134 



THE AMERICAN MONTHLY 



[July, 



Filaments free, unbranched, hetero- 

 cystsatbase. Mastigonema^ io6. 



Filaments radial, in gelatin, with 

 basal heterocysts, branched; with 

 resting cells. Glxotrichia^ 107. 



Filaments radial, in gelatin, basal 

 heterocysts, no resting cells. 



Rivularia, loS. 



Frond flat, otherwise as above. 



Isactis^ 109. 



10 V Genus Calothrix (Agardh) 

 Thuret. 



Filaments branched, straight, not 

 in gelatinous masses, growing in tufts. 

 Heterocysts at the base of branches. 



106. Genus Alastigonema Fischer 

 (enlarged) . 



Filaments free, unbranched, not in 

 gelatin, growing single, or in bunches. 

 Heterocysts at the base of filaments. 

 Resting cells unknown. 



107. Genus Glceotrichia Agardh. 



Filaments radially disposed, em- 

 bedded in solid gelatin in spherical 

 masses ; branching by lateral out- 

 growth from the old filament beneath 

 the heterocyst. The latter basal ; 

 resting cells single, over the hetero- 

 cysts. 



[Wide, gelatinous, transversely pli- 

 cate sheaths enclose the trichomes, 

 especiallv about the lower part. The 

 resting cells or spores are elongated 

 cells, which otherwise usually resem- 

 ble the other cells. The next genus 

 onlv differs in the absence of spores, 

 a featvire that cannot be regarded as 

 constant.] 



loS. Genus Rividaria Roth. 



The same characters as glceotri- 

 chia, but resting cells (spores) not 

 known. 



109. Genus Isactis Thuret. 



Filaments parallel and erect in gel- 

 atin, often encrusted with lime ; 

 frond flat, otherwise like Rivularia. 



b. SCYTONEME^. GrOUp 2. 



Sy7topsis of Ge)icra. 



Filaments sheathed ; branch ing 

 double, at right-angles ; branches par- 

 allel. Scyionenia, no. 



Filaments united in bands bv a 



common sheath. 



Symfhyosiphon , 1 1 1 . 

 Filaments sheathed, branching be- 

 low one or more heterocysts. 



Tolypothrix^ 1 1 2 . 



Branching irregular, no hetero- 



c^'sts. Plectonema, 113. 



1 10. Genus Scytoiiema Agardh. 

 Each filament with its special 



sheath ; branching usually double as 

 the filament bends and ruptures out- 

 side the sheath, and two parallel 

 branches are thus produced, which 

 run oft' at right-angles to the original 

 filament. Heterocysts distributed 

 without relation to the branching. 



111. Genus SymphyosipJwn Kiitz- 

 ing. 



Filaments as in Scytouema, but 

 vmited in bands by the lateral expan- 

 sion of the sheaths. 



113. Gqww?, Tolypot/n-ix Klitzing. 



Each filament with a sheath; 

 branching usually single, by lateral 

 outgrowth of the filament through 

 the sheath below the one or more 

 heterocvsts. The latter, therefore, 

 are always found at the place of 

 branching. 



113. Plectoi/etiia ThuYct. 

 Filaments irregularly branched, 



with single or geminate branching, 

 each in its special sheath. No heter- 

 ocysts. Color blue-green. 



c. Stigoxeme.e. Group 3. 



Synopsis of Genera. 



Several series of cells in a single 



filament. Stigonema, 114. 



Cells in single series, very wide 



sheath. Haplosiphoti., 115. 



114. Genus Stigouema Agardh. 

 Cells of the filaments often in 



series of two, three, or more, side 

 by side, owing to division in various 

 directions ; walls thick, very distinct 

 in old filaments ; sheath very wide ; 

 heterocvsts distributed without order. 



11^. Genus Hapalosiphon Niigeli 

 (extended) . 



Cells in a single series, sheaths 

 thick or delicate, with heterocysts. 

 Plants resembling Tolypothrix. 

 \To be continued.'^ 



