﻿THE 
  STEM 
  AND 
  THE 
  LEAF 
  

  

  77 
  

  

  FIG. 
  60. 
  Branch 
  of 
  Eucalyptus, 
  

  

  with 
  leaves 
  hanging 
  almost 
  

  

  vertically 
  downward 
  

  

  About 
  one 
  fourth 
  natural 
  size. 
  

   After 
  Bonnier 
  and 
  Sablon 
  

  

  75. 
  Daily 
  movements 
  of 
  leaves. 
  Any 
  one 
  who 
  walks 
  through 
  

   a 
  clover 
  field 
  at 
  dusk 
  is 
  likely 
  to 
  be 
  struck 
  with 
  the 
  peculiar 
  

   pale 
  appearance 
  of 
  the 
  leaves, 
  very 
  different 
  from 
  the 
  dark- 
  

   green 
  color 
  which 
  they 
  have 
  in 
  full 
  

   sunshine. 
  This 
  paleness 
  is 
  due 
  to 
  

   the 
  fact 
  that 
  as 
  the 
  daylight 
  fades 
  

   the 
  leaflets 
  droop, 
  as 
  shown 
  in 
  figure 
  

   61, 
  so 
  that 
  little 
  except 
  the 
  under 
  

   surfaces 
  are 
  seen. 
  A 
  large 
  propor- 
  

   tion 
  of 
  the 
  plants 
  of 
  the 
  Pea 
  family 
  

   and 
  many 
  other 
  plants 
  have 
  leaves 
  

   that 
  take 
  a 
  special 
  night 
  position. 
  

   Some 
  leaves, 
  as 
  those 
  of 
  the 
  bean 
  

   and 
  the 
  black 
  locust, 
  have 
  three 
  

   positions 
  - 
  - 
  one 
  at 
  night, 
  another 
  

   in 
  ordinary 
  daylight, 
  and 
  a 
  third 
  

   in 
  intense 
  sunlight. 
  The 
  daylight 
  

   position 
  is 
  usually 
  almost 
  horizon- 
  

   tal 
  ; 
  the 
  position 
  for 
  brilliant 
  sunlight 
  is 
  vertical. 
  In 
  the 
  locust 
  

   the 
  change 
  from 
  vertical 
  to 
  horizontal 
  occurs 
  quickly 
  enough 
  

   to 
  make 
  it 
  worth 
  while 
  to 
  watch 
  it 
  coming 
  on 
  as 
  the 
  sun 
  

   moves 
  westward 
  after 
  noon 
  and 
  the 
  leaves 
  are 
  left 
  in 
  the 
  shade. 
  

  

  In 
  plants 
  of 
  the 
  Pea 
  

   family 
  the 
  daily 
  leaf 
  move- 
  

   ments 
  are 
  brought 
  about 
  

   by 
  means 
  of 
  a 
  sensitive, 
  

   cushion-like 
  organ, 
  the 
  jnil- 
  

   vinus, 
  situated 
  at 
  the 
  base 
  

   of 
  the 
  leafstalk. 
  It 
  is 
  

   easy 
  to 
  see 
  the 
  use 
  of 
  the 
  

   horizontal 
  and 
  the 
  verti- 
  

   cal 
  leaf 
  position, 
  but 
  the 
  

   importance 
  of 
  the 
  night 
  position 
  is 
  not 
  so 
  well 
  understood. 
  

  

  76. 
  Self-pruning 
  of 
  leaves 
  and 
  twigs. 
  Many 
  trees 
  and 
  shrubs 
  

   begin 
  to 
  shed 
  some 
  of 
  their 
  leaves 
  even 
  in 
  the 
  spring, 
  very 
  

   soon 
  after 
  the 
  leaves 
  are 
  well 
  grown. 
  Examples 
  of 
  this 
  are 
  

  

  FIG. 
  61. 
  A 
  leaf 
  of 
  red 
  clover 
  

  

  At 
  the 
  left, 
  leaf 
  by 
  day 
  ; 
  at 
  the 
  right, 
  the 
  

   same 
  leaf 
  at 
  night. 
  Natural 
  size 
  

  

  