1 62 FRESH-WATER BIOLOGY 



199 (211, 212, 213) The chromatophore single, a parietal plate or cylinder. 200 



200 (205) Filaments without gelatinous envelop 201 



201 (204) Filament always simple, composed of a single row of cells. . 202 



202 (203) Cells cylindrical. Reproduction by zoospores and in some cases 



by resting spores Hormidium Kutzing. 



Zoospores formed singly in each cell; they have two cilia but no pig- 

 ment spot. Resting spores occur with reduction of moisture. 



FIG. 213. Hormidium nitenz Meneghini. X 400. (Original.) 



203 (202) Cells but little longer than broad. Reproduction by zoospores 

 and isogametes. Ulothrix Kiitzing. 



Cells relatively short; chromatophore lining the entire 

 membrane, or only a part, with a pyrenoid. Reproduc- 

 tion by zoospores and isogametes. Zoospores with four 

 cilia and a pigment spot; gametes smaller, with two cilia, 

 capable of germinating without copulation. 



Ulothrix occurs frequently among other algae in ponds, 

 lakes, and watering troughs, though not often in great 

 quantities. 



The resemblance to Hormidium is great, though the 

 species of the latter genus are apt to be somewhat smaller, 

 and the length of the cells relatively longer in proportion to 

 the breadth. 



Ulothrix yields readily to cultivation, and different phases 

 of its development may be controlled by changes in the 

 environment. 



FIG. 214. Ulothrix zonata Kutzing; a. vegetative filament. X 

 225. b. macrozoospore. Xa88. c. microzoospore. (After Klebs.) 



204 (201) Filament at first simple, later becoming a solid mass of many cells. 



Schizomeris Kutzing. 



