becomes apparent that there is much confusion in the nomenclature. 

 Hapalosiphon pumilus in nature shows great variation in size, in 

 habit of branching, and in color of the sheaths. Some of the ex- 

 pressions cannot be separated from herbarium specimens bearing 

 other names, and it seems likely that a critical study of the genus 

 will reduce some names to synonymy. It seems best to retain the 

 present names for the forms which appear in our collections, pending 

 the appearance of a specialist's monographic study. 



Key to the Species 



1. Filaments irregularly branching from all sides of the main axis 2 



1. Filaments mostly branching from one side of the main axis; bilateral 

 branches not infrequent 3 



2. Heterocysts and cells elliptical; filament up to Sfi in diameter H. fiexuosus 



2. Heterocysts and cells quadrate to cylindrical; filaments up to 



20m in diameter H. confervaceus 



3. Sheath ochraceous or golden-brown, filaments 10-25/u wide 4 



3. Sheath colorless; filaments averaging mostly less than 10m wide 6 



4. Filaments up to llfi wide; branches narrower than 



the main filament H. brasiliensis 



4. Filaments larger, 11.5-25/4 wide 5 



5. Main filaments 11-12.5ai in diameter; sheath golden-brown, thick 



over the branches H. aureus 



5. Main filaments up to 25/j. in diameter; sheath colorless to 



ochraceous, thin over the branches _ H. pumilws 



6. Branches crooked, arising at various angles from the main axis; 



cells up to 3 times their diameter in length H. intricatus 



6. Branches straight, arising at right angles to the main axis; cells up 



to 8 times their diameter in length H. hibernicus 



Hapalosiphon aureus West & West 1897, p. 241 

 PI. 128, Figs. 1-3 



Creeping, forming a loosely entangled mat with numerous, mostly 

 short, branches arising from one side (rarely from both sides) of 

 the main filament. Cells ellipsoid, quadrate, or cylindrical, especially 

 in the apices of the branches, 6-9/a in diameter, 12-24/a long; sheath, 

 thin, close, colorless in the branches, golden-brown in the main 

 filament, which is ll-12.5;u, in diameter. 



Sometimes our specimens had colorless sheaths throughout a part 

 of the plant, with the cell membrane ochraceus. Many herbarium 

 specimens of this plant have been studied critically. I believe that 

 these cannot be separated from the many expressions of H. pumilus, 

 which is extremely variable. 



In Sphagnum bogs and other soft water habitats. Mich., Wis. 



[544] 



