EXPLANATION OF PLATES. 



PLATE I. 



Fig. 1. A single filament of Oscillatoria chlorina, Kutzing, magnified 750 diameters. 



Fig. 2. The end of a filament of an Oscillatoria supposed to be identical with 0. Frohlichii 

 Kiitzing. 



Fig. 3. 0. nigra, Yaueher. 



Fig. 3 a. Represents a portion of a mat or mass of Oscillatoria nigra, Vaucher; there is loo 

 much green in the color. 



Fig. 3 6. Represents several filaments separated from the edge of the mass and slightly magni^ 

 fied. 



Fig. 3 c. A portion of a filament. 



Fig. 3d. A portion of another filament still more highly magnified. The color in 3 c is more 

 natural than that of 3 d. 



Fig. 4. A portion of a filament of O. limosa, Ag.ardh, magnified 1250 diameters. The articles in 

 this filament are more distinctly separated than natural. 



Fig. 5. 0. neglecta, Wood. 



Fig. 5 a. An outline view of a filament, magnified 450 diameters. 



Fig. 5 6. A full figure of the same, magnified 500 diameters. 



Fig. 6 0. imperator, Wood. 



Fig. 6 a. Represents the end of a filament, magnified 250 diameters. In the centre of the plate 

 is a fragment (marked simply fig. 6.), out of which "the endochrome has been partially squeezed to 

 show the markings of the sheath at the joints. 



Fig. T. Lyngbya bicolor, Wood. Fig. 1 represents a moderately magnified portion of a filament. 

 Fig. a (near to fig. 8) represents a portion of an ordinary filament very slightly magnified. 

 Fig. Y c. A portion of a filament containing a heterocyst, magnified 800 diameters. 

 Fig. t d. A broken end of a filament showing the sheath extending beyond the endocTirome, 

 magnified 800 diameters. 



Fig. 8. A variety(?) of Lyngbya bicolor. Wood, from the Schuylkill River, magnified 200 dia- 

 meters. 

 Fig. 9, Gosmarium Quimbyii, Wood. The bands between the cells are too heavy and prominent. 



PLATE II. 



Figs. 1 b and 1 c. Different stages of germination of the spore of a Cylindrospermum of unknown 

 species, magnified respectively 800 and 1200 diameters. 



Fig. 1 a. A chain of spores, believed to belong to the same species; one of these spores has 

 commenced to germinate. 



Fio- 2 A portion of the upper surface of a frond of Nostoc calidarium, Wood. 



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