FRESH-WATER ALG^ OP THE UNITED STATES. 33 



Remarhs. — This plant was sent to me by Dr. C. C. Parry, from whose letter the 

 following is extracted : " I send enclosed specimens of a singular land Alga? which 

 I met with in this vicinity ; lightly attached to bare patches of soil interspersed 

 with buffalo grass. In the adjoining bluffs are cretaceous shales full of seams and 

 layers of selenite, from the decomposition of which the bottom soil becomes 

 strongly impregnated with various saline matters. The present season has been 

 characterized by unusual quantities of rain, causing extensive floods over what is 

 usually a dry, arid district." 



The agreement between the mature forms is essentially perfect. There can be 

 scarcely any doubt as to the identification, although I have not seen the Ameri- 

 can plant in its young state. The fronds appeared to be 1 — 2 lines in thickness, 

 with its surface smooth, or sometimes with close subparallel ridges or wrinkles. 



According to Eabenhorst, the young European N. cesatii is in the beginning 

 globose, and pale golden-yellow ; soon, however, bursting and spreading out into an 

 indefinitely expanded thallus. 



Among the algae collected by Prof. Ravenel in Texas is a Nostoc, labelled " On 

 Mud Flats, Cedar Bayou, Harris Co.," which comes so close to N. cesatii, that I 

 think it must be referred to it. It differs only in being more olivaceous, some- 

 what firmer and in the size of the heterocysts — the largest of the latter which I 

 have examined, attaining the size only of .00027". The largest vegetative cells are 

 .00017 in diameter. 



]¥. calcicola? Aa. 



N. thallo irregulariter expanse, enormiter sublobato, tenue, membranaceo, cartilagineo, elastico, 

 pellucido, aut laete viride, vel brunneo, vel dilute viride, irregulariter undulato plicato vel 

 bullatoo ; peridermate plerumque subnullo ; trichomatibus cum filis leptothriehoideis ramosis 

 intermixtis, flexuosis, plerumque distantibus, rarissime e cellulis biseriatis compositis ; cellulis 

 subglobosis, oblongis, ovalibus, cum ceteris ellipticis intermixtis, plerumque laxe connexis; 

 cellulis perdurantibus spnsericis, interjectis et terminalibus. 



Diam.—A.Yi. ^^ij/_j^i^/ = .0001"4— .0001"; cell, perdur. ^^^^"—^^\^^" = .0003"— 

 .0002". 



Syn. — N. calcicola, Ag. Rabenhorst, Flora Europ., Sect. II. p. 174. 



Hab. — In rupibus, Georgia. (Prof. Ravenel.) 



Thallus irregularly expanded, membranaceous, thin, cartilaginous, elastic, pellucid, bright green, 

 pale green or brownish, thin, irregularly undulately plicate or bullate ; periderm mostly 

 scarcely distinguishable ; filaments intermixed with branched leptothrix filaments, flexuous, 

 mostly distant, very rarely composed of biseriate cells ; cells subglobose, oblong, oval, inter- 

 mingled with elliptical ones, mostly loosely connected ; heterocysts spherical, interspersed or 

 terminal. 



Remarhs. — This species is one of those sent me by Dr. Billings. It was collected 

 near Catoosa Springs, Georgia, by Prof. H. W. Eavenel. In the dried state it is 

 of a dirty olive-green, and very much wrinkled and irregular on its surface. The 

 largest specimens are about an inch long. There is no very distinct periderm, 

 although in some places the filaments are placed more closely together on the outer 

 portions of the frond. This plant seems to agree with the descriptions of the 



5 March, 1872. 



