172 FRESH-WATER ALG^ OF THE UNITED STATES. 



Cffispitose aud mostly floating or diffused 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 sometimes at the same time lateral) ; zygospores globose ; spore coat smooth. 



Eemarhs. — 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 ofi". This goes on until the ends of the 

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

 soon separate. In this way f&g. 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 the 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 were 

 formed in the connecting tubes. 



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



Z. cruciatuin,(VAucH.) Ag. 



Z. pallide viride, siccatum fuscescens vel fuseo-nigrescens ; articulis sterilibua brevicylindricis 

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

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

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

 mihi ignota. 



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

 III. p. 251. 



Tyndaridea'cruciata, Hassall, Fresh- Water Algae, vol. i. p. 160. — Harvey. Bailey, 

 Microscopical Observations, p. 21. 

 Hob. — 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 (diam. 0.0016"— 0.00195"), after division 

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

 mature, obscure fuscous, their coat minutely punctate. 



Genus SIROGONIUM, Ktz. 



" Cellulae vegetativae cylindricue, sporifers subinflatK! orculiformEe. Fascia chlorophyllosffi longi- 

 tudinales, parietales, leviter flexuosas, nodosae (plerumque 2-3, rarius 4 in quaquo cellula) grannla 

 amylacea t-8 involutes. Copulatio genuflexa, sine tubo connexivo." R. In specie Americana 

 fasciae chlorophyllosae spirales et Spirogyrse illis similes. 



Vegetative cells cylindrical, spore bearing cells somewhat inflated, or orculiform Chlorophyl fila- 

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

 1-8 starch grannies; conjugation genuflexuous, without any connecting tubes. (Rabenhorst) la 

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



Remarhs.—T\i\^ genus was originally made by Kiitzing to contain a single 

 species, which possesses the characters given in the diagnosis of Prof. Rabenhorst 



