SPIROGYRA. 215 



SPIROGYRA FUSCO-ATRA, Rab. 



Diameter of filaments, 40-55 yw ; cells 2-4 times longer than 

 broad, one spiral, making 2-3 turns in cell. Zygospore 

 polymorphous, globose, elliptic or oval, one to two times 

 longer than the diameter ; color changes to lighter or darker 

 chestnut. 



Found this form most abundant in good fruiting condition 

 in sluggish and stagnant waters of Paxtoii Creek, near 

 Harrisburg, Pa. 



Occasionally a filament with two spirals was intermingled. 



Plate CXL, figs. 4 and 7, two sterile filaments, one of them 

 with two spirals ; figs. 5, 6, two fertile filaments. 



SPIROGYRA CONDENSATA, (Yauch.) Kg. 



Diameter of vegetative filaments, 48-54 // (var. 62-75 /u); 

 cells 1-1* times longer than the diameter, spiral slender, 

 making one to four (ante-division) turns in cell. Fruc- 

 tiferous cells not, or but slightly swollen, not shorter than 

 the vegetative cells. Zygospores broadly elliptic, about 

 one-half longer than the diameter. 



Var. RUSBYI, Wolle. 



Not essentially different from the type-form or from the 

 variety Fleclisigii described by Rabenhorst, except in size, 

 being as much larger than Rabenhorst' s variety, as the same 

 is larger than the type, measuring 62-75 yw in diameter. 



Collected by H. H. Rusby in New Mexico, January, 1881. 

 A sterile form, probably this species, occurs in New Jersey ; 

 frequent in vicinity of Hammonton, but found no fruit. 



Syn. Conjugata condensata, Vauch. ; Zygnema condensata, Ag. 



Plate CXXXIX, figs. 7, 8, 9, two sterile filaments, and 

 two in conjugation of var. EUSBYI. 



b. Membrane of the spores punctate. 



SPIROGYRA PUNCTATA, Cleve. 



Diameter of vegetative filaments, 24-27 yw; cells 6-12 

 times longer than the diameter ; spiral single, rather slender, 

 containing some starch grains; describing 3 -7 turns in a 

 cell ; fructiferous cells much inflated and much shorter than 

 the vegetative cells. Zygospore elliptic, yellow at maturity, 

 about one-half longer than the diameter; the membrane 

 punctate. 



The mode of conjugation of this species is somewhat pecu- 

 liar; the connecting tube arises from one cell only and 



