﻿Selection 
  of 
  Elementary 
  Species 
  119 
  

  

  Nature 
  has 
  constituted 
  them 
  as 
  groups 
  of 
  

   slightly 
  different 
  constant 
  forms, 
  quite 
  in 
  the 
  

   same 
  way 
  as 
  wheat 
  and 
  oats 
  and 
  corn. 
  Assum- 
  

   ing 
  that 
  this 
  happened 
  ages 
  ago 
  somewhere 
  in 
  

   central 
  Europe, 
  it 
  is 
  of 
  course 
  probable 
  that 
  

   the 
  same 
  differences 
  in 
  respect 
  to 
  the 
  influence 
  

   of 
  climatic 
  conditions 
  will 
  have 
  prevailed 
  as 
  

   with 
  cereals. 
  Subsequent 
  to 
  the 
  period 
  which 
  

   has 
  produced 
  the 
  numerous 
  elementary 
  spe- 
  

   cies 
  of 
  the 
  whitlow-grass 
  came 
  a 
  period 
  of 
  wide- 
  

   spread 
  distribution. 
  The 
  process 
  must 
  have 
  

   been 
  wholly 
  comparable 
  with 
  that 
  of 
  acclimati- 
  

   zation. 
  Some 
  species 
  must 
  have 
  been 
  more 
  

   adapted 
  to 
  northern 
  climates, 
  others 
  to 
  the 
  soils 
  

   of 
  western 
  or 
  eastern 
  regions 
  and 
  so 
  on. 
  These 
  

   qualities 
  must 
  have 
  decided 
  the 
  general 
  lines 
  of 
  

   the 
  distribution, 
  and 
  the 
  species 
  must 
  have 
  

   been 
  segregated 
  according 
  to 
  their 
  respective 
  

   climatic 
  qualities, 
  and 
  their 
  adaptability 
  to 
  soil 
  

   and 
  weather. 
  A 
  struggle 
  for 
  life 
  and 
  a 
  natural 
  

   selection 
  must 
  have 
  accompanied 
  and 
  guided 
  

   the 
  distribution, 
  but 
  there 
  is 
  no 
  reason 
  to 
  as- 
  

   sume 
  that 
  the 
  various 
  forms 
  were 
  changed 
  

   by 
  this 
  process, 
  and 
  that 
  we 
  see 
  them 
  now 
  en- 
  

   dowed 
  with 
  other 
  qualities 
  than 
  they 
  had 
  at 
  the 
  

   outset. 
  

  

  Natural 
  selection 
  must 
  have 
  played, 
  in 
  this 
  

   and 
  in 
  a 
  large 
  number 
  of 
  other 
  cases, 
  quite 
  the 
  

   same 
  part 
  as 
  the 
  artificial 
  method 
  of 
  variety- 
  

  

  