﻿MOSSES, 
  LIVERWORTS, 
  AND 
  FERNS 
  

  

  273 
  

  

  The 
  epidermis 
  of 
  the 
  leaf 
  is 
  quite 
  different 
  from 
  anything 
  

   seen 
  in 
  the 
  liverworts 
  or 
  mosses. 
  When 
  examined 
  with 
  the 
  

   microscope, 
  it 
  is 
  seen 
  to 
  consist 
  of 
  a 
  single 
  layer 
  of 
  cells, 
  

   whose 
  irregular 
  walls 
  fit 
  into 
  one 
  another 
  quite 
  closely. 
  

   In 
  the 
  lower 
  epidermis, 
  rarely 
  in 
  the 
  upper, 
  are 
  the 
  stomata 
  

   (sect. 
  33). 
  In 
  a 
  transverse 
  section 
  of 
  the 
  leaf 
  (fig. 
  210) 
  the 
  

   other 
  leaf 
  tissues 
  are 
  seen. 
  They 
  are 
  the 
  veins 
  (which 
  appear 
  

  

  FIG. 
  211. 
  Opening 
  (vernation) 
  of 
  the 
  leaves 
  of 
  Clayton's 
  fern 
  

   A 
  skunk-cabbage 
  plant 
  stands 
  in 
  front 
  of 
  the 
  ferns 
  

  

  in 
  cross 
  section 
  as 
  bundles 
  of 
  very 
  small, 
  heavy-walled 
  cells), 
  

   the 
  chlorophyll-bearing 
  cells, 
  and 
  the 
  sporangia. 
  Between 
  the 
  

   chlorophyll-bearing 
  cells 
  there 
  are 
  many 
  air 
  spaces. 
  

  

  258. 
  Fern 
  sporangia. 
  On 
  the 
  undersides 
  of 
  most 
  fern 
  leaves 
  

   the 
  sporangia 
  appear 
  from 
  time 
  to 
  time 
  (fig. 
  210). 
  An 
  entire 
  

   group 
  of 
  sporangia 
  is 
  called 
  a 
  soms. 
  The 
  sorus 
  is 
  usually 
  par- 
  

   tially 
  or 
  entirely 
  covered 
  by 
  an 
  outgrowth 
  of 
  the 
  leaf 
  known 
  

   as 
  the 
  inchtsium. 
  The 
  position 
  of 
  the 
  sori 
  (plural 
  of 
  sonts) 
  

   and 
  the 
  nature 
  of 
  the 
  indusium 
  Y 
  ai 
  T 
  widely 
  in 
  different 
  ferns 
  

  

  