﻿38 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  ordinarily 
  in 
  the 
  ratio 
  of 
  about 
  3 
  parts 
  in 
  10,000 
  parts 
  of 
  air. 
  

   Inside 
  the 
  leaf, 
  therefore, 
  is 
  a 
  supply 
  of 
  the 
  so-called 
  raw- 
  

   materials 
  for 
  fond 
  -water, 
  carbon 
  dioxide, 
  and 
  substances 
  

   that 
  were 
  in 
  solution 
  hi 
  soil 
  water. 
  

  

  37. 
  The 
  manufacture 
  of 
  food. 
  Carbon 
  dioxide 
  and 
  water 
  

   must 
  undergo 
  changes 
  before 
  they 
  can 
  be 
  used 
  in 
  nourishing 
  

   and 
  building 
  up 
  the 
  plant. 
  The 
  sun 
  shines 
  upon 
  the 
  leaf 
  and 
  

   the 
  chlorophyll 
  absorbs 
  some 
  of 
  the 
  energy 
  from 
  the 
  sun's 
  

   rays. 
  In 
  some 
  way, 
  as 
  yet 
  unknown, 
  this 
  energy 
  serves 
  to 
  

   break 
  up 
  the 
  compounds 
  water 
  and 
  carbon 
  dioxide 
  into 
  the 
  

   carbon, 
  hydrogen, 
  and 
  oxygen 
  of 
  which 
  they 
  are 
  made. 
  The 
  

   carbon, 
  hydrogen, 
  and 
  some 
  of 
  the 
  oxygen 
  immediately 
  unite 
  

   again 
  - 
  - 
  not, 
  however, 
  into 
  the 
  compounds 
  carbon 
  dioxide 
  and 
  

   water, 
  but 
  into 
  new 
  compounds. 
  These 
  rapidly 
  pass 
  through 
  

   several 
  changes 
  and 
  may 
  finally 
  become 
  sugar 
  and 
  starch. 
  At 
  

   present 
  the 
  changes 
  that 
  take 
  place 
  before 
  starch 
  and 
  sugar 
  

   are 
  formed 
  are 
  not 
  all 
  known, 
  but 
  enough 
  is 
  known 
  of 
  them 
  

   to 
  show 
  that 
  they 
  are 
  quite 
  intricate. 
  Some 
  of 
  the 
  oxygen 
  

   resulting 
  from 
  the 
  breaking 
  up 
  of 
  water 
  and 
  carbon 
  dioxide 
  

   is 
  set 
  free 
  and 
  may 
  pass 
  out 
  into 
  the 
  air. 
  The 
  oxygen 
  thus 
  

   set 
  free 
  by 
  plants 
  may 
  be 
  collected 
  as 
  shown 
  in 
  figure 
  27, 
  and 
  

   then 
  tested. 
  1 
  This 
  process 
  that 
  is 
  carried 
  on 
  by 
  green 
  plants 
  is 
  

   a 
  principal 
  factor 
  in 
  maintaining 
  the 
  oxygen 
  supply 
  that 
  is 
  so 
  

   necessary 
  to 
  the 
  life 
  of 
  animals. 
  Plants 
  also 
  use 
  free 
  oxygen 
  

   in 
  some 
  of 
  their 
  later 
  food-making 
  processes. 
  This 
  series 
  of 
  

   occurrences, 
  by 
  means 
  of 
  which 
  green 
  plants 
  under 
  the 
  influ- 
  

   ence 
  of 
  sunlight 
  make 
  foods 
  such 
  as 
  starch 
  and 
  sugar 
  from 
  car- 
  

   bon 
  dioxide 
  and 
  water, 
  is 
  known 
  as 
  photosynthesis. 
  The 
  word 
  

   photosynthesis 
  means 
  " 
  putting 
  together 
  by 
  means 
  of 
  light." 
  2 
  

  

  Sugar 
  and 
  starch 
  (carbohydrates) 
  may 
  be 
  used 
  in 
  the 
  nutri- 
  

   tion 
  of 
  the 
  living 
  parts 
  of 
  the 
  plant 
  ; 
  or, 
  by 
  the 
  addition 
  of 
  

  

  1 
  If 
  a 
  test 
  for 
  oxygen 
  is 
  made, 
  it 
  is 
  best 
  to 
  precede 
  the 
  ordinary 
  test 
  by 
  an 
  

   experiment 
  with 
  oxygen 
  that 
  has 
  been 
  prepared 
  by 
  the 
  electrolysis 
  of 
  water. 
  

   Test 
  the 
  oxygen 
  so 
  prepared 
  with 
  a 
  lighted 
  splinter, 
  as 
  more 
  meaning 
  will 
  

   then 
  attach 
  to 
  the 
  test 
  of 
  oxygen 
  set 
  free 
  by 
  the 
  plant. 
  

  

  a 
  See 
  Appendix, 
  page 
  343. 
  

  

  