﻿Theories 
  of 
  Evolution 
  17 
  

  

  mentary 
  species 
  are 
  far 
  more 
  rare, 
  but 
  I 
  have 
  

   discovered 
  in 
  the 
  great 
  evening-primrose, 
  or 
  

   Oenothera 
  lamarckiana 
  a 
  strain 
  which 
  is 
  pro- 
  

   ducing 
  them 
  yearly 
  in 
  the 
  wild 
  state 
  as 
  well 
  as 
  

   in 
  my 
  garden. 
  These 
  observations 
  and 
  pedi- 
  

   gree-experiments 
  will 
  be 
  dealt 
  with 
  at 
  due 
  

   length 
  in 
  subsequent 
  lectures. 
  

  

  Having 
  proved 
  the 
  existence 
  and 
  importance 
  

   of 
  mutations, 
  it 
  remains 
  to 
  inquire 
  how 
  far 
  the 
  

   improvements 
  may 
  go 
  which 
  are 
  due 
  only 
  to 
  

   fluctuating 
  variability. 
  As 
  the 
  term 
  indicates, 
  

   this 
  variability 
  is 
  fluctuating 
  to 
  and 
  fro, 
  oscil- 
  

   lating 
  around 
  an 
  average 
  type. 
  It 
  never 
  fails 
  

   nor 
  does 
  it, 
  under 
  ordinary 
  circumstances, 
  de- 
  

   part 
  far 
  from 
  the 
  fixed 
  average. 
  

  

  But 
  the 
  deviation 
  may 
  be 
  enlarged 
  by 
  a 
  choice 
  

   of 
  extremes. 
  In 
  sowing 
  their 
  seed, 
  the 
  aver- 
  

   age 
  of 
  the 
  strain 
  is 
  seen 
  to 
  be 
  changed, 
  and 
  in 
  

   repeating 
  the 
  experiment 
  the 
  change 
  may 
  be 
  

   considerable. 
  It 
  is 
  not 
  clear, 
  whether 
  theo- 
  

   retically 
  by 
  such 
  an 
  accumulation, 
  deviations 
  

   might 
  be 
  reached 
  which 
  could 
  not 
  be 
  attained 
  at 
  

   once 
  in 
  a 
  single 
  sowing. 
  This 
  question 
  is 
  hard- 
  

   ly 
  susceptible 
  of 
  an 
  experimental 
  answer, 
  as 
  it 
  

   would 
  require 
  such 
  an 
  enormous 
  amount 
  of 
  seed 
  

   from 
  a 
  few 
  mother 
  plants 
  as 
  can 
  scarcely 
  ever 
  

   be 
  produced. 
  

  

  The 
  whole 
  character 
  of 
  the 
  fluctuations 
  shows 
  

   them 
  to 
  be 
  of 
  an 
  opposite 
  nature, 
  contrasting 
  

  

  