152 Ulothricaceae 



of U. zonata. When kept in stagnant water the chromatophore 

 becomes reduced to a small plate, and the filament looks very 

 much like that of U. variabilis. From the latter, however, it 

 seems always to be distinguishable by its greater diameter. It 

 might seem at first sight that this is only a large form of U. vari- 

 abilis, but from careful observation of the living plants the points 

 of distinction are convincing though not easily described. 



The plant did not make its appearance in the two stations 

 where we have observed it earlier than August, and probably not 

 until during September. The chromatophores seemed to be some- 

 what injured by the first frosts ; whether the plant would have 

 been killed before winter could not be determined, because of the 

 fact that the water was drained from both basins at the approach 

 of cold weather. 



6. Ulothrix variabilis (Kiitz.) Kiitz. Spec. Alg. 346. 1849; 



Tab. Phyc. 2 : pi. 85. f. 3. 1852. Rabenh. Krypt. Flor. Sachs. 



I : 263. 1863 ; Flor. Eur. Alg. 3 : 365. 1868. Cooke, Brit. 



F. W. Alg. 182.//. jo.f. 4. 1883. (?) Wittrock; Nordensk. 



Stud, och Forskning. pi. j.f. 27, 28. 1883. (?) 



Hormidhun variabile Kiitz. Phyc. Germ. 192. 1845. 



Ulothrix subtilis variabilis Kirchner, Krypt. Flor. Schles. 

 2 1 : 77. 1878. Wolle, F. W. Alg. 136. pi. nS.f. 15, 16.18S7. (?) 



Hormiscia subtilis variabilis DeToni, Syll. Alg. 1 : 160. 1889. 



Filaments forming floccose masses : cells 5-6 /1 in diameter, 

 y 2 — I y 2 times as long, often square in optical section ; cell-wall 

 very thin and delicate ; chromatophore rarely covering more than 

 half the cell-wall, sometimes taking the form of a rectangular 

 plate, sometimes that of an angular mass contracted into one 

 corner of the cell ; the pyrenoid small but distinct (J>1. 21, f. 5-7). 



In brooks and in stagnant waters. 



Massachusetts: Ipswich, May (557). 



New York : East Chester, May (590). 



New Jersey : Undercliff, Bergen county, April (278), May 

 (369, 427^, 574). 



It is a matter of great difficulty, if not impossible, to obtain from 

 the exsiccatae any valuable evidence as to the essential character 

 of such species as Ulothrix tenerrima, U. variabilis, and U. subtilis ; 

 the last two we have been unable to restore from dried specimens 



