﻿804 
  Fluctuations 
  

  

  neighboring 
  continent. 
  This 
  local 
  difference 
  is 
  

   ascribed 
  by 
  Behrens 
  to 
  a 
  more 
  severe 
  selection 
  

   by 
  the 
  pollinating 
  insects 
  in 
  consequence 
  of 
  their 
  

   lesser 
  frequency 
  on 
  these 
  very 
  windy 
  isles. 
  

   Seeds 
  of 
  the 
  pines 
  from 
  the 
  Himalayas 
  yield 
  

   cold-resisting 
  young 
  plants 
  if 
  gathered 
  from 
  

   trees 
  in 
  a 
  high 
  altitude, 
  while 
  the 
  seeds 
  of 
  the 
  

   same 
  species 
  from 
  lower 
  regions 
  yield 
  more 
  

   sensitive 
  seedlings. 
  Similar 
  instances 
  are 
  af- 
  

   forded 
  by 
  Rhododendron 
  and 
  other 
  mountain 
  

   species. 
  According 
  to 
  Cieslar 
  corresponding 
  

   differences 
  are 
  shown 
  by 
  seeds 
  of 
  firs 
  and 
  

   larches 
  from 
  alpine 
  and 
  lowland 
  provinces. 
  

  

  Such 
  changes 
  are 
  directly 
  dependent 
  on 
  ex- 
  

   ternal 
  influences. 
  This 
  is 
  especially 
  manifest 
  

   in 
  experiments 
  extending 
  the 
  cultures 
  in 
  higher 
  

   or 
  in 
  more 
  northern 
  regions. 
  The 
  shorter 
  

   summer 
  is 
  a 
  natural 
  agent 
  of 
  selection; 
  it 
  ex- 
  

   cludes 
  all 
  individuals 
  which 
  cannot 
  ripen 
  their 
  

   seeds 
  during 
  so 
  short 
  a 
  period. 
  Only 
  the 
  short- 
  

   lived 
  ones 
  survive. 
  Schiibeler 
  made 
  very 
  strik- 
  

   ing 
  experiments 
  with 
  corn 
  and 
  other 
  different 
  

   cereals, 
  and 
  has 
  succeeded 
  in 
  making 
  their 
  cul- 
  

   ture 
  possible 
  in 
  regions 
  of 
  Norway 
  where 
  it 
  for- 
  

   merly 
  failed. 
  In 
  the 
  district 
  of 
  Christiania, 
  corn 
  

   had 
  within 
  some 
  few 
  years 
  reduced 
  its 
  lifetime 
  

   from 
  123 
  to 
  90 
  days, 
  yielding 
  smaller 
  stems 
  and 
  

   fewer 
  kernels, 
  but 
  still 
  sufficient 
  to 
  make 
  its 
  

   culture 
  profitable 
  under 
  the 
  existing 
  conditions. 
  

  

  