54 CONTKIBUTIONS FROM THE NATIONAL HERBAEIUM. 



Blades once to several times pinnatitid or pinnate. 

 Margins of pinnae with numerous slender bristle-like teeth; sori confined to 

 the contracted uppermost pinnae of some of the blades, large, contiguous, 



nearly covering the under surface 10. POLYSTICHTJM. 



Margins not with bristle-tipped teeth; sori not confined to tip of blade. 



Veins partly united to form a single series of narrow meshes along the mid- 

 veins of the pinnae and segments, the sori confined to these. 



11. ANCHISTEA. 

 Veins all free. 

 Sori oblong to linear. 

 Plants mostly small, 5-30 cm. high, the leaves evergreen; sori straight 



or slightly curved 12. ASPLENITJM. 



Plants larger, mostly 50-100 cm. high, the leaves herbaceous, winter- 

 killing; sori curved, often crossing the veinlet and recurved upon it. 



13. ATHYRIUM. 

 Sori roundish. 

 Blades cut nearly to the midrib, the segments entire or faintly toothed. 



14. POLYPODITJM. 

 Blades 1-3 times pinnate, the primary pinnae sessile or stalked. 



Indusia attached beneath the sporangia and at first inclosing them, 



at length splitting into several spreading lobes 15. WOODSIA. 



' • Induaia attached laterally (wanting in one species of Dryopteris), 



thrust to one side by the ripening sporangia. 

 Indusia hood-shaped, attached by the broad base, early pushed 

 back by the developing sporangia and partly concealed by 



them, withering 16. FILIX. 



Indusia, if present (lacking in D. hexagonoptera) , reniform or 

 rounded-reniform, flat or convex, attached at the sinus, usually 

 persistent .17. DRYOPTERIS. 



1. LORINSERIA Presl. 



1. Lorinseria areolata (L.) Presl. Chain fern. 



Swamps and other low, permanently moist, shaded situations; not uncommon. 

 Late summer. Me. to the Gulf states; also in Mich. {Woodwardia angustifolia .1. E. 

 Smith; W. areolata Moore.) 



2. ONOCLEA L. 

 1. Onoclea sensibilis L. Sensitive fern. 



Moist situations generally; abundant. Late summer. Newf. to the Gulf states, 



westward. 



3. PTERETIS Raf. 



1. Pteretis nodulosa (Michx.) Nieuwland. Ostrich fern. 



Shaded alluvial flood plain of the Potomac, on both .«ides above Cabin John; rare. 

 First of Sept. N. S. to Va., westward. (Struthiopteris germanica and Maiteuccia stru- 

 thiopteris of American authors.) 



4. DENNSTEDTIA Bernh. 



1. Dennstedtia punctilobula (Michx.) Moore. Hay-scented fern. 



Low woods or moist banks; fairly common. Aug. N. S. to Ga., westward. {Dick- 

 tonia pilosiuscula Willd.) 



5. PTERIDIUM Scop. 



1. Pteridium latiusculum (Desv.) Maxon. Brake. Bracken. 



Sunny sandy slopes, low thin woods, or old fields, and acid soil situations generally ; 

 abundant. Midsummer. Eastern N. Amer. (Pteris aquilina and Pteridium aquilinum 

 of most authors, in part.) 



