﻿Unbalanced 
  Crosses 
  271 
  

  

  have 
  been 
  able 
  to 
  ascertain, 
  this 
  hybrid 
  never 
  

   produces 
  seed. 
  

  

  Another 
  instance 
  of 
  an 
  absolutelv 
  sterile 
  

  

  / 
  

  

  hybrid 
  is 
  the 
  often 
  quoted 
  Cytisus 
  adami. 
  It 
  

   is 
  a 
  cross 
  between 
  the 
  common 
  laburnum 
  

   (Cytisus 
  Laburnum) 
  and 
  another 
  species 
  of 
  the 
  

   same 
  genus, 
  C. 
  purpureus, 
  and 
  has 
  some 
  traits 
  

   of 
  both. 
  But 
  since 
  the 
  number 
  of 
  differentiat- 
  

   ing 
  marks 
  is 
  very 
  great 
  in 
  this 
  case, 
  most 
  of 
  the 
  

   organs 
  have 
  become 
  intermediate. 
  It 
  is 
  abso- 
  

   lutely 
  sterile. 
  But 
  it 
  has 
  the 
  curious 
  peculiar- 
  

   ity 
  of 
  splitting 
  in 
  a 
  vegetative 
  way. 
  It 
  has 
  been 
  

   multiplied 
  on 
  a 
  large 
  scale 
  by 
  grafting, 
  and 
  was 
  

   widely 
  found 
  in 
  the 
  parks 
  and 
  gardens 
  of 
  

   Europe 
  during 
  the 
  last 
  century. 
  Nearly 
  all 
  

   these 
  specimens 
  reverted 
  from 
  time 
  to 
  time 
  to 
  

   the 
  presumable 
  parents. 
  Not 
  rarely 
  a 
  bud 
  of 
  

   Adam's 
  laburnum 
  assumed 
  all 
  the 
  qualities 
  of 
  

   the 
  common 
  laburnum, 
  its 
  larger 
  leaves, 
  richer 
  

   flowered 
  racemes, 
  large 
  and 
  brightly 
  yellow 
  

   flowers 
  and 
  its 
  complete 
  fertility. 
  Other 
  buds 
  

   on 
  the 
  same 
  tree 
  reverted 
  to 
  the 
  purple 
  parent, 
  

   with 
  its 
  solitary 
  small 
  flowers, 
  its 
  dense 
  shrub- 
  

   like 
  branches 
  and 
  very 
  small 
  leaves. 
  These 
  too 
  

   are 
  fertile, 
  though 
  not 
  producing 
  their 
  seeds 
  as 
  

   abundantly 
  as 
  the 
  C. 
  Laburnum 
  reversions. 
  

   Many 
  a 
  botanist 
  has 
  sown 
  the 
  seeds 
  of 
  the 
  latter 
  

   and 
  obtained 
  only 
  pure 
  common 
  C. 
  Laburnum 
  

   ill 
  ants. 
  I 
  had 
  a 
  lot 
  of 
  nearly 
  a 
  hundred 
  seed- 
  

  

  