ALGAE 



Algae are microscopic plants that are included in the botanical 

 division Thallophyta, being unlike higher flowering plants in that the 

 plant tissue is not differentiated into stems, roots, and leaves. The plant 

 body is referred to as a thallus. Sometimes plants of this division that 

 grow in irrigation systems are incorrectly called moss. True mosses, as 

 previously described, are a much higher type plant. 



There are a multitude of types and species of algae that grow in 

 freshwater. The type most generally considered to be important in the 

 operation of irrigation systems is the filamentous green algae. These 

 are considered to be of a higher botanical type, but still are very 

 primitive compared to the flower-producing pondweeds. 



A number of microscopic or more primitive one-celled algae (that 

 are either unicellular or colonial) are usually found in irrigation waters 

 and often create the problem of reducing the carrying capacity of water 

 distribution systems. These algae range from green types to blue-green 

 types, often causing the water to be murky or green in appearance, 

 or produce distinctive colonies that vary widely in character. Some of 

 these algae are responsible for odors and tastes in water and some can 

 be toxic to animals when ingested. Certain higher forms of green algae 

 develop a thallus that bears a certain resemblance to the leaf and stem 

 tissue of higher plants. These plants, known as stonewarts or Chara, 

 are discussed in a later section. 



41 



