﻿CHAPTER 
  VI 
  

  

  SPECIAL 
  FUNCTIONS 
  AND 
  FORMS 
  OF 
  STEMS 
  

  

  82. 
  Stems 
  not 
  always 
  for 
  the 
  support 
  of 
  leaves. 
  In 
  Chap- 
  

   ter 
  V 
  considerable 
  space 
  was 
  given 
  to 
  explanations 
  of 
  some 
  of 
  

   the 
  ways 
  in 
  which 
  stems 
  serve 
  to 
  support 
  leaves 
  in 
  advan- 
  

   tageous 
  positions 
  for 
  photosynthetic 
  work. 
  This 
  is 
  not, 
  how- 
  

   ever, 
  by 
  any 
  means 
  the 
  only 
  function 
  of 
  the 
  stem 
  or 
  portions 
  

   of 
  the 
  stem. 
  Something 
  was 
  said 
  in 
  Chapter 
  IV 
  about 
  the 
  

   importance 
  of 
  food 
  storage 
  

  

  in 
  stems, 
  and 
  something 
  in 
  

   section 
  56 
  about 
  their 
  work 
  

   of 
  photosynthesis. 
  Some 
  

   other 
  important 
  things 
  done 
  

   by 
  whole 
  stems, 
  or 
  by 
  more 
  

   or 
  less 
  highly 
  specialized 
  

   portions 
  of 
  them, 
  will 
  be 
  

   discussed 
  in 
  the 
  present 
  

   chapter. 
  

  

  83. 
  Storage 
  of 
  air 
  or 
  

  

  water 
  in 
  the 
  stem. 
  It 
  sel- 
  FlG 
  - 
  8 
  - 
  Cross 
  section 
  of 
  stem 
  of 
  P 
  nd 
  - 
  

  

  weed 
  (Fotamoyeton), 
  showing 
  air 
  passages 
  

   dom 
  happens 
  that 
  the 
  same 
  

  

  a, 
  much 
  magnified. 
  After 
  Green 
  

  

  plant 
  would 
  be 
  benefited 
  

  

  by 
  storing 
  both 
  air 
  and 
  water 
  abundantly 
  in 
  its 
  roots 
  or 
  stems 
  ; 
  

   but 
  marsh 
  and 
  water 
  plants 
  may 
  evidently 
  be 
  much 
  aided 
  in 
  

   their 
  respiration 
  by 
  holding 
  a 
  good 
  deal 
  of 
  air 
  inside 
  the 
  plant 
  

   body. 
  In 
  some 
  such 
  plants 
  the 
  air 
  passages 
  and 
  air 
  cavities 
  

   form 
  a 
  complex 
  system, 
  which 
  extends 
  all 
  the 
  way 
  from 
  the 
  

   stomata 
  to 
  the 
  tips 
  of 
  the 
  roots. 
  A 
  section 
  across 
  the 
  stem 
  of 
  

   any 
  of 
  the 
  common 
  pondweeds 
  (Potamogetori) 
  (fig. 
  68) 
  shows 
  

   clearly 
  how 
  large 
  and 
  abundant 
  its 
  ah? 
  passages 
  are. 
  

  

  85 
  

  

  