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222 FERNS OF N O R TH AMERICA.
the crown. The fertile pinnæ are somewhere near the middle
of the fronds, most frequently rather above the middle. Above
these fertile pinnæ the sterile pinnæ again appear ; and this
upper part of the fertile frond is more or less cur\'ed outward,
like the sterile fronds. But this distinction in the bearing of
the sterile and the fertile fronds is not always so evident,
especially in plants of moderate growth. When the fronds
first rise from the ground, they are covered with a light-brown
coating of entangled webby fibres. These are shed during the
early summer, and the fronds with their stalks become nearly
smooth, a little of the wool clinging in the axils of the pinnæ
and along the midribs or the veins.
The stalks are greenish in color, and have the back
rounded, and the front slightly convex near the base, but considerably
furrowed in its upper portion. The transverse section
shows a single horseshoe-shaped fibro-vascular bundle, its
edges considerably rolled inward. The length of the stalks is
from a few inches to nearly or quite two feet. The sterile
frond in large plants is fully three feet long, perhaps sometimes
longer. A frond three feet long is a foot wide in the
middle, and decreases moderately from near the middle to the
base ; so that the lowest pinnæ are scarcely half as long as
the middle ones. S ix or eight inches from the end the frond
begins to narrow, and narrows so rapidly that the apex is
barely acute, and very often somewhat rounded. In the frond
here described the lowest pinnæ are nearly opposite, but the
successive ones-more and more decidedly alternate. The pin-
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FERNS OF NORTH AMERICA. 223
næ number twenty-three on each side ; the lower ones separated
by intervals of two and a half inches, and the rest
gradually more approximated.
The pinnæ are short-stalked, and in shape arc lanceolate
from a broad base ; the largest ones measured being seven
inches long, and one and a quarter inches wide at the base.
They are pinnatifid about four-fifths of the depth to the midrib,
the segments being eighteen or twenty on each side, close-
placed, oblique, oblong-ovate, and rounded at the ends; the
apex of the pinna being barely acute, but never acuminate. In
each segment there are about eleven to thirteen veins on each
side, the lowest one being on the inferior side of the midvein,
and not unfrequently leaving the midrib of the pinna at a
point just below the separation of the midvein from the midrib.
These veins are almost always forked but once, the forking
very near the midvein, and the two veinlets running nearly
straight in an oblique direction to the margin of the segment,
which is commonly entire, or at most obscurely crenulate towards
the apex. In fronds of less ample dimensions the pinnæ are
of course fewer and smaller, and the segments also smaller in
due proportion.
The lower and the upper pinnæ of the fertile fronds are precisely
like those of the sterile fronds. The fertile pinnæ vary
in number from one to four pairs, and in position from near
the bottom to near the top of the frond. In one frond, of
twenty-six pinnæ on each side, the third, fourth, fifth, and
sixth on each side are fertile, leaving twenty sterile pinnæ
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