LIMESTONE POLYPODY. 87 



The Three-branched Polypody, having thin delicate fronds 

 that readily shrivel on exposure to sun or wind, is equally fond 

 with the Mountain Polypody of sheltered and shady places ; 

 but whereas the latter species must have abundant moisture 

 dryopleris likes a much drier situation, where at least its 

 rootstock will be free from moisture, though its fronds may 

 be bathed in mist or damp air. It is a fern of the mountain 

 side, and in the Highlands reaches an altitude of 2700 feet. It 

 may be said to be abundant in Scotland and Wales, its main 

 range in this country extending from Shetland to Derby, the 

 whole of Wales, and sparingly in Gloucestershire, Devon, and 

 Cornwall. It is rare in Ireland, where it is restricted to the 

 counties Antrim and Leitrim, at eighteen hundred and eight 

 hundred feet respectively. Beyond our coasts it is found pretty 

 generally throughout the North Temperate Zone. 



The next fern on our list Polypodium robertianum\h.Qu$\ 

 commonly accorded specific rank, is more correctly to be 

 regarded as a sub-species of P. dryopteris. 



Limestone Polypody (Polypodium robertianum). 



It is not necessary to recapitulate our description of the 

 Three-branched Polypody, the typical form, of which the 

 Limestone Polypody is a permanent variety on the way to 

 becoming a distinct species. It will be sufficient to mention 

 those respects in which this differs from the type differences 

 which may have been brought about directly or indirectly as a 

 result of changed habitat. For " Limestone Polypody " is no 

 fancy name, though it is quite modern and of book origin. This 

 fern will be found nowhere except on limestone rocks. (Plate 97.) 



In general appearance no one can doubt its close relationship 

 to P. dryopteris, but the rootstock is stouter, the frond of 

 firmer, more leathery texture, downy instead of smooth, and the 

 stipes is longer than the rachis. Examined through a lens the 



