﻿448 
  Ever-sporting 
  Varieties 
  

  

  such 
  a 
  way 
  as 
  to 
  make 
  them 
  better 
  adapted 
  to 
  

   life, 
  under 
  prevailing 
  circumstances. 
  Nageli 
  

   gave 
  to 
  this 
  conception 
  the 
  name 
  " 
  Theory 
  

   of 
  direct 
  causation 
  : 
  (Theorie 
  der 
  direc- 
  

   ten 
  Bewirkung), 
  and 
  it 
  has 
  received 
  the 
  ap- 
  

   proval 
  of 
  Von 
  Wettstein, 
  Strasburger 
  and 
  other 
  

   German 
  investigators. 
  According 
  to 
  this 
  con- 
  

   ception 
  a 
  plant, 
  when 
  migrating 
  from 
  lowlands 
  

   into 
  the 
  mountains 
  would 
  slowly 
  be 
  changed 
  

   and 
  gradually 
  assume 
  alpine 
  habits. 
  Once 
  ac- 
  

   quired 
  this 
  habit 
  would 
  become 
  fixed 
  and 
  attain 
  

   the 
  rank 
  of 
  specific 
  characters. 
  In 
  testing 
  this 
  

   theory 
  by 
  field-observations 
  and 
  culture-exper- 
  

   iments, 
  the 
  defenders 
  of 
  the 
  Nagelian 
  principle 
  

   could 
  easily 
  produce 
  evidence 
  upon 
  the 
  first 
  

   point. 
  The 
  change 
  of 
  lowland-plants 
  into 
  al- 
  

   pine 
  varieties 
  can 
  be 
  brought 
  about 
  in 
  numer- 
  

   ous 
  cases, 
  and 
  corresponding 
  changes 
  under 
  

   the 
  influence 
  of 
  soil, 
  or 
  climate, 
  or 
  life-condi- 
  

   tions 
  are 
  on 
  record 
  for 
  the 
  most 
  various 
  charac- 
  

   ters 
  and 
  qualities. 
  

  

  The 
  second 
  point, 
  however, 
  is 
  as 
  difficult 
  to 
  

   prove 
  as 
  the 
  first 
  is 
  of 
  easy 
  treatment. 
  If 
  after 
  

   hundreds 
  and 
  thousands 
  of 
  years 
  of 
  exposure 
  to 
  

   alpine 
  or 
  other 
  extreme 
  conditions 
  a 
  fixed 
  

   change 
  is 
  proved 
  to 
  have 
  taken 
  place, 
  the 
  ques- 
  

   tion 
  remains 
  unanswered, 
  whether 
  the 
  change 
  

   has 
  been 
  a 
  gradual 
  or 
  a 
  sudden 
  one. 
  Darwin 
  

   pointed 
  out 
  that 
  long 
  periods 
  of 
  life 
  afford 
  a 
  

  

  