206 FRESII-WATER ALG^ OF TUE UNITED STATES. 



Aquatic, paludal, or rarely terrestrial algte, mostly raonaeeious or diajcious. Filaments various 

 often dichotomously, but not rarely fasciculately branched, mostly aggregated into turl'y masses or 

 little cushions, and generally surrounded by a firm or subliquid gelatinous mucus. Propagation hoih 

 by zoos|)ores and resting .spores. Zoospores arising either singly or by the division of the cytiopla^u 

 into 8-16 in each sporangium. 



Genus STIGEOCLONIUM. 



Fila arliculata, siniplicifcr raniosa; rami ranniliquc sparsi, rarius faseiculatini approximati, in 

 apiccni acutum, .siBiio piliferum achroum attcuuati et picruuique longe prutcusi, sspius ramollis 

 brevibus subulatis instructi. (R.) 



Filaments articulate, simply branched ; branches and branchlets sparse, rarely fasciculately ap- 

 proximated, with their ends acute and frequently prolonged into an attenuate transparent seta or 

 hair, and very often furnished with short subulate branches. 



Eevmrl-s. — Plants which are certainly referable to this genus are abuiulant in 

 every place in which I have ever looked for fresh-water algae. I confess, how- 

 ever, that although very much time has been given to their study, I have not been 

 able to make out any distinct specific characters, nor any identifications from tlie 

 diagnoses of M. Rabenhorst. In a certain spring northeast of the city, there grows 

 one of these forms, which I have closely watched for several seasons. In tlie 

 earlier state it appears at times to possess the characters of a young Cliaiophora 

 (pi. 19, fig. 1), forming a small gelatinous base out of which the threads soon 

 escape as they lengthen. It constituted a sort of mucoid layer adhering to the 

 boards lining the stones witli waving masses of projecting filaments six or even 

 eight inches in length. The filaments were mostly about -^-^-^i^" in diameter and 

 much interlaced. 



The cells varied greatly in length, some being scarcely as long as broad, whilst 

 others were eight or ten times longer. The short cells were generally densely 

 filled with endochrome, whilst the long ones were nearly empty. The branches 

 often ended abruptly, but were more frequently tipped with a long seta-like 

 point. The method of branching is as varied as can be imagined, as is shown 

 by fig. 4, pi. 16, and fig. 1, pi. 20, all taken from diff'ercnt plants of this species. 

 I have frequently seen the production of zoospores, but no other method of repro- 

 duction. In all cases a single motile body (fig. 4, pi. 16) was formed in each 

 cell. These minute bodies are globular or pyriform, and within the cell exhibit 

 no motion whatever. Their escape takes place very slowly through a lateral slit 

 in the wall. No cause of the motion is visible, and during the passage the 

 zoospore is often very much squeezed out of shape. According to Braun (Vcr- 

 jungung), these zoospores possess a red eye-spot. I had not read his description 

 at the time my observations were made, but did not notice any. The zoospores 

 germinated in the usual way, elongating and growing into a cell with a transparent 

 seta-like end, and finally undergoing repeated divisions to form the plant. 



M. Braun states that he has observed another process, in which the contents of 

 a single cell undergoes a perpendicular division, so as to form four small zoospores, 

 wliich escape from the cell in the same way as the larger one, and fiu'tlier says 

 that he has never known these microgonidia to germinate. 



