﻿ROOTS 
  AND 
  THEIR 
  RELATION 
  TO 
  PLANTS 
  27 
  

  

  growth, 
  is 
  one 
  of 
  the 
  most 
  serious 
  calamities 
  that 
  can 
  befall 
  a 
  

   country. 
  It 
  is 
  especially 
  formidable 
  in 
  hilly 
  regions, 
  winch 
  

   may 
  become 
  wholly 
  uninhabitable 
  if 
  the 
  forests 
  are 
  cut 
  off 
  

   and 
  the 
  turf 
  on 
  the 
  hillsides 
  is 
  destroyed 
  by 
  too 
  constant 
  

   grazing 
  and 
  trampling 
  of 
  sheep 
  or 
  goats. 
  Throughout 
  south- 
  

   ern 
  Europe 
  immense 
  areas 
  of 
  land 
  once 
  valuable 
  for 
  timber 
  

   and 
  for 
  grazing 
  have 
  thus 
  been 
  ruined, 
  and 
  the 
  same 
  process 
  

   is 
  under 
  way 
  in 
  our 
  own 
  country 
  all 
  the 
  way 
  from 
  New 
  Eng- 
  

   land 
  to 
  the 
  Pacific 
  coast 
  region. 
  One 
  of 
  the 
  clearest 
  ways 
  in 
  

   which 
  the 
  idea 
  of 
  loss 
  by 
  the 
  washing 
  away 
  of 
  the 
  soil 
  can 
  

   be 
  presented 
  is 
  by 
  considering 
  how 
  the 
  land 
  is 
  carried 
  into 
  

   the 
  sea 
  by 
  great 
  rivers. 
  The 
  delta 
  of 
  the 
  Mississippi 
  covers 
  

   an 
  area 
  of 
  more 
  than 
  12,000 
  square 
  miles. 
  It 
  consists 
  of 
  mate- 
  

   rial 
  brought 
  down 
  by 
  the 
  river 
  in 
  the 
  form 
  of 
  mud, 
  which 
  

   now 
  forms 
  a 
  deposit 
  of 
  unknown 
  thickness, 
  probably 
  averag- 
  

   ing 
  more 
  than 
  500 
  feet. 
  It 
  is 
  calculated 
  that 
  the 
  river 
  carries 
  

   every 
  year 
  enough 
  solid 
  matter 
  to 
  form 
  a 
  layer 
  one 
  foot 
  thick 
  

   over 
  an 
  area 
  of 
  about 
  268 
  square 
  miles. 
  Remembering 
  that 
  

   this 
  mud 
  consists 
  mainly 
  of 
  the 
  choicest 
  part 
  of 
  the 
  rich 
  soil 
  

   of 
  the 
  Mississippi 
  basin, 
  it 
  is 
  easy 
  to 
  see 
  that 
  the 
  land 
  is 
  robbed 
  

   every 
  year 
  of 
  the 
  material 
  to 
  support 
  enormous 
  harvests 
  1 
  

   (see 
  Chapter 
  XIX). 
  

  

  25. 
  Air 
  supply 
  of 
  earth 
  roots. 
  Earth 
  roots 
  require 
  a 
  consid- 
  

   erable 
  supply 
  of 
  air. 
  This 
  is 
  shown 
  by 
  the 
  fact 
  that 
  most 
  

   trees 
  are 
  injured 
  or 
  killed 
  when 
  the 
  soil 
  in 
  which 
  they 
  grow 
  is 
  

   long 
  flooded 
  with 
  water, 
  as 
  is 
  often 
  the 
  case 
  when 
  a 
  stream 
  is 
  

   greatly 
  widened 
  by 
  the 
  construction 
  of 
  a 
  dam 
  across 
  it. 
  The 
  

   same 
  result 
  is 
  seen 
  when 
  low 
  fields 
  of 
  corn, 
  wheat, 
  oats, 
  or 
  

   cotton 
  are 
  flooded 
  after 
  heavy 
  rains. 
  Unglazed 
  earthen 
  flower- 
  

   pots 
  are 
  better 
  for 
  house 
  plants 
  than 
  glazed 
  ones 
  or 
  glass 
  jars, 
  

   because 
  they 
  allow 
  air 
  to 
  pass 
  freely 
  through 
  the 
  porous 
  

   material 
  of 
  the 
  pot. 
  

  

  How 
  do 
  the 
  earth 
  roots 
  of 
  such 
  plants 
  as 
  water 
  lilies 
  get 
  

   their 
  air 
  supply 
  ? 
  

  

  1 
  See 
  " 
  Forest 
  Influences," 
  Bulletin 
  No. 
  7, 
  Division 
  of 
  Forestry, 
  U.S. 
  Dept. 
  

   Agr., 
  1893. 
  

  

  