FRESH-W ATKK AI.C.K O F T II E U N I T E D 8 T A TE 8. H9 



(DofiiJinm Khr?it>H'r,jii. RALFS.) Frond slender, linear,- suture forming a rcrj sharply 

 delim-d rim ; segments 8-12 times longer than broad, basal inflation having another smaller 

 one above it, siiU-s otherwise straight, parallel; ends crenate, owing to a number of cmargi na- 

 tions on the edge of the truncate extremities, from three to five of the crenations being 

 usually visible ; e. f. punctate or rough with minute granules. Sporangium suborbiculur or 

 elliptic, or slightly angular, smooth, placed between the deciduous empty fronds. Ciliated 

 /.""spores formed by segmentation of the cell contents, and their emission effected through 

 the opened apex of each one, two or three, especially, formed lateral tubes arising from be- 

 neath the Imse of one of the segments. Archer. 



*. This species is quite common around Philadelphia; but I do not 

 n 'member ever to have seen one with the cell-wall granulate. The smaller of the 

 two umlxmations near the centre is often wanting or exceedingly small, and the 

 crenulaticms in the ends are very often obsolete. 



Fig. 9, pi. 12, represents a cell of this species magnified 160 diameters. 



1>. lint ilium, (Hutu.) DE BART. 



P. priori simile, sed gracilius, angnstius et plerumque longius, mcdio tantnm semcl constrict um ; 



rytiodermate laevi. (K.) Species mihi iynola. 

 Diam. 0.00054" 0.0009". (K.) 



.Vy/i. P.Baculum, (Bafefl) DuBA&Y. RABENHORST, Flora Europ. Algarnm, Sect. III. p. 141 

 Hub. Oeorgia ; Bailey. 



Frond slender, suture not prominent; segments very many times longer than broad, basal in- 

 flation very conspicuous, solitary, sides otherwise straight, very nearly parallel, large gran- 

 ules of the endochrome in a single series ; ends entire; e. f. without puucta. L. , J ," B 

 1*7". 

 P. breve, WOOD. 



P. robustuin, diametro 48 plo longins, in mcdio distincte constrictum sed hand undulatum, 

 utroque polo nonnihil attenuatum ; apicibus truncatis et nonnihil rotundatis ; cytiodermate 

 crassissimo, dense granulato-puuctato; marginibus vel rectis, vel breve undulatis. 



Diam. . 0038". 000 95". 



Syn. P. breve, WOOD. Proc. Acad. Nat. Sciences, 1869. 



Hab. District of Columbia. (Billings.) 



Robust, 4-8 times longer than broad, distinctly constricted but not undulated in the middle, 

 slightly attenuated towards the ends; apex truncate and somewhat rounded ; cytioderm very 

 thick, densely minutely granulate; margins either straight or shortly undulate. 



/,'< marks. This species was sent to me by Dr. Billings, who obtained it near 

 ^ -liington, D. C. The margins are sometimes straightish, but in other fronds there 

 are three or more distinct short undulations, or rounded projections in each half 

 margin. The cell-wall is excessively thick, especially at the end in many cases 

 much thicker than the drawing. 



Fig. 2, pi. 21, represents an empty frond of this plant magnified 750 diameters. 



P. crcnulatum, (EHRB.) RABENHORST. 



P. robustum, cylindraceo-subclavatnm, octies-duodecies longins qnam latum, medio nndnlato- 

 nodulosntn, strictune mediae margine tumido, apicibns late Iruncatis, altero stepe creuulato ; 

 cytiodermate granulato-punctato. (R.) Species mihi ignota. 



Diam. 0.0023". (R.) 



Syn. P. crenulatum, (EiiRB.) RABENHORST, Flora Enrop. Algarum, Sect III. p. 142. 



