FILICES. (TRUE FERNS.) 439 



ally collected in little masses (fruit-dots or son), which are often covered 

 by a scale (indusium), which is produced by a cellular outgrowth from 

 the frond, or by a general involucre funned from the infolded margin of 

 the frond. Eaton, Ferns of North America. 



Tribe I. Sori round or oblong, placed on the veins or at the ends of the veins, without 

 indusium. Stalk articulated to the rootstock. Veins free or reticulated. POLYPODIES. 



1. Polypodium. Character of the tribe. 



Tribe II. Sori more or less elongated, without indusium, on the back of the frond or its 

 divisions, and usually following the veins, or only at the tips of the latter. Fronds often 

 scaly or tomentose, or covered beneath with colored powder. GKAMMITIDE^E. 



2. Notholaena. Sori but little elongated, often of very few sporangia, placed below the 



tips of the veins near the margin of the lobes of the frond. 



Tribe III. Sori close to the margin of the frond or its divisions, sometimes extending 

 down the veins, covered (at least when young) by an involucre opening inward and 

 either consisting of the margin or produced from it. PTERIDEJE. 



3. Cheilanthes. Sori minute, at the ends of the unconnected veins, covered by a usually 



interrupted involucre. Small ferns, often woolly, chaffy, or pulverulent. 



4. Pellaea. Sori near the ends of the veins, often confluent. Involucre membranaceous, 



continuous round the pinnules. Sterile and fertile fronds much alike and smooth ; 

 the stalk dark -colored. 



5. Cryptogramme. Sori extending down the free veins. Involucre very broad, at 



length flattened out and exposing the now confluent sori. Sterile and fertile fronds 

 unlike, smooth ; the stalk light-colored. 



6. Pteris. Sporangia borne on a continuous vein-like marginal receptacle, which connects 



the ends of the veins. Involucre continuous round the pinnules. Stalk light- 

 colored. 



7. Adiantnm. Sporangia borne at the ends of the veins, on the under side of the re- 



flexed margin of the frond. Midvein of the pinnules mostly eccentric or dissipated 

 into forking veinlets. Stalk dark-colored. 



Tribe IV. Sori more or less elongated, borne on veins oblique to the midvein, covered by 

 a usually flattened indusium, which is attached to the fertile veinlet by one edge and 

 free at the other. ASPLENIE^E. 



8. Asplenium. Sori on the upper side of the fertile veinlet, less commonly on both sides 



of it. Veins free. 



Tribe V. Sori round or roundish, on the back or sometimes at the tip of the fertile vein- 

 lets, naked or with an indusium. Stalk not articulated to the rootstock. ASPIDIE^E. 

 9. Phegopteris* Sori dot-like, minute, borne on the back of the fruiting veinlets ; indu- 

 sium none. 



10. Aspidium. Sori round, borne on the back or at the apex of the veinlets ; indusium 



orbicular or round-reniform. Mostly large ferns. 



11. Cystopteris. Indusium convex, delicate, fixed across the back of the veinlet by a 



broad base, usually turned back by the ripening sporangia. Delicate ferns with 

 small fronds. 



12. Woodsia. Indusium placed beneath the sorus, and partly or wholly enclosing it, 



divided into irregular lobes or into a delicate fringe. Fronds small. 



1. POLYPODIUM, L. POLYPODY. 



In ours the veins are uniformly free. 



1. P. vulgar e, L. Fronds evergreen, subcoriaceous, 2 to 10 inches long, 

 ovate-oblong to oblong-linear, pinnatifid into linear-oblong obtuse or acute 



