
THE BRITISH FERNS. 
Genus X: BLECHNUM, Linneus. 
GEN. Cuar.—Sori indusiate, linear, continuous or rarely inter- 
rupted, seated on a transverse receptacle, approximate to the costa ; 
Sometimes central or submarginal by the contraction of the fronds. 
Indusium linear, opening along the inward side. Veins of the 
sterile fronds simple or forked from a central costa, the venules 
direct, free, thickened at the apex; those of the fertile fronds 
combined near the base or within the margin of the transverse 
receptacle. 
Fronds simple pinnatifid or pinnate, subcoriaceous, the fertile 
sometimes more or less contracted. 
Caudex short, erect, often producing elongated creeping stolones. 
This genus is closely allied to an exotic one named Lomaria, in 
which the fertile fronds are always contracted, and thus have an 
entirely different aspect from the sterile ones. There are several 
species of Blechnum, the native British one among the number, 
which having contracted fertile fronds, and altogether the aspect of 
Lomaria, have been sometimes referred to that genus. _ This 
narrowing of the fertile parts is met with, moreover, in various 
degrees, so that it is necessary to understand what are the technical 
differences between the two genera, in order to ascertain the proper 
position of such osculant species. We do not adopt the opinion 
that the two groups should be united. jg 
The distinction between Lomaria and Blechnum becomes easy 
when full force is given to the technical characters assigned to each 
respectively. The peculiar characteristic of Lomaria is that the sori 
are produced at the margin; whilst the characteristic of Blechnum 
is to have the sori distinetly within the margin, and near to the 
costa. "Thus in technical and exact terms the sori in Lomaria are 
marginal and in Blechnum costal or intramarginal The fructifi- 
cation of Lomaria is determined by the indusium being a continua- 
tion of the margin of the frond, which becomes membranaceous, 
and is inflected over the spore-cases. The fructification peculiar to 

