1920] Setchell-Gardnrr: Chlorophyceae 285 



which, while comparativeh' slender (10-25/x diam.) in the vegetative 

 condition, thicken very considerably (up to 60/a or even 80/tx,) when 

 producing zoospores or gametes. The cells when younger may be 

 almost or quite quadrate, but become in the fertile condition very 

 much shorter than the diameter. 



3. Ulothrix pseudoflacca Wille 



Filaments 8-32/x diam., free from one another, attached by an 

 ehmgated, downwardly gradually tapering cell ; cells from 0.25 as 

 long as broad to nearly quadrate; cell walls thin; chromatophore 

 parietal, completely covering the outer cell wall, thickened in the 

 region of tlie single pyrenoid, fertile cells not exceeding the vegetative 

 in diameter, from flattened to nearly globular. 



On rocks and algae, upper littoral belt. Alaska (Sitka) to Cali- 

 fornia (San Francisco). 



Wille, Stud. ueb. Chloroph., 1901, p. 22, pi. 2, f. 64-81. 



Ulothrix pseudoflacca varies as follows: f. minor Wille {loc. cit., 

 p. 23, pi. 2, f. 67-69), 8-16/. diam.; f. major Wille (loc. cit., p. 23), 

 10-22/x diam.; f. maxima Setchell and Gardner {in Gardner, 1919, 

 p. 488, pi. 42, f. 6), 28-32/t, up to 40jLt diam. Plate 9, fig. 6 A, B. 



Of these f. iuinor has been collected at Sitka, Alaska, f. major and 

 f. iiKi.ri 111(1 cit Lands End, San Francisco, California (all by Gardner). 



Ulothrix pseudoflacca bears a considerable resemblance to U. flacca 

 except that in its fertile condition it does not reach so considerable 

 a diameter and the fertile cells are usually more or less rounded. The 

 chromatophore in U. pseudoflacca is a broken ring while that of 

 U. flaccu is a complete ring. 



Ulothrix pseudoflacca varies much in diameter and, as shown 

 above, may be separated more or less readily into three overlapping 

 forms, the f. minor approximating forms of U. implexa in slenderness, 

 while f. maxima approaches forms of U. flacca.. As filaments of U. 

 pseudoflacca approach the fertile condition, it is difficult to detect 

 the gap in the chromatophore. 



Jonsson (1904, pp. 55-57) has reviewed this species as well as 

 others of the genus and has made valuable suggestions. He has also 

 described a related new species [loc. cit., pp. 57-60, f. 8, 9), Ulothrix 

 scutaid, wliich has not been thus far detected ani()ii<i' tin' specimens 

 available from our territory. 



