﻿Selection 
  of 
  Elementary 
  Species 
  103 
  

  

  always 
  changing. 
  No 
  two 
  successive 
  years 
  show 
  

   exactly 
  the 
  same 
  proportions. 
  At 
  one 
  time 
  one 
  

   species 
  prevails, 
  at 
  another 
  time 
  one 
  or 
  two 
  or 
  

   more 
  other 
  species. 
  The 
  weather 
  during 
  the 
  

   spring 
  and 
  summer 
  benefits 
  some 
  and 
  hurts 
  

   others, 
  the 
  winter 
  may 
  be 
  too 
  cold 
  for 
  some, 
  but 
  

   again 
  harmless 
  for 
  others, 
  the 
  rainfall 
  may 
  

   partly 
  drown 
  some 
  species, 
  while 
  others 
  re- 
  

   main 
  uninjured. 
  Some 
  weeds 
  may 
  be 
  seen 
  flow- 
  

   ering 
  profusely 
  during 
  some 
  years, 
  while 
  in 
  

   other 
  summers 
  they 
  are 
  scarcely 
  to 
  be 
  found 
  in 
  

   the 
  same 
  meadow. 
  The 
  whole 
  population 
  is 
  in 
  a 
  

   fluctuating 
  state, 
  some 
  thriving 
  and 
  others 
  de- 
  

   teriorating. 
  It 
  is 
  a 
  continuous 
  response 
  to 
  the 
  

   ever 
  changing 
  conditions 
  of 
  the 
  weather. 
  Bare- 
  

   ly 
  a 
  species 
  is 
  wholly 
  annihilated, 
  though 
  it 
  

   may 
  apparently 
  be 
  so 
  for 
  years 
  ; 
  but 
  either 
  from 
  

   seeds 
  or 
  from 
  rootstocks, 
  or 
  even 
  from 
  neigh- 
  

   boring 
  lands, 
  it 
  may 
  sooner 
  or 
  later 
  regain 
  its 
  

   foothold 
  in 
  the 
  general 
  struggle 
  for 
  life. 
  

  

  This 
  phenomenon 
  is 
  a 
  very 
  curious 
  and 
  in- 
  

   teresting 
  one. 
  The 
  struggle 
  for 
  life, 
  which 
  

   plays 
  so 
  considerable 
  a 
  part 
  in 
  the 
  modern 
  

   theories 
  of 
  evolution, 
  may 
  be 
  seen 
  directly 
  at 
  

   work. 
  It 
  does 
  not 
  alter 
  the 
  species 
  themselves, 
  

   as 
  is 
  commonly 
  supposed, 
  but 
  it 
  is 
  always 
  

   changing 
  their 
  numerical 
  proportion. 
  Any 
  

   lasting 
  change 
  in 
  the 
  external 
  conditions 
  will 
  of 
  

   course 
  alter 
  the 
  average 
  oscillation 
  and 
  the 
  in- 
  

  

  