﻿Artificial 
  and 
  Natural 
  Selection 
  805 
  

  

  This 
  change 
  was 
  not 
  permanent, 
  but 
  was 
  ob- 
  

   served 
  to 
  diminish 
  rapidly 
  and 
  to 
  disappear 
  

   entirely, 
  whenever 
  the 
  Norwegian 
  strain 
  was 
  

   cultivated 
  in 
  the 
  southern 
  part 
  of 
  Germany. 
  It 
  

   was 
  a 
  typical 
  improved 
  race, 
  dependent 
  on 
  con- 
  

   tinual 
  selection 
  by 
  the 
  short 
  summers 
  which 
  had 
  

   produced 
  it. 
  Similar 
  results 
  have 
  been 
  reached 
  

   by 
  Von 
  Wettstein 
  in 
  the 
  comparison 
  of 
  kinds 
  

   of 
  flax 
  from 
  different 
  countries. 
  The 
  analogy 
  

   between 
  such 
  cultivated 
  local 
  races 
  and 
  the 
  lo- 
  

   cal 
  races 
  of 
  nature 
  is 
  quite 
  striking. 
  The 
  prac- 
  

   tice 
  of 
  seed-exchange 
  rests 
  for 
  a 
  large 
  part 
  on 
  

   the 
  experience 
  that 
  the 
  characters, 
  acquired 
  un- 
  

   der 
  the 
  definite 
  climatic 
  and 
  cultural 
  conditions 
  

   of 
  some 
  select 
  regions, 
  hold 
  good 
  for 
  one 
  or 
  two, 
  

   and 
  sometimes 
  even 
  more 
  generations, 
  before 
  

   they 
  decrease 
  to 
  practical 
  uselessness. 
  The 
  

   Probstei, 
  the 
  Hanna 
  and 
  other 
  districts 
  owe 
  

   their 
  wealth 
  to 
  this 
  temporary 
  superiority 
  of 
  

   their 
  wheat 
  and 
  other 
  cereals. 
  

  

  Leaving 
  these 
  intermediate 
  forms 
  of 
  selec- 
  

   tion, 
  we 
  now 
  come 
  to 
  our 
  principal 
  point. 
  It 
  

   has 
  already 
  been 
  discussed 
  at 
  some 
  length 
  in 
  the 
  

   previous 
  lecture, 
  but 
  needs 
  further 
  consider- 
  

   ation. 
  It 
  is 
  the 
  question 
  whether 
  intra-specific 
  

   selection 
  may 
  be 
  regarded 
  as 
  a 
  cause 
  of 
  last- 
  

   ing 
  and 
  ever-increasing 
  improvement. 
  This 
  

   is 
  assumed 
  by 
  biologists 
  who 
  consider 
  fluc- 
  

   tuating 
  variability 
  as 
  the 
  main 
  source 
  of 
  pro- 
  

  

  