CLASSIFICATION. 19 



into long, straight, wavy, or spiral filaments. These filaments may 

 break up into cocci-like reproductive elements " arthrospores. " 



LEPTOTRICHE^E (Zopf). The vegetative cells present rod-shaped 

 and spiral forms, and grow out into straight, wavy, or spiral fila- 

 ments ; these may show a difference between the two extremities, 

 of base and apex. Cocci-like reproductive bodies are formed by seg- 

 mentation of the rod-shaped elements in these filaments. In some 

 of the species the segments are enclosed in a common sheath. Sub- 

 genera: LEPTOTHRIX, BEGGIATOA, CRENOTHRIX, PHRAGMIDIO- 

 THRIX (for generic characters see page 12). 



CLADOTRICHE^E (Zopf). The vegetative cells are rod-shaped 

 or spiral, and grow out into straight or spiral filaments, which may 

 present pseudo-ramifications. A single genus, CLADOTHRIX (see 

 page 12). 



