﻿THE 
  STEM 
  AND 
  THE 
  LEAF 
  

  

  63 
  

  

  ep 
  

  

  cort 
  

  

  sh 
  

  

  groups 
  : 
  one 
  with 
  no 
  continuous 
  woody 
  cylinder, 
  like 
  the 
  stem 
  

   of 
  such 
  a 
  climber 
  as 
  the 
  Dutchman's-pipe 
  (fig. 
  42, 
  A), 
  and 
  one 
  

   with 
  a 
  continuous 
  woody 
  cylinder, 
  like 
  that 
  of 
  the 
  sunflower 
  

   (fig. 
  42, 
  2?). 
  The 
  real 
  difference 
  between 
  the 
  two 
  kinds 
  of 
  stem 
  

   is 
  that, 
  like 
  -most 
  climbers, 
  the 
  stem 
  of 
  the 
  Dutchman's-pipe 
  

   begins 
  the 
  season's 
  growth 
  with 
  a 
  set 
  of 
  separate 
  fibrovascular 
  

   bundles 
  which 
  remain 
  separate, 
  while 
  in 
  the 
  sunflower 
  the 
  

   bundles 
  are 
  at 
  first 
  sepa- 
  

   rate 
  but 
  soon 
  join 
  each 
  other. 
  

   The 
  boundary 
  between 
  bark 
  

   and 
  wood 
  is 
  a 
  layer 
  of 
  thin- 
  

   walled 
  cells 
  (c, 
  fig. 
  42, 
  A), 
  

   the 
  cambium 
  lai/cr. 
  It 
  is 
  

   this 
  cambium, 
  its 
  cells 
  filled 
  

   with 
  mucilaginous 
  proto- 
  

   plasm, 
  that 
  makes 
  up 
  the 
  

   slimy 
  layer 
  just 
  outside 
  

   the 
  wood, 
  from 
  which 
  the 
  

   bark 
  peels 
  so 
  readily 
  in 
  

   early 
  spring, 
  when 
  boys 
  are 
  

   making 
  whistles 
  or 
  strip- 
  

   ping 
  off 
  sheets 
  of 
  slippery- 
  

   elm 
  bark. 
  It 
  is 
  important 
  

   to 
  notice 
  that 
  each 
  fibro- 
  

   vascular 
  bundle 
  consists 
  of 
  

   an 
  outer 
  portion, 
  o, 
  which 
  belongs 
  to 
  the 
  bark, 
  and 
  an 
  inner 
  

   portion, 
  w, 
  which 
  belongs 
  to 
  the 
  wood. 
  

  

  A 
  much 
  better 
  idea 
  of 
  the 
  details 
  of 
  structure 
  of 
  the 
  several 
  

   regions 
  of 
  the 
  stem 
  can 
  be 
  gained 
  from 
  a 
  lengthwise 
  section, 
  

   like 
  that 
  shown 
  in 
  figure 
  43, 
  than 
  from 
  cross 
  sections, 
  like 
  

   those 
  of 
  figure 
  42. 
  1 
  The 
  uses 
  of 
  some 
  of 
  the 
  parts 
  shown 
  

   in 
  figure 
  43 
  are 
  briefly 
  stated 
  on 
  the 
  following 
  page. 
  

  

  1 
  Since 
  the 
  type 
  of 
  stem 
  structure 
  shown 
  in 
  figure 
  43 
  is 
  not 
  exactly 
  like 
  

   that 
  of 
  the 
  other 
  two 
  figures, 
  it 
  will 
  not 
  be 
  possible 
  to 
  identify 
  all 
  the 
  kinds 
  

   of 
  cells 
  shown 
  in 
  figure 
  43 
  with 
  those 
  of 
  the 
  other 
  two. 
  Note 
  especially 
  that 
  

   in 
  figure 
  43 
  the 
  cambium 
  is 
  not 
  readily 
  distinguished 
  from 
  the 
  overlying 
  

   tissues, 
  and 
  that 
  no 
  distinct 
  layer 
  of 
  heavy-walled 
  bast 
  fibers 
  is 
  found. 
  

  

  FIG. 
  43. 
  Lengthwise 
  section 
  of 
  a 
  young 
  

   dicotyledonous 
  stem 
  

  

  ep, 
  epidermis 
  ; 
  cort, 
  cortex 
  ; 
  b, 
  liast; 
  v, 
  ves- 
  

   sels; 
  sh, 
  sheath 
  surrounding 
  pith; 
  p, 
  pith; 
  

   si, 
  sieve 
  cells 
  of 
  the 
  hast. 
  Magnified 
  ahout 
  

   90 
  diameters. 
  After 
  Bonnier 
  and 
  Sablon 
  

  

  