﻿480 
  Mutations 
  

  

  tendency 
  to 
  mutation 
  must 
  be 
  universally 
  

   present 
  in 
  the 
  whole 
  species. 
  Another 
  observa- 
  

   tion, 
  although 
  it 
  is 
  of 
  a 
  negative 
  character, 
  

   gains 
  in 
  importance 
  from 
  this 
  point 
  of 
  view. 
  

   I 
  refer 
  to 
  the 
  total 
  lack 
  of 
  intermediate 
  steps 
  

   between 
  normal 
  and 
  peloric 
  individuals. 
  If 
  

   such 
  links 
  had 
  ordinarily 
  been 
  produced 
  pre- 
  

   vious 
  to 
  the 
  purely 
  peloric 
  state 
  they 
  would 
  no 
  

   doubt 
  have 
  been 
  observed 
  from 
  time 
  to 
  time. 
  

   This 
  is 
  so 
  much 
  the 
  more 
  probable 
  as 
  Linaria 
  

   is 
  a 
  perennial 
  herb, 
  and 
  the 
  ancestors 
  of 
  a 
  

   mutation 
  might 
  still 
  be 
  in 
  a 
  flowering 
  condi- 
  

   tion 
  together 
  with 
  their 
  divergent 
  offspring. 
  

   But 
  no 
  such 
  intermediates 
  are 
  on 
  record. 
  The 
  

   peloric 
  toad-flaxes 
  are, 
  as 
  a 
  rule, 
  found 
  sur- 
  

   rounded 
  by 
  the 
  normal 
  type, 
  but 
  without 
  inter- 
  

   grading 
  forms. 
  This 
  discontinuity 
  has 
  already 
  

   been 
  insisted 
  upon 
  by 
  Hofmeister 
  and 
  others, 
  

   even 
  at 
  the 
  time 
  when 
  the 
  theory 
  of 
  descent 
  was 
  

   most 
  under 
  discussion, 
  and 
  any 
  link 
  would 
  

   surely 
  have 
  been 
  produced 
  as 
  a 
  proof 
  of 
  a 
  slow 
  

   and 
  continuous 
  change. 
  But 
  no 
  such 
  proof 
  has 
  

   been 
  found, 
  and 
  the 
  conclusion 
  seems 
  admissible 
  

   that 
  the 
  mutation 
  of 
  toad-flaxes 
  ordinarily, 
  if 
  

   not 
  universally, 
  takes 
  place 
  by 
  a 
  sudden 
  step. 
  

   Our 
  experiment 
  may 
  simply 
  be 
  considered 
  as 
  a 
  

   thoroughly 
  controlled 
  instance 
  of 
  an 
  often 
  re- 
  

   curring 
  phenomenon. 
  It 
  teaches 
  us 
  how, 
  in 
  the 
  

  

  