242 FRESH-WATER ATuGJE OF THE UNITED STATES. 



and length ; first flagelliform, then linear and much elon- 

 gated. All indicating that these so-called Mastigonema 

 forms are not fully developed plants. 



Plate CLXXVI, fig. 8, young conditions gradually devel- 

 oping into larger forms ; figs. 6, 7, in mass producing a dark 

 olive coating on old planks subject to inundation from 

 marine waters. These forms I named some years since, 

 Mastigonema velutina, but have now reason to believe they 

 are the young condition of Lyngbya aestuarii. Compare 

 L. aestuarii; figs. 9-11, a variety of sizes, similar to figs. 2-4, 

 having the peculiarity of interstitial heterocysts not here- 

 tofore noticed. 



Plate CLXXIII, figs. 4, 5. A variety frequently occur 

 ring, from Florida ; juvenile and maturer forms, correspond- 

 ing with Plate CLXXI, fig. 7, also from Florida ; figs. 5, 6, 

 of latter plate, represent filaments from a large floating 

 mass, heterocysts torn off; probably the same, but older con- 

 dition of fig. 7. Filaments instead of being bright aerugi- 

 nous many are partially changed to yellow or light brown, 

 and others brownish red. Fig. 1-4, appear distinct in a 

 process of fruiting ; the basal articulations develop niacro- 

 gonidia which pass out through a rupture at the end. These 

 trichomes also have interstitial heterocysts. The clinging 

 of the young to two of the older trichomes indicates a 

 relation to Calothrijc. The formation of the rnacrogonidia in 

 the basal cell is worthy of a note. Prof. A. Borzi remarks 

 in his Morfologia e Biologia, etc., p. 297, that nearly all, or 

 quite all of the Rivulariacece multiply not only by ormogons, 

 but also by the spores which originate in the basal portion 

 of the trichomes. These are true spores capable of hiber- 

 nation. 



Plate CLXXVII, figs. 1, 2, somewhat distinct in hetero- 

 cysts and the fibrillose sheath ; from wet moss and rocks, 

 Niagara ; figs. 3, 4, more usual forms of variable sizes ; fig. 

 11, more elongated form ; fig. 12, very turgid specimens ; 

 fig. 13, heterocysts wider than the filaments. 



Plate CLXXVI, fig. 1, a parasitic form on Lyngbya WoUei, 

 and probably a young development of it. 



MASTIGONEMA HALOS, Wood. 



In little tufts ; filaments simple, in mature state greatly 

 elongated, and with the sheath truncate and open ; in the 

 young condition shorter and often ending in a rather short 



