﻿Periodic 
  Mutations 
  707 
  

  

  mutations 
  at 
  sufficient 
  length 
  on 
  a 
  previous 
  oc- 
  

   casion. 
  Only 
  the 
  instance 
  of 
  the 
  peloric 
  toad- 
  

   flax 
  might 
  be 
  recalled 
  here, 
  because 
  the 
  historic 
  

   and 
  geographic 
  evidence, 
  combined 
  with 
  the 
  re- 
  

   sults 
  of 
  our 
  pedigree-experiment, 
  plainly 
  show 
  

   that 
  peloric 
  mutations 
  are 
  quite 
  independent 
  of 
  

   any 
  periodic 
  condition. 
  They 
  may 
  occur 
  any- 
  

   where 
  in 
  the 
  wide 
  range 
  of 
  the 
  toad-flax, 
  and 
  the 
  

   capacity 
  of 
  repeatedly 
  producing 
  them 
  has 
  

   lasted 
  some 
  centuries 
  at 
  least, 
  and 
  is 
  perhaps 
  

   even 
  as 
  old 
  as 
  the 
  species 
  itself. 
  

  

  Leaving 
  aside 
  such 
  stray 
  mutations, 
  we 
  may 
  

   now 
  consider 
  the 
  probable 
  constitution 
  of 
  the 
  

   great 
  lines 
  of 
  the 
  genealogic 
  tree 
  of 
  the 
  evening- 
  

   primroses, 
  and 
  of 
  the 
  whole 
  vegetable 
  and 
  ani- 
  

   mal 
  kingdom 
  at 
  large. 
  The 
  idea 
  of 
  drawing 
  up 
  

   a 
  pedigree 
  for 
  the 
  chief 
  groups 
  of 
  living 
  organ- 
  

   isms 
  is 
  originally 
  due 
  to 
  Ha,eckel, 
  who 
  used 
  this 
  

   graphic 
  method 
  to 
  support 
  the 
  Darwinian 
  the- 
  

   ory 
  of 
  descent. 
  Of 
  course, 
  Haeckel's 
  genealogic 
  

   trees 
  are 
  of 
  a 
  purely 
  hypothetic 
  nature, 
  and 
  have 
  

   no 
  other 
  purpose 
  than 
  to 
  convey 
  a 
  clear 
  concep- 
  

   tion 
  of 
  the 
  notion 
  of 
  descent, 
  and 
  of 
  the 
  great 
  

   lines 
  of 
  evolution 
  at 
  large. 
  Obviously 
  all 
  de- 
  

   tails 
  are 
  subject 
  to 
  doubt, 
  and 
  many 
  have 
  ac- 
  

   cordingly 
  been 
  changed 
  by 
  his 
  successors. 
  These 
  

   changes 
  may 
  be 
  considered 
  as 
  partial 
  improve- 
  

   ments, 
  and 
  the 
  somewhat 
  picturesque 
  form 
  of 
  

   Haeckel's 
  pedigree 
  might 
  well 
  be 
  replaced 
  by 
  

  

  