﻿Elementary 
  Species 
  in 
  Nature 
  47 
  

  

  many 
  dozens 
  of 
  elementary 
  forms, 
  each 
  of 
  which 
  

   remains 
  constant 
  and 
  unchanged 
  in 
  successive 
  

   generations, 
  even 
  if 
  cultivated 
  in 
  the 
  same 
  gar- 
  

   den 
  and 
  under 
  similar 
  external 
  conditions. 
  

  

  Leaving 
  the 
  violets, 
  we 
  may 
  take 
  the 
  vernal 
  

   whitlow-grass 
  or 
  Drab 
  a 
  verna 
  for 
  a 
  second 
  illus- 
  

   tration. 
  This 
  little 
  annual 
  cruciferous 
  plant 
  is 
  

   common 
  in 
  the 
  fields 
  of 
  many 
  parts 
  of 
  the 
  

   United 
  States, 
  though 
  originally 
  introduced 
  

   from 
  Europe. 
  It 
  has 
  small 
  basal 
  rosettes 
  which 
  

   develop 
  during 
  summer 
  and 
  winter, 
  and 
  pro- 
  

   duce 
  numerous 
  leafless 
  flowering 
  stems 
  early 
  in 
  

   the 
  spring. 
  It 
  is 
  a 
  native 
  of 
  central 
  Europe 
  

   and 
  western 
  Asia, 
  and 
  may 
  be 
  considered 
  as 
  one 
  

   of 
  the 
  most 
  common 
  plants, 
  occurring 
  anywhere 
  

   in 
  immense 
  numbers 
  on 
  sandv 
  soils. 
  Jordan 
  

  

  */ 
  

  

  was 
  the 
  first 
  to 
  point 
  out 
  that 
  it 
  is 
  not 
  the 
  same 
  

   throughout 
  its 
  entire 
  range. 
  Although 
  a 
  hasty 
  

   survey 
  does 
  not 
  reveal 
  differences, 
  they 
  show 
  

   themselves 
  on 
  closer 
  inspection. 
  De 
  Bary, 
  

   Thuret, 
  Rosen 
  and 
  many 
  others 
  confirmed 
  this 
  

   result, 
  and 
  repeated 
  the 
  pedigree-cultures 
  of 
  

   Jordan. 
  Every 
  type 
  is 
  constant 
  and 
  remains 
  

   unchanged 
  in 
  successive 
  generations. 
  The 
  an- 
  

   thers 
  open 
  in 
  the 
  flower-buds 
  and 
  pollinate 
  the 
  

   stigmas 
  before 
  the 
  expansion 
  of 
  the 
  flowers, 
  

   thus 
  assuring 
  self-fertilization. 
  Moreover, 
  

   these 
  inconspicuous 
  little 
  flowers 
  are 
  only 
  spar- 
  

   ingly 
  visited 
  by 
  insects. 
  Dozens 
  of 
  subspecies 
  

  

  