THE BRITISH FERNS. 

Gzxvs I: POLYPODIUM, Linneus. 
Gun. CHAR.—Sori non-indusiate, circular or ovoid, superficial or 
immersed; the receptacles terminal or medial on the free veins. . 
Veins simple or forked, from a central costa, or simple costeeform in 
the ultimate segments ; venules free. 
Fronds coriaceous herbaceous or membranaceous, simple pinna- 
üfid pinnate or bi-tri-pinnate, articulated or continuous with the 
rhizome, the pinne sometimes articulated with the rachis. 
Stem rhizomatous or caudiciform—rhizome creeping; caudex 
short erect, or decumbent. 
The British species of Polypodium belong to two distinct sections 
of the genus, of which the type is Polypodiwm vulgare. The dis- 
tinctive features of the group consist in the presence of circular or 
punetiform sori, and in the absence of covers or indusia; and by 
these marks it is easily distinguished from other British Ferns: 
but when exotic species are taken into account, another peculiarity, 
that of the free or disunited veins becomes necessary to distinguish 
it from the various generic groups subdivided from it, which have 
the veins more or less, and in various ways, reticulated. 
Even the two groups into which the British species naturally fall, 
have by some modern writers been regarded as distinct genera, the 
habit of the plants being chiefly relied on to furnish distinguishing 
characters. There seems to us, however, to be such.a complete 
conformity in the character of the sori, and such a conformity also 
in the nature of the venation, so far as words can express its chief 

