178 THE ALG^E 



extensive water bloom caused by a filamentous blue-green alga 

 (Trichodesmium) which at times fills the water, and whose color, 

 a reddish brown, gives then a peculiar tint to the sea. 



Some forms (Analcena, Clatlirocystis, and certain species of 

 Oscillatoria) are frequently responsible for the fouling of water 

 supplies which take on what is called the " pigpen odor," and 

 are otherwise unfit for public use. All of these blue-green algae, 

 together with the flagellate Uroglena, can be killed by treating 

 the reservoir or other body of water with copper sulphate (see 

 Sec. 204), a perfectly safe and inexpensive remedy for contami- 

 nated water supplies. 



Perhaps the most remarkable display of the blue-green algae 

 is in the waters of certain hot springs, as in Yellowstone 

 National Park. It is doubtful whether any algie except the 

 CyanopliycecB can live in water warmer than 100 F. (40 C.), 

 but some of the blue-green algae grow luxuriantly in hot springs 

 at 137-145 F. (58-63 C.). It is probable that their simple 

 cell structure makes possible a greater power of resistance to 

 these extraordinary life conditions. 



211. Summary of the blue-green algae. The Cyanopliycece 

 are distinguished from 'other groups of algae by the simpli- 

 city of their cell structure, the absence of sexual reproduction, 

 and the presence of a blue-green pigment uniformly diffused 

 through the outer region of the cells. The method of growth 

 by rapid divisions or splitting of the cells throughout the entire 

 plant body is a very characteristic feature of the group, and 

 the blue-green algae are sometimes called the "fission algae" 

 (Scliizopliyccce) . 



The blue-green algae agree with the bacteria, or "fission fungi" 

 (Schizomycetes), in their simplicity of cell structure and methods 

 of reproduction, but the bacteria are of course generally without 

 pigment. It is quite clear that the Cyanopliycece and the Schizo- 

 mycetes are closely related, and some authors place them together 

 in a separate division of the plant kingdom below the Thallo- 

 pliyta, named the SchizopJiyta, or " fission plants." 



