BLUE-GREEN ALGAE 



III 



50 (49, 51) FUaments short, straight, densely aggregated in parallel bundles to 



form small, feathery, plate-like masses. 



. „ Aphanizomenon Morren. 



Filaments without sheath, 

 straight or somewhat taper- 

 ing at the end; united in 

 small, spindle - shaped or 

 plate-like, free-floating bun- 

 dles; spores much elongated, 

 cylindrical, solitary, not bor- 

 dering on the intercalary 

 heterocyst. A . Jlos-aquac 



Ralfs is sometimes found floating in great abundance in the still waters of 



ponds and lakes. 



51 (49, 50) Filaments free; cells shorter than their diameter. 



Nodularia Mertens. 



lBc<^.l;^t^MAW^*..mi-j»aiTgg^ 



Fig. 55. Aphanizomenon Jlos-aquaeRsMs. X 465. (Original.) 



ssia^^^ 



52 (48) 



Fig. 57. 



Filaments enclosed in a thin, often evanescent sheath; 

 free-floating as single filaments or united into colonies of 

 indefinite form; heterocysts intercalary, depressed; spores 

 almost spherical, in rows, not bordering on the hetero- 

 cysts. 



Fig. 56. Nodularia sp. X 465. (Original.) 



Heterocysts terminal and the spores always contiguous to them. 



Cylindrospermum Kiitzing. 



Filaments without sheath 

 relatively short, aggregated to 

 form an expanded film or 

 colony of indefinite shape; 

 vegetative cells cylindrical, 

 longer than the diameter; het- 

 erocyst terminal; spores gen- 

 erally soHtary, borne next to 

 Common on damp earth and stones. 



Cylindrospermum 

 X465. 



stagnale Bornet and Flahault 

 (Original.) 



53 (27) 



54 (60) 



the heterocyst 



Filaments with true or false branches 54 



Filaments bearing false branches; sheaths firm, of more or less equal 

 thickness; filaments consisting of a single row of cells, with 

 heterocysts (except Plectonema). 



Family Scytonemaceae . . 55 



55 (56, 59) Without heterocysts or spores Plectonema Thuret. 



Filaments consisting 

 only of vegetative cells, 

 without heterocysts; false- 

 ly branched, branches 

 single or in pairs; borne 

 singly in a firm, colorless 

 or yellowish sheath. P. 

 U'ollci Farl. occurs in 

 some abundance in 

 ponds, attached to stones, 

 etc. 



Fig. 58. Plectonema uolUi 

 Farlow. X 260. (After 

 Kirchner.) 



56 (55, 59) With intercalary heterocysts. One filament in each sheath. . 57 



