﻿Artificial 
  and 
  Natural 
  Selection 
  815 
  

  

  ternal 
  causes. 
  First 
  come 
  those 
  that 
  have 
  

   influenced 
  the 
  young 
  germs 
  of 
  the 
  plant 
  

   during 
  its 
  most 
  sensitive 
  period, 
  when 
  still 
  

   an 
  embryo 
  within 
  the 
  ripening 
  seed. 
  They 
  

   give 
  a 
  new 
  limitation 
  to 
  the 
  average 
  con- 
  

   dition, 
  which 
  once 
  and 
  forever 
  becomes 
  fixed 
  

   for 
  this 
  special 
  individual. 
  In 
  the 
  second 
  

   place 
  the 
  young 
  seedling 
  is 
  affected 
  dur- 
  

   ing 
  the 
  development 
  of 
  its 
  crown 
  of 
  leaves, 
  

   and 
  of 
  its 
  roots, 
  by 
  numerous 
  factors, 
  

   which 
  cannot 
  change 
  this 
  average, 
  but 
  may 
  in- 
  

   duce 
  deviations 
  from 
  it, 
  increasing 
  or 
  decreas- 
  

   ing 
  the 
  amount 
  of 
  sugar, 
  which 
  will 
  eventually 
  

   be 
  laid 
  down 
  in 
  the 
  root. 
  The 
  best 
  young 
  beet 
  

   may 
  be 
  injured 
  in 
  many 
  ways 
  during 
  periods 
  of 
  

   its 
  lifetime, 
  and 
  produce 
  less 
  sugar 
  than 
  could 
  

   reasonably 
  be 
  expected 
  from 
  it, 
  It 
  may 
  be 
  sur- 
  

   passed 
  by 
  beets 
  of 
  inferior 
  constitution, 
  but 
  

   growing 
  under 
  more 
  favorable 
  circumstances. 
  

  

  Considered 
  from 
  this 
  point 
  of 
  view 
  the 
  result 
  

   of 
  the 
  polarization-test 
  is 
  not 
  a 
  single 
  value, 
  but 
  

   consists 
  of 
  at 
  least 
  two 
  different 
  factors. 
  It 
  

   may 
  be 
  equal 
  to 
  the 
  algebraic 
  sum 
  of 
  these, 
  or 
  

   to 
  their 
  difference, 
  according 
  to 
  whether 
  the 
  

   external 
  conditions 
  on 
  the 
  field 
  were 
  locally 
  and 
  

   individually 
  favorable 
  or 
  unfavorable. 
  A 
  large 
  

   amount 
  of 
  sugar 
  may 
  be 
  due 
  to 
  high 
  individual 
  

   value, 
  with 
  slight 
  subsequent 
  deviation 
  from 
  it, 
  

  

  