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  INTRODUCTION 
  TO 
  BOTANY 
  

  

  Another 
  kind 
  of 
  reproduction 
  may 
  occur 
  at 
  the 
  same 
  time 
  

   that 
  zoospores 
  are 
  being 
  formed, 
  though 
  it 
  usually 
  occurs 
  at 
  

   other 
  times. 
  Upon 
  the 
  sides 
  of 
  the 
  plant 
  special 
  short 
  branches 
  

   are 
  formed. 
  Two 
  kinds 
  of 
  branches 
  arise 
  near 
  one 
  another 
  

   (fig. 
  178). 
  One 
  is 
  short 
  and 
  irregularly 
  spherical, 
  and 
  has 
  a 
  

   beak. 
  This 
  branch 
  forms 
  one 
  large 
  cell 
  within 
  it. 
  The 
  other 
  

   branch 
  is 
  longer, 
  somewhat 
  coiled, 
  and 
  has 
  a 
  terminal 
  cell 
  that 
  

   is 
  cut 
  off 
  by 
  means 
  of 
  a 
  cross 
  wall. 
  In 
  the 
  terminal 
  segment 
  

   many 
  small 
  cells 
  are 
  formed. 
  Through 
  a 
  small 
  opening 
  in 
  

  

  the 
  tip 
  of 
  this 
  coiled 
  

   branch 
  these 
  cells 
  es- 
  

   cape, 
  some 
  of 
  them 
  

   entering 
  the 
  beak 
  of 
  

  

  A\ 
  S, 
  the 
  other 
  branch 
  and 
  

  

  one 
  of 
  them 
  uniting 
  

   with 
  the 
  large 
  cell. 
  

   This 
  union 
  forms 
  a 
  

   FIG. 
  178. 
  The 
  sexual 
  reproductive 
  structures 
  spore 
  which 
  proceeds 
  

  

  of 
  Viwkc.na 
  (V. 
  sessUis) 
  to 
  develop 
  a 
  heavy 
  

  

  o, 
  oogonia; 
  A, 
  antheridium. 
  Note 
  the 
  opening 
  in 
  protecting 
  wall. 
  Alter 
  

   the 
  antheridium 
  for 
  exit 
  of 
  sperms, 
  and 
  in 
  the 
  a 
  p 
  er 
  i 
  o 
  d 
  of 
  rest 
  this 
  

   oogonia 
  for 
  their 
  entrance 
  to 
  the 
  large 
  eggs. 
  . 
  

  

  Greatly 
  enlarged 
  spore 
  germinates 
  and 
  

  

  produces 
  a 
  new 
  plant. 
  1 
  

  

  If 
  this 
  spore 
  had 
  been 
  formed 
  by 
  the 
  union 
  of 
  similar 
  gam- 
  

   etes, 
  as 
  in 
  S]>in><///,-<i, 
  we 
  should 
  have 
  called 
  it 
  a 
  zygospore; 
  

   but 
  it 
  is 
  formed 
  by 
  the 
  union 
  of 
  gametes 
  that 
  are 
  very 
  unlike, 
  

  

  one 
  large 
  gamete 
  (the 
  egy, 
  or 
  oo'sphere) 
  and 
  the 
  other 
  a 
  small 
  

  

  gamete 
  (the 
  sperm), 
  --and 
  the 
  resulting 
  spore 
  is 
  called 
  an 
  

   oospore, 
  which 
  means 
  " 
  egg 
  spore." 
  When 
  similar 
  gametes 
  

   unite 
  to 
  form 
  a 
  zygospore, 
  the 
  process 
  is 
  called 
  conjugation, 
  

   but 
  \\hen 
  dissimilar 
  gametes 
  unite 
  to 
  form 
  an 
  oospore, 
  the 
  

   process 
  is 
  called 
  fertilization. 
  The 
  special 
  sex 
  organ 
  which 
  

   produces 
  the 
  sperm 
  is 
  the 
  aniheri<linm, 
  or 
  sperm 
  case, 
  and 
  that 
  

   which 
  produces 
  the 
  egg 
  is 
  the 
  oogonium, 
  or 
  egg 
  case. 
  

  

  1 
  To 
  THE 
  TEACHER. 
  No 
  attempt 
  is 
  made 
  to 
  present 
  the 
  difficult 
  and 
  tech- 
  

   nical 
  questions 
  relative 
  to 
  the 
  alternation 
  of 
  generations 
  in 
  the 
  thallophytes 
  

  

  