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  smallest 
  portion 
  of 
  this 
  doughy 
  mass 
  under 
  a 
  compound 
  microscope 
  

   we 
  will 
  find 
  it 
  not 
  merely 
  slime 
  but 
  a 
  highly 
  organized 
  tissue 
  made 
  

   up 
  of 
  countless 
  minute 
  cells, 
  each 
  with 
  a 
  delicate 
  wall 
  about 
  it 
  and 
  

   containing 
  a 
  thickish 
  liquid 
  (protoplasm). 
  The 
  cambium 
  cells 
  are 
  

   brick-shaped, 
  and 
  are 
  placed 
  end 
  to 
  end, 
  with 
  layer 
  overlapping 
  

   layer, 
  like 
  bricks 
  in 
  the 
  wall 
  of 
  a 
  building. 
  The 
  microscopic 
  struc- 
  

   ture 
  of 
  cambium 
  tissue 
  gives 
  us 
  a 
  clearer 
  conception 
  of 
  its 
  extreme 
  

   delicacy. 
  It 
  is 
  one 
  of 
  the 
  most 
  sensitive 
  and 
  delicate 
  substances 
  in 
  

   all 
  nature. 
  Exposure 
  to 
  the 
  air 
  will 
  kill 
  it 
  and 
  completely 
  destroy 
  

   its 
  functions 
  in 
  a 
  few 
  seconds. 
  It 
  is 
  easily 
  crushed 
  by 
  slight 
  pres- 
  

   sure 
  and 
  quickly 
  killed 
  by 
  exposure 
  to 
  drying, 
  frost, 
  moisture 
  and 
  

   sunlight. 
  Nature 
  shows 
  her 
  extreme 
  care 
  of 
  it 
  for 
  in 
  making 
  bark 
  

   she 
  has 
  formed 
  for 
  the 
  delicate 
  cambium 
  a 
  perfect 
  protective 
  cover- 
  

   ing. 
  Like 
  the 
  cambium 
  the 
  bark 
  is 
  composed 
  of 
  cells, 
  as 
  in 
  fact 
  are 
  

   all 
  animal 
  and 
  vegetable 
  structures. 
  But 
  the 
  cells 
  of 
  the 
  bark 
  have 
  

   thick 
  walls 
  of 
  a 
  tough, 
  corky 
  substance, 
  and 
  each 
  cell 
  contains 
  air 
  

   instead 
  of 
  protoplasm. 
  The 
  corkiness 
  of 
  the 
  bark 
  makes 
  it 
  an 
  im- 
  

   pervious, 
  waterproof 
  covering 
  that 
  does 
  not 
  allow 
  the 
  cambium 
  to 
  

   be 
  dried 
  out 
  or 
  to 
  be 
  washed 
  by 
  external 
  moisture. 
  The 
  air 
  in 
  the 
  

   bark 
  cells 
  being 
  in 
  a 
  still 
  condition 
  is 
  a 
  non-conductor 
  of 
  heat, 
  and 
  

   layer 
  of 
  bark 
  overlapping 
  layer, 
  the 
  cambium 
  is 
  completely 
  covered 
  

   with 
  a 
  dead-air 
  blanket. 
  This 
  keeps 
  it 
  from 
  being 
  frozen 
  in 
  winter 
  

   and 
  from 
  being 
  overheated 
  in 
  summer, 
  just 
  as 
  a 
  dead-air 
  space 
  in 
  

   the 
  walls 
  of 
  a 
  building 
  protects 
  from 
  extremes 
  of 
  heat 
  and 
  cold. 
  

   From 
  this 
  it 
  is 
  plain 
  that 
  nature 
  takes 
  great 
  pains 
  to 
  cover 
  and 
  pro- 
  

   tect 
  the 
  delicate 
  cambium 
  from 
  all 
  external 
  influences. 
  This 
  stands 
  

   in 
  striking 
  contrast 
  to 
  the 
  careless 
  manner 
  in 
  which 
  many 
  propa- 
  

   gators 
  and 
  planters 
  handle 
  the 
  delicate 
  parts 
  of 
  trees. 
  It 
  also 
  

   explains 
  why 
  some 
  budders 
  get 
  such 
  a 
  small 
  percentage 
  of 
  living 
  

   buds 
  and 
  some 
  planters 
  so 
  few 
  living 
  trees. 
  

  

  Cambium 
  is 
  the 
  building 
  material 
  of 
  plants 
  and 
  without 
  it 
  growth 
  

   is 
  impossible. 
  It 
  covers 
  every 
  portion 
  of 
  the 
  tree 
  from 
  the 
  topmost 
  

   terminal 
  bud 
  to 
  the 
  deepest 
  root 
  tip 
  like 
  a 
  living 
  blanket. 
  During 
  

   the 
  growing 
  season 
  the 
  cambium 
  cells 
  divide 
  lengthwise 
  forming 
  

   new 
  cells. 
  These 
  divide 
  again 
  and 
  grow, 
  and 
  new 
  cells 
  are 
  formed, 
  

   until 
  by 
  fall 
  a 
  complete 
  mantle 
  of 
  bark 
  covers 
  the 
  outer 
  surface 
  of 
  

   the 
  cambium, 
  while 
  within 
  it 
  has 
  built 
  up 
  a 
  solid 
  layer 
  of 
  the 
  woody 
  

   structure 
  of 
  the 
  tree. 
  A 
  few 
  rows 
  of 
  cambium 
  cells 
  are 
  left 
  in 
  an 
  

   embryonic 
  condition 
  to 
  carry 
  on 
  growth 
  the 
  following 
  year. 
  The 
  

   cambium 
  is 
  thus 
  the 
  only 
  tissue 
  of 
  the 
  tree 
  that 
  retains 
  from 
  year 
  

   to 
  year 
  the 
  power 
  of 
  active 
  growth. 
  The 
  layers 
  of 
  wood 
  and 
  bark, 
  

   after 
  performing 
  their 
  functions 
  for 
  a 
  few 
  seasons, 
  gradually 
  die 
  

  

  