28o 



PART IV. VEGETABLE TAXONOMY. 



FlG. 471. — Portion of filament of Oscillatoria, magnified 

 about 1,000 diameters. 



The Oscillatoriece are blue-green or brownish-green filament- 

 ous organisms, found abundantly in filthy ditches and ponds. 

 The filaments are slender, usually somewhat coiled, and com- 

 posed of compactly arranged disc-like cells, which are all alike. 

 These are separated from each other by delicate transverse par- 

 titions. The filaments are commonly agglomerated in masses, 



and each possesses a 

 peculiar writhing or 

 oscillating motion. It 

 is to this that the 

 name, Oscillatoria, is 

 due. Frequently the filaments break up transversely into short 

 segments, each of which, by cell-division in a transverse direc- 

 tion, becomes a new filament. This is the only mode of repro- 

 duction that has been observed in the group. Fig. 471 represents 

 a portion of one of the filaments. 



The Scytonemece are also filamentous greenish or brownish 

 plants, but they branch in a peculiar manner, as shown in the 

 illustration, Fig. 472. Moreover, there are often more than one 

 row of cells side by side, particularly in older filaments, and the 

 cells are enclosed in a thick gelatinous 

 envelope. Besides increasing by ordi- /£§j 18-1 

 nary cell-division, they produce hetero- W\ M? 

 cysts and asexual spores. 



Fig. 472. — Portion of filament of Scytonema Naegellii, magnified 250 diameters. 



The Rimdariece occur as small roundish gelatinous masses of 

 radiating, somewhat branching filaments, each tipped with a 

 transparent hair. At the opposite or basal end of the filament is a 



Fig. 473. — Filament of Rivularia dura, magnified about 500 diameters. 



large rounded cell, the heterocyst. The plants, or rather colonies, 

 either float in the water or are attached to water-weeds, submerged 

 rocks, etc. Fig. 473 shows a filament of one of the species. 



