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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  is 
  soon 
  exhausted, 
  and 
  the 
  excretions 
  from 
  the 
  bacteria 
  them- 
  

   selves 
  interfere 
  with 
  their 
  growth 
  and 
  reproduction. 
  But 
  in 
  

   situations 
  where 
  bacteria 
  can 
  grow 
  they 
  really 
  do 
  reproduce 
  

   themselves 
  and 
  increase 
  their 
  number 
  with 
  astonishing 
  rapidity 
  

   (fig. 
  166). 
  The 
  possibilities 
  of 
  production 
  and 
  growth 
  of 
  large 
  

  

  FIG. 
  1(56. 
  Gelatin 
  culture 
  of 
  bacteria 
  

  

  The 
  sterilized 
  gelatin 
  in 
  the 
  dish 
  was 
  exposed 
  in 
  the 
  hallway 
  of 
  a 
  schoolroom 
  for 
  

   five 
  minutes, 
  and 
  then 
  kept 
  covered 
  for 
  live 
  days, 
  during 
  which 
  time 
  the 
  different 
  

   colonies 
  of 
  bacteria 
  ure\v. 
  Each 
  colony 
  grew 
  from 
  one. 
  or 
  possibly, 
  in 
  some 
  cases, 
  

   from 
  a 
  few 
  individual 
  bacteria, 
  and 
  the 
  number 
  of 
  bacteria 
  that 
  have 
  grown 
  in 
  

   each 
  colony 
  is 
  so 
  large 
  that 
  the 
  colony 
  is 
  easily 
  seen 
  

  

  numbers 
  are 
  evident 
  when 
  we 
  remember 
  that 
  many 
  millions 
  

   of 
  bacteria 
  could 
  live 
  for 
  a 
  considerable 
  time 
  in 
  a 
  cubic 
  inch 
  

   of 
  milk 
  or 
  beef 
  broth. 
  

  

  In 
  a 
  few 
  kinds 
  of 
  bacteria 
  the 
  interior 
  of 
  the 
  cell 
  sometimes 
  

   becomes 
  rounded 
  and 
  inclosed 
  by 
  a 
  relatively 
  heavy 
  wall. 
  

   This 
  heavy-walled 
  body 
  may 
  remain 
  inactive 
  for 
  a 
  long 
  period, 
  

  

  