14 OUR NATIVE FERNS AND THEIR ALLIES. 



ing the sori at or near the ends of the veins, covered by an in- 

 dusium formed of the margin of the frond. 



In § Adiantopsis the indusia 

 are distinct, and confined to a 

 single veinlet. One of our species 

 varies from the typical species of 

 this section, and has even been 

 assigned to a separate genus. 

 E^2^^^^^^^^^)^^^ In§EuCHEiLANTHEStheindu- 



FiG. 6.—f'fejh tongijoiia L. En- sia are more or less confluent but 



lareed sesrment of pinna, showing the ^ ^. 11 ^ a- 



vein-like receptacle under the margi- not COntmuoUS, usually extending 



nai indusium. over the apices of several veinlets. 



In § Physapteris the ultimate segments are bead- like, and 

 the indusium is continuous all round the margin. 



§ Aleuritopteris has the fronds farinose below, and m- 

 cludes a single species somewhat doubtfully assigned to cur 

 limits. 



38. Cryptogramma has dimorphous fronds, the margins 

 of the fertile being closely rolled toward the midvein, thus cov- 

 ering the confluent sori. At maturity these open flat in order 

 to discharge the spores. 



39. Pellaea has representatives of three sections within 

 our limits, all agreeing in possessing intramarginal sori, which 

 finally became confluent and form a marginal line covered by 

 an indusium formed of the margin of the frond. 



§ Cheiloplecton includes herbaceous species with visible 

 veins and broad indusia. 



§ Allosorus includes coriaceous species having wide 

 indusia, while § Platyloma includes species similar in texture, 

 but with extremely narrow indusia and broad segments. 



4-0. Ceratopteris is an anomalous genus from southern 

 Florida, having a few sori arranged on two or three veins par- 

 allel to the midvein, and covered by the broadly refiexed margin 

 of the frond. 



41. Lomaria (Fig. 7) stands intermediate between those 

 genera, in whicli there is an indusium formed of the revolute 

 margin of the frond and those in which the indusium is remote 

 from tiie margin. Our single species has dimorphous fronds, 

 free veins, and the fructification in a broad band next the mid- 



