THE BRISTLE FERN. 
Genus XV: TRICHOMANES, Linneus. 
Gen. Onan.—Sori involucrate, i. e. seated within extrorse-mar- 
ginal (rarely recurved) urn-like cysts (involucres), sessile upon or 
more or less sunk in the margins of the fronds; the veins continued 
to form exserted filiform sometimes capitate receptacles, which are 
free within the cysts or involueres, and. bear sessile lenticular spore- 
cases at their base. Involucres funnel-pitcher-shaped or shortly bell- 
shaped, truneate and entire at the mouth, or two-lipped. Veins 
simple forked or pinnate from a central costa, simple costa-like in 
the ultimate segments, or flabellate-dichotomous; venules free, some- 
times excurrent in the marginal teeth. 
Fronds simple pinnate or decompound, pellucid-membranaceous, 
rarely sub-coriaceous. 
Caudex rhizomiform, creeping (sometimes filiform), or erect 
cæspitose. 
The species of this beautiful and extensive genus of Ferns may in 
almost all cases be known from those of other genera, except Hymeno- 
phyllum, by their being of a semi-transparent texture, which is a 
feature apparently common to the whole family, although some of 
the species having fronds thicker than others, acquire a somewhat 
coriaceous texture in the dried state. From Hymenophyllum, 
which has some representatives among British Ferns, the present 
genus is separated by the form and nature of the involucres. 
The general structure of these two genera, which differ only in 
technical points, and are indeed in a few cases not easily separated, 
may be thus described :-—From the stipites, which are harsh and 
wiry, branch out in a pinnate or flabellate manner a series of wiry 
branches of smaller size; these according to the degree of divi- 
sion occurring in the frond form, the rachides (primary secondary 
or tertiary), the coste, or the veins and venules, which all. have . 
more or less a wiry character. The ultimate divisions of these 
parts are bordered, so as to form a flat expansion, with thin loosely- 

