34 POLYPODIACEAE (FERN FAMILY^ 



when young) by a membrane called the indusium (or less properly the involucre;-, 

 growing either from the back or the margin of the frond. 



u, Indusium none or abortive and obscure b. 

 h. Sterile fronds simply pinnatifid (the segments rarely toothed or lobed). 



Fertile fronds similar to the sterile, flat and leaf-Uke . . 1- PoLYi'ODurM. 



Fertile fronds much contracted ; segments pod-like . . . .18. Onoclea. 

 h Sterile fronds '^~4-piniiate or -pinnatifid. 

 Sterile fronds green on both surfaces. 



Fertile fronds similar to the sterile, leaf-like 2. Pheuoi'tbri.s. 



Fertile fronds much contracted ; segments pod-like , . 18. Onoci.ca. 



Sterile fronds whitened beneath . . 3. Notiiulaena. 



«. Indusium present c. 

 e. Indusium formed entirely or in part by the revolute edge of the frond d. 

 d. Sori clearly distinct. 



Indusium single, covering the sorus . . .... 4. Adiantum. 



Indusium double, cup-like or 2-valved 17. Dioksonia. 



d. Sori soon confluent as a more or less continuous marginal band. 



Btipe stout (8-4 mm. in diam.), commonly solitary .... 5. Pteris. 

 Stipes filiform (0.5-1.3 mm. in diam.), clustered. 

 Segments of the sterile frond glabrous. 

 Green or greenish. 

 Segments petiolulate or articulated at cordate or rounded base 7. Pellaea. 

 Seg-ments of sterile frond cuneate at sessile unarticulated base 8. Cryptogb^ .ima 



Ohalky-white beneath S. NoTnoLAE.^A. 



Segments of the sterile frond pubescent . ... 6. Oheilasthes. 



c. Indusium not continuous with the edge of the frond e. 



e. Indusium peltate or laterally attached, covering the sorus when young /. 

 /. Sori more or less elongated. 



Sori parallel to the midrib ... 9. "Woodwakdia. 



Sori parallel to the oblique lateral veins. 

 Veins free ; fronds 1-3-pinnate. 

 Sori separate, straight or horseshoe-shaped . . . .10. Asplenium. 

 Sori linear, confluent in pairs (appearing like single sori 



but with Indusla on both sides) 11. Soolopendrium. 



Veins reticulated; fronds simple, rooting at the tip . . 12, Camptosorus. 



/. Sori orbicular or reniform g. 



ff. Indusium evident at least when young ; fertile fronds leaf-like h. 

 h. Indusium fixed by the center. 



Indusium orbicular-peltate, without a sinus . . 18. Polystiohum. 



Indusium reniform or if orbicular with a narrow sinus . . 14. Aspidium. 



h. Indusium attached at the side 15. Cystopteris. 



g. Indusium obscure, lunate ; fertile segments much contracted, 



pod-like 18. Onoolea. 



6. Indusium inferior, cup-like or Involucre-like. 



Indusium 2-valved, cup-like . . , 17. Dioksonia. 



Indusium cleft into naiTOw segments . ^ 16. Woodbia. 



1. P0LYP6dIUM [Toum.] L. Polypody 



Fruit dots round, naked, arranged on the back of the frond in one or more 

 rows each side of the midrib or central vein, or irregularly scattered, each borne 

 in our species on the end of a free yeinlet. Rootstocks creeping, branched, often 

 covered with chaffy scales, bearing scattered roundish knobs, to which the stipes 

 are attached by a distinct articulation. (Name from ttoXiJ-, many^ and Troiis, foot^ 

 alluding to the branching rootstock.) 



1. P. Yulgslre L. Fronds evergreen, oblong, smooth both sides^ 8-40 cm 

 high, simple and deeply pinnatifid ; the divisions linear-oblong, obtuse or some- 

 what acute, remotely and obscurely toothed ; veins once or twice forked ; 

 fruit dots large, midway between the midrib and the margin. — Rocks ; common. 

 July. (Eu., etc.) Variable. Some of the more noteworthy forms have been 

 distinguished as : Var. attenuXtum Milde, with segments attenuate-acuminate, 

 serrulate toward the end. Var, auritum Willd., with the lowest segments auri- 

 cled. Var. cAmbiiicum (L.) Willd., with the segments more or less strongly 

 toothed or pinnatifid. Var. cristXtum Moore, with segments 1-several times 

 forked at the ends. 



V 2. P. polypodioides (L.) Hitchc. Frond evergreen and coriaceous, oblong, 

 6-25 cm. high, grayish and very scurfy underneath with peltate scales., simply 

 pinnatifid ; the divisions oblong-linear, obtuse ; fruit dots rather small, near the 

 margin; veins forking, free in the N. American plant! (P. incanum Sw.) — 

 Rooks and trunks of trees, Va. and 0. to la., and south w. ; reported on 

 Staten I., N. y. (Trop.) 



