﻿24 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  20. 
  Amount 
  of 
  water 
  pressure 
  in 
  woody 
  plants. 
  When 
  very 
  

   little 
  water 
  is 
  briii'.;- 
  lost 
  by 
  evaporation 
  from 
  the 
  leaves, 
  the 
  

   sap 
  pressure 
  in 
  trees 
  and 
  large 
  shrubs 
  is 
  often 
  great. 
  As 
  a 
  

   result 
  of 
  this 
  pressure, 
  in 
  early 
  spring 
  sap 
  escapes 
  freely 
  from 
  

   cuts 
  or 
  borings 
  made 
  into 
  the 
  roots, 
  trunks, 
  or 
  branches 
  of 
  

   many 
  kinds 
  of 
  trees 
  and 
  shrubs. 
  The" 
  bleeding" 
  of 
  grapevines 
  

   pruned 
  too 
  late 
  in 
  the 
  season 
  is 
  familiar 
  to 
  many 
  people, 
  as 
  is 
  

   also 
  the 
  flow 
  of 
  sap 
  from 
  sugar 
  maples. 
  Woody 
  plants 
  cut 
  

   off 
  near 
  the 
  root 
  may 
  have 
  a 
  pressure 
  gauge 
  of 
  any 
  convenient 
  

   sort 
  attached 
  to 
  the 
  cut 
  surface, 
  and 
  the 
  pressure 
  can 
  thus 
  be 
  

   measured 
  with 
  accuracy. 
  A 
  severed 
  grapevine 
  has 
  been 
  found 
  

   to 
  exert 
  a 
  pressure 
  sufficient 
  to 
  sustain 
  a 
  column 
  of 
  water 
  

   more 
  than 
  43 
  feet 
  high, 
  and 
  the 
  root 
  of 
  a 
  black 
  birch 
  tree 
  

   a 
  pressure 
  equivalent 
  to 
  about 
  86 
  feet 
  of 
  water. 
  

  

  In 
  the 
  tallest 
  trees, 
  the 
  giant 
  redwoods 
  and 
  the 
  Australian 
  

   gum 
  trees 
  (/vy//o/a, 
  Eucalyptus), 
  water 
  is 
  sometimes 
  raised 
  

   to 
  a 
  height 
  of 
  from 
  300 
  to 
  400 
  feet. 
  It 
  is 
  not 
  yet 
  known 
  how 
  

   large 
  a 
  part 
  of 
  the 
  force 
  required 
  for 
  this 
  is 
  due 
  to 
  the 
  pres- 
  

   sure 
  with 
  which 
  the 
  sap 
  from 
  the; 
  roots 
  is 
  impelled 
  up 
  into 
  

   the 
  stem, 
  nor 
  what 
  other 
  causes 
  are 
  mainly 
  responsible 
  for 
  

   the 
  rise 
  of 
  water 
  into 
  the 
  highest 
  portions 
  of 
  the 
  tree. 
  

  

  21. 
  What 
  roots 
  do 
  for 
  the 
  plant. 
  All 
  plants 
  must 
  have 
  

   water, 
  at 
  any 
  rate 
  during 
  the 
  part 
  of 
  their 
  lives 
  when 
  they 
  

   are 
  actively 
  manufacturing 
  plant 
  food, 
  and 
  it 
  is 
  by 
  means 
  

   of 
  their 
  roots 
  that 
  most 
  familiar 
  plants 
  absorb 
  water 
  and 
  the 
  

   substances 
  that 
  are 
  dissolved 
  in 
  it. 
  Yet 
  absorption 
  of 
  water 
  

   is 
  not 
  the 
  only 
  function 
  of 
  roots. 
  They 
  often 
  absorb 
  oxygen 
  : 
  

   they 
  commonly 
  serve 
  to 
  anchor 
  the 
  plant; 
  they 
  may 
  aid 
  it 
  to 
  

   climb; 
  they 
  frequently 
  store 
  food, 
  water, 
  or 
  both: 
  and 
  in 
  or 
  

   on 
  them 
  are 
  sometimes 
  carried 
  on 
  important 
  chemical 
  opera- 
  

   tions 
  which 
  result 
  in 
  gaining 
  material 
  for 
  the 
  production 
  of 
  

   plant 
  food. 
  Many 
  kinds 
  of 
  roots 
  reproduce 
  the 
  plant; 
  that 
  

   is, 
  a 
  root 
  or 
  part 
  of 
  one 
  may 
  grow 
  into 
  a 
  new 
  individual 
  plant 
  

   like 
  the 
  one 
  to 
  which 
  the 
  root 
  belonged. 
  

  

  The 
  great 
  importance 
  of 
  roots 
  to 
  life 
  and 
  growth 
  is 
  well 
  

   shown 
  by 
  the 
  results 
  which 
  follow 
  from 
  any 
  severe 
  injury 
  to 
  

  

  