414 Annals New York Academy of Sciences 



the Chroococcales, and 8 families which diverge in morphological characteristics 

 in a single evolutionary sequence (Drouet, in press). The coccoid families 

 include the Chroococcaceae, Chamaesiphonaceae and Clastidiaceae. Fila- 

 mentous famihes consist of the Stigonemataceae, Nostocaceae, Rivulariaceae, 

 Scytonemataceae, and Oscillatoriaceae. Consideration of the first three 

 families is given according to a recent comprehensive revision (Drouet and 

 Daily, 1956), that of the other famihes follows the starting points according 

 to the International Rules of Nomenclature (Gomont, 1892; Bornet and 

 Flahault, 1886-1 888a and b). 



A representative member of each family is given (figures 1 to 8). These 

 members are not to be construed as "typical" because there can be wide varia- 

 tion inter- and intraspecifically in nature as well as in culture. However, 

 Anacystis montana (figure 1) is the most frequently collected of the coccoid 

 species (Drouet, 1954). Nostoc musconim (figure 5) is of common occurrence 

 on soil, and Calothrix parielina (figure 6) is of wide distribution in moist 

 habitats (Fan, 1956). Scytonema Iwfmannii (figure 7) is also a frequently 

 encountered species, and Microcoleus vaginatus (figure 8) is an oscillatorioid 

 member often found on soil as well as in aquatic habitats. These species have 

 been recently described with others found in the United States north of the 

 Rio Grande River (Drouet, 1959). 



The Chroococcaceae consist of uni- or multicellular, micro- or macroscopic 

 plants which are subaerial or aerial, free, as cushions or strata. The cells are 

 spherical, discoid, ovoid, ellipsoid, cylindrical, or pyriform, in regular or ir- 

 regular order, each cell dividing into 2 ecjual daughter cells which become sepa- 

 rated from each other by the gelatinous matrix. Reproduction is by fragmen- 

 tation as for most of the blue-green algae, but in some cases by cell division. 

 Under most conditions, except for Coccochloris, cells are found in the process 

 of division. Species of Anacystis, represented here by A. montana (figure 1) 

 have cells at first hemispherical, later becoming spherical. The cells then di- 

 vide in 3 planes perpendicular to each other. Coccochloris resembles Anacystis, 

 but has subspherical to long cylindrical cells and division at right angles to the 

 long axis. Other genera include Johannesbaptistia which has a linear series of 

 discoid cells within an elongate gelatinous matrix, and AgmeneUum, Micro- 

 crocis, and Gomphosphaeria which have cells that divide successively in 2 

 planes perpendicular to each other. Plants of the first two genera are plate- 

 like, whereas those of the latter genus are unique in that the cells are frequently 

 cordiform in division and the remains of individual sheaths form branched 

 stalks radiating from the center of the plant. 



The Chamaesiphonaceae contain one genus, represented here by Entophy- 

 salis lemaniae (figure 2). Plants of this family are uni- or multicellular, 

 aquatic, micro-, or macroscopic. The cells are at first solitary and affixed to 

 the substratum, each dividing serially into first unequal then equal daughter 

 cells which are not separated by gelatinous material. Subsequently, a stratum 

 or cushion is developed above the substratum, and branched filaments grow 

 downward from this into the substratum. Any cell is then capable of enlarg- 

 ing and dividing internally into a few or many endospores. Reproduction is 

 by fragmentation as well as by endospores. 



Plants of the Clastidiaceae are infrequently collected. The plants consist 



