_Aspídium cristàtum X marginàle_
Both the crested fern and Clinton's fern appear to hybridize with the
marginal shield fern with the result that the upper part of the frond is
like _marginale_ and the lower like _cristàtum_, including the veining and
texture.
This form was discovered by Raynal Dodge, verified by Margaret Slosson and
described by Geo. E. Davenport, who had a small colony under cultivation in
his fern garden at Medford, Mass., and to him the writer and other friends
are indebted for specimens.
Found occasionally throughout New England and New Jersey. Other supposed
hybrids have been found between the marginal shield and the spinulose fern
and its variety _intermèdium_, and with Goldie's fern; also between the
crested fern, including Clinton's variety and each of the others mentioned;
and, in fact, between almost all pairs of species of the wood ferns,
although we do not think they have been positively verified. Still other
species of ferns are known to hybridize more or less, as we saw in the case
of Scott's spleenwort.
[Illustration: Crested Marginal Fern. A Hybrid. _Aspidium Cristatum X
marginale_ (Fernery of Geo. E. Davenport)]
[Illustration: _Aspidium cristatum X marginale_ One of the very best for
cultivation]
(5) BOOTT'S SHIELD FERN
_Aspidium Boottii_. THELÝPTERIS BOOTTII
_Dryopteris Boottii. Nephrodium Boottii_
Fronds one to three feet high, oblong-lanceolate, bipinnate, the upper
pinnæ lanceolate, the lower triangular with spinulose teeth. Sori in rows
each side of the midvein, one to each tooth and often scattering on the
lower pinules. Indusium large, minutely glandular, variable.
This fern has been thought to be a hybrid between the crested and spinulose
ferns, but is now regarded as distinct. Like the crested fern its fertile
fronds wither in autumn, while its sterile blades remain green throughout
the winter. It differs from it, however, by being twice pinnate below, and
from the typical spinulose fern by its glandular indusium; but from the
intermediate variety it is more difficult to separate it, as that also has
indusiate glands. The collector needs to study authentic specimens and
have in mind the type, with its rather long, narrow blade as an aid to the
verbal description, and even then he will often find it an interesting
puzzle. Shaded swamps throughout our area.
[Illustration: _Aspidium Boottii_]
(6) SPINULOSE SHIELD FERN
_Aspidium spinulòsum. THELÝPTERIS SPINULÒSA