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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  The 
  well-protected 
  chlorophyll 
  tissue 
  is 
  able 
  to 
  withstand 
  

   severe 
  cold 
  and 
  drought, 
  and 
  lives 
  through 
  periods 
  that 
  would 
  

   kill 
  deciduous 
  leaves. 
  The 
  amount 
  of 
  leaf 
  surface 
  is 
  compara- 
  

   tively 
  small, 
  but 
  pine 
  leaves 
  probably 
  begin 
  their 
  work 
  earlier 
  

   in 
  the 
  season 
  than 
  deciduous 
  leaves 
  do, 
  and 
  continue 
  their 
  

   work 
  later. 
  

  

  270. 
  New 
  leaves 
  and 
  branches. 
  When 
  the 
  growth 
  buds 
  open 
  

   in 
  the 
  spring, 
  the 
  branch 
  extends, 
  the 
  ne\v 
  needle 
  leaves 
  begin 
  

   to 
  elongate 
  (fig. 
  220), 
  and 
  within 
  a 
  few 
  weeks 
  the 
  leaves 
  reach 
  

   their 
  full 
  si/.e. 
  This 
  new 
  gro\\th 
  was 
  started 
  in 
  the 
  preceding 
  

   summer 
  and 
  autumn, 
  so 
  that 
  within 
  the 
  bud 
  during 
  the 
  winter 
  

   there 
  were 
  the 
  very 
  small 
  stem 
  and 
  leaves 
  of 
  the 
  next 
  spring's 
  

   growth. 
  The 
  scales 
  from 
  the 
  growth 
  buds 
  fall 
  away 
  and 
  leave 
  

   scars, 
  by 
  means 
  of 
  which 
  the 
  former 
  position 
  of 
  the 
  end 
  of 
  the 
  

   stem 
  may 
  be 
  located. 
  Also, 
  by 
  observing 
  these 
  bud 
  scars 
  from 
  

   the 
  tip 
  to 
  older 
  portions 
  of 
  the 
  branch, 
  the 
  age 
  of 
  the 
  branch 
  

   and 
  the 
  rate 
  of 
  elongation 
  may 
  be 
  determined. 
  

  

  271. 
  The 
  branch 
  and 
  stem. 
  From 
  transverse 
  sections 
  of 
  

   branches 
  and 
  stems 
  of 
  different 
  ages 
  their 
  general 
  structure 
  

   may 
  be 
  observed. 
  1 
  Innermost 
  is 
  a 
  small 
  pith 
  region, 
  which 
  in 
  

   older 
  stems 
  is 
  compressed 
  until 
  it 
  is 
  not 
  usually 
  noticeable. 
  

   Around 
  this 
  is 
  the 
  woody 
  tissue 
  (r//A'm) 
  of 
  the 
  fibrovascular 
  

   bundles. 
  The 
  woody 
  tissues 
  are 
  joined 
  together 
  in 
  such 
  a 
  

   way 
  as 
  to 
  form 
  a 
  solid 
  woody 
  cylinder. 
  It 
  is 
  possible 
  to 
  de- 
  

   termine 
  the 
  age 
  of 
  the 
  twig 
  approximately 
  by 
  counting 
  the 
  

   layers 
  or 
  rings 
  of 
  wood, 
  except 
  when 
  two 
  or 
  more 
  distinct 
  

   growth 
  periods 
  occur 
  in 
  the 
  same 
  season. 
  In 
  such 
  cases 
  more 
  

   than 
  one 
  ring 
  would 
  be 
  formed 
  in 
  the 
  same 
  year. 
  At 
  the 
  outer 
  

   edge 
  of 
  the 
  woody 
  tissue 
  is 
  a 
  thin 
  layer 
  of 
  cells 
  (<'iiil>hnii) 
  

   which 
  separates 
  the 
  woody 
  tissue 
  < 
  .////,///) 
  from 
  the 
  outer 
  tissue 
  

   (jphHo&m). 
  The 
  cambium 
  is 
  actively 
  growing 
  tissue 
  which 
  pro- 
  

   duces 
  new 
  wood 
  within 
  and 
  new 
  phloem 
  without. 
  The 
  tissues 
  

   outside 
  the 
  phloem 
  which 
  we 
  need 
  to 
  notice 
  are 
  the 
  green 
  bark 
  

   and 
  the 
  dead 
  bark. 
  Dead 
  bark 
  is 
  constantly 
  being 
  formed 
  from 
  

   the 
  green 
  bark 
  within. 
  This 
  results 
  in 
  making 
  the 
  dead 
  bark 
  

  

  1 
  A. 
  hand 
  li'iis 
  will 
  enable 
  students 
  to 
  observe 
  these 
  regions 
  of 
  the 
  sU-m. 
  

  

  