﻿EOOTS 
  AND 
  THEIR 
  RELATION 
  TO 
  PLANTS 
  31 
  

  

  produce 
  only 
  water 
  roots 
  (if 
  they 
  have 
  roots 
  at 
  all), 
  is 
  rather 
  

   small. 
  Some 
  of 
  the 
  commonest 
  are 
  the 
  so-called 
  water 
  hya- 
  

   cinth 
  and 
  the 
  little 
  duckweeds 
  (fig. 
  21). 
  

  

  Plants 
  like 
  the 
  pond 
  weeds, 
  water 
  crowfoot, 
  water 
  weed 
  

   (Eloded), 
  and 
  others, 
  which 
  grow 
  entirely 
  submerged, 
  do 
  not 
  

   need 
  an 
  extensive 
  root 
  system, 
  as 
  they 
  are 
  in 
  no 
  danger 
  of 
  

   drying 
  and 
  so 
  use 
  their 
  roots 
  mainly 
  for 
  anchorage. 
  

  

  29. 
  Air 
  roots. 
  Many 
  plants 
  which 
  root 
  in 
  the 
  earth, 
  such 
  

   as 
  corn, 
  poison 
  ivy, 
  and 
  English 
  ivy, 
  produce 
  roots 
  from 
  

   portions 
  of 
  the 
  stem 
  above- 
  

   ground. 
  These 
  are 
  called 
  

  

  aerial 
  roots. 
  In 
  some 
  cases, 
  

  

  as 
  in 
  corn 
  (fig. 
  22) 
  and 
  in 
  the 
  

  

  mangrove 
  tree, 
  which 
  grows 
  

  

  along 
  tropical 
  coasts, 
  the 
  aerial 
  

  

  roots 
  finally 
  reach 
  the 
  earth 
  

  

  and 
  serve 
  as 
  braces 
  to 
  prop 
  

  

  the 
  stem 
  of 
  the 
  plant 
  upright. 
  

  

  In 
  other 
  instances 
  the 
  roots 
  

  

  never 
  reach 
  the 
  ground, 
  and 
  

  

  then 
  they 
  may 
  serve 
  to 
  enable 
  

  

  the 
  plant 
  to 
  climb, 
  as 
  in 
  the 
  

  

  case 
  of 
  the 
  poison 
  ivy 
  and 
  the 
  

  

  English 
  ivy, 
  or 
  they 
  may 
  serve 
  

  

  to 
  anchor 
  the 
  plant 
  to 
  stones 
  or 
  to 
  the 
  bark 
  of 
  trees 
  and 
  at 
  

  

  the 
  same 
  time 
  to 
  absorb 
  rain 
  water 
  or 
  dew. 
  Many 
  tropical 
  

  

  air 
  plants 
  are 
  perched 
  on 
  the 
  bark 
  of 
  trees, 
  or 
  even 
  on 
  their 
  

  

  leaves, 
  and 
  get 
  their 
  water 
  supply 
  from 
  dangling 
  aerial 
  roots 
  

  

  which 
  are 
  covered 
  with 
  a 
  layer 
  of 
  absorbent 
  bark 
  that 
  catches 
  

  

  water 
  and 
  then 
  gradually 
  gives 
  it 
  to 
  the 
  plant. 
  

  

  30. 
  Parasitic 
  roots. 
  Certain 
  plants, 
  such 
  as 
  the 
  dodders 
  

   (fig. 
  34) 
  and 
  many 
  kinds 
  of 
  mistletoe 
  (figs. 
  23 
  and 
  35), 
  live 
  

   wholly 
  or 
  partly 
  at 
  the 
  expense 
  of 
  other 
  plants, 
  into 
  which 
  

   their 
  sucking 
  roots, 
  or 
  haustoria, 
  penetrate, 
  sometimes 
  very 
  

   deeply. 
  The 
  mode 
  of 
  life 
  of 
  such 
  parasites 
  will 
  be 
  further 
  

   discussed 
  in 
  Chapter 
  IV. 
  

  

  FIG. 
  23. 
  Base 
  of 
  stem 
  and 
  sucking 
  

  

  roots 
  of 
  the 
  mistletoe, 
  growing 
  on 
  an 
  

  

  apple 
  branch 
  

  

  In 
  the 
  figure 
  the 
  bark 
  of 
  the 
  branch 
  has 
  

   been 
  removed 
  so 
  as 
  to 
  show 
  how 
  the 
  

   mistletoe 
  roots 
  spread 
  between 
  the 
  bark 
  

   and 
  the 
  wood 
  of 
  the 
  host 
  plant. 
  In 
  the 
  

   section 
  of 
  the 
  branch 
  at 
  the 
  left 
  is 
  shown 
  

   the 
  way 
  in 
  which 
  short 
  portions 
  of 
  the 
  

   mistletoe 
  root 
  penetrate 
  into 
  the 
  wood 
  

   of 
  the 
  host. 
  One 
  half 
  natural 
  size. 
  After 
  

   Bonnier 
  and 
  Sablon 
  

  

  