﻿42 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  can 
  penetrate 
  has 
  received 
  the 
  special 
  name 
  of 
  osmosis. 
  Os- 
  

   mosis 
  is 
  not 
  quite 
  so 
  simple 
  as 
  diffusion, 
  since 
  the 
  movement 
  

   of 
  particles 
  of 
  the 
  liquids 
  is 
  a 
  good 
  deal 
  affected 
  by 
  the 
  nature 
  

   of 
  the 
  partition. 
  In 
  Chapter 
  II 
  it 
  was 
  stated 
  that 
  soil 
  water 
  may 
  

   be 
  taken 
  up 
  by 
  root 
  hairs. 
  It 
  may 
  now 
  be 
  seen 
  how 
  osmotic 
  

   action 
  affects 
  this 
  process 
  of 
  taking 
  up 
  water 
  by 
  root 
  hairs. 
  

   By 
  osmosis 
  soil 
  water 
  may 
  pass 
  through 
  the 
  root-hair 
  walls 
  

  

  into 
  the 
  interior 
  of 
  

   the 
  root 
  hair 
  and 
  

   thence 
  to 
  other 
  root 
  

   cells. 
  Obviously, 
  

   when 
  the 
  liquids 
  of 
  

   the 
  soil 
  are 
  more 
  

   dense 
  than 
  the 
  liq- 
  

   uids 
  within 
  the 
  root 
  

   hairs, 
  the 
  root 
  hairs 
  

   will 
  lose 
  some 
  of 
  

   their 
  water 
  to 
  the 
  

   soil 
  outside, 
  and 
  if 
  

   enough 
  water 
  is 
  

   lost 
  in 
  this 
  way, 
  

   the 
  contents 
  of 
  the 
  

   root 
  hair 
  may 
  be- 
  

   come 
  plasmolyzed. 
  

   41. 
  How 
  food 
  is 
  carried 
  through 
  plants. 
  Applying 
  the 
  prin- 
  

   ciples 
  of 
  osmotic 
  action 
  to 
  the 
  case 
  of 
  a 
  starch-loaded 
  leaf, 
  it 
  

   is 
  evident 
  that, 
  as 
  fast 
  as 
  the 
  starch 
  grains 
  temporarily 
  de- 
  

   posited 
  in 
  the 
  chloroplasts 
  of 
  the 
  leaf 
  are 
  changed 
  into 
  sugar, 
  

   some 
  of 
  the 
  sugar 
  in 
  the 
  denser 
  cell 
  sap 
  thus 
  produced 
  will 
  

   pass 
  on 
  to 
  the 
  more 
  watery 
  sap 
  of 
  adjacent 
  cells. 
  From 
  these 
  

   cells, 
  in 
  turn, 
  portions 
  of 
  sugar 
  will 
  pass 
  on 
  to 
  still 
  more 
  dis- 
  

   tant 
  cells. 
  In 
  a 
  similar 
  way, 
  when 
  a 
  potato 
  tuber 
  is 
  planted 
  

   and 
  begins 
  to 
  sprout, 
  the 
  sugar 
  formed 
  from 
  the 
  reserve 
  starch 
  

   in 
  the 
  potato 
  passes 
  into 
  the 
  more 
  watery 
  sap 
  contained 
  in 
  

   the 
  sprouts. 
  This 
  sap 
  is 
  constantly 
  losing 
  sugar 
  that 
  is 
  used 
  

   as 
  building 
  material 
  for 
  the 
  young 
  growing 
  stems 
  and 
  leaves, 
  

  

  FIG 
  29. 
  Root 
  hairs 
  

  

  A, 
  in 
  normal 
  condition 
  ; 
  B, 
  the 
  same 
  root 
  hairs 
  after 
  

   being 
  treivted 
  with 
  a 
  solution 
  of 
  common 
  salt 
  

  

  