﻿Multiplication 
  of 
  Extremes 
  745 
  

  

  selection-process. 
  In 
  practice 
  it 
  is 
  of 
  secondary 
  

   importance, 
  and 
  in 
  nature 
  it 
  takes 
  a 
  very 
  subor- 
  

   dinate 
  position. 
  For 
  this 
  reason 
  it 
  will 
  be 
  best 
  

   to 
  confine 
  further 
  discussions 
  to 
  the 
  experience 
  

   of 
  the 
  breeders. 
  

  

  Two 
  different 
  ways 
  are 
  open 
  to 
  make 
  fluctuat- 
  

   ing 
  variability 
  profitable. 
  Both 
  consist 
  in 
  the 
  

   multiplication 
  of 
  the 
  chosen 
  extremes, 
  and 
  this 
  

   increase 
  may 
  be 
  attained 
  in 
  a 
  vegetative 
  man- 
  

   ner, 
  or 
  by 
  the 
  use 
  of 
  seeds. 
  Asexual 
  and 
  sexual 
  

   propagation 
  are 
  different 
  in 
  many 
  respects, 
  and 
  

   so 
  they 
  are 
  also 
  in 
  the 
  domain 
  of 
  variability. 
  

  

  In 
  order 
  to 
  obtain 
  a 
  clear 
  comprehension 
  of 
  

   this 
  difference, 
  it 
  is 
  necessary 
  to 
  start 
  from 
  the 
  

   distinction 
  between 
  individual 
  and 
  partial 
  fluc- 
  

   tuations, 
  as 
  given 
  in 
  the 
  last 
  lecture. 
  This 
  

   distinction 
  may 
  be 
  discussed 
  more 
  understand- 
  

   ingly 
  if 
  the 
  causes 
  of 
  the 
  variability 
  are 
  taken 
  

   into 
  consideration. 
  We 
  have 
  dealt 
  with 
  them 
  

   at 
  some 
  length, 
  and 
  are 
  now 
  aware 
  that 
  inner 
  

   conditions 
  only, 
  determine 
  averages, 
  while 
  some 
  

   fluctuation 
  around 
  them 
  is 
  allowable, 
  as 
  influ- 
  

   enced 
  by 
  external 
  conditions. 
  These 
  outward 
  

   influences 
  act 
  throughout 
  life. 
  At 
  the 
  very 
  first 
  

   they 
  impress 
  their 
  stamp 
  on 
  the 
  whole 
  organism, 
  

   and 
  incite 
  a 
  lasting 
  change 
  in 
  distinct 
  directions. 
  

   This 
  is 
  the 
  period 
  of 
  the 
  development 
  of 
  the 
  

   germ 
  within 
  the 
  seed 
  ; 
  it 
  begins 
  with 
  the 
  fusion 
  

   of 
  the 
  sexual 
  cells, 
  and 
  each 
  of 
  them 
  may 
  be 
  in- 
  

  

  