﻿Theories 
  of 
  Evolution 
  23 
  

  

  inquiry 
  into 
  the 
  real 
  nature 
  of 
  the 
  change. 
  For 
  

   experimental 
  purposes 
  a 
  single 
  mutation 
  does 
  

   not 
  suffice; 
  it 
  must 
  be 
  studied 
  repeatedly, 
  and 
  

   be 
  produced 
  more 
  or 
  less 
  arbitrarily, 
  according 
  

   to 
  the 
  nature 
  of 
  the 
  problems 
  to 
  be 
  solved. 
  And 
  

   in 
  order 
  to 
  do 
  this, 
  it 
  is 
  evidently 
  not 
  enough 
  

   to 
  have 
  in 
  hand 
  the 
  mutated 
  individual, 
  but 
  it 
  is 
  

   indispensable 
  to 
  have 
  also 
  the 
  mutable 
  parents, 
  

   or 
  the 
  mutable 
  strain 
  from 
  which 
  it 
  sprang. 
  

  

  All 
  conditions 
  previous 
  to 
  the 
  mutation 
  are 
  to 
  

   be 
  considered 
  as 
  of 
  far 
  higher 
  importance 
  than 
  

   all 
  those 
  subsequent 
  to 
  it. 
  

  

  Now 
  mutations 
  come 
  unexpectedly, 
  and 
  if 
  the 
  

   ancestry 
  of 
  an 
  accidental 
  mutation 
  is 
  to 
  be 
  

   known, 
  it 
  is 
  of 
  course 
  necessary 
  to 
  keep 
  ac- 
  

   counts 
  of 
  all 
  the 
  strains 
  cultivated. 
  It 
  is 
  evi- 
  

   dent 
  that 
  the 
  required 
  knowledge 
  concerning 
  the 
  

   ancestry 
  of 
  a 
  supposed 
  mutation, 
  must 
  neces- 
  

   sarily 
  nearly 
  all 
  be 
  acquired 
  from 
  the 
  plants 
  in 
  

   the 
  experimental 
  garden. 
  

  

  Obviously 
  this 
  rule 
  is 
  as 
  simple 
  in 
  theory, 
  as 
  

   it 
  is 
  difficult 
  to 
  carry 
  out 
  in 
  practice. 
  First 
  of 
  

   all 
  comes 
  the 
  book-keeping. 
  The 
  parents, 
  

   grandparents 
  and 
  previous 
  ancestors 
  must 
  be 
  

   known 
  individually. 
  Accounts 
  of 
  them 
  must 
  be 
  

   kept 
  under 
  two 
  headings. 
  A 
  full 
  description 
  of 
  

   their 
  individual 
  character 
  and 
  peculiarities 
  

   must 
  always 
  be 
  available 
  on 
  the 
  one 
  hand, 
  and 
  

   on 
  the 
  other, 
  all 
  facts 
  concerning 
  their 
  heredi- 
  

  

  