172 FRESU-WATER ALG.^ OF THE UNITED STATES. 



Csespitose and mostly floating or difTused in the water, deep green, or a dirty yellowish-green; 

 sterile joints about as long as broad, or twice as long; conjugation scalariform (according 

 to Rabenhorst somctiujes at tiie same time lateral) ; zygospores globose ; spore coat smootli. 



JRemarks. — This species is very common around Philadelphia, forming great 

 masses in the ditches of the " Neck," growing in the semistagnant water along the 

 railroads, and forming with other algse slimy coatings on the dripping rocks of the 

 Wissahicon and various railroad cuttings. At certain times the cells are found 

 crowded with endochrome, at other times they are almost empty. At certain 

 seasons this plant multiplies with great rapidity after a somewhat peculiar fashion. 

 Constrictions first appear in the filament at the junctions of the cells, which thus 

 look as though their ends were rounding off. This goes on until the ends of the 

 cells are greatly rounded, and are attached simply by their central parts, whicli 

 soon separate. In this way I'fig. 8b, pi. xv.) the filament is resolved into its com- 

 ponent cells, or more generally into as many pairs of cells as compose it, which 

 when once set free in the water rapidly grow into filaments by tlie ordinary pro- 

 cess of cell multiplication by division. In most cases the zygospores are placed 

 in one of the parent-cells, but I have seen instances in which some of them wore 

 formed in the connecting tubes. 



Fig. 8, pi. 15, represents this species. 



Z. ci'iiciatuiii,(VAucH.) Ag. 



Z. pallide viride, siccatnm fuscescens vel fusco-nigrescens ; articnlis sterilibua brevicylindricis 

 diametro (0.0016" — 0.00195") fequalibus vel dimidio longioribus, rarius duplo longioribna, 

 post divisionem factam haud raro dimidio brevioribus, fructiferis non tumidis; zygosporis 

 plerumque globosis, maturis obscure fuscis, sporodermate subtiliter pungtatis. (R.) Species 

 mihi ignola. 



Syn. — Zygnema cruciaium, (Yaucher) Agardh. Rabenhorst, Flora Europ. Algarum, Sect. 



III. p. 251. 

 Tyndaridea cruciala, Hassall, Fresh-Water Algte, vol. i. p. ICO. — Uarvey. Bailes', 



Microscopical Observations, p. 21. 

 Eab. — Northern States ; Virginia ; Florida ; Bailey. 



Pale green, when dried subfuscous or blackish fuscous. Sterile joints shortly cylindrical, equal or 

 a little longer, or more rarely twice as long as broad (diani. O.OOIC" — 0.00195"), after division 

 sometimes shorter than broad ; fruiting cells not tumid ; zygospores mostly globose ; wbeu 

 mature, obscure fuscous, their coat minutely punctate. 



Genus SIROGONIUM, Ktz. 



" CelluloB vegetativae cylindricce, sporiferae subinflatse orculiformsB. Fasciae chlorophylloss loiigi- 

 tudmales, parietales, leviter fle.xuosfe, nodosae (plerumque 2-3, rarius 4 in quaquo cellula), graiiula 

 amylacoa 7-8 involutiB. Copulatio genuflexa, sine tubo conue.Yivo." R. In specie Americana 

 fasciae chlorophyllosoe spirales et Spirogyraj illis similes. 



Tegetative cells cylindrical, spore bearing cells somewhat inflated, or orcnliform. Chlorophyl fila- 

 ment longitudinal, parietal, somewhat flexuous, nodose (mostly 2-3 rarely 4 in each cell), coutaining 

 7-8 starch granules; conjugation genuflexuous, without any connecting tubes. (Rabenhorst). In 

 American species the chlorophyl filament spiral and like to that of Spirogyra. 



ItemarJ:«. —This genus Avas originally made by Kiitzing to contain a single 

 species, wliich possesses the characters "iven in the diao-nosis of Prof Pvibcnhorst 



