﻿THE 
  PLANT 
  AS 
  A 
  WORKING 
  MACHINE 
  13 
  

  

  and 
  let 
  it 
  remain 
  for 
  a 
  few 
  minutes, 
  and 
  then 
  remove 
  it 
  and 
  

   examine 
  it 
  by 
  sectioning, 
  definitely 
  stained 
  regions 
  would 
  be 
  

   seen, 
  other 
  regions 
  being 
  unstained, 
  thus 
  showing 
  not 
  only 
  

   that 
  the 
  liquid 
  passed 
  upward 
  through 
  the 
  leafstalk, 
  but 
  that 
  

   it 
  passed 
  through 
  certain 
  tissues 
  of 
  the 
  stalk. 
  If 
  a 
  leafstalk 
  

   of 
  celery 
  is 
  carefully 
  broken 
  and 
  one 
  part 
  pulled 
  slowly 
  away 
  

   from 
  the 
  other, 
  there 
  are 
  seen 
  fibers, 
  or 
  threads, 
  which 
  are 
  

   quite 
  like 
  those 
  shown 
  in 
  the 
  cornstalk 
  (fig. 
  7). 
  These 
  threads 
  

   are 
  known 
  as 
  fibrovascular 
  bundles, 
  which 
  means 
  simply 
  " 
  col- 
  

   lections 
  of 
  thread-like 
  tubes." 
  It 
  is 
  through 
  these 
  fibrovas- 
  

   cular 
  bundles 
  that 
  water 
  and 
  substances 
  in 
  solution 
  in 
  water 
  

   pass 
  from 
  the 
  soil 
  through 
  roots, 
  through 
  stems, 
  and 
  into 
  

   leaves. 
  Through 
  them 
  also 
  plant 
  foods 
  may 
  pass 
  from 
  leaves 
  

   downward 
  through 
  the 
  plant, 
  Indeed, 
  there 
  are 
  certain 
  parts 
  

   of 
  each 
  bundle 
  through 
  which 
  water 
  passes 
  upward, 
  and 
  other 
  

   parts 
  through 
  which 
  the 
  organized 
  plant 
  foods 
  are 
  carried. 
  

   The 
  fibrovascular 
  bundles, 
  therefore, 
  are 
  the 
  chief 
  transporta- 
  

   tion 
  lines 
  of 
  the 
  plant. 
  

  

  11. 
  Leaves. 
  Most 
  leaves 
  are 
  expanded 
  so 
  that 
  they 
  expose 
  

   much 
  more 
  surface 
  than 
  would 
  stems 
  of 
  equal 
  weight. 
  In 
  

   some 
  cases 
  (fig. 
  3) 
  the 
  entire 
  leaf 
  is 
  expanded, 
  while 
  in 
  others 
  

   there 
  is 
  a 
  leafstalk, 
  or 
  petiole, 
  and 
  the 
  expanded 
  portion, 
  the 
  

   blade. 
  The 
  leaf 
  blade 
  may 
  be 
  single 
  (simple') 
  or 
  sub-divided 
  

   (compound*). 
  From 
  the 
  plant 
  stem 
  the 
  fibrovascular 
  bundles 
  

   extend 
  into 
  the 
  leaf, 
  where 
  they 
  are 
  known 
  as 
  the 
  veins 
  of 
  the 
  

   leaf. 
  They 
  terminate 
  in 
  the 
  leaf, 
  sometimes 
  in 
  its 
  tip 
  and 
  

   sometimes 
  in 
  the 
  margin 
  as 
  well 
  as 
  in 
  the 
  tip. 
  Water 
  from 
  

   the 
  soil 
  may 
  therefore 
  pass 
  through 
  the 
  fibrovascular 
  bundles 
  

   of 
  the 
  roots, 
  the 
  stem, 
  and 
  the 
  leaves, 
  into 
  the 
  interior 
  of 
  the 
  

   leaf. 
  From 
  the 
  leaf 
  some 
  of 
  this 
  water 
  is 
  evaporated 
  into 
  

   the 
  air. 
  

  

  Part 
  of 
  the 
  water 
  in 
  the 
  leaf, 
  instead 
  of 
  being 
  evaporated 
  

   into 
  the 
  air, 
  is 
  used 
  in 
  the 
  construction 
  of 
  plant 
  food 
  by 
  means 
  

   of 
  a 
  process 
  which 
  is 
  of 
  very 
  great 
  importance 
  to 
  all 
  living 
  

   things. 
  Carbon 
  dioxide 
  from 
  the 
  air 
  enters 
  the 
  leaf 
  through 
  

   its 
  surface. 
  The 
  leaf 
  is 
  green 
  because 
  of 
  the 
  presence 
  of 
  a 
  

  

  