186 FRESH-WATER ALG^E OF THE UNITED STATES. 



The species is exceedingly common in the later summer and early fall months 

 in the ditches and sluggish streams around the city, especially in the Neck. 



FAMILY CONFERVACE^E. 



Fila articulata aut simplicia ant ramosa, vegetatione terminal! non limitata instructa. Articuli 

 plerumque plus rainasve elongati, sed nonnunquam diamctro breviores, cylindrici, ran us tumidi. 

 Cytioderma plerumque manifesto lamellosum. Massa chloropliyllosa granulata, vesiculas amylaceas 

 involvens, parietalis vel in setate provecta ssepe in cellules centre contracta. 



Vegetatio fit utriculi priinordialis divisione semper in unam eandemque (transversam) directionem 

 repetitia. Propagatio fit zoogonidiis. 



Filaments articulate, simple or branched, growth terminal, unlimited. Joints mostly more or less 

 elongated, but sometimes shorter than long, cylindrical rarely tumid. Cytioderm mostly plainly 

 lamellate, chlorophyl masses granular, surrounding fine starch granules, parietal or often in the centre 

 of the cell. 



Growth taking place by division of the primordial utricle always in one direction, namely trans- 

 versely. Propagation by means of zoospores. 



Genus CONFERVA, (LiNN.) LINK. 



" Fila articulata simplicia. Articuli cylindrici. Massa chlorophyllosa homogenea vel granu- 

 lata, vesiculas amylaceas involvens. Propogatio ignota." (R.) 



Threads articulate simple. Articles cylindrical. Chlorophyl mass homogeneous or granulate, 

 including amylaceous vesicles. 



Remarks. A large number of forms of the genus Conferva have been described 

 as distinct species by Kiit/ing and other authors. The characters assigned to 

 these species, however, do not seem to me in any way distinctive. I cannot believe 

 it possible at present to recognize, define, and describe species in this genus, and 

 believe that further studies must be made in their life-history, and other characters 

 discovered before the different forms can be separated. Probably, as was the case 

 with the CEdogoniacece, when their sexual life is made out, in it will be found the 

 vital differences. No doubt there are many species common to Europe and Ame- 

 rica, but I have been entirely unable to determine them. Among the very earliest 

 of my observations upon the fresh-water alga3, before experience had taught how 

 and what to observe, was one made upon what I suppose was a species of this 

 genus. I have never met with the plant since, but as the observation has direct 

 bearing upon the method of propagation, I mention it here, imperfect as it un- 

 fortunately is. The plant was found growing on the mud along the Schuylkill 

 River, near Gray's Ferry Bridge, below the city. The filaments were simple, of 

 great length, and uniform in diameter ; fig. 7 a, pi. 18, represents a portion of 

 one magnified 500 diameters. The cells varied from about as long as broad to 

 three times as long. The amount of endochrome in the cells also varied very much. 

 In most of them, it was not nearly sufficient to fill the cavity, and was arranged as 

 a central superficial band. Many of the cells were seen engaged in the production 

 of zoospores. (Fig. 7 &, pi. 18.) Such were well filled with endochrome, which 

 gradually condensed itself into a globular or pyriform mass in the centre of the 

 cell. This, after a short time, began to exhibit activity, rolling upon itself and 

 finally pushing about as much as its confined quarters would allow, until at last it 



