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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  is 
  a 
  sac 
  fungus 
  which 
  has 
  almost 
  lost 
  the 
  habit 
  of 
  reproduction 
  

   by 
  means 
  of 
  ascospores, 
  the 
  sac 
  being 
  rarely 
  formed. 
  It 
  repro- 
  

   duces 
  itself 
  very 
  abundantly 
  by 
  means 
  of 
  conidia 
  (fig. 
  191). 
  

   The 
  number 
  of 
  these 
  conidia 
  is 
  often 
  so 
  large 
  that 
  when 
  the 
  

   substance 
  supporting 
  the 
  plants 
  is 
  slightly 
  shaken, 
  a 
  small 
  

   cloud 
  of 
  spores 
  arises. 
  

  

  234. 
  Yeasts. 
  The 
  yeasts 
  constitute 
  a 
  group 
  of 
  plants 
  of 
  

   somewhat 
  doubtful 
  classification. 
  Since 
  they 
  occasionally 
  form 
  

   sacs 
  in 
  which 
  spores 
  are 
  formed, 
  they 
  are 
  often 
  classed 
  with 
  

   the 
  sac 
  fungi. 
  They 
  are 
  extremely 
  simple, 
  and 
  are 
  more 
  inter- 
  

   esting 
  because 
  of 
  their 
  manner 
  of 
  life 
  than 
  because 
  of 
  their 
  

  

  structure. 
  A 
  yeast 
  plant 
  is 
  

   a 
  single 
  cell 
  (fig. 
  192). 
  It 
  

   usually 
  reproduces 
  itself 
  by 
  

   a 
  method 
  of 
  vegetative 
  repro- 
  

   duction 
  known 
  as 
  fun/i/fm/. 
  

   The 
  buds, 
  before 
  becoming 
  

   FIG. 
  192. 
  Yeast 
  plants 
  separated 
  from 
  the 
  parent 
  

  

  a, 
  a 
  plant 
  from 
  which 
  a 
  bu.i 
  has 
  begun 
  cells, 
  may 
  bud 
  again 
  and 
  

   to 
  grow; 
  i, 
  and 
  c, 
  plants 
  with 
  two 
  again 
  until 
  a 
  chain 
  of 
  plants 
  

  

  buds. 
  Note 
  the 
  vacuoles 
  in 
  the 
  plants. 
  . 
  . 
  , 
  Tf 
  , 
  ^ 
  

  

  Greatly 
  enlarged 
  ls 
  lormeu. 
  It 
  a 
  cake 
  or 
  com- 
  

  

  mercial 
  yeast 
  is 
  examined, 
  it 
  

  

  is 
  found, 
  in 
  addition 
  to 
  the 
  large 
  starch 
  grains 
  nearly 
  always 
  

   occurring 
  in 
  yeast 
  cakes, 
  to 
  consist 
  of 
  hundreds 
  of 
  thousands 
  

   of 
  yeast 
  cells, 
  some 
  single 
  and 
  some 
  in 
  process 
  of 
  budding. 
  

   If 
  a 
  cake 
  of 
  yeast 
  is 
  kept 
  at 
  room 
  temperature, 
  the 
  plants 
  

   soon 
  continue 
  their 
  growth, 
  and 
  other 
  organisms 
  (bacteria 
  and 
  

   molds) 
  also 
  grow, 
  so 
  that 
  the 
  yeast 
  " 
  spoils." 
  

  

  When 
  yeast 
  plants 
  are 
  placed 
  in 
  dough, 
  they 
  grow 
  with 
  

   great 
  rapidity. 
  They 
  live 
  upon 
  the 
  solutions 
  in 
  the 
  dough, 
  

   and 
  in 
  so 
  doing 
  they 
  break 
  down 
  the 
  sugar, 
  thus 
  forming 
  from 
  

   it 
  small 
  quantities 
  of 
  alcohol 
  and 
  carbon 
  dioxide. 
  The 
  carbon- 
  

   dioxide 
  gas 
  forms 
  air 
  spaces 
  which 
  cause 
  the 
  phenomenon 
  

   known 
  as 
  r/*/ii</. 
  1 
  During 
  the 
  process 
  of 
  baking, 
  the 
  air 
  spaces 
  

  

  1 
  Salt-rising 
  bivad 
  .PUTS 
  its 
  peculiar 
  quality 
  to 
  the 
  fact 
  that, 
  instead 
  of 
  

   yeasts, 
  certain 
  bacteria 
  produce 
  fermentation 
  within 
  the 
  dough. 
  

  

  