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  Retrograde 
  Varieties 
  

  

  group 
  of 
  negative 
  variations, 
  as 
  we 
  have 
  defined 
  

   them. 
  But 
  the 
  same 
  thing 
  occurs 
  also 
  with 
  

   positive 
  varieties, 
  though 
  of 
  course, 
  such 
  cases 
  

   are 
  very 
  rare. 
  The 
  best 
  known 
  instance 
  is 
  that 
  

   of 
  the 
  ever-flowering 
  begonia, 
  Begonia 
  semper- 
  

   florens, 
  which 
  has 
  green 
  leaves 
  and 
  white 
  flow- 
  

   ers, 
  but 
  which 
  has 
  produced 
  garden 
  varieties 
  

   with 
  a 
  brown 
  foliage 
  and 
  pink 
  flowers. 
  Here 
  

   also 
  the 
  new 
  quality 
  manifests 
  itself 
  in 
  different 
  

   organs. 
  

  

  Enough 
  has 
  now 
  been 
  said 
  on 
  correlative 
  

   changes, 
  to 
  convince 
  us 
  that 
  they 
  are 
  as 
  a 
  rule 
  

   to 
  be 
  considered 
  as 
  the 
  expression 
  of 
  some 
  gen- 
  

   eral 
  internal 
  or 
  physiologic 
  quality, 
  which 
  is 
  not 
  

   limited 
  to 
  a 
  single 
  organ, 
  but 
  affects 
  all 
  parts 
  

   of 
  the 
  organism, 
  provided 
  they 
  are 
  capable 
  of 
  

   undergoing 
  the 
  change. 
  Such 
  characters 
  are 
  

   therefore 
  to 
  be 
  considered 
  as 
  units, 
  and 
  should 
  

   be 
  referred 
  to 
  the 
  group 
  of 
  single 
  characters. 
  

  

  Opposed 
  to 
  these 
  are 
  the 
  true 
  compound 
  char- 
  

   acters, 
  which 
  consist 
  of 
  different 
  units. 
  These 
  

   may 
  be 
  segregated 
  by 
  the 
  production 
  of 
  varie- 
  

   ties, 
  and 
  thereby 
  betray 
  the 
  separate 
  factors 
  of 
  

   the 
  complex 
  group. 
  

  

  The 
  most 
  beautiful 
  instances 
  of 
  such 
  complex 
  

   characters 
  are 
  offered 
  by 
  the 
  colors 
  of 
  some 
  of 
  

   the 
  most 
  prized 
  garden-flowers. 
  Earely 
  these 
  

   are 
  of 
  a 
  single 
  hue, 
  often 
  two 
  or 
  three 
  shades 
  

   contribute 
  to 
  the 
  effect, 
  and 
  in 
  some 
  cases 
  spe- 
  

  

  