﻿THE 
  STEM 
  AND 
  THE 
  LEAF 
  83 
  

  

  their 
  actively 
  transpiring 
  leaves 
  were 
  to 
  remain 
  at 
  work 
  while 
  

   the 
  ground 
  was 
  almost 
  or 
  quite 
  frozen, 
  the 
  tree 
  would 
  suffer 
  

   a 
  fatal 
  loss 
  of 
  water. 
  

  

  It 
  has 
  been 
  found 
  that 
  the 
  larch 
  (which 
  sheds 
  its 
  leaves) 
  is 
  

   more 
  resistant 
  to 
  such 
  conditions 
  than 
  are 
  most 
  of 
  the 
  ever- 
  

   green 
  conifers, 
  although 
  the 
  latter 
  have 
  leaves 
  of 
  a 
  highly 
  xero- 
  

   phytic 
  type. 
  In 
  a 
  rainless 
  summer 
  some 
  shrubs 
  retain 
  or 
  shed 
  

   their 
  leaves 
  in 
  proportion 
  to 
  the 
  amount 
  of 
  soil 
  moisture 
  with 
  

   which 
  they 
  are 
  supplied. 
  The 
  Euphorbia 
  splendens 
  (fig. 
  67) 
  is 
  

   a 
  commonly 
  cultivated 
  plant 
  which 
  well 
  illustrates 
  this 
  capac- 
  

   ity 
  to 
  adjust 
  the 
  amount 
  of 
  leaf 
  surface 
  to 
  a 
  varying 
  moisture 
  

   supply. 
  In 
  regions 
  like 
  Southern 
  California 
  and 
  the 
  coast 
  of 
  

   the 
  Mediterranean, 
  where 
  the 
  long, 
  hot 
  summers 
  are 
  nearly 
  

   rainless, 
  some 
  trees 
  and 
  many 
  shrubs 
  are 
  summer 
  deciduous, 
  

   losing 
  almost 
  or 
  quite 
  all 
  of 
  their 
  leaves 
  at 
  the 
  beginning 
  of 
  

   summer. 
  Twigs 
  in 
  this 
  leafless 
  summer 
  condition 
  have 
  been 
  

   found 
  to 
  lose 
  in 
  a 
  given 
  time 
  only 
  about 
  one 
  thirty-sixth 
  as 
  

   much 
  water 
  as 
  they 
  do 
  when 
  in 
  full 
  leaf. 
  

  

  The 
  shedding 
  of 
  the 
  leaf 
  is 
  a 
  somewhat 
  complicated 
  process 
  ; 
  

   a 
  waterproof 
  layer 
  of 
  tissue 
  is 
  formed 
  at 
  the 
  base 
  of 
  the 
  leaf- 
  

   stalk, 
  and 
  this 
  cuts 
  the 
  leaf 
  off 
  from 
  communication 
  with 
  the 
  

   stem. 
  Before 
  this 
  layer 
  is 
  formed, 
  the 
  plant 
  food 
  in 
  the 
  leaf 
  

   has 
  often 
  been 
  conveyed 
  into 
  other 
  parts 
  of 
  the 
  plant, 
  so 
  that 
  

   when 
  the 
  leaf 
  falls, 
  it 
  takes 
  with 
  it 
  little 
  of 
  value. 
  

  

  PROBLEMS 
  

  

  1. 
  Show 
  that 
  the 
  roots, 
  stem, 
  and 
  leaves 
  of 
  ordinary 
  trees 
  cooperate 
  

   to 
  do 
  the 
  work 
  of 
  food-making. 
  

  

  2. 
  Why 
  is 
  it 
  that 
  trees 
  which 
  are 
  left 
  standing 
  after 
  their 
  forest 
  neigh- 
  

   bors 
  have 
  been 
  cut 
  away 
  are 
  more 
  liable 
  to 
  injury 
  from 
  windstorms 
  than 
  

   are 
  those 
  which 
  have 
  always 
  grown 
  in 
  the 
  open 
  ? 
  

  

  3. 
  Discuss 
  the 
  various 
  ways 
  of 
  climbing, 
  and 
  show 
  which 
  are 
  gener- 
  

   ally 
  the 
  most 
  effective 
  in 
  securing 
  a 
  good 
  light 
  supply 
  under 
  great 
  

   difficulties. 
  

  

  4. 
  From 
  what 
  you 
  have 
  seen, 
  does 
  it 
  seem 
  probable 
  that 
  the 
  different 
  

   kinds 
  of 
  plants 
  in 
  a 
  piece 
  of 
  woodland 
  all 
  require 
  about 
  the 
  same 
  inten- 
  

   sity 
  of 
  light? 
  Discuss 
  this 
  matter, 
  giving 
  examples. 
  

  

  