100 OSCILLATORIACEiE. 



straight ; at first they are simple, but now and then they emit lateral branches, which 

 issue at considerable angles, and generally in pairs. When a filament is about to 

 branch, a rupture takes place in the side of the sheath, and the endochrome issues in two 

 portions, one connected with the upper, the other with the lower half of the filament ; 

 these form the nuclei or medullary portion of two new branches, and become duly 

 invested with a membranous sheath, and gradually put on the aspect of the adult 

 filament. The endochrome is granular, dark-brown, and annulated at short intervals, the 

 transverse rings being placed very close together in the youngest portions, and less 

 closely in the older, where they are distant from each other about twice the diameter of 

 the column. This annulated endochrome is interrupted at certain fixed places, where an 

 ellipsoidal cell is formed, separating the endochrome of the lower from that of the upper 

 portions. These cells may be compared to nodes, and indicate, if I mistake not, the 

 points where the twin branches issue. I have not, however, noticed their development 

 into branches. 



Plate XL VIII. A. Fig 1. Portion of the stratum formed by Petalonema alatum ; 

 andj^^. 2. Fronds removed from the same ; the natural size. Fig. 3. Portion of two 

 filaments magnified. Fig. 4. Apex of a filament, more highly magnified. 



II. SCYTONEMA, ^^. 



Filaments tufted, mostly basifixed, erect or decumbent, free, flexible, branched. 

 Tube or sheath cylindrical, continuous, membranaceous, tough ; endochrome olive-brown, 

 annulated. Branches lateral, issuing in pairs, formed by the division and protrusion 

 of the endochrome of the original filament. 



When at Niagara Falls in the autumn of 1849, 1 collected on the rocks under Biddle 

 Stairs specimens of a large decumbent Scytonema^ which may possibly be referable to 

 one or other of the 50 species named and described by Kiitzing, but whose characters 

 appear to me to be founded, often, on insufiicient data. I am unwilling to add to the 

 synonyms by giving a new name to the American species, and I have not at hand the 

 means of comparing it with more than a few of the recorded species. It is of large 

 size, its filaments being nearly twice the diameter of those of the British S. myochrous., 

 which it resembles in its branching. The endochrome is narrower in proportion to the 

 sheath and distinctly annulate ; the annuli rather distant. The sheath is of a deep 

 chestnut brown colour. 



Probably several other /orw5, if not species, occur in North America. 



