﻿10G 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  In 
  tree-like 
  monocotyledons 
  the 
  leaves 
  are 
  not 
  shed 
  as 
  they 
  

  

  are 
  hv 
  the 
  common 
  trees 
  of 
  temperate 
  climates. 
  Frequently 
  

   the 
  leaves 
  persist 
  tor 
  years 
  but 
  finally 
  decay 
  and 
  leave 
  the 
  

   trunk 
  of 
  tin- 
  tree 
  covered 
  with 
  a 
  rough 
  coating 
  formed 
  by 
  

   the 
  persistent 
  liases 
  of 
  the 
  leafstalks, 
  as 
  is 
  the 
  case 
  with 
  the 
  

   date 
  palm 
  and 
  many 
  other 
  kinds 
  of 
  palms. 
  

  

  99. 
  Lenticels. 
  Alonu' 
  the 
  twi^s 
  and 
  vounger 
  branches 
  of 
  

  

  o 
  o 
  / 
  o 
  

  

  most 
  trees 
  and 
  shrubs 
  there 
  are 
  found 
  many 
  dots 
  or 
  larger 
  

   areas 
  of 
  rough, 
  spongy 
  bark. 
  These 
  are 
  called 
  lfntii-i'1*. 
  They 
  

   are 
  especially 
  distinct 
  on 
  the 
  bark 
  of 
  most 
  birches 
  and 
  cherry 
  

   trees, 
  and 
  in 
  these 
  finally 
  reach 
  a 
  rather 
  large 
  size. 
  Each 
  len- 
  

   ticel 
  covers 
  the 
  position 
  originally 
  occupied 
  by 
  a 
  stoma 
  in 
  the 
  

   epidermis 
  of 
  the 
  very 
  voung 
  bark. 
  As 
  the 
  stoma 
  grew 
  older 
  

   its 
  characteristic 
  cells 
  disappeared 
  and 
  were 
  replaced 
  by 
  a 
  

   spongy 
  mass 
  of 
  thin-walled 
  cells. 
  The 
  lenticels 
  serve 
  for 
  the 
  

   entrance 
  of 
  gases 
  into 
  the 
  stem 
  and 
  for 
  their 
  passage 
  out 
  of 
  it, 
  

   and 
  the 
  respiration 
  of 
  the 
  stem 
  is 
  considerably 
  aided 
  by 
  the 
  

   readiness 
  with 
  which 
  an 
  exchange 
  of 
  gases 
  goes 
  on 
  through 
  

   these 
  porous 
  spots. 
  

  

  