﻿FOODS 
  IN 
  PLANTS 
  47 
  

  

  gases 
  between 
  the 
  exterior 
  and 
  the 
  interior 
  of 
  the 
  living 
  body 
  

   - 
  between 
  the 
  lungs 
  and 
  the 
  air 
  in 
  the 
  case 
  of 
  the 
  higher 
  ani- 
  

   mals 
  and 
  between 
  the 
  leaves 
  and 
  the 
  air 
  in 
  the 
  case 
  of 
  the 
  

   higher 
  plants. 
  This 
  interchange 
  is, 
  however, 
  no 
  longer 
  re- 
  

   garded 
  as 
  the 
  fundamental 
  thing 
  in 
  respiration, 
  since 
  respira- 
  

   tion 
  takes 
  place 
  in 
  active, 
  living 
  protoplasm 
  in 
  all 
  parts 
  of 
  the 
  

   plant. 
  It 
  consists 
  of 
  decomposition 
  of 
  protoplasm 
  or 
  of 
  some 
  

   of 
  its 
  parts, 
  or 
  (as 
  is 
  supposed 
  by 
  some 
  botanists) 
  it 
  may 
  con- 
  

   sist 
  of 
  decomposition 
  of 
  food 
  materials 
  that 
  have 
  not 
  yet 
  become 
  

   assimilated 
  so 
  as 
  to 
  become 
  protoplasm. 
  Through 
  respiration 
  

   complex 
  plant 
  substances 
  are 
  broken 
  down, 
  and 
  the 
  energy 
  

   released 
  by 
  this 
  decomposition 
  is 
  the 
  energy 
  by 
  means 
  of 
  

   which 
  plants 
  carry 
  on 
  their 
  work. 
  Energy 
  in 
  the 
  form 
  of 
  heat 
  

   is 
  also 
  one 
  of 
  the 
  results 
  of 
  respiration. 
  Respiration 
  may 
  occur 
  

   in 
  the 
  absence 
  of 
  free 
  oxygen, 
  but 
  it 
  is 
  more 
  complete, 
  and 
  

   thus 
  releases 
  more 
  energy, 
  when 
  oxygen 
  is 
  present. 
  When 
  

   respiration 
  is 
  complete, 
  it 
  results 
  in 
  the 
  formation 
  of 
  various 
  

   compounds, 
  of 
  which 
  carbon 
  dioxide 
  and 
  water 
  are 
  conspicu- 
  

   ous. 
  Carbon 
  dioxide 
  and 
  water 
  may 
  be 
  carried 
  away 
  from 
  the 
  

   plant 
  through 
  the 
  leaf 
  or 
  other 
  parts, 
  and 
  the 
  oxygen 
  supply 
  

   may 
  enter 
  in 
  the 
  same 
  way. 
  It 
  is 
  evident, 
  however, 
  that 
  the 
  

   transfer 
  of 
  these 
  gases 
  is 
  merely 
  an 
  incident 
  associated 
  with 
  

   the 
  real 
  respiration, 
  which 
  consists 
  in 
  the 
  decomposition 
  of 
  

   complex 
  substances 
  and 
  the 
  release 
  of 
  energy 
  therefrom. 
  It 
  is 
  

   also 
  evident 
  that, 
  so 
  far 
  as 
  respiration 
  is 
  concerned, 
  plants 
  and 
  

   animals 
  behave 
  in 
  the 
  same 
  way. 
  It 
  should 
  be 
  noted 
  that 
  in 
  

   photosynthesis 
  green 
  plants 
  utilize 
  carbon 
  dioxide, 
  though 
  they, 
  

   like 
  other 
  plants 
  and 
  animals, 
  may 
  produce 
  carbon 
  dioxide 
  as 
  

   one 
  of 
  the 
  products 
  of 
  respiration. 
  

  

  47. 
  Importance 
  of 
  the 
  food 
  cycle 
  in 
  plants. 
  The 
  importance 
  

   of 
  the 
  food 
  cycle 
  of 
  green 
  plants 
  can 
  scarcely 
  be 
  overestimated. 
  

   The 
  human 
  race 
  depends, 
  directly 
  or 
  indirectly, 
  upon 
  photo- 
  

   synthesis 
  and 
  the 
  storage 
  of 
  food 
  by 
  plants. 
  Men 
  have 
  selected 
  

   and 
  improved 
  those 
  plants 
  which 
  produce 
  the 
  most 
  desirable 
  

   food 
  in 
  the 
  largest 
  quantities. 
  They 
  have 
  studied, 
  and 
  must 
  

   continue 
  to 
  study, 
  the 
  conditions 
  of 
  soil 
  and 
  the 
  climatic 
  

  

  