﻿THE 
  PLANT 
  AS 
  A 
  WORKING 
  MACHINE 
  9 
  

  

  7. 
  Roots. 
  In 
  places 
  such 
  as 
  very 
  steep 
  hillsides 
  or 
  along 
  

   river 
  banks 
  one 
  may 
  often 
  see 
  plants 
  whose 
  roots 
  have 
  been 
  

   uncovered 
  by 
  removal 
  of 
  the 
  soil 
  in 
  which 
  they 
  grew. 
  When 
  

   the 
  soil 
  is 
  removed, 
  the 
  roots 
  sooner 
  or 
  later 
  are 
  unable 
  to 
  

   hold 
  the 
  rest 
  of 
  the 
  plant 
  in 
  place, 
  and 
  it 
  may 
  fall 
  to 
  the 
  

   ground 
  (fig. 
  4). 
  When 
  their 
  roots 
  are 
  partially 
  uncovered, 
  

   trees 
  that 
  have 
  withstood 
  heavy 
  winds 
  for 
  years 
  may 
  suc- 
  

   cumb 
  to 
  winds 
  that 
  are 
  less 
  severe 
  than 
  many 
  which 
  they 
  

   had 
  previously 
  been 
  able 
  to 
  withstand. 
  In 
  cultivated 
  hilly 
  

   fields 
  heavy 
  rains 
  often 
  erode 
  the 
  soil 
  from 
  above 
  the 
  roots 
  

   to 
  an 
  extent 
  that 
  allows 
  the 
  plants 
  to 
  fall. 
  Obviously 
  one 
  

   function 
  served 
  by 
  roots 
  is 
  that 
  of 
  holding 
  plants 
  in 
  place; 
  

   this 
  is 
  called 
  anchorage. 
  

  

  But 
  oftentimes 
  one 
  may 
  observe 
  plants 
  whose 
  roots 
  are 
  

   partially 
  uncovered, 
  the 
  plant 
  still 
  erect 
  in 
  position 
  but 
  wilt- 
  

   ing 
  or 
  with 
  yellow 
  leaves 
  and 
  evidently 
  not 
  growing 
  well. 
  

   Furthermore, 
  in 
  some 
  cases 
  the 
  roots 
  on 
  one 
  side 
  have 
  

   been 
  uncovered 
  and 
  the 
  plant 
  has 
  fallen, 
  but 
  its 
  branches 
  

   and 
  leaves 
  are 
  still 
  in 
  a 
  thrifty 
  condition. 
  If 
  all 
  or 
  nearly 
  all 
  

   the 
  roots 
  are 
  exposed, 
  or 
  if 
  the 
  soil 
  is 
  extremely 
  dry, 
  the 
  water 
  

   supply 
  of 
  the 
  plant, 
  which 
  comes 
  through 
  the 
  roots, 
  is 
  inter- 
  

   fered 
  with, 
  and 
  because 
  of 
  a 
  shortage 
  of 
  water 
  the 
  leaves 
  may 
  

   wilt 
  ; 
  but 
  if 
  a 
  part 
  of 
  the 
  roots 
  are 
  still 
  well 
  imbedded 
  in 
  

   moist 
  soil, 
  though 
  the 
  stem 
  and 
  branches 
  may 
  have 
  fallen, 
  a 
  

   fairly 
  adequate 
  supply 
  of 
  water 
  may 
  still 
  reach 
  the 
  stem 
  and 
  

   leaves, 
  and 
  wilting 
  and 
  death 
  may 
  not 
  follow. 
  Roots, 
  there- 
  

   fore, 
  serve 
  not 
  only 
  for 
  anchorage 
  but 
  also 
  as 
  structures 
  

   through 
  which 
  the 
  plant 
  receives 
  its 
  water 
  supply, 
  that 
  is, 
  as 
  

   organs 
  of 
  ivater 
  absorption. 
  

  

  8. 
  Rootlets 
  and 
  root 
  hairs. 
  In 
  examining 
  the 
  root 
  system 
  

   of 
  any 
  common 
  plant 
  (fig. 
  3) 
  it 
  is 
  usually 
  seen 
  that 
  the 
  roots 
  

   directly 
  joined 
  to 
  the 
  stem 
  are 
  relatively 
  few 
  and 
  large, 
  and 
  

   that 
  they 
  divide 
  and 
  redivide 
  until 
  extremely 
  fine 
  rootlets 
  are 
  

   formed. 
  In 
  most 
  plants 
  the 
  larger 
  roots 
  are 
  covered 
  by 
  bark, 
  

   through 
  which 
  water 
  does 
  not 
  pass 
  readily. 
  Even 
  rather 
  small 
  

   root 
  branches 
  are 
  covered 
  with 
  root 
  bark. 
  But 
  the 
  smallest 
  

  

  