THE FRESH-WATER ALGAE 



135 



5 (n) Cells cylindrical, with no constriction, or at most a very shallow and 



broad constriction, giving a slightly undulating outline. 6 



6 (7, 8) Cells not longer than broad, sometimes with a very shallow, broad 



constriction; chroma tophore central, with 6 to 10 rays about 

 a pyrenoid Hyalotheca Ehrenberg. 



Filaments long, often twisted, and slippery to the touch. 

 The different diameters of the cells nearly equal, varying 

 from 20 to 35 /z. The median constriction often very slight. 

 Chromatophore in each cell-half of radiating plates placed 

 about a pyrenoid. 



A broad gelatinous envelop is always present but it is in- 

 visible without reagents. 



Hyalotheca is frequent among filamentous forms of the 

 Conjugates. 



FIG. 107. Hyalotheca dissiliens Br6bisson. a. side view. b. end 

 view. X 575. (Original.) 



7 (6, 8) Cells but little longer than broad, attenuated at the end. 



Leptozosma Turner. 



Filaments long, cateniform; not twisted, or 

 but slightly so. Joints united by a strongly 

 marked suture; near to Bambuscina Kiitzing, 

 but differing therefrom in the suture. 



FIG. 1 08. Leptozosma calenulata Turner. X 300. 

 (After Turner.) 



8 (6, 7) Cells much longer than broad 9 



9 (10) Chromatophore a central plate containing a row of pyrenoids. 



Gonatozygon de Bary. 



Length of cells 100 to 200 /*; breadth 10 to 20/1, 

 much like a cell of Mougeotia except that the 

 membrane is covered with minute projections; 

 FIG. 109. Gonatozygon raljsii de Bary. cells sometimes slightly swollen at the ends. 



X about 230. (After de Bary.) 



10 (9) Chromatophores consisting of several parietal spiral bands. 



Genicularia de Bary. 



Diameter of cells 17 to 22.5 ju; length 

 10 to 20 times as great. Membrane cov- 

 ered with fine projections as in Gonatozygon. 

 FIG. no. Genicularia spirotaenia Bre"bisson. X 265. Spiral chromatophores with many pyrenoids. 

 (After de Bary.) 



11 (5) Cells not cylindrical 12 



12 (19) End view of cells circular, oval, or elliptical, rarely triangular. . 13 



13 (16) Cells not deeply constricted at the middle 14 



14 (15) Cells cask-shaped, placed end to end, with a shallow narrow con- 



striction at the middle; end view circular, with two oppo- 

 sitely placed projections Gymnozyga. 



The membrane frequently shows longitudinal stripes. 

 Chromatophores in each cell-half composed of a number 

 of radially-placed plates arranged about a pyrenoid at 

 the center. 



FIG. in. Gymnozyga br (bissonii Nordstedt. X 568. (Original.) 



