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  Retrograde 
  Varieties 
  

  

  as 
  to 
  the 
  true 
  value 
  of 
  some 
  form, 
  by 
  its 
  rela- 
  

   tionship 
  to 
  the 
  allied 
  types 
  in 
  the 
  way 
  of 
  retro- 
  

   gressive 
  modification. 
  Color-differences 
  are 
  so 
  

   showy, 
  that 
  they 
  easily 
  overshadow 
  other 
  char- 
  

   acters. 
  The 
  white 
  and 
  the 
  blue 
  thorn-apple, 
  

   the 
  white 
  and 
  the 
  red 
  campion 
  (Lychnis 
  ves- 
  

   pertina 
  and 
  diurna) 
  and 
  many 
  other 
  illustrative 
  

   cases 
  could 
  be 
  given, 
  in 
  which 
  two 
  forms 
  are 
  

   specifically 
  separated 
  by 
  some 
  authors, 
  but 
  

   combined 
  by 
  others 
  on 
  the 
  ground 
  of 
  the 
  retro- 
  

   grade 
  nature 
  of 
  some 
  differentiating 
  mark. 
  

  

  Hitherto 
  we 
  have 
  dealt 
  with 
  negative 
  charac- 
  

   ters 
  and 
  tried 
  to 
  prove 
  that 
  the 
  conception 
  of 
  

   latency 
  of 
  the 
  opposite 
  positive 
  characteristics 
  

   is 
  a 
  more 
  natural 
  explanation 
  of 
  the 
  phenome- 
  

   non 
  than 
  the 
  idea 
  of 
  a 
  complete 
  loss. 
  We 
  have 
  

   now 
  to 
  consider 
  the 
  positive 
  varieties, 
  and 
  to 
  

   show 
  that 
  it 
  is 
  quite 
  improbable 
  that 
  here 
  the 
  

   species 
  have 
  struck 
  out 
  for 
  themselves 
  a 
  wholly 
  

   new 
  character. 
  In 
  some 
  instances 
  such 
  may 
  

   have 
  been 
  the 
  case, 
  but 
  then 
  I 
  should 
  prefer 
  to 
  

   treat 
  these 
  rather 
  as 
  elementary 
  species. 
  But 
  

   in 
  the 
  main 
  we 
  will 
  have 
  to 
  assume 
  the 
  latency 
  

   of 
  the 
  character 
  in 
  the 
  species 
  and 
  its 
  reassump- 
  

   tion 
  by 
  the 
  variety 
  when 
  originating, 
  as 
  the 
  most 
  

   probable 
  explanation. 
  

  

  Great 
  stress 
  is 
  laid 
  upon 
  this 
  conception 
  by 
  

   the 
  fact, 
  that 
  positive 
  varieties 
  are 
  so 
  exces- 
  

   sively 
  rare 
  when 
  compared 
  with 
  the 
  common 
  oc- 
  

  

  