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  Retrograde 
  Varieties 
  

  

  sive 
  evolution. 
  It 
  is 
  equally 
  universal, 
  per- 
  

   haps 
  never 
  failing. 
  No 
  great 
  changes 
  have 
  

   been 
  attained, 
  without 
  acquiring 
  new 
  qualities 
  

   on 
  one 
  side, 
  and 
  reducing 
  others 
  to 
  latency. 
  

   Everywhere 
  such 
  retrogressions 
  may 
  be 
  seen. 
  

   The 
  polypetalous 
  genera 
  Pyrola, 
  Ledum, 
  and 
  

   Monotropa 
  among 
  the 
  sympetalous 
  heaths, 
  are 
  

   a 
  remarkable 
  instance 
  of 
  this. 
  The 
  whole 
  evo- 
  

   lution 
  of 
  the 
  monocotyledons 
  from 
  the 
  lowest 
  

   orders 
  of 
  dicotyledons 
  implies 
  the 
  seeming 
  

   loss 
  of 
  cambial 
  growth 
  and 
  many 
  other 
  quali- 
  

   ties. 
  In 
  the 
  order 
  of 
  aroids, 
  from 
  the 
  cala- 
  

   mus-root 
  or 
  sweet 
  flag, 
  with 
  its 
  small 
  but 
  com- 
  

   plete 
  flowers, 
  up 
  to 
  the 
  reduced 
  duckweeds 
  

   (Lemna), 
  almost 
  an 
  unbroken 
  line 
  of 
  interme- 
  

   diate 
  steps 
  may 
  be 
  traced 
  showing 
  everywhere 
  

   the 
  concurrence 
  of 
  progressive 
  and 
  retrogres- 
  

   sive 
  evolution. 
  

  

  Degressive 
  evolution 
  is 
  not 
  so 
  common 
  by 
  far, 
  

   and 
  is 
  not 
  so 
  easy 
  to 
  recognize, 
  but 
  no 
  doubt 
  it 
  

   occurs 
  very 
  frequently. 
  It 
  is 
  generally 
  called 
  

   atavism, 
  or 
  better, 
  systematic 
  atavism, 
  and 
  the 
  

   clearest 
  cases 
  are 
  those 
  in 
  which 
  a 
  quality 
  which 
  

   is 
  latent 
  in 
  the 
  greater 
  part 
  of 
  a 
  family 
  or 
  

   group, 
  becomes 
  manifest 
  in 
  one 
  of 
  its 
  members. 
  

   Bracts 
  in 
  the 
  inflorescence 
  of 
  crucifers 
  are 
  or- 
  

   dinarily 
  wanting, 
  but 
  may 
  be 
  seen 
  in 
  some 
  

   genera, 
  Erucastrum 
  pollichii 
  being 
  perhaps 
  the 
  

  

  