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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  plants, 
  placed 
  side 
  by 
  side, 
  to 
  make 
  a 
  row 
  that 
  would 
  reach 
  

   across 
  the 
  unsharpened 
  end 
  of 
  an 
  ordinary 
  lead 
  pencil. 
  I 
  low 
  

   does 
  Pleurococcus 
  compare 
  in 
  size 
  with 
  average 
  bacteria 
  ? 
  

  

  The 
  spherical 
  plants 
  consist 
  each 
  of 
  a 
  small 
  mass 
  of 
  living 
  

   material, 
  or 
  protoplasm, 
  surrounded 
  by 
  a 
  cell 
  wall. 
  The 
  pro- 
  

   toplasm 
  is 
  so 
  thoroughly 
  colored 
  by 
  chlorophyll 
  that 
  usually 
  it 
  

   is 
  not 
  easy 
  to 
  see 
  the 
  centrally 
  placed 
  nucleus 
  (fig. 
  1 
  74). 
  Some- 
  

   times 
  in 
  these 
  plants 
  special 
  parts 
  

   of 
  the 
  protoplasm 
  hold 
  the 
  chloro- 
  

   phyll, 
  ano/ 
  each 
  of 
  these 
  is 
  known 
  

   as 
  a 
  chloroplast, 
  which 
  means 
  

   "a 
  green 
  body," 
  or 
  a 
  chlorophyll- 
  

   containing 
  body. 
  Parts 
  of 
  the 
  pro- 
  

   toplasm 
  that 
  surrounds 
  the 
  nucleus 
  

   and 
  the 
  chloroplasts 
  are 
  granular 
  

   and 
  are 
  called 
  cytoplasm. 
  Some 
  of 
  

   the 
  internal 
  space 
  of 
  this 
  one-celled 
  

   plant 
  may 
  be 
  occupied 
  by 
  one 
  or 
  

   more 
  vacuoles, 
  which 
  are 
  regions 
  

   surrounded 
  by 
  cytoplasm 
  and 
  filled 
  

   with 
  air 
  or 
  water. 
  

  

  206. 
  The 
  food 
  of 
  Pleurococcus. 
  

   The 
  bark 
  or 
  other 
  substance 
  upon 
  

   which 
  Pleurococcus 
  grows 
  is 
  often 
  

   sufficiently 
  moist 
  to 
  provide 
  it 
  with 
  water. 
  Rains 
  and 
  dew 
  sup- 
  

   ply 
  water 
  intermittently. 
  AVhen 
  dry, 
  the 
  plants 
  remain 
  dormant 
  

   until 
  conditions 
  again 
  become 
  favorable. 
  Carbon 
  dioxide 
  (and 
  

   possibly 
  some 
  moisture) 
  may 
  be 
  absorbed 
  directly 
  from 
  the 
  air, 
  

   and 
  with 
  carbon 
  dioxide 
  and 
  water, 
  and 
  favorable 
  temperature 
  

   and 
  light, 
  Pleurococcus 
  plants 
  may 
  carry 
  on 
  photosynthesis, 
  

   thus 
  making 
  their 
  own 
  foods. 
  Heat, 
  cold, 
  and 
  extreme 
  drought 
  

   are 
  some 
  of 
  the 
  severe 
  conditions 
  which 
  this 
  plant 
  must 
  be 
  

   able 
  to 
  resist 
  in 
  order 
  to 
  live. 
  When 
  plants 
  from 
  any 
  of 
  these 
  

   extreme 
  conditions 
  are 
  placed 
  in 
  favorable 
  moisture, 
  tempera- 
  

   ture, 
  and 
  light, 
  they 
  become 
  bright 
  green 
  within 
  a 
  few 
  hours, 
  

   showing 
  that 
  they 
  are 
  manufacturing 
  foods. 
  

  

  FIG. 
  174. 
  Green 
  slime 
  

   (Pleurococcus) 
  

  

  a, 
  single 
  plants 
  showing 
  cell 
  wall, 
  

   granular 
  cytoplasm, 
  and 
  nucleus 
  ; 
  

  

  b, 
  plants 
  in 
  process 
  of 
  reproduc- 
  

   tion 
  by 
  divisi;n:, 
  or 
  lission 
  : 
  < 
  and 
  

   d, 
  further 
  divisions 
  sometimes 
  re- 
  

   sulting 
  in 
  formation 
  of 
  colonies 
  of 
  

  

  plants. 
  Greatly 
  enlarged 
  

  

  