﻿Unbalanced 
  Crosses 
  269 
  

  

  p 
  r 
  i 
  m 
  us.' 
  The 
  latter 
  is 
  a 
  cross 
  between 
  the 
  

   Californian 
  dewberry 
  and 
  the 
  Siberian 
  rasp- 
  

   berry 
  and 
  is 
  certainly 
  to 
  be 
  regarded 
  as 
  a 
  good 
  

   stable 
  species, 
  artificially 
  produced. 
  Bell 
  

   Salter 
  crossed 
  the 
  willow-herbs 
  Epilobium 
  tet- 
  

   ragonum 
  and 
  E. 
  montanum, 
  and 
  secured 
  inter- 
  

   mediate 
  hybrids 
  which 
  remained 
  true 
  to 
  their 
  

   type 
  during 
  four 
  successive 
  generations. 
  

  

  Other 
  instances 
  might 
  be 
  given. 
  Many 
  of 
  

   them 
  are 
  to 
  be 
  found 
  in 
  horticultural 
  and 
  bo- 
  

   tanical 
  journals 
  which 
  describe 
  their 
  system- 
  

   atic 
  and 
  anatomical 
  details. 
  The 
  question 
  of 
  

   stability 
  is 
  generally 
  dealt 
  with 
  in 
  an 
  inci- 
  

   dental 
  manner, 
  and 
  in 
  many 
  cases 
  it 
  is 
  diffi- 
  

   cult 
  to 
  reach 
  conclusions 
  from 
  the 
  facts 
  given. 
  

   Especially 
  disturbing 
  is 
  the 
  circumstance 
  that 
  

   from 
  a 
  horticultural 
  point 
  of 
  view 
  it 
  is 
  quite 
  

   sufficient 
  that 
  a 
  new 
  type 
  should 
  repeat 
  itself 
  in 
  

   some 
  of 
  its 
  offspring 
  to 
  be 
  called 
  stable, 
  and 
  

   that 
  for 
  this 
  reason 
  absolute 
  constancy 
  is 
  rarely 
  

   proved. 
  

  

  The 
  range 
  of 
  constant 
  hybrids 
  would 
  be 
  

   larger 
  by 
  far 
  were 
  it 
  not 
  for 
  two 
  facts. 
  The 
  

   first 
  is 
  the 
  absolute 
  sterility 
  of 
  so 
  many 
  beauti- 
  

   ful 
  hybrids, 
  and 
  the 
  second 
  is 
  the 
  common 
  occur- 
  

   rence 
  of 
  retrogressive 
  characters 
  among 
  culti- 
  

   vated 
  plants. 
  To 
  describe 
  the 
  importance 
  of 
  

   both 
  these 
  groups 
  of 
  facts 
  would 
  take 
  too 
  much 
  

  

  