﻿78 
  

  

  INTRODUCTION 
  TO 
  15OTANV 
  

  

  the 
  lilacs, 
  the 
  syringa 
  (Philadelphia), 
  the 
  cottonwood, 
  the 
  

   horse-chestnut, 
  the 
  box 
  elder, 
  and 
  some 
  lindens. 
  Still 
  more 
  

   common 
  is 
  the 
  loss 
  of 
  leaves 
  during 
  the 
  su 
  miner, 
  which 
  may 
  

   amount 
  to 
  oO 
  per 
  cent 
  of 
  the 
  total 
  number 
  of 
  leaves. 
  This 
  

   leaf 
  fall, 
  coming 
  long 
  before 
  the 
  leaves 
  are 
  cast 
  off 
  in 
  the 
  

   autumn 
  as 
  a 
  preparation 
  for 
  winter, 
  affects 
  chiefly 
  the 
  leaves 
  

   inside 
  the 
  crown 
  of 
  the 
  tree, 
  which 
  have 
  such 
  scanty 
  light 
  

   that 
  they 
  evidently 
  cannot 
  accomplish 
  much 
  photosynthesis. 
  

  

  FIG. 
  02. 
  The 
  poud 
  lily, 
  au 
  aquatic 
  with 
  floating 
  leaves 
  and 
  submerged 
  steins 
  

  

  Leaves, 
  twigs, 
  and 
  even 
  larger 
  branches 
  which 
  are 
  not 
  get- 
  

   ting 
  an 
  adequate 
  supply 
  of 
  light 
  or 
  of 
  water 
  are 
  pruned 
  away 
  by 
  

   the 
  tree. 
  \\Yre 
  it 
  not 
  for 
  this, 
  the 
  dense 
  growth 
  in 
  the 
  interior 
  

   of 
  the 
  tree 
  top 
  and 
  along 
  the 
  trunk 
  would 
  soon 
  render 
  further 
  

   branching 
  mechanically 
  impossible. 
  What 
  one 
  sees 
  on 
  looking 
  

   up 
  along 
  the 
  trunk 
  into 
  the 
  top 
  of 
  a 
  large 
  tree 
  is 
  mainly 
  dead 
  

   or 
  dying 
  branches, 
  with 
  few 
  leaves. 
  It 
  is 
  this 
  self-pruning 
  

   and 
  that 
  due 
  to 
  the 
  shade 
  of 
  neighboring 
  trees 
  that 
  makes 
  

   the 
  trunks 
  free 
  from 
  knots 
  and 
  most 
  valuable 
  for 
  timber 
  in 
  

  

  