212 FRESH-WATER ALG^ OF THE UNITED STATES. 



Threads distinctly articulate, prostrate, creeping, sometimes more or less concreted into an irregular 

 stratum ; branches creeping or ascending ; chlorophyllous cells with the dorsum or apex setigerous. 

 Propagation by zoospores. 



iJemarfe.— Sexual reproduction has not as yet been discovered in this genus. 

 According to Dr. Braun (Verjiing., Translation of the Eay Society, p. 184, &c.) 

 two zoospores are generally formed in a cell by a division of its contents parallel 

 to the septa, but occasionally this division not taking place, the cell contents are 

 resolved into a single zoospore. The zoospores themselves are nearly globular, 

 biciliate, and unprovided with any reddish eye-spot. 



A. repens, Braun. 



A. filis procumbentibns plernmque simplicibus ; artieulis cylindricis aut tnmidis, diametro sub- 

 sequalibns ad 1-2 plo longioribus ; setis e cellularum dorso egressis, plerumque singulis sed in- 

 terdum geminis, interdum nullis. 



Diom.— Artie. t-5§^/—t-^§^/ = .00025— .0004". 



Syn. — A. repens, Bratjn. Rabenhokst, Flora. Enrop Algarum, Sect. Ill p. 391. 



Eab. — In CEdogoniis, prope Philadelphia ; Wood. 



Filaments procumbent, mostly simple; articles cylindrical or tumid, from as long as broad to 

 twice as long ; seta arising from the back of the cells, generally single, sometimes geminate, 

 sometimes wanting. 



Bemarhs. — The specimens from which the above description was drawn up, were 

 found growing on the filaments of CEdogonium mirabile, Wood. They were re- 

 markable for the rarity with which they were branched, for in but two or three 

 cases out of a great number, were any branches detected. The articles were fre- 

 quently twice as long as broad. In -both these particulars the plant differs from 

 the typical European A. repens, but the descriptions of that form are so short and 

 imperfect that I have preferred retaining the name for the American plant. 



Fig. 5, pi. 14, represents an ordinardy formed specimen magnified 460 diameters. 

 It had been kept for some time in weak carbolic-acid solution, and although the 

 green of the chlorophyll was perfectly preserved, the stumps only of the setae 

 were visible. How long the perfect setse are I canndt at present say, not having 

 made any notes on the fresh specimens. 



Genus COLEOCH^TE, Breb. (1844). 



Fila articulata ramosa aut in pulvinulum conjuncta aut in thallnra planum subdisciformem 

 parenchymaticum concreta ; articnli oblongi, antiee plus minus dilatati, angulo superiori Tel dorso 

 ssepe in setam basi vaginatam producti. Propagatio fit turn oosporis foecundatione sexuali ortis, 

 turn zoogonidiis. Zoogonidia in quaque cellula fructifera unica, forma subglobosa vel late ovalia, 

 polo antico ciliis vibratoriis binis instructa. (R.) 



Filaments articulated, branched, either conjoined into a little cumulated mass or parenchematously 

 concreted into a plain subdisci&rm thallus ; articles oblong anteriorly, more or less dilated, often 

 furnished with a long seta on their dorsum or superior angle. Propagation occurring by means of 

 oospores, formed by sexual organs or by zoospores. Zoospores subglobosfc or broadly oval, formed 

 singly in the fertile cell, furnished at their anterior pole with vibratile cilia. 



Bemarhs.— I have seen a large number of specimens of, as I believe, two distinct 

 species of this genus, but never having found any fruiting fronds, have not been 



