﻿THE 
  ALG.E 
  

  

  221 
  

  

  Oscillatoria, 
  grows 
  in 
  the 
  same 
  kind 
  of 
  region 
  as 
  Nostoc, 
  but 
  

   is 
  more 
  abundant. 
  It 
  appears 
  as 
  floating 
  mats 
  or 
  as 
  slimy 
  coat- 
  

   ings 
  upon 
  objects 
  in 
  the 
  water. 
  Frequently- 
  sticks 
  and 
  stones 
  

   on 
  the 
  bottom 
  are 
  covered 
  with 
  a 
  beautiful 
  velvety 
  layer 
  con- 
  

   sisting 
  of 
  multitudes 
  of 
  these 
  simple 
  plants. 
  The 
  individual 
  

   plants 
  are 
  thread-like 
  (fig. 
  173) 
  and 
  often 
  have 
  a 
  swinging, 
  glid- 
  

   ing, 
  or 
  oscillating 
  movement, 
  from 
  which 
  the 
  name 
  of 
  the 
  plant 
  

   is 
  derived. 
  In 
  stagnant 
  or 
  foul 
  

   water 
  Oscillatoria 
  plants 
  grow 
  

   vigorously, 
  being 
  able 
  to 
  thrive 
  

   throughout 
  a 
  wide 
  range 
  of 
  tem- 
  

   perature. 
  The 
  cells 
  of 
  the 
  plant 
  

   divide, 
  thus 
  lengthening 
  the 
  

   plant. 
  Later 
  the 
  threads 
  break 
  

   into 
  two 
  or 
  more 
  new 
  threads, 
  

   each 
  of 
  which 
  continues 
  to 
  grow 
  

   as 
  an 
  independent 
  plant. 
  The 
  

   cells 
  of 
  one 
  plant 
  are 
  inclosed 
  

   in 
  jelly-like 
  sheaths, 
  but 
  there 
  is 
  

   no 
  jelly 
  mass 
  which 
  holds 
  many 
  

   plants 
  together, 
  as 
  in 
  Nostoc. 
  

  

  It 
  is 
  evident 
  that 
  blue-green 
  

   alga? 
  live 
  and 
  reproduce 
  them- 
  

   selves 
  in 
  very 
  simple 
  ways. 
  

  

  205. 
  The 
  green 
  algae 
  : 
  Pleurococcus. 
  This 
  green 
  alga 
  is 
  very 
  

   widely 
  distributed 
  and 
  is 
  often 
  called 
  green 
  slime, 
  because 
  of 
  

   the 
  appearance 
  it 
  presents 
  when 
  growing 
  upon 
  partially 
  shaded 
  

   tree 
  trunks, 
  fences, 
  rocks, 
  and 
  old 
  buildings. 
  It 
  is 
  not 
  usually 
  

   recognized 
  as 
  being 
  a 
  plant. 
  When 
  there 
  is 
  abundant 
  moisture 
  

   in 
  the 
  air, 
  the 
  coating 
  of 
  plants 
  presents 
  the 
  appearance 
  of 
  a 
  

   coating 
  of 
  green 
  paint 
  upon 
  the 
  surface 
  which 
  supports 
  them. 
  

  

  When 
  examined 
  under 
  suitable 
  magnification, 
  the 
  green 
  slime 
  

   is 
  seen 
  to 
  be 
  composed 
  of 
  many 
  thousands 
  of 
  single-celled 
  

   plants. 
  A 
  careful 
  measurement 
  of 
  a 
  number 
  of 
  plants 
  showed 
  

   their 
  average 
  diameter 
  to 
  be 
  about 
  -%-Q-Q-Q 
  inch 
  (.014 
  mm.). 
  In 
  

   other 
  words, 
  it 
  would 
  reouire 
  approximately 
  500 
  of 
  these 
  

  

  FIG. 
  173. 
  Oscillatoria 
  

  

  A, 
  tips 
  of 
  several 
  plants; 
  B, 
  part 
  of 
  

  

  one 
  plant, 
  enlarged 
  to 
  show 
  cellular 
  

  

  structure. 
  Both 
  magnified, 
  B 
  much 
  

  

  more 
  than 
  A 
  

  

  