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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  Although 
  usually 
  grayish 
  green 
  in 
  color, 
  some 
  of 
  the 
  lichens 
  are 
  

   yellow, 
  red, 
  brown, 
  or 
  even 
  black. 
  Lichens 
  can 
  endure 
  severe 
  

   drought, 
  cold, 
  and 
  prolonged 
  exposure 
  to 
  intense 
  light 
  and 
  to 
  

   strong 
  winds 
  ; 
  hence 
  it 
  is 
  evident 
  that 
  they 
  can 
  live 
  under 
  con- 
  

   ditions 
  which 
  would 
  be 
  destructive 
  to 
  most 
  kinds 
  of 
  plants. 
  

  

  On 
  account! 
  if 
  this 
  

   ability 
  to 
  undergo 
  

   severe 
  conditions, 
  

   lichens 
  are 
  found 
  

   at 
  as 
  great 
  altitudes 
  

  

  O 
  

  

  and 
  throughout 
  

   as 
  great 
  a 
  range 
  

   north 
  and 
  south 
  

   as 
  are 
  any 
  plants. 
  

   They 
  may 
  remain 
  

   dormant 
  through 
  

   long 
  periods 
  of 
  un- 
  

   favorable 
  weather 
  

   and, 
  when 
  favora- 
  

   ble 
  moisture 
  and 
  

   temperature 
  return, 
  

   FIG. 
  103. 
  A 
  common 
  lichen 
  (1'nrtniHii) 
  upon 
  the 
  

  

  bark 
  of 
  the 
  shagbark 
  hickory 
  

  

  almost 
  immedi- 
  

   ately 
  assume 
  the 
  

  

  Note 
  the 
  expanded 
  and 
  flat 
  part 
  of 
  the 
  lichen, 
  also 
  the 
  greenish 
  appear- 
  

   cups 
  in 
  which 
  spores 
  of 
  the 
  fungus 
  part 
  of 
  the 
  lichen 
  

  

  are 
  formed 
  an< 
  ' 
  (> 
  which 
  llldl- 
  

  

  cates 
  their 
  renewed 
  

  

  activity. 
  The 
  lichen 
  known 
  as 
  reindeer 
  moss 
  is 
  brittle 
  and 
  

   pallid 
  when 
  dry, 
  but 
  when 
  moist, 
  it 
  is 
  green 
  and 
  soft. 
  

  

  Those 
  lichens 
  which 
  adhere 
  very 
  closely 
  to 
  their 
  support 
  

   and 
  are 
  scale-like 
  are 
  called 
  crustaceans; 
  those 
  that 
  adhere 
  less 
  

   closely 
  and 
  are 
  leaf-like 
  &YG 
  foliose 
  ; 
  and 
  those 
  thai 
  branch 
  and 
  

   are 
  partially 
  free 
  from 
  their 
  sub-stratum 
  are 
  frnticose. 
  Foliose 
  

   forms 
  are 
  common 
  upon 
  rougher-barked 
  lives 
  and 
  upon 
  old 
  

   fences, 
  crustaceous 
  forms 
  grow 
  upon 
  smooth-barked 
  trees 
  and 
  

   upon 
  stones, 
  while 
  fruticose 
  forms 
  grow 
  upon 
  the 
  ground 
  or 
  

   hang 
  from 
  branches 
  of 
  trees. 
  

  

  