﻿CHAPTER 
  XX 
  

   WEEDS 
  

  

  310. 
  What 
  is 
  a 
  weed 
  ? 
  The 
  term 
  weed 
  is 
  not 
  a 
  botanical 
  

   one 
  but 
  is 
  a 
  common 
  word 
  for 
  the 
  conspicuous 
  troublesome 
  

   or 
  injurious 
  plants. 
  It 
  is 
  not 
  customary 
  to 
  apply 
  the 
  name 
  

   weed 
  to 
  lower 
  forms 
  of 
  plant 
  life, 
  such 
  as 
  bacteria 
  and 
  fungi, 
  

   even 
  though 
  they 
  may 
  be 
  extremely 
  harmful 
  to 
  field 
  and 
  

   garden 
  crops, 
  orchards, 
  or 
  forests. 
  Most 
  weeds 
  are 
  flower- 
  

   ing 
  plants, 
  but 
  horsetails 
  and 
  a 
  few 
  ferns 
  (as 
  the 
  sensitive 
  

   fern, 
  fig. 
  216) 
  are 
  sometimes 
  troublesome 
  enough 
  to 
  be 
  classed 
  

   in 
  the 
  list. 
  

  

  The 
  same 
  plant 
  may 
  be 
  counted 
  a 
  weed 
  in 
  one 
  place 
  and 
  

   not 
  in 
  another. 
  The 
  sensitive 
  plant, 
  not 
  uncommon 
  as 
  a 
  curi- 
  

   osity 
  in 
  our 
  greenhouses, 
  is 
  a 
  troublesome 
  weed 
  over 
  immense 
  

   areas 
  in 
  the 
  tropics. 
  Wild 
  carrots, 
  of 
  the 
  same 
  species 
  as 
  the 
  

   cultivated 
  ones, 
  are 
  a 
  nuisance 
  in 
  New 
  England 
  mowing 
  lands 
  

   and 
  are 
  rapidly 
  extending 
  westward 
  ; 
  field 
  garlic, 
  melilot, 
  horse- 
  

   radish, 
  tansy, 
  oxeye 
  daisy, 
  and 
  orange 
  hawkweed, 
  or 
  " 
  paint- 
  

   brush," 
  were 
  all 
  introduced 
  as 
  valued 
  garden 
  plants, 
  afterwards 
  

   becoming 
  noxious 
  weeds. 
  

  

  311. 
  Why 
  weeds 
  succeed. 
  The 
  characteristics 
  which 
  enable 
  

   weeds 
  to 
  flourish 
  where 
  farm 
  and 
  garden 
  crops 
  need 
  care 
  to 
  

   enable 
  them 
  to 
  grow 
  are 
  too 
  numerous 
  to 
  be 
  stated 
  and 
  ex- 
  

   plained 
  at 
  length 
  in 
  a 
  very 
  elementary 
  book. 
  Some 
  of 
  the 
  

   important 
  characteristics 
  which 
  distinguish 
  most 
  weeds 
  are 
  : 
  

  

  1. 
  Great 
  reproductive 
  power. 
  

  

  2. 
  Capacity 
  for 
  rapid 
  growth, 
  which 
  enables 
  them 
  to 
  shade 
  

   and 
  destroy 
  other 
  plants. 
  

  

  3. 
  Ability 
  to 
  resist 
  drought, 
  shading, 
  frost, 
  and 
  plant 
  

   diseases. 
  

  

  333 
  

  

  