﻿Retrograde 
  Varieties 
  137 
  

  

  wards, 
  and 
  their 
  lower 
  surfaces 
  downwards, 
  and 
  

   all 
  of 
  them 
  are 
  by 
  this 
  means 
  placed 
  in 
  a 
  single 
  

   horizontal 
  plane, 
  and 
  branching 
  takes 
  place 
  in 
  

   the 
  same 
  plane. 
  Evidently 
  this 
  general 
  ar- 
  

   rangement 
  is 
  another 
  response 
  to 
  gravity, 
  and 
  

   it 
  is 
  the 
  failure 
  of 
  this 
  reaction 
  which 
  induces 
  

   the 
  branches 
  to 
  grow 
  upwards 
  and 
  to 
  behave 
  

   like 
  stems. 
  

  

  Both 
  weeping 
  and 
  fastigiate 
  characters 
  are 
  

   therefore 
  to 
  be 
  regarded 
  as 
  steps 
  in 
  a 
  negative 
  

   direction, 
  and 
  it 
  is 
  highly 
  important 
  that 
  even 
  

   such 
  marked 
  departures 
  occur 
  without 
  transi- 
  

   tions 
  or 
  intermediate 
  forms. 
  If 
  these 
  should 
  

   occur, 
  though 
  ever 
  so 
  rarely, 
  they 
  would 
  proba- 
  

   bly 
  have 
  been 
  brought 
  to 
  notice, 
  on 
  account 
  of 
  

   the 
  great 
  prospect 
  the 
  numerous 
  instances 
  

   would 
  offer. 
  The 
  fact 
  that 
  they 
  are 
  lacking, 
  

   proves 
  that 
  the 
  steps, 
  though 
  apparently 
  great, 
  

   are 
  in 
  reality 
  to 
  be 
  considered 
  as 
  covering 
  single 
  

   units, 
  that 
  cannot 
  be 
  divided 
  into 
  smaller 
  parts. 
  

   Unfortunately 
  we 
  are 
  still 
  in 
  the 
  dark 
  as 
  to 
  the 
  

   question 
  of 
  the 
  inheritance 
  of 
  these 
  forms, 
  

   since 
  in 
  most 
  cases 
  it 
  is 
  difficult 
  to 
  obtain 
  pure 
  

   seed. 
  

  

  We 
  now 
  consider 
  the 
  cases 
  of 
  the 
  loss 
  of 
  su- 
  

   perficial 
  organs, 
  of 
  which 
  the 
  nectarines 
  are 
  

   example. 
  These 
  are 
  smooth 
  peaches, 
  lacking 
  

   the 
  soft 
  hairy 
  down, 
  that 
  is 
  a 
  marked 
  pecul- 
  

   iarity 
  of 
  the 
  true 
  peaches. 
  They 
  occur 
  in 
  differ- 
  

  

  