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Habitats. Limestone districts of England and Wales. 
Local in its distribution. 
(See also page 54.) 
GROUP I; GENUS XI; SPECIES III. 
POLYPODIUM DRYOPTERIS. (Oak Fern.) 
Plate XV. 
Eronds. This fern is conspicuously three-branched, 
the lowest pair of pinnae forming the first 
and second, and the remainder of the leafy 
frond the third branch. Each branch is 
pinnate or bi-pinnate towards its base, and 
pinnatifid towards its upper part. Pinnae 
linear, and convex on their upper surface. 
Pinnules or lobes oblong, and slightly indented 
on the margin. Rachis and stipes very slender, 
and dark-coloured ; the latter very long, being 
frequently twice the length of the leafy portion 
of the frond. 
Growth. Fronds rising from a thin black wiry rhi- 
zoma, at first resembling three little balls set 
on thin wires, each branch being coiled up 
separately. When mature, the branches are 
much reflexed at their junction with the 
common stem, and are lax and drooping. 
