278 
HISTOEY OF BRITISH FERNS. 
branches not growing in whorls, but springing singly from 
the joints, and having much similarity to the stem itself : 
it is the erect form of the species, chiefly, which thus 
becomes branched. The stems grow about a foot high, 
and, in what is taken as the typical plant, their surface 
is very rough, and impressed with from four to ten furrows, 
with alternating, rather prominent ridges, each ridge mar- 
gined on both sides with a line of minute siliceous points, 
which give it the appearance of being grooved, and impart 
to it its peculiar roughness. The sheaths are slightly 
enlarged towards their margin, ribbed like the stem, green 
in the lower part, black above, and terminate in a fringe 
of black teeth, equalling the ribs in number, with a broad 
white membranous border, in form ovate, and tipped by a 
deciduous bristle. Sometimes the contrast between the 
black ring and teeth, and the white border to the latter, is 
very conspicuous. 
A certain number of the stems, usually the most vigorous, 
terminate in a cone of fructification. This is siliall, elliptic, 
crowned by a prominent point or apiculus. It is usually 
black, and sessile in the uppermost sheath, but sometimes 
elevated on a short stalk. All the stalked cones we have 
seen have been much paler in colour than the sessile ones. 
