202 Minnesota Algae 



Plate X. fig. 8. 



Trichomes S.6-9.8 mic. in diameter, So-ioS mic. in length, short, 

 straight or nearly straight, thickened at the apices, living as endopkytes 

 in the cells of Rhizosoleniae styliformis; heterocysts 9.8- 

 II. 2 mic. in diameter, spherical or somewhat spherical, single, basal; cells 

 somewhat spherical or barrel-shaped; apical cell often a little larger than 

 the others, somewhat spherical; cell contents finely granular, or showing 

 a few large granules, pale blue-green. 



Hawaii. Plankton. On Rhizosolenia and Hemiaulus deli- 

 catulus Lemm. (Schauinsland). 



Genus AULOSIRA Kirchner. 

 Krypt. von Schles. Algen. 238. 1878. 



Filaments free, equal, scattered or in fascicles; sheaths membranaceous, 

 close; cells cylindrical or barrel-shaped; heterocysts intercalary; gonidia 

 developed at intervals between the heterocysts, remote from or contiguous 

 to them, cylindrical, in catenate series. 



373. Aulosira schauinslandii Lemmermann. Die Algenflora der Sandwich- 

 Inseln. Bot. Jahrb. 34: 622. pi. 7. f. 9-11. 1905. De Toni. Syll. Al- 

 gar. 5: 482. 1907. 



Plate X. fig. 9. 



Filaments lo-ii mic. in diameter, flexuous or spiral; sheaths firm, 

 colorless; trichomes 9.5 mic. in diameter, slightly constricted at joints; 

 apical cell hemispherical, about 8 mic. in length, containing coarse gran- 

 ules; cells 3 mic. in length, short; heterocysts usually 9.5 mic. in diameter, 

 II mic. in length, always intercalary, somewhat spherical or cylindrical; 

 gonidia not known. 



Hawaii. On Turbinaria. Laysan. (Schauinsland). 



Genus MICROCHAETE Thuret. 

 Essai Class. Nostochinees. 7. 1875. 



Plants small, living in fresh or salt water, aggregated into star-shaped 

 or cushion-shaped tufts; filaments unbranched, erect, attached at the base; 

 sheaths present; trichomes single within the sheath; heterocysts basal and 

 intercalary; gonidia developed from the lower cells. 



I Plants living in fresh water; heterocysts basal and intercalary. 



I. Filaments 4.4-S-i mic. in diameter; sheaths colorless, wide 



M. tenuissima 



2 Filaments 10 mic. in diameter; sheaths simple, thin, close 



M. tenera 



3 Filaments 16-18 mic. in diameter; sheaths at first thin, later be- 



coming lamellose, colorless M. robusta 



