Filices—Polypodiune. 551 
which is derived from zrodvs, many, and ods, a foot, probably in. 
allusion to the numerous creeping rhizomes of P. vulgare. 
1. P. vulgare—This Fern is readily distinguished from all 
other native species by its creeping densely scaly aboveground 
rhizomes and alternate pinnatifid glabrous stipitate fronds with 
oblong obtuse pinnules and conspicuous yellow eventually 
reddish-brown naked sori. It flourishes best on stumps of trees, 
etc., by the side of brooks or moist places, but it may frequently 
be seen on old walls, etc. The variety Cémbricwm has the 
pinnules finely divided. 
2. P. Drydpteris. Oak Fern.—An elegant species with 
slender creeping rootstocks and alternate bipinnate deltoid 
membranous fronds of a pale green colour, rarely more than 6 
to 9 inches high. Stipes slender, scaly at the base. Frond 
divided into three nearly equal branches, forming a triangle ; 
pinnules obtuse, obscurely toothed. This is found in shady 
mountainous districts in Britain, and is widely distributed in 
the northern hemisphere. 
P. Robertianum, syn. P. calcarewm, is very near the last, 
and perhaps only a variety of it. The fronds are more 
coriaceous and glandular, and the lateral branches of the frond 
are smaller than the central one. It is a rare Fern in Britain, 
growing on limestone rocks. 
3. P. Phegépteris. Beech Fern.—A delicate small-growing 
species with pale-green pinnate triangular fronds from 6 
inches to a foot high. Pinne pinnatifid, the lower pair much 
smaller than the others and deflexed. Pinnules obtuse, ciliate ; 
stipes very slender and brittle, exceeding the leafy portion of 
the frond, slightly scaly at the base. Moist shady woods and 
rocks throughout Britain. Distribution general in the north 
temperate zone. 
4. P. alpéstve, syn. Pseuduthyrium alpéstre. — This is 
strictly an alpine species, resembling the Lady Fern in general 
appearance. It has a stout rhizome and lanceolate bipinnate 
fronds varying from 6 inches to % or even 3 feet in height. 
Pinne pinnatifid; pinnules toothed. Stipes 4 to 6 inches 
high, scaly at the base. Sori arranged in a single row on each 
side of the midrib. In Britain only on the lofty mountains of 
Scotland, and in arctic and alpine Europe, North America, 
and Western Asia. ; 
P. fléwile or hivmile is a variety with looser narrower fronds, 
and more distant deflexed pinnae. 
