EXPLANATION OF THE PLATES. 255 



Fig. 7 b. The first broaldng-up of the contents of the large cell into a hrooil of cells. 

 Figs. 7 d and 7 c. Diflereut stages in the life of the latter brood-cells and their progeny. 



PLATE IV. 



Fig. L Mastigonema fertile, Wood, a single plant {not magnified 750 diameters, as marked on 

 the plate). 



Pig. 16. A heterocyst magnified 750 diameters, also a spore cell and spore similarly amplified. 



Fig. 2 a. A portion of the frond of 3Iasiirjonema sejunctum, Wood, amplified 250 diameters. 

 Fig. 2 6. A single filament magnified 800 diameters. 



Fig. 3. A single filament of Zonotrivhia mollis, Wood, enlarged 260 diameters. 



Fig. 4. A section of the frond of Zonolrichia parvezonata, Wood, magnified a few diameters. 



Fig. 5. The base of a filament of Dasyactis mollis, Wood. 



Fig. 5 a. Section of the frond, magnified 450 diameters. 



Figs. 5 b and 5 c. Young filaments ; each magnified 450 diameters. 



Fig. 6. Fronds of Cstlosphaerium dubium, Wood. 



PLATE V. 



Fig. la. A portion of the frond of Blasligonema elongo.tum, Wood, slightly magnified to show 

 the filaments radiating from the fragment of matter to which they are attached. 

 Fig. 16. A single filament magnified 4G0 diameters. 



Fig. 2 c. A cluster of youngish filaments of Mastigonema halos, Wood. 



Fig. 2 6. A portion of an older filament to .show the spore-like divisions of the eudochronie, mag- 

 nified 400 diameters. 



Fig. 3. A pair of young connate filaments of Masligothrix fibrosa, Wood, magnified 450 

 diameters. 



Fig. 3 a. An old filament magnified 800 diameters. 



Fig. 3 6. A young filament with heterocyst, enlarged 450 diameters. , 



Fig. 3d A filament with two basal cells magnified 450 diameters. 



Fig. 4 a. A portion of filament of Sc>jfo)iema Ravenellii, Wood, magnified IGO diameters. 

 Fig. 4 6. The end of a branch magnified 450 diameters. 



Figs. 5 a, 6, c, &c. Different forms of Chroococcus refractus, Wood. Fig. 5 h is not n good 

 one. I was not able to express well the peculiar tran.slucent shining tint, and the artist who copied 

 my drawing failed even more decidedly in simulating it ; the pink shade is altogether wrong, I 

 never saw any such color in the plant. 



Fig. 6. Different forms of Chroococcus viiilticoloratus, Wood. 



Fig. 6 c. Represents what was thought to be possibly a hybernating form of the species. 



PLATE VI. 



Fig. la. A portion of a frond of Scytonema thermale, Ktz,, magnified 2fi0 diameters. 

 Fig. 1 6. Outline sketch, showing the form of the heterocyst, magnified 750 diameters. 



Fig. 2. Trichoma or frond of Scytonema callitrichoides, Ktz., amplified 250 diameters. 



Fig. 3 a. Outline sketch showing the cells or chambers of Scytonema dubium. Wood, magnified 

 750 diameters. 



Figs. 3 6 and 3 c. Portions of the filaments or trichoma, magnified 4G0 diameters. 



