FRESH-WATER ALG^ OF THE UNITED STATES. 27 



nostocs has been shown, but only reason to study also their relations with the vari- 

 ous collema. 



In regard to the Spermosirece, there is as yet no direct proof whatever connect- 

 ing them with lichens. It is very possible that they are not so closely related to 

 the true nostocs as is generally believed, so that the probabilities of their being 

 lichens are at present so remote, that for the systematist to refuse to take note of 

 their distinct forms, seems to me most unwarrantable. 



Subfamily NOSTOCEiE. 



Thallus peridermate plus minus distincto instructus, sporis destitutus. 



Thallus provided witli a more or less distinct integument, and destitute of spores. 



Genus NOSTOC, Vaucher, (1803.) 



Thallus gelatinosus, varie coloratus, aut globosus vel subglobosus aut foliaceo-membranaceus et 

 irregulariter expansus, saepe bullatus. Trichomata plus minus moniliformia. Cellulse perdurantes 

 exacte spheericse vel rare oblongae. 



Thallus gelatinous, variously colored, either globose or subglobose, or foliaceously membranous 

 and indefinitely expanded, often a bulla. Filaments more or less moniliforme. Heterocysts exactly 

 spherical or rarely oblong. 



a. Thallus globosus vel subglobosus, vel disciformis. 

 Thallus globose, subglobose or discoid. 



]¥. Austinii, Wood, (sp. nov.) 



N. subglobosum, parvum, plernmque magnitudine ovorum piscium, rare ad 2", fuscescente, 

 vel nigrescente, interdum durum interdum submolle, superficie sspe corrugata ; tricho- 

 matibus varie curvatis, dense intricatis vel distantibas et laxissime intricatis, viridibus, 

 fuscescentibus, subplumbeis vel luteo-brunneis, in thallis minoribus ssepe distincte vaginatis, 

 in thallis majoribus baud vel indistincte vaginatis ; articulis maturis globosis, ssepe didymis, 

 crasse granulatis; cellulis perdurantibus articnlorum diametro iequalibus vel paulo majoribus, 

 globosis, interjectis vel terminalibus, plerumque sparsis. 



Biam.—GeYl. Veg., tsV— t^^tf/ = .0026"— 00033"; cell, perdurant, .00033". 



ffab. — in rupibus irroratis, New Jersey. (Austin.) 



Subglobose, small, mostly the size of fish-eggs, but reaching the diameter of nearly two lines, 

 fuscous or blackish, sometimes very hard, sometimes much softer; surface often corrugated; 

 filaments variously curved, densely intricate or distantly and loosely interwoven, greenish, 

 fuscous, subplumbeis or yellowish-brown, in the smaller fronds often distinctly vaginate, in 

 the larger indistinctly or not all vaginate ; mature joints globose, often didymous, coarsely 

 granulate ; heterocysts equal to the diameter of the other joints or a little larger, globose 

 interspersed or terminal. 



Remarks. — The fronds of this distinct species vary greatly in appearance; the 

 larger of them are often almost colorless, and, when viewed with the microscope, 

 are seen to be composed of a transparent colorless jelly, with remarkably large 

 filaments scattered through it. These filaments are generally without sheaths, 

 though occasionally a sheath can be faintly traced. The smaller fronds are much 

 firmer than the larger and are more decidedly colored. Some of them are entirely 

 opaque, looking simply black when viewed by transmitted light under the micro- 

 scope. In these the filaments are densely crowded together, often misshapen and 



