﻿Theories 
  of 
  Evolution 
  15 
  

  

  as 
  well 
  as 
  in 
  the 
  collateral 
  branches 
  of 
  the 
  gen- 
  

   ealogical 
  tree. 
  Sometimes 
  it 
  prevails, 
  and 
  

   the 
  monocotyledons 
  are 
  obviously 
  a 
  reduced 
  

   branch 
  of 
  the 
  primitive 
  dicotyledons. 
  In 
  or- 
  

   chids 
  and 
  aroids, 
  in 
  grasses 
  and 
  sedges, 
  reduc- 
  

   tion 
  plays 
  a 
  most 
  important 
  part, 
  leaving 
  its 
  

   traces 
  on 
  the 
  flowers 
  as 
  well 
  as 
  on 
  the 
  embryo 
  of 
  

   the 
  seed. 
  Many 
  instances 
  could 
  be 
  given 
  to 
  prove 
  

   that 
  progression 
  and 
  retrogression 
  are 
  the 
  two 
  

   main 
  principles 
  of 
  evolution 
  at 
  large. 
  Hence 
  

   the 
  conclusion 
  that 
  our 
  analysis 
  must 
  dissect 
  the 
  

   complicated 
  phenomena 
  of 
  evolution 
  so 
  far 
  as 
  

   to 
  show 
  the 
  separate 
  functions 
  of 
  these 
  two 
  con- 
  

   trasting 
  principles. 
  Hundreds 
  of 
  steps 
  were 
  

   needed 
  to 
  evolve 
  the 
  family 
  of 
  the 
  orchids, 
  but 
  

   the 
  experimenter 
  must 
  take 
  the 
  single 
  steps 
  

   for 
  the 
  object 
  of 
  his 
  inquiry. 
  He 
  finds 
  that 
  

   some 
  are 
  progressive 
  and 
  others 
  retrogressive 
  

   and 
  so 
  his 
  investigation 
  falls 
  under 
  two 
  heads, 
  

   the 
  origin 
  of 
  progressive 
  characters, 
  and 
  the 
  

   subsequent 
  loss 
  of 
  the 
  same. 
  Progressive 
  steps 
  

   are 
  the 
  marks 
  of 
  elementary 
  species, 
  while 
  re- 
  

   trograde 
  varieties 
  are 
  distinguished 
  by 
  ap- 
  

   parent 
  losses. 
  They 
  have 
  equal 
  claim 
  to 
  our 
  

   interest 
  and 
  our 
  study. 
  

  

  As 
  already 
  stated 
  I 
  propose 
  to 
  deal 
  first 
  with 
  

   the 
  elementary 
  species 
  and 
  afterwards 
  with 
  the 
  

   retrograde 
  varieties. 
  I 
  shall 
  try 
  to 
  depict 
  them 
  

   to 
  you 
  in 
  the 
  first 
  place 
  as 
  they 
  are 
  seen 
  in 
  

  

  