﻿THE 
  STEM 
  AND 
  THE 
  LEAF 
  

  

  71 
  

  

  the 
  fibrovascular 
  bundles 
  connecting 
  it 
  with 
  the 
  stem. 
  The 
  im- 
  

   portance 
  of 
  this 
  is 
  clear 
  from 
  what 
  has 
  already 
  been 
  said 
  

  

  (sect. 
  37) 
  about 
  photosynthesis 
  as 
  a 
  

   process 
  of 
  food-making 
  in 
  which 
  the 
  

   elements 
  of 
  water 
  from 
  the 
  soil 
  and 
  of 
  

   carbon 
  dioxide 
  from 
  the 
  air 
  are 
  brought 
  

   together 
  in 
  the 
  leaf 
  to 
  form 
  sugar 
  and 
  

   starch. 
  

  

  Have 
  the 
  veins 
  of 
  the 
  leaf 
  .other 
  uses 
  

   besides 
  their 
  function 
  as 
  conveyers 
  of 
  

   water 
  t 
  Explain. 
  

  

  69. 
  Alternate 
  and 
  opposite 
  arrange- 
  

  

  FIG. 
  52. 
  Top 
  view 
  of 
  ver- 
  

  

  tical 
  shoot 
  -of 
  syringa 
  

  

  (Philadeiphus) 
  

  

  The 
  leaves 
  are 
  arranged 
  in 
  ment 
  of 
  leaves. 
  When 
  a 
  leafy 
  apple 
  

   ies 
  the 
  spaces 
  between 
  the 
  

  

  pail's, 
  and 
  each 
  pair 
  over- 
  se 
  c-i^ 
  i 
  -it. 
  

  

  twig 
  (fig. 
  51) 
  IS 
  compared 
  With 
  One 
  of 
  

  

  pair 
  immediately 
  below 
  it. 
  maple 
  or 
  box 
  elder, 
  it 
  is 
  evident 
  that 
  

  

  One 
  fourth 
  natural 
  size 
  , 
  ., 
  i 
  -i 
  

  

  the 
  former 
  has 
  its 
  leaves 
  arranged 
  in 
  a 
  

  

  spiral 
  order, 
  while 
  the 
  latter 
  bears 
  its 
  leaves 
  in 
  pairs. 
  One 
  

   leaf 
  of 
  each 
  pair 
  is 
  on 
  

   the 
  opposite 
  side 
  of 
  

   the 
  twig 
  from 
  its 
  mate, 
  

   and 
  a 
  leaf 
  of 
  each 
  

   pair 
  covers 
  the 
  inter- 
  

   val 
  between 
  the 
  two 
  

   leaves 
  next 
  above 
  or 
  

   the 
  two 
  leaves 
  next 
  be- 
  

   low 
  (fig. 
  52). 
  Leaves 
  

   borne 
  in 
  spirals 
  are 
  

   said 
  to 
  be 
  alternate, 
  

   and 
  those 
  in 
  pairs, 
  

   like 
  maple 
  leaves, 
  are 
  

  

  The 
  leaves 
  spring 
  from 
  the 
  branch 
  in 
  the 
  same 
  

   order 
  as 
  do 
  those 
  of 
  the 
  vertical 
  branch, 
  but 
  by 
  

   a 
  twisting 
  of 
  the 
  leafstalks 
  the 
  blades 
  are 
  made 
  to 
  

   lie 
  in 
  a 
  nearly 
  horizontal 
  position, 
  and 
  thus 
  secure 
  

   abundant 
  illumination. 
  One 
  fourth 
  natural 
  size 
  

  

  FIG. 
  53. 
  Top 
  view 
  of 
  a 
  horizontal 
  shoot 
  from 
  

   the 
  shrub 
  shown 
  in 
  figure 
  52 
  

  

  said 
  to 
  be 
  opposite. 
  

  

  The 
  spiral 
  arrange- 
  

   ment 
  is 
  much 
  the 
  

  

  commoner, 
  being 
  char- 
  

   acteristic 
  of 
  most 
  herbs, 
  most 
  shrubs, 
  and 
  very 
  many 
  hard-wood 
  

   and 
  fruit 
  trees. 
  Some 
  of 
  the 
  most 
  familiar 
  opposite-leaved 
  

  

  