THE BLUE-GEEEN ALG^ (CYANOPHYCE^) 187 



New plants are established by the blue-green algse in the 

 simplest ways that are possible. Reproduction takes place by 

 means of fission of the single-celled forms, or by the breaking 

 into two or more parts of the chains or filaments of the less sim- 

 ple forms. Sometimes in certain species of Nostoc reproduction 

 is said to occur by means of a special heavy-walled cell which, 

 after lying quiet for a time, may grow into a new plant. 



The growing plant is often spoken of as the vegetative 

 plant, and when reproduction occurs as it does in the blue- 

 green algfe, by division to produce new plants, the process is 

 known as vegetative reproduction. Such reproduction is charac- 

 teristic of the blue-green algae. 



The blue-green algse have a very wide distribution. They 

 are found in both fresh and salt waters, in warm and cool tem- 

 peratures, and at high and low altitudes. They thrive in water, 

 and also upon land, provided they have a supply of moisture. 

 Many of them are most luxuriant near the mouths of sewers, 

 in case light and temperature conditions are favorable. In re- 

 gions where moisture is intermittent they thrive part of the year 

 and are dormant the rest of the time. Often they grow in such 

 numbers as to tinge the water with green, or whatever other 

 color the plant may have. Fresh-water lakes are often distinctly 

 green from the growth of Rivularia, Gloeotrichia, and other 

 forms. The Red Sea owes its hue to the abundant growth of a 

 reddish-brown member of this group. The margins of some of 

 the pools about geysers and lakes in the Yellowstone National 

 Park, and shores of lakes and streams, are often so colored. 



172. Classification of the Fission Plants (Schizophytes): 



Thallophytes 

 Schizophytes 



Class I. Sohizomycetes (bacteria) 



Illustrated by numerous type forms and various methods of 

 living 

 Class II. Sohizophyceae, or Cyanophycese (the blue-green algse) 

 Leading genera used as illustrations, — Gl(Eocapsa, Nostoc, 

 Oscillatoria 



