1920] Setchell-Gardner : Chlorophyceae 261 



Linnaeus, Gen. Plant., 1737, p. 326, Sp. Plant., vol. 2, 1753, p. 1163 

 (in part). 



The name Ulva goes back into classical Latin and was used to 

 designate some marsh plant. It was adopted by some of the botanists 

 to designate the expanded or gelatinous algae of any color. Linnaeus 

 used it, at first, for a combination of species now referred to Ulva, 

 Monostroma{?), Enteromorpha, Porphyra, Botrydiuni and Nosioc, 

 later extending it to other expanded or non-Fucus species of all four 

 groups of algae. If we are to follow some weighty authorities, we 

 may be compelled to believe that Linnaeus included in his original 

 list no one of the species generally referred to TJlvd. If Viva Lactuca 

 L. is reallj^ a Monostroma; if Ulva laUssima L. (at least of the Species 

 Plantarum) was founded on a portion of the blade of Lammaria 

 saccharina; and if we refer Ulva Lima to the genus Enteromorpha, 

 then there is no species of Ulva, in the sense in which it is now used, 

 left in the original list of Linnaeus. 



As genera came to be more strictly delimited, Ulva came more 

 and more to be reserved for membranous or tubular forms and ulti- 

 mately for those belonging to the Chlorophyceae. Finally, in 1854, 

 Thuret gave it its final description and content by the separation 

 of the species of Monostroma. J. G. Agardh (1883, p. 160), although 

 differing from Thuret as to some details, followed Thuret 's segrega- 

 tions, and since that time the general concept has been the same for 

 all writers. The genus Ulva, therefore, may be defined as including 

 those species of the Chlorophyceae which have a parietal chromato- 

 phore and with the cells arranged, in large part at least, in a two- 

 layered membrane. We have arranged our plants under Ulva in 

 accordance with this idea, including even those like Ulva Lima which, 

 in habit, seem to belong to Ulva and the greater portion of whose 

 fronds remain as two layers closely applied to one another. 



The species of Ulva are generally regarded as being not readily 

 separable from one another, and the universal tendency has been to 

 divide the genus into a few widely distributed and variable species. 

 There is, however, great need of careful and extensive monographic 

 work on this genus. In our attempt to distinguish the species and 

 forms of our own coast, we have come to the conclusion that the plants 

 fall into certain groups, fairly readily to be distinguished from one 

 another. We have been able, also, to refer these narrower groups of 

 forms to described species with plausible certainty. We trust that we 

 may be able to stimulate, at least, careful scrutiny of these species and 



