BLUE-GREEN ALGAE 297 



Blue-green Algae. Cyanophyceae 



The Blue-green Algae are the simplest forms of Algae and are 

 the simplest known plants that make their own food. They 

 are so named because of their bluish green color which is due 

 to the presence of chlorophyll and a blue pigment called Phyco- 

 cyanin. Although their size is microscopical, they form aggre- 

 gations that are often quite conspicuous. There are about 1200 

 species of Blue-green Algae, and they are widely distributed, 

 occurring nearly everywhere in fresh and salt water and also on 

 wet soil, rocks, and logs. On wet surfaces they form bluish 

 green slimy layers or jelly-like lumps, and in sluggish streams 

 and ponds they form bluish green scums or mats which float on 

 or near the surface of the water. They thrive best where there 

 is organic matter and consequently prefer stagnant to running 

 waters. Some forms are so resistant to heat that they can live 

 in hot springs where the temperature is near the boiling point 

 of water. Some, called endophytes, live in the cavities of some of 

 the more highly organized plants, such as the Liverworts and 

 Ferns. Some are associated with Fungi in the formation of 

 Lichens. The Blue-green Algae are of only slight economic im- 

 portance. When allowed to accumulate, they impart offensive 

 odors to water supplies, but are easily controlled by use of 

 copper salts. It is claimed that livestock are sometimes killed 

 by drinking water that has become foul with Blue-green Algae. 



The plant body in the Blue-green Algae is a single cell or a 

 colony of cells so joined as to form a filament or plate. When 

 cell division is in only one direction and the cells formed do not 

 separate, then as a result of a number of successive cell divisions 

 a chain or filament of cells is formed. When cell division is in 

 more than one direction and the cells do not separate, then 

 colonies of other shapes are formed. Colonies, although they 

 may resemble multicellular plants, are aggregates of essentially 

 independent cells. One notable feature of the plant body of the 

 Blue-green Algae is the secretion of a gelatinous substance which 

 forms a sheath about the plant. As plants grow and multiply, 

 the gelatinous secretion accumulates and commonly forms a 

 matrix which holds the plants together in slimy layers or jelly- 

 like lumps. The gelatinous sheath holds water and thus protects 

 the plants from drying out. Another notable feature of this 



