﻿62 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  60. 
  Internal 
  structure 
  of 
  the 
  young 
  dicotyledonous 
  stem. 
  1 
  It 
  

   is 
  a 
  difficult 
  process, 
  involving 
  much 
  careful 
  work 
  with 
  the 
  

   microscope, 
  to 
  trace 
  the 
  earliest 
  steps 
  in 
  the 
  development 
  of 
  

   stem 
  structure 
  in 
  the 
  seedling 
  plant, 
  It 
  is 
  therefore 
  better, 
  

   for 
  our 
  purpose, 
  to 
  begin 
  with 
  the 
  study 
  of 
  the 
  stem 
  ;it 
  the 
  

  

  end 
  of 
  the 
  first 
  season's 
  growth. 
  

  

  In 
  early 
  spring, 
  before 
  the 
  buds 
  

   begin 
  to 
  open, 
  a 
  twig 
  of 
  willow, 
  

   alder, 
  or 
  hickory 
  is 
  readily 
  stripped 
  

   of 
  its 
  bark. 
  When 
  split 
  through 
  the 
  

   middle 
  it 
  shows 
  a 
  hollow 
  cylinder 
  

  

  e 
  b 
  c 
  p 
  

  

  A 
  

  

  Fir,. 
  42, 
  A. 
  Diagrammatic 
  cross 
  

   section 
  of 
  one 
  quarter 
  of 
  a 
  one- 
  

   year-old 
  stem 
  of 
  Dutchman's- 
  

   pipe 
  (Arifitolochia) 
  

  

  e, 
  region 
  of 
  epidermis 
  ; 
  h, 
  hard 
  hast; 
  

   o, 
  outer, 
  or 
  hark, 
  part 
  of 
  a 
  bundle 
  

   (the 
  cellular 
  portion 
  under 
  the 
  let- 
  

   ter) 
  ; 
  to, 
  inner, 
  or 
  woody, 
  part 
  of 
  bun- 
  

   dle 
  ; 
  c, 
  cambium 
  layer 
  ; 
  ]>, 
  region 
  of 
  

   pith; 
  in, 
  medullary 
  ray. 
  The 
  space 
  

   between 
  the 
  hard 
  bast 
  and 
  the 
  

   bundles 
  is 
  occupied 
  by 
  thin-walled, 
  

   somewhat 
  cubical 
  cells 
  of 
  the 
  bark. 
  

   Magnified 
  about 
  l.~> 
  diameters 
  

  

  D 
  

  

  FIG. 
  42, 
  7>. 
  Diagrammatic 
  cross 
  sec- 
  

   tion 
  of 
  one 
  quarter 
  of 
  a 
  sunflower 
  stem 
  

  

  /<, 
  pith 
  ; 
  /;, 
  woody, 
  or 
  tihrovasciilar, 
  bun- 
  

   dles: 
  (\ 
  epidermis: 
  ', 
  bundles 
  of 
  ha 
  rd-bast 
  

   tibers 
  of 
  the 
  bark. 
  Somewhat 
  magnified 
  

  

  of 
  wood 
  inclosing 
  the 
  cylindrical 
  pith. 
  These 
  structural 
  con- 
  

   stituents 
  - 
  - 
  bark, 
  wood, 
  and 
  pith 
  - 
  - 
  make 
  up 
  almost 
  the 
  ent 
  ire 
  

   bulk 
  of 
  the 
  stem. 
  

  

  Examined 
  in 
  section 
  by 
  the 
  aid 
  of 
  a 
  good 
  lens, 
  young 
  dicoty- 
  

   ledonous 
  stems 
  are 
  readily 
  seen 
  to 
  be 
  classifiable 
  into 
  two 
  

  

  1 
  See 
  also 
  sections 
  (11 
  (i">. 
  The 
  steins 
  of 
  many 
  .iryinnospernis- 
  fur 
  example, 
  

   trees 
  of 
  the 
  Pino 
  family 
  in 
  their 
  general 
  structure 
  much 
  resemble 
  the 
  

   dicotyledonous 
  stems. 
  For 
  a 
  general 
  account 
  of 
  the 
  stem 
  structure 
  of 
  dicoty- 
  

   ledons 
  and 
  monocotyledons 
  sec 
  Coulter, 
  Barnes, 
  and 
  Cowles's 
  ''Textbook 
  

   of 
  Botany," 
  Chap, 
  iv, 
  A. 
  ANGIOSTERMS. 
  

  

  