﻿224 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  When 
  Spirogyra 
  cells 
  divide, 
  the 
  division 
  wall 
  is 
  at 
  right 
  

   angles 
  to 
  the 
  length 
  of 
  the 
  plant. 
  This 
  results 
  in 
  an 
  increase 
  

   in 
  the 
  number 
  of 
  cells 
  and 
  usually 
  in 
  the 
  growth 
  in 
  length 
  

  

  of 
  the 
  whole 
  plant. 
  

   Growth 
  occurs 
  so 
  rap- 
  

   idly 
  that, 
  in 
  a 
  few 
  

   days 
  after 
  the 
  plants 
  

   are 
  first 
  seen 
  in 
  the 
  

   spring, 
  they 
  become 
  

   so 
  abundant 
  that 
  they 
  

   pollute 
  the 
  water 
  in 
  

   which 
  they 
  grow, 
  and 
  

   it 
  is 
  often 
  necessary 
  

   to 
  remove 
  these 
  and 
  

   other 
  algal, 
  as 
  is 
  seen 
  

   later 
  (sect. 
  216). 
  

  

  210. 
  The 
  reproduc- 
  

   tion 
  of 
  Spirogyra. 
  It 
  

   is 
  possible 
  for 
  a 
  sin- 
  

   gle 
  plant 
  to 
  become 
  

   broken 
  into 
  two 
  or 
  

   more 
  pieces, 
  when 
  

   each 
  one 
  may 
  grow 
  

   into 
  a 
  new 
  plant 
  ; 
  this 
  

   is 
  vegetative 
  repro- 
  

   duction 
  and 
  resem- 
  

   bles 
  the 
  vegetative 
  

   reproduction 
  that 
  was 
  

   seen 
  in 
  Pleurococcus. 
  

   But 
  this 
  is 
  not 
  the 
  

   usual 
  method 
  of 
  repro- 
  

   duction 
  in 
  Spiroi/i/rn. 
  

  

  FIG. 
  175. 
  Spirogyra 
  

  

  A, 
  a 
  vegetative 
  cell, 
  showing 
  the 
  form 
  of 
  the 
  cell 
  

   and 
  of 
  the 
  spiral 
  chlonrplast 
  (ch), 
  also 
  the 
  nucleus 
  

   () 
  and 
  cytoplasm 
  (<?/); 
  />', 
  beginning 
  of 
  conjuga- 
  

   tion 
  (a 
  and 
  b), 
  and 
  tubes 
  which 
  failed 
  to 
  conjugate 
  

   (c 
  and 
  d) 
  ; 
  C, 
  completed 
  zygospores 
  (z) 
  

  

  The 
  cells 
  of 
  two 
  plants 
  that 
  lie 
  near 
  one 
  another 
  may 
  unite 
  

   in 
  pairs 
  by 
  means 
  of 
  tubes 
  growing 
  out 
  from 
  the 
  walls 
  of 
  both 
  

   of 
  the 
  uniting 
  cells 
  (fig. 
  175). 
  These 
  tubes 
  meet 
  and 
  then- 
  

   end 
  walls 
  are 
  absorbed, 
  so 
  that 
  there 
  is 
  a 
  continuous 
  tube 
  

  

  