﻿218 
  Retrograde 
  Varieties 
  

  

  shape 
  proper 
  to 
  the 
  young 
  trees, 
  bearing 
  sessile 
  

   and 
  opposite 
  leaves. 
  

  

  It 
  seems 
  quite 
  unnecessary 
  to 
  give 
  further 
  

   instances. 
  They 
  are 
  familiar 
  to 
  every 
  student. 
  

   It 
  is 
  almost 
  safe 
  to 
  say 
  that 
  every 
  character 
  has 
  

   its 
  periods 
  of 
  activity 
  and 
  of 
  inactivity, 
  and 
  

   numbers 
  of 
  flowers 
  and 
  fruits 
  can 
  be 
  mentioned 
  

   as 
  illustrations. 
  One 
  fact 
  may 
  be 
  added 
  to 
  

   show 
  that 
  nearly 
  every 
  part 
  of 
  the 
  plant 
  must 
  

   have 
  the 
  power 
  of 
  producing 
  all 
  or 
  nearly 
  all 
  

   the 
  characters 
  of 
  the 
  individual 
  to 
  which 
  it 
  

   belongs. 
  This 
  proof 
  is 
  given 
  by 
  the 
  formation 
  

   of 
  adventitious 
  buds. 
  These, 
  when 
  once 
  

   formed, 
  may 
  grow 
  out 
  into 
  twigs, 
  with 
  leaves 
  

   and 
  flowers 
  and 
  roots. 
  They 
  may 
  even 
  be 
  sep- 
  

   arated 
  from 
  the 
  plants 
  and 
  used 
  as 
  cuttings 
  

   to 
  reproduce 
  the 
  whole. 
  Hence 
  we 
  may 
  

   conclude 
  that 
  all 
  tissues, 
  which 
  possess 
  the 
  

   power 
  of 
  producing 
  adventitious 
  buds, 
  must 
  

   conceal 
  in 
  a 
  latent 
  state, 
  all 
  the 
  numerous 
  char- 
  

   acters 
  required 
  for 
  the 
  full 
  development 
  of 
  the 
  

   whole 
  individual. 
  

  

  Adventitious 
  buds 
  may 
  proceed 
  from 
  spe- 
  

   cialized 
  cells, 
  as 
  on 
  the 
  margin 
  of 
  the 
  leaves 
  of 
  

   Bryophyllum 
  calycinum; 
  or 
  from 
  the 
  cells 
  of 
  

   special 
  tissues, 
  as 
  in 
  the 
  epidermis 
  of 
  the 
  be- 
  

   gonias; 
  or 
  they 
  may 
  be 
  provoked 
  by 
  wounds 
  

   in 
  nearly 
  every 
  part 
  of 
  the 
  plant, 
  provided 
  it 
  

   be 
  able 
  to 
  heal 
  the 
  wound 
  by 
  swelling 
  tissues 
  or 
  

  

  