﻿THE 
  SEED 
  PLANTS 
  

  

  285 
  

  

  cells 
  (the 
  strengthening 
  cells). 
  Other 
  parts 
  of 
  the 
  leaf 
  are 
  the 
  

   stomata, 
  which 
  are 
  deeply 
  placed 
  in 
  the 
  epidermis 
  and 
  arc 
  often 
  

   so 
  clogged 
  with 
  dust 
  that 
  they 
  are 
  quite 
  dark 
  in 
  appearance 
  ; 
  

  

  --sci 
  

  

  rd 
  

  

  FIG. 
  221. 
  Part 
  of 
  a 
  cross 
  section 
  of 
  a 
  pine 
  leaf 
  

  

  The 
  epidermis 
  (ep) 
  , 
  upon 
  which 
  is 
  a 
  layer 
  of 
  cuticle 
  ; 
  a 
  layer 
  of 
  heavy-walled 
  cells, 
  

   or 
  sclerenchyma 
  (scl) 
  ; 
  stomata 
  with 
  deeply 
  placed 
  guard 
  cells 
  (st) 
  ; 
  chlorophyll- 
  

   bearing 
  tissue 
  (chl) 
  ; 
  resin 
  ducts, 
  or 
  channels 
  (rd) 
  ; 
  bundle 
  sheath 
  (bsh), 
  which 
  in- 
  

   closes 
  two 
  vascular 
  bundles 
  (vb). 
  Greatly 
  magnified 
  

  

  the 
  chlorophyll 
  tissue, 
  through 
  which 
  run 
  the 
  resin 
  ducts 
  ; 
  the 
  

   pith 
  region, 
  through 
  which 
  run 
  two 
  groups 
  of 
  fibrovascular 
  

   bundles, 
  but 
  one 
  of 
  which 
  is 
  shown 
  hi 
  the 
  figure. 
  

  

  