Kingdom Mychota [35 



3. Filaments more or less reduced, re- 

 producing by minute spores (gon- 

 idia) formed by repeated division 



in all planes Family 9. Pleurocapsacea. 



2. Colorless; filamentous, reproducing by 



gonidia Family 10. Crenotrichacea. 



Family 1. Oscillatoriacea [Oscillatoriaceae] Harvey 1858. Blue-green algae con- 

 sisting of unbranched filaments, not tapering, without spores or heterocysts; mostly 

 actively motile by mechanisms as yet unknown. In the commonest genus, Oscillatoria, 

 the filaments are straight and lack sheaths. Lyngbya and Phormidium produce 

 sheathed filaments, in the latter genus very slender. Microculeus and Hydrocoleum 

 have more than one filament in each sheath. In Arthrospira and Spirulina the fila- 

 ments are coiled; those of Spirulina are not visibly septate, and are said to be uni- 

 cellular. 



Family 2. Beggiatoacea [Beggiatoaceae] Migula 1895. Beggiatoa Trevisan includes 

 slender colorless filaments, actively writhing, containing granules of sulfur, found 

 in foul waters and sulfur springs. The species were originally included in Oscillatoria. 

 Winogradsky (1887) showed that they live by chemosyn thesis, and discovered the 

 related genera Thiothrix and Thioploca. From the time of these discoveries, these 

 organisms were construed as bacteria of an order Thiobacteria. Under the current 

 hypri thesis that chemosynthesis is a derived character, we are free to believe that the 

 position originally assigned to the species of Beggiatoa was the natural one. 



Family 3. Chamaesiphonacea [Chamaesiphonaceae] Borzi 1882. Order Chamaesi- 

 pkonales Smith Freshw. Alg. 74 (1933). The only genus is Chamaesiphon, minute 

 organisms epiphytic on freshwater plants. The ellipsoid cells are attached at one 

 end and are enclosed in tenuous sheaths. They reproduce by transverse division, which 

 cuts loose small cells from the free ends. By the time two or three such cells are 

 produced, the sheath is ruptured at the free end, and the small cells drift away to 

 repi educe the organism elsewhere. 



Family 4. Nostocacea [Nostocaceae] (Nageli) Rabenhorst Kryptog.-Fl. Sachsen 

 1: 95 (1863). Order Nostocaceae Nageli 1847. Of this family the most familiar genus 

 is Nostoc, seen as gelatinous bodies, usually globular, green, blue-green, yellow, or 

 brown, of sizes from barely visible to the naked eye up to 10 cm. or more in diameter, 

 in fresh water or on damp earth. Under the microscope, these bodies or colonies are 

 seen to consist of myriad crooked and tangled filaments of bead-like cells imbedded 

 in a gelatinous matrix. Heterocysts are always, and spores usually, present. 



If in water one finds filaments of much the same structure as those of Nostoc, 

 but comparatively short, straight, and free or at least not in definite colonies, these 

 represent the genus Anabaena. Filaments floating on water, with cylindrical spores 

 not confined to the ends of the filaments, are Aphanizomenon. Filaments each with 

 one heterocyst and one spore at one end are Cylindrospermum. 



Family 5. Scytonematacea [Scytonemataceae] Rabenhorst op. cit. 106. Members 

 of this family produce heavily sheathed filaments like those of Lyngbya, with the 

 difference that heterocysts are usually present. The multiplication of the cells of a 

 filament may produce the result that the cell next to a heterocyst is driven out of line 

 and forced obliquely through the sheath. With further growth, the file of cells ending 

 in one which was forced out of line may appear to be the main axis of a system of 

 branches, while the original summit of the filament appears to be a lateral branch. 

 The description of "false" branching thus given applies particularly to Tolypothrix. 



