﻿Elementary 
  Species 
  in 
  Nature 
  51 
  

  

  simultaneous 
  or 
  successive. 
  According 
  to 
  the 
  

   geographic 
  distribution, 
  the 
  place 
  of 
  common 
  

   origin 
  must 
  probably 
  be 
  sought 
  in 
  the 
  southern 
  

   part 
  of 
  central 
  Europe, 
  perhaps 
  even 
  in 
  the 
  

   vicinity 
  of 
  Lyons. 
  Here 
  we 
  may 
  assume 
  that 
  

   the 
  old 
  Draba 
  verna 
  has 
  produced 
  a 
  host 
  or 
  a 
  

   swarm 
  of 
  new 
  types. 
  Thence 
  they 
  must 
  have 
  

   spread 
  over 
  Europe, 
  but 
  whether 
  in 
  doing 
  so 
  

   they 
  have 
  remained 
  constant, 
  or 
  whether 
  some 
  

   or 
  many 
  of 
  them 
  have 
  repeatedly 
  undergone 
  

   specific 
  mutations, 
  is 
  of 
  course 
  unknown. 
  

  

  The 
  main 
  fact 
  is, 
  that 
  such 
  a 
  small 
  species 
  as 
  

   Draba 
  verna 
  is 
  not 
  at 
  all 
  a 
  uniform 
  type, 
  but 
  

   comprises 
  over 
  two 
  hundred 
  well 
  distinguished 
  

   and 
  constant 
  forms. 
  

  

  It 
  is 
  readily 
  granted 
  that 
  violets 
  and 
  whitlow- 
  

   grasses 
  are 
  extreme 
  instances 
  of 
  systematic 
  

   variability. 
  Such 
  great 
  numbers 
  of 
  elementary 
  

   species 
  are 
  not 
  often 
  included 
  in 
  single 
  species 
  

   of 
  the 
  system. 
  But 
  the 
  numbers 
  are 
  of 
  second- 
  

   ary 
  importance, 
  and 
  the 
  fact 
  that 
  systematic 
  

   species 
  consist, 
  as 
  a 
  rule, 
  of 
  more 
  than 
  one 
  inde- 
  

   pendent 
  and 
  constant 
  subspecies, 
  retains 
  its 
  al- 
  

   most 
  universal 
  validity. 
  

  

  In 
  some 
  cases 
  the 
  systematic 
  species 
  are 
  man- 
  

   ifest 
  groups, 
  sharply 
  differentiated 
  from 
  one 
  

   another. 
  In 
  other 
  instances 
  the 
  groups 
  of 
  ele- 
  

   mentary 
  forms 
  as 
  they 
  are 
  shown 
  by 
  direct 
  ob- 
  

   servation, 
  have 
  been 
  adjudged 
  by 
  many 
  authors 
  

  

  