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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  ...yc 
  

  

  needle 
  leaves 
  grow. 
  The 
  needle 
  leaves 
  are 
  really 
  continua- 
  

   tions 
  of 
  these 
  small 
  branches. 
  The 
  inward 
  faces 
  of 
  the 
  leaves 
  

   are 
  so 
  arranged 
  that 
  all 
  of 
  one 
  cluster, 
  when 
  put 
  together, 
  

   compose 
  a 
  cylindrical 
  leaf 
  mass. 
  That 
  is, 
  when 
  two 
  leaves 
  

   compose 
  the 
  cluster, 
  the 
  leaf 
  branch 
  is 
  divided 
  into 
  halves; 
  

   when 
  three 
  or 
  five 
  are 
  in 
  one 
  cluster, 
  the 
  branch 
  is 
  divided 
  

  

  into 
  three 
  or 
  five 
  parts. 
  

  

  Gymnosperms 
  are 
  chiefly 
  

   evergreen 
  (that 
  is, 
  keep 
  their 
  

   old 
  leaves 
  until 
  after 
  new 
  

   ones 
  have 
  come), 
  but 
  some 
  

   of 
  them, 
  as 
  the 
  larch, 
  or 
  

   tamarack, 
  and 
  the 
  bald 
  cy- 
  

   press, 
  are 
  deciduous 
  (that 
  

   is, 
  shed 
  their 
  old 
  leaves 
  

   before 
  the 
  appearance 
  of 
  

   the 
  new 
  ones). 
  The 
  periods 
  

   during 
  which 
  the 
  leaves 
  

   endure, 
  range 
  in 
  different 
  

   species 
  from 
  two 
  to 
  four 
  

   years. 
  By 
  determining 
  the 
  

   age 
  of 
  the 
  branches 
  through 
  

   FIG. 
  220. 
  A 
  branch 
  of 
  a 
  pine 
  a 
  study 
  of 
  the 
  yearly 
  bud 
  

  

  At 
  the 
  left 
  is 
  a 
  one-year-old 
  cone 
  (), 
  and 
  at 
  SCai'S 
  OIK' 
  may 
  readily 
  aSCCr- 
  

   the 
  tip 
  of 
  the 
  shoot 
  (.v) 
  a 
  very 
  youn^ 
  cone 
  

   (i/c) 
  just 
  open 
  and 
  ready 
  to 
  receive 
  pollen. 
  

   On 
  the 
  younii 
  shoot 
  are 
  the 
  voiuii,' 
  needle 
  

   leaves, 
  and 
  at 
  the 
  tip 
  is 
  the 
  hud 
  (In, 
  \\hich 
  

  

  continues 
  the 
  growth 
  of 
  the 
  stem 
  

  

  tain 
  how 
  long 
  the 
  leaves 
  

   last 
  on 
  any 
  pine 
  tree. 
  

  

  The 
  c 
  1 
  u 
  st 
  ers 
  of 
  pine 
  leaves 
  

   are 
  arranged 
  spirally 
  around 
  

   the 
  stem, 
  as 
  may 
  be 
  learned, 
  when 
  they 
  have 
  fallen, 
  by 
  an 
  

   examination 
  of 
  the 
  leaf 
  scars. 
  

  

  269. 
  Internal 
  structure 
  of 
  needle 
  leaves. 
  The 
  stiffness 
  of 
  

   pine 
  leaves 
  is 
  one 
  of 
  their 
  most 
  noticeable 
  features, 
  and 
  when 
  

   we 
  examine 
  a 
  cross 
  section, 
  we 
  are 
  able 
  to 
  locate 
  the 
  tissues 
  

   that 
  give 
  the 
  leaves 
  their 
  rigidity. 
  The 
  outer 
  layer 
  of 
  cells, 
  

   the 
  epidermic 
  (fig. 
  221), 
  has 
  an 
  extremely 
  heavy 
  covering, 
  the 
  

   cuticle; 
  beneath 
  the 
  epidermis 
  there 
  are 
  other 
  heavy-walled 
  

  

  