Ulothrix 149 



cient to convince one of their relation, as young forms, to this 

 largest species of the genus. 



In May the rocky borders of the lake in Central Park become 

 fringed with a growth which rapidly develops into the typical 

 U. sonata. We have never found this growth early in the season, 

 and it disappears soon after the first hot days at the end of May 

 or in June. 



A number of species and varieties of European authors have 

 not been satisfactorily distinguished as more than growth forms of 

 U. sonata. Such are U. pectinalis Kiitz., U. inaequlis Kiitz., 

 U. sonata attenuata (Kiitz.) Rabenh., U. sonata varians (Kiitz.) 

 Rabenh., U. sonata valida (Nag.) Rabenh., and U. sonata rigidula 

 (Kiitz.) Hansg. 



2. Ulothrix tenuissima Kiitz. Flora, 16 : 518. 1833; Phyc. 

 Gen. 252. 1843* 



Ulothrix tenuis Kiitz. Phyc. Germ. 197. 1845 5 Spec. Alg. 



347. 1849 (Not U. tennis, ibid., 346) ; Tab. Phyc. 2 : pi. 89. 



f. 1. 1852. Rabenh. Flor. Eur. Alg. 3: 366. 1868. Cooke, 



Brit. F. W. Alg. 182. pi. 70. f. 6. 1883. Wolle, F. W. Alg. 



134. //. 118. f. 1. 2. 1887. 



Myxonema tenirissimnm Rabenh. Deutsch. Krypt. Flor. 2 2 : 

 99. 1847. 



Hormiscia tenuis De Toni, Syll. Alg. I : 165. 1889. Hansg. 

 Prod. Alg. Bohm. 2: 213. 1892. 



Dark green ; vegetative cells always thin-walled, 1 5-20 fi 

 (rarely 25 //) in diameter in mature filaments, generally about half 

 as long or shorter, sometimes in younger filaments as long as the 

 diameter, cylindrical, not at all constricted at the septations ; chro- 

 matophore broad ; zoosporiferous filaments somewhat moniliform 

 (//. 20./. J, 6). 



In running water in brooks and watering troughs. 



New York : Central Park, April (265, 535), May (380). 



New Jersey : Fairview, April (297). 



Numerous specimens that were at first referred to this species, 

 have been proved, after subsequent collection in the same stations, 



* Kiitzing abandoned this name first given to the species without any expressed 

 reason, but probably because he felt that it was not properly descriptive of the plant 

 after he added to the genus several species that were smaller in respect to diameter. 



