﻿2G 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  ami 
  full 
  dandelion, 
  pull 
  tlieir 
  rosettes 
  down 
  tightly 
  against 
  the 
  

   surface 
  of 
  a 
  lawn, 
  kill 
  the 
  surrounding 
  grass, 
  and 
  thus 
  secure 
  

   for 
  themselves 
  a 
  little 
  elear 
  space 
  in 
  which 
  to 
  grow. 
  

  

  24. 
  Effects 
  of 
  roots 
  on 
  the 
  soil. 
  If 
  we 
  dig 
  up 
  a 
  spadeful 
  of 
  

   earth 
  from 
  a 
  well-grassed 
  meadow 
  or 
  from 
  a 
  little 
  inside 
  the 
  

   circumference 
  of 
  the 
  circle 
  formed 
  by 
  the 
  roots 
  of 
  a 
  tree, 
  we 
  

   shaH 
  find 
  the 
  soil 
  bound 
  together 
  by 
  the 
  living 
  roots 
  or 
  full 
  

  

  l-'n.. 
  is. 
  C'yinvss 
  trees 
  (Taxudiiun) 
  growing 
  in 
  a 
  swamp 
  

  

  The 
  conical 
  " 
  knees'' 
  jjrowin;; 
  from 
  the 
  routs 
  ami 
  nearly 
  always 
  above 
  water 
  are 
  

   thought 
  to 
  serve 
  as 
  channels 
  to 
  supply 
  air 
  to 
  the 
  rods 
  

  

  of 
  little, 
  crooked, 
  tubular 
  channels 
  left 
  by 
  the 
  decay 
  of 
  dead 
  

   ones. 
  Thus 
  the 
  soil 
  is 
  in 
  the 
  one 
  case 
  held 
  together 
  so 
  as 
  to 
  

   prevent, 
  its 
  becoming 
  gullied 
  and 
  washed 
  away 
  by 
  rains, 
  and 
  in 
  

   the 
  other 
  case 
  made 
  more 
  porous 
  and 
  more 
  easily 
  penetrated 
  

   by 
  air 
  and 
  water. 
  The 
  latter 
  effect 
  is 
  a 
  very 
  important 
  one 
  in 
  

   the 
  case 
  of 
  stiff 
  day 
  soils, 
  which, 
  when 
  closely 
  packed, 
  are 
  

   almost, 
  waterproof. 
  

  

  The 
  extensive 
  washing 
  away 
  of 
  soils 
  when 
  they 
  are 
  unpro- 
  

   tected 
  by 
  a 
  covering 
  of 
  plants, 
  such 
  as 
  grass, 
  shrubs, 
  or 
  forest 
  

  

  