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  Mutations 
  

  

  have 
  been 
  shown 
  to 
  be 
  in 
  reality 
  composite 
  as- 
  

   semblages. 
  Roses 
  and 
  brambles, 
  hawkweeds 
  

   and 
  willows 
  are 
  the 
  best 
  known 
  examples. 
  Vio- 
  

   lets 
  and 
  Draba 
  verna, 
  dandelions 
  and 
  helian- 
  

   themmns 
  and 
  many 
  other 
  instances 
  were 
  dealt 
  

   with 
  in 
  previous 
  lectures. 
  Even 
  wheat 
  and 
  bar- 
  

   ley 
  and 
  corn 
  afford 
  instances 
  of 
  large 
  groups 
  

   of 
  elementary 
  species. 
  Formerly 
  mixed 
  in 
  

   the 
  fields, 
  they 
  became 
  separated 
  during 
  the 
  

   last 
  century, 
  and 
  now 
  constitute 
  constant 
  races, 
  

   which, 
  for 
  brevity's 
  sake, 
  are 
  dealt 
  with 
  under 
  

   the 
  name 
  of 
  varieties. 
  

  

  In 
  such 
  groups 
  of 
  nearly 
  allied 
  forms 
  the 
  sin- 
  

   gle 
  members 
  must 
  evidently 
  be 
  of 
  common 
  or- 
  

   igin. 
  It 
  is 
  not 
  necessary 
  for 
  them 
  to 
  have 
  orig- 
  

   inated 
  all 
  in 
  the 
  same 
  place 
  or 
  at 
  the 
  same 
  time. 
  

   In 
  some 
  cases, 
  as 
  with 
  Draba 
  verna, 
  the 
  present 
  

   geographic 
  distribution 
  points 
  to 
  a 
  common 
  

   birthplace, 
  from 
  whence 
  the 
  various 
  forms 
  may 
  

   about 
  the 
  same 
  period 
  have 
  radiated 
  in 
  all 
  direc- 
  

   tions. 
  The 
  violets 
  on 
  the 
  other 
  hand 
  seem 
  to 
  

   include 
  widely 
  diffused 
  original 
  forms, 
  from 
  

   which 
  branches 
  have 
  started 
  at 
  different 
  times 
  

   and 
  in 
  different 
  localities. 
  

  

  The 
  origin 
  of 
  such 
  groups 
  of 
  allied 
  forms 
  

   must 
  therefore 
  be 
  the 
  object 
  of 
  our 
  research. 
  

   Perhaps 
  we 
  might 
  find 
  a 
  whole 
  group, 
  perhaps 
  

   only 
  part 
  of 
  it. 
  In 
  my 
  opinion 
  we 
  have 
  the 
  

   right 
  to 
  assume 
  that 
  if 
  Draba 
  and 
  violets 
  and 
  

  

  