﻿196 
  Retrograde 
  Varieties 
  

  

  taining 
  as 
  much 
  as 
  20$ 
  of 
  red-flowered 
  speci- 
  

   mens. 
  

  

  Many 
  fine 
  varieties 
  are 
  recorded 
  to 
  come 
  true 
  

   from 
  seed, 
  as 
  in 
  the 
  case 
  of 
  the 
  holly 
  with 
  

   yellow 
  fruits, 
  tested 
  by 
  Darwin. 
  Others 
  have 
  

   been 
  found 
  untrue 
  to 
  a 
  relatively 
  high 
  degree, 
  

   as 
  is 
  notorious 
  in 
  the 
  case 
  of 
  the 
  purple 
  beech. 
  

   Seeds 
  of 
  the 
  laciniated 
  beech 
  gave 
  only 
  1( 
  

   of 
  laciniated 
  plants 
  in 
  experiments 
  made 
  by 
  

   Strasburger; 
  seeds 
  of 
  the 
  monophyllous 
  aca- 
  

   cia, 
  Robinia 
  Pseud-Acacia 
  monophylla, 
  were 
  

   found 
  to 
  be 
  true 
  in 
  only 
  30$ 
  of 
  the 
  seedlings. 
  

   Weeping 
  ashes 
  often 
  revert 
  to 
  the 
  upright 
  type, 
  

   red 
  May-thorns 
  (Crataegus) 
  sometimes 
  revert 
  

   nearly 
  entirely 
  to 
  the 
  white 
  species 
  and 
  the 
  

   yellow 
  cornel 
  berry 
  is 
  recorded 
  to 
  have 
  reverted 
  

   in 
  the 
  same 
  way 
  to 
  the 
  red 
  berries 
  of 
  the 
  Cor- 
  

   nus 
  Mas. 
  

  

  Varieties 
  have 
  to 
  be 
  freed 
  by 
  selection 
  from 
  

   all 
  such 
  impurities, 
  since 
  isolation 
  is 
  a 
  means 
  

   which 
  is 
  quite 
  impracticable 
  under 
  ordinary 
  

   circumstances. 
  Isolation 
  is 
  a 
  scientific 
  require- 
  

   ment 
  that 
  should 
  never 
  be 
  neglected 
  in 
  ex- 
  

   periments, 
  indeed 
  it 
  may 
  be 
  said 
  to 
  be 
  the 
  first 
  

   and 
  most 
  important 
  requisite 
  for 
  all 
  exact 
  re- 
  

   search 
  in 
  questions 
  of 
  variability 
  and 
  inherit- 
  

   ance. 
  But 
  in 
  cultivating 
  large 
  fields 
  of 
  allied 
  va- 
  

   rieties 
  for 
  commercial 
  purposes, 
  it 
  is 
  impossible 
  

   to 
  grow 
  them 
  at 
  such 
  distances 
  from 
  each 
  other 
  

  

  