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  currence 
  of 
  negative 
  ones. 
  Indeed, 
  if 
  we 
  put 
  

   aside 
  the 
  radiate 
  and 
  the 
  color-varieties 
  of 
  

   flowers 
  and 
  foliage, 
  hardly 
  any 
  cases 
  can 
  be 
  

   cited. 
  We 
  have 
  dealt 
  with 
  this 
  question 
  in 
  a 
  

   former 
  lecture, 
  and 
  may 
  now 
  limit 
  ourselves 
  to 
  

   the 
  positive 
  color- 
  varieties. 
  

  

  The 
  latency 
  of 
  the 
  faculty 
  of 
  producing 
  the 
  

   red 
  pigment 
  in 
  leaves 
  must 
  obviously 
  be 
  ac- 
  

   cepted 
  for 
  nearly 
  the 
  whole 
  vegetable 
  kingdom. 
  

   Oaks 
  and 
  elms, 
  the 
  beautiful 
  climbing 
  species 
  

   of 
  Ampelopsis, 
  many 
  conifers, 
  as 
  for 
  instance 
  

   Cryptomeria 
  japonica, 
  some 
  brambles, 
  the 
  

   Guelder-rose 
  (Viburnum 
  Opulus) 
  and 
  many 
  

   other 
  trees 
  and 
  shrubs 
  assume 
  a 
  more 
  or 
  less 
  

   bright 
  red 
  color 
  in 
  the 
  fall. 
  During 
  summer 
  

   this 
  tendency 
  must 
  have 
  been 
  dormant, 
  and 
  that 
  

   this 
  is 
  so, 
  is 
  shown 
  by 
  the 
  young 
  leaves 
  of 
  oaks 
  

   and 
  others, 
  which, 
  when 
  unfolding 
  in 
  the 
  spring 
  

   show 
  a 
  similar 
  but 
  paler 
  hue. 
  Moreover, 
  there 
  

   is 
  a 
  way 
  of 
  awakening 
  the 
  concealed 
  powers 
  at 
  

   any 
  time. 
  We 
  have 
  only 
  to 
  inflict 
  small 
  wounds 
  

   on 
  the 
  leaves, 
  or 
  to 
  cut 
  through 
  the 
  nerves 
  or 
  to 
  

   injure 
  them 
  by 
  a 
  slight 
  bruising, 
  and 
  the 
  leaves 
  

   frequently 
  respond 
  with 
  an 
  intense 
  reddening 
  of 
  

   the 
  living 
  tissues 
  around 
  and 
  especially 
  above 
  

   the 
  wounds. 
  Azolla 
  caroliniana, 
  a 
  minute 
  moss- 
  

   like 
  floating 
  plant 
  allied 
  to 
  the 
  ferns, 
  responds 
  

   to 
  light 
  and 
  cold 
  with 
  a 
  reddish 
  tinge, 
  and 
  to 
  

   shade 
  or 
  warmth 
  with 
  a 
  pure 
  green. 
  The 
  foli- 
  

  

  