﻿-46 
  Elementary 
  Species 
  

  

  derived 
  exactly 
  in 
  the 
  same 
  way 
  as 
  the 
  tricol- 
  

   ored 
  field-pansies. 
  

  

  Summarizing 
  the 
  general 
  result 
  of 
  this 
  de- 
  

   scription 
  we 
  see 
  that 
  the 
  original 
  species 
  Viola 
  

   tricolor 
  may 
  be 
  split 
  up 
  into 
  larger 
  and 
  lesser 
  

   groups 
  of 
  separate 
  forms. 
  These 
  last 
  prove 
  to 
  

   be 
  constant 
  in 
  pedigree-cultures, 
  and 
  therefore 
  

   are 
  to 
  be 
  considered 
  as 
  really 
  existent 
  units. 
  

   They 
  are 
  very 
  numerous, 
  comprising 
  many 
  

   dozens 
  in 
  each 
  of 
  the 
  two 
  larger 
  subdivisions. 
  

  

  All 
  systematic 
  grouping 
  of 
  these 
  forms, 
  and 
  

   their 
  combination 
  into 
  subspecies 
  and 
  species 
  

   rests 
  on 
  the 
  comparative 
  study 
  of 
  their 
  charac- 
  

   ters. 
  The 
  result 
  of 
  such 
  studies 
  must 
  neces- 
  

   sarily 
  depend 
  on 
  principles 
  which 
  underlie 
  

   them. 
  According 
  to 
  the 
  choice 
  of 
  these 
  

   principles, 
  the 
  construction 
  of 
  the 
  groups 
  

   will 
  be 
  found 
  to 
  be 
  different. 
  Wittrock 
  trusts 
  

   in 
  the 
  first 
  place 
  to 
  morphologic 
  charac- 
  

   ters, 
  and 
  considers 
  the 
  development 
  as 
  passing 
  

   from 
  the 
  more 
  simple 
  to 
  the 
  more 
  complex 
  

   types. 
  On 
  the 
  other 
  hand 
  the 
  geographic 
  dis- 
  

   tribution 
  may 
  be 
  considered 
  as 
  an 
  indication 
  of 
  

   the 
  direction 
  of 
  evolution, 
  the 
  wide-spread 
  

   forms 
  being 
  regarded 
  as 
  the 
  common 
  parents 
  of 
  

   the 
  minor 
  local 
  species. 
  

  

  However, 
  such 
  considerations 
  are 
  only 
  of 
  sec- 
  

   ondary 
  importance. 
  It 
  must 
  be 
  borne 
  in 
  mind 
  

   that 
  an 
  ordinary 
  systematic 
  species 
  may 
  include 
  

  

  