ii •, I iii :
IÉÍM
230 HISTORY OF BRITISH FERNS.
brown underground stems, which also produce whorls of
black fibrous roots.
The stems are, though firmly ribbed, very smooth to the
touch, their furrows being very shallow ; their smoothness
no doubt arising from the presence of a very slight coating
of the siliceous particles, which, when more abundant, give
their peculiar harshness to some of the species ; probably,
also, the particles themselves are in this species much
finer and less prominent. Sometimes the stems are quite
unbranched ; sometimes furnished with irregular whorls of
branches along all their central portion ; and between these
two extremes there occurs every conceivable degree of
branching, from the single shoot produced here and there,
through every gradation of imperfect whorls up to whorls
of short branches almost complete. The branches, which
are simple, nearly erect, and never acquire much length,
are smooth like the stem. There is no material difference
between the barren and fertile stems, except the presence
of the fructification in the one case and not in the other ;
they are, therefore, said to be similar in structure.
The surface of the stem is marked with from sixteen to
twenty very slight ridges, and the sheaths, which are short,
rather closely fitted to the stem, and of the same colour in
the lower part, terminate in an equal number of dark-
coloured awl-shaped teeth, which sometimes have a pale
membranous margin. The branches are four- to eightangled.
Owing to the shallowness of the ridges and furrows, the
section of the stem shows a nearly smooth exterior outline,
and the cylinder of the stem is furnished only with a row
of minute cavities near the inner margin; this cylinder is
very thin, compared with the diameter of the stem, the central
cavity being unusually large. The present plant, therefore,
though it has been considered a variety of E. pahistre,
is most strikingly distinct from that species in the structure
of its stem.
The fructification is produced by a portion of the
branches, in cones, at their apex; these cones are ovate
obtuse, and very frequently sessile in the uppermost sheath.
The scales are black, exceeding a hundred in number; the
spore-cases are pale-coloured. Usually only the termination
of the central stem bears fructification, but it sometimes
happens, though rarely, that some of the uppermost
branches are also fertile.
This plant is the most fodder-like of any of the Equise-
tums, owing to its less flinty cuticle, but in this point of
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