﻿22 
  Descent 
  

  

  tral 
  line. 
  This, 
  and 
  approximately 
  this 
  only, 
  is 
  

   the 
  essential 
  difference 
  between 
  experimental 
  

   and 
  accidental 
  observation. 
  

  

  Mutations 
  are 
  occurring 
  from 
  time 
  to 
  time 
  in 
  

   the 
  wild 
  state 
  as 
  well 
  as 
  in 
  horticulture 
  and 
  

   agriculture. 
  A 
  selection 
  of 
  the 
  most 
  interest- 
  

   ing 
  instances 
  will 
  be 
  given 
  later. 
  But 
  in 
  all 
  

   such 
  cases 
  the 
  experimental 
  proof 
  is 
  wanting. 
  

   The 
  observations 
  as 
  a 
  rule, 
  only 
  began 
  when 
  the 
  

   mutation 
  had 
  made 
  its 
  appearance. 
  A 
  more 
  or 
  

   less 
  vague 
  remembrance 
  about 
  the 
  previous 
  

   state 
  of 
  the 
  plants 
  in 
  question 
  might 
  be 
  avail- 
  

   able, 
  though 
  even 
  this 
  is 
  generally 
  absent. 
  But 
  

   on 
  doubtful 
  points, 
  concerning 
  possible 
  crosses 
  

   or 
  possible 
  introduction 
  of 
  foreign 
  strains, 
  mere 
  

   recollection 
  is 
  insufficient. 
  The 
  fact 
  of 
  the 
  mu- 
  

   tation 
  may 
  be 
  very 
  probable, 
  but 
  the 
  full 
  proof 
  

   is, 
  of 
  course, 
  wanting. 
  Such 
  is 
  the 
  case 
  with 
  

   the 
  mutative 
  origin 
  of 
  Xanthium 
  commune 
  

   Wootoni 
  from 
  New 
  Mexico 
  and 
  of 
  Oenothera 
  

   biennis 
  crucial 
  a 
  from 
  Holland. 
  The 
  same 
  

   doubt 
  exists 
  as 
  to 
  the 
  origin 
  of 
  the 
  Capsella 
  

   keegeri 
  of 
  Solms-Laubach, 
  and 
  of 
  the 
  oldest 
  

   recorded 
  mutation, 
  that 
  of 
  Chelidonium 
  lacinia- 
  

   tum 
  in 
  Heidelberg 
  about 
  1600. 
  

  

  First, 
  we 
  have 
  doubts 
  about 
  the 
  fact 
  itself. 
  

   These, 
  however, 
  gradually 
  lose 
  their 
  impor- 
  

   tance 
  in 
  the 
  increasing 
  accumulation 
  of 
  evi- 
  

   dence. 
  Secondly, 
  the 
  impossibility 
  of 
  a 
  closer 
  

  

  