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1925 ] Setch ell-Gardner: Melanophyceae 535
24. Ilea Fries
Fronds solid, or rarety with occasional small cavities, membran-
aceous, considerably flaccid, simple, ligulate, tapering at the base to a
small, solid stipe, attached by a parenchymatous disk-shaped holdfast,
or by rhizoids, differentiated into two distinct tissues, a medulla com-
posed of more than one layer of mostly large, more or less colorless
cells and a cortex of small, cuboidal, color bearing cells ; the cortical
cells on both surfaces giving rise by numerous horizontal divisions to
gametangia with uniseriate loculi, gametes escaping by the complete
dissolution of the entire wall; zoosporangia unknown; paraphyses( ?)
and hairs present in some species.
Fries, Flor. Scan., 1835, p. 321 (pro parte) ; not Ilea Fries, Syst.
Orb. Veg., part 1 (pi. homon.), 1825, p. 336; not Ilea J. G. Agardh,
Till Alg. Syst., afd. 3, 1883, p. 114. Phyllitis Kuetzing, Phyc. Gen.,
1843, p. 342 (not Phyllitis Hill). Petalonia Derbes et Solier, Sur les
org. repr. des alg., 1850, p. 265.
As to the confusion and the different views concerning the adoption
of Ilea as the name for this genus, one may consult Nordstedt (1911,
p. 265) and M. A. Howe (1914, p. 51). Petolonm is preferable from
the point of view of possible confusion, but Ilea seems to have the
right of way. The genus tends toward complanate forms of Scyto-
siphon in certain forms which, while not completely hollow, never-
theless are not completely solid. The type species is Ilea Fascia
(Muell.) Fries, whose type specimens come from somewhere on the
coast of Norway. In the genus Ilea, a condition exists very similar to
that found in Seytosiphon and in Colpomenia, that is, of a number of
fairly striking form-types between which it is extremely difficult to
make other than very arbitrary distinctions. We are inclined to
recognize a single species, Ilea, Fascia, and refer the other described
species or forms to it.
Ilea Fascia (Muell.) Fries
Plate 44, figs. 68-71, 73
Fronds attached by a small, parenchymatous disk, often fasciculate
and several disks coalescing, thin, plane or at times more or less
crisped, linear-lanceolate to oblanceolate, often rounded and more or
less eroded above, 6-12 cm. (up to 25 cm.) high, mostly 1.5-2.5 cm.
wide, but at times up to 12 cm. wide, exceedingly variable in thickness;