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



SPHAEROZYGA SACCATA, Wolle. 



Thalli forming elongated, vertical, submembranaceous 

 tubes, closed at the apex, 2-4 inches long and about one- 

 fourth inch thick, in clusters of 10-15 more or less, attached 

 to pond weeds (Potamogeton ? etc.,) in shallow water at mar- 

 gins of pond, or to the bottom where the water is not more 

 than a few inches deep. Each tube contains numerous fila- 

 ments, erect, parallel or slightly curved, composed of ob- 

 long or cylindrical aeruginous cells, closely connected ; het- 

 erocysts oval or subglobose yellow ; spores numerous, 

 cylindrical, dull aeruginous, nearly twice as long as wide. 



Diameter of filaments, 4-5 u. 



Diameter of spores, 7 /w. 



Diameter of heterocysts, 6 yw. 



Frequent in Cranberry Pond, New Jersey. 

 Specimens, No. 397, Wittrock and Nordstedt's Algw Ex- 

 siccatce. 



Plate CXOIX, fig. 1, a normal cluster of saccate forms ; 

 fig. 2, detached tubes floating ; figs. 3-5, various specimens 

 of filaments as contained in the tubes. 



SPHAEROZYGA SMITHII, (Thwaites) Wolle. 



Trichomes straight, included in a definite gelatinous 

 sheath, usually single but sometimes two or three in a 

 sheath ; joints subspherical, about as long as wide or a little 

 longer. Heterocysts subspherical or oval. Spores cylin- 

 drical, unequal in length, usually about twice as long as 

 wide, with the ends rounded. 



Diameter of cells, 4-6 ^ heterocysts, 8-9 // ; spores, 9-12 yu. 



Syn. Dolychospermum Smithii, Thwaites ; Anabcena timithii, Thur. 



This plant might also be placed to the genus Hilsia, 

 Kirch., having often two or three filaments in a sheath, but 

 in general character it is too much like a Sphaerozyga to be 

 separated. It is not strictly in accord with S. Smith ii of 

 Thwaites, but the deviation is more pardonable in a plant 

 of this genus than it would be to make a new species of it. 

 Other changes in the character of the cells are worthy of 

 note. The cells instead of remaining as in the young state 

 rather longer than broad, become about three times as broad 

 as long, evidencing a tendency to change and develop an 

 Oscillaria or a Lyngbya-form. 



Plate CXCIX, figs. 17-19, typical filaments ; figs. 20-22, 

 filaments two or three in a sheath ; fig. 23, cells dividing 

 and increasing in width ; fig. 24, two filaments more ad- 

 vanced toward the character of Oscillaria. 



