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1 5 6 F E K N S OF NORTH AM E R IC A .
side, the lower ones slightly diminishing in length, more distant
and mostly opposite, the upper ones either alternate or opposite.
Most of the pinnæ have very short stalks ; the lower ones
are broadly ovate-triangular, the higher ones gradually narrower
at the base, and so becoming ovate-oblong. In the sterile
fronds the pinnæ are pinnately lobed about two-thirds of the
way to the midrib ; in the fertile fronds they are pinnatifid to
within half a line of the midrib. The number of lobes on each
side is usually about eight pairs, the higher ones gradually
passing into mere teeth of the short and only sub-acute apex of
the pinnæ. The lobes are oblong, and mostly serrated with
short incurved barely mucronate teeth. The basal lobes are
incised-serrate, the teeth being again serrated. The apex of the
lobes is rounded and obtuse : in the form called Aspidium
Lancastriense the lobes are shorter and more triangular, and
consequently less obtuse. A character which can be seen only
in the living fronds is noticed by Moore : it is that the stalks
of the pinnæ are twisted just enough to turn the upper surface
of the pinnæ towards the apex of the frond. This condition
may be seen in very many kinds of ferns, but is especially
evident in the fertile fronds of the present species.
The fronds are dark-green and somewhat lustrous above,
paler beneath, and perfectly smooth, save for a little chaff
which commonly persists along the rachis. The texture is
firmly herbaceous.
The veins are marked on the upper surface by impressed
lines, which almost disappear in dried specimens.
F E R N S OF NO R TH AM E R IC A . 157
They are pinnately arranged on the midvein. The lowest
superior veinlet is often simple, but nearly as often forked,
the lower branch sometimes again forking. The rest of the
veins are mostly once forked. Most of the veinlets terminate
in the teeth, and are slightly enlarged at the apex. The
superior veinlets of the several veins bear sori about midway of
their length, the number of sori being often ten or twelve on
the basal lobes, and from four to eight on all but the uppermost
of the others.
The indusium is at first rather large, flat, orbicular-
reniform, the sinus not very deep, and the surface and margin
without hairs or glands. As the fruit matures the indusia
commonly become a good deal shrivelled, or even fall off.
The sporangia have about fifteen articulations in the ring.
The spores do not ripen until late in the season, and
are bean-shaped, the surface so rough as to be almost
muricate.
Var. Ctintonianum differs chiefly in its much greater size,
and consequently larger and more numerous pinnæ and lobes.
It does not occur in Europe, and in America it has often
been mistaken for A . Gotdianum, from which it differs evidently
in having the fertile and sterile fronds unlike, in the
narrower outline of the fertile fronds, and especially in having
all the pinnæ broadest at the base instead of in the
middle. In both forms of A . cristatum the lobes of the pinnæ
are commonly closely placed, though in some large specimens
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