166 Ulothricaceae 



In cascades on oblique surfaces of rocks dashed with spray or 

 covered by a thin sheet of water. Melrose, Mass., 28 April, 1901 

 (548). UnderclifT, New Jersey, 9 April, 16 April, 1900 (279, 

 30;), 20 May, 1901 (575). 



The conditions in these two stations are exactly similar. On 

 certain rocks, the plants form a cespitose covering presenting the 

 appearance of a short Myxoncma. By this habit and by its yel- 

 lowish green color, this species is always distinguishable to the 

 naked eye, from the long, darker green skeins of Stichococcits 

 subtilis, which frequently hang from adjacent rocks. The speci- 

 mens from both stations showed, in the most marked degree, the 

 tendency to dissociation of the filaments. Within a few hours after 

 being removed from the rapid current on the rock, a very large 

 proportion of the filaments had broken up into single cells or 

 chains of two to four. 



Our American specimens show a distinct, though not strongly 

 marked torulose character of the filaments, which is not mentioned 

 by Gay, while the geniculate character emphasized by him does 

 not appear prominent. However, as the identification of Mr. 

 Collins' specimen wa,s made by Professor Wille, we do not feel 

 justified in making a different disposition of the plant without 

 further evidence from the author of this species, and this we have 

 been unable to obtain. 



7. Stichococcus rivularis (Kiitz.) 



Hormidium rivulare Kiitz. Phyc. German. 192. 1845. 



Ulothrix rivularis Kiitz. Spec. Alg. 346. 1849 ; Tab. Phyc. 2 : 

 //. 86, f. 2. 185 1; not Alg. Dec. 4.9. 1833 (= Rhizocloniiwi). 

 Rabenh. Flor. Eur. Alg. 3: 366. 1868. Wolle, F. W. Alg. 

 136.//. 118. f. 6-8. 1887. 



Ulothrix rivularis var. cataracta Wolle, ibid. pi. 1 18. f. 29-33. 



Hormiscia rivularis DeToni, Syll. Alg. I : 167. 1889. 



Filaments forming somewhat elongated bright green tufts, fre- 

 quently geniculate, but not easily breaking apart, composed of 1-3 

 cells, developing rhizoidal hooks from the terminal cells and from 

 those of the knees ; cells somewhat constricted at the dissepiments, 

 rather thick- walled, 8-1 1 fi in diameter, 1-2 times as long ; chromat- 

 ophore orbicular to elliptical or rhomboidal, with clear-cut out- 

 line, containing a large pyrenoid (/>/. 22, f. 10-13). 



