﻿Retrograde 
  Varieties 
  139 
  

  

  pubescence 
  in 
  some 
  hairy 
  species, 
  as 
  in 
  Galeop- 
  

   sis 
  Ladanum 
  canescens, 
  Lotus 
  corniculatus 
  

   hirsutus 
  and 
  so 
  on. 
  But 
  Veronica 
  scutellata 
  is 
  

   smooth 
  and 
  has 
  a 
  pubescent 
  variety, 
  and 
  Cyti- 
  

   sus 
  prostratus 
  and 
  C. 
  spinescens 
  are 
  each 
  re- 
  

   corded 
  to 
  have 
  a 
  ciliate 
  form. 
  

  

  Comparable 
  with 
  the 
  occurrence 
  and 
  the 
  lack 
  

   of 
  hairs, 
  is 
  the 
  existence 
  or 
  deficiency 
  of 
  the 
  

   glaucous 
  effect 
  in 
  leaves, 
  as 
  is 
  well 
  known 
  in 
  the 
  

   common 
  Ricinus. 
  Here 
  the 
  glaucous 
  appear- 
  

   ance 
  is 
  due 
  to 
  wax 
  distributed 
  in 
  fine 
  particles 
  

   over 
  the 
  surface 
  of 
  the 
  leaves, 
  and 
  in 
  the 
  green 
  

   variety 
  this 
  wax 
  is 
  lacking. 
  Other 
  instances 
  

   could 
  be 
  given 
  as 
  in 
  the 
  green 
  varieties 
  of 
  Pap- 
  

   aver 
  alpinum 
  and 
  Rumex 
  scutatus. 
  No 
  positive 
  

   instances 
  are 
  recorded 
  in 
  this 
  case. 
  

  

  Spines 
  and 
  prickles 
  may 
  often 
  disappear 
  and 
  

   give 
  rise 
  to 
  unarmed 
  and 
  defenceless 
  types. 
  

   Of 
  the 
  thorn-apples 
  both 
  species, 
  the 
  white- 
  

   flowered 
  Datura 
  Stramonium 
  and 
  the 
  purple 
  

   D. 
  Tatula 
  have 
  such 
  varieties. 
  Spinach 
  has 
  

   a 
  variety 
  called 
  the 
  " 
  Dutch,' 
  which 
  lacks 
  

   the 
  prickles 
  of 
  the 
  fruit; 
  it 
  is 
  a 
  very 
  old 
  

   form 
  and 
  absolutely 
  constant, 
  as 
  are 
  also 
  

   the 
  thornless 
  thorn-apples. 
  Last 
  year 
  a 
  very 
  

   curious 
  instance 
  of 
  a 
  partial 
  loss 
  of 
  prickles 
  was 
  

   discovered 
  by 
  Mr. 
  Cockerell 
  of 
  East 
  Las 
  Vegas 
  

   in 
  New 
  Mexico. 
  It 
  is 
  a 
  variety 
  of 
  the 
  American 
  

   cocklebur, 
  often 
  called 
  sea-burdock, 
  or 
  the 
  

  

  