POLYPODIUM. 85 



are by far the more numerous, they are generally, though not always, terminal 

 on the veins. 



Eaton further states (vol. i., p. 119) : " The genus Polypodium—evQu when 

 limited, as by Mettenius, to the Ferns having round or roundish, naked sori, 

 composed of sporangia with an incomplete vertical ring, the stalks of the 

 fronds articulated to the rhizome — contains several hundred species. Mettenius 

 gives 260, and in the Second Edition of ' Synopsis Filicum ' Baker brings 

 up the number to 340.* The great difference in the size and outhnes of the 

 frond, in the venation, in the texture, and in the surface — whether smooth, 

 hairy, tomentose, or scaly — and in the presence or absence of peltate scales 

 among the sporangia, have induced writers on the subject, especially Link, 

 J. Smith, Presl, Fee, and Moore, to propose dividing the genus into many 

 genera, founded on the characters just referred to. But Mettenius has 

 satisfactorily shown that the intermediate forms are so many and so perplexing 

 that the whole is best regarded as forming but one natural genus ; and in this 

 view he has been followed by Sir W. J. Hooker and Mr. Baker, who, however, 

 retain in Polypodium those Ferns which differ from Nephrodium only in the 

 absence of an indusium — a character which is often the result of accident 

 or of arrested development. These species, nearly a hundred in number, 

 constitute the genus Phegopteris, and are technically distinguished from the 

 true Polypodia by having the stalks continuous with the rhizome or caudex." 



As previously stated, the genus Polypodium was formerly divided by 

 various authors into an almost unlimited number of sub-genera ; the following 

 list of the best-known of these, with the names of their authors, will show at 

 a glance the importance of the genus : 



Abacopteris, Fee. Arthropteris, J. Smitli. 



Adenophorus, Hooker and Greville. Calymmodon, Presl. 



Aglaomorpha, Schott. Campyloneuron, Presl. 



Amblia, Presl. Chrysopteris, Link. 



Ampelopteris , Kunze. Coelopteris, A. Brongniart. 



Anapeltis, J. Smith. Colysis, Presl. 



Anaxetum, Link. Craspedaria, Fee. 



Apalophlehia, Presl. Crypsinus, Presl. 



* Nicholson, in the " Dictionary of Gardening " (vol. iii., p. 186), states that this genus comprises upwards 

 of 450 species. 



