﻿LECTURE 
  XXII 
  

  

  SYSTEMATIC 
  ATAVISM 
  

  

  The 
  steady 
  cooperation 
  of 
  progression 
  and 
  re- 
  

   trogression 
  is 
  one 
  of 
  the 
  important 
  principles 
  

   of 
  organic 
  evolution. 
  I 
  have 
  dwelt 
  upon 
  this 
  

   point 
  more 
  than 
  once 
  in 
  previous 
  lectures. 
  I 
  

   have 
  tried 
  to 
  show 
  that 
  both 
  in 
  the 
  more 
  im- 
  

   portant 
  lines 
  of 
  the 
  general 
  pedigree 
  of 
  the 
  

   vegetable 
  kingdom, 
  and 
  in 
  the 
  numerous 
  lateral 
  

   branches 
  ending 
  in 
  the 
  genera 
  and 
  species 
  with- 
  

   in 
  the 
  families, 
  progression 
  and 
  retrogression 
  

   are 
  nearly 
  always 
  at 
  work 
  together. 
  Your 
  at- 
  

   tention 
  has 
  been 
  directed 
  to 
  the 
  monocotyledons 
  

   as 
  an 
  example, 
  where 
  retrogression 
  is 
  every- 
  

   where 
  so 
  active 
  that 
  it 
  can 
  almost 
  be 
  said 
  to 
  be 
  

   the 
  prevailing 
  movement. 
  Reduction 
  in 
  the 
  veg- 
  

   etative 
  and 
  generative 
  organs, 
  in 
  the 
  anatomical 
  

   structure 
  and 
  growth 
  of 
  the 
  stems, 
  and 
  in 
  sun- 
  

   dry 
  other 
  ways 
  is 
  the 
  method 
  by 
  which 
  the 
  

   monocotyledons 
  have 
  originated 
  as 
  a 
  group 
  

   from 
  their 
  supposed 
  ancestors 
  among 
  the 
  lower 
  

   dicotyledonous 
  families. 
  Retrogression 
  is 
  the 
  

   leading 
  idea 
  in 
  the 
  larger 
  families 
  of 
  the 
  group, 
  

  

  630 
  

  

  