﻿636 
  Mutations 
  

  

  general 
  rule 
  that 
  in 
  the 
  higher 
  plants 
  side 
  

   branches 
  are 
  situated 
  in 
  the 
  axils 
  of 
  leaves. 
  

   Bracts 
  are 
  reduced 
  leaves, 
  but 
  the 
  spikes 
  of 
  the 
  

   cruciferous 
  plants 
  are 
  generally 
  devoid 
  of 
  

   them. 
  The 
  flower-stalks, 
  with 
  naked 
  bases, 
  

   seem 
  to 
  arise 
  from 
  the 
  common 
  axis 
  at 
  indefinite 
  

   points. 
  

  

  Hence 
  the 
  inference 
  that 
  crucifers 
  are 
  an 
  ex- 
  

   ception 
  to 
  a 
  general 
  rule, 
  and 
  that 
  they 
  must 
  

   have 
  originated 
  from 
  other 
  types 
  which 
  did 
  

   comply 
  with 
  this 
  rule, 
  and 
  accordingly 
  were 
  in 
  

   the 
  possession 
  of 
  floral 
  bracts. 
  Or, 
  in 
  other 
  

   words, 
  that 
  the 
  bracts 
  must 
  have 
  been 
  lost 
  dur- 
  

   ing 
  the 
  original 
  evolution 
  of 
  the 
  whole 
  family. 
  

   This 
  conclusion 
  being 
  accepted, 
  the 
  accidental 
  

   re-apparition 
  of 
  bracts 
  within 
  the 
  family 
  must 
  

   be 
  considered 
  as 
  a 
  case 
  of 
  systematic 
  atavism, 
  

   quite 
  analogous 
  to 
  the 
  re-appeara,nce 
  of 
  the 
  

   scapes 
  in 
  the 
  acaulescent 
  primrose. 
  The 
  sys- 
  

   tematic 
  importance 
  of 
  this 
  phenomenon, 
  how- 
  

   ever, 
  is 
  far 
  greater 
  than 
  in 
  the 
  first 
  case, 
  in 
  

   which 
  we 
  had 
  only 
  to 
  deal 
  with 
  a 
  specific 
  char- 
  

   acter, 
  while 
  the 
  abolition 
  of 
  the 
  bracts 
  has 
  be- 
  

   come 
  a 
  feature 
  of 
  a 
  whole 
  family. 
  

  

  This 
  reversion 
  is 
  observed 
  to 
  take 
  place 
  ac- 
  

   cording 
  to 
  two 
  widely 
  different 
  principles. 
  On 
  

   one 
  hand, 
  bracts 
  may 
  be 
  met 
  with 
  in 
  a 
  few 
  

   stray 
  species, 
  assuming 
  the 
  rank 
  of 
  a 
  specific 
  

   character. 
  On 
  the 
  other 
  hand 
  they 
  may 
  be 
  seen 
  

  

  