﻿706 
  Mutations 
  

  

  great 
  numbers 
  in 
  which 
  our 
  dwarf 
  variety 
  of 
  the 
  

   Oenothera 
  are 
  yearly 
  produced 
  are 
  suggestive 
  

   of 
  such 
  a 
  condition. 
  On 
  the 
  other 
  hand, 
  the 
  

   laevi 
  folia 
  and 
  brevistylis 
  mutations 
  have 
  not 
  

   been 
  repeated, 
  at 
  least 
  not 
  in 
  a 
  visible 
  way. 
  

  

  From 
  this 
  discussion 
  we 
  may 
  infer 
  that 
  it 
  is 
  

   quite 
  possible 
  that 
  a 
  large 
  part 
  of 
  the 
  progres- 
  

   sive 
  changes, 
  and 
  a 
  smaller 
  part 
  of 
  the 
  retro- 
  

   grade 
  mutations, 
  are 
  combined 
  into 
  groups, 
  ow- 
  

   ing 
  their 
  origin 
  to 
  common 
  external 
  agencies. 
  

   The 
  periods 
  in 
  which 
  such 
  groups 
  occur 
  would 
  

   constitute 
  the 
  mutative 
  periods. 
  Besides 
  them 
  

   the 
  majority 
  of 
  the 
  retrograde 
  changes 
  and 
  

   some 
  progressive 
  steps 
  might 
  occur 
  separately, 
  

   each 
  being 
  due 
  to 
  some 
  special 
  cause. 
  De- 
  

   gressive 
  mutations, 
  or 
  those 
  which 
  arise 
  by 
  

   the 
  return 
  of 
  latent 
  qualities 
  to 
  activity, 
  would 
  

   of 
  course 
  belong 
  with 
  the 
  latter 
  group. 
  

  

  This 
  assumption 
  of 
  a 
  stray 
  and 
  isolated 
  pro- 
  

   duction 
  of 
  varieties 
  is 
  to 
  a 
  large 
  degree 
  sup- 
  

   ported 
  by 
  experience 
  in 
  horticulture. 
  Here 
  

   there 
  are 
  no 
  real 
  swarms 
  of 
  mutations. 
  Sud- 
  

   den 
  leaps 
  in 
  variability 
  are 
  not 
  rare, 
  but 
  then 
  

   they 
  are 
  due 
  to 
  hybridization. 
  Apart 
  from 
  this 
  

   mixture 
  of 
  characters, 
  varieties 
  as 
  a 
  rule 
  appear 
  

   separately, 
  often 
  with 
  intervals 
  of 
  dozens 
  of 
  

   years, 
  and 
  without 
  the 
  least 
  suggestion 
  of 
  a 
  com- 
  

   mon 
  cause. 
  It 
  is 
  quite 
  superfluous 
  to 
  go 
  into 
  

   details, 
  as 
  we 
  have 
  dealt 
  with 
  the 
  horticultural 
  

  

  