13 



Polypodium calcareum, Smith. Lastrea Robertiana, Newman. 

 Gymnocarpium Robertianum, Newm. Hist. Brit. Ferns, 63. 



Apparently confined in its natural growth to limestone districts. 

 Sir J. E. Smith first noticed it as a distinct species, and it is 

 perhaps more frequent than generally supposed. In the rocky 

 parts of Derbyshire it is far from uncommon, occurring among 

 grass and bushes in broken limestone and tufa ; the Cheddar cliffs 

 and Ingleborough are other stations ; and the growing specimens 

 in my garden are from the vicinity of Kenil worth, where it accom- 

 panied P. Dryopteris, a species with which it has often been con- 

 founded, although in habit and other respects very dissimilar. 

 The rhi/oma is thicker and less spreading than that of the latter 

 plant ; the frond less distinctly ternate or three-branched, the lower 

 branches being shorter than the terminal or middle one ; all the 

 three are rigid, expanding upward on the same plane, and not at 

 all drooping. The colour of the frond is of a dull green, owing to 

 the presence of numerous minute stalked glands that give a mealy 

 appearance to the surface, and similar glands communicate a 

 glaucous hue to the rachis. The sori arising from the extremities 

 of the lateral veins of the segments form a more distinct intro- 

 marginal series than those of P. Dryopteris, and generally become 

 confluent when the thecse open. 



Being of less compact growth than the last species, and more 

 rigid, it is a much less ornamental plant ; but it bears exposure 

 better. Most persons who have had it under cultivation complain 

 of its liability to die off, but 1 believe this to be the effect of con- 

 finement and superabundant moisture : left to itself, few ferns are 

 more hardy, but it likes pure air and perfect drainage. Even in 

 the wild state it cannot be styled a " free-grower," and being a 

 very local plant, its natural condition must be considered as much 

 as possible in our efforts to naturalize it in the fern garden. It 

 flourishes best on a sloping bank, planted near the surface, with 

 an admixture of lime rubbish to the ordinary compost, the ground 

 about it being studded with fragments of stone or burs from the 

 brick-kiln to prevent evaporation. Under these circumstances it 

 does not seem to be injured by daily exposure to four or five hours 

 of the mid-day sun. If grown in pots, they should be large, and 

 about one-third filled with draining material. 



Genus 2. WOODSIA. 



GEN. CHAR. Sori circular ; invested by an inferior involucre, the 

 margin of which is divided into numerous jointed, generally 

 capillary segments. 



A very small genus of alpine ferns, named in memovy of Joseph 



