﻿120 
  INTRODUCTION 
  TO 
  BOTANV 
  

  

  leaves 
  and 
  brandies. 
  Not 
  infrequently 
  it 
  is 
  covered 
  with 
  moss. 
  

   The 
  soil 
  of 
  the 
  forest, 
  abounding 
  in 
  limmis, 
  retains 
  water 
  much 
  

   longer 
  than 
  average 
  soil 
  in 
  ojien 
  lields. 
  All 
  of 
  these 
  factors 
  

   cooperate 
  to 
  hold 
  hack 
  the 
  run-off 
  from 
  wooded 
  areas. 
  It 
  is 
  

   then-lore 
  of 
  the 
  highest 
  importance 
  that 
  such 
  regions 
  as 
  the 
  

   White 
  Mountains, 
  1 
  the 
  Adirondack*, 
  the 
  central 
  and 
  southern 
  

   Appalachians, 
  and 
  western 
  mountain 
  ranges 
  \\hieh 
  are 
  used 
  

   as 
  sources 
  of 
  water 
  for 
  irrigation 
  should 
  be 
  forested. 
  

  

  112. 
  Forest 
  growth 
  prevents 
  erosion. 
  Along 
  with 
  the 
  value 
  

   of 
  the 
  forest 
  in 
  regulating 
  the 
  How 
  of 
  streams, 
  account 
  must 
  

   be 
  taken 
  of 
  its 
  importance 
  in 
  preventing 
  the 
  washing 
  away, 
  or 
  

   erosion, 
  of 
  the 
  earth's 
  surface. 
  Not 
  only 
  mountains 
  and 
  hill- 
  

   sides 
  but 
  cultivated 
  slopes 
  everywhere 
  are 
  subject 
  to 
  great 
  

   losses 
  by 
  washing 
  during 
  thaws 
  after 
  snows 
  and 
  during 
  rain- 
  

   storms. 
  How 
  much 
  earth 
  is 
  thus 
  annually 
  carried 
  to 
  the 
  Gulf 
  

   by 
  the 
  Mississippi 
  alone 
  has 
  already 
  been 
  stated 
  (sect, 
  24). 
  

   Figure 
  239 
  represents 
  an 
  early 
  stage 
  in 
  the 
  formation 
  of 
  gul- 
  

   lies 
  on 
  a 
  steep 
  slope 
  after 
  clearing. 
  The 
  land 
  is 
  already 
  past 
  

   the 
  .stage 
  in 
  which 
  it 
  can 
  be 
  cultivated 
  in 
  the 
  ordinary 
  wav. 
  

   Left 
  to 
  itself 
  the 
  tendency 
  is 
  for 
  the 
  washing 
  to 
  continue 
  

   until 
  the 
  hillside 
  becomes 
  a 
  series 
  of 
  miniature 
  ravines, 
  strewn 
  

   with 
  bowlders 
  and 
  separated 
  by 
  bare 
  ridges. 
  Thousands 
  of 
  

   acres 
  in 
  the 
  southern 
  I'liited 
  States 
  and 
  hundreds 
  of 
  thou- 
  

   sands 
  in 
  some 
  of 
  what 
  were 
  once 
  the 
  most 
  fertile 
  parts 
  of 
  

   southern 
  Kurope 
  have 
  been 
  ruined 
  in 
  this 
  wav. 
  Such 
  de- 
  

   struction 
  may 
  be 
  prevented 
  by 
  retaining 
  hillsides 
  in 
  a 
  wooded 
  

   condition, 
  or 
  at 
  least 
  by 
  leading 
  belts 
  of 
  trees 
  at 
  intervals, 
  run- 
  

   ning 
  at 
  right 
  angles 
  to 
  the 
  lines 
  of 
  slope. 
  The 
  early 
  stages 
  of 
  

   erosion 
  may 
  be 
  checked 
  by 
  damming 
  the 
  principal 
  Bullies 
  with 
  

   lo-s, 
  stones, 
  and 
  brushwood, 
  and 
  then 
  replanting 
  witli 
  suitable 
  

  

  1 
  Kerenf 
  investigations 
  in 
  (lie 
  \Vhili- 
  Mountain 
  region 
  by 
  tin- 
  I'nifi-d 
  Stairs 
  

   (ieolo-iral 
  Survey 
  sln>\\ 
  that 
  flic 
  run-off 
  mi 
  two 
  drainage 
  basins, 
  carh 
  of 
  

   a 
  1 
  MM 
  it 
  live 
  scjiiaiv 
  miles, 
  on 
  the 
  lYmi-c\\ 
  as-et 
  l,'i\cr, 
  was 
  very 
  unequal. 
  One 
  

   basin 
  was 
  covered 
  with 
  virgin 
  forest 
  ; 
  the 
  other 
  had 
  liccn 
  deforested 
  and 
  

   liurned. 
  The 
  run-oft' 
  from 
  the 
  latter 
  basin 
  diirin- 
  seventeen 
  days 
  in 
  April 
  

   (including 
  three 
  extensive 
  storms) 
  was 
  about 
  double, 
  that 
  from 
  the 
  forest- 
  

   COVt-red 
  basin. 
  

  

  