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236 HISTORY OF BEITISH FERNS.
The stems are usually, except at the base, furnished with
whorls of numerous simple branches, the number of the
branches generally corresponding with the furrows of the
stem. These are slender, four- or five-ribbed, and their
sheaths set nearly close, and terminate in pale brown lanceshaped
teeth, having a membranous border.
In this species, when a section of the stem is examined,
it shows a series of prominent ridges on the outer face;
just within these, and over against the furrows, occur a
circle of moderate sized cavities; and alternating with
these, and near the inner margin, is a series of much
smaller circular cavities. The central cavity of the stem
is comparatively very small, not very much larger than the
series of openings near the outer surface. The resemblance
is considerable between its section and that of E. arvense.
The fructification is a blunt oblong cone, more than an
inch long, terminating the main stem, and supported on a
stalk about equal to its own length above the uppermost
sheath. The whorls of scales in the mature cone are quite
separated, and expose the white spore-cases attached to the
margin. The scales in this species exceed a hundred in
number. The fructification is mature about June.
Besides the more usual form just described, there are
some curious variations to which this plant is liable. One
of the most remarkable has been called the variety pohf-
stachion. It is remarkable in having more or less of the
branches of the two upper whorls terminating in cones of
fructification; the usual habit of the plant being to produce
only one cone, and that on the central stem. The
cones produced by the branches are, we believe, always
much smaller than the ordinary cone of fructification produced
by the main stem, and they are darker-coloured and
more compact. It has been suggested, that the production
of these lateral fructifications is accidental, owing to the
destruction of the top of the main stem, hut this explanation
is quite insufficient, since they are sometimes produced
along with the central head, which moreover varies when
accompanied by them, being sometimes of the usual size,
and sometimes reduced in size like the lateral heads. The
'lateral heads are usually later in their appearance than the
central ones. Occasionally we have seen some of the
branches of the lowest whorl become elongated, and terminate
in one of these small cones.
Another form is called nudum, and a very similar variety
is sometimes called alpinum. There appears to be no advantage
in attempting to distinguish these, both being de