82 OUR NATIVE FERNS AND THEIR ALLIES. 



I. ACROSTICHUM L. 



Sporangia spread over the whole surface of the frond or upper 

 pinnae, or occasionally over both surfaces. Venation and cut- 

 ting various (in our species simply pinnate). Name from Gr. 

 aKpoS, the summit, and OTIXO?, a row. A tropical genus con- 

 taining over 170 species. 



CHRYSODIUM. 



1. A. aureum L. Stipes i 2 long, tufted, strong, erect, 

 glossy; fronds 2 6 long, i 2 broad, upper pinnae fertile, 

 slightly smaller than the barren ones ; texture coriaceous ; 

 areolae small, copious, without free veinlets. Florida. 



II. POLYPODIUM L. 



Sori round, naked, dorsal, in one or more rows each side of 

 midrib, or irregularly scattered. Stipes articulated to root- 

 stock. Name from Gr. TfoAuS, many, and itovS, itoSoS, foot, allud- 

 ing to the branching rootstock. The largest, most cosmopolitan 

 genus of ferns, containing 350 or more species. 



I. EUPOLYPODIUM. Veins free ; fronds (in our species) 

 pinnate. 



* Sori large. 



1. P. vulgare L. Stipes 2' 4' long, firm, erect; fronds 4' 

 10' long, i' 3' broad, cut nearly or quite to the rachis into entire 

 or slightly toothed, usually blunt pinnae ; veins once or twice 

 forked. Larger fronds with their pinnae sharply serrated and 

 long-pointed form the var. occidental Hook. New England 

 westward to Oregon and southward to Alabama. 



2. P. falcatum Kellogg. Stipes 5' 8' long, stramineous; 

 fronds 12' 15' long, 4' 8' broad ; pinnae numerous, tapering to 

 a slender point, sharply serrate; sori nearest the midrib; veins 

 with 2 4 veinlets. (P. glycyrrhiza D. C. Eaton.) California to 

 Washington Territory. 



** Sori smaller, often minute. 



3. P. plumula H. B. K. Stipes i' 4' long, black, slender; 

 fronds narrowly lanceolate, 9' iS'long, i' 2' broad; pinnae nu- 

 merous, narrow, entire, blunt, lower gradually reduced ; surfaces 

 naked except the black wiry rachis; veinlets forked, obscure. 

 (P. elasticum Rich.) Florida. 



