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



uniting to form the spore. This at first sight appears to be a good ground for sepa- 

 ration, but there are certain species in which, undoubtedly, both the former and 

 the latter method of conjugation take place indifferently. Such species make a 

 third group so precisely between the two others as, to my mind, to fuse them toge- 

 ther and necessitate either the acknowledgment of three genera or the denial of 

 more than one. The latter seems to me the more philosophical course. 



A. CONJUGATIO LATERAUS (RlIYNCHONEMA). 

 A. CONJUGATION LATERAL. 



Sp. elongata, WOOD. 



Sp. articulis vegetativis diametro 7-20 plo longioribus; articulis sporiferis multo brevioribus, 

 valde tumidis ; cytiodermate utroque fine protenso et replicato ; fascia uuica, laxissime spiral!; 

 anfractibus plerumque 7 ; sporis ellipticis, diametro 1-2^ plo longioribus. 



Diam. Spor. y/^" = .00106". Artie, vegetat. 7 ^" =.0005". 



Syn. BhynchonemaelongatumJffoo'D, Prodromus, Proc. Amer. Philos. Soc. 1809, p. 137. 



Hob. In aquis limpidis, prope Philadelphia. 



Sterile joints 7-20 times longer than broad; fertile joints much shorter, greatly swollen ; cell 

 wall at each end produced or folded in ; chlorophyl filament 1, spiral lax ; turns mostly 7 ; 

 spores elliptical, 2-2^ times longer than broad. 



Remarks. I found this species about the middle of March, fruiting in a little 

 pool near Chelten Hills, six or eight miles north of this city. It did not form a 

 distinct stratum by itself, but was floating, intermingled with great numbers of 

 other filamentous alga3, such as fragillaricB, zygnemce, &c. It seems to be most 

 closely allied to the European R. minimum ; it however not only attains a some- 

 what larger size but also differs from that plant in the proportionate length of the 

 sterile cells, in the number of the turns of the chlorophyl spiral in the cell, and in 

 the proportionate length and breadth of the spore. 



Fig. 1, pi. 14, represents portions of sterile filaments magnified 450 diameters; 

 1 a, a part of a fertile filament, magnified 450 diameters. 



Sp. pulchella, WOOD. 



Sp. articulis sterilibus diametro 2-3 plo longioribus; sporiferis nonnihil tumidis; fascia unica, 



anfractibus 3-4 ; sporis ellipticis, diametro fere duplo longioribus ; cytiodermate utroque fine 



protenso et replicato. 



Diam. Artie. Steril.^V 7!^"=. 00033" .0013". Spor. 7S V_ 7 ig/=.0012" .00133". 

 Syn. Bhynconemapulchellum,Woon,Prodrowu8, Proc. Amcr. Philos. Soc. 1869, p. 138. 

 Hob. In stagnis, prope Philadelphia. 

 Sterile' joints 2-3 times longer than broad ; fertile joints somewhat swollen ; chlorophyl band 



one ; turns of spiral 3-4 ; spores elliptical, almost twice as long as broad ; cell wall at each 



end produced or folded in. 



Remarks. This species was found by myself fruiting in April, 1869, in stagnant 

 ditches below the city, and in similar localities near Camden, New Jersey. It did 

 not occur in masses but singly, intermixed with great numbers of other fruiting 

 spirogyras. Most of the filaments seen were about .0010" in diameter; in but a 

 single instance did they come much short of this. This species differs from R. 

 elongatwm, among other points, in the shortness of the tubes connecting the fertile 



