POLYPODIUM ROBERTIANUM. 



21 



Veins alternately branched; venules simple or forked, and 

 reaching the margin, and bearing a sorus near the margin. 



Sori dispersed over the under side of the fronds, small, 

 circular, and sub-marginal. Spore-cases light-brown coloured; 

 spores nearly ovate in form. 



The pubescent covering of the fronds gives the plant the 

 appearance of being dusted over with lime. 



It is rather remarkable that it has not been found in Scotland. 

 One especial distinction of this species was pointed out by- 

 Mr, Xewman, — the three portions of the young rolled-up frond 

 never assume the appearance of three little balls, as in P. 

 dryojiteris ; and, moreover, imlike that species, it delights to 

 grow in sunshine. 



Hoffman's name of P. Rohertianum has a prior claim to that 

 of P. calcareiim of Smith: this is to be regretted, as the 

 latter is very appropriate. 



Poly podium Rohertianum is not subject to variety. 

 Mr. INIoore remarks, that in the AVest of England this species 

 only descends to two bundled 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 to 

 eight thousand feet. 



Bolton was the first to point out the difference between the 

 present species and P. dryojyfcris, and Hoffmann to pronounce 

 it a distinct species. 



I am indebted to Mr. Joseph Sidebotham, of Manchester, 

 and to the Eev. W. Miller, (late curate of Wirksworth,) for 

 plants of this species from different localities. 



Very readily propagated from the extensive creeping rhizomas. 

 It is handsome in a Fernery. 



The illustration is from a plant gathered on a limestone 

 wall at Matlock Bath. 



