88 HISTORY OF BRITISH FERNS. 



■with Lastrea, formed part of the genus Aspidiiim, in 

 consequence of their having round seed-patches covered 

 by a scale. From Lastrea, however, the Polystichvms are 

 known by their having the scale-like cover of the sori 

 circular, without a lateral notch, its attachment being by 

 a little stalk in the centre of the under side ; which form 

 of attachment is called peltate. To a practised eye they 

 are also known by their more rigid texture, and by their 

 having altogether a more spiny appearance than even 

 the spinulose species of Lastrea. The P. LoncMtis, the 

 alpine form of the genus, is strictly evergreen ; and the 

 other species acquire this character when in a sheltered 

 situation ; but if they are much exposed, the fronds will be 

 killed by severe frosts. In general, they retain their fronds 

 without much disfigurement from frost quite through the 

 autumn, and often far into winter. The British species 

 of Pohjstichum are three in number, one of these being very 

 prolific of interesting varieties. 



The name Pohjstichum is compounded of two Greek 

 words — poly, and stickos, signifying many, and order ; and 

 it is applied to these plants in allusion to the numerous 

 regular lines of sori, which are seen distributed over the 

 fronds. 



