THE LIMESTONE POLYPODY, 



bipinuate, with the lowest pair of pinna; sometimes subbipinnate on the posterior side, which is the 

 most developed. 



Pinna variable, opposite below, the lower pair largest, obliquely triangular, Btalkcd, Often bipinnato ; 

 the next pair stalked or sessile, pinnato-pinnatifid; the upper ones all sessile, pinnate or pinnatifid, 

 becoming gradually less divided towards the apex. Pinnules of the lower pair larger on the posterior 

 side, those of the other pinnae nearly equal, those of each succeeding pair resembling the smaller ones of 

 the pair next below them. Pinnuhts or Mulcts oblong obtuse, entire or erenatcd. 



Venation of the lower posterior pinnules consisting of a stout midvein, with a Jlexuoso vein running 

 up the centre of each lobulet; this is alternately branched, the venules extending to the margin, simple, 

 Or very commonly forked ; the venule if simple, and the anterior veinkl if divided, bearing a soras near 

 to the margin. Or, the vein extending up the lobulet may be regarded as a midvein ; its branches, some- 

 times simple and soriferous, veins, and the branches of these, of which the anterior is fertile, venules. 



Fructification on the back of the frond, scattered over its whole surface. AW small, circular, consisting 

 of numerous crowded spore-cases, entirely without indusia, arranged in a linear submargiiml scries along 

 each side of the lobulcts ; or about the sinus, in a scries between the midrib and margin, when the lobules 

 &re but slightly develojKrd ; often more or less confluent Spore-cmes pale-brown, roundish-obovale, 

 small, numerous. Sjwres ovate, or oblong, muriculate. 



Duration. The rhizome is perennial The fronds are annual, the earlier ones growing up about 

 May, and the latest perishing in autumn. 



We advisedly retain this 0petie», as well as those represented on Platks IV, and V., in the genus 

 Poli/podium, from a persuasion of the inconvenience and impropriety,— nay the folly — of needlessly 

 multiplying genera. Characterised among the annulate Ferns by free veins and round naked sori, the 

 genus Poli/podium, thereby relieved of a host of species having reticulated veins, is perfectly 

 intelligible, and though extensive is not unwieldy, Mr. Newman would separate from it the three 

 plants above referred to, under the name of tw'ymnocarpium, which group, so far as any intelligible 

 characters have been assigned to it> would be distinguished by having a slender black underground 

 caudcx— a feature which is assuredly not of generic value- Presl had indeed, as we have already 

 remarked, proposed at a much earlier date a nearly correspondent group as a section of Pvlypodium ; 

 and M. Fee had adopted this group under tlie name of Pheffopteris as a genus, in his admirable Genera 

 Filteum, distinguishing it by a character which would be of far more importance than the nature of the 

 rhizome, if constant, namely, that of having medial sori, or, in other words, the receptacle of the sori 

 seated below the apex of the vein. Unfortunately, however, in this very genus, there arc species which 

 produce, at the same time, both medial and terminal sori. so that the character is not distinctive. The 

 three species referred to possess, however, in common, a peculiarity of some importance, their fronds 

 being adherent to, not articulated with, the creeping rhizome. 



The chief differences between /'. ttobertianum and /\ /Jtgojrfem have been already pointed out 

 under the latter species. The most important of these is the pinnate rather than teruate mode of 

 division of its fronds ; and this combined with the distinctive features afforded by ita stouter, creel, and 

 rigid habit, the glandulosity of its entire surface, and its constancy both iu the wild and cultivated 

 state, leaves no reasonable ground to doubt its permanent distinctness from its near ally. 



This is a hardy-growing plant under cultivation, provided its roots arc well drained, and the soil in 

 which it is planted is kept rather drier than is usual with Ferns, This latter point may be effected, both 

 by withholding excess of water, and by adding porous material to the compost. Limestone or old mortar 

 are congenial additions. It bears exposure to sun also better than the majority of Ferns. The creeping 

 rhizome affords a ready means of propagation. 



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