254 EXPLANATION OP THE PLATES. 



Pig. 2 6. A "first form" filament of the same species. 

 Pig. 2 a. A filament from an old frond of the same plant. 



Pig. 2 c. Pragments of tissue from the upper surface of a mature, actively growing plant of the 

 same species. 



Pig. 3. A filament of Nostoc comminutum, Ktz , magnified 800 diameters. 



Pig. 4. A filament of Anabsena gelatinosa, Wood, magnified 750 diameters, showing the large 

 globular body at the end, supposed to be a spore. 



Pig. 5. A filament of Anabsena gigantea, Wood, magnified 750 diameters. 



Pig. 6. A portion of a filament of Gylindrospermum minutum, Wood, magnified 800 diameters. 

 The number has been omitted from this figure on the plate ; the figure is immediately under A. 

 gigantea, Wood; the hairs on the heterocyst are too coarse and rigid. 



Pig. 7. A spore and outline of heterocyst of Gylindrospermum macrospermum, Ktz., magnified 

 750 diameters. 



Pig. 8. Tnfe end of a filament of Gylindrospermum comatum, Wood, magnified 1375 diameters. 

 The appendages to the heterocyst are coarser than natural. 



Pig. 9 a. A section of an immature frond of Bivularia cartilaginea, Wood. 

 Pig. 9 6. The base of a fertile filament, showing the spore and basal cells, magnified 800 dia- 

 meters. 



Pig. 10. An ordinary filament of Nostoc sphsericum, Poiret, 



Pigs. 10 a and 10 c. Pilaments enlarging preparatory to longitudinal division. 



Pig. 10 &. A filament already partially divided into two. 



PLATE III. 



Pig. 1 a. Gylindrospermum flexuosum (Ag.), a fertile filament, magnified 450 diameters. 

 Pig. 1 6. The end of a fertile filament, magnified 750 diameters. 



Pig. 2. Dolichospermum {Sphserozyga) subrigidum, Wood, magnified 975 diameters. 



Fig. 3. Portion of a fertile filament oi Dolichospermum {Sphserozyga)polysperma, Ktz., magnified 

 750 diameters. 



Pig. 4 a. A section of a frond of Gloiotrichia incrustata, Wood, showing youngish filaments, 

 masses of lime, and an organic body of unknown nature, all inclosed in a transparent jelly. 



Fig. 4 c. Single filaments with immature spores, magnified 260 diameters. 



Pig. 4 b. The base of a filament, showing the nearly matured spore, and empty cells situated 

 beyond it. 



Fig. 5. Ghlorococcus of undetermined species. 

 Pig. 5 a. The motile state. 



Pig. 5 b. The condition of the plant after having lost its cilia and commenced its quiescent 

 life. 



Figs. 5 and 5 c. Different stages in this life after division. 



Pig. 5 d. The Heematococcus or resting condition, the form assumed by the plant during slow 

 desiccation. 



Pig. 6. Nostochopsis lobatus, Wood. 



Pig. 6 a. Part of a section, from within outwards, of the frond, showing the tortuous branched 

 filaments, withont sheaths in the gelatinous matrix. 



Pig. 6 6. A portion of a fertile filament with the lateral spores. 

 Fig. 6 c. A sterile filament. 



Fig. 7. Protococcus of undetermined species. 



Pig. 7 a. A cell supposed to belong to the resting or winter condition of the plant. 



