﻿THE 
  STEM 
  AND 
  THE 
  LEAF 
  

  

  75 
  

  

  The 
  development 
  and 
  mode 
  of 
  operation 
  of 
  tendrils 
  is 
  espe- 
  

   cially 
  interesting 
  (figs. 
  58 
  and 
  59). 
  The 
  tendril 
  is 
  either 
  a 
  

   leafless, 
  thread-like 
  branch, 
  as 
  in 
  the 
  grapevine, 
  or 
  a 
  highly 
  

   modified 
  leaf 
  or 
  part 
  of 
  a 
  leaf, 
  as 
  in 
  the 
  cucumber. 
  When 
  a 
  

   living 
  and 
  active 
  tendril 
  comes 
  into 
  contact 
  with 
  any 
  suitable 
  

  

  FIG. 
  58. 
  Bur 
  cucumber 
  (Sicyos), 
  a 
  tendril 
  climber 
  

  

  At 
  a, 
  b, 
  c, 
  d, 
  e, 
  and 
  /successive 
  stages 
  in 
  the 
  history 
  of 
  tendrils 
  are 
  shown. 
  The 
  

  

  tendril, 
  at 
  first 
  curved, 
  becomes 
  straighter, 
  then 
  curls 
  up 
  at 
  the 
  tip, 
  and 
  finally 
  

  

  (after 
  becoming 
  attached 
  to 
  some 
  object) 
  coils 
  itself 
  into 
  a 
  close 
  spiral 
  and 
  thus 
  

  

  draws 
  the 
  plant 
  with 
  considerable 
  force 
  toward 
  the 
  sustaining 
  object 
  

  

  support 
  for 
  the 
  climber, 
  this 
  contact 
  brings 
  about 
  more 
  active 
  

   growth 
  on 
  the 
  exterior 
  side 
  of 
  the 
  tendril 
  (that 
  side 
  which 
  

   does 
  not 
  touch 
  the 
  foreign 
  object). 
  In 
  this 
  way 
  the 
  tendril 
  

   is 
  made 
  to 
  coil 
  about 
  the 
  support. 
  Soon 
  after 
  the 
  tendril 
  has 
  

   become 
  attached, 
  the 
  free 
  portions 
  are 
  thrown 
  into 
  coils, 
  and 
  

   the 
  shortening 
  which 
  results 
  draws 
  the 
  stem 
  of 
  the 
  climber 
  

   closer 
  to 
  the 
  support. 
  

  

  