or cylindrical (sometimes elongate-ovate), either adjacent to or 

 remote from the heterocysts. 



See notes under Nostoc, which point out the chief characteristics 

 separating these two genera. 



Key to the Species 



1. Filaments endophytic A. Azollae 



( See also A. cycadearum Reinke, not reported from this region. ) 



1. Filaments free-Uving, planktonic, epiphytic, or on moist earth 2 



2. Euplanktonic, mostly sohtary or forming free-floating fascicles 3 



2. Tychoplanktonic, entangled among other algae; 



epiphytic or on moist soil - 20 



3. Trichomes contorted and twisted, regularly or irregularly spiralled. „- 4 



3. Trichomes straight or flexuous but not coiled 8 



4. Trichomes coiled or spiralled - 5 



4. Trichomes irregularly twisted and snarled; gonidia 



formed near the center of the tangle A. flos-aquae 



5. Spiral regular; trichome forming a definite coil 6 



5. Trichome sigmoid or twisted irregularly A. circinalis 



6. Gonidia subglobose to oblong. A. spiroides 



6. Gonidia cylindrical 7 



7. Vegetative cells 3.5/n in diameter; gonidia 



up to 17^ long - — - -A. helicoidea 



7. Vegetative cells 4-6-(8)m in diameter; 



gonidia 24-30;n long - - A. flos-aquae 



8. Gonidia adjoining the heterocysts on one or both sides 9 



8. Gonidia scattered, near or remote from the 



heterocysts but not adjoining 10 



9. Cells globose; gonidia on both sides of the heterocysts A. Bornetiana 



9. Cells rectangular, elongate; gonidia on one 



side of the heterocyst only..... — - A. unispora 



10. Trichomes lying parallel in bundles or forming loose fascicles; 



with 1, rarely 2, gonidia in a trichome— - - -A. wisconsinense 



10. Trichomes not in a bundle or fascicle; with 



2 or more gonidia in a trichome - - H 



11. Gonidia globose, sometimes shghtly ellipsoid ....12 



11. Gonidia ellipsoid, oblong or cylindrical 13 



12. Cell contents highly vacuolate; gonidia mostly globose A. Scheremetievi 



12. Cell contents not vacuolate; gonidia globose, 



( sometimes ovate or elongate ) - - — A. planctonica 



13. Gonidia ovate or ellipsoid 14 



13. Gonidia cylindrical— 16 



14. Vegetative cells round, sometimes barrel-shaped 15 



14. Vegetative cells barrel-shaped to short-cyUndric A. Viguieri 



15. Gonidia oblong, separated from the heterocyst 



usually by a single cell A. limnetica 



15. Gonidia spheroidal or broadly ovate, separated from the 



heterocyst by 2 or more cells-.___ — A. planctonica 



16. Gonidia short-cyhndric, not more than twice the diameter in 



length, hexagonal in optical cross section— ..__ A. macrospora 



16. Gonidia usually more than twice the diameter in 



length, round in optical cross section . 17 



[511] 



