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72 F E R N S O F NORTH AM E R IC A .
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ovate-lanceolate and pointed, narrowed to a sub-cordate and
obscurely-stalked base, and deeply pinnately-lobed. This is
var. elegans of Professor Robinson. Professor Lawson has
a var. Traillæ, which has “ very large bipinnate fronds, all
the pinnules pinnatifid.” A very common form noticed by
Mr. L. M. Underwood in Bulletin of the Torrey Botanical
Club, has fronds only four or five inches long, the lower
pinnæ only pinnatifid and the upper ones lobed, the sori
mostly solitary on the lobes.
The veins and veinlets of the frond are very distinct,
being marked by depressions in the upper surface in the living
fronds, and visible as dark lines in the dried specimens.
Ih e veins fork near the midvein; the upper branch. may be
fertile at its tip; the lower branch is either simple, or forks
a second, and perhaps a third time. All the veinlets are
curved. On account of the venation Presl referred this plant
to his section Arthrobotrys.
The sori are close to the margin of the lobes, and vary
from one to twelve to a lobe. They are very large and
prominent, and have firm lead-colored orbicular-reniform indusia,
which are slightly incurved round the edge, and depressed
at the sinus. As the fronds mature the indusia become
brownish. The spores are ovoid-reniform and have a narrow
crenulate wing.
Plate LV.—Aspidium marginale, from the vicinity of Boston.
Fig. 2 is a pinnule, enlarged; Fig. 3, a sorus; Fig. 4, a sporangium;
Fig- 5 - ^ spore; Fig. 6, a section of the stalk.
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