﻿696 
  Mutations 
  

  

  tematic 
  type. 
  Still 
  others 
  are 
  more 
  distant 
  or 
  

   even 
  belong 
  to 
  different 
  genera. 
  The 
  latter, 
  

   and 
  even 
  the 
  diverging, 
  though 
  nearly 
  allied, 
  

   elementary 
  species, 
  do 
  not 
  yield 
  adequate 
  evi- 
  

   dence 
  in 
  any 
  direction. 
  

  

  They 
  may 
  as 
  well 
  have 
  lived 
  together 
  in 
  

   the 
  long 
  ages 
  before 
  the 
  separation 
  of 
  the 
  now 
  

   widely 
  distant 
  floras, 
  or 
  have 
  sprung 
  from 
  a 
  

   common 
  ancestor 
  living 
  at 
  that 
  time, 
  and 
  subse- 
  

   quently 
  have 
  changed 
  their 
  habits. 
  After 
  ex- 
  

   cluding 
  these 
  unreliable 
  instances, 
  a 
  good 
  num- 
  

   ber 
  of 
  species 
  remain, 
  which 
  are 
  quite 
  the 
  same 
  

   in 
  the 
  arctic 
  and 
  alpine 
  regions 
  and 
  on 
  the 
  sum- 
  

   mits 
  of 
  distant 
  mountain-ranges. 
  As 
  no 
  trans- 
  

   portation 
  over 
  such 
  large 
  distances 
  can 
  have 
  

   brought 
  them 
  from 
  one 
  locality 
  to 
  the 
  other, 
  no 
  

   other 
  explanation 
  is 
  left 
  than 
  that 
  they 
  have 
  

   been 
  wholly 
  constant 
  and 
  unchanged 
  ever 
  since 
  

   the 
  glacial 
  period 
  which 
  separated 
  them. 
  Ob- 
  

   viously 
  they 
  must 
  have 
  been 
  subjected 
  to 
  widely 
  

   changing 
  conditions. 
  The 
  fact 
  of 
  their 
  stability 
  

   through 
  all 
  these 
  outward 
  changes 
  is 
  the 
  best 
  

   proof 
  that 
  the 
  ordinary 
  external 
  conditions 
  do 
  

   not 
  necessarily 
  have 
  an 
  influence 
  on 
  specific 
  evo- 
  

   lution. 
  They 
  may 
  have 
  such 
  a 
  result 
  in 
  some 
  

   instances, 
  in 
  others 
  they 
  obviously 
  have 
  not. 
  

   Many 
  arctic 
  forms 
  bearing 
  the 
  specific 
  name 
  of 
  

   alpinus 
  justify 
  this 
  conclusion. 
  Astragalus 
  al- 
  

   pinus, 
  Phleum 
  alpinunij 
  Hieracium 
  alpinum 
  and 
  

  

  