56 WISCONSIN PHYTOPLANKTON 



times entirely lacking. Cells spherical to barrel-shaped, rarely cylindri- 

 cal, never disciform. Heterocysts approximately spherical, always in- 

 tercalary, generally solitary and with several in a filament. Spores 

 variously shaped, contiguous to or remote from heterocysts, solitary or 

 in short catenate series. Cell contents homogeneous, granulose, or with 

 numerous pseudovacuoles ; grey, blue-green, or variously colored. 

 Reproduction by hormogones and spores. 



KEY TO THE SPECIES. 



Filaments straight or slightly curved. 



Spores spherical A. PLANCTONICA 



Spores longer than they are broad. 

 Length of spores not over twice their breadth. 

 Breadth of spores less than twice that of vegetative cells. 

 Spores oval to elliptic in optical cross section. 



Vegetative cells less than 8 M broad A. AFFINIS 



Vegetative cells over 10 M broad A. LIMITETICA 



Spores hexagonal in optical cross section A. MACEOSPORA 



Breadth of spores more than twice the vegetative cells A. LEVANDERI 



Length of spores at least three times their breadth A. BOENETIANA 



Filaments spirally, circinately, or irregularly twisted. 

 Trichomes solitary, not forming floccose masses. 



Curving of trichome a definite spiral A. SPIEOIDKS 



Curving of trichome not a definite spiral. 



Length of spore at least four times breadth . . A. AUGSTUMALIS I. C. MAECHIA 



Length of spore about twice the breadth A. CIBCINALIS 



Trichomes forming a floccose mass. 



Spores in a mass at center of colony A. LEMMEBMANNI 



Spores not in a mass at the center of the colony. 

 Trichomes loosely associated, individual filaments some- 

 times in spiral turns A. CIBCINALIS 



Trichomes greatly and irregularly twisted to form com- 

 pact masses A. FLOS-AQTJAB 



ANABAENA PLANCTONICA Brunnthaler. PL 8, Fig. 2. 

 Sitzenbr. d. kais. Ak. d. Wiss. Wien 112, Abt. 1 : 292. 1903. 



Filaments free-floating, solitary, straight, or slightly bent. Trichomes 

 enclosed by a copious, hyaline, very gelatinous sheath. Vegetative cells 

 spherical, hemispherical, or broadly elliptic. Heterocysts spherical. 

 Spores solitary, remote from or adjacent to heterocysts, spherical or 

 slightly elongate, somewhat broader than the vegetative cells. Cell con- 

 tents rarely homogeneous, usually with numerous pseudovacuoles. (Eu- 

 planktont) . 



Vegetative cells 9-15 p broad; heterocysts 12-14 p. broad; spores 

 12.5-20 ^ broad, 12.5-30 p. long. 



Birch (1) (cc), Center (cc), Cranberry (cc), Devils (2) (ss), Rock (cc). 



