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  Ever-sporting 
  Varieties 
  

  

  Pinnate 
  and 
  palmate 
  leaves 
  are 
  no 
  doubt 
  

   derivative 
  types. 
  They 
  must 
  have 
  originated 
  

   from 
  the 
  ordinary 
  simple 
  leaf. 
  The 
  monophyl- 
  

   ly 
  may 
  therefore 
  be 
  considered 
  as 
  a 
  reversion 
  to 
  

   a 
  more 
  primitive 
  state 
  and 
  the 
  monophyllous 
  

   varieties 
  may 
  be 
  called 
  atavistic. 
  

  

  On 
  the 
  other 
  hand 
  we 
  have 
  seen 
  that 
  these 
  

   atavistic 
  varieties 
  may 
  revert 
  to 
  their 
  nearest 
  

   progenitors, 
  and 
  this 
  leads 
  to 
  the 
  curious 
  con- 
  

   ception 
  of 
  positive 
  and 
  negative 
  atavism. 
  For 
  

   if 
  the 
  change 
  of 
  compound 
  leaves 
  into 
  single 
  

   ones 
  is 
  a 
  retrograde 
  or 
  negative 
  step, 
  the 
  con- 
  

   version 
  of 
  single 
  or 
  ternate 
  leaves 
  into 
  pinnate 
  

   and 
  palmate 
  ones 
  must 
  evidently 
  be 
  considered 
  

   in 
  this 
  case 
  as 
  positive 
  atavism. 
  

  

  This 
  discussion 
  seems 
  to 
  throw 
  some 
  light 
  on 
  

   the 
  increase 
  of 
  leaflets 
  in 
  the 
  clover. 
  The 
  pea- 
  

   family, 
  or 
  the 
  group 
  of 
  papilionaceous 
  plants, 
  

   has 
  pinnate 
  leaves 
  ordinarily, 
  which, 
  according 
  

   to 
  our 
  premises, 
  must 
  be 
  considered 
  as 
  a 
  deriva- 
  

   tive 
  type. 
  In 
  the 
  clovers 
  and 
  their 
  allies 
  this 
  

   type 
  reverts 
  halfway 
  to 
  the 
  single 
  form, 
  pro- 
  

   ducing 
  only 
  three 
  leaflets 
  on 
  each 
  stalk. 
  If 
  now 
  

   the 
  clover 
  increases 
  its 
  number 
  of 
  leaflets, 
  this 
  

   may 
  be 
  considered 
  as 
  a 
  reversion 
  to 
  its 
  nearest 
  

   progenitors, 
  the 
  papilionaceous 
  plants 
  with 
  pin- 
  

   nate 
  leaves. 
  Hence 
  a 
  halfway 
  returning 
  and 
  

   therefore 
  positive 
  atavism. 
  And 
  as 
  I 
  have 
  al- 
  

   ready 
  mentioned 
  in 
  a 
  former 
  lecture, 
  pinnate 
  

  

  