﻿THE 
  SEED 
  PLANTS 
  

  

  293 
  

  

  known 
  as 
  the 
  pollen 
  tube. 
  While 
  the 
  tube 
  is 
  developing, 
  its 
  

   contents 
  divide 
  and 
  produce 
  several 
  cells, 
  two 
  of 
  which 
  are 
  

   male 
  cells 
  (fig. 
  225). 
  The 
  tube 
  makes 
  its 
  way 
  to 
  the 
  egg, 
  and 
  

   when 
  it 
  arrives, 
  its 
  tip 
  opens 
  and 
  the 
  two 
  male 
  cells 
  pass 
  out. 
  

  

  B 
  

  

  C 
  

  

  FIG. 
  225. 
  Stamens, 
  pollen, 
  and 
  pollen 
  tube 
  of 
  the 
  pine 
  

  

  A, 
  a 
  few 
  of 
  the 
  stamens 
  arid 
  pollen 
  sacs 
  from 
  a 
  staminate 
  cone 
  ; 
  somewhat 
  mag- 
  

   nified. 
  JB, 
  an 
  enlarged 
  pollen 
  grain 
  ; 
  much 
  magnified. 
  C, 
  the 
  tip 
  of 
  a 
  pollen 
  tuhe 
  

   at 
  the 
  time 
  when 
  it 
  has 
  almost 
  reached 
  the 
  egg 
  ; 
  just 
  back 
  of 
  the 
  two 
  nourishing 
  

   cells 
  are 
  the 
  two 
  darkly 
  colored 
  male 
  cells, 
  either 
  of 
  which 
  may 
  fertilize 
  an 
  egg 
  ; 
  

  

  much 
  magnified 
  

  

  Either 
  of 
  the 
  male 
  cells 
  may 
  unite 
  with 
  the 
  egg 
  to 
  produce 
  

   an 
  oospore 
  ; 
  the 
  other 
  disappears. 
  These 
  male 
  cells 
  would 
  be 
  

   called 
  sperms 
  if 
  they 
  had 
  cilia, 
  but 
  they 
  have 
  not. 
  There 
  are 
  

   a 
  few 
  gymnosperms 
  (the 
  older 
  ones 
  most 
  resembling 
  the 
  ferns) 
  

   in 
  which 
  the 
  male 
  cells 
  have 
  cilia, 
  can 
  swim 
  actively, 
  and 
  are 
  

   true 
  sperms, 
  but 
  even 
  these 
  are 
  carried 
  by 
  the 
  pollen 
  tube. 
  

  

  