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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  is 
  not 
  settled, 
  notable 
  experiments 
  that 
  have 
  been 
  carried 
  

   on 
  at 
  the 
  experimental 
  station 
  at 
  Harpenden, 
  England, 
  since 
  

   1848 
  will 
  show 
  the 
  nature 
  of 
  some 
  of 
  these 
  studies. 
  Certain 
  

   crops 
  have 
  there 
  been 
  grown 
  year 
  after 
  year 
  upon 
  the 
  same 
  

   soil. 
  A 
  barley 
  field 
  which 
  has 
  been 
  unfertilized 
  since 
  the 
  

   experiments 
  began, 
  produced, 
  in 
  the 
  year 
  1849, 
  a 
  little 
  <>\rr 
  

   40 
  bushels 
  per 
  acre. 
  Each 
  year 
  thereafter, 
  with 
  no 
  fertilization, 
  

  

  FIG. 
  238. 
  Effect 
  of 
  quality 
  of 
  soil 
  on 
  growth 
  of 
  roots 
  

  

  The 
  eueumhc-r 
  plant 
  shown 
  in 
  the 
  figure 
  was 
  grown 
  in 
  a 
  shallow 
  box, 
  one 
  end 
  of 
  

   which 
  was 
  tilled 
  with 
  sand 
  and 
  the 
  other 
  with 
  rich 
  loam. 
  The 
  seed 
  wa> 
  planted 
  

   in 
  the 
  sand, 
  quite 
  near 
  the 
  partition 
  (p) 
  of 
  mosquito 
  netting 
  which 
  separated 
  the 
  

   sand 
  from 
  the 
  loam. 
  When 
  the 
  plant 
  was 
  one 
  foot 
  high, 
  the 
  earth 
  and 
  sand 
  \\ 
  en- 
  

   cashed 
  away 
  and 
  the 
  roots 
  sketched. 
  Those 
  grown 
  in 
  the 
  loam 
  weighed 
  nine 
  

   times 
  as 
  much 
  as 
  those 
  in 
  the 
  sand. 
  Three 
  eighths 
  natural 
  size 
  

  

  barley 
  has 
  been 
  grown 
  on 
  the 
  same 
  field, 
  and 
  the 
  yield 
  has 
  

   steadily 
  decreased, 
  so 
  that 
  during 
  the 
  twenty 
  years 
  ending 
  with 
  

   lUO'J 
  the 
  average 
  per 
  year 
  was 
  less 
  than 
  15 
  bushels 
  per 
  acre. 
  

   Another 
  piece 
  of 
  ground 
  was 
  used 
  for 
  wheat, 
  turnips, 
  and 
  

   clover 
  in 
  rotation 
  (with 
  three 
  years 
  given 
  to 
  each 
  rotation), 
  

   and 
  was 
  1'ert 
  ili/ed 
  by 
  the 
  use 
  of 
  nitrogen 
  and 
  mineral 
  fertilizers. 
  

   Considering 
  only 
  the 
  wheat 
  records, 
  we 
  have 
  the 
  following 
  : 
  

   In 
  the 
  first 
  twenty 
  years 
  the 
  average 
  yield 
  of 
  wheat 
  for 
  the 
  

   years 
  in 
  which 
  wheat 
  was 
  grown 
  was 
  35.3 
  bushels 
  per 
  acre 
  ; 
  

   in 
  the 
  second 
  period 
  of 
  twenty 
  years 
  32 
  bushels 
  per 
  acre 
  was 
  

  

  