﻿86 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  Desert 
  plants, 
  or 
  those 
  which 
  for 
  any 
  reason 
  may 
  often 
  be 
  

   expose 
  1 
  to 
  intensely 
  hot, 
  dry 
  ah-, 
  are 
  safer 
  without 
  large 
  ah- 
  cavi- 
  

   ties 
  anywhere 
  hi 
  the 
  interior 
  of 
  the 
  plant, 
  but 
  stored 
  water 
  is 
  of 
  

   the 
  greatest 
  use 
  to 
  such 
  plants, 
  and 
  it 
  may 
  be 
  found 
  in 
  the 
  

   roots 
  (fig. 
  20), 
  in 
  the 
  stem 
  (fig. 
  66), 
  or 
  in 
  the 
  leaves 
  (fig. 
  65). 
  

   84. 
  Characteristics 
  of 
  underground 
  stems. 
  The 
  popular 
  

   notion 
  of 
  a 
  stem 
  includes 
  the 
  idea 
  that 
  it 
  is 
  an 
  aerial 
  part 
  of 
  

  

  the 
  plant. 
  It 
  is 
  easier 
  to 
  recog- 
  

   1 
  1 
  i/. 
  e 
  as 
  roots 
  such 
  structures 
  as 
  

   the 
  a 
  ^ 
  r 
  i 
  a 
  l 
  ro 
  ts 
  of 
  corn 
  and 
  of 
  

  

  \// 
  /\cniBk 
  poison 
  ivy 
  than 
  it 
  is 
  to 
  recog- 
  

  

  X\\ 
  TW^t 
  

   x 
  ^ 
  A 
  nize 
  as 
  stems 
  the 
  thickened 
  

  

  underground 
  portions 
  of 
  iris, 
  

   jaek-in-the-pulpit, 
  dragon-root, 
  trillium, 
  

   or 
  potato. 
  Frequently, 
  like 
  aerial 
  steins, 
  

   underground 
  stems 
  are 
  divided 
  into 
  

   nodes 
  and 
  internodes; 
  many 
  of 
  them 
  

   bear 
  scales 
  which 
  represent 
  leaves, 
  and 
  

   in 
  the 
  axils 
  of 
  these 
  scales 
  they 
  produce 
  

  

  5t, 
  2 
  

  

  FIG. 
  69. 
  A 
  May-apple 
  plant, 
  showing 
  the 
  history 
  of 
  the 
  rootstock 
  

  

  7 
  is 
  the 
  oldest 
  surviving 
  portion 
  of 
  the 
  rootstock; 
  2 
  is 
  a 
  year 
  younger; 
  .? 
  a 
  y'iir 
  

   younger 
  than 
  2, 
  and 
  so 
  on. 
  At 
  each 
  figure 
  the 
  cluster 
  of 
  roots 
  marks 
  the 
  position 
  

   of 
  the 
  hase 
  of 
  the 
  upright 
  stem 
  for 
  that 
  year, 
  as 
  is 
  shown 
  at 
  6. 
  b, 
  bud 
  for 
  the 
  new 
  

   year's 
  growth; 
  br, 
  bract 
  at 
  the 
  base 
  of 
  the 
  present 
  stem. 
  One 
  sixth 
  natural 
  size 
  

  

  buds. 
  Such 
  buds 
  are 
  w'ell 
  shown 
  in 
  the 
  underground 
  stems 
  

   of 
  some 
  grasses. 
  Dicotyledonous 
  underground 
  stems 
  usually 
  

   have 
  distinct 
  bark, 
  wood, 
  and 
  pith; 
  most 
  dicotyledonous 
  roots 
  

   do 
  not 
  have 
  pith, 
  though 
  some 
  do. 
  

  

  Some 
  of 
  the 
  principal 
  forms 
  of 
  underground 
  stems 
  have 
  for 
  

   convenience 
  been 
  given 
  special 
  names. 
  The 
  elongated 
  forms, 
  

  

  