﻿60 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  where 
  they 
  can 
  cover 
  the 
  surface 
  of 
  the 
  ground 
  closely 
  enough 
  

   to 
  prevent 
  too 
  severe 
  competition 
  from 
  plants 
  that 
  might 
  shade 
  

   them. 
  

  

  As 
  a 
  result 
  of 
  this 
  competition 
  for 
  light, 
  plant 
  stems 
  often 
  

   become 
  greatly 
  lengthened. 
  Any 
  one 
  who 
  is 
  observant 
  and 
  

   familiar 
  with 
  things 
  out 
  of 
  doors 
  must 
  have 
  noticed 
  the 
  dif- 
  

   ference 
  in 
  form 
  (liabit 
  it 
  is 
  called 
  by 
  botanists) 
  of 
  such 
  plants 
  

   as 
  giant 
  ragweed 
  (Ambrosia 
  trifida) 
  and 
  hemp; 
  they 
  grow 
  

   tall 
  and 
  little 
  branched 
  when 
  in 
  dense 
  clumps, 
  but 
  low 
  and 
  

   spreading 
  when 
  they 
  stand 
  alone. 
  Full-grown 
  trees, 
  such 
  as 
  

   pines, 
  are 
  nearly 
  branchless 
  for 
  most 
  of 
  their 
  height 
  when 
  

   growing 
  in 
  dense 
  forests, 
  but 
  are 
  low 
  and 
  broad-topped, 
  with 
  

   many 
  lateral 
  branches, 
  when 
  growing 
  alone 
  in 
  a 
  pasture. 
  

  

  58. 
  Plants 
  blown 
  down 
  by 
  wind. 
  Most 
  farmers 
  who 
  grow 
  

   any 
  kind 
  of 
  grain 
  have 
  had 
  losses 
  from 
  lodged 
  grain 
  --that 
  

   is, 
  from 
  crops 
  which 
  have 
  been 
  more 
  or 
  less 
  completely 
  blown 
  

   down 
  by 
  a 
  windstorm, 
  and 
  especially 
  by 
  a 
  wind 
  accompanied 
  

   by 
  a 
  heavy 
  rain. 
  Forest 
  trees 
  are 
  often 
  blown 
  down 
  by 
  severe 
  

   winds 
  (fig. 
  41). 
  Where 
  they 
  pass 
  through 
  forest 
  tracts, 
  the 
  

   violent 
  rotary 
  storms 
  commonly 
  known 
  as 
  cyclones 
  frequently 
  

   leave 
  behind 
  them 
  windfalls, 
  in 
  which 
  the 
  tree 
  trunks 
  lie 
  in 
  

   piles 
  for 
  long 
  distances. 
  Individual 
  plants 
  of 
  any 
  kind 
  of 
  

   grain, 
  and 
  tall, 
  slender 
  forest 
  trees 
  growing 
  under 
  usual 
  con- 
  

   ditions, 
  are 
  greatly 
  protected 
  by 
  their 
  neighbors. 
  The 
  whole 
  

   mass 
  of 
  plants, 
  standing 
  as 
  close 
  together 
  as 
  they 
  do, 
  inter- 
  

   cepts 
  much 
  of 
  the 
  wind, 
  so 
  that 
  the 
  single 
  plant 
  is 
  exposed 
  

   to 
  only 
  a 
  small 
  fraction 
  of 
  its 
  total 
  force. 
  

  

  59. 
  Growth 
  in 
  length 
  of 
  stem. 
  Under 
  favorable 
  conditions 
  

   the 
  younger 
  regions 
  of 
  the 
  stem 
  continue 
  for 
  some 
  time 
  to 
  

   increase 
  in 
  length. 
  The 
  rate 
  of 
  growth 
  varies 
  greatly 
  in 
  

   dirt'tTciil 
  plains: 
  the 
  giant 
  ragweed 
  and 
  certain 
  kinds 
  of 
  sun- 
  

   flowers 
  may 
  grow 
  to 
  a 
  height 
  of 
  10 
  or 
  12 
  feet, 
  and 
  climbers 
  

   like 
  gourds 
  and 
  hops, 
  to 
  a 
  length 
  of 
  perhaps 
  40 
  feet, 
  in 
  a 
  

   single 
  summer. 
  On 
  the 
  other 
  hand, 
  pine 
  seedlings, 
  during 
  

   their 
  first 
  summer, 
  grow 
  to 
  be 
  only 
  from 
  1 
  to 
  3 
  inches 
  high, 
  

   and 
  oak 
  seedlings 
  less 
  than 
  5 
  inches. 
  For 
  a 
  time 
  the 
  growth 
  

  

  