﻿606 
  Mutations 
  

  

  avoidable 
  cross-fertilizations 
  with 
  the 
  parent- 
  

   form, 
  or 
  with 
  neighboring 
  varieties, 
  and 
  conse- 
  

   quent 
  impurity 
  of 
  the 
  new 
  strain. 
  This 
  impurity 
  

   we 
  have 
  called 
  vicinism, 
  and 
  in 
  a 
  previous 
  lec- 
  

   ture 
  have 
  shown 
  its 
  effects 
  upon 
  the 
  horticul- 
  

   tural 
  races 
  on 
  one 
  hand, 
  and 
  on 
  the 
  other, 
  on 
  the 
  

   scientific 
  value 
  that 
  can 
  be 
  ascribed 
  to 
  the 
  ex- 
  

   perience 
  of 
  the 
  breeder. 
  We 
  have 
  established 
  

   the 
  general 
  rule 
  that 
  stability 
  is 
  seldom 
  met 
  

   with, 
  but 
  that 
  the 
  observed 
  instability 
  is 
  always 
  

   open 
  to 
  the 
  objection 
  of 
  being 
  the 
  result 
  of 
  vicin- 
  

   ism. 
  Often 
  this 
  last 
  agency 
  is 
  its 
  sole 
  cause; 
  

   or 
  it 
  may 
  be 
  complicated 
  with 
  other 
  factors 
  

   without 
  our 
  being 
  able 
  to 
  discern 
  them. 
  

  

  Though 
  our 
  assertion 
  that 
  the 
  practice 
  of 
  the 
  

   horticulturist 
  in 
  producing 
  new 
  varieties 
  is 
  lim- 
  

   ited 
  to 
  isolation, 
  whenever 
  chance 
  affords 
  them, 
  

   is 
  theoretically 
  valid, 
  it 
  is 
  not 
  always 
  so. 
  We 
  

   may 
  discern 
  between 
  the 
  two 
  chief 
  groups 
  of 
  

   varieties. 
  The 
  retrograde 
  varieties 
  are 
  con- 
  

   stant, 
  the 
  individuals 
  not 
  differing 
  more 
  from 
  

   one 
  another 
  than 
  those 
  of 
  any 
  ordinary 
  species. 
  

   The 
  highly 
  variable 
  varieties 
  play 
  an 
  important 
  

   part 
  in 
  horticulture. 
  Double 
  flowers, 
  striped 
  

   flowers, 
  variegated 
  leaves 
  and 
  some 
  others 
  yield 
  

   the 
  most 
  striking 
  instances. 
  Such 
  forms 
  have 
  

   been 
  included 
  in 
  previous 
  lectures 
  among 
  the 
  

   ever-sporting 
  varieties, 
  because 
  their 
  peculiar 
  

   characters 
  oscillate 
  between 
  two 
  extremes, 
  viz. 
  : 
  

  

  