

94 THE BRITISH FERNS. 
but slightly developed; often more or less confluent.  Spore-cases 
pale-brown, roundish-obovate, small, numerous. Spores ovate, or 
oblong, somewhat granulate. 
Duration. The caudex is perennial. The fronds are annual, 
the earlier ones growing up about May, and the latest perishing in 
autumn. 
The chief differences between P. Robertianum and P. Dryopteris 
have been already pointed out in our remarks on the latter species. 
The most important of these is the pinnate rather than ternate 
plan of division of its fronds. This combined with the distinctive 
features afforded by its stouter, more erect, and more rigid habit, 
the glandulosity of its entire surface, and its constancy both in the 
wild and cultivated state, leaves no reasonable ground to doubt 
its permanent distinctness from its near ally. 
We advisedly retain this species, together with P. Dryopteris 
and P. Phegopteris in the genus Polypodium, from a conviction that 
it is mere folly to multiply genera on grounds so slight as are 
depended on for distinguishing them in this instance. Distinctly 
and unmistakeably characterised among the annulate Ferns by 
free veins and round naked sori, the genus Polypodium, thereby 
relieved of a host of species having reticulated veins, is perfectly 
intelligible, and though extensive is not unwieldy. Mr. Newman 
would, however, separate from Polypodium, under the name of Gym- 
nocarpium, the three plants above referred to; and so far as any 
intelligible characters have been assigned to it, this group would be 
distinguished by having a slender black underground caudex—a 
feature which is assuredly not of generic value. Presl had indeed 
at a much earlier date, as we have already remarked, proposed a 
nearly corresponding group as a section of Polypodium; and M. Fée 
had adopted this group under the name of Phegopteris as a genus, 
in his admirable Genera Filicum, distinguishing it by a character 
which would be of far more importance than the nature of the 
stem or caudex, if constant, namely, that of having medial fructi- 
fication, the receptacle of the sori being placed below the apex of 
the vein. Unfortunately, however, in this very genus, there are 
species which produce, at the same time, both medial and terminal 

