78 
HISTORY OF BRITISH FERNS. 
in Scotland it is distributed pretty generally; it is very 
rare in Ireland. 
This species has been called Polystichum Dryopteris, 
Lastrea Dryopteris, Phegopteris Dryopteris, and Gymno- 
carpium Dryopteris. 
Polypodinm Robertianum, Hoffman . 
The Limestone Polypody. (Plate III. fig. 1.) 
This Fern is known from P. Dryopteris —to which it 
is so nearly related that some botanists do not consider it 
distinct—by having its fronds less decidedly, though some¬ 
what three-branched, and by having its surface covered 
with small stalked glands, which give a mealy appearance 
to every part. In addition to these points of difference, 
the fronds in this species are of a dull deep green, more 
rigid, and without the marked deflection of the rachis so 
obvious in P. Dryopteris. The young fronds, moreover, 
instead of being rolled up in three little balls, have their 
pinnae all rolled up separately. The glandular surface of 
the frond is very readily seen with a good pocket lens, 
which is a very necessary aid to the study of Ferns. 
The Limestone Polypody grows from six inches to a foot 
in height. The fronds are nearly triangular, with the 
