116 HISTORY OF BRITISH FERNS. 



Genus IV. LASTKEA, Presl. 



ONE group of the Ferns were formerly called Aspidiums, 

 or Shield-Ferns. This group, so far as English species are 

 concerned, is now divided into three, bearing the names of 

 Lastrea, Polystichum, and Cystopteris. The Lastreas are 

 known among these by having the indusium, or seed-cover, 

 round in outline with a lateral notch, thus becoming 

 kidney-shaped; they are attached to the frond by the 

 notched part. This group includes some of the largest and 

 most common of our native species, and nearly all of them 

 are remarkable for their elegance. Several of them retain 

 their fronds through the winter in sheltered situations, but 

 they are not strictly evergreen, and in exposed situations are 

 always bare during winter. 



Of the Lastreas eight British species are usually recog- 

 nized, but the number varies according to the value put 

 upon certain differences in the plants, by different authors. 



The name Lastrea commemorates a zealous botanist and 

 microscopical observer, M. Delastre of Chatelleraut. 



LASTREA CRISTATA, Presl. The Crested Fern. (Plate 

 VI. fig. 2.) 



This is the simplest of the British forms of a group of 



