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 XLYIII. A. Fig 1 . Portion of the stratum formed by Petalonema alatum ; 
and jig. 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, Ag. 
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 Kutzing, but whose characters 
appear to me to be founded, often, on insufficient 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 forms, if not species, occur in North America. 
