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FERNS OF NORTH AMERICA.
ovate in shape, and, in large fronds, pinnate with bipinnatifid
lanceolate acute pinnæ. The middle primary division is broadly
triangular, and has its lower pinnæ ample and bipinnatifid, and
the successive ones gradually smaller and less compound. The
ultimate divisions arc oblong or oblong - ovate, and commonly
incised-toothed along the sides and at the ends. Milde notices
that the basal pinnæ of the lowest primary segments are on
the upper side of the secondary rachis fanadromous), but that
towards the apex of the frond the lowest pinnæ are on the
lower side (catadromous), and that this arrangement prevails
also in the divisions of the secondary segments. Var. gracile
is nothing but a small form of the usual type. Var. cicutarimn
I have not seen ; Milde gives Hayti and New Granada as the
regions wdiere it occurs. Var. Mexicanum has often a long
stalk to the panicle, and the other differences are not any too
constant.
The sterile segment is much thinner than in B . ternatum,
and the epidermis is composed of cellules with sinuous margins.
The fronds wither at the first frost.
Plate X X X II I. Botrychium Virginianum. — Fig. i is a plant of
medium size, from Lynn, Massachusetts. The cleft at the bottom of
the stalk, with its thin and semi-transparent edges, is well represented,
and permits the enclosed bud to be distinctly seen. Fig. 2 is a cluster
of sporangia, magnified. Fig. 3 is a spore, highly magnified.
1 1