30 BRITISH FERNS. 



its fronds smooth and divided into three branches. When 

 the fronds are but partially developed this latter character- 

 istic is very obvious ; for the three branches are seen to be 

 rolled up separately at the end of these little wire-like stalks, 

 the whole supported by one which is longer and stouter. It 

 is a slender and delicate plant, its height being commonly 

 not more than six inches, often less, though sometimes more, 

 and its texture fragile. 'Hence it is at once destroyed by 

 frost, and soon becomes rusty and withered by exposure to 

 heat and drought. When growing in a cool, shady situation, 

 however, it continues fresh and cheerful-looking from April, 

 when it usually starts into growth onwards until it is 

 affected by autumnal cold. In pots, in Wardian cases, or 

 on sheltered shady rock-work, it is alike desirable for culti- 

 vation. 



P. Dryopteris is not an uncommon species, but it occurs 

 only in mountainous situations and the drier parts of clamp 

 woods : in England mostly in the north ; in Scotland distri- 

 buted pretty generally ; very rare in Ireland. 



LIMESTONE POLYPODY. 



The proper name of this Fern is Polypodium Robertianum, 

 but it is more commonly known as P. calcareum, that name 

 having been much used by English writers. Other names 

 applied to it are Lastrea Rdbertiana, Phegopteris calcarea, and 

 Gymnocarpium Robei1,ianum. 



The Limestone Polypody grows from six inches to a foot in 

 height. The fronts are nearly triangular, with the base 

 shorter than the sides, the stipes about equalling the leafy 

 portion in length. They are partially three-branched, but 

 the lateral branches are much smaller than the central one, 

 and attached to the stipes by a more slender rachis. The 

 lower branches are pinnate, with pinnatifid pinnae; the 

 upper branch pinnate, with its lower pinnae again pinnate, 

 and the upper ones pinnatifid, as also is the apex of the frond 

 and of the lower branches. The pinnules, or lobes, have a 

 distinct midvein, with simple or slightly branched venules, 

 near the termination of which, in a marginal series, the son 

 are produced. 



This Fern is known from P. Dryopteris, to which it is so 

 nearly related, that some botanists do not consider it dis- 

 tinct, by having its fronds less decidedly, though somewhat 

 three-branched, and by having its surface covered with small 

 stalked glands, which give a mealy appearance to every part. 

 In addition to these points of difference- the fronds of this 



