172 BRITISH FERNS 



POLYPODIUM VULGARE (THE COMMON POLYPODY) 



(Plate XXV) 



P. vulgar e, which is by far the most widely distributed species 

 of this genus, differs very markedly from the other three. It has 

 once-divided, tough fronds, consisting of a long stalk, continuing as 

 a midrib bearing two rows of normally bluntly tipped side divisions, 



as seen in Fig. 194, forming a sort of double comb with well- 

 separated broad-based teeth, the frond tapering gradually to a 

 blunt point, or perhaps with pinnae set on endwise, even the 

 normals varying somewhat in different districts. Its native habitats 

 are on the tops of old walls or roofs, where dense colonies some- 

 times accumulate, along the hedges in the stony dykes which back 

 them, in the forks of old trees, and even on the trunks, and in the 

 woods on elevated masses of woodland debris and rocky detritus. 

 Its fronds may attain a length of two feet under very favourable 

 circumstances, but ordinarily are less than half that size. The 

 spores are borne in very conspicuous round masses on the frond 

 backs, and are of a brilliant orange yellow, the spores themselves 

 being of similar colour, a solitary exception in British species. 

 Both capsules and spores are also comparatively large, the spore 

 heaps, under a lens, resembling heaps of oranges. The rootstocks 

 branch and spread on the surface, not burrowing, as in the other 

 species of the same family ; they are also much thicker and fleshier, 

 often as thick as one's little finger. The fronds spring from these 

 singly, and do not form clumps. As their tree resorts indicate, 

 leaf mould and good drainage are essentials to successful culture, 

 and shallow pans, providing room for the travelling rootstocks, are 

 preferable to pots. This species is perfectly evergreen, the fronds 

 lasting well into the second season, until new ones arise to replace 

 them. The other members of the family will be treated of under 

 their respective headings. This species has been very liberal in 

 " sports," many of which are of great beauty, as is seen by the 

 nature prints in the Appendix. 



