1 86 Minnesota Algae 



circinate, free or aggregated without order to form a flocculent mass; cells 

 equal to or longer than their diameter; apical cells sometimes conical; 

 heterocysts numerous and intercalary; gonidia variously disposed, sometimes 

 solitary, sometimes lying on each side of a heterocyst, rarely in short 

 catenate series. 



I Gonidia oval or spherical. 



1 Gonidia oval or barrel-shaped, remote from the heterocysts in cate- 



nate series 

 (i) Wall of gonidium smooth A. variabilis 



(2) Wall of gonidium papillose A. hallensis 



2 Gonidia spherical, contiguous to heterocysts, solitary or in short 



series, 12-20 mic. in diameter A. sphaerica 



II Gonidia variously disposed, sometimes contiguous to heterocysts, some- 



times remote from them, cylindrical, straight or curved. 



1 Trichomes usually circinate; gonidia curved, obliquely truncate at the 



apices 



(i) Gonidia 7-13 mic. in diameter, 20-50 mic. in length, curved, obliqite, 

 inequilateral, contiguous to or rarely remote from the hetero- 

 cysts; wall of gonidium smooth, colorless or yellowish; trich- 

 omes 4-8 mic. in diameter A. flos-aquae 



(2) Gonidia 16-18 mic. in diameter, up to 30 mic. in length, curved, 

 oblique or cylindrical, the younger ones somewhat spherical, 

 usually remote from the heterocysts; wall of gonidium smooth, 

 colorless; trichomes 8-14 mic. in diameter A. circinalis 



2 Trichomes straight; gonidia cylindrical, straight, usually remote from 



the heterocysts, solitary or in series 



(i) Trichomes 4-5 mic. in diameter; sheaths sometimes present; go- 

 nidia 14-17 mic. in length A. inaequalis 



(2) Trichomes S-8 mic. in diameter; sheaths occasionally present; 



gonidia 7-10 mic. in diameter, up to 30 mic. and more in length 



A. catenula 



(3) Trichomes 4.2-6 mic. in diameter; sheaths present; gonidia 6 mic. 



in diameter, 14-20 mic. in length A. laxa 



III Gonidia contiguous to heterocysts on each side, developed centripe- 



tally, cylindrical or somewhat cylindrical 



1 Gonidia 7-12 mic. in diameter, 18-28 mic. in length, short, somewhat 



cylindrical, often slightly constricted in the center; apical cell con- 

 ical A. torulosa 



2 Gonidia 8-10 mic. in diameter, 20-40 mic. in length, especially cylin- 



drical; apical cells obtuse A. oscillarioides 



3 Gonidia 15-20 mic. in diameter, 50-90 mic. in length, cylindrical or 



more commonly tapering slightly from the middle to the rounded 

 ends A. bornetiana 



