﻿642 
  Mutations 
  

  

  partly 
  because 
  the 
  division 
  of 
  labor 
  is 
  indicative 
  

   of 
  a 
  higher 
  degree 
  of 
  evolution. 
  But 
  sometimes 
  

   these 
  dimorphic 
  species 
  are 
  seen 
  to 
  revert 
  to 
  the 
  

   primary 
  condition, 
  developing 
  a 
  fertile 
  cone 
  at 
  

   the 
  summit 
  of 
  the 
  green 
  summer-stem. 
  I 
  have 
  

   had 
  the 
  opportunity 
  of 
  collecting 
  an 
  instance 
  of 
  

   this 
  anomaly 
  on 
  the 
  tall 
  Equisetum 
  telmateja 
  

   in 
  Switzerland, 
  and 
  other 
  cases 
  are 
  on 
  record 
  in 
  

   teratological 
  literature. 
  It 
  is 
  an 
  obvious 
  ex- 
  

   ample 
  of 
  systematic 
  atavism, 
  occurring 
  sud- 
  

   denly 
  and 
  with 
  the 
  full 
  development 
  of 
  all 
  the 
  

   qualities 
  needed 
  for 
  the 
  normal 
  production 
  of 
  

   sporangia 
  and 
  spores. 
  All 
  of 
  these 
  must 
  be 
  

   concealed 
  in 
  a 
  latent 
  condition 
  within 
  the 
  young 
  

   tissues 
  of 
  the 
  green 
  stems. 
  

  

  More 
  than 
  once 
  I 
  have 
  had 
  occasion 
  to 
  deal 
  

   with 
  the 
  phenomenon 
  of 
  torsions, 
  as 
  exhibited 
  

   by 
  the 
  teasels 
  and 
  some 
  other 
  plants. 
  This 
  

   anomaly 
  has 
  been 
  shown 
  to 
  be 
  analogous 
  to 
  the 
  

   cases 
  described 
  as 
  double 
  adaptations. 
  The 
  

   capacity 
  of 
  evolving 
  antagonistic 
  characters 
  is 
  

   prominent 
  in 
  both. 
  The 
  antagonists 
  are 
  as- 
  

   sumed 
  to 
  lie 
  quietly 
  together 
  while 
  inactive. 
  

   But 
  as 
  soon 
  as 
  evolution 
  calls 
  them 
  into 
  activity 
  

   they 
  become 
  mutually 
  exclusive, 
  because 
  only 
  

   one 
  of 
  them 
  can 
  come 
  to 
  full 
  display 
  in 
  the 
  same 
  

   organ. 
  External 
  influences 
  decide 
  which 
  of 
  the 
  

   two 
  becomes 
  dominant 
  and 
  which 
  remains 
  dor- 
  

   mant. 
  This 
  decision 
  must 
  take 
  place 
  separately 
  

  

  