﻿Periodic 
  Mutations 
  687 
  

  

  of 
  the 
  mutability 
  of 
  the 
  evening-primrose 
  lies 
  

   in 
  its 
  usefulness 
  as 
  a 
  guide 
  for 
  further 
  work. 
  

   The 
  view 
  that 
  it 
  might 
  be 
  an 
  isolated 
  case, 
  lying 
  

   outside 
  of 
  the 
  usual 
  procedure 
  of 
  nature, 
  can 
  

   hardly 
  be 
  sustained. 
  On 
  such 
  a 
  supposition 
  it 
  

   would 
  be 
  far 
  too 
  rare 
  to 
  be 
  disclosed 
  by 
  the 
  

   investigation 
  of 
  a 
  small 
  number 
  of 
  plants 
  from 
  

   a 
  limited 
  area. 
  Its 
  appearance 
  within 
  the 
  lim- 
  

   ited 
  field 
  of 
  inquiry 
  of 
  a 
  single 
  man 
  would 
  have 
  

   been 
  almost 
  a 
  miracle. 
  

  

  The 
  assumption 
  seems 
  justified 
  that 
  analo- 
  

   gous 
  cases 
  will 
  be 
  met 
  with, 
  perhaps 
  even 
  in 
  

   larger 
  numbers, 
  when 
  similar 
  methods 
  of 
  ob- 
  

   servation 
  are 
  used 
  in 
  the 
  investigation 
  of 
  plants 
  

   of 
  other 
  regions. 
  The 
  mutable 
  condition 
  may 
  not 
  

   be 
  predicated 
  of 
  the 
  evening-primroses 
  alone. 
  

   It 
  must 
  be 
  a 
  universal 
  phenomenon, 
  although 
  

   affecting 
  a 
  small 
  proportion 
  of 
  the 
  inhabitants 
  

   of 
  any 
  region 
  at 
  one 
  time: 
  perhaps 
  not 
  more 
  

   than 
  one 
  in 
  a 
  hundred 
  species, 
  or 
  perhaps 
  not 
  

   more 
  than 
  one 
  in 
  a 
  thousand, 
  or 
  even 
  fewer 
  may 
  

   be 
  expected 
  to 
  exhibit 
  it. 
  The 
  exact 
  proportion 
  

   is 
  immaterial, 
  because 
  the 
  number 
  of 
  mutable 
  

   instances 
  among 
  the 
  many 
  thousands 
  of 
  species 
  

   in 
  existence 
  must 
  be 
  far 
  too 
  large 
  for 
  all 
  of 
  

   them 
  to 
  be 
  submitted 
  to 
  close 
  scrutiny. 
  

  

  It 
  is 
  evident 
  from 
  the 
  above 
  discussion 
  that 
  

   next 
  in 
  importance 
  to 
  the 
  discovery 
  of 
  the 
  pro- 
  

   totype 
  of 
  mutation 
  is 
  the 
  formulation 
  of 
  meth- 
  

  

  