1925] Setchell-Gardner: Melanophyceae 535 



24. Ilea Fries 



Fronds solid, or rarely M'ith occasional small cavities, membran- 

 aceous, considerably flaccid, simple, ligiilate, 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). Peialonm 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 Scytosiphan and in Colpcmienia, 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 ; 



