CHAPTER V 

 BLUE-GREEN ALGAE (CYANOPHYCEAE) 



By EDGAR W. OLIVE 



Curator of the Brooklyn Botanic Garden 



The blue-green algae are found principally in fresh waters, 

 although numerous forms occur also in the sea, and are almost 

 universally distributed over the whole earth. In moist climates 

 they are particularly abundant, growing in almost every conceiv- 

 able situation as gelatinous masses or strata on rocks, stones, the 

 trunks of trees, damp ground, etc. Many of them occur abun- 

 dantly in both marine and fresh-water plankton. The pecuHar 

 phenomenon of "water-bloom" (or "working" or "blooming" of 

 the lakes, "breaking of the meres," "Flos aquae," "Wasserbliite") 

 is due to the sudden appearance in lakes and ponds of a surface 

 scum formed of vast quantities of certain plankton species of these 

 organisms. This frothy scum, forming the so-called "water- 

 bloom," is of conunon occurrence in midsummer in quiet waters, 

 especially after a protracted period of heat. Disagreeable "pig- 

 pen" odors and bad tastes are caused by such masses when decay 

 sets in, due, according to Jackson and Ellms, to the decay of highly 

 nitrogenous organic matter in which partially decomposed sulphur 

 and phosphorous compounds play a large part. The occurrence of 

 blue-green algae in public water supplies often thus becomes of 

 great economic importance; and Moore has found in this connec- 

 tion that such algal growths in reservoirs may be readily eradicated 

 or their growth prevented by the use of a dilute solution of copper 

 sulphate. 



In addition to their importance as polluting organisms in water 

 reservoirs, some recent observations appear to indicate that cer- 

 tain plankton forms of blue-green algae are sometimes used as food 

 by fish fry. Their indirect importance in this respect may be 

 regarded as well estabhshed, since Birge has shown that the com- 



