OAK FERN ,. 
89 
thirds of the upper portion of its length. The sori 
are small, circular, distinct, but become confluent in 
maturity. There is usually no indusium, but in some 
specimens there appears to be an abnormal develop¬ 
ment of a membrane covering the sori. The fronds 
are annual, and perish early in the autumn. 
It is only lately that this fern has been added to 
our British Flora, and as yet has only been found in 
the Highlands of Scotland, where it grows in the 
greatest profusion, particularly in Forfarshire. 
It is a fern which does not generally flourish well 
in artificial circumstances. Free air and shade, with 
a pure atmosphere, seem essential to it, and it is 
therefore not desirable to inclose it in a glass case or 
greenhouse, but rather to imitate its natural conditions 
as much as possible. 
OAK FERN. 
POL YPODIUM DR YOPTERIS, 
Linnaeus, Bentham, and Newman. 
(Plate XIV. Fig. 2 .) 
SYNONYMS. 
Gymnocarpium Dryopteris, Newman. 
Polystichum Dryopteris, Roth. 
This is one of the most delicate and elegant of our 
species of ferns. The roots are creeping, fibrous, and 
black, forming a dense, matted mass. The young 
fronds make their appearance in March and April, as 
