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  Retrograde 
  Varieties 
  

  

  Heretofore 
  we 
  have 
  generally 
  assumed, 
  that 
  

   varieties 
  differ 
  from 
  the 
  parent-species 
  in 
  a 
  sin- 
  

   gle 
  character 
  only, 
  or 
  at 
  least 
  that 
  only 
  one 
  need 
  

   be 
  considered. 
  We 
  now 
  come 
  to 
  the 
  study 
  of 
  

   those 
  varieties, 
  which 
  differ 
  in 
  more 
  than 
  one 
  

   character. 
  Of 
  these 
  there 
  are 
  two 
  types. 
  In 
  

   the 
  first 
  the 
  points 
  of 
  dissimilarity 
  are 
  inti- 
  

   mately 
  connected 
  with 
  one 
  another, 
  in 
  the 
  

   second 
  they 
  are 
  more 
  or 
  less 
  independent. 
  

  

  The 
  mutually 
  related 
  peculiarities 
  may 
  be 
  

   termed 
  correlative, 
  and 
  we 
  therefore 
  speak, 
  in 
  

   such 
  cases, 
  of 
  correlative 
  variability. 
  This 
  

   phenomenon 
  is 
  of 
  the 
  highest 
  importance 
  and 
  

   is 
  of 
  general 
  occurrence. 
  But 
  before 
  describing 
  

   some 
  examples, 
  it 
  is 
  as 
  well 
  to 
  note 
  that 
  in 
  the 
  

   lecture 
  on 
  fluctuating 
  variability, 
  cases 
  of 
  a 
  

   totally 
  different 
  nature 
  will 
  be 
  dealt 
  with, 
  which 
  

   unfortunately 
  are 
  designated 
  by 
  the 
  same 
  

   term. 
  Such 
  merely 
  fluctuating 
  variations 
  are 
  

   therefore 
  to 
  be 
  left 
  out 
  of 
  the 
  present 
  dis- 
  

   cussion. 
  

  

  The 
  purple 
  thorn-apple, 
  which 
  is 
  considered 
  

   by 
  some 
  writers 
  as 
  a 
  variety 
  of 
  the 
  white-flow- 
  

   ered 
  species 
  or 
  Datura 
  Stramonium, 
  and 
  by 
  

   others 
  as 
  a 
  separate 
  species, 
  D. 
  Tatula, 
  will 
  

   serve 
  as 
  an 
  illustration. 
  But 
  as 
  its 
  distinguish- 
  

   ing 
  attributes, 
  as 
  far 
  as 
  we 
  are 
  concerned 
  with 
  

   them 
  here, 
  are 
  of 
  the 
  nature 
  described 
  above 
  as 
  

   characteristic 
  of 
  varietal 
  peculiarities 
  no 
  ob- 
  

  

  