﻿PLANT 
  BREEDING 
  

  

  187 
  

  

  of 
  no 
  use 
  in 
  fertilizing, 
  but 
  sometimes 
  it 
  succeeds 
  perfectly, 
  1 
  

   as 
  when 
  pollen 
  from 
  one 
  species 
  of 
  plum 
  is 
  used 
  for 
  pollinating 
  

   flowers 
  of 
  another 
  species, 
  or 
  when 
  one 
  parent 
  flower 
  is 
  a 
  plum 
  

   and 
  the 
  other 
  a 
  cherry, 
  or 
  one 
  a 
  plum 
  and 
  the 
  other 
  an 
  apri- 
  

   cot. 
  Any 
  plant 
  grown 
  from 
  seed 
  thus 
  produced 
  is 
  called 
  a 
  

   hybrid. 
  The 
  terms 
  hybrid 
  and 
  hybridization 
  are 
  also 
  coming 
  

   to 
  be 
  generally 
  used 
  in 
  cases 
  of 
  breeding 
  between 
  varieties 
  as 
  

   well 
  as 
  between 
  species. 
  Crossing 
  is 
  another 
  term 
  used 
  in- 
  

   stead 
  of 
  hybridization, 
  and 
  the 
  result 
  of 
  the 
  process 
  or 
  hybrid 
  

   is 
  called 
  a 
  cross. 
  

  

  FIG. 
  160. 
  Results 
  of 
  hybridizing 
  plums 
  

  

  A, 
  a 
  stoneless 
  wild 
  plum 
  ; 
  B, 
  C, 
  D, 
  E, 
  fruits 
  of 
  seedlings 
  obtained 
  by 
  crossing 
  

   A 
  with 
  the 
  French 
  prune. 
  About 
  one 
  half 
  natural 
  size. 
  Modified 
  from 
  a 
  photo- 
  

   graph 
  by 
  Burbank 
  

  

  Hybrids 
  are 
  often 
  extremely 
  variable 
  (figs. 
  160 
  and 
  161), 
  

   and 
  for 
  this 
  reason 
  it 
  has 
  become 
  a 
  common 
  practice 
  to 
  hybrid- 
  

   ize 
  plants 
  for 
  the 
  sake 
  of 
  getting 
  a 
  variety 
  of 
  new 
  combina- 
  

   tions 
  of 
  characters 
  in 
  the 
  hybrid 
  seedlings, 
  and 
  then 
  to 
  select 
  

   the 
  desirable 
  kinds 
  for 
  breeding 
  purposes. 
  Until 
  recently 
  it 
  

   was 
  supposed 
  to 
  be 
  impossible 
  to 
  predict 
  the 
  way 
  in 
  which 
  the 
  

   characters 
  of 
  the 
  parents 
  would 
  be 
  inherited 
  by 
  the 
  successive 
  

   generations 
  of 
  hybrids. 
  But 
  a 
  law 
  known 
  from 
  its 
  discoverer 
  

   as 
  MendcTs 
  law 
  often 
  enables 
  the 
  breeder 
  to 
  foretell 
  the 
  char- 
  

   acters 
  which 
  the 
  hybrid 
  plants 
  will 
  inherit. 
  Gregor 
  Mendel, 
  

  

  1 
  The 
  plants 
  grown 
  from 
  seed 
  which 
  was 
  the 
  result 
  of 
  pollination 
  between 
  

   different 
  species 
  are 
  often 
  vigorous 
  but 
  incapable 
  of 
  producing 
  seed. 
  This 
  

   sterility 
  of 
  plants 
  bred 
  by 
  cross-pollination 
  between 
  different 
  species 
  is 
  so 
  

   common 
  that 
  it 
  was 
  formerly 
  often 
  used 
  as 
  a 
  test 
  to 
  determine 
  whether 
  two 
  

   kinds 
  of 
  plants 
  that 
  seemed 
  to 
  be 
  different 
  species 
  were 
  really 
  such 
  or 
  were 
  

   only 
  varieties. 
  

  

  