﻿598 
  Mutations 
  

  

  We 
  are 
  trained 
  to 
  the 
  appreciation 
  of 
  the 
  dif- 
  

   ferentiating 
  marks 
  of 
  systematic 
  species. 
  When 
  

   we 
  have 
  succeeded 
  in 
  discerning 
  these 
  as 
  given 
  

   by 
  our 
  local 
  flora 
  lists, 
  we 
  rest 
  content. 
  Meet- 
  

   ing 
  them 
  again 
  we 
  are 
  in 
  the 
  habit 
  of 
  greeting 
  

   them 
  with 
  their 
  proper 
  names. 
  Such 
  is 
  the 
  

   satisfaction 
  ensuing 
  from 
  this 
  knowledge 
  that 
  

   we 
  do 
  not 
  feel 
  any 
  inclination 
  for 
  further 
  in- 
  

   quiry. 
  Striking 
  deviations, 
  such 
  as 
  many 
  

   varietal 
  characters, 
  may 
  be 
  remarked, 
  but 
  then 
  

   they 
  are 
  considered 
  as 
  being 
  of 
  only 
  secondary 
  

   interest. 
  Our 
  minds 
  are 
  turned 
  from 
  the 
  deli- 
  

   cately 
  shaded 
  features 
  which 
  differentiate 
  ele- 
  

   mentary 
  species. 
  

  

  Even 
  in 
  the 
  native 
  field 
  of 
  the 
  evening-prim- 
  

   roses, 
  no 
  botanist 
  would 
  have 
  discovered 
  the 
  

   rosettes 
  with 
  smaller 
  or 
  paler 
  leaves, 
  constitut- 
  

   ing 
  the 
  first 
  signs 
  of 
  the 
  new 
  species. 
  Only 
  by 
  

   the 
  guidance 
  of 
  a 
  distinct 
  theoretical 
  idea 
  were 
  

   they 
  discovered, 
  and 
  having 
  once 
  been 
  pointed 
  

   out 
  a 
  closer 
  inspection 
  soon 
  disclosed 
  their 
  

   number. 
  

  

  Variability 
  seems 
  to 
  us 
  to 
  be 
  very 
  general, 
  but 
  

   very 
  limited. 
  The 
  limits 
  however, 
  are 
  distinct- 
  

   ly 
  drawn 
  by 
  the 
  struggle 
  for 
  existence. 
  Of 
  

   course 
  the 
  chance 
  for 
  useful 
  mutations 
  is 
  a 
  very 
  

   small 
  one. 
  We 
  have 
  seen 
  that 
  the 
  same 
  muta- 
  

   tions 
  are 
  as 
  a 
  rule 
  repeated 
  from 
  time 
  to 
  time 
  

   by 
  the 
  same 
  species. 
  Now, 
  if 
  a 
  useful 
  mutation, 
  

  

  