1920] Setchcll-Gardncr: Chlorophyceae 2W 



We have followed the conception of J. G. Agardh (1883, pp. 164- 

 166) as to the proper nature of the Linnaean species and have referred 

 here those ample floating forms, with thin membranes, and cells which 

 are cubical or horizontally elongated in section. AVe find very few 

 such plants on our coast, their place as ample, expanded, floating 

 membranes being taken by U. expansa. One specimen, however, col- 

 lected near Douglas, Alaska, bv Mi'. Eldred Jenne seems clearly to 

 belong here, and otlicr specimens may be expected in quiet waters. 

 The specimen from Douglas, Ala.ska, agrees fairly well with no. 

 LXXVI of the Pliyeotlu'ca Boreali-Americana, but is somewhat 

 thinner. 



6. Ulva fenestrata P. and K. 



Frond ample, usually soon free and expanded, yellowish green, 

 completely, and more or less uniformly, perforated with larger and 

 smaller round or elongated openings with undulate edges, margins 

 often wavy ; membrane up to 60/a thick ; cells in section nearly square 

 or slightly vertically elongated (about 20/a high by 16/x broad in 

 thicker sections) ; chromatophore cucullate at outer end of cell. 



Growing on rocks in the lower littoral and upper sublittoral belts. 

 Alaska (Sitka) to Puget Sound, Washington. 



Postels and Ruprecht, 111. Alg., 1840, p. 21, pi. 37. 



The question as to the origin of the perforations found apparently 

 regularly in some species of Ulva and occurring more or less sporad- 

 ically in many or all species, has not, as yet, been at all carefully 

 investigated. Greville (1830, p. 172) speaks of the frond of Viva 

 lati^sima as being "frequently much perforated by marine animals." 

 On the other hand, J. G. Agardh (1882, p. 171) in speaking of U. 

 rigida and its forms, states that the holes found in this species, as 

 well as in U. reticulata Forsk., are not the work of animals, but due 

 to inequalities of growth. We find holes fre(iuently in considerable 

 numbers in various of the Ulvae, as well as of the Porphyrae, of our 

 coast and we feel certain that in manj- cases, at least, they are the 

 work of mollusks, but we also find specimens of a large species of 

 Ulva, which seems likely to be U. fenestrata, in which the holes are so 

 numerous and so regular, and so constantly found that we are inclined 

 to believe them to be the results of groMh of the uninjured frond. 

 We have, conse^iuently, referred them here, although with much doubt, 

 since other than as to perforations, they agree well with specimens 

 of Ulva expansa. Some of the specimens in our possession are as long 

 as 4 meters and up to 13 decimeters wide. As to details of perforation, 

 our specimens agree with those figured b}'' Postels and Ruprecht. 



