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  Retrograde 
  Varieties 
  

  

  In 
  the 
  first 
  place 
  it 
  shows 
  that 
  a 
  species- 
  

   hybrid 
  may 
  inherit 
  the 
  distinguishing 
  marks 
  

   of 
  both 
  parents. 
  In 
  this 
  way 
  it 
  may 
  become 
  in- 
  

   termediate 
  between 
  them, 
  having 
  some 
  charac- 
  

   ters 
  in 
  common 
  with 
  the 
  pollen-parent 
  and 
  others 
  

   with 
  the 
  pistil-parent. 
  As 
  far 
  as 
  these 
  charac- 
  

   ters 
  do 
  not 
  interfere 
  with 
  each 
  other, 
  they 
  may 
  

   be 
  fully 
  developed 
  side 
  by 
  side, 
  and 
  in 
  the 
  main 
  

   this 
  is 
  the 
  way 
  in 
  which 
  hybrid 
  characters 
  are 
  

   evolved. 
  But 
  in 
  most 
  cases 
  our 
  existing 
  knowl- 
  

   edge 
  of 
  the 
  units 
  is 
  far 
  too 
  slender 
  to 
  give 
  a 
  

   complete 
  analysis, 
  even 
  of 
  these 
  distinguishing 
  

   marks 
  alone. 
  We 
  recognize 
  the 
  parental 
  marks 
  

   more 
  or 
  less 
  clearly, 
  but 
  are 
  not 
  prepared 
  for 
  

   exact 
  delimitations. 
  Leaving 
  these 
  theoretical 
  

   considerations, 
  we 
  will 
  pass 
  to 
  the 
  description 
  

   of 
  some 
  illustrative 
  examples. 
  

  

  In 
  the 
  first 
  place 
  I 
  will 
  describe 
  a 
  hybrid 
  

   between 
  two 
  species 
  of 
  Oenothera, 
  which 
  I 
  

   made 
  some 
  years 
  ago. 
  The 
  parents 
  were 
  the 
  

   common 
  evening-primrose 
  or 
  Oenothera 
  Men- 
  

   nis 
  and 
  of 
  its 
  small-flowered 
  congener, 
  Oeno- 
  

   thera 
  miiricata. 
  These 
  two 
  forms 
  were 
  distin- 
  

   guished 
  by 
  Linnaeus 
  as 
  different 
  species, 
  but 
  

   have 
  been 
  considered 
  by 
  subsequent 
  writers 
  as 
  

   elementary 
  species 
  or 
  so-called 
  systematic 
  va- 
  

   rieties 
  of 
  one 
  species 
  designated 
  with 
  the 
  name 
  

   of 
  the 
  presumably 
  older 
  type, 
  the 
  0. 
  biennis. 
  

   Varietal 
  differences 
  in 
  a 
  physiologic 
  sense 
  they 
  

  

  