56 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Demonstrated to be a hybrid between Camptosorus rhizophyllus and Asplenium 

 platyneuron. 



3. Asplenium platyneuron (L.) Oakes. Ebony spleenwort. 

 Grassy or rocky banks and partially shaded situations generally; abundant. Mid- 

 summer. N. Eng. to Colo., southward to the Gulf states. (A. cbeneum Ait.) 



4. Asplenium trichomanes L. Maidenhair spleenwort. Dwarf spleenwort. 

 Crevices of cool shaded cliffs; upper Potomac region chiefly; infrequent. Summer. 



Temperate N. Amer., north of Mex.; also in Eur. and Ada. 



6. Asplenium montanum Willd. Mountain spleenwort. 



Crevices of dryish cliffs; a single station, above Great Falls on the Virginia side of 

 river; very rare. Conn, to Ohio, southward. 



13. ATHYRIUM Roth. 



Pinnae narrowly linear, entire or lightly crenulate 1. A. pycnocarpon. 



Pinnae lanceolate, pinnatifid or pinnate. 



Segments fully adnate, lightly crcnate-serrate 2. A. thelypteroides. 



Segments or pinnules mostly sessile, deeply serrate or pinnately incised with 

 toothed lobes 3. A. asplenioides. 



1. Athyrium pycnocarpon (Spreng.) Tidestrom. 



Moist cool woods and shaded alluvial banks; not common; several localities in 

 Rock Creek Park and along the Potomac. Summer. Que. to Ga., westward. (As- 

 plenium angustifolium Michx.) 



2. Athyrium thelypteroides (Michx.) Desv. Silvery spleenwort. 

 Moist rich woods, chiefly in alluvial situations; fairly common, especially along the 



upper Potomac. Summer. Eastern N. Amer. (Asplenium thelypteroides Michx.; 

 Asplenium acrostichoides Swartz.) 



3. Athyrium asplenioides (Michx.) Desv. Lady fern. 

 Low woods and moist, thickets; abundant. Summer. Eastern U. S. (Asplenium 



filix-foemina in part of American writers, not L.) 



14. POLYPODIUM L. 



Plants grayish beneath, the lower surface of the blades very densely covered with 



pale dark-centered peltate scales; sori small, sunken 1. P. polypodioides. 



Plants green, the blades devoid of scales; sori superficial 2. P. vulgare. 



1. Polypodium polypodioides (L.) Ilitchc. Gray polypody. Resurrection fern. 

 Flat mossy rocks or tree trunks; gorge of the Potomac below Great Falls, Maryland 



ride, the only locality. Summer. Pa. to Iowa, southward to the Gulf states and 

 trop. Amer. generally. (P. incanum Swartz.) 



2. Polypodium vulgare L. Polypody. 

 Rocks or rocky banks; common along the upper Potomac and found in a few other 



localities. Summer. Eastern N. Amer.; also in Eur. 



15. WOODSIA R. Br. 



1. Woodsia obtusa (Spreng.) Torr. 



Rocky banks and shaded cliffs; common, especially along the upper Potomac and 

 the canal. Summer. Eastern N. Amer. 



16. FILIX Adans. Bladder fern. 



Blades very narrowly triangular-lanceolate, the apex long-tapering to a slender tip , 

 usually bearing numerous fleshy bulblets beneath 1. P. bulbifera. 



Blades broadly lanceolate, slightly narrowed at the base, the apex short-pointed; 

 bulblets wanting 2. F. fragilis. 



