126 ALGAE IN PHYTOPT.ANKTON OF THE UNITED STATES 



Division Cyanophyta 

 Class Cyanophyceae 

 Order Hormogonales 

 Family Oscillatoriaceae 

 GENUS PHORMIDIUM Kutzing, 1843 (fig. 57) 



MORPHOLOGY 



Cells are discoidal and adjoined at the flat surfaces into trichomes. 

 Trichomes are unbranched, cylindrical, and enclosed by watery 

 gelatinous sheaths, which are partially or wholly confluent. Apices are 

 varied, sometimes capitate, often having calyptra. The plant mass is 

 aquatic or subaerial; it often forms an extensive stratum. 



REPRODUCTION 



Reproduction is by hormogonia. 



OCCURRENCE 



The genus is found primarily on moist rocks or damp soil (Smith, 

 1950); however, it is commonly found in the euplankton, 

 tychoplankton, and periphyton. It occurs most commonly in hard 

 water. 



ENVIRONMENTAL CONDITIONS 



Range 



Temperature degrees Celsius 0.0 - 32.5 



pH 4.8 - 8.8 



Dissolved oxygen milligrams per liter 1.2 - 13.3 



Specific conductance micromho 30 -48,000 



Total alkalinity milligrams per liter - 363 



Total hardness do 7 - 1,200 



Total nitrogen do .02- 13.0 



Total phosphorus do .0 - 3.3 



SPECIES INFORMATION 



Refer to Gomont (1892a, b), Geitler (1932), and Prescott (1962). 



