A . spinulosum genuinum, indicating the fact that the basal
pinnules are shorter than the next. Dr. Gray also examined
the Willdenovian specimens of intermedium, and his notes
show that he recognized in them what we now call var.
intermedium. Willdenow’s words “ pinnulis pinnatifido-incisis”
also point towards var. intevmedmm ; since of A . spinulostim
he says: “ pinnulis iiiciso-dentatis.” It is therefore right to
keep for this form the time-honored name of intermedium;
and to consider it a variety of A . spinulosum, because neither
in the form and details of the frond, the position of the sori,
nor the glandulosity of the surface and indusia can any specific
distinction be fairly discovered.
Var. dilatatum has dark-green deltoid-ovate or broadly
ovate fronds often considerably larger than in the other
forms: Milde gives three feet as the extreme length, but
such fronds are rarely preserved for herbarium specimens.
The pinnæ diverge from the rachis at from sixty to eighty
degrees. The lowest ones are frequently but not invariably
longest, but always broadest: in one example from Mount
Mansfield they are eight or nine inches long, and five
inches wide at the base. They are broadly triangular,
nearly twice pinnate, the secondary rachis wingless and the
tertiary very narrowly winged, and the inferior basal pinnules
are over three inches long. The inferior basal pinnules
are longer than the next ones in this- form, but the superior
basal pinnules are shorter than the next. The pinnules
generally are so deeply pinnatifid as to render the frond
almost tripinnate, and the frond has a generous breadth which
distinguishes the variety from those already described. The
sori are either apical, sub-terminal or medial, seated on the
lowest anterior veins or on short veinlets derived from them,
the position varying according to the size of the pinnules.
In American specimens the indusium is smooth, so far as I
have observed, and the spores are irregularly winged or
cristate. In the plant of Europe the indusium is said to be
usually glandular. In writing the Synopsis Filicum, Swartz
at first united this form with A . spimdosum, but in the
addenda he separated the two, in which he was followed
for a long time by most writers. I do not know that the
first edition of the British Flora (1830) is the earliest publication
in which A . dilatatum is made a variety of A .
spimdosum, but it is the earliest that I can find.
Var. dumetorum {Aspidium dtimetorum. Smith) is a form
of var. dilatahtm having dwarfish deltoid-ovate compactly
bipinnate fronds and large pinnules, the inferior basal ones
of the lowest pinnæ not much elongated. It is found in
mountainous parts of Europe ; but I have seen nothing
exactly corresponding to it in America. It seems to be
only var. dilatatum dwarfed and compacted by exposure to
the sun, and will probably be found ere long in northern
New England or Canada. Other European sub-varieties are
mentioned by Moore and Milde, and the student is referred
to their writings for descriptions or figures of them.
Var. Boottii, Gray, has been variously referred to A .
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