Mr. J. Ralfs on the Mode of Growth in Calothrix, §e. 349 
In Scytonema, Calothrix, Arthronema, &e. the sheath is some- 
what cartilaginous and closely surrounds the contained filament. 
As its texture is comparatively firm, it admits only a slight degree 
of dilatation : it neither separates as in Oscillatoria, nor allows 
the bundling of the filaments as in Microcoleus. 
In all these genera the structure of the filament, irrespective 
of the sheath, is alike, and consists of a single, longitudinal series 
of disciform cells which are often confluent or have indistinct 
dissepiments. 
Ifa specimen of Calothrix or Cenocoleus be examined we may 
frequently observe, especially near the extremities of the branches, 
short separated portions of filaments in every respect similar to 
those which sometimes occur in Oscillatoria. At first such a 
portion is separated from the original filament by a short in- 
terval ; but as there is no division of the sheath and both portions 
continue to elongate, they are soon in contact again. In the act 
of passing each other the extremities sometimes become atte- 
nuated. In this state the filament looks as if it had divided 
obliquely, and the upper portion becoming impacted between 
the filament and the sheath presents the appearance of a branch. 
From this explanation it will be evident that the branches in 
these genera are produced, not by an adhesion of other fila- 
ments, but by a dislocation of the filament itself. 
Both portions continue to elongate upwards, and branches are 
thus repeatedly formed by dislocation. The upper portions or 
branches, however, always retain their original advantage and 
extend beyond the trunk. This fact seems to me a strong proof 
of the correctness of the view I have given, for it could scarcely 
be constant if the branches originated in any other manner. 
The frond or sheath is itself truly branched or divided in the 
ordinary way. Sometimes, as in Calothriz, it is forked as soon 
as the upper portion becomes impacted, and the plant presents no 
peculiarity to the eye in its mode of branching except that the 
branches at the base are not united to the trunk. 
In Cenocoleus the branching of the sheath does not occur at 
the same spot as the dislocation of the filament. Upon this cir- 
cumstance depends the peculiar character of the genus, for after 
the dislocation the inferior portion as it elongates necessarily 
pushes itself up by the side of the superior one. Sometimes the 
filaments are again branched by dislocation before the sheath 
divides, and thus from two to four (or even more). filaments pass 
up side by side within a common sheath. Where the sheath 
forks the filaments are in general equally distributed between its 
branches. 
From what I have stated it will be seen that in Calothrix and 
Cenocoleus the dislocated ends pass each other without any 
