
  like 
  the 
  

   parent 
  plants. 
  The 
  fact 
  that 
  the 
  prothallia 
  should 
  be 
  all 
  green 
  is 
  entirely 
  

   unexpected 
  and 
  creates 
  a 
  distinct 
  problem, 
  but 
  it 
  is 
  evident 
  that 
  segregation 
  

   must 
  occur 
  either 
  in 
  some 
  of 
  the 
  cell-divisions 
  by 
  which 
  the 
  prothallia 
  

   proliferate, 
  or 
  in 
  those 
  by 
  which 
  the 
  gametes 
  are 
  formed, 
  in 
  either 
  case 
  in 
  

   haploid 
  tissue. 
  This 
  segregation 
  is 
  essentially 
  different 
  from 
  that 
  by 
  which 
  

   the 
  differentiation 
  of 
  organs, 
  such 
  as 
  the 
  archegonia 
  and 
  antheridia 
  is 
  

   accomplished, 
  inasmuch 
  as 
  it 
  relates 
  to 
  elements 
  determining 
  the 
  characters 
  

   of 
  the 
  next 
  generation. 
  

  

  From 
  the 
  evidence 
  given 
  it 
  is 
  clear 
  that 
  in 
  a 
  wide 
  view 
  of 
  living 
  things 
  

   segregation 
  cannot 
  be 
  exclusively 
  a 
  property 
  of 
  the 
  reduction-division, 
  and 
  

   for 
  the 
  present, 
  it 
  should 
  be 
  regarded 
  as 
  a 
  possibility 
  which 
  may 
  occur 
  at 
  any 
  

   division 
  in 
  the 
  life-cycle. 
  

  

  * 
  ' 
  Jour. 
  Gen.,' 
  vol. 
  8, 
  p. 
  145 
  (1918-9). 
  

  

  t 
  I 
  have 
  not 
  satisfied 
  myself 
  that 
  spores 
  are 
  produced 
  in 
  sori 
  on 
  the 
  white 
  areas. 
  

  

  