﻿Periodic 
  Mutations 
  699 
  

  

  Species 
  of 
  algae 
  belonging 
  to 
  the 
  well-pre- 
  

   served 
  group 
  of 
  the 
  diatoms, 
  are 
  said 
  to 
  have 
  

   remained 
  unchanged 
  from 
  the 
  Carboniferous 
  

   period 
  up 
  to 
  the 
  present 
  time. 
  

  

  Summing 
  up 
  the 
  results 
  of 
  this 
  very 
  hasty 
  

   survey, 
  we 
  may 
  assert 
  that 
  species 
  remain 
  un- 
  

   changed 
  for 
  indefinite 
  periods, 
  while 
  at 
  times 
  

   they 
  are 
  in 
  the 
  alternative 
  condition. 
  Then 
  at 
  

   once 
  they 
  produce 
  new 
  forms 
  often 
  in 
  large 
  

   numbers, 
  giving 
  rise 
  to 
  swarms 
  of 
  subspecies. 
  

   All 
  facts 
  point 
  to 
  the 
  conclusion 
  that 
  these 
  pe- 
  

   riods 
  of 
  stability 
  and 
  mutability 
  alternate 
  more 
  

   or 
  less 
  regularly 
  with 
  one 
  another. 
  Of 
  course 
  

   a 
  direct 
  proof 
  of 
  this 
  view 
  cannot, 
  as 
  yet, 
  be 
  

   given, 
  but 
  this 
  conclusion 
  is 
  forced 
  upon 
  us 
  by 
  

   a 
  consideration 
  of 
  known 
  facts 
  bearing 
  on 
  the 
  

   principle 
  of 
  constancy 
  and 
  evolution. 
  

  

  If 
  we 
  are 
  right 
  in 
  this 
  general 
  conception, 
  we 
  

   may 
  ask 
  further, 
  what 
  is 
  to 
  be 
  the 
  exact 
  place 
  

   of 
  our 
  group 
  of 
  new 
  evening-primroses 
  in 
  this 
  

   theory? 
  In 
  order 
  to 
  give 
  an 
  adequate 
  answer, 
  

   we 
  must 
  consider 
  the 
  whole 
  range 
  of 
  the 
  obser- 
  

   vations 
  from 
  a 
  broader 
  point 
  of 
  view. 
  First 
  of 
  

   all 
  it 
  is 
  evident 
  that 
  the 
  real 
  mutating 
  period 
  

   must 
  be 
  assumed 
  to 
  be 
  much 
  longer 
  than 
  the 
  

   time 
  covered 
  by 
  my 
  observations. 
  Neither 
  the 
  

   beginning 
  nor 
  the 
  end 
  have 
  been 
  seen. 
  It 
  is 
  

   quite 
  obvious 
  that 
  Oenothera 
  lamarckiana 
  

   was 
  in 
  a 
  mutating 
  condition 
  when 
  I 
  first 
  

  

  