FRESH-WATER ALG^ OP THE UNITED STATES. 37 



rate fronds are not distinct. The filaments are very long, mostly closely intricate, 

 very much curved; in some places they are more sparse. Their color is mostly a 

 sort of yellowish ferruginous-green, sometimes they are, decidedly, almost purely 

 ferruginous, more rarely a bright green. This plant agrees pretty well with the 

 descriptions of the European Nostoc comminutum, and I believe is the same 

 species; if, however, N. lacustre of Kiitzing is distinct from N. comminutum, this 

 is also ; but I incline to the opinion that they are all different forms of one plant. 

 Fig. 3, pi. 2, represents a single filament magnified 800 diameters. 



N. commune, Yauch. 



N. terrestre, thallo irvegulariter expanse, difformi, undulato-plicato, tremulo, intus aquose gela- 

 tinoso, setate provecta plerumque excavate, peridermate subcoriaceo firmo, olivaceo, luteo- 

 fuscescente vel luteo-fusco cincto ; trichomatibus flexuoso-carvatis, pallide serugineis, laxe 

 implicatis, aequalibus vel subaequalibus, baud raro a basi ad medium usque cellulis biseriatis 

 compositis; articulis sphsericis vel e mutua pressione subquadrangularibus, laxe connexis, 

 passim distantibus, puncto centrali turbato praeditis; cellulis perdurantibus globosis, articu- 

 lorum diametro duplo majoribus, interstialibus terminalibusque. 



Dtam.— Cell, vegetat. .00012"— .00016" ; cell, perdurant. .00025"— .00033". 



Syn. — N. commune, Yauch. Rabenhorst, Flora Europ. Algarum, Sect. II. p. 115. 



Hah. — In terrestre. New Jersey. (Austin.) "Rio Bravo. Schott." Harvey. 



Terrestrial ; thallus irregularly expanded, shapeless, undulate-plicate, tremulous, within of the 

 consistence of thin jelly, in advanced age mostly hollow ; periderm subcoriaceous, firm, oliva- 

 ceous, yellowish-fuscous ; filaments flexuously curved, pale green, laxly implicate, equal or 

 snbequal, not rarely composed of a double series of cells from their base to their middle ; 

 articles spherical or subquadrangular from mutual pressure, loosely connected, here and there 

 distant, furnished with a central spot ; heterocysts globose, twice as large as the vegetative 

 articles, interstitial and terminal. 



Remarks. — The only specimens I have seen of this species are very old ones, 

 which have burst and discharged their central portions. I have consequently pre- 

 ferred to copy the diagnosis of Prof Rabenhorst. My specimens agree pretty 

 closely with it. The filaments, and also the single cells, are closer together than 

 his words would seem to indicate. My measurements of the heterocysts, as given 

 above, are larger than those of Prof Eabenhorst. They agree, however, with his 

 text, which his own measurements do not. I am indebted to Prof Austin for 

 specimens of this species, which he collected in Northern New Jersey. According 

 to Professor Harvey this plant was collected by Dr. Schott along the Eio Bravo, 

 where it is common on dry flats after rains. 



Subfamily SPERMOSIRE.^. 



Thallus sine peridermate, interdum nullus. Trichomata sporis instructa. 



Thallus without any periderm, sometimes absent. Filaments furnished with spores. 



Genus ANAB^NA, Bory. 



Trichomata moniliformia, evaginata; sporis sphsricis, aureis vel aureo-fuscis, plerumque singulis, 

 cum cellulis vegetativis vel perdurantibus conjunctis. 



