0(5 POLYPODIUM ROBERTIANUM. 



Switzerland, and the United States, Canada, Norway, and Asia. 



Although strictly speaking it is a North of England Fern, yet 

 it is somewhat strange that it has not been discovered in Scot- 

 land, nor indeed in Ireland. 



Found in the counties of Durham, Cumberland, Westmorland, 

 Yorkshire, Lancashire, Derbyshire, Gloucestershire, Somerset- 

 shire, and less sparingly in Oxfordshire and Wiltshire. In Wales 

 it is found in Denbighshire. 



One especial distinction Mr. Newman points out — the three 

 portions of the young frond never assume the appearance of 

 three little balls; also, unlike P. dryopteris, it seems to delight 

 in sunshine: all the plants which I have seen growing at Mat- 

 lock were on sunny rocks. 



The same light soil is requisite for this species as for P. 

 dryopteris, with the addition of abundance of limestones. 



Hoffmann's name of P. Roherticmum has a prior claim to that 

 of P. calcareum of Smith; this is to be regretted, as the latter 

 is very appropriate. 



The present species is known as the "Limestone Polypody," 

 "Smith's Polypody," and the "Rigid Three-branched Polypody." 



This Fern is not subject to variety from seed. 



Mr. Moore, in the "Ferns of Great Britain and Ireland," 

 remarks that in the West of England it only descends to two 

 hundred and fifty feet above the sea, and in the north ascends 

 to nine hundred feet. Dr. Hooker found it on the Himalaya 

 mountains at an elevation of from five thousand to eight thou- 

 sand feet. 



In a wild state it seems to occur only in the limestone districts. 



A British Fern. 



The fronds are bipinnate, with the lowest pair of pinnae 

 occasionally sub-bipinnate on the posterior side. Pinnse variable, 

 the lowest pair largest, triangular in form, stalked, and fre- 

 quently bipinnate; the pinnse nearer the apex of the frond 

 sessile, pinnate, or pinnatifid. Pinnules, the lowest larger on 

 the posterior side, each succeeding pinnules like the smaller 

 ones of the pair immediately below them. The whole frond 

 triangular in form, and three-branched. Veins simple, or forked. 



Sori round, small, and scattered over the whole under surface 

 of the frond, becoming partially confluent. 



Fronds from six to eighteen inches in length, somewhat rigid, 



