﻿Genetic 
  Segregation. 
  

  

  359 
  

  

  variations 
  in 
  colour 
  and 
  many 
  other 
  substantive 
  characteristics. 
  The 
  

   evidence 
  as 
  to 
  meristie 
  differences 
  is 
  however 
  still 
  scanty, 
  and 
  it 
  is 
  too 
  

   soon 
  to 
  decide 
  what 
  importance 
  should 
  be 
  attached 
  to 
  this 
  preliminary 
  

   impression. 
  

  

  With 
  more 
  confidence 
  we 
  recognise 
  that 
  merely 
  quantitative 
  differences 
  

   seldom, 
  if 
  ever, 
  have 
  a 
  perfectly 
  simple 
  inheritance. 
  There 
  are 
  two 
  obvious 
  

   interpretations: 
  (1) 
  that 
  the 
  factors 
  do 
  not 
  usually 
  segregrate 
  clean; 
  

   (2) 
  that 
  the 
  number 
  of 
  factors 
  involved 
  is 
  so 
  large 
  that 
  their 
  effects 
  are 
  

   masked. 
  Adequate 
  discussion 
  of 
  these 
  two 
  possibilities 
  could 
  only 
  be 
  given 
  

   at 
  considerable 
  length. 
  On 
  the 
  whole, 
  I 
  incline 
  to 
  the 
  former 
  alternative, 
  

   but 
  the 
  material 
  for 
  a 
  decision 
  scarcely 
  exists 
  as 
  yet. 
  Certain 
  examples 
  

   should 
  be 
  noticed 
  in 
  which, 
  though 
  the 
  most 
  obvious 
  differentiating 
  feature 
  

   is 
  quantitative, 
  the 
  underlying 
  physiological 
  distinction 
  is 
  more 
  probably 
  to 
  

   be 
  referred 
  fo 
  a 
  qualitative 
  factor. 
  Height 
  in 
  certain 
  plants 
  is 
  a 
  good 
  

   illustration. 
  It 
  is 
  ostensibly 
  a 
  quantitative 
  feature, 
  and 
  the 
  talis 
  segregate 
  

   clean 
  from 
  the 
  dwarfs. 
  But 
  in 
  various 
  cases, 
  e.g., 
  Peas 
  and 
  Sweet 
  Peas, 
  the 
  

   dwarfs 
  are 
  also 
  a 
  darker 
  green. 
  The 
  dwarf 
  of 
  Campanula 
  persicifolia, 
  

   especially 
  (about 
  8 
  inches 
  high), 
  is 
  a 
  plant 
  so 
  strikingly 
  different 
  from 
  the 
  

   type 
  (2-3 
  feet 
  high), 
  that 
  it 
  is 
  sold 
  as 
  a 
  species 
  " 
  C. 
  nitida." 
  The 
  leaves 
  of 
  

   the 
  dwarf 
  are 
  an 
  intense, 
  dark 
  green.* 
  This 
  variety 
  is, 
  of 
  course, 
  a 
  recessive 
  

   and 
  segregates 
  without 
  intermediates, 
  yet, 
  if 
  the 
  qualitative 
  distinctions 
  were 
  

   less 
  evident 
  it 
  might 
  easily 
  be 
  classed 
  as 
  a 
  variety 
  in 
  quantity. 
  But 
  the 
  

   critical 
  distinction 
  is 
  certainly 
  qualitative 
  and 
  the 
  great 
  difference 
  in 
  size 
  is 
  

   consequential. 
  Though 
  in 
  such 
  cases 
  segregation 
  is 
  complete, 
  it 
  may 
  almost 
  

   be 
  said 
  to 
  be 
  characteristic 
  of 
  purely 
  quantitative 
  distinctions 
  that 
  one 
  or 
  

   other 
  of 
  the 
  original 
  parental 
  types 
  fails 
  to 
  reappear 
  in 
  its 
  extreme 
  form 
  

   after 
  a 
  cross. 
  So 
  usual 
  is 
  this 
  feature 
  in 
  quantitative 
  segregation 
  that 
  the 
  

   phenomenon 
  must 
  have 
  special 
  significance. 
  

  

  Another 
  fact 
  is 
  beginning 
  to 
  emerge 
  which 
  must 
  contribute 
  to 
  the 
  shaping 
  

   of 
  a 
  conception 
  of 
  the 
  physiological 
  nature 
  of 
  segregation. 
  We 
  have 
  learnt 
  

   that 
  groups 
  or 
  complexes 
  of 
  factors 
  may 
  segregate 
  whole. 
  To 
  such 
  a 
  complex 
  

   the 
  distinction 
  in 
  sex 
  is 
  due, 
  but 
  in 
  certain 
  cases 
  it 
  may 
  break 
  up. 
  The 
  

   occurrence 
  of 
  a 
  large 
  spur 
  in 
  fertile 
  hens 
  (Leghorns, 
  for 
  instance) 
  must 
  be 
  

   regarded 
  as 
  due 
  to 
  the 
  absence 
  of 
  that 
  part 
  of 
  the 
  sex-complex 
  which 
  in 
  the 
  

   normal 
  hen 
  inhibits 
  the 
  growth 
  of 
  the 
  spur. 
  In 
  ordinary 
  fowls 
  the 
  whole 
  

   inhibiting 
  group 
  remains 
  on 
  the 
  female 
  side, 
  but 
  the 
  spur-inhibiting 
  element 
  

   can 
  evidently 
  separate 
  from 
  the 
  rest. 
  On 
  the 
  other 
  hand, 
  when 
  in 
  the 
  cocks 
  

   of 
  certain 
  breeds 
  (as 
  occasionally 
  in 
  Wyandottes) 
  there 
  is 
  no 
  spur, 
  we 
  

  

  The 
  ovary 
  projects 
  in 
  a 
  curious 
  way 
  above 
  the 
  sepals 
  so 
  much, 
  that 
  were 
  the 
  plant 
  

   not 
  a 
  Campanula, 
  botanists 
  would 
  describe 
  this 
  ovary 
  as 
  superior. 
  

  

  