1920] Setchell-Gardner : Chlorophyc&ae 283 



also are less numerous in each ehromatopliore in Ulothrix, the majority 

 of species containing only one. 



The species of Ulothrix still need careful study especially in cul- 

 tures. These cultures, however, are not easy to carry on. The fila- 

 ments vary considerably in diameter in different stages of growth, 

 often increasing very considerably in diameter as they pass over into 

 reproductive condition. The chromatophores of the different species 

 seem distinctly different in the earlier vegetative conditions but lose 

 their character as the cells pass on towards reproductive stages. Wille 

 (1901 and 1906) has made the more recent and more considerable 

 studies of the marine species and has brought out many new points 

 of view, showing how necessary it is to have plants for study in prac- 

 tically all stages of development. Dried plants are often very unsatis- 

 factory^ in that chromatophore structure is generally difficult of exact 

 determination. Specimens preserved in liquid are much more favor- 

 able for investigation. 



Key to the Species 



1. Filaments always free, no branches 2 



1. Filaments often grown together, occasional branches 4. U. laetevirens (p. 286) 



2. Cells (especially fertile) much shorter than broad 3 



2. Cells (including fertile) usually as long as, or longer than broad 



1. U. implexa (p. 283) 



3. Chromatophore a complete ring, fertile filaments broad (up to 60m or even 80m 



diam.) 2. U. flacca (p. 284) 



3. Chromatophore an incomplete ring, fertile filaments much narrower (not over 

 38-40m diam.) 3. U. pseudofiacca (p. 285) 



1. Ulothrix implexa Kuetz. 



Plants light green, forming soft masses, cells 6-15/a diam., some- 

 times slightly swollen at the middle, nearly quadrate, chromatophore, 

 when young, occupying only the middle part of the cell, often an 

 incomplete ring ; fertile cells nearly quadrate, not swollen or increased 

 in width. 



Growing on rocks near the mouths of streams, and on wood in 

 quiet water, in the littoral belt. Alaska (St. Michael) to California 

 (San Francisco). 



Kuetzing, Sp. Alg., 1849, p. 349 ; Collins, Green Alg. N. A., 1909, 

 p. 185 ; Setchell and Gardner, Alg. N.W. Amer., 1903, p. 217. Ulothrix 

 suhflaccida Wille, Stud. ueb. Chloroph., I-VII, 1901, p. 27, pi. 3, 

 f. 90-100 ( ?) ; Collins, Green Alg. N. A., 1909, p. 186 ; Collins, Holden 

 and Setchell, Phyc. Bor.-Amer. (Exsicc), no. 1275. 





