90 
HISTORY OF BRITISH FERNS. 
auricle, while the lower side of the base is, as it were, cut 
away. The margin is set with spinous teeth. The veins 
are twice branched, the branches extending to the margin ^ 
without joining with others. The clusters of spore-cases 
form a line parallel with, and on each side of the midrib, 
and are covered each by a membranous circular scale, 
which is attached by a short central stalk. 
This is a true Rock Fern, occurring on the bleak moun- 
tains of Scotland and in the milder climate of Ireland, as 
well as, rarely, in the north of England and Wales. It is 
very distinct, and, when vigorous and healthy, not inele- 
gant, but is exceedingly diflB.cult of cultivation, and is 
seldom seen thriving under artificial treatment. 
The Holly Fern has been at different times called Aspi- 
dium Lonchitis and Polypodium Lonchitis, 
Polystichum aculeatum, Both 
The Common Prichly Shield Fern, 
This species is almost evergreen in a sheltered situation, 
and is one of those which are well suited by boldness of 
character for the decoration of rocky scenery. It is a stout 
plant, having the fronds a couple of feet or more long, and 
springing from a stout tufted stem or crown, whence they 
